Diltiazem

Diltiazem combined with metoprolol increases the risk of bradycardia and AV block through additive negative chronotropic and dromotropic effects.

Diltiazem (calcium channel blocker) combined with lithium may increase risk of lithium toxicity and neurotoxic adverse effects including bradycardia.

Diltiazem inhibits CYP3A4 and P-glycoprotein, increasing tacrolimus blood concentrations by 40–70% and heightening the risk of dose-related tacrolimus toxicity.

Diltiazem inhibits CYP3A4-mediated methylprednisolone metabolism, increasing methylprednisolone exposure and the risk of steroid side effects including immunosuppression, hyperglycaemia, and hypertension.

Diltiazem inhibits CYP3A4-mediated tamsulosin metabolism, increasing tamsulosin plasma concentrations by up to 2-fold and heightening the risk of orthostatic hypotension and dizziness.

Diltiazem increases dabigatran plasma levels through P-glycoprotein inhibition, potentially raising bleeding risk without a change in INR (dabigatran has no INR to monitor).

Diltiazem significantly increases digoxin plasma levels through P-gp inhibition and may additionally slow AV nodal conduction, exacerbating bradycardia or heart block.

Diltiazem inhibits CYP3A4-mediated atorvastatin metabolism, increasing atorvastatin plasma concentrations and the risk of myopathy and rhabdomyolysis.

Carvedilol combined with diltiazem increases the risk of bradycardia, hypotension, and AV block through additive cardiac depressant effects and pharmacokinetic interaction.