• nelfinavir;
  • once daily;
  • pharmacokinetics;
  • ritonavir


  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Aims This study was performed to evaluate the steady-state pharmacokinetics, food intake requirements and short-term tolerability of once-daily combinations of nelfinavir and low-dose ritonavir.

Methods Twenty-seven healthy volunteers were randomized over three groups to receive a once-daily regimen of nelfinavir/ritonavir 2000/200 mg (group 1), 2000/400 mg (group 2) or 2500/200 mg (group 3) with food for 14 days. Pharmacokinetic parameters for nelfinavir and its active metabolite M8 were assessed on study days 15 and 16, after administration of the regimens with a full (610 kcal) or light (271 kcal) breakfast, respectively.

Results Pharmacokinetic data were evaluable for eight volunteers in group 1, eight in group 2 and four in group 3. Administration of nelfinavir/ritonavir with a full breakfast resulted in geometric mean (GM) nelfinavir AUC24h values of 76.8, 51.3, and 61.9 h*mg/l in group 1, 2 and 3, respectively. GM 24-h Cmin concentrations of nelfinavir were 0.76 mg l−1, 0.43 mg l−1 and 0.47 mg l−1, respectively. Co-administration of ritonavir increased M8 concentrations more than nelfinavir concentrations, resulting in GM AUC24h and Cmin values for nelfinavir plus M8 that were higher than or comparable to reference values for the approved regimen of nelfinavir (1250 mg BID without ritonavir). In the 2000/200 mg group, seven out of eight subjects had a Cmin value of nelfinavir plus M8 above a threshold of 1.0 mg l−1. Administration of the combinations with a light breakfast resulted in significant decreases in the AUC24h and Cmin of nelfinavir and nelfinavir plus M8, compared with intake with a full breakfast. For the Cmin of nelfinavir plus M8, the GM ratio (light/full breakfast) was 0.76 (90% confidence interval 0.67–0.86, participants from all groups combined). Short-term tolerability was satisfactory, apart from a higher than expected incidence of mild rash (12%).

Conclusions Administration of nelfinavir in a once-daily regimen appears feasible. A nelfinavir/ritonavir 2000/200 mg combination appears appropriate for further evaluation. Once-daily nelfinavir/ritonavir should be taken with a meal containing at least 600 kcal.


  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

The availability of highly active antiretroviral therapy (HAART) has dramatically decreased mortality and morbidity in HIV infection [1]. However, up to 50% of treatment-naive patients do not have sustained antiviral response after 1 year of therapy [2, 3]. To a considerable extent this can be ascribed to difficulties in achieving adequate adherence to the complex HAART regimens [4, 5]. Simpler dosing regimens are associated with better adherence [6–8], and there is a move to decrease the frequency of HAART dosing to a once-daily regimen.

Pharmacokinetic interactions between protease inhibitors (PIs) can be exploited as a means of decreasing the dosing frequency of these antiretroviral drugs. More specifically, exposure to PIs can be raised, and their half-lives can be prolonged, by coadministration of low-dose ritonavir [9]. The latter impairs the metabolism of other PIs by potent inhibition of cytochrome (CYP) 3A4. Data from recent studies suggest that ritonavir can adequately boost concentrations of amprenavir, indinavir and saquinavir, to allow for once-daily dosing of these PIs [10–15].

Nelfinavir is another PI that is widely used for treatment of HIV infection. It is approved for twice-daily dosing (1250 mg BID), and should be taken with food [16]. In vitro studies revealed that nelfinavir is metabolized by at least five different pathways, catalysed by several CYP isoenzymes (CYP3A4, CYP2C19, CYP2D6 and CYP2C9 [17]). CYP3A4 and CYP2C19 are the predominant contributors to nelfinavir metabolism. CYP2C19 catalyses exclusively the conversion of nelfinavir to an active metabolite termed M8, which in turn is metabolized by CYP3A4 [18]. Plasma concentrations of M8 are about 30% of those of nelfinavir after BID dosing of the latter [19]. M8 has equipotent activity to nelfinavir in vitro, binds to plasma protein in vivo to a similar extent to nelfinavir (≥ 98%), and has an almost identical molar weight [20]. Assuming additive virological efficacy, this suggests that the sum nelfinavir and M8 plasma concentrations may represent all active drug after administration of the parent drug.

Nelfinavir appears to be an appropriate PI for once-daily administration, because of its pharmacokinetic properties and its good tolerability. Nelfinavir shows slow oral absorption and an elimination half-life that is relatively long (3.5–5 h) compared with most other PIs [16]. In addition, previous pharmacokinetic studies have demonstrated that exposure to nelfinavir can be increased by coadministration of low-dose ritonavir (100–400 mg BID) [21, 22]. In these studies, ritonavir also increased M8 concentrations, as well as the M8:nelfinavir ratio, enhancing the relative contribution of M8 to the antiviral efficacy of nelfinavir. Thus, it appeared feasible that therapeutic plasma concentrations of nelfinavir plus M8 could be maintained over 24 h after once-daily administration of nelfinavir and ritonavir.

With respect to the tolerability of such a once-daily regimen, it appeared advantageous that no clear relationship has been demonstrated between the adverse effects of nelfinavir and its plasma concentration, particularly Cmax[23, 24].

Therefore this study was performed to characterize the steady-state pharmacokinetics and short-term tolerability of possible once-daily nelfinavir/ritonavir combinations. We also evaluated whether ingestion with a light meal would permit adequate absorption of these combinations.


  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References


Male or female healthy volunteers, aged 18–65 years, were eligible for enrolment. Subjects were excluded if they were hepatitis B- or C-seropositive, pregnant, hypersensitive to PIs or loperamide, if they had positive serology for HIV infection or prespecified abnormal laboratory parameters, and if they were taking any medication or illicit drugs.

All subjects gave written informed consent after full explanation of the study details. The study was approved by the Institutional Review Board of University Medical Centre Nijmegen, The Netherlands.

Study design and procedures

This study had an open-label, randomized, multiple-dose, parallel-group design. Twenty-seven volunteers were randomized (stratified by gender) to three dosage groups.

