Address correspondence to Willi Cawello, UCB Pharma, Alfred Nobel Str., D40789 Monheim, Germany. E-mail: email@example.com
Purpose: To test for bioequivalence of 200 mg lacosamide oral tablet and syrup formulations. Additional objectives were to compare the pharmacokinetic profile of lacosamide in saliva and plasma, and to evaluate its tolerability.
Methods: This open-label, randomized, two-way crossover trial was conducted in 16 healthy Caucasian male participants in Germany. The bioequivalence of 200 mg lacosamide tablet and syrup was evaluated using plasma to determine maximum measured concentration (Cmax) and area under the curve from zero to the last time point (AUC)(0–tz). Plasma and saliva samples for evaluation of pharmacokinetic parameters of lacosamide and the major metabolite O-desmethyl lacosamide (SPM 12809) were taken over 15 time points (0.5–72 h) and used to statistically compare bioavailability of the two. Urine samples were collected predose and over five time points (0–48 h) to evaluate the cumulative amount of unchanged drug and metabolite.
Key Findings: Lacosamide median time to reach Cmax (tmax) was 1 h for tablet and 0.5 h for syrup in plasma and saliva. Mean terminal half life (t½) for tablet and syrup was 12.5 and 12.4 h in plasma, and 13.1 and 13.3 h in saliva, respectively. Tablet and syrup mean plasma AUC(0–tz) was 84.5 and 83.3 μg/mL*h, respectively. Mean AUC(0–tz) in saliva was 93.2 μg/mL*h for tablet and syrup. Mean Cmax for tablet was 5.26 μg/mL in plasma and 5.63 μg/mL in saliva. Syrup mean Cmax was 5.14 and 8.32 μg/mL in plasma and saliva, respectively. Within 2 h of syrup administration, elevated lacosamide concentration in saliva compared to plasma was observed. The ratio of lacosamide syrup to tablet was 0.98 for Cmax and 0.99 for AUC(0–tz) in plasma, and 1.00 for AUC(0–tz) in saliva; the 90% confidence intervals (CIs) for these parameters were within the range of 0.80–1.25, which meets accepted bioequivalence criteria. The syrup-to-tablet ratio for Cmax in saliva was 1.48, and the 90% CIs exceeded the accepted upper boundary for bioequivalence (1.32–1.66). Both formulations were well tolerated. Metabolite concentration versus time profiles for saliva were similar to plasma following tablet and syrup administration.
Significance: The tablet and syrup formulations of lacosamide 200 mg were bioequivalent and well tolerated. Saliva samples were demonstrated to be a suitable surrogate to evaluate lacosamide tablet pharmacokinetics in the central compartment. Due to residual syrup in the buccal cavity, limitations exist when using saliva to evaluate the pharmacokinetics of lacosamide syrup <2 h after administration.
Plasma is the primary tissue sampled and analyzed for drug in pharmacokinetic (PK) studies. Drug plasma concentrations are sufficient to calculate PK parameters that characterize drug transport, quantify drug exposure in the body, and provide the basis for PK and pharmacodynamic (PKPD) modeling. A statistical comparison of these PK parameters from two different drug formulations or routes of administration are also used to test for bioequivalence.
In humans, saliva is generated by paired salivary glands (parotid, sublingual, and submaxillary) at a rate of approximately 1 mL/min, increasing to 6 mL/min upon stimulation by the autonomic nervous system (Liu & Delgado, 1999). Saliva secreted during rest periods contains small amounts of proteins as well as sodium, potassium, and other electrolytes. The pH ranges from 5.8 to 7.8; however, this can rise following stimulation (Drobitch & Svensson, 1992; Liu & Delgado, 1999).
The ratio of drug concentration in saliva versus plasma for antiepileptic drugs (AEDs) ranges from 0.1 for phenytoin to about 1 for primidone (Gorodischer & Koren, 1992; Liu & Delgado, 1999). A low ratio does not preclude the suitability of saliva to determine PK parameters. For example, although the ratio for tolbutamide was reported as 0.012, saliva samples were suitable for compartmental PK evaluation (Matin et al., 1974).
Lacosamide [(R)-2-acetamido-N-benzyl-3-methoxypropionamide] is an AED approved as adjunctive therapy for adults with partial onset seizures. Following oral administration, plasma concentrations of lacosamide increased rapidly and reached a maximum at about 1–2 h post dose. PK analysis indicated high oral bioavailability, plasma elimination half-life of approximately 12–14 h, and low interindividual and intraindividual variability of PK parameters (Cawello et al., 2010; Nickel et al., 2008). Lacosamide is eliminated primarily by renal excretion; approximately 40% of the dose is excreted unchanged, 30% is excreted as the pharmacologically inactive major metabolite O-desmethyl lacosamide (SPM 12809), and the remainder as structurally unknown polar fraction (VIMPAT, UCB Pharma SA, Brussels, Belgium).
