Diphenidol: a new agent for the treatment of digitalis-induced arrhythmias. Electrophysiologic and hemodynamic studies

High frequency transcutaneous electrical nerve stimulation with diphenidol administration results in an additive antiallodynic effect in rats following chronic constriction injury

The impact of coadministration of transcutaneous electrical nerve stimulation (TENS) and diphenidol is not well established. Here we estimated the effects of diphenidol in combination with TENS on mechanical allodynia and tumor necrosis factor-α (TNF-α) expression. Using an animal chronic constriction injury (CCI) model, the rat was estimated for evidence of mechanical sensitivity via von Frey hair stimulation and TNF-α expression in the sciatic nerve using the ELISA assay. High frequency (100Hz) TENS or intraperitoneal injection of diphenidol (2.0μmol/kg) was applied daily, starting on postoperative day 1 (POD1) and lasting for the next 13 days. We demonstrated that both high frequency TENS and diphenidol groups had an increase in mechanical withdrawal thresholds of 60%. Coadministration of high frequency TENS and diphenidol gives better results of paw withdrawal thresholds in comparison with high frequency TENS alone or diphenidol alone. Both diphenidol and coadministration of high frequency TENS with diphenidol groups showed a significant reduction of the TNF-α level compared with the CCI or HFS group (P<0.05) in the sciatic nerve on POD7, whereas the CCI or high frequency TENS group exhibited a higher TNF-α level than the sham group (P<0.05). Our resulting data revealed that diphenidol alone, high frequency TENS alone, and the combination produced a reduction of neuropathic allodynia. Both diphenidol and the combination of diphenidol with high frequency TENS inhibited TNF-α expression. A moderately effective dose of diphenidol appeared to have an additive effect with high frequency TENS. Therefore, multidisciplinary treatments could be considered for this kind of mechanical allodynia.

Electrophysiological effects of AFD-21 and AFD-19, new antiarrhythmic compounds on papillary muscles and single ventricular myocytes isolated from guinea-pig hearts

1. The effects of AFD-21, a newly synthesized antiarrhythmic compound, and AFD-19, its active metabolite, on transmembrane action potentials were examined in right ventricular papillary muscles and single ventricular myocytes isolated from guinea-pig hearts. 2. In papillary muscles, AFD-21 10(-5) M caused a slight prolongation of action potential duration (APD), while AFD-19 above 10(-6) M shortened APD in a dose-dependent manner. 3. Both AFD-21 and AFD-19 above 10(-6) M caused a significant and dose-dependent decrease in the maximum upstroke velocity (Vmax) of the action potential without affecting the resting membrane potential. 4. In the presence of AFD-21 or AFD-19, trains of stimuli at rates greater than or equal to 0.2 Hz led to an exponential decline in Vmax. This use-dependent block was enhanced at higher stimulation frequencies. A time constant for the recovery of Vmax from the use-dependent block was 2.9 s for AFD-21 and 3.6s for AFD-19. 5. The curves relating membrane potential and Vmax were shifted by AFD-21 (10(-5) M), or AFD-19 (10(-5) M) to the direction of more negative potentials by 5.3 mV and 5.1 mV respectively. 6. In single ventricular myocytes treated with AFD-21 (10(-5) M) or AFD-19 (10(-5) M), Vmax of test action potentials preceded by conditioning clamp pulses to 0 mV was decreased progressively as the clamp pulse duration was prolonged. 7. These findings suggest that both AFD-21 and AFD-19 have use- and voltage-dependent inhibitory action on the sodium channel by binding to the channel during its inactivated state, and that the unbinding rate is comparable to that of Class I antiarrhythmic drugs with intermediate kinetics.

The effect of diphenidol on ouabain cardiotoxicity in the cat

The capacity of diphenidol to influence ouabain-induced cardiotoxicity was studied in anaesthetized cats with and without spinal cord transection. 2 Diphenidol pretreatment increased the lethal dose of ouabain in both intact cats and cats in which the spinal cords had been transected. Diphenidol pretreatment increased the myocardial content of ouabain associated with death in the intact animals, but failed to influence the lethal ventricular concentration in cats with transected spinal cords. 3 The failure of diphenidol to influence tissue thresholds for toxicity in the spinal cat and the equivalence of tissue ouabain requirements for death in spinal cats and diphenidol-treated intact animals, suggest a neural mechanism for the protective effect in intact animals. 4 Ouabain administration prolonged atrio-ventricular conduction time in all animals and diphenidol attenuated this effect. Thus, the influence of both drugs on antrioventricular conduction may not be entirely mediated by central neurones.

Diphenidol treatment of arrhythmias

The antiarrhythmic activity of diphenidol, an antiemetic, has been demonstrated both in electrophysiologic studies of patiens and in experimental arrhythmias in animals. Accordingly, 18 patients with tachyarrhythmias were treated with intravenous diphenidol in doses of 0.5 to 1.5 mg/kg. In six patients with atrial arrhythmias, there was no notable effect. Similarly, 12 patients with premature ventricular contractions were treated and studied. In six of them, ectopic beats were abolished, at least transiently; in three the number of ventricular premature contractions decreased; in two there was no effect; and in one, the number of premature beats was increased. Of the total number of 18 patients, 14 suffered adverse effects related to the central nervous system. These adverse effects were of such severity as to suggest that further studies with diphenidol as an antiarrhythmic are not warranted.