diltiazem and atorvastatin

Diltiazem inhibits CYP3A4, the enzyme primarily responsible for atorvastatin metabolism, resulting in reduced hepatic clearance and increased plasma concentrations of atorvastatin. This is a pharmacokinetic interaction at the metabolic level.

Elevated atorvastatin levels increase the risk of dose-related adverse effects, particularly myopathy and rhabdomyolysis, which can present with muscle pain, weakness, and dark urine. Severe cases may lead to acute kidney injury and death. The risk is higher with high atorvastatin doses and in elderly patients or those with renal impairment.

Avoid co-prescription if possible. If used together, limit the atorvastatin dose (e.g., no more than 20 mg daily) and monitor patients for symptoms of myopathy. Consider alternative statins not reliant on CYP3A4, such as pravastatin or rosuvastatin. If monitoring, check creatine kinase (CK) at baseline and if symptoms occur.

Well-established interaction based on pharmacokinetic studies and case reports. Diltiazem has been shown to increase atorvastatin AUC by approximately 50% in healthy volunteers. The clinical risk of myopathy is well-recognised in guidelines.