A 58-year-old man with myasthenia gravis admitted for urosepsis is about to receive empiric coverage for Pseudomonas. The resident suggests gentamicin. Why should this be avoided?

• A It induces hepatic microsomal enzymes that accelerate pyridostigmine metabolism
• B It causes rhabdomyolysis by inhibiting sarcoplasmic calcium uptake
• C It competitively antagonizes acetylcholinesterase inhibitors at the motor end plate
• D It impairs acetylcholine release at the neuromuscular junction and can precipitate respiratory paralysis ✓

Explanation

Aminoglycosides reduce the release of acetylcholine from the presynaptic nerve terminal by competing with calcium entry, and they also decrease postsynaptic sensitivity to acetylcholine. This produces a curare-like neuromuscular blockade that is exaggerated in myasthenia gravis and can cause fatal apnea, especially when given rapidly intravenously or with neuromuscular blockers. Calcium gluconate and neostigmine reverse it. Hepatic enzyme induction and rhabdomyolysis are not described mechanisms.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.