Objectives To determine, in a double-blind placebo-controlled crossover study, whether l-arginine improves the symptoms of interstitial cystitis (IC), a chronic condition in which nitric oxide (NO) may be important, as previous open pilot studies suggested that l-arginine reduced the pain and frequency associated with IC.
Patients and methods Patients fulfilling the standard diagnostic criteria for IC were randomized to receive l-arginine (2.4 g/day) or placebo for one month. After a 2-week ‘washout’ period they received the other medication. Patients were assessed at each stage using a validated symptom index, a voiding diary, urine analysis and records of adverse events. Patients were asked about overall efficacy at the close of the study. The results were compared using a t-test, with significance indicated at P < 0.05.
Results Sixteen (16) patients (mean age 51.3 years) were enrolled; the mean duration of IC was 5.4 years, the IC symptom index score 29.1, their nocturnal frequency 3.5 (voided volume 182 mL) and daytime frequency 12.7 (124 mL). Patients on placebo showed no differences in any recorded variable over the baseline values. l-arginine caused a statistically significant reduction in the overall symptom score of 2.2 over baseline, but there was no difference in voided volume, frequency or nocturia. As there was no significant difference for any variable between l-arginine and placebo, this reduction in score should be regarded with caution. Three patients withdrew because of side-effects (severe headaches, night sweats and flushing).
Conclusion Oral l-arginine produces a statistically significant improvement in the IC symptom index in patients with IC, but the effect is small. This effect may not be clinically significant as there were no improvements in the other variables assessed and no significant difference between the response to l-arginine and placebo. From these results the use of l-arginine cannot be recommended for treating IC.