Participants took once-daily doses of either 2000 mg nelfinavir plus 200 mg ritonavir (group 1), 2000 mg nelfinavir plus 400 mg ritonavir (group 2), or 2500 mg nelfinavir plus 200 mg ritonavir (group 3). Nelfinavir (Viracept®) was administered as film-coated tablets, each containing 250 mg. Ritonavir (Norvir®) was given as capsules containing 100 mg.

Nelfinavir and ritonavir in all three combinations were ingested concomitantly with food (at least two slices of bread) at 24-h intervals and for 14 days.

Participants in the 2000/400 mg group (group 2) started with a 4-day lead-in period of 300 mg (instead of 400 mg) ritonavir combined with nelfinavir in order to attenuate possible ritonavir-associated adverse events in the initial period of the study [9].

Blood samples for two consecutive 24-h pharmacokinetic profiles were collected on study days 15 and 16. Participants attended in the morning after an overnight fast and a predose blood sample was drawn. On day 15 they ingested nelfinavir and ritonavir with a standardized, full breakfast, which consisted of 130 ml water and four slices of bread, filled with butter plus cheese, ham, paste or jam (610 kcal: 33% fat, 16% proteins and 51% carbohydrates). Blood samples were drawn at 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 10.0, 12.0, 16.0 and 24.0 h postdose. Plasma was isolated by centrifugation within 12 h of sampling and was stored at −20°C until analysis.

After an overnight fast, the same procedure was repeated on day 16. However, the drugs were ingested with a light instead of a full breakfast. This comprised one slice of bread with butter and cheese and 130 ml of semiskimmed milk (271 kcal: 37% fat, 24% proteins, 39% carbohydrates).

The study was conducted on an outpatient basis. Subjects received their study medication in a vial that contained sealed plastic sachets, each holding the appropriate number of tablets and capsules for 1 day. Drug administration was witnessed on days 1, 4, 11, 15 and 16. Compliance with study medication at home was verified at every study visit by inspection of drug-taking diaries, counting of sachets, measurement of plasma drug concentrations, and electronic monitoring of opening of vials, using the Medication Event Monitoring System (MEMS®) [25].

Drug analysis

Nelfinavir and ritonavir concentrations were assayed using a previously described validated reversed-phase HPLC method with u.v. detection [26]. M8 concentrations were determined simultaneously using the same method without modifications. The retention time of M8 was 12.7 min. The accuracy of the method for nelfinavir ranged from 96% to 100%, depending on the concentration. Those for ritonavir and M8 were 102–108% and 93–108%, respectively. Intra-day precision and between-day precision were 2.1–7.5% and 0.4–3.5% for nelfinavir, 2.0–8.1% and 0–2.4% for ritonavir, and 2.8–4.3% and 2.0–3.0% for M8. The limit of determination was 0.04 mg l−1 for nelfinavir, ritonavir and M8.

Pharmacokinetic analysis

Pharmacokinetic parameters for nelfinavir, ritonavir and M8 were obtained by noncompartmental methods [27]. The highest observed plasma concentration was defined as Cmax, with the corresponding sampling time as tmax. Cmin was the concentration at 24 h after ingestion of the drugs. The terminal, log-linear period (log C vs t) was defined by visual inspection of the last data points (n ≥ 3). The value of the slope (–β/2.303) was calculated by least-squares linear regression analysis, where β is the first-order elimination rate constant. The elimination half life (t1/2) was calculated from the expression 0.693/β.

The area under the concentration vs time curve (AUC24h) was calculated using the trapezoidal rule from 0 to 24 h. The time of ingestion of nelfinavir/ritonavir on day 14 (the day preceding pharmacokinetic assessments) varied among participants, resulting in different contributions of this dose to the AUC24h on day 15. Therefore AUC24h values for study day 15 were corrected for the contribution of the previous dose by subtraction of C0/β (where C0 is the concentration just before ingestion of nelfinavir/ritonavir at t = 0), and area under the curve was extrapolated to infinity by adding Cmin/β. Accordingly, the corrected AUC24h value (AUC24h,corr) for day 15 was obtained from the equation:

  • AUC24h,corr =  AUC24h  −  C0day15 + Cminday15.

The AUC24h for day 16 was corrected in the same way, but the contribution of the predose AUC was calculated using the elimination rate constant β determined on day 15:

  • AUC24h,corr =  AUC24h  −  C0day15 + Cminday16.

Apparent clearance (CL/F, where F is bioavailability) was calculated by dividing dose (D) by AUC24h,corr, and apparent volume of distribution (Vd/F) was obtained by dividing CL/F by β. Both were corrected for weight.

Safety and tolerability

Safety and tolerability were assessed by a questionnaire that described 15 possible adverse events that could occur during treatment with nelfinavir or ritonavir. The questionnaire was completed four times each, on study days 4, 8, 11 and 15. Participants were asked to grade every event as mild (symptoms do not interfere with daily activities), moderate (symptoms interfere with daily activities) or severe (symptoms markedly interrupt daily activities). An extensive blood chemistry and haematology screen and urinalysis were performed on the same four study days. If WHO grade 2 diarrhoea occurred, use of loperamide was allowed.

Data analysis

The study was not powered to enable formal statistical comparisons of pharmacokinetic parameters between the study groups. Therefore pharmacokinetic parameters are presented descriptively for each study group.

To assess the effect of the composition of the concurrent meal on the pharmacokinetics of nelfinavir, M8, nelfinavir plus M8, and ritonavir, a two-way mixed analysis of variance (anova) was performed on the logarithmically transformed values of AUC24h,corr, Cmax and Cmin. Absence of an effect of the meal composition on AUC24h,corr, Cmax or Cmin was concluded if the 90% CI for a geometric mean ratio was contained within 80–125% limits [28]. Tmax values were not log-transformed and were compared using the Wilcoxon signed-ranks test.