This article presents the results from trial SP657, conducted to evaluate the bioequivalence of the tablet and syrup formulations of 200 mg lacosamide, and the PK of lacosamide and its major metabolite O-desmethyl lacosamide in plasma, urine, and saliva, and to evaluate tolerability.
This randomized, single-center, open-label, two-period, crossover phase 1 trial was conducted between November 2004 and January 2005 in Kiel, Germany. The trial was approved by the regional ethics committee of the Chamber of Physicians in Schleswig-Holstein. Subjects were randomly assigned to first receive a single 200 mg lacosamide dose (tablet or syrup) followed by a 6-day washout period prior to treatment crossover. The tablet dose consisted of two 100-mg film-coated lacosamide tablets, and the 20-mL syrup dose consisted of lacosamide at 10 mg/mL.
Sixteen healthy Caucasian male volunteers between the ages of 18 and 45 years with a body mass index (BMI) of 19–30 kg/m2 were recruited to participate in the trial. All were required to provide consent, comply with trial requirements, and to have no clinically relevant cardiovascular, renal, gastrointestinal, hepatic, metabolic, endocrine, neurologic, or psychiatric abnormalities. Volunteers were excluded if they participated in another trial of an investigational product within the last 3 months; performed heavy physical exertion 2 days before the confinement; consumed >40 g of alcohol/day; tested positive for alcohol (breath test) and/or drugs (urine test) during study enrollment; had a history of alcohol or drug abuse within the last 6 months; smoked more than five cigarettes per day or had done so within 6 months prior to commencement of the trial; had a diet that deviated notably from the normal amounts of protein, carbohydrate, and fat (as judged by the investigators); consumed >600 mg caffeine per day; donated blood or had a comparable blood loss (>350 mL) within the last 3 months prior to the first day of dosing; had abnormal vital signs; were taking any concomitant medication currently or within 2 weeks prior to the first day of dosing (with the exception of 1 g/dose paracetamol, which was allowed up to 48 h prior to dosing); tested positive for HIV, hepatitis B, or hepatitis C; had clinically relevant out-of-range laboratory results; had known hypersensitivity to any component of the investigational products; had a clinically relevant allergy; or had a current malignancy condition or a seizure disorder.
Trial investigators withdrew volunteers if they showed clinically relevant electrocardiography (ECG) changes, experienced an adverse event (AE) that did not justify a continuation of the trial, had an inability to obtain plasma samples, or had a protocol deviation that jeopardized the performance of the trial. Volunteers could also decide to withdraw from the trial at any time—those who withdrew were requested to take part in the final medical examination, which included blood draw for laboratory screening for safety purposes.
Sample collection and handling
Fifteen blood samples (6 mL each) were drawn by venous puncture or indwelling venous catheter into lithium-heparinized tubes on days 1–4 during each treatment period (a total of 30 plasma samples per participant). Blood samples were drawn prior to the morning dose (predose sample) and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24, 36, 48, 60, and 72 h after lacosamide administration. Samples were placed into an ice bath immediately after blood draw (for a maximum of 15 min) and then centrifuged for 10 min at 1,600 g at 4°C. Supernatants were transferred into two polypropylene tubes (one tube with at least 1.5 mL for primary analysis and one tube with the remaining supernatant as reserve). The tubes were sealed and stored at a temperature of −20°C or below to await analysis.
Saliva samples (minimum 2 mL each) were collected following each blood sample draw. Sampling was done by spontaneous expectoration (no stimulation). Samples were transferred into polypropylene tubes, which were sealed and stored at −20°C or below within 15 min after sampling.
Urine was collected on day 1 (predose) and 0–4, 4–8, 8–12, 12–24, and 24–48 h thereafter. During each collection period, bottles with collected urine were stored at approximately 4–8°C. After completion of the collection period, two 5 mL aliquots were taken and frozen in polypropylene tubes.
