Skeletal muscle relaxants baclofen

The mode of action of many skeletal muscle relaxants, for example carisoprodol (Soma), baclofen (Lioresal), and chlorzoxazone (Paraflex), is not clearly understood. Many of tiiese dragp do not directly relax skeletal muscles, but dieir ability to relieve acute painful musculoskeletal conditions may be due to their sedative action. Cyclobenzaprine (Flexeril) appears to have an effect on muscle tone, tiius reducing muscle spasm. 

The skeletal muscle relaxants are contraindicated in patients with known hypersensitivity. Baclofen is contraindicated in skeletal muscle spasms caused by rheumatic disorders. Carisoprodol is contraindicated in patients with a known hypersensitivity to meprobamate. Cyclobenzaprine is contraindicated in patients with a recent myocardial infarction, cardiac conduction disorders, and hyperthyroidism, hi addition, cyclobenzaprine is contraindicated within 14 days of the administration of a monoamine oxidase inhibitor. Oral dantrolene is contraindicated in patients with active hepatic disease and muscle spasm caused by rheumatic disorders and during lactation. See Chapter 30 for information on diazepam. 

Baclofen, labeled as a skeletal muscle relaxant binds to GABA receptors and depresses excitation. It is also useful in the treatment of paroxysms of trigeminal neuralgia. Baclofen is effective in patients with carbamazepine-resistant pain and has been used successfully to relieve attacks in patients previously unresponsive to carbamazepine or phenytoin. 

LITHIUM BACLOFEN Enhancement of hyperkinesias associated with lithium Uncertain Consider alternative skeletal muscle relaxant... 

GABAj receptors are of the seven-transmembrane G-protein-coupled type, and they have a widespread distribution in the body. Agonists at this receptor site include L-baclofen, CGP 27492 and CGP 35024. The receptors are negatively coupled to cAMP, and typical responses in neurons are to inhibit excitability by opening potassium channels or closing calcium channels. These inhibitory actions can be harnessed clinically for instance, baclofen is used as a muscle relaxant and has actions mainly at the spinal level within the GNS (see SKELETAL MUSCLE RELAXANTS). See GABA RECEPTOR ANTAGONISTS. 

Trade names Alpha-Baclofen Baclofen (Watson) Baclon Baclosal Baklofen Clofen Dom-Baclofen Gen-Baclofen Lebic Lioresal (Medtronic) Nu-Baclo Pacifen PMS-Baclofen Spinax Indications Spasticity resulting from multiple sclerosis Category GABA receptor agonist Skeletal muscle relaxant Half-life 2.5-4 hours... 

Atropine - emergency treatment of hypotension with bradycardia Azathioprine - immunosuppressant cancer chemotherapy, rheumatoid arthritis Baclofen - skeletal muscle relaxant spasticity Barbiturate - hypnotic (little therapeutic use)... 

FIGURE 29 Baclofen, a skeletal muscle relaxant, acts at the spinal cord level to inhibit transmission of monosynaptic and polysynaptic reflexes. 

Various drugs have been used to treat muscle spasm. Most compounds in this group act as simple sedative-hypnotic agents and produce skeletal muscle relaxation indirectly. The drugs commonly used as skeletal muscle relaxants are listed in Table 11-53. Carisoprodol (Soma ) and baclofen have been abused as recreational drugs. I. Mechanism of toxicity... 

Baclofen is a centrally acting skeletal muscle relaxant that is used to treat spasticity. It is a chemical analog of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, and is a specific agonist at GABA-B receptors. 

ANTI HYPERTENSIVES AND HEART FAILURE DRUGS MUSCLE RELAXANTS -SKELETAL t hypotensive effect with tizanidine and baclofen Additive hypotensive effect Monitor BP at least weekly until stable. Warn patients to report symptoms of hypotension (light-headedness, dizziness on standing, etc.)... 

NS AIDs MUSCLE RELAXANTS -SKELETAL t baclofen levels with ibuprofen 1 renal excretion of baclofen Avoid co-administration... 

PARACETAMOL MUSCLE RELAXANTS-SKELETAL Baclofen may slow the onset of action of intermittent-dose paracetamol Anticholinergic effects delay gastric emptying and absorption Warn patients that the action of paracetamol may be delayed. This will not be the case when paracetamol is taken regularly... 

Dantrolene has a direct action on skeletal muscle to cause relaxation baclofen inhibits transmission at the spinal cord by acting on inhibitory presynaptic gamma-aminobutyric acid B (GABAb) receptors benzodiazepines cause muscle relaxation by some central action and tizanidine is an a2 adrenoreceptor agonist presumably with a central action. 

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