Combined effect of disopyramide and erythromycin on ventricular repolarization in dogs with complete atrioventricular block.
(57/169)
The combined effects of disopyramide (DP) and erythromycin (EM) on ventricular repolarization and the inciden-ces of ventricular premature contractions (VPCs) and torsades de pointes (TdP) were investigated in 12 anesthetized dogs with complete atrioventricular block. Monophasic action potentials (MAPs) were measured from the left and right ventricular (LV and RV) endocardium. The right or left ventricle was paced at a cycle length of 750-1000 msec. Dogs were divided into 2 groups and given either intravenous DP at 3 mg/kg and then intravenous EM at 50 mg/kg (group 1, n = 8), or intravenous EM at 50 mg/kg and then intravenous DP at 3 mg/kg (group 2, n = 4). MAP duration at 90% repolarization (MAPD(90)) was measured before drug administration (baseline) and again after administration of each drug. RV MAPD(90) and LV MAPD(90) increased significantly (P < 0.02) after administration of each drug in group 1 (RV MAPD(90): from 247.0 +/- 36.3 [baseline] to 283.5 +/- 38.3 to 321.8 +/- 56.7; LV MAPD(90): from 262.6 +/- 49.1 (baseline) to 296.1 +/- 58.8 to 351.0 +/- 80.6). Early afterdepolarizations developed in 2 group 1 dogs after administration of DP and in 4 additional dogs after administration of EM. Frequent VPCs occurred in 1 dog after administration of DP and in 2 additional dogs after administration of EM, and TdP and ventricular tachycardias developed in 2 of the 3 dogs after administration of EM. Similar trends occurred in group 2. These results indicate a potentially fatal interaction between DP and EM administered in clinically relevant doses. (+info)
Comparison of cardiovascular effects of pirmenol with those of disopyramide in isolated canine heart preparations cross-circulated with a donor dog.
(58/169)
To assess the cardiovascular profiles of pirmenol, a new antiarrhythmic drug, and to compare them with those of disopyramide, isolated canine sinoatrial node, papillary muscle and atrioventricular node preparations cross-circulated with a donor dog were used. Pirmenol injected intraarterially into the isolated preparations showed negative chronotropic and inotropic effects, which were comparable to those of disopyramide; and it also showed coronary vasodilator and negative dromotropic effects on atrio-His as well as His-ventricular conduction, which were significantly more potent than those of disopyramide. Similarly, pirmenol administered intravenously into the donor dog showed more potent negative dromotropic effects on the PQ interval and QRS width than disopyramide, while in the isolated preparations cross-circulated by the donor dog, pirmenol and disopyramide showed equipotent cardiodepressant effects. In the same preparation, pirmenol decreased coronary blood flow following a transient increase, while disopyramide only decreased coronary blood flow. Since the antiarrhythmic action of class I drugs is considered to result from inhibition of the fast inward current, which generates and propagates action potentials and also induces ventricular automaticity, our results suggest that pirmenol possesses an electrophysiologic effect typical to an efficacious class I agent such as disopyramide. (+info)
Treatment of obstructive hypertrophic cardiomyopathy symptoms and gradient resistant to first-line therapy with beta-blockade or verapamil.
(59/169)
Simultaneous determination of disopyramide and mono-N-dealkyldisopyramide enantiomers in plasma and urine by use of a chiral cellulose-derivative column.
(60/169)
This assay allows simultaneous determination of the enantiomers of both disopyramide and its active metabolite, mono-N-dealkyldisopyramide, in 1 mL of plasma or 0.1 mL of urine within approximately 35 min by HPLC with a chiral cellulose-derivative column and ultraviolet detection. Recoveries for the analytes and the internal standard (racemic verapamil) with an extraction from alkalinized plasma or urine into diethyl ether were greater than 90%. Intra- and interassay CVs for disopyramide enantiomers were less than 5.5% at 2.5 mg/L in plasma and less than 6.5% at 25 mg/L in urine; for mono-N-dealkyldisopyramide enantiomers they were less than 6.3% and less than 8.9%, respectively. Intra- and interassay relative errors for determining these analytes in plasma and urine at 2.5 and 25 mg/L, respectively, ranged from -5.9% to +2.5%. The calibration curves for the respective analytes were linear (r = 0.995 or greater, P less than 0.01) from 0.025 to 5.0 mg/L in plasma and from 0.5 to 10 mg/L in urine. The lower detection limits (signal-to-noise ratio of 3) for S(+)-disopyramide and the other analytes were 0.010 and 0.025 mg/L, respectively. We evaluated clinical applicability of this method by determining steady-state plasma concentrations and urinary excretions of the respective analytes in a pediatric patient being treated with racemic disopyramide. (+info)
Molecular and structural basis of resting and use-dependent block of sodium current defined using disopyramide analogues.
