The effects of digoxin and beta-methyldigoxin on the heart rate of decompensated patients with atrial fibrillation

Massive doses of procainamide for ventricular tachyarrhythmias due to myocardial infarction

Three patients are described in whom malignant ventricular arrhythmias appeared in connection with a reinfarction some days after hospitalization for an acute myocardial infarction and in whom massive doses of procainamide, up to 7.5 g/day i.v., were necessary to prevent these arrhythmias. The serum concentration of procainamide was 2--4 times higher than the recommended upper level, but no side-effects were observed. With the dose given, one would have expected still higher serum concentrations. Several reasons for this finding are discussed, including the effects of renal function, intestinal leakage, storage of the drug in tissues and hitherto unknown metabolic pathways of procainamide in patients, who are slow acetylators.

Population-based investigations of drug relative clearance using nonlinear mixed-effect modelling from information generated during the routine clinical care of patients

Interpatient variability in drug disposition and response is a therapeutic premise, and thus evaluation and management of such variability are the basis for individualized pharmacotherapy. If the mathematical approach to determining drug doses were accurate and practical, the use of calculated doses could reduce the potential for toxicity and decrease the need for repetitious drug assays. The major strength of the population pharmacokinetics approach is that useful information can be extracted from sparse data collected during routine clinical care. Population pharmacokinetics can be defined as the study of the variability in serum drug concentrations between individuals when standard dosage regimens are administered. An approach to population pharmacokinetic data analysis has been implemented in the Nonlinear Mixed Effects Model (NONMEM) computer program. This report shows the feasibility of using a simple pharmacokinetic screen approach to estimate the population mean relative drug clearance and detecting drug-drug interaction by use of NONMEM. In clinical application of multiple trough screen or multiple peak screen, the variability of drug relative clearance within the population is assessed and a mathematical relationship between drug relative clearance and individual patient characteristics, such as age, body weight, gender, disease state or drug interaction with concomitant drug is derived. In this report I describe this approach and its application using several examples previously reported by us and others.

Pharmacokinetics of beta-methyldigoxin in subjects with normal and impaired renal function

Beta-methyldigoxin (beta-MD) was administered orally (0.2 mg) to 24 patients with various degrees of renal function, to investigate its pharmacokinetic characteristics related to renal function. Serum and urine collected until 120 hours after dosing were assayed for beta-MD and digoxin by high-performance liquid chromatography and fluorescence polarization immunoassay method. The steady-state volume of distribution decreased proportionately as creatinine clearance (CLCR) decreased, although steady-state volume of distribution of hemodialysis patients had large interindividual variability, and their mean value was not different from that of patients with normal renal function. Both renal clearance of beta-MD and digoxin were significantly correlated with CLCR (r = .820, P < .001 and r = .822, P < .01, respectively), and the slope of regression line for beta-MD was only 44% that for digoxin. Significantly reduced urinary excretion of total drug (beta-MD plus digoxin) was shown in patients with CLCR below 50 mL/minute/1.48 m2. This study suggests that the dosage modification is not necessary until CLCR decreases to below 50 mL/minute/1.48 m2, but careful attention should be given in the use of beta-MD in patients with CLCR below this value.