A patient, Renata Fairburn, presents a new prescription for the macrolide clarithromycin to treat a respiratory infection. Her active profile shows she takes simvastatin 40 mg each evening for hyperlipidaemia. The technician is reviewing the profile before the pharmacist verifies the order. Which interaction concern should the technician flag as the PRIMARY safety issue?
- AClarithromycin inhibits the metabolism of simvastatin, raising the risk of myopathy and rhabdomyolysis. Correct
- BClarithromycin reduces the absorption of simvastatin, making the statin therapeutically ineffective.
- CClarithromycin and simvastatin compete for renal excretion, causing the antibiotic to accumulate to toxic levels.
- DClarithromycin chelates with simvastatin in the gut, forming an inactive complex that passes unabsorbed.
Why A is correct: Clarithromycin is a strong CYP3A4 inhibitor and simvastatin is a CYP3A4 substrate, so co-administration markedly raises simvastatin levels and the risk of muscle injury, which is the correct primary flag.
Why B is wrong: This is tempting because absorption interactions exist for some drugs, but the clarithromycin-simvastatin interaction is metabolic inhibition that raises, not lowers, statin exposure, so this is wrong.
Why C is wrong: A renal competition mechanism sounds plausible, but the recognised concern is hepatic CYP3A4 inhibition affecting the statin, not antibiotic accumulation, so this misstates the mechanism.
Why D is wrong: Chelation is a real interaction type for tetracyclines and divalent cations, which makes it familiar, but it does not apply to this macrolide and statin pair, so this is incorrect.