The incidence of adverse events was expressed as the percentage of participants who reported a particular event at least once. Consequently every reported mild, moderate or severe adverse event was assigned a severity score of 1, 2 or 3 points, respectively. Scores were added up for each participant and were divided by the number of each subject. In this way mean toxicity scores over the study period were obtained.

All statistical evaluations were performed with SPSS for Windows, version 10.0 (SPSS Inc., Chicago, IL, USA).


  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Twenty-seven volunteers were enrolled into the study. Five male and four female subjects were included in each group. Median ages were 28, 23 and 25 years in groups 1, 2, and 3, respectively, and median weights were 71, 73 and 71 kg. All subjects were Caucasians.

Twenty-one volunteers completed the study and data for 20 volunteers were evaluated (eight in group 1, eight in group 2 and four in group 3).

One subject in group 1, one in group 2 and three in group 3 were withdrawn because of toxicity concerns. An additional volunteer in group 3 withdrew his informed consent. One subject in group 3 did not convert nelfinavir to M8, probably because of CYP2C19 poor metabolizer genotype status, which occurs in 3–5% of Caucasian subjects [18]. Because of this, pharmacokinetic data for this volunteer were not analysed, which reduced the number of evaluable participants in group 3 to four.

Table 1 summarizes the pharmacokinetic parameters for nelfinavir, M8 and nelfinavir plus M8 after once-daily administration of the combinations for 14 days. Figures 1 and 2 display the corresponding plasma concentration–time curves for nelfinavir and M8, showing that coadministration of nelfinavir and ritonavir in once-daily combinations resulted in detectable and appreciable concentrations of nelfinavir and M8 throughout the 24-h dosing interval. Concentration–time curves for nelfinavir and M8 after administration of nelfinavir alone are shown for reference.

Table 1.  Pharmacokinetics of nelfinavir, M8, and nelfinavir plus M8 after once-daily administration of nelfinavir/ritonavir combinations for 14 days. *
ParameterValues (geometric mean + range)
Group 1:nelfinavir/ritonavir2000/200 mg(= 8)Group 2:nelfinavir/ritonavir2000/400 mg(= 8)Group 3:nelfinavir/ritonavir2500/200 mg(= 4)
  1. *Pharmacokinetic parameters were assessed after intake of drugs with a full breakfast: 610 kcal, 33% fat, 16% proteins, 51% carbohydrates and 130 ml water (study day 15). AUC24h,corr, Corrected 24 h area under the concentration–time curve (see text); Cmin, trough concentration at 24 h; Cmax, highest observed plasma concentration; tmax, sampling time for Cmax; CL/, total clearance corrected for weight; Vd/, volume of distribution corrected for weight; t1/2, elimination half-life; F, bioavailability. Median (and range). §CL/ and Vd/ can not be calculated for M8, as dose is unknown.

 AUC24h,corr ( l−1) 76.8 (32.4–121.3)51.3 (23.5–114.8) 61.9 (48.1–89.3)
 Cmax (mg l−1)  7.2 (3.4–9.3) 5.1 (2.9–9.4)  6.7 (6.4–7.6)
 Cmin (mg l−1)  0.76 (0.28–2.1) 0.43 (0.16–1.8)  0.47 (0.18–1.8)
 Tmax (h)  4.0 (2.5–5.0) 4.6 (2.6–6.0)  4.5 (3.0–5.0)
 CL/ (  0.35 (0.16–0.84) 0.51 (0.24–0.95)  0.52 (0.27–0.74)
 Vd/ (l kg−1)  3.2 (1.8–5.4) 4.5 (2.9–9.2)  4.3 (3.6–5.0)
 T1/2 (h)  6.5 (4.4–11.3) 6.1 (4.3–9.2)  5.8 (4.0–9.1)
 AUC24h,corr ( l−1) 38.5 (21.5–57.7)40.9 (30.1–58.8) 45.3 (30.0–63.4)
 Cmax (mg l−1)  3.4 (2.3–5.6) 3.7 (2.8–4.9)  4.3 (2.9–5.9)
 Cmin (mg l−1)  0.63 (0.46–1.1) 0.59 (0.32–1.1)  0.67 (0.35–1.7)
 Tmax (h)  5.0 (4.0–5.0) 5.0 (4.0–6.1)  4.5 (4.0–5.0)
 T1/2 (h)  9.7 (7.5–13.6) 8.6 (6.0–11.8)  8.9 (7.4–13.3)
Nelfinavir + M8
 AUC24h,corr ( l−1)116.4 (53.9–172.6)94.6 (61.6–173.7)108.3 (94.6–152.8)
 Cmin (mg l−1)  1.4 (0.81–3.2) 1.1 (0.61–2.9)  1.2 (0.77–3.5)
M8:nelfinavir ratio
Ratio for AUC24h,corr  0.50 (0.32–0.75) 0.80 (0.42–1.6)  0.73 (0.46–0.98)
Ratio for Cmin  0.83 (0.43–1.9) 1.36 (0.50–4.3)  1.43 (0.61–3.3)

Figure 1. Nelfinavir steady-state plasma concentrations on day 15 (geometric mean values) after administration of once daily (OD) nelfinavir/ritonavir combinations. In-house reference data for nelfinavir 1250 mg BID are displayed for reference (see also Table 5). ○, 2000/200 mg OD; □, 2000/400 mg OD; ▵ 2500/200 mg OD, •, 1250 mg OD.

Download figure to PowerPoint


Figure 2. M8 steady-state plasma concentrations on day 15 (geometric mean values) after administration of once daily (OD) nelfinavir/ritonavir combinations. In-house reference data for M8 (after administration of nelfinavir 1250 mg) are displayed for reference (see also Table 5). ○, 2000/200 mg OD; □, 2000/400 mg OD; ▵ 2500/200 mg OD, •, 1250 mg OD.

Download figure to PowerPoint

M8 concentrations after once-daily administration of nelfinavir and ritonavir (Table 1, Figure 2) were relatively high compared with those of nelfinavir. Coadministration of nelfinavir and ritonavir appeared to raise M8 concentrations to a greater extent than nelfinavir concentrations, resulting in high M8:nelfinavir ratios for AUC24h,corr and especially for Cmin (Table 1).

