INCREASED POTENCY OF NONDEPOLARIZING RELAXANTS AFTER POLIOMYELITIS

The pathophysiology of poliomyelitis and the recognition of the “post‐polio syndrome” suggest that susceptibility to muscle relaxants of patients previously affected by this disease, may be altered. We compared the effects of d‐tubocurarine (dTc), pancuronium (P), and gallamine (G) on two pediatric surgical patient groups: one with a previous history of polio disease, occurring 6 to 12 years prior admission (N = 30, average age: 13 yrs, weight: 43 kg) and another without history of this disease (N = 51, average age: 11 yrs, weight: 39 kg). Following uniform premedication, thiopental, N2O/O2 + narcotic (fentanyl) anesthesia was given for reconstructive surgeries. For orotracheal intubation the patients were briefly paralyzed with 0.7 mg/kg suxamethonium. The thumb adductor responses to supramaximal 1/5 Hz impulses (continuous mode) and to 50 Hz tetanic stimuli (periodically) were recorded. After full recovery from the effect of suxamethonium (100% return of the neurally evoked muscle response) cumulative ED50 values and the recovery index (minutes elapsed from 90% to 50% block of the twitch response) of the three nondepolarizing muscle relaxants were determined. The ED50 of dTc and P were significantly lower with both neuromuscular responses in the post‐polio groups (dTc, N = 12 and P, N = 10) as compared to the controls (N = 24 and 18). A tendency toward lower ED50 values in the polio group was also observed with G (N = 6). The differences, however, as compared to the control group (N = 9) were not significant (P < .2). Recovery times were identical in the polio versus non‐polio groups. These results indicate an approximately twofold increase of potency with nondepolarizing muscle relaxants (e.g., dTc and P) in pediatric patients on a clinically unaffected upper extremity which showed no vasting or motor weakness several years following an acute phase of polio disease. We suggest that a changed receptor sensitivity or density rather than a pharmacokinetic difference could explain these findings. 1990 American College of Clinical Pharmacology