An isolated report describes cardiac failure in a patient given ajmaline with lidocaine. Quinidine causes a very considerableincrease in plasma levels of ajmaline, and phenobarbital appears to cause a marked reduction.
Clinical evidence,mechanism, importance and management
A study(See reference number 2) in 4 healthy subjects found that if a single 200mg oral dose of quinidine was given with a single 50mg oral dose of ajmaline, AUC of ajmaline was increased 10- to 30-fold and maximum plasma concentrations increased from 18 to 141 nanograms/mL. Another single-dose
study in 5 healthy subjects found that metabolism of ajmaline was inhibited by quinidine, possibly because quinidine becomes competitively bound to enzymes that metabolise ajmaline (See reference number 3).
Therefore clinical effects of ajmaline would be expected to be markedly diminished in those taking phenobar
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Hori R,Okumura K, Inui K-I, Yasuhara M, Yamada K, Sakurai T, Kawai C. Quinidine-induced rise in ajmaline plasma concentration. J Pharm Pharmacol (1984) 36, 202–4.
Köppel C,Tenczer J, Arndt I. Metabolic disposition of ajmaline. Eur J Drug Metab Pharmacokinet (1989) 14, 309–16.
Köppel C,Wagemann A, Martens F. Pharmacokinetics and antiarrhythmic efficacy of intravenous ajmaline in ventricular arrhythmia of acute onset. Eur J Drug Metab Pharmacokinet (1989) 14, 161–7.