(61/169)
The effects of disopyramide (Norpace) and 14 closely related structural analogues on the Na current of voltage clamped squid axons were examined to determine which physico-chemical properties and which changes in the structure of the Norpace molecule can alter the nature of its sodium channel blocking actions. Conventional voltage clamp technique for internally perfused giant axons was used. Axons were exposed to 100 microM concentrations via the internal perfusion solution, and the actions of the 15 analogues to produce resting and use-dependent block of Na current were assessed. The roles of Na ions and the activation and inactivation processes in the development of and recovery from use-dependent block of Na current induced by the Norpace analogues were also examined. The results indicate that for both mono-tertiary and bis-tertiary amines the potency to produce use-dependent block was proportional to molecular weight, whereas the correlation between potency to produce resting block and molecular weight was significant only for bis-tertiary amines. The mono- were more potent than the bis-compounds. However, comparisons between compounds having similar molecular weights and/or pKa values indicate that other factors also can influence blocking potency. For compounds within each homologous mono- or bis-tertiary amine series, hydrophobicity as estimated from log P values (P = octanol/water partition coefficient) was found to influence the potency to produce use dependent block of Na current. Use-dependent block was extant in axons internally exposed to pronase to remove the inactivation process, which indicates that inactivation is not an obligate condition for development of use-dependent block of Na current. An important role for the activation process in the development of use-dependent block of Na current is suggested by the finding that, in general, the voltage dependence of Na current activation paralleled that of use-dependent block. However, the potential dependence of use-dependent block produced by less hydrophobic but not by more hydrophobic compounds was shifted in the hyperpolarizing direction by removing Na+ from the external solution. Compounds with intermediate hydrophobicities altered the time course of Na current during its activating and inactivating phases. This finding can be explained by the kinetics of association and dissociation of drug molecules with channel receptor sites during the development and relaxation of use-dependent block rather than by postulating any major effect of drug to alter channel gating kinetics. In summary, a comprehensive study of the structure-activity relationship of the Norpace molecule was achieved and the implications of the findings with respect to several factors believed to influence drug potency for resting and use-dependent block of the Na current in squid axon are examined and discussed. (+info)
A kinetic analysis of the endplate ion channel blocking action of disopyramide and its optical isomers.
(62/169)
The effects of the antiarrhythmic agent disopyramide was studied on responses from voltage-clamped endplates at the neuromuscular junction of the garter snake. Disopyramide reduced endplate current amplitude and decay time constant in a concentration- and voltage-dependent manner. Endplate current decays remained monophasic in the presence of the drug. These results were interpreted in terms of the drug blocking the open form of the acetylcholine receptor-ion channel complex. Disopyramide produced a greater reduction of the amplitude of endplate currents than of miniature endplate currents. The reduction in miniature endplate current amplitude was not voltage-dependent. Analysis of endplate current driving functions showed that this was due to the rapid occurrence of channel block during the rising phase of the endplate current. The residual reduction, apart from that produced by channel block, is most probably due to receptor block. Disopyramide had a voltage-dependent blocking rate constant of about 10(7) M-1 S-1 at -90 mV. The unblocking rate constant was estimated from the results of experiments using paired ionophoretically applied pulses of acetylcholine. This value was again voltage-dependent and approximately 1 s-1. The actions of the (+)- and (-)-stereoisomers of disopyramide on endplate current decay were identical, indicating that the channel binding site at the neuromuscular junction is not stereoselective. (+info)
A receptor for type I antiarrhythmic drugs associated with rat cardiac sodium channels.
(63/169)
We assessed the effects of type I antiarrhythmic drugs on the binding of ligands to receptors on voltage-sensitive sodium channels of rat cardiac myocytes. The radioligand was [3H]batrachotoxinin A 20 alpha-benzoate ([3H]BTXB), a toxin that binds to the sodium channel. The 8 drugs tested inhibited [3H]BTXB binding in a dose-dependent fashion with IC50 values from 1.34 microM for O-demethylencainide to 811 microM for procainamide. A log-log plot of IC50 versus mean therapeutic serum concentration yielded a regression line with slope of 1.17 and r of 0.95. Scatchard analysis of [3H]BTXB binding showed that lidocaine reduced the maximal binding without altering the KD for [3H]BTXB binding, indicating allosteric inhibition. The inhibition by lidocaine of [3H]BTXB binding was reversible within 30 minutes when the samples were diluted from 390 to 39 microM lidocaine. In other studies, the stereoisomers of tocainide were shown to have a threefold to fourfold difference in IC50 for inhibition of [3H]BTXB binding. The binding of antiarrhythmic drugs to this site is saturable, reversible, and stereospecific and occurs at pharmacologically relevant concentrations with similar rank order of potency in vivo and in vitro. This suggests that binding at this site relates to pharmacologic activity. (+info)
The effects of external and internal application of disopyramide on the ionic currents of the squid giant axon.
(64/169)
1 The actions of the class I anti-arrythmic agent, disopyramide, on the ionic currents of the voltage-clamped squid axon have been investigated, by use of both extra-axonal and intra-axonal routes of application. 2 Extra-axonal application of 0.1 mM disopyramide produced no significant effects on the membrane currents. External disopyramide at 1.0 mM caused small, poorly reversible inhibition of both sodium and potassium currents. This block was use-dependent and was enhanced by use of test stimuli to more positive membrane potentials. 3 Intra-axonal application of 0.1 mM disopyramide caused a 40% reduction in the first-pulse sodium current (tonic block) and an additional use-dependent block. Analysis of first-pulse currents in terms of the Hodgkin-Huxley formalism indicated that the block resulted mainly from a reduction in the maximum available sodium conductance (gNa); there were no effects on the voltage dependence of the steady-state activation and inactivation parameters, m infinity and h infinity. 4 The use-dependent actions of disopyramide were investigated with a double voltage-clamp pulse protocol. The significant use-dependent effects of the drug were a further reduction in gNa and an increase in the time constant of inactivation (tau h). 5 Disopyramide appears to enter a blocking site in the sodium channel which is only readily accessible from the axoplasmic phase. Partition to the site depends on membrane voltage and on the state of the channel gates. Disopyramide binds at a significant rate to both open and inactivated forms of the sodium channel. (+info)