Urinary excretion of drugs in chronic renal impairment with respect to changes their tubular handling by residual nephrons.

Decrease of the relative value of the renal clearance (the ratio between the value observed and the normal value) of a drug may be slower than the decrease of the relative value of the glomerular filtration rate. A slower decrease of drug renal clearance may be due to an increase in its effective secretion or a decrease in its effective reabsorption by residual nephrons. The mechanisms underlying these changes still remain obscure. One of the factors is assumed to be sodium osmotic diuresis in residual nephrons (associated with functional adaptation).