Dosage adjustment in renal insufficiency

Paracetamol disposition and metabolite kinetics in patients with chronic renal failure

The disposition of paracetamol following an oral dose of 1.0 g was compared in 10 healthy volunteers, 7 patients with moderate chronic renal failure and 6 patients with end stage renal failure on maintenance haemodialysis. Paracetamol absorption was normal in the patients with renal failure. The mean plasma half-life of paracetamol from 2 to 8 h was similar in the 3 groups (2.1 to 2.3 h) but from 8 to 24 h it disappeared much more slowly in the renal failure patients (half-life 11.7 compared with 4.9 h in the healthy volunteers). Plasma concentrations of paracetamol glucuronide and sulphate conjugates were greatly increased in the patients with moderate renal failure and the mean plasma half-lives were 30.5 and 21.8 h respectively compared with about 3 h in the healthy volunteers. Plasma concentrations of these metabolites were even higher in the dialysis patients and there was no significant fall over 24 h. The cysteine and mercapturic acid conjugates of paracetamol could only be measured in plasma in the patients with renal failure and concentrations were very low. The fractional urinary recovery of paracetamol and its glucuronide, sulphate, cysteine and mercapturic acid conjugates was similar in healthy volunteers and patients with moderate renal failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors contributing to variability in drug pharmacokinetics. IV. Renal excretion

The renal excretion of drugs is mainly controlled by three factors: glomerular filtration, tubular secretion and tubular reabsorption. Only relatively polar drugs are excreted in appreciable amounts by the kidneys. Factors affecting renal excretion of drugs include: kidney function, protein binding, urine pH and urine flow. Impaired renal function may lead to a clinically significant accumulation of drugs eliminated by the kidneys, if more than 50% of the dose is normally excreted unchanged in the urine and the renal function is less than 50% of the normal value. Successful removal of a drug by dialysis requires that it possesses a polar character, low protein binding and a small to moderate volume of distribution.