Lacosamide and O-desmethyl lacosamide plasma and urine concentrations were measured using high-performance liquid chromatography methods with mass spectrometric detection (HPLC-MS); hepta-deuterated lacosamide and tris-deuterated O-desmethyl lacosamide were used as internal standards. Internal standard solution (20 μL) and 30% trichloracetic acid (TCA) (30 μL) were added to 0.1 mL of plasma sample. The solution was vortexed for 5 s and centrifuged (2,680 g 10 min, room temperature). The supernatant (25 μL) was mixed with distilled water (0.5 mL) and transferred to an autosampler vial. Urine (10 μL) and internal standard solution (20 μL) were added to water (5 mL) and vortexed for 5 s. A 0.1-mL aliquot was then diluted with 0.4 mL of distilled water and vortexed and transferred to an autosampler vial. For plasma and urine samples, 40 μL was injected for analysis.
Chromatography was performed on a reverse-phase column (Lichrospher 60 RP select B, 125 × 4 mm) using a mixture of water, acetonitrile, ammonium acetate, and acetic acid as mobile phase (1.5 L water, 0.5 L acetonitrile, 0.5 g ammonium acetate, 5 mL concentrated acetic acid). Chromatography was isocratic with a flow rate of 0.5 mL/min. The detection of analytes and the respective deuterated internal standards was accomplished by atmospheric pressure ionization in the positive mode. Molecular ions for quantification were m/z = 251.10 (lacosamide), m/z = 258.30 (hepta-deuterated lacosamide), m/z = 237.10 (O-desmethyl lacosamide), and m/z = 240.00 (tris-deuterated O-desmethyl lacosamide). Respective calibration ranges for lacosamide and O-desmethyl lacosamide were 0.1–20 and 0.02–4.0 μg/mL for plasma samples, and 5.0–500 and 1.0–100 μg/mL for urine samples. Intra-assay and interassay accuracies and precisions were ≤15.0% for each moiety over their respective calibration range. The lower limit of quantification (LLQ) in plasma for lacosamide and metabolite were 0.1 and 0.02 μg/mL, respectively; corresponding values for urine samples were 5 and 1 μg/mL, respectively.
Measurements of lacosamide and O-desmethyl lacosamide concentrations in saliva samples were conducted using HPLC-MS. Saliva sample preparation was performed by solid-phase extraction on Isolute (Biotage, Uppsala, Sweden) C18 cartridges. Following chromatography with a narrow bore SymmetryShiel (Waters Corporation, Milford, MA, U.S.A.) RP8 column, lacosamide, and O-desmethyl lacosamide were detected by electrospray single-stage mass spectrometry. The calibration range was 0.02–12.0 μg/mL for both analytes, and the calibration curves were calculated by linear regression with 1/χ2 weighting. Intra-assay and interassay accuracies and precisions were ≤10.0% in the calibration range. The lower limit of quantification in saliva samples was 0.02 μg/mL for lacosamide and O-desmethyl lacosamide. Assays for plasma, urine, and saliva samples were validated according to the “Guidelines for Industry” (FDA, 2001).
The main PK parameters for bioequivalence testing were the area under the concentration time curve from zero to the last time point (tz) with a concentration above the lower limit of quantification [AUC(0–tz)] and maximum measured concentration (Cmax) of lacosamide in plasma. Additional PK parameters were AUC(0–tz) and Cmax of lacosamide in saliva; AUC(0–tz) and Cmax of O-desmethyl lacosamide in plasma and saliva; half-life (t½), time to reach Cmax (tmax), and relative bioavailability of test formulation (syrup) versus tablet reference (frel) of lacosamide and O-desmethyl lacosamide in plasma and saliva. Urine samples were used to evaluate the cumulative amount of excreted (Ae) unchanged drug as well as metabolite.
AEs, changes in laboratory parameters relevant to safety, ECG, and vital signs (pulse rate, blood pressure) were evaluated to assess safety and tolerability of both formulations.
Sample size was chosen based on known low intraindividual variability of PK parameters for lacosamide. Main PK parameters AUC(0–tz) and Cmax of lacosamide were analyzed using an analysis of variance (ANOVA) including the factors sequence, subject within sequence, treatment and period. Statistical analysis of PK parameters provided confidence intervals (CIs) for lacosamide syrup-to-tablet ratio to evaluate bioequivalence of the two formulations. Bioequivalence was concluded if the 90% CIs for the treatment ratios were within the acceptance range of 0.80 and 1.25 for AUC(0–tz) and Cmax (EMA, 2001, FDA, 2002). For the analysis of the correlation between saliva and plasma concentrations of lacosamide and O-desmethyl lacosamide a linear regression was carried out with the corresponding data.
Of the 16 individuals who volunteered to participate in the trial, all were enrolled and completed the trial without any major protocol deviation. Per enrollment criteria, all were healthy Caucasian male participants; demographic and characteristics data are presented in Table 1.
