[Intrathecal baclofen. Experimental and pharmacokinetic studies].

Baclofen, the most effective drug to treat spasticity, is a specific agonist of gamma-aminobutyric acid-B receptors, and is very abondant in the superficial layers of the spinal cord. Given orally, baclofen does not easily penetrate the blood-barrier, and is distributed equally to the brain and spinal cord. After oral administration of baclofen, the drug is resorbed by more than 80-90% in the stomach and bowel and is eliminated by urinary excretion. Failure of oral medication to produce sufficient relief of spasticity is due to the poor passage of the drug across the blood-brain barrier. In animals the concentration in brain is less than 1/10 of the blood levels. The problem of insufficient anti-spastic efficacy (in relation to the rate of side-effects) after systemic medication may be overcome by local application in spinal CSF. Direct intrathecal administration of baclofen in the treatment of severe spasticity was proposed in 1984 by Richard Penn with the objective to carry out a selective spinal distribution of the active principle thus avoiding supraspinal side effects. The pharmacokinetics of baclofen in animal and man after intrathecal administration have been investigated to determine the CSF pharmacokinetic parameters.