Pharmacokinetics and pharmacodynamics of guanidine hydrochloride in an hereditary myasthenia gravis-like disorder in dogs.

The pharmacokinetic parameters of guanidine hydrochloride were analysed in dogs with an hereditary neuromuscular transmission disorder by the use of 14C-guanidine hydrochloride. The content of intravenously administrated 14C-guanidine hydrochloride in plasma, urine and faeces was determined by liquid scintillation counting. The drug was rapidly distributed in the organism with a plasma half-life of 7-8 h and most was eliminated in the urine. The clinical and electrophysiological effects of guanidine hydrochloride on the muscular weakness and fatigue induced by exercise were determined after oral and intravenous administration. Guanidine hydrochloride improved muscle-function, but had no apparent effect when administered during an attack of weakness. An effective level of guanidine in plasma (2-10 micrograms/ml) changed the muscle response evoked by trains of repetitive stimulation. The myasthenic decrement during short stimulation trains was unchanged.