Drug-induced renal calculi: epidemiology, prevention and management.

Drug-induced calculi represent 1-2% of all renal calculi. The drugs reported to produce calculi formation may be divided into two groups. The first one includes poorly soluble drugs with high urine excretion that favours crystallisation in the urine. Among poorly soluble molecules, triamterene was the leading cause of drug-containing urinary calculi in the 1970s, and it is still currently responsible for a significant number of calculi. In the last decade, drugs used for the treatment of HIV-infected patients, namely indinavir and sulfadiazine, have become the most frequent cause of drug-containing urinary calculi. Besides these drugs, about twenty other molecules may induce nephrolithiasis in patients receiving long-term treatment or high doses. Calculi analysis by physical methods, including infrared spectroscopy or x-ray diffraction, is needed to demonstrate the presence of the drug or its metabolites within the calculi. The second group includes drugs that provoke urinary calculi as a consequence of their metabolic effects. Here, diagnosis relies on careful clinical inquiry because physical methods are ineffective to differentiate between urinary calculi induced by the metabolic effects of a drug and common metabolic calculi. The incidence of such calculi, especially those resulting from calcium/vitamin D supplementation, is probably underestimated. Although drug-induced urinary calculi most often complicate high-dose, long-duration drug treatments, there also exist specific patient risk factors in relation to urine pH, urine output and other parameters, which provide a basis for preventive or curative treatment of calculi. Better awareness of the possible occurrence of lithogenic complications, preventive measures based on drug solubility characteristics and close surveillance of patients on long-term treatment with drugs with lithogenic potential, especially those with a history of urolithiasis, should reduce the incidence of drug-induced nephrolithiasis.