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

Anticholinergics

This class of medication is probably the most commonly used for bladder dysfunction caused by SCI. These medications are used primarily in those who have detrusor hyperreflexia to relax the bladder detrusor muscle. They act by blocking the acetylcholine receptors within the bladder detrusor muscle and thus prevent uninhibited bladder contractions and allow the bladder to hold a larger volume of urine, and therefore help prevent unwanted episodes of incontinence.40 Medications in this class include: oxybutynin (Ditropan), tolteridine (Detrol), and propanthelene.

The side effect profiles of these medications include dry mouth, constipation, pupillary dilatation and blurred vision, drowsiness, and tachycardia.40 Some longer acting formulations of oxybutynin and tolterodine have been developed to lessen the anticholinergic side effects (particularly the dry mouth) and allow the medications to be taken once daily. It should also be said that the dry mouth induced by anticholinergic medications might stimulate the patients to drink more to counteract this side effect. By increasing fluid intake, the SCI patient will then make increased urine volume and potentially cause more detrusor hyperreflexia and incontinence. Thus it is important to determine the correct balance of anticholinergic medication and fluid restriction that works best for each individual. Some tricyclic antidepressants may also be used to inhibit bladder contractions, as they also possess anticholinergic effects.42

Alpha adrenergic blockers

Those who use reflex voiding for their method of bladder drainage may benefit from the addition of alpha-adrenergic blockers. These agents have shown significant improvement in bladder emptying by decreasing the residual urine volume.43 They work by relaxing the smooth muscle sphincter at the base of the bladder and thus lessen the force required by the bladder muscle to empty. Some common medications in this class include tamsulosin (Flomax), terazosin (Hytrin), doxazosin (Cardura), and prazosin (Minipress).

The main side effect of these medications is hypotension as alpha receptors also exist within the blood vessel walls. These effects may be desirable if the patient also has hypertension. However, most people with SCI tend to have a baseline low blood pressure (systolic blood pressure

BOWEL DYSFUNCTION IN SCI

Many individuals with SCI consider bowel dysfunction is considered a major life-limiting problem.44 The loss of voluntary control and the fear of having a bowel accident in public often will prevent people from participation in social activities. In addition, it is always important to consider constipation and/or fecal impaction as a cause of autonomic dysreflexia.

Bowel programs in SCI are designed to train the bowel to empty at regular and predictable times. In general, patients who have sustained a SCI demonstrate 2 types of neurogenic bowel patterns. An 'upper motor neuron' bowel describes the loss of voluntary control but retention of reflex activity (bulbocavernosus and other sacral reflexes). A 'lower motor neuron' bowel (usually from a cauda equina injury) lacks voluntary control as well as reflexive control and responds less successfully to bowel programs. The bowel program is designed to use the intact reflexes (if present) along with a combination of diet and pharmacological agents to achieve an effective, predictable program.45