Dabigatran

Mechanism

Apixaban inhibits factor Xa; dabigatran inhibits thrombin. Additive anticoagulation with no therapeutic benefit and high risk of major bleeding.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage, gross haematuria with renal colic, spontaneous retroperitoneal haematomas. Symptoms may appear within days of co-prescription.

Management

The combination is not prescribed. When switching DOACs, stop the first and start the second at the next scheduled dose. Overlap is only acceptable via a parenteral anticoagulant when bridging is needed.

Mechanism

Dabigatran etexilate is a substrate of the efflux transporter P-glycoprotein (P-gp). Ciclosporin inhibits this transporter, so dabigatran plasma concentrations rise (dabigatran and ciclosporin labels). There are no clinical studies of the pair (ciclosporin label, US Food and Drug Administration, FDA). Based on in vitro data, the dabigatran manufacturer expects an effect similar to that of ketoconazole. Ketoconazole 400 mg increased the dabigatran area under the concentration–time curve (AUC) 2.38-fold after a single dose and 2.53-fold after multiple once-daily doses (dabigatran label, European Medicines Agency, EMA). The kidneys clear dabigatran mainly unchanged, and ciclosporin often raises serum creatinine and urea (dabigatran and ciclosporin labels). According to the FDA dabigatran label, P-gp inhibition and impaired renal function are the major independent factors that increase dabigatran exposure. Together, they are expected to raise it more than either factor alone.

Symptoms

The main risk is bleeding from the nose, stomach and gut, rectum and haemorrhoids, and the urinary and genital tract, with blood in the urine. Bleeding into the skin and joints, bruising, coughing up blood and, less often, intracranial haemorrhage can also occur (dabigatran label). Bleeding can present as weakness, pallor, dizziness, headache, shortness of breath, or unexplained swelling or shock (dabigatran label). An unexplained fall in haemoglobin, haematocrit or blood pressure points to hidden bleeding (dabigatran label).

Management

The combination is contraindicated. The dabigatran label lists ciclosporin among its contraindications (European Medicines Agency, EMA). The ciclosporin label lists dabigatran among its contraindications (Spanish Agency of Medicines and Medical Devices, AEMPS). The ciclosporin label of the US Food and Drug Administration (FDA) says the combination should be avoided. The table of the European Heart Rhythm Association (EHRA 2021) marks the pair red, meaning contraindicated or not advisable because dabigatran levels rise. If a patient taking ciclosporin needs an oral anticoagulant, the same table marks apixaban and rivaroxaban with ciclosporin yellow with hatching (caution required, no clinical or pharmacokinetic data). For edoxaban, it gives a dose reduction to 30 mg once daily according to the edoxaban label (EHRA 2021). If the two drugs have already been taken together, watch closely for signs of bleeding or anaemia. Look for the bleeding site if haemoglobin, haematocrit or blood pressure falls without explanation (dabigatran label, EMA). The international normalised ratio (INR) is unreliable with dabigatran and should not be measured. Diluted thrombin time, ecarin clotting time and activated partial thromboplastin time can help detect excess dabigatran (dabigatran label, EMA). Check renal function often during ciclosporin treatment (ciclosporin label, AEMPS). Stop dabigatran if acute kidney failure develops (dabigatran label, EMA). In severe bleeding, stop dabigatran and find the cause. In adults, the specific reversal agent idarucizumab can be considered, and haemodialysis can remove dabigatran (dabigatran label, EMA).

Mechanism

Dronedarone strongly inhibits intestinal P-glycoprotein, the clearance route of dabigatran. Dabigatran plasma levels rise 2-fold or more. FDA Multaq Section 4.3 specifically lists dabigatran etexilate as an absolute contraindication.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage, gross haematuria with renal colic, spontaneous retroperitoneal haematomas. Symptoms may appear within days of co-prescription.

Management

The combination is not prescribed. For atrial fibrillation patients on dronedarone, anticoagulate with warfarin, apixaban, or rivaroxaban (the latter two use P-glycoprotein less and are acceptable without dose change).

Mechanism

Ketoconazole strongly blocks P-glycoprotein, the main transporter of dabigatran. Dabigatran plasma levels double, especially in renal impairment.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage. Risk rises in patients over 65 and with prior peptic ulcer disease.

Management

The AEMPS label for dabigatran lists systemic ketoconazole as a contraindicated combination. The combination is not prescribed. Alternative antifungals: terbinafine (no P-glycoprotein use) for dermatophytosis, or echinocandins for systemic mycoses.

Mechanism

Rivaroxaban blocks factor Xa; dabigatran blocks thrombin. Different targets but additive anticoagulation with no therapeutic benefit.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage, gross haematuria with renal colic, spontaneous retroperitoneal haematomas. Symptoms may appear within days of co-prescription.

Management

The combination is not prescribed. When switching DOACs, stop the first and start the second at the next scheduled dose without overlap. For high thrombotic risk with renal impairment, bridge with a parenteral anticoagulant (low molecular weight heparin).

Mechanism

Warfarin blocks vitamin K-dependent clotting factor synthesis; dabigatran is a direct thrombin inhibitor. The two mechanisms are additive with bleeding risk.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage, gross haematuria with renal colic, spontaneous retroperitoneal haematomas. Symptoms may appear within days of co-prescription.

Management

The combination is not prescribed. Switching from warfarin to dabigatran: stop warfarin, wait for INR below 2.0, then start dabigatran. Reverse switch: start warfarin 3 days before stopping dabigatran if creatinine clearance is over 50 mL/min, 2 days if 30–50 mL/min, 1 day if below 30 mL/min.

Mechanism

Amiodarone inhibits P-glycoprotein (P-gp), the efflux transporter for dabigatran. After a single 600 mg dose of amiodarone, dabigatran AUC rose about 1.6-fold and Cmax about 1.5-fold (EMA SmPC). Because amiodarone has a long half-life, the effect may persist for weeks after it is stopped.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, black stools, blood in urine. Risk is higher in renal impairment.

Management

After elective hip or knee replacement, reduce dabigatran for thromboprophylaxis to 150 mg once daily (two 75 mg capsules); the EMA SmPC requires this for all patients on amiodarone. In atrial fibrillation and in treatment of deep vein thrombosis and pulmonary embolism, amiodarone does not call for a dose change (EMA SmPC; for atrial fibrillation also the FDA label). At creatinine clearance (CrCl) 30–50 mL/min, choose 110 mg twice daily individually based on bleeding risk (EMA SmPC). The FDA label says to avoid P-gp inhibitors at CrCl below 50 mL/min in deep vein thrombosis, pulmonary embolism and after hip replacement. Dabigatran is contraindicated at CrCl below 30 mL/min (EMA SmPC). Keep watching for signs of bleeding and anaemia for several weeks after amiodarone is stopped.

Mechanism

Carbamazepine induces P-glycoprotein, the main dabigatran clearance route