Wayne F. Phillips wayne at phillips.boulder.co.us
Thu Apr 7 09:25:42 EST 1994

In <2ntudn$155b at inca.gate.net> odin at gate.net () writes:

>Can someone tell me what it is exactly that baclofen does? Is it a 
>relaxant or does it affect the firing of the synapses much like tegretol? 
>I recently had it prescribed for tic deleroux in lieu of dillantin to be 
>taken along with tegretol [which seems to be effective] and I would like 
>to know how baclofen is expected to work with the tegretol? 

Mechanism of action/Effect: The precise mechanism of
   action of baclofen has not been fully determined. It acts
   mainly at the spinal cord level to inhibit the transmission
   of both monosynaptic and polysynaptic reflexes, possibly by
   hyperpolarization of primary afferent fiber terminals
   resulting in antagonism of the release of putative
   excitatory transmitters (i.e., glutamic and aspartic acids).
   Actions at supraspinal sites may also be involved.

Other actions/effects: Baclofen has general central
   nervous system (CNS)-depressant actions.

Absorption: Rapid and extensive but subject to
   interpatient variation. Also, the rate and extent of
   absorption may decrease with increasing doses.

Protein binding: Low.

Biotransformation: Hepatic; only about 15% of a dose
   is metabolized.

Half-life: 2.5 to 4 hours.

Onset of action: Highly variable; may range from
   hours to weeks.

Time to peak concentration: 2 to 3 hours.

Peak serum concentration: 500 to 600 nanograms per
   mL (ng/mL) (2.34 to 2.81 micromoles/L) following a 40-mg
   single dose; concentration remains above 200 ng/mL (0.94
   micromoles/L) for 8 hours.

Therapeutic serum concentration: 80 to 400 ng/mL
   (0.37 to 1.87 micromoles/L).

Elimination: Renal; 70 to 85% of a dose is excreted
   unchanged within 24 hours. Small amounts may also be
   excreted via the feces. About 40% of a dose is usually
   excreted within 6 hours, and excretion is usually complete
   within 3 days; however, with chronic use the rate of
   excretion is subject to interpatient variation.

(From US Pharmacopea)

Wayne Phillips                        	wayne at phillips.boulder.co.us
Boulder PTSD Center, Boulder, CO	(303)440-4599

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