The geometric mean values for the AUC24h,corr and especially Cmin for nelfinavir were highest in group 1 (nelfinavir/ritonavir 2000/200 mg once daily). In contrast, the geometric mean AUC24h,corr andCmin values for M8 appeared remarkably similar across the study groups (Table 1). As a result, the summed AUC24h,corr andCmin values for nelfinavir plus M8 were also highest in group 1. Neither increasing the dosage of ritonavir to 400 mg (group 2), nor increasing the nelfinavir dose to 2500 mg (group 3) led to a proportional increase in nelfinavir (or nelfinavir plus M8) concentrations.

High interindividual variability in pharmacokinetic parameters was noted in all three once-daily groups (Table 1,Figure 3). It appeared that 7/8 participants in group 1 had a nelfinavir Cmin above a proposed therapeutic threshold of 0.45 mg l−1 for nelfinavir (M8 not included [29]), compared with 2/8 participants in group 2 and 2/4 participants in group 3 (Figure 3, left panel). Comparison of individual's Cmin with a higher threshold concentration of 0.8 mg l−1 for nelfinavir [30, 31] revealed that 4/8, 2/8 and 1/4 participants in groups 1, 2 and 3 had nelfinavir Cmin values above this concentration. The latter for nelfinavir corresponds roughly to a third threshold of 1.0 mg l−1 for nelfinavir and M8 together (0.8 + (30% × 0.8) = 1.0 mg l−1). When nelfinavir and M8 Cmin concentrations were summed (Figure 3, right panel), 7/8 volunteers in group 1 had a nelfinavir plus M8 Cmin above 1.0 mg l−1, compared with 4/8 and 1/4 volunteers in groups 2 and 3, respectively.


Figure 3. Individual 24-h trough concentrations (Cmin) for nelfinavir (left panel) or nelfinavir plus M8 (right panel). Group 1: nelfinavir/ritonavir 2000/200 mg once daily. Group 2: nelfinavir/ritonavir 2000/400 mg once daily. Group 3: nelfinavir/ritonavir 2500/200 mg once daily. Proposed threshold values for treatment-naive patients are depicted as dotted lines (see text): nelfinavir 0.45 mg l−1 and 0.8 mg l−1; nelfinavir plus M8 1.0 mg l−1.

Download figure to PowerPoint

In group 1, a linear association was found between the AUC24h,corr values for M8 and ritonavir (rs = 0.786, P = 0.021), but the AUC24h,corr values for nelfinavir and ritonavir, or nelfinavir and M8 were not related. No corresponding associations were found in group 2. Correlation analyses were not performed for group 3, because of the small number of participants.

The geometric mean AUC24h,corr, Cmin and Cmax for ritonavir in groups 1 and 3 (200 mg of ritonavir once daily) were comparable (Table 2). Increasing the dose of ritonavir from 200 mg to 400 mg (group 2) resulted in a more than proportional increase in the AUC24h,corr for ritonavir. The latter in group 2 was significantly higher than that in groups 1 and 3 (P ≤ 0.001).

Table 2.  Pharmacokinetics of ritonavir after once daily administration of nelfinavir/ritonavir combinations for 14 days. *
ParameterValues (geometric mean + range)
Group 1:nelfinavir/ritonavir2000/200 mg(= 8)Group 2:nelfinavir/ritonavir2000/400 mg(= 8)Group 3:nelfinavir/ritonavir2500/200 mg(= 4)
  1. *Pharmacokinetic parameters were assessed after intake of drugs with a full breakfast: 610 kcal, 33% fat, 16% proteins, 51% carbohydrates and 130 ml water (study day 15). †Abbreviations of pharmacokinetic parameters: see Table 1. ‡Median (and range).

 AUC24h,corr ( l−1)12.2 (8.2–18.3)32.4 (14.0–53.7)11.8 (7.9–23.4)
 Cmax (mg l−1) 1.7 (1.1–2.9) 4.0 (2.3–5.7) 1.8 (1.2–3.9)
 Cmin (mg l−1) 0.04 (0.00–0.12) 0.15 (0.06–0.24) 0.04 (0.02–0.13)
 tmax (h)‡ 4.0 (2.0–5.0) 4.1 (1.0–6.0) 5.0 (1.5–5.0)
 CL/ ( 0.22 (0.16–0.35) 0.15 (0.06–0.30) 0.22 (0.12–0.37)
 Vd/ (l kg−1) 1.1 (0.58–1.5) 0.95 (0.32–2.2) 1.3 (0.62–2.6)
 t½ (h) 3.4 (2.4–5.7) 4.4 (3.7–7.0) 4.1 (2.7–5.4)

A significant effect of meal composition on the AUC24h,corr and Cmin values for nelfinavir and nelfinavir plus M8 was found. No significant differences between study groups could be demonstrated for these parameters and the interaction between study group and meal composition was never significant.

The geometric mean ratios (light/full breakfast) and 90% CI were 0.70 (0.62–0.78) and 0.76 (0.68–0.85) for nelfinavir AUC24h,corr and Cmin, respectively, and 0.71 (0.63–0.81) and 0.76 (0.67–0.86) for the AUC24h,corr and Cmin of nelfinavir plus M8 (data from all three groups combined).

As the lack of significant between-group differences and the lack of an group-by-period interaction could be attributable to the small number of participants in each group, Table 3 shows geometric mean ratios and CIs for each of the study groups separately. The statistical power to detect a relevant food effect was low (about 0.5) in group 3, due to the small number of participants. This implies that the absence of a significant food effect for some pharmacokinetic parameters in this group (see Table 3) does not exclude the existence of such an effect.

