EFFECT OF CALCIUM-CHANNEL BLOCKERS ON CALCIUM-PHOSPHATE METABOLISM INPATIENTS WITH END-STAGE RENAL-DISEASE

Background. After EDTA-induced hypocalcaemia, healthy volunteers treat ed with diltiazem display more severe hyperparathyroidism than subject s on felodipine studied under identical conditions. Therefore patients with end-stage renal disease (ESRD) and severe secondary hyperparathy roidism might be particularly sensitive to this side-effect. Methods. To test this hypothesis, seven patients with ESRD on chronic haemodial ysis (3 women and 4 men) with serum levels of intact PTH ranging from 204 to 675 pg/ml were studied both before and during the first 180 min of haemodialysis against a dialysate with low calcium concentration ( 0.75 mmol/l, n = 6 and 1 mmol/l, n = 1) under the following three expe rimental conditions: control, felodipine (10 mg/day) and diltiazem (12 0 mg b.i.d.). Results. At onset of dialysis, plasma phosphorus level w as higher on diltiazem (2.03+/-0.08 mM) than on felodipine (1.64+/-0.1 0, P<0.02), and on the latter it was lower than in control condition ( 1.88+/-0.16, P<0.02). As a probable consequence, blood ionized calcium concentration was lower on diltiazem (1.14 mM+/-0.02, mean+/-SEM) tha n on felodipine (1.2+/-0.03, P<0.05) or in control condition (1.17+/-0 .01, NS). There was a trend for intact PTH to be higher on diltiazem ( 324+/-47 pg/ml) than on felodipine (246+/-55) or in control condition (305+/-49) and 1,25-dihydroxyvitamin D was higher indeed on diltiazem (6.70+/-92 pg/ml) than on felodipine (4.75+/-0.91, P<0.02) or control (3.87+/-0.63, P<0.05). Area under the curve PTH over the first 60 min of dialysis was higher by 16+/-7% on diltiazem than on felodipine (P<0 .05). Conclusions. While on diltiazem rather than on felodipine, patie nts with ESRD display higher plasma phosphorus levels, and slightly ag gravate the degree of severity of hyperparathyroidism recorded during haemodialysis against low-calcium dialysate. The longterm effect of th is new observation remains to be evaluated.