3,4‐diaminopyridine base effectively treats the weakness of Lambert‐Eaton myasthenia

Introduction: 3,4‐diaminopyridine has been used to treat Lambert‐Eaton myasthenia (LEM) for 30 years despite the lack of conclusive evidence of efficacy. Methods: We conducted a randomized double‐blind placebo‐controlled withdrawal study in patients with LEM who had been on stable regimens of 3,4‐diaminopyridine base (3,4‐DAP) for ≥ 3 months. The primary efficacy endpoint was >30% deterioration in triple timed up‐and‐go (3TUG) times during tapered drug withdrawal. The secondary endpoint was self‐assessment of LEM–related weakness (W‐SAS). Results: Thirty‐two participants were randomized to continuous 3,4‐DAP or placebo groups. None of the 14 participants who received continuous 3,4‐DAP had > 30% deterioration in 3TUG time versus 72% of the 18 who tapered to placebo (P < 0.0001). W‐SAS similarly demonstrated an advantage for continuous treatment over placebo (P < 0.0001). Requirement for rescue and adverse events were more common in the placebo group. Discussion: This trial provides significant evidence of efficacy of 3,4‐DAP in the maintenance of strength in LEM. Muscle Nerve 57: 561–568, 2018