Penicillamine‐induced myasthenic responses in the guinea pig

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Abstract
To study the basis for the myasthenic illness that develops in some patients receiving D-penicillamine (D-P), we measured neuromuscular transmission in D-P-treated guinea pigs. Treated animals manifested edrophonium chloride–repairable decremental responses to 30-Hz nerve stimulation (8.5% ± 1.5%—mean ± SEM; N = 16) compared with the response in saline-treated control animals (−0.3% ± 0.85%, N = 10, p <0.005). Posttetanic phenomena were studied in 5 treated animals; 3 revealed posttetanic exhaustion. Miniature endplate potential (MEPP) amplitudes were significantly reduced in 11 treated animals (0.612 ± 0.016 mV) compared with 6 controls (0.713 ± 0.024 mV, p <0.01). The MEPP frequency appeared reduced in treated animals. Both MEPP amplitude and MEPP frequency correlated with the decrement.