Skeletal muscle relaxants
Direct-Acting Skeletal Muscle Relaxants
mechenism of action
Dantrolene acts within skeletal muscle fibers and interfere with calcium ion release from the muscle tubules. Therefore, the fibers are prevented from contracting. It does not interfere with neuromuscular transmission and does not affect skeletal muscle surface membrane.
Indications
Children
Safety and effectiveness not established in children.
Dantrolene is used to treat upper motor neuron spasticity in children.
Dose should be accurately calculated based on body weight and it increases over time.
Children are at increased risk of CNS and GI toxicity.
sides effects
Adult
They should be cautioned to avoid activities that require alertness (e.g. driving) because drugs can cause confusion and drowsiness.
Pregnant and lactating women should be advised to use contraception and alternative method of feeding, respectively.
Premenopausal women are at increased risk for hepatotoxicity in association with use of dantrolene.
CNS: drowsiness, fatigue, weakness, confusion, headache, insomnia, visual disturbances
GI: GI irritation, diarrhea, constipation, abdominal cramps
GU: urinary frequency, enuresis, urinary urgency , crystalline urine with pain or burning on urination
Others: acne, abnormal hair growth, rashes, photosensitivity, abnormal sweating, chills, nyalgia
Dantrolene can cause direct hepatocellular damage and potentially fatal hepatitis
Botulinom toxins are associated with anaphylactic reactions characterized by headache, dizziness, muscle pain, paralysis
storage condition and route of administration
Route Onset Peak Duration
Oral Slow 4-6 h 8-10 h
IV Rapid 5 h 6-8 h
T1/2: 9 h (oral), 4-8 h (IV)
Metabolism: N/A
Excretion: kidney (urine)
contraindications
Allergy to direct-acting skeletal muscle relaxants. Prevent hypersensitivity reactions
Spasticity that contributes to locomotion, upright position, increased function. These functions will be lost if spasticity were blocked
Active hepatic disease. Interfere with metabolism of drug
Pregnancy. Potential adverse effects to the fetus
Lactation. May cross breast milk and may cause adverse effects in the infant
Women and patients older than age 35. Caution is applied because of increased risk of potentially fatal hepatocellular disease
History of liver disease or previous dysfunction. Increases liver’s susceptibility to cellular toxicity
Respiratory depression. Exacerbated by muscular weakness
Cardiac disease. Cardiac muscle depression may be a risk
Centrally Acting Muscle Relaxants
mechenism of action
The exact mechanism of action of skeletal muscle relaxants is not fully understood but it is thought that it involves the participation of upper or spinal interneurons.
It inhibits monosynaptic and polysynaptic spinal reflexes. Other than that, it is a CNS depressant.
indications
The exact mechanism of action of skeletal muscle relaxants is not fully understood but it is thought that it involves the participation of upper or spinal interneurons
.
It inhibits monosynaptic and polysynaptic spinal reflexes. Other than that, it is a CNS depressant.
contraindications
Allergy to centrally acting skeletal muscle relaxants. Prevent hypersensitivity reactions.
Skeletal muscle spasms caused by rheumatic disorders. Do not benefit from these drugs.
History of epilepsy. CNS depression and imbalance caused by drugs may exacerbate seizure disorder.
Cardiac dysfunction. Muscle function may be depressed.
Condition marked by muscle weakness. Can be exacerbated by drugs.
Hepatic, renal dysfunction. Interfere with drug metabolism and excretion.
Baclofen is not indicated for treatment of spasticity that contributes to locomotion, upright function, or increased function. Blocking this spasticity results in loss of these functions.
sides effects
CNS: depression, drowsiness, fatigue, weakness, confusion, headache, insomnia.
CV: hypotension, arrhythmias
GI: nausea, dry mouth, anorexia, constipation.
GU: urinary frequency, enuresis, urinary urgency
Chlorzoxazone may turn urine into purple-red color.
Tizanidine has been associated with liver toxicity and hypotension in some patients.
Baclofen is tapered over 1-2 weeks to prevent development of psychoses and hallucinations.
storage conditions and route of administration
Route Onset Peak Duration
Oral 1 h 2 h 4-8 h
Intrathecal 30-60 min 4 h 4-8 h
T1/2: 3-4 h
Metabolism: not metabolized
Excretion: kidney (urine)