Baclofen

Baclofen

File:BaclofenStructure.png
Clinical data
Pregnancy category	US: C (Risk not ruled out)
Routes of administration	Oral, intrathecal
ATC code	M03BX01 (WHO)
Pharmacokinetic data
Bioavailability	well absorbed
Protein binding	30%
Elimination half-life	1.5 - 4 hours
Excretion	renal (70-80%)
Identifiers
IUPAC name 4-amino-3-(4-chlorophenyl)-butanoic acid
CAS Number	1134-47-0
PubChem CID	2284
DrugBank	APRD00551
E number	{{#property:P628}}
ECHA InfoCard	{{#property:P2566}}
Chemical and physical data
Formula	C10H12ClNO2
Molar mass	213.661 g/mol

Overview

Baclofen (brand names Kemstro and Lioresal) is a derivative of gamma-aminobutyric acid, and is an agonist specific to mammalian but not fruit fly (Drosophila) GABA_B receptors[2][3]. It is used for the treatment of spastic movement, especially in instances of spinal cord injury, spastic diplegia, multiple sclerosis, amyotrophic lateral sclerosis (Lou Gehrig's Disease) and trigeminal neuralgia. Its beneficial effects result from actions at spinal and supraspinal sites. Baclofen can also be used to treat hiccups.

Description of compound

Baclofen is a white (or off white) mostly odorless crystalline powder, with a molecular weight of 213.66 g/mol. It is slightly soluble in water, very slightly soluble in methanol, and insoluble in chloroform.

Routes of administration

Baclofen can be administered either orally or intrathecally (directly into the spinal fluid). Intrathecal administration is often indicated in spasticity patients, as very little of the oral dose actually reaches the spinal fluid.

Intrathecal administration is particularly used in patients with multiple sclerosis who have severe painful spasms which are not controllable by oral baclofen, or patients with spastic diplegia in whom managament of spasticity is made easier by regular self-ministering of the drug through its pump. A test dose is given to assess the effect, and if successful a chronic intrathecal catheter is inserted and connected to a computer-controlled implanted pump. The reservoir in the pump can be replenished by percutaneous injection. These pump systems are quite sophisticated and expensive, so careful patient selection is required.

History

Historically Baclofen was designed to be a drug for epilepsy in the 1920’s, and was derived from GABA. The effect on epilepsy was disappointing but it was found that in certain patients spasticity decreased. Baclofen was and is still given orally with variable effects. In severely affected children, the oral dose is so high that side effects appear and the treatment loses its benefit. How and when baclofen came to be used in the spinal sac is not really clear but this is now an established method for the treatment of spasticity in many conditions. Recently some trials have been conducted in using Bacolfen to treat cocaine addiction. While no final study has been released, people have said once they took Baclofen they felt their desire for cocaine plummet almost over night.

How Baclofen works

Baclofen affects the spinal cord, which is the main connection between the brain and the rest of the body. The spinal cord plays a role as a reflex system that functions as a feedback loop. Our most obvious reflex is the withdrawal of our appendages from extreme heat. Baclofen works on this reflex circuit's Renshaw cells. These cells are very sensitive to a neurotransmitter produced by the nervous system, GABA (gamma-amino-butyric-acid), which slows this reflex circuit down. Baclofen mimics the effects of GABA. The dose of intrathecal Baclofen necessary to slow down the reflex circuit is variable but is generally one thousand times (three orders of magnitude) smaller than the oral dose.

Baclofen is a direct agonist of GABA_B receptors, which upon activation utilize a G-protein coupled mechanism to increase transmembrane potassium conductance through specific ion channels. Since potassium has a positive charge, and since intracellular potassium concentrations are normally at least ten times that of the extracellular environment, opening potassium channels has an inhibitory, hyperpolarizing effect on a cell's resting electrochemical potential. This tends to decrease the rate of neuronal action potentials, which accounts for Baclofen's anti-spastic effects.

Pharmacokinetics

The drug is rapidly absorbed after oral administration and is widely distributed throughout the body. Biotransformation is low and the drug is predominantly excreted in the unchanged form by the kidneys.

Overdose

Symptoms of a baclofen overdose include vomiting, weakness, drowsiness, slow breathing, seizures, unusual pupil size, and coma.

Underdose

Symptoms of baclofen underdose (via intrathecal delivery) include itching, hypotension, paresthesias, fever, and altered mental state (including delusions and hallucinations).

See also

• Intrathecal baclofen pump
• Phenibut

References

• Intrathecal Baclofen Therapy Cleveland Clinic Information Center. 15 June 2001.

External links

• Patient Site for Intrathecal Baclofen Treatment for Spasticity as a result of Cerebral Palsy