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Skeletal Muscle Relaxant.
Pharmacology: Pharmacodynamics and Pharmacokinetics: Baclofen, an analogue of gamma-aminobutyric acid, is a centrally acting skeletal muscle relaxant. It interferes with the release of excitatory neurotransmitters and inhibits monosynaptic and polysynaptic transmission at the spinal cord level. It may also act at supraspinal sites producing CNS depression.
Baclofen is rapidly and almost completely absorbed from the gastrointestinal tract after an oral dose. Peak plasma concentrations occur about 0.5 to 3 hours after ingestion, but the rate and extent of absorption vary between patients, and may vary inversely with the dose. After oral doses some baclofen crosses the blood-brain barrier, with concentrations in CSF about 12% of those in the plasma. About 30% of baclofen is bound to plasma proteins. About 70% to 80% of a dose is excreted in the urine mainly as unchanged drug; 15% metabolised in the liver. The elimination half-life of baclofen is about 3 to 4 hours in plasma and about 1 to 5 hours in CSF. Baclofen crosses the placenta and is distributed into breast milk.
