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PubMed1983

Blockade of sodium and potassium channels in the node of Ranvier by ajmaline and N-propyl ajmaline.

The inhibition of sodium and potassium currents in frog myelinated fibres by ajmaline (AM) and its quaternary derivative, N-propyl ajmaline (NPA), depends on voltage-clamp pulses and the state of channel gating mechanisms. The permanently charged NPA and protonated AM interact only (or mainly) with open channels, while unprotonated AM affects preferently inactivated Na channels. Inhibition of Na currents by NPA and AM does not depend on the current direction and Na ion concentration in external or internal media. In contrast only the outward potassium currents can be blocked by NPA and AM; the inward potassium currents in high K+ ions external media are resistant to the blocking action of these drugs. The voltage dependence of ionic current inhibition by charged drugs suggests the location of their binding sites in the inner mouths of Na and K channels. Judging by the kinetics of current restoration after cessation of pulsing, the drug-binding site complex is much more stable in Na than in potassium channels. Batrachotoxin and aconitine, unlike veratridine and sea anemone toxin, decrease greatly the affinity of Na channel binding sites to NPA and AM. The effects of NPA and AM are compared with those of local anesthetics and other amine blocking drugs.

Aconitine↗
PubMed1981

[Dynamic electrocardiography evaluation of the effectiveness of prajmalium bitartrate, disopyramide and procainamide in patients with stabilized ventricular extrasystole].

20 patients with chronic premature ventricular contractions (P.V.Cs) underwent several Holter ECG monitorings to assess clinical effectiveness of three antiarrhythmic drugs: Prajmalium Bitartrate (P.B.) 80 mg/daily, Disopyramide (D.) 600 mg/daily and Procainamide (P.) 2400 mg/daily, to assess the most effective antiarrhythmic medication in every patient. Clinical effectiveness was considered as 80% reduction of P.V.Cs or 50% reduction with suppression of all complex ventricular ectopy (repetitive, polymorph, bigeminy). These results were observed respectively, for 80% reduction, in 5/20 patients for P.B., in 9/20 for D., and in 3/19 for P; and for 50% reduction in 11/20 for P.B., in 18/20 for D., and in 9/19 for P. Comparison in the same patient, using Holter ECG monitoring with a computer assisted analysis, of the effects of different antiarrhythmic medications, is a rational procedure to assess clinical efficacy of new antiarrhythmic drugs and to choose the most effective in each case.

Adolescent↗
PubMed1980

[Stimulus dependent sodium channel blockade in node of Ranvier membranes by the quaternary antiarrhythmic N-propyl ajmaline (neogiluritmal)].

The blocking action of neo-gilurytmal (NG), a quaternary derivative of aimalin, on sodium channels was studied in the voltage-clamped node of Ranvier. NG exerted no action on the resting membrane unless the repetitive pulsing was turned on. A series of repetitive depolarizing pulses of short duration (5 ms) produced the accumulating "stimulus-dependent" blockade of sodium channels. The rate and degree of the blockade increased with the increasing of pulse voltage even over the potential range where all the sodium channels were open. Recovery from the blockade occurred within several tens of minutes. Unlike the repetitive pulsing, long-lasting (1 s) depolarization of the membrane produced only a slight increase in the blockade of sodium channels. Elimination of sodium inactivation by aconitine prevented the blocking action of NG. The results of the experiments indicate that NG blocks only the open sodium channels with intact inactivation gate.

Aconitine↗
PubMed1982

[Differences in the blocking action of benzocaine and amino compounds on batrachotoxin-modified node of Ranvier sodium channels].

Voltage-clamp experiments on the frog Ranvier node have shown that batrachotoxin (BTX) decreases drastically the sensitivity of sodium channels to the blocking action of various tertiary (procaine, trimecaine, ajmalin, strychnine) and quaternary (QX-572, N-propylajmaline) amine drugs but does not affect noticeably sodium channels blockade produced by neutral benzocaine. The inhibition of BTX-modified sodium current by large concentrations of trimecaine (3.5 mM) is time- and voltage-dependent. Neither of the amines used proved to be able to cause frequency-dependent (cummulative) block of modified channels. Unblocking of these channels during washing of the node with Ringer solution proceeds much faster than that of normal channels. On the contrary, restoration of normal and modified currents blocked previously by benzocaine has the same time course. The relationships between "receptors" for BTX and various sodium channel blockers are discussed.

