Urinary acidification response to furosemide administration in patients on low-dose cyclosporine therapy.

The response of urinary acidification parameters and electrolytes to furosemide administration was prospectively studied in 9 psoriatic patients treated with a low-dose cyclosporine A schedule (initial dose: 5 mg/kg body weight) before beginning cyclosporine A, after 3 months on cyclosporine A and 1 month after cyclosporine A withdrawal. The test was also performed in 29 psoriatic patients after 3 months on 5 mg/kg body weight cyclosporine A treatment. There were no significant differences between before and after cyclosporine A treatment regarding furosemide-induced changes in urinary volume, sodium or potassium excretion. Contrarily, the post-furosemide urinary pH decrease and ammonium and titrable acid increase were significantly lower in cyclosporine-A-treated patients. Five of the 29 studied patients showed abnormal furosemide tests (17%). These patients had lower total serum CO2, urea and creatinine but similar serum potassium and fractional potassium excretion. We conclude that some patients treated with low-dose cyclosporine A therapy develop an abnormal tubular distal response to furosemide administration, suggesting an alteration in the H(+)-ATPase pump or a voltage-dependent mechanism.