Pharmacology of spinal cord injury: Basic mechanism of action and side effects of commonly used drugs

Journal of Neurologic Physical Therapy, Sep 2003 by Scelza, William, Shatzer, Matthew

Dantrolene sodium (Dantrium) is an agent that is used to reduce spasticity by acting directly on the muscle.This medication works by preventing calcium from being released from the sarcoplasmic reticulum and thus preventing muscle contraction.34 Sedation is less problematic with dantrolene than with benzodiazepines and the alpha-adrenergic agonists. However, liver toxicity is a concern with dantrolene and frequent monitoring of the liver transaminases need to be conducted.

Intrathecal baclofen pumps are designed to locally administer, using a catheter, into the spinal cord, a small dose of the drug, thus limiting systemic side effects. The catheter is tunneled to the spine at the L4-L5 level and the tip is threaded up to the L1 level. Implantation of the pump into the abdomen is performed only after the patient passes a baclofen screening protocol confirming that the medication is effective at reducing tone. Complications associated with the pump include infection and dislodgement, kinking, or blockage of the catheter. Pump malfunction may be associated with either baclofen overdose or withdrawal. Signs of overdose include sedation, confusion, hypotonia, respiratory depression, and even coma. Signs of withdrawal include increased tone, hyperthermia, puritis, agitation, and hallucinations. Intrathecal baclofen is more effective at reducing lower extremity tone than upper extremity spasticity due to the location of the catheter. Frequent evaluation of tone by both the physician and therapist is important in determining dose. Modalities such as ultrasound, electrical stimulation or any other deep heat treatment are contraindicated over the pump site or catheter tubing."

Nerve blocks with injections of phenol or absolute alcohol have been used to help spasticity. These techniques generally destroy the axon of the nerve and thus directly remove nerve impulses to muscles. The length of the effect of this medication is variable depending on the technique but can last up to several years. Ten percent of patients receiving phenol injections end up with disabling paresthesias.33

Botulinum toxin is another medication that has been used to reduce spasticity. The medication is injected directly into the muscle. It acts at the presynaptic nerve terminal and prevents the release of acetylcholine at the neuromuseular junction, essentially paralyzing the muscle. In general, the onset of action for botulinum toxin is 4 to 7 days with a peak at about 2 weeks and a length of effect from 3 to 6 months. The advantage of injecting botox directly into the spastic region, is that systemic side effects (ie, sedation seen in benzodiazepines and baclofen) are avoided.33

HETEROTOPIC OSSIFICATION

Heterotopic ossification (HO) is the formation of true bone in ectopic sites, usually around joints. The incidence in SCI is approximately 50% with about 20% experiencing significant loss in ROM.35 Heterotopic ossification usually develops within 1 to 4 months after injury; however, late occurrence has also been noted.36 The hip is the most common place of presentation of HO but it may also be present in any joint below the level of the injury.35