Table 1. Demographic and characteristics of study volunteers (n = 16)
Mean ± SD
BMI, body mass index; SD, standard deviation.
28.8 ± 5.7
181.4 ± 6.8
77.2 ± 8.7
23.5 ± 2.2
Pharmacokinetics of lacosamide
Lacosamide plasma concentrations rapidly reached Cmax immediately following tablet or syrup administration. The median plasma tmax for tablet and syrup were 1 and 0.5 h post dose, respectively (Table 2). Mean plasma t½ for tablet was 12.5 and 12.4 h for syrup.
Table 2. Pharmacokinetic parameters (geometric mean with coefficient of variation as percent of mean) estimated from plasma, urine, and saliva samples (as noted) for lacosamide and SPM 12809 after single oral administration of 200 mg as tablet or syrup (n = 16 volunteers)
aArithmetic mean ± SD.
Plasma and urine samples
77.58 ± 12.85
75.42 ± 11.87
51.43 ± 21.44
46.00 ± 20.13
For saliva, the mean lacosamide concentration versus time curve up to 24 h following tablet administration was consistently greater at all time points (range 3–10%) than the corresponding lacosamide plasma curve (Fig. 1A). Following syrup administration, mean lacosamide saliva concentrations were 16–77% greater than plasma at 0.5 and 1 h; however, the difference between saliva and plasma lacosamide concentrations at all other sampling times up to 24 h was 2–12% (Fig. 1B). The slope of the regression line of lacosamide concentrations in saliva versus plasma was 1.025 (Fig. 3B).
Tablet and syrup PK parameters [AUC(0–tz), Cmax, Ae, tmax, and t½] from plasma, saliva, and urine samples for lacosamide are presented in Table 2. All parameters, with the exception of saliva Cmax for lacosamide syrup, were comparable for tablet and syrup.
Pharmacokinetics of O-desmethyl lacosamide
Metabolite PK parameters obtained from plasma, saliva, and urine stratified by tablet and syrup dose are presented in Table 2. All parameters were similar for the tablet and syrup formulations. Metabolite concentration versus time profiles for saliva samples were similar to plasma samples following tablet and syrup administration (Fig. 2).
Correlation between plasma and saliva concentration
High correlation exists between saliva and plasma lacosamide concentrations for all samples collected later than 0.5 h after syrup administration (Fig. 3A; slope 1.10) and for all samples after tablet administration (Fig. 3B; slope 1.03). High correlation was also observed for O-desmethyl lacosamide (Fig. 4; slope 1.05).
Bioequivalence using saliva samples
AUC(0–tz) and Cmax syrup to tablet ratios and 90% CIs for lacosamide and O-desmethyl lacosamide in saliva and plasma are presented in Table 3. The ratios for lacosamide AUC(0–tz) and Cmax in plasma, and AUC(0–tz) in saliva were each approximately 1 and the 90% CIs were within the accepted bioequivalence limits of 0.80 and 1.25. Lacosamide Cmax ratio for all saliva samples was 1.48, and the 90% CIs exceeded the accepted upper boundary for bioequivalence (1.32–1.66).
Table 3. ANOVA results (estimate, 90% confidence interval) for the syrup-to-tablet ratio of primary pharmacokinetic parameters of lacosamide and SPM 12809 with data from plasma and saliva samples (n = 16 volunteers)
Overall, 38 AEs were reported by the volunteers during the trial, with 18 and 20 AEs reported following lacosamide tablet and syrup administration, respectively. Overall, 35 AEs (92.1%) were mild and 3 AEs (7.9%; two incidents of dizziness and one of thrombophlebitis) were moderate in intensity. Fatigue was the most commonly reported AE following both treatments (Table 4), and all incidences were mild in intensity. Thirty-four AEs were considered to be at least possibly related to trial medication by the investigator. All AEs resolved by the end of the trial. No clinically relevant changes in laboratory and ECG parameters or vital signs were observed.
Table 4. Incidence of adverse events by lacosamide formulation (safety set, n = 16 volunteers)
System organ class (MedDRA)
Lacosamide tablet n (%)
Lacosamide syrup n (%)
MedDRA, Medical Dictionary for Regulatory Activities.
Volunteers with at least 1 AE
A number of different objectives were evaluated in the current trial: notably the bioequivalence of the tablet and syrup formulations of 200 mg lacosamide, comparison of the PK profiles of the two formulations in plasma, urine, and saliva, and their tolerability in healthy males. All 16 volunteers enrolled in the trial received two single doses of lacosamide as a tablet and syrup in randomized order and completed the trial.