Table 3.  Effect of food on the steady-state pharmacokinetics of nelfinavir/ritonavir given once daily.
Parameter*Geometric mean ratio (light/full breakfast) + 90% CI†‡
Group 1:nelfinavir/ritonavir2000/200 mg(= 8)Group 2:nelfinavir/ritonavir2000/400 mg(= 8)Group 3:nelfinavir/ritonavir2500/200 mg(= 4)
  1. *Abbreviations of pharmacokinetic parameters: see Table 1. CI, Confidence interval. If the CI does not contain one, this implies a significant difference at the 10% significance level between administration of nelfinavir/ritonavir with a light or full breakfast. A ratio refers to the fraction of a pharmacokinetic parameter after administration of nelfinavir/ritonavir with a light breakfast (day 16) to the same parameter after administration with a full breakfast (day 15). Full breakfast: 610 kcal, 33% fat, 16% proteins, 51% carbohydrates, 130 ml water. Light breakfast: 27 1 kcal, 37% fat, 24% proteins, 39% carbohydrates, 130 ml fluid. §Median difference in tmax after administration of nelfinavir/ritonavir with a light breakfast compared with a full breakfast (tmax day 16 − tmax day 15), and range. No significant differences in tmax values (light breakfast vs full breakfast) were found for nelfinavir, M8, or ritonavir, except for M8 in group 1 (P = 0.03, Wilcoxon signed ranks test).

 AUC24h,corr ( l−1) 0.75 (0.67–0.84) 0.75 (0.66–0.85) 0.53 (0.29–0.98)
 Cmax (mg l−1) 0.88 (0.80–0.97) 0.84 (0.75–0.94) 0.57 (0.32–1.00)
 Cmin (mg l−1) 0.78 (0.65–0.94) 0.77 )0.61–0.99) 0.69 (0.53–0.90)
 tmax (h)§+0.1 (−2.4 to +1.0)−0.5 (−3.0 to +5.0)−0.75 (−2.0 to 0.0)
 AUC24h,corr ( l−1) 0.83 (0.68–1.01) 0.77 (0.65–0.91) 0.55 (0.28–1.06)
 Cmax (mg l−1) 0.93 (0.90–0.96) 0.84 (0.71–0.98) 0.63 (0.40–0.99)
 Cmin (mg l−1) 0.83 (0.69–0.99) 0.82 (0.63–1.07) 0.62 (0.36–1.05)
 tmax (h)§−1.0 (−1.0 to 0.0)−1.0 (−2.0 to +5.0)−0.75 (−2.0 to 0.0)
Nelfinavir + M8
 AUC24h,corr ( l−1) 0.78 (0.68–0.91) 0.75 (0.65–0.87) 0.53 (0.28–1.00)
 Cmin (mg l−1) 0.80 (0.67–0.96) 0.80 (0.62–1.02) 0.63 (0.43–0.91)
 AUC24h,corr ( l−1) 0.78 (0.66–0.92) 0.92 (0.78–1.08) 0.52 (0.29–0.95)
 Cmax (mg l−1) 0.95 (0.78–1.15) 1.07 (0.89–1.27) 0.49 (0.24–0.98)
 Cmin (mg l−1) 0.90 (0.74–1.09) 1.03 (0.59–1.80) 1.17 (0.91–1.50)
 tmax (h)§+0.5 (−1.0 to +2.0)+0.5 (−1.0 to +5.1)−0.5 (−2.0 to 0.0)

With respect to ritonavir, it appeared that the AUC24h,corr in group 2 (400 mg of ritonavir) was not significantly affected by the composition of the breakfast, in contrast to the findings in groups 1 and 3 (200 mg of ritonavir).

Safety and tolerability

Five volunteers were withdrawn because of concerns over toxicity. Three of these (one in each study group) suffered a mild rash. A second subject in group 3 was withdrawn as a precautionary measure, as he complained of, for example, localized itch, feeling of thick lips, but showed no objective sign of toxicity. A third subject in group 3 was withdrawn because of severe fatigue (WHO grade 3 toxicity) after 11 days of nelfinavir/ritonavir. One day after stopping the medication, increased liver transaminases were found in this subject (AST grade 2, ALT grade 3 toxicities), but these readings normalized in the next 3 weeks.

Apart from these events, the nelfinavir/ritonavir regimens were tolerated reasonably well. The most common adverse reactions are shown in Table 4.

Table 4.  Adverse events: incidence and toxicity scores. *
Adverse eventStudy group
Group 1:nelfinavir/ritonavir2000/200 mg(= 9)Group 2:nelfinavir/ritonavir2000/400 mg(= 9)Group 3:nelfinavir/ritonavir2500/200 mg(= 8)*All groups:(= 26)
  • *

    Data are from all participants, including those who withdrew. One participant in group 3 withdrew informed consent before taking the drugs and before the first evaluation of adverse events.

  • Incidence expressed as the percentage of participants who reported a particular adverse event at least once.

  • A severity score of 3.0 represents three mild adverse events, or one moderate adverse event (2 points) plus a mild one, or one severe adverse event (3 points).

Incidence (any severity)
 Flatulence 56783858
 Nausea 11562531
 Vomiting  0112512
 Abdominal pain 22445038
 Asthenia 11223823
 Fatigue/somnolence 22567550
 Fever  0 013 4
 Headache 56332538
 Skin reaction or rash 22336338
 Taste perversion 11112515
 Peroral paraesthesia 33111319
 Peripheral paraesthesia 22221319
 Arthralgia 22222523
 Myalgia 11221315
Median severity score1.

Median toxicity scores were 1.5, 2.5 and 3.1 in study groups 1, 2 and 3, respectively. This means that subjects in group 1 had an average of 1.5 mild adverse events. No significant correlations were found between the toxicity scores and the AUC24h,corr, Cmax or Cmin of nelfinavir, nelfinavir plus M8, or ritonavir.

Small increases in fasting cholesterol were observed in the majority of participants who completed the study (6/8, 6/8 and 2/4 participants in groups 1, 2 and 3, respectively). Median changes in cholesterol were +0.50, +0.25 and 0.0 mmol l−1 in groups 1, 2 and 3, whereas median changes in triglycerides were negligible (+0.04, +0.04 and +0.16 mmol l−1 in groups 1, 2 and 3). The study medication had no material effect on other laboratory parameters.


