Baclofen

Baclofen
Systematic (IUPAC) name
(RS)-4-amino-3-(4-chlorophenyl)butanoic acid
Identifiers
CAS number	1134-47-0
ATC code	M03BX01
PubChem	2284
DrugBank	APRD00551
ChemSpider	2197
Chemical data
Formula	C10H12ClNO2
Mol. mass	213.661 g/mol
SMILES	eMolecules & PubChem
Pharmacokinetic data
Bioavailability	well absorbed
Protein binding	30%
Metabolism	85% excreted in urine/faeces unchanged. 15% metabolised by deamination
Half life	1.5 to 4 hours
Excretion	renal (70-80%)
Therapeutic considerations
Pregnancy cat.	C(US)
Legal status
Routes	Oral, intrathecal
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Baclofen (brand names Kemstro and Lioresal) is a derivative of gamma-aminobutyric acid (GABA) primarily used to treat spasticity.

It is an agonist specific to mammalian but not fruit fly (Drosophila) GABA_B receptors.^[1][2] Its beneficial effects result from actions at spinal and supraspinal sites. Baclofen can also be used to treat hiccups. It has been shown to prevent rises in body temperature induced by the drug MDMA in rats. ^[3] A very beneficial property of baclofen is that tolerance does not seem to occur to any significant degree in that baclofen retains its therapeutic anti-spasmodic effects even after many years of chronic use.^[4]

Use

Baclofen 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 and glossopharyngeal neuralgias.

Baclofen has been shown to be as effective as diazepam in uncomplicated alcohol withdrawal syndrome.^[5] An Italian study showed that it was effective in promoting alcohol abstinence in patients with severe liver cirrhosis.^[6]

Mechanism of action

Baclofen produces its effect via modulating the GABA_B receptor, similar to the drug GHB which also has the same mechanism of action and also similar effects. However, there are some pharmacological differences in that baclofen appears to have reduced abuse and dependence potential.^[7][8] The modulation of the GABA_B receptor is what produces baclofen's range of therapeutic properties.

History

Historically baclofen was designed to be a drug for epilepsy in the 1920s. 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.

As a treatment for addictions

Dr. Olivier Ameisen, a French-American associate professor of medicine and a cardiologist at Weill Cornell Medical College of Cornell University, reported in 2004 in the journal Alcohol and Alcoholism that he successfully used Baclofen to completely suppress his own alcohol addiction. In his paper, he called for randomized trials of high-dose baclofen to be conducted to test the therapeutic model he had proposed. He renewed his call for clinical trials in the Journal of the American Medical Association (JAMA). His therapeutic model was reproduced by Dr. William Bucknam, who published a case report in Alcohol and Alcoholism, and by Roberta Agabio et al. who published another case in Journal of Clinical Psychopharmacology. Ameisen believes, based on his own experience and other anecdotal evidence, that Baclofen acts on some mechanism within the brains of addicts to suppress cravings brought on by addiction to various substances such as alcohol, cocaine, and heroin.

Ameisen, who currently is a visiting professor of medicine at State University of New York Downstate Medical Center, authored Le Dernier Verre (The Last Glass, titled The End of My Addiction in English) to inform public opinion and physicians. ^[9][10] Since his book has been released, hundreds of patients have been treated in academic centers and rapidly become "indifferent to alcohol".^{[citation needed]} Also, clinical trials are being mounted as a result of public pressure.^{[citation needed]}

Recently, based on Ameisen's therapeutic model, some trials have been conducted in using Baclofen to treat cocaine addiction. In 2007, an Italian team has demonstrated the effectiveness and the safety of baclofen as a treatment for alcohol-addiction^[11] People have said once they took Baclofen they felt their desire for cocaine plummet almost overnight.^{[citation needed]} There is also a report that baclofen has beneficial role in the management of reflux disease.^[12]

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.

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.

Routes of administration

Baclofen can be administered either orally or intrathecally (directly into the cerebral spinal fluid). Intrathecal administration is often preferred 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 management of spasticity is made easier by regular self-administering of the drug through its pump.

With pump administration, 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. In about 5% of patients, the intrathecal route has no effect on the nervous system. Because of their placement just beneath the skin, baclofen pumps are notably vulnerable to infection at least, or at worst, to breakage which releases the whole of the baclofen supply.

Dosage

Baclofen therapy is usually started with an initial low dose of about 10 mg daily in divided doses and gradually titrated up in a stepwise fashion until symptomatic relief occurs. The usual maximum dose is 80 mg per day.^[13]

Withdrawal syndrome

Discontinuation of baclofen can be associated with a withdrawal syndrome which resembles benzodiazepine withdrawal and alcohol withdrawal. Withdrawal symptoms are more likely if baclofen is used for long periods of time (more than a couple of months) and can occur from low or high doses. The severity of baclofen withdrawal depends on the rate at which baclofen is discontinued. Thus to minimise baclofen withdrawal symptoms the dose should be tapered down slowly when discontinuing baclofen therapy. Abrupt withdrawal is most likely to result in severe withdrawal symptoms. Acute withdrawal symptoms can be stopped by recommencing baclofen.^[14]

Withdrawal symptoms may include auditory hallucinations, visual hallucinations, tactile hallucinations, delusions, confusion, agitation, delirium, disorientation, fluctuation of consciousness, insomnia, inattention, memory impairments, perceptual disturbances, anxiety, depersonalization, hypertonia, hyperthermia, formal thought disorder, psychosis, mania, mood disturbances, restlessness, and behavioral disturbances, tachycardia, seizures, tremors, autonomic dysfunction, hyperpyrexia, extreme muscle rigidity resembling neuroleptic malignant syndrome and rebound spasticity.^[14][15]

Overdose

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

References

External links

• Intrathecal Baclofen Therapy Cleveland Clinic Information Center. 15 June 2001.
• FYI: Baclofen (Lioresal), from the New York State Office of Alcoholism and Substance Abuse Services
• http://www.baclofen.info/ (from University Hospital Nottingham - QMC)