diltiazem and dabigatran

Diltiazem inhibits P-glycoprotein (P-gp), an efflux transporter in the intestinal wall that limits absorption of dabigatran etexilate. Reduced efflux increases systemic exposure to dabigatran, although the effect is modest (20–30% increase in AUC). Dabigatran is not a CYP450 substrate.

Increased dabigatran exposure can raise the risk of bleeding, including serious events such as gastrointestinal haemorrhage. The magnitude is modest, so the interaction is often clinically manageable, but it becomes more relevant in patients with renal impairment or other bleeding risk factors.

If co-administration is needed, monitor for signs of bleeding and consider reducing the dabigatran dose (e.g., 110 mg twice daily) or switching to an alternative anticoagulant. Pay particular attention to patients with CrCl <50 mL/min. Avoid this combination in severe renal impairment (CrCl <30 mL/min) or high bleeding risk.

Established by pharmacokinetic studies and drug labelling; diltiazem is a recognised moderate P-gp inhibitor. The interaction is highlighted in regulatory guidance for dabigatran.