  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

The results of this study suggest it is possible to achieve effective exposure to nelfinavir and M8 after once-daily dosing of nelfinavir in combination with low-dose ritonavir. These data are in agreement with results from a similar study, presented in abstract [32]. A nelfinavir-based HAART regimen with once-daily dosing for all drugs is simple and also facilitates witnessed therapy of HAART. Both these advantages may result in improved long-term adherence [6–8], which is associated with improved efficacy of HAART [4, 5]. Once-daily administration of HAART may be particularly useful for a subgroup of patients who cannot adhere to more complex drug regimens, due to unstable lifestyles, imprisonment, or injectable drug misuse.

Whereas once-daily administration of nelfinavir may prove more convenient, the number of tablets that need to be taken and food restrictions still make a once-daily regimen quite complex. The proposed development of 625-mg tablets of nelfinavir will enable further simplification of the regimen. With respect to food restrictions, once-daily administration offers patients the flexibility to adapt dosing to their dietary habits, assuming that the pharmacokinetics of nelfinavir/ritonavir do not change with the time of dosing.

It is important not to over-interpret the apparent pharmacokinetic differences or similarities between the three nelfinavir/ritonavir regimens in this exploratory study. Each study group comprised a relatively small number of participants, and considerable interindividual variability was observed for all pharmacokinetic parameters. The number of participants who completed group 3 of the study was particularly small (n = 4). Therefore, no firm conclusions can be drawn with regard to the nelfinavir/ritonavir 2500/200 mg combination.

Comparison of Table 1 and Table 5 reveals that the geometric mean AUC24h,corr values for once-daily nelfinavir are similar to values reported for the approved BID regimen, and are considerably higher when the contribution of M8 is included. Therefore efficacy is predicted for all three once-daily regimens. In contrast, only group 1 (nelfinavir/ritonavir 2000/200 mg once daily) yielded a geometric mean 24-h Cmin value for nelfinavir that was comparable to the lowest 12-h Cmin values reported for the BID regimen. When M8 concentrations are taken into consideration, the mean 24-h Cmin values in all groups are comparable to reference data, with group 1 showing the most favourable results.

Table 5.  Reference pharmacokinetic data for nelfinavir, M8 and nelfinavir plus M8 after twice-daily administration of nelfinavir (1250 mg BID). *
[16, 34]= 10Intens. PK‡‡[31]= 84Pop. PK[19]= 355Pop. PK[22]§**= 12/12Intens. PK[in house data]††= 5Intens. PK
  1. *Reference data were assessed in HIV-infected patients, except for [22] (healthy volunteers). AUC24h, 24 h area under the concentration–time curve; Cmax, highest observed plasma concentration; Cmin, trough concentration, either in the morning (before the morning dose) or in the evening (before the evening dose). Median values. §Mean values. Geometric means. **Reference 22 was a two-group study; data for both groups are shown. Mean values for AUC24h were estimated by summing mean AUC12h values reported for the morning dose and evening dose. Cmax values refer to the morning dose. ††In-house reference data were retrieved from our own dataset of intensive pharmacokinetic assessments. These data were assessed after intake of nelfinavir with a full breakfast that was identical to the breakfast used in the study, and the same bioanalytical method was used for measurement of drug concentrations (see text). ‡‡Reference data were assessed by intensive (intens.) pharmacokinetic (PK) measurements in a limited number of individuals, or by population (pop.) pharmacokinetic approaches. §§AUC24h values were obtained by doubling AUC12h values that were reported in the references. ¶¶Values for Nelfinavir + M8 and for M8:nelfinavir ratios were derived from the mean values reported for nelfinavir and M8 separately (this is an approximation).

 AUC24h ( l−1)51.052.0§§48.0§§52.5/55.5**41.8§§
 Cmax (mg l−1) 4 8.33 3.43.39/4.25** 3.9
 Cmin, morning (mg l−1)2.2 1.02 1.601.16/1.24 1.30
 Cmin, evening (mg l−1)0.7  0.851.76/1.35 0.65
 AUC24h ( l−1)  15.2§§24.6/26.7**12.9§§
 Cmax (mg l−1)   1.11.76/1.95** 1.4
 Cmin, morning (mg l−1)   0.410.44/0.48 0.39
 Cmin, evening (mg l−1)   0.280.71/0.65 0.05
Nelfinavir + M8¶¶
 AUC24h ( l−1)  63.277.1/82.254.7
 Cmin, morning (mg l−1)   2.011.60/1.72 1.69
 Cmin, evening (mg l−1)   1.132.47/2.00 0.70
M8:nelfinavir ratio¶¶
 Ratio for AUC24h   0.320.47/0.48 0.31
 Ratio for Cmin, morning   0.260.38/0.39 0.30
 Ratio for Cmin, evening   0.330.40/0.48 0.08

Comparing experimental data to reference data could be confounded by differences across studies. The current study was performed in healthy volunteers, whereas most reference data are from HIV-infected patients. No substantial differences in nelfinavir pharmacokinetics have been observed between these two groups [16], but they can not be excluded. Differences in the composition of meals taken with nelfinavir as well as different analytical methods could also confound interpretation of its pharmacokinetic parameters. Our in-house reference data (Table 5) were obtained using the same breakfast content and the same bioanalytical method as in the current study. Thirdly, some reference AUC12h values reported for the BID regimen were doubled to enable comparison with once-daily AUC24h,corr values. However, this neglects relatively modest circadian variations that occur in the pharmacokinetics of nelfinavir.

The 0.45 mg l−1 (800 nm) threshold for nelfinavir is based upon in vitro 95% effective concentrations against HIV, with adjustment for in vivo protein binding and the elevated concentrations of α1-acid glycoprotein in HIV-infected patients [29]. Thresholds derived from in vivo patient response data may be more relevant, and the 0.8 mg l−1 value defined for wild-type HIV-1 (ie in treatment-naive patients) has been independently assessed in two patient cohorts [30, 31]. This threshold corresponds to about 1.0 mg l−1 when the Cmin values of nelfinavir and M8 are summed. Regardless of the threshold chosen and the inclusion or exclusion of M8 concentrations, the 2000/200 mg regimen (group 1) appeared to be the most favourable. As this combination was also associated with the lowest toxicity score, it appears to be an appropriate regimen for further evaluation.