The PK profiles of lacosamide tablet versus syrup in saliva, plasma, and urine were comparable, with the exception of lacosamide syrup Cmax in saliva. Lower correlation was observed for saliva versus plasma lacosamide syrup samples, especially those taken 0.5–1 h after syrup administration. This result was not surprising, as residual lacosamide in the buccal cavity from the syrup likely led to concentration discrepancies in saliva samples at earlier time points. A similar outcome was observed for levetiracetam solution as drug concentrations in saliva compared to plasma were higher than expected 2 h following administration of the solution (Lins et al., 2007).
The PK profile of metabolite O-desmethyl lacosamide in saliva and plasma for lacosamide syrup and tablet were comparable. Good correlation for O-desmethyl lacosamide concentrations was observed between saliva and plasma samples at all time points. As the metabolite appears after lacosamide administration, interference with salivary O-desmethyl lacosamide concentrations was not observed following lacosamide syrup administration.
Previous studies have shown that for some AEDs the saliva-to-total-plasma drug concentration ratio is an indirect measure of drug plasma protein binding (Fuse et al., 2005; Incecayir et al., 2007). For AEDs, only unbound drug can cross biologic barriers that separate tissue compartments (Drobitch & Svensson, 1992); therefore, a low ratio of saliva to total drug is indicative of high plasma protein binding, whereas a ratio closer to 1 is indicative of minimal plasma protein binding. In the present trial, the saliva to plasma lacosamide concentration ratios, determined by the inverse slope of each regression analysis, were 0.98 and 0.91 for lacosamide samples collected following tablet administration and for those collected after 0.5 h following syrup administration, respectively. The ≤10% difference for saliva and total plasma lacosamide concentration ratio is indicative of low lacosamide protein binding. These results match findings determined by equilibrium dialysis of plasma samples (Fountain et al., 2012). Furthermore, in comparison with other neutral drugs with a similar logP (a measure of lipophilicity) and known plasma protein binding, lacosamide logP of 0.25 also suggests low lacosamide plasma protein binding (Rodgers & Rowland, 2006).
In contrast, a recent publication by Greenaway et al. (2011), reported 10-fold lower lacosamide concentrations in saliva than in serum and concluded from their results that lacosamide has high (90%) protein binding. The differences in findings for protein binding (90% for Greenaway et al. using serum samples, and <15% for our results using plasma samples, Fountain et al. ) may be due to a difference in methodology. To determine free lacosamide plasma concentrations, Greenaway et al. used a microfiltration (Amicon Centrifree Micropartition System; Amicon, Stonehouse, United Kingdom) and centrifuged the system at 25°C rather than physiologic temperature (37°C); whereas Fountain et al. determined lacosamide binding by equilibrium dialysis at 37°C using plasma from lacosamide-naive patients with epilepsy 12 h following an infusion of 300 mg lacosamide. The equilibrium dialysis results support the salivary concentrations reported in the present study, indicating that lacosamide has low (<15%) protein binding.
Point estimates of the lacosamide syrup-to-tablet ratio in plasma were close to 1 for AUC(0–tz) and Cmax , and the 90% CIs were within the accepted bioequivalence range of 0.80–1.25. Therefore, 20 mL of a 10 mg/mL lacosamide syrup (200 mg) was shown to be bioequivalent to two 100-mg lacosamide tablets.
Overall, the tablet and syrup formulations of 200 mg lacosamide were well tolerated. All reported AEs were mild or moderate in intensity and all resolved by the end of the trial. No clinically relevant changes in laboratory and ECG parameters or vital signs were observed.
In conclusion, the results from this trial demonstrate the bioequivalence, safety, and tolerability of the tablet and syrup formulations of 200 mg lacosamide in healthy individuals. The trial results also support the use of saliva samples to estimate lacosamide PK parameters immediately following tablet intake and 1–2 h after syrup administration. Both saliva and plasma sampling effectively described the PK of lacosamide in the central circulation.
This study was funded by UCB Pharma, Germany. Writing and editorial support was provided by Apurva Davé, PhD, of Prescott Medical Communications Group in Chicago, Illinois, U.S.A. The authors also wish to thank Azita Tofighy, PhD, of UCB Pharma for her assistance in the development of this manuscript.
W. Cawello, H. Bökens, B. Nickel, and J-O. Andreas are employees of UCB Pharma and have no financial disclosures. A. Halabi does not have any conflicts of interest to disclose. We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.