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

Clinical presentation of HO includes fever, edema, warmth, and decreased range of motion (ROM) around a specific joint. The presentation may be similar to other serious conditions such as DVT, infection, or fracture so the presence of these diagnoses must be ruled out.

There is no definitive treatment for HO; the goals of management include maintaining functional ROM and limiting the formation of ectopic bone as much as possible. Careful ROM exercises a mainstay in the management of HO, appear to be beneficial in maintaining range of motion and does not accelerate the formation of ectopic bone.37 Etidronate (Didronel), a bisphosphonate, is the only FDA approved medication in the treatment of HO. Etidronate blocks the late phase of bone mineralization but has no effect on the early stage of osteoid production.38 Common side effects present in 10% to 20% of patients are mostly gastrointestinal (ie, esophagitis, abdominal pain, nausea, and vomiting).39 It is unclear what effect etidronate has on bone healing. Other treatments of HO include the use of NSAIDs, radiation, and surgery.

BLADDER DYSFUNCTION IN SPINAL CORD INJURY

Bladder dysfunction is another common problem for individuals with SCI. Complications from a neurogenic bladder may include urinary tract infections (UTI), kidney stones, and renal damage. In addition maintenance of urinary continence is important for social integration. Autonomic dysreflexia is also a significant side effect of an over distended bladder and is an important factor in deciding which methods of bladder drainage will be used.40

In a healthy individual, voiding is under volitional control and activated primarily by the autonomic nervous system. The sacral micturition center in the conus medullaris portion of the spinal cord is the parasympathetic nucleus that regulates the bladder detrusor muscle to contract and promote voiding. The neurotransmitter used in the parasympathetic nervous system is acetylcholine and its primary effect is to stimulate the bladder detrusor to contract and thus empty the bladder. In contrast, the sympathetic nervous system with its adrenergic receptors exits the spinal cord at the low thoracic and upper lumbar regions. Its primary neurotransmitter is norepinephrine and its main function is to promote storage of urine. There are alpha-receptors located in the internal sphincter which, when stimulated, contract to prevent leakage of urine from the bladder. In addition, beta-receptors are present throughout the detrusor muscle and when activated, produce relaxation of the bladder to promote storage. With SCI, there is limited or absent volitional input to these centers to control voiding. Under most conditions however, they will continue to act under reflex control and will often act in an uncoordinated fashion.41

There are 2 general patterns of bladder dysfunction for individuals with SCI. Those with suprasacral injuries will have detrusor hyperreflexia. These patients will have unopposed detrusor contractions with small volume bladders and incontinence. Those with cauda equina syndrome will have a flaccid areflexic bladder. These patients will have large capacity bladders with little to no capability of producing voluntary bladder contractions. Each individual will undergo a urodynamic study to determine the specific type of bladder dysfunction and aid in determination of appropriate and effective methods of bladder drainage. Common methods of bladder drainage include intermittent catheterization (IC), reflex voiding with a condom catheter (useful for men only), indwelling Foley/suprapubic catheter, or surgical bladder augmentation. The type of bladder dysfunction, upper extremity function, availability of assistance, and secondary medical conditions determine the specific method of urinary drainage. In addition, there are numerous medications available to help maintain bladder health and continence. The medications which are often used for long-term management, their mode of action, and side effect profiles are discussed below.