TITLE: Clinically Significant Drug Interaction: Simvastatin and Clarithromycin

Primary Drug

Simvastatin / Zocor

Interacting Drug

Clarithromycin / Biaxin

Type of Interaction

Pharmacokinetic

Mechanism

Clarithromycin is a strong inhibitor of CYP3A4, the enzyme responsible for the metabolism of simvastatin. This inhibition leads to increased plasma concentrations of simvastatin, as its breakdown is significantly reduced.

Clinical Significance

The increased levels of simvastatin can result in an elevated risk of severe adverse effects such as myopathy and rhabdomyolysis. These conditions can lead to muscle pain, weakness, and potentially life-threatening kidney damage.

Management / Monitoring

Patients who require both medications should either switch to a statin not metabolized by CYP3A4, such as pravastatin or rosuvastatin, or consider an alternative antibiotic. If co-administration is unavoidable, close monitoring for signs of muscle pain or weakness is essential. Liver function tests and creatine kinase levels should be regularly checked.

Pharmacy Technician Notes

- Advise patients to immediately report unexplained muscle pain, tenderness, or weakness, particularly if accompanied by malaise or fever. - Ensure that any signs of muscle breakdown, such as dark urine, are promptly communicated to the healthcare provider. - Encourage patients to discuss all current medications with their healthcare provider to avoid harmful interactions.