Amines↗
PubMed1983

[Stimulus-dependent blockade of the Na channels of isolated myocardial cells in the rat by the anti-arrhythmia agent N-propyl ajmaline (neogiluritmal)].

The patch-clamp method was used to study the effect of N-propyl ajmaline (NPA) on sodium currents (INa) in enzymatically isolated cells of adult rats. When applied at concentrations of 10(-5)--2 X 10(-5) M NPA produced a use-dependent inhibition of INa. The rate and depth of this blockade increased with NPA concentration, frequency and magnitude of depolarizing pulses. Voltage dependence of the blockade was revealed beyond the potential range where the fraction of activated Na channels was close to 1.0. Turning on the strong hyperpolarizing prepulse (100-ms duration) before each test pulse induced a prompt increase of INa (due to the removal of resting inactivation) which declined pulse by pulse during subsequent repetitive stimulation. A single long-lasting (3000 ms) depolarizing step, in contrast to the train of short (5 ms) depolarizing pulses did not enhance appreciably the blocking action of NPA. From an analysis of the data obtained it was inferred that NPA inhibits INa due to a voltage-dependent interaction with open Na channels. It is emphasized that NPA has similar blocking effects on Na channels in myocardial cells and nerve fibers.

Ajmaline↗
PubMed1983

Comparison of tocainide and prajmalium bitartrate for the treatment of ventricular arrhythmias.

The antiarrhythmic efficacy of tocainide, a new antiarrhythmic substance, has been compared with that of prajmalium bitartrate, a drug in clinical use for many years in the German speaking countries. The investigation was performed as a double-blind cross-over study in 20 patients with ventricular arrhythmias (VA) of various origin. The efficacy was assessed by serial Holter monitoring. Plasma levels were measured to study the dose-effect relationship. Applying to the criterion of a reduction of VA of more than 75% or an improvement according to the Lown grading 8 pts. under tocainide and 7 under prajmalium bitartrate were responders. Side effects were few and under tocainide only 2 pts. had to discontinue the therapy. From the present findings tocainide and prajmalium bitartrate have the same efficient antiarrhythmic effects in the majority of patients.

Adult↗
PubMed1983

[Pharmacokinetics and Antiarrhythmic effects of Prajmalium Bitartrate].

8 patients with ventricular premature contractions were treated with prajmalium bitartrate (Neo-Gilurytmal) 20 mg q.i.d. The electrocardiograms were continuously monitored by a computerized arrhythmia monitoring system. For definition of the drug's pharmacokinetic properties plasma concentrations were determined. 7 patients showed a marked arrhythmia reduction. Mean ventricular premature contraction frequency was significantly reduced 6 h after onset of treatment, maximum arrhythmia suppression to 34% of control was observed after 24 h of treatment. The correlation of antiarrhythmic response and plasma concentrations was good. Mean plasma concentrations during steady state conditions were 218 ng/ml. Plasma half-life was determined 7.3 h. The lower limit of therapeutic plasma concentrations was between 43 and 145 ng/ml. A mean total clearance of 344 ml/min indicates a low hepatic extraction of prajmalium bitartrate. Moreover, the distribution volume of 204 l suggests a high tissue affinity of the drug.

Adult↗
PubMed1981

Experience with immunological tests in drug-induced hepatitis.

Nine patients are reported who developed hepatic injury following the administration of therapeutic agents. The drugs incriminated were prajmalium bitartrate (4 patients), quinidine (3 patients), procainamide and nifedipine (one patient each). In all patients the clinical features indicated an allergic process, which in three cases was substantiated by positive response to reexposure. The detection of immunologic processes in our patients by various in vitro methods supports the assumption that immune mechanisms may be involved in the production of drug-induced hepatic disease and confirm allergy.

Aged↗