The boosting effect of ritonavir on nelfinavir AUC24h,corr values appears less pronounced than those seen after addition of ritonavir to indinavir and especially saquinavir therapy. This could be explained by the relatively small contribution of CYP3A to nelfinavir metabolism, compared with the other PIs. The increase in M8 concentrations may reflect the possible inducing effect of ritonavir on CYP2C19 (leading to enhanced formation of M8) and inhibition of CYP3A4 (which limits the clearance of M8) [9]. Exposures to M8 seemed similar among study groups, which may suggest saturation of M8 formation, or a lack of additional effects of ritonavir (above a dose of 200 mg once daily) on the subsequent metabolism of M8.

The apparent lack of increase in nelfinavir concentrations with further dose escalations of ritonavir or nelfinavir may reflect the low power of this exploratory study. However, the effect of ritonavir on the pharmacokinetics of nelfinavir is hard to predict, due to the complex metabolism of nelfinavir, the influence of ritonavir as both an inhibitor or inducer of the metabolic enzymes involved, and the presence of such enzymes in both the gut wall and liver. For example, it could be argued that higher doses of ritonavir increase the first-pass metabolism of nelfinavir in the gut wall, resulting in lower nelfinavir Cmax and AUC24h,corr values in group 2.

Any differences in the pharmacokinetics after increasing the dose of nelfainavir should be interpreted more cautiously, considering the small number of participants in group 3 of the study. Nevertheless, the apparent lack of increase in nelfinavir concentrations after a higher dose of nelfinavir corresponds to other literature data [19, 21] and may be explained by saturation of absorption from the gut.

It has been hypothesized that food restrictions should be modified when nelfinavir is coadministered with ritonavir, as has been demonstrated for indinavir in combination with ritonavir (400/400 mg BID) [9]. However, AUC24h,corr and Cmin values for nelfinavir and M8 significantly decreased after administration with a light compared with a full breakfast. Accordingly, it is recommended that once-daily regimens of nelfinavir/ritonavir are administered with a meal comparable in calories (600 kcal) and fat content (∼33%) to the full breakfast used in this study.

The spectrum of adverse events was as expected. Mild diarrhoea is a common adverse effect of both nelfinavir and ritonavir. The incidence of rash in this study (11%) was higher than the 3% value reported for phase III studies in which nelfinavir was administered without ritonavir [29]. The occurrence requires close study when once-daily nelfinavir/ritonavir regimens are tested in HIV-infected patients.

The observed increases in cholesterol values warrant close monitoring of blood lipids when the nelfinavir/ritonavir regimen is used in HIV-infected patients, especially if combined with other antiretroviral agents with known lipid-elevating effects.

In conclusion, data from this study demonstrate that coadministration of nelfinavir and low-dose ritonavir offers the potential for once-daily administration of nelfinavir. A once-daily regimen of 2000 mg nelfinavir and 200 mg ritonavir seems appropriate for further evaluation. This regimen should be taken with a meal containing at least 600 kcal. Short-term tolerability was satisfactory, apart from a higher than expected incidence of rash. Follow-up pharmacokinetic and tolerability assessments in HIV-infected patients are warranted to confirm the findings of this study in healthy volunteers.

The healthy volunteers are thanked for their participation. H. ter Hofstede, D. Telgt, A. Bergshoeff, C. la Porte and M. de Graaff are acknowledged for their assistance during the study. The technicians of the Department of Clinical Pharmacy are thanked for analysis of the plasma samples. This study was funded by an unrestricted grant from F. Hoffmann-La Roche Ltd.


