Baclofen chemical structure
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Baclofen

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) GABAB receptors. It is used for the treatment of spastic movement, especially in instances of spinal cord injury and in multiple sclerosis. Its beneficial effects result from actions at spinal and supraspinal sites. Baclofen can also be used to treat hiccups. more...

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Description of compound

Baclofen is a white to off-white, odorless or practically odorless crystalline powder, with a molecular weight of 213.66. 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. A test dose is given to assess the effect, and if successful a chronic intrathecal catheter in inserted and connected to a computer-controlled implanted pump. The reservoir in the pump can be replenished by percutaneous injuection. 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 diazepam (Valium©). 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 the 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 sack is not really clear but this is now an established method for the treatment of spasticity in many conditions.

How Baclofen works

Baclofen has its effect in the spinal cord, which is the main connection between the brain and then rest of the body. The spinal cord is a reflex system, a feedback loop. The most obvious reflex is the withdrawal to heat. This movement is brisk and not very well controlled. This is what happens in Cerebral Palsy. Without adequate control from the brain, every movement is like a reflex, being rough and uncontrolled. The reflex can spread through the body causing spasms or “arching”. These spasms can be painful and interrupt sleep.

Baclofen works on this reflex circuit. The reflex circuit in the spinal cord contains the Renshaw cells. These cells are very sensitive to a natural chemical produced by the nervous system: GABA, gamma-amino-butyric-acid. GABA slows the reflex circuit down and Baclofen acts like GABA. The dose of intrathecal Baclofen necessary to slow down the reflex circuit is variable but is generally one thousand times smaller than the oral dose.

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.

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PLACE OF INTRATHECAL BACLOFEN TEST FOR ASSESSING NEURO-ORTHOPAEDIC COMPLICATIONS INVOLVING RETRACTION OF THE LOWER LIMBS
From Journal of Bone and Joint Surgery, 1/1/04 by Denormandie, P

Purpose: Multiple deformations of the lower limbs are common orthopaedic complications of central nervous system disease. Assessment is difficult. Intrathecal Lioresal® was proposed for the patients to establish the relative effects of spasticity and musculo-tendinos retraction and define a medico-surgical therapeutic strategy.

Material and methods: Between January 1999 and December 2000, 31 patients consulted for persistent knee flexion. Baclofen tests (75 - 100 µg Baclofen intrathecal) were performed in ten patients because the relative contribution of spasticity and retraction was difficult to assess. The anti-spasticity effect was observed within the first hour, with a maximal effect between the second and fourth hour. Motor function, joint motion, and function were tested during this time interval. The test was repealed approximately three days later, sometimes with higher doses depending on the level of the anti-spastic effect. Residual orthopaedic limitations were explained by musculotendinous retractions.

Results: For the ten evaluated patients, three presented musculotendinous retractions amendable by surgical treatment (tendon lengthening, proximal disinsertion), sometimes in combination with arthrolysis. For the seven patients who had hypertonic spastic contractions, medical treatment was given with, for three patients, continuous intrathecal Lioresal via pump delivery. There was a correlation between the deformation assessed after the test and the test conducted under general anaesthesia during the procedure in all patients.

Discussion: Other methods for evaluating orthopaedic deformities of the lower limbs can be used. Selective motor blocks using local anasethetics are generally reserved for patients with localised stiffness or when it may be difficult to achieve in certain patients (hip flexion). Mobilisation under general anaesthesia is another solution, but does not allow an assessment of functional gain, particularly if the goal is walking. The intrathecal Baclofen test not only allows an accurate assessment of orthopaedic retraction, but also an assessment of the functional impact of the spasticity. sometimes useful for verticalisation or walking.

Conclusion: The Baclofen intrathecal test is a simple test with a particular place in the preoperative and functional assessment of neuro-orthpaedic stiffness of the lower limbs.

P. Denormandie, E. Lo, C. Kieffer, D. Ben Smail, B. Bussel. J.B. Elis, T. Judet

Service de Chirurgie Orthopaedic, Hopital Raymond-Poincare, 104 boulevard Raymond-Poincare, 92380 Garches, France

Copyright British Editorial Society of Bone & Joint Surgery 2004
Provided by ProQuest Information and Learning Company. All rights Reserved

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