PHARMACODYNAMIC BEHAVIOR OF VECURONIUM IN PRIMARY HYPERPARATHYROIDISM

This study evaluated the potency and time course of action of vecuroni um in patients with primary hyperparathyroidism (HPT) and marked hyper calcaemia during nitrous oxide-opioid anaesthesia. Twenty ASA physical status I and Il patients were studied by measuring the force of contr action of the adductor pollicis in response to stimulation of the ulna r nerve: ten control patients and ten patients with HPT and ionized ca lcium concentration over 2.80 mEq.L(-1). After induction of anaesthesi a with thiopentone and maintenance with N2O/O-2 and fentanyl, vecuroni um was administered to determine cumulative dose-response curves. When maximum block had been obtained twitch height was maintained at 10% o f baseline value over 20 min by adjusting the infusion rate of a syrin ge-pump containing vecuronium and vecuronium plasma concentration (EC( 90ss)) was determined. During spontaneous recovery, after termination of infusion, the recovery index, the time from 25 to 75% recovery, was measured. The dose to produce 90% block was greater in the HPT than i n control group: 69 (24) vs 54 (18) mu g.kg(-1) (P < 0.02). The calcul ated ED(50) was also greater in HPT: 42 (4) vs 31 (5) mu g.kg(-1) in c ontrols (P < 0.001). (Values are given as mean and coefficient of vari ation). The slope of the dose-response curve, the dose necessary to ma intain 90% block, and the EC(90ss) did not differ. The RI(25-75) was s lower in the HPT group although the difference did not reach statistic al significance. It is concluded that hyperparathyroidism with hyperca lcaemia increases vecuronium requirement; only during the onset of neu romuscular blockade.