  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References
  • 1
    Palella FJ Jr, Delaney KM, Moorman AC et al. Declining morbidity and mortality among patients with advanced human immunodeficiency virus infection. N Engl J Med 1998; 338: 853860.
  • 2
    Wit FW, Van Leeuwen R, Weverling GJ et al. Outcome and predictors of failure of highly active antiretroviral therapy: one year follow-up of a cohort of human immunodeficiency type-1-infected persons. J Infect Dis 1999; 179: 790798.
  • 3
    Deeks SG, Hecht FM, Swanson M et al. HIV RNA and CD4 cell count response to protease inhibitor therapy in an urban AIDS clinic: response to both initial and salvage therapy. AIDS 1999; 13: F35F43.
  • 4
    Paterson DL, Swindells S, Mohr J et al. Adherence to protease inhibitor therapy and outcomes in patients with HIV infection. Ann Intern Med 2000; 133: 2130.
  • 5
    Nieuwkerk PT, Sprangers MA, Burger DM et al. Limited patient adherence to highly active antiretroviral therapy for HIV-1 infection in an observational cohort study. Arch Intern Med 2001; 161: 19621968.
  • 6
    Tseng AL. Compliance issues in the treatment of HIV infection. Am J Health Syst Pharm 1998; 55: 18171824.
  • 7
    Stone VE, Hogan JW, Schuman P et al. Antiretroviral regimen complexity, self-reported adherence, and HIV patients’ understanding of their regimens: a survey of women in the HER study. J Acquir Immune Def Syndr 2001; 28: 124131.
  • 8
    Stone VE. Strategies for optimizing adherence to highly active antiretroviral therapy: lessons from research and clinical practice. Clin Infect Dis 2001; 33: 865872.
  • 9
    Hsu A, Granneman GR, Bertz RJ. Ritonavir. Clinical pharmacokinetics and interactions with other anti-HIV agents. Clin Pharmacokinet 1998; 35: 275291.
  • 10
    Sale M, Sadler BM, Stein DS. Pharmacokinetic modeling and simulations of interaction of amprenavir and ritonavir. Antimicrob Agents Chemother 2002; 46: 746754.
  • 11
    Burger DM, Hugen PWH, Van Der Ende ME et al. Once-daily indinavir plus ritonavir: preliminary results of the PIPO study. AIDS 2000; 14: 26212623.
  • 12
    Mole L, Schmidgall D, Holodniy M. A pilot trial of indinavir, ritonavir, didanosine, and lamivudine in a once-daily four-drug regimen for HIV-infection. J Acquir Immune Defic Syndr 2001; 27: 260265.
  • 13
    Heeswijk van RPG, Veldkamp AI, Mulder JW et al. Once daily dosing of saquinavir and low-dose ritonavir in HIV-1-infected individuals. A pharmacokinetic pilot study. AIDS 2000; 14: F95F99.
  • 14
    Kilby JM, Sfakianos G, Gizzi N et al. Safety and pharmacokinetics of once-daily regimens of soft-gel capsule saquinavir plus minidose ritonavir in human immunodeficiency virus-negative adults. Antimicrob Agents Chemother 2000; 44: 26722678.
  • 15
    Cardiello PG, Van Heeswijk RP, Hassink EA et al. Simplifying protease inhibitor therapy with once-daily dosing of saquinavir soft-gelatin capsules/ritonavir (1600/100 mg): HIVNAT 001.3 study. J Acquir Immune Defic Syndr 2002; 29: 464470.
  • 16
    Bardsley-Elliott A, Plosker GL. Nelfinavir, an update of its use in HIV infection. Drugs 2000; 59: 581620.
  • 17
    Sandoval TM, Grettenberger HM, Zhang KE et al. Metabolism of nelfinavir mesylate, an HIV-1 protease inhibitor, by human liver microsomes and recombinant human isoforms [Abstract 1096]. 12th Annual Meeting and Exposition of the American Association of Pharmaceutical Scientists. San Francisco: , November 1998.
  • 18
    Lillibridge JH, Lee CA, Pithavala YK et al. The role of polymorphic CYP2C19 in the metabolism of nelfinavir mesylate. 12th Annual Meeting and Exposition of the American Association of Pharmaceutical Scientists. San Francisco: , November 1998[Abstract 3035].
  • 19
    Baede-van Dijk PA, Hugen PWH, Verweij-van Wissen CPWGM et al. Analysis of variation in plasma concentrations of nelfinavir and its active metabolite M8 in HIV-positive patients. AIDS 2001; 15: 991998.
  • 20
    Zhang KE, Wu E, Patick AK et al. Circulating metabolites of the human immunodeficiency virus protease inhibitor nelfinavir in humans: structural identification, levels in plasma, and antiviral activities. Antimicrob Agents Chemother 2001; 45: 10861093.
  • 21
    Flexner C. Steady–state pharmacokinetic interactions between ritonavir (RTV), nelfinavir (NFV) and the nelfinavir active metabolite M8 (AG1402). 12th World AIDS Conference, Geneva, 28 June to 3 July, 1998[Abstract 42265].
  • 22
    Kurowski M, Kaeser B, Sawyer A et al. Low-dose ritonavir moderately enhances nelfinavir exposure. Clin Pharmacol Ther 2002; 72: 123132.
  • 23
    Reijers MH, Weigel HM, Hart AA et al. Toxicity and drug exposure in a quadruple drug regimen in HIV-1 infected patients participating in the ADAM study. AIDS 2000; 14: 5967.
  • 24
    Hsyu P, Flexner C, Chu A et al. Correlation of efficacy, nelfinavir pharmacokinetics, and diarrhea in treatment-naive HIV positive patients receiving nelfinavir, zidovudine and lamivudine. 2nd International Workshop on Clinical Pharmacology of HIV Therapy. Noordwijk: April 24, 2001[Abstract 4.4].
  • 25
    Urquhart J. The electronic medication event monitor. Lessons for pharmacotherapy. Clin Pharmacokinet 1997; 32: 345356.
  • 26
    Hugen PWH, Verweij-van Wissen CPWGM, Burger DM et al. Simultaneous determination of the HIV-protease inhibitors indinavir, nelfinavir, saquinavir and ritonavir by reversed-phase high-performance liquid chromatography. J Chrom B Biomed Sci Appl 1999; 727: 139149.
  • 27
    Compartmental and noncompartmental pharmacokinetics. In Biopharmaceutics and Clinical Pharmacokinetics, Ed GibaldiM. Philadelphia and London: Lea and Febiger, 1991: 1423.
  • 28
    US Department of Health and Human Services. Food and Drug Administration. Center for Drug Evaluation and Research. Guidance for Industry. Food-Effect Bioavailability and Fed Bioequivalence Studies: Study Design, Data Analysis, and Labeling (Draft Guidance) URL:, accessed 2002, July 3.
  • 29
    Viraceptâ Product Monograph. Basel: Hoffmann-La Roche Ltd,
  • 30
    Burger DM, Hugen PWH, Aarnoutse RE et al. Treatment failure of nelfinavir-containing triple therapy can largely be explained by low nelfinavir plasma concentrations. AIDS 2000; 14 (S4): 258.
  • 31
    Pellegrin I, Breilh D, Montestruc F et al. Virologic response to nelfinavir-based regimens: pharmacokinetics and drug resistance mutations (VIRAPHAR study). AIDS 2002; 16: 13311340.
  • 32
    Hsyu PH, Lewis RH, Tran JQ et al. Pharmacokinetics (PK) of nelfinavir (NFV) after once daily dosing in combination with mini-doses of ritonavir (RTV) in healthy volunteers. XIII International AIDS Conference, Durban: July 914, 2000.
  • 33
    Acosta EP, Kakuda TN, Brundage RC et al. Pharmacodynamics of human immunodeficiency virus type 1 protease inhibitors. Clin Infect Dis 2000; 30 (Suppl. 2): S151S159.
  • 34
    Johnson M, Petersen A, Johnson M et al. Comparison of BID and TID dosing of Viracept (nelfinavir, NFV) in combination with stavudine (d4T) and lamivudine (3TC). Fifth Conference on Retroviruses and Opportunistic Infections. Chicago: February 1998[Abstract 373].