Fluorescence photometric determination of disopyramide and mono-N-dealkylated disopyramide in plasma after separation by thin-layer chromatography

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

Disopyramide pharmacokinetics in patients with acute myocardial infarction

To study the effects of acute myocardial infarction on the pharmacokinetics of disopyramide a single oral dose of disopyramide base (200 mg) was administered to 6 patients with myocardial infarction both in the acute (Study I) and recovery (Study II) phases. An intravenous tracer dose of 14C-disopyramide (2.5 micrograms/0.3 mg) was given simultaneously with the oral dose. On the basis of the intravenous tracer data, the volume of distribution, binding to plasma proteins, total plasma clearance, renal clearance and elimination half-life of disopyramide and mono-N-dealkyl disopyramide were the same in Studies I and II. The peak serum concentrations of disopyramide after oral dosing in Studies I and II were 2.6 +/- 1.2 (SEM) and 6.4 +/- 1.9 microgram/ml, respectively (p less than 0.05), the peak times 3.29 +/- 1.22 and 1.21 +/- 0.39 h (N.S.) and the AUCINF 38.0 +/- 7.7 and 60.7 +/- 9.9 micrograms . h . ml-1 (p less than 0.05). The recovery of disopyramide in urine over 3 days averaged 46% and 47% of dose, and that of mono-N-dealkyl disopyramide 22% and 16% of the dose, respectively. Thus, the gastrointestinal absorption of disopyramide was disturbed, resulting in low plasma concentrations after oral dosing, whereas the elimination of disopyramide was unaltered in the acute phase of myocardial infarction.

Simultaneous determination of disopyramide and its mono-N-dealkyl metabolite in plasma and urine by high-performance liquid chromatography

A high-performance liquid chromatographic procedure is described for the determination of disopyramide and its mono-N-dealkyl metabolite which offers simplicity of extraction with excellent selectivity, sensitivity and reproducibility. The drug and metabolite, following basic diethyl ether extraction and back-extraction with acetic acid, are injected into a reversed-phase high-performance liquid chromatographic column and the absorbance of the eluate measured at 254 nm. Detectability limits of 0.05 micrograms/ml were obtained with both compounds, and studies of the reproducibility, precision, recovery, stability during storage and effect of time in separating plasma from erythrocytes are described. Applications of this high-performance liquid chromatographic procedure to plasma samples from patients on disopyramide therapy and to plasma and urine from a healthy dog administered single doses are reported.

Absorption and antidysrhythmic activity of oral disopyramide phosphate after acute myocardial infarction

1 In a prophylactic, double-blind, randomized placebo-controlled trial of oral disopyramide phosphate, initiated within 12 h of suspected acute myocardial infarction (MI), antidysrhythmic effect was evaluated. The loading dose was 150, 200, or 300 mg followed 6 h later by 100, 150, or 200 mg every 6 h for patients assessed to weigh <55, 55-85, or >85 kg, respectively. After each loading dose and a maintenance dose on one of days 4-7, 2 and 6 h venous blood samples were obtained for determination of plasma disopyramide and mono-N-dealkylated disopyramide (MND) concentrations (expressed herein as levels), by a technique incorporating fluorescence photometry and thin layer chromatography. Of 121 patients entering the trial, 101 had confirmed acute MI and of these, 12 on active drug were recalled during convalescence and restudied after a loading dose.

2 In acute MI patients on disopyramide phosphate, an important degree of antidysrhythmic effect was observed (on active drug and placebo, 19% v 37%, respectively (P = 0.047), received lignocaine for `warning arrhythmias'), even though in the first 6 h post-loading dose, disopyramide and MND levels were low and variable.

3 Disopyramide levels 2 h post-loading dose were lower in acute MI than in non-MI patients (P = 0.004), and similarly in the limited within patient study corresponding levels after acute MI were lower than during convalescence (P = 0.013). At 6 h post-loading dose, the levels had increased in acute MI patients but decreased in non-MI patients, this change being significantly different (P = 0.048). A similar significant difference existed in the limited within patient data available during acute MI and convalescence (P = 0.002).

