Drug administration in patients with renal insufficiency. Minimising renal and extrarenal toxicity.

Renal insufficiency has been associated with an increased risk of adverse effects with many classes of medications. The risk of some, but not all, adverse effects has been linked to the patient's degree of residual renal function. This may be the result of inappropriate individualisation of those agents that are primarily eliminated by the kidney, or an alteration in the pharmacodynamic response as a result of renal insufficiency. The pathophysiological mechanism responsible for alterations in drug disposition, especially metabolism and renal excretion, is the accumulation of uraemic toxins that may modulate cytochrome P450 enzyme activity and decrease glomerular filtration as well as tubular secretion. The general principles to enhance the safety of drug therapy in patients with renal insufficiency include knowledge of the potential toxicities and interactions of the therapeutic agent, consideration of possible alternatives therapies and individualisation of drug therapy based on patient level of renal function. Although optimisation of the desired therapeutic outcomes are of paramount importance, additional pharmacotherapeutic issues for patients with reduced renal function are the prevention or minimisation of future acute or chronic nephrotoxic insults, as well as the severity and occurrence of adverse effects on other organ systems. Risk factors for the development of nephrotoxicity for selected high-risk therapies (e.g. aminoglycosides, nonsteroidal anti-inflammatory drugs, ACE inhibitors and radiographic contrast media) are quite similar and include pre-existing renal insufficiency, concomitant administration of other nephrotoxins, volume depletion and concomitant hepatic disease or congestive heart failure. Investigations of prophylactic approaches to enhance the safety of these agents in patients with renal insufficiency have yielded inconsistent outcomes. Hydration with saline prior to drug exposure has given the most consistent benefit, while sodium loading and use of pharmacological interventions [e.g. furosemide (frusemide) dopomine/dobutamine, calcium antagonists and mannitol] have resulted in limited success. The mechanisms responsible for altered dynamic responses of some agents (benzodiazepines, theophylline, digoxin and loop diuretics) in renally compromised patients include enhanced receptor sensitivity secondary to the accumulation of endogenous uraemic toxins and competition for secretion to the renal tubular site of action. Application of the pharmacotherapeutic principles discussed into clinical practice will hopefully enhance the safety of these agents and optimise patient outcomes.