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Biomedical subjects

D E Drayer

Publications and source records attributed to D E Drayer.

61 records · Page 4Linked to original sources
PubMed1976

Correlation of the electrophysiological and antiarrhythmic properties of the N-acetyl metabolite of procainamide with plasma and tissue drug concentrations in the dog.

N-acetylprocainamide (NAPA), a major metabolite of procainamide (PA) in man, has been reported recently to be biologically active. The present study compares the electrophysiological and antiarrhythmic effects of NAPA and PA and correlates their activity with plasma and tissue drug concentrations. In isolated canine Purkinje fibers, NAPA, in bath concentrations of 10 and 20 mg/l reduced automaticity and prolonged repolarization time. These effects were similar to those observed with similar concentrations of PA. Tissue concentrations of NAPA (77 +/- 2 mug/g) were significantly greater than those of PA (43+/-2 mug/g). Neither drug was metabolized by the fibers. In in vivo studies, NAPA (140-220 mg/kg) significantly suppressed the incidence of arrhythmias following coronary occlusion and digitalis intoxication. Similar protection was obtained with 40 to 60 mg/kg of PA. This difference in potency could not be attributed to differences in plasma and tissue concentrations of the drugs. These results show that NAPA is equally efficacious but less potent than PA as an antiarrhythmic drug in dogs.

Action Potentials↗
PubMed1975

Polymorphic acetylation procainamide in man.

N-Acetylprocainamide (NAPA) and procainamide plasma and urine concentrations were determined by thin-layer chromatography (TLC) densitometry in people of known acetylator phenotype (dapsone phenotyping) taking procainamide for more than 3 days. The plasma NAPA/procainamide ratio 3 hr after the last dose for fast acetylators (mean plus or minus SD) is 1.8 plus or minus 0.59 (N equal to 8) and for slow acetylators, 0.61 plus or minus 0.09 (N equal to 6) P smaller than 0.001). The renal clearance of NAPA averaged 1.2 times the simultaneously measured endogenous creatinine clearance, whereas procainamide clearance was approximately double the creatinine clearance. There was no difference between slow and rapid acetylators in the renal clearance of either drug or the urine pH, indicating that the difference in plasma NAPA/procainamide ratios between these two groups is due to differences in their rates of acetylation. Therefore, procainamide is probably acetylated by the polymorphic N-acetyltransferase in man. Reflecting the blood level differences, the NAPA/procainamide ratio in urine (collected 99 to 180 min after last dose) was found to be higher in rapid than in slow acetylators. The plasma protein binding of NAa and of procainamide are similar. Since NAPA seems to have an antiarrhythmic potency similar to procainamide, NAPA probably contributes to the antiarrhythmic activity of procainamide therapy, especially in genetic rapid acetylators.

Acetylation↗
PubMedDate not supplied

Pharmacologically active drug metabolites: therapeutic and toxic activities, plasma and urine data in man, accumulation in renal failure.

Drugs that are administered to man may be biotransformed to yield metabolites that are pharmacologically active. The therapeutic and toxic activities of drug metabolites and the species in which this activity was demonstrated are compiled for the metabolites of 58 drugs. The metabolite to parent drug ratio in the plasma of non-uraemic man and the percentage urinary excretion of the metabolite in non-uraemic man are also tabulated. Those active metabolites with significant pharmacological activity and high plasma levels, both relative to that of the parent drug, will probably contribute substantially to the pharmacological effect ascribed to the parent drug. Active metabolites may accumulate in patients with end stage renal disease if renal excretion is a major elimination pathway for the metabolite. This is true even if the active metabolite is a minor metabolite of the parent drug, as long as the minor metabolite is not further biotransformed and is mainly excreted in the urine. Minor metabolite accumulation may also occur if it is further biotransformed by a pathway inhibited in uraemia. Some clinical examples of the accumulation of active drug metabolites in patients with renal failure are: (a) The abolition of premature ventricular contractions and prevention of paroxysmal atrial tachycardia in some cardiac patients with poor renal function treated with procainamide are associated with high levels of N-acetylprocainamide. (b) The severe irritability and twitching seen in a uraemic patient treated with pethidine (meperidine) are associated with high levels of norpethidine. (c) The severe muscle weakness and tenderness seen in patients with renal failure receiving clofibrate are associated with excessive accumulation of the free acid metabolite of clofibrate. (d) Patients with severe renal insufficiency taking allopurinol appear to experience a higher incidence of side reactions, possibly due to the accumulation of oxipurinol. (e) Accumulation of free and acetylated sulphonamides in patients with renal failure is associated with an increase in toxic side-effects (severe nausea and vomiting, evanescent macular rash). (f) Peripheral neuritis seen after nitrofurantoin therapy in patients with impaired renal function is thought to be due to accumulation of a toxic metabolite. The high incidence of adverse drug reactions seen in patients with renal failure may for some drugs be explained in part, as the above examples illustrate, by the accumulation of active drug metabolites. Monitoring plasma levels of drugs can be an important guide to therapy. However, if a drug has an active metabolite, determination of parent drug alone may cause misleading interpretations of blood level measurements. The plasma level of the active metabolite should also be determined and its time-action characteristics taken into account in any clinical decisions based on drug level monitoring.

Acetaminophen↗