Pharmacokinetic studies of propoxyphene IV: Effect of renal failure on systemic clearance in rats

Drug dosing in chronic kidney disease

Patients with chronic kidney disease (CKD) are at high risk for adverse drug reactions and drug-drug interactions. Drug dosing in these patients often proves to be a difficult task. Renal dysfunction-induced changes in human pathophysiology regularly results may alter medication pharmacodynamics and handling. Several pharmacokinetic parameters are adversely affected by CKD, secondary to a reduced oral absorption and glomerular filtration; altered tubular secretion; and reabsorption and changes in intestinal, hepatic, and renal metabolism. In general, drug dosing can be accomplished by multiple methods; however, the most common recommendations are often to reduce the dose or expand the dosing interval, or use both methods simultaneously. Some medications need to be avoided all together in CKD either because of lack of efficacy or increased risk of toxicity. Nevertheless, specific recommendations are available for dosing of certain medications and are an important resource, because most are based on clinical or pharmacokinetic trials.

Pharmacokinetics and toxicity testing

The pharmacokinetic basis for the design of toxicity tests is discussed with reference to the absorption and clearance of drugs. The absorption and clearance of a wide range of drugs by laboratory animals and man has been examined and reviewed to provide a firm basis against which new drugs can be compared. Some pitfalls in either the empirical approach to toxicology or the incorrect interpretation of kinetic data are highlighted. An approach is outlined for the rational application of animal pharmacokinetic data in the assessment of the safety in man of a new therapeutic agent.

Comparison of vancomycin disposition in rats with normal and abnormal renal functions

Vancomycin levels in the tissues and urine of rats with renal damage were compared with those of control rats. Renal damage was induced by a single intravenous injection of uranyl nitrate. After 5 days, when the plasma urea nitrogen levels had increased 7- to 22-fold, a single intraperitoneal vancomycin injection of 10 mg/kg yielded significantly higher plasma and tissue levels in these rats than in the control rats that did not receive uranyl nitrate. At 73 h after the vancomycin injection, the plasma vancomycin concentration in the rats with renal damage was 1.8 +/- 1.1 microgram/ml (mean +/- standard deviation), whereas in control rats the level had fallen to 0.004 +/- 0.002 microgram/ml. Control rats excreted 50.5% of a single dose in the urine within the 3 days, whereas rats with renal damage excreted only 35.6%. These results indicate that vancomycin pharmacokinetics is affected by renal function in rats. Therefore, the drug should be used very cautiously in patients with impaired renal function. The serum levels must be monitored, and the frequency and size of doses may have to be reduced.

Evaluation of methods for producing renal dysfunction in rats

The following methods for producing renal dysfunction in rats were compared: single-step 5/6th nephrectomy, two-step 5/6th nephrectomy, bilateral ureteral ligation, and uranyl nitrate injection. Control groups consisted of single- and two-step sham-operated animals and animals that received an injection of normal saline solution. The methods were evaluated on the basis of the following criteria, which were assessed daily for 6 days: survival, body weight, hematocrit, serum creatinine concentration, serum urea nitrogen concentration, serum glutamic pyruvic transaminase activity, serum albumin concentration, and serum protein binding of salicylate (determined every other day). Animals with bilateral ureteral ligation survived only 2 days, single-step 5/6th nephrectomy caused a high incidence of fatalities. Some of the methods were associated with the development of hypoalbuminemia, but no significant elevation of transaminase activity occurred. Serum protein binding of salicylate was reduced in rats with renal dysfunction. A strong positive correlation between the creatinine and urea nitrogen concentrations in the serum of animals with renal dysfunction (r = 0.91, p less than 0.001) and a negative correlation between the serum albumin concentration and salicylate free fraction (r = -0.71, p less than 0.001) were found. Uranyl nitrate injection has the advantages of technical simplicity, a high survival rate (no deaths in this study), and relatively consistent and sustained diminution of renal function (as reflected by serum creatinine and urea nitrogen concentrations).