4 Acute MI patients on active drug developing `warning arrhythmias' had lower post-loading dose, 2 and 6 h levels than in those without `warning arrhythmias' (P = 0.012 and P = 0.0002, respectively).

5 One patient who developed renal insufficiency developed excessive disopyramide levels.

6 On any given dose, there was no significant correlation between disopyramide level and body weight.

7 In acute MI patients given oral disopyramide phosphate (a) there was marked interindividual variation in the ensuing drug and metabolite levels, (b) absorption of disopyramide into the circulation was delayed, (c) prophylactic antidysrhythmic activity was present at levels of about 1.5 mg/l which is about half the minimal level recommended hitherto, (d) disopyramide accumulated in renal insufficiency, (e) elaborate dosage adjustments based on body weight are not useful.

A placebo-controlled study to determine the efficacy of oral disopyramide phosphate for the prophylaxis of ventricular dysrhythmias after acute myocardial infarction

1 To evaluate oral disopyramide phosphate in the prophylaxis of dysrhythmias occurring in acute myocardial infarction (MI) patients (presenting within 12 h of symptoms, age 21-70 years), a placebo-controlled, randomized double-blind, in hospital trial was conducted. After prognostic stratification (anterior and non-anterior MI at each of 4 regional hospitals) patients were randomly assigned to receive oral disopyramide phosphate (loading dose 150, 200, or 300 mg followed 6 h later by 100, 150, or 200 mg every 6 h for patients assessed to weigh less than 55, 55-85, or greater than 85 kg, respectively or matching placebo. The primary exclusion criteria were overt heart failure, systolic BP less than 100 mmHg, significant heart block or history of urinary retention. Active drug or placebo was continued for 7 days or until (a) detection of "warning arrhythmias' requiring i.v. lignocaine intervention (greater than 5 for 7 days or until (a) detection of "warning arrhythmias' requiring i.v. lignocaine intervention (greater than 5 premature ventricular contractions (PVCs)/min, R on T PVCs, multifocal PVCs, bigeminal PVCs, ventricular tachycardia or ventricular fibrillation) or (b) onset of exclusion criteria. In addition, plasma drug concentrations were determined and 24 h electrocardiographic tapes were obtained on day 1, and on one of days 4-7 but these results are not presented here. 2 Out of 121 patients entering the trial, 101 had confirmatory ECG and enzyme changes. Of these, 9 of 47 patients receiving disopyramide phosphate required lignocaine compared to 20 of 54 receiving placebo (19% v 37%; P = 0.047). Corresponding numbers for patients discontinuing trial medication for other non-fatal complications of MI were 5 and 3, and for those dying, were 3 (2 infarct extensions and 1 massive infarction), and 0, respectively. Respective numbers discontinuing trial medication for possible drug side effects (viz. urinary retention requiring catheterization) were 6 and 1 (P = 0.031). 3 In circumstances where i.v. therapy is deemed impractical, use of oral disopyramide phosphate given prophylactically in patients with acute MI may reduce the incidence of "warning arrhythmias' by a clinically significant extent.

Disposition kinetics of disopyramide in patients with renal insufficiency

The pharmacokinetics of an intravenous injection of disopyramide was studied in five normal subjects and six patients with varying degrees of renal impairment. The elimination rate constant (beta) was related to the endogenous creatinine clearance (Clcr). However, a decrease in beta was not observed until the Clcr was reduced below 40 ml min-1. Below 40 ml min-1 a linear relationship existed between beta and Clcr. Similarly, the plasma elimination half-life (t 1/2 beta) showed a significant increase when the Clcr was less than 30 ml min-1. Hence, dosage modification for disopyramide is necessary only when renal function is severely impaired. Overall, the apparent volume of distribution in patients with renal insufficiency was reduced to two-thirds of that in normal subjects. Therefore, in patients with Clcr less than 40 ml min-1 both the loading and maintenance dose of disopyramide should be reduced.