Hypouricemia and urate excretion in small cell lung carcinoma patients with syndrome of inappropriate antidiuresis.

Urate concentrations in serum and renal urate clearance were prospectively evaluated in patients with small cell lung cancer (SCLC). Serum urate and renal urate clearance were measured before and during cytostatic treatment until disease progression (PD) in 12 patients with the syndrome of inappropriate antidiuresis (SIAD) and in 8 patients without. Hypouricemia occurred in 4 SIAD patients before treatment and also when tumor regression was obtained. Two normouricemic SIAD patients developed hypouricemia when PD occurred. No patient without SIAD experienced hypouricemia. Serum urate in patients with SIAD was lower than in those without SIAD before cytostatic treatment but not 3 months after the treatment. Hypouricemic patients had higher urate clearance than normouricemic and it remained higher even after tumor regression. Serum urate was invalid as marker of tumor regression or relapse. SIAD patients have higher glomerular filtration rates than patients without SIAD, which may influence the renal excretion of cytostatic drugs.