Peripherally acting muscle relaxants which are also known as direct-acting skeletal muscle relaxants, ease skeletal muscle spasms that occur as a result of cerebrovascular accident or stroke, spinal cord injury, multiple sclerosis, and cerebral palsy. Peripherally acting muscle relaxants act directly on skeletal muscle tissue by inhibiting the release of calcium, which is necessary for normal muscle contraction. By blocking the action potential of calcium, muscle contraction does not occur. This results in muscle relaxation or relief of muscle spasticity.

The usual medication of choice for this category is dantrolene.

Adverse effects of dantrolene include muscle weakness, drowsiness, dizziness, and diarrhea. Liver toxicity is another adverse effect and occurs more frequently with higher doses and long-term therapy. Start oral dantrolene at low doses and gradually increase to prevent CNS side effects. Inhibition of the release of calcium in skeletal muscle may decrease strength and function in addition to relieving spasticity. It is important that patient’s monitor their muscle strength during treatment to make sure that weakness does not develop, as it will make ambulation more difficult and put the patient at a higher risk for falls. Inform the provider if muscle weakness occurs, especially if it interferes with activities of daily living.

Contraindications for dantrolene include patients who have liver disease. Use with caution in patients who have cardiac or pulmonary disease or a neuromuscular disorder. The incidence of liver damage increases in clients older than age 35, so closely monitor liver function tests. Female clients older than 35 who use estrogen have an increased risk of liver toxicity if they use dantrolene. Dantrolene may cause cardiac dysrhythmias in clients who also take calcium channel blockers.