Psychiatric Drugs and Medications Q 44
Drugs classified as centrally acting skeletal muscle relaxants are most effective in relieving:
A. Spasm due to trauma or inflammation
B. Chronic spasm due to old injury
C. Pain from arthritis
D. Surgical complications
Correct Answer: A. Spasm due to trauma or inflammation
Centrally acting skeletal muscle relaxants are most effective in relieving spasm due to trauma or inflammation. The centrally acting muscle relaxants are a group of drugs that act in the central nervous system (CNS) to mitigate tension and spasm of skeletal muscles. Drugs within this group are structurally heterogeneous and act at a variety of receptors in the CNS.
Option B: In theory, involuntary muscle spasm may result from a protective reflex preventing movement that would otherwise cause injury. In some cases, muscle spasm itself may become painful and debilitating. This phenomenon, known as the “pain-spasm-pain cycle,” has not been confirmed in rigorous clinical and electrophysiologic studies.
Option C: One proposed mechanism is anticholinergic inhibition of the midbrain reticular activating system resulting in depressed polysynaptic reflexes and decreased muscle tone. This is also described as an indirect inhibition of the interneuronal junction of the spinal cord.
Option D: The onset of action of oral methocarbamol is 30 minutes. The drug is completely absorbed by the gastrointestinal tract and reaches peak plasma concentrations at two hours. It has a variable half-life of one to two hours and is metabolized in the liver by dealkylation, hydroxylation, and glucuronidation.