Dihydroquinidine versus disopyramide: Efficacy in patients with chronic stable ventricular ectopy

Dihydroquinidine (DQ) is contained in substantial amounts in quinidine salts, but its direct antiar‐rhythmic action has not been studied. The efficacy of oral DQ (300 mg t.i.d.) compared to disopyramide (D) (200 mg t.i.d.) was thus investigated using a double‐blind crossover placebo‐controlled protocol in 12 patients, aged 13 to 67 years, with chronic stable high frequency premature ventricular beats (PVB), defined as > 100 PVB/h during 48‐72‐h control Holter monitoring. The protocol included three 72‐h treatment periods: DQ, D, and placebo at random. On days 2 and 3 of each period a 24‐h Holter recording was carried out; drug blood levels were determined at peak (days 2 and 3) and trough time (day 3). No significant difference in the mean PVB/h was found between control (735±400) and placebo periods (564 ±388), or between the two Holter recordings of each period. Compared to placebo both DQ (106±113, p<0.005) and D (240±263, p<0.05) reduced the mean PVB/h, but the decrease was significantly higher with DQ (78 versus 53%, p<0.02). Nine patients (75%) on DQ and 5 (42%) on D had a >70% decrease in mean PVB/h; complex PVBs were abolished in 3 of 6 patients on both treatments. On day 3, DQ plasma levels were 1.31 ±0.44 (peak) and 0.92 ±0.45 (trough) mg/1; D plasma levels were 2.88±0.64 (peak) and 2.02±0.31 (trough) mg/1; no significant difference was found between day 2 and day 3 samples. Side effects were cutaneous rashes in one patient on DQ and pyrosis in one patient on D. The conclusion is that DQ at the doses used is a very effective and well‐tolerated antiarrhythmic agent. In this study it appeared to be superior to average doses of D for suppressing chronic ventricular arrhythmias.