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Chapter 25 Drugs for Muscle Spasm and Spasticity Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Drugs for Muscle Spasm and Spasticity Two groups of drugs that cause skeletal muscle relaxation One group for localized muscle spasm Other group for spasticity Most produce their effects through actions in the CNS (except dantrolene). Groups are not interchangeable. Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 2 Drugs for Muscle Spasm and Spasticity Muscle spasm: involuntary contraction of muscle or muscle group Causes Epilepsy Hypocalcemia Pain syndromes: adult and chronic Trauma: localized skeletal muscle injury Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 3 Drug Therapy of Muscle Spasm Treatment of spasm Physical measures • Immobilization of affected muscle • Cold compresses • Whirlpool baths • Physical therapy Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 4 Drug Therapy of Muscle Spasm Treatment of spasm Drug therapy Analgesic anti-inflammatory (aspirin) Centrally acting muscle relaxants • Diazepam • Tizanidine Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 5 Centrally Acting Muscle Relaxants Mechanism of action (MOA) unclear – may result from sedative properties of the drugs Diazepam • MOA through enhancing effects of GABA Tizanidine • MOA through agonist action at presynaptic alpha2 receptors Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 6 Centrally Acting Muscle Relaxants Therapeutic use Relieve local muscle spasm Decrease local muscle pain Increase range of motion No studies to indicate superiority of one drug over another Drug selection prescriber preference and patient response Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 7 Centrally Acting Muscle Relaxants Adverse effects Generalized CNS depression Hepatic toxicity • Tizanidine (Zanaflex) and metaxalone (Skelaxin) can cause damage. • Chlorzoxazone (Paraflex) can cause hepatitis and necrosis. Physical dependence • Abstinence syndrome Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 8 Drugs for Spasticity Spasticity Movement disorders of CNS origin Most common causes: multiple sclerosis and cerebral palsy Characteristics include • Heightened muscle tone • Spasm • Loss of dexterity Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 9 Three Drugs for Spasticity Baclofen (Lioresal) Diazepam (Valium) Acts in the CNS Acts in the CNS Dantrolene (Dantrium) Acts directly on smooth muscle Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 10 Baclofen (Lioresal) Mechanism Acts in the spinal cord Suppresses hyperactive reflexes Mechanism unknown May mimic the action of GABA on spinal neurons Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 11 Fig. 25-1. Structural similarity between baclofen and gamma-aminobutyric acid (GABA). Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 12 Baclofen (Lioresal) Therapeutic uses Multiple sclerosis, spinal cord injury, cerebral palsy NOT with stroke Decreases flexor and extensor spasms Suppresses resistance to passive movement No direct effect on skeletal muscle Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 13 Baclofen (Lioresal) Adverse effects No antidote for overdose Gradual withdrawal over 1 to 2 weeks • Abrupt intrathecal withdrawal: risk for rhabdomyolysis CNS depressant GI symptoms (nausea, constipation) Urinary retention Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 14 Diazepam (Valium) Member of the benzodiazepine family (see Chapter 34) Mechanism The only one labeled to treat spasticity Acts in the CNS Mimics action of GABA Adverse effect Sedation Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 15 Dantrolene (Dantrium) Mechanism Acts directly on skeletal muscle Suppresses the release of calcium from the sarcoplasmic reticulum (SR) Therapeutic uses Spasticity associated with multiple sclerosis, cerebral palsy, spinal cord injury Malignant hyperthermia • Potentially fatal condition caused by succinylcholine and general anesthetics Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 16 Dantrolene (Dantrium) Adverse effects Hepatic toxicity Muscle weakness Drowsiness Diarrhea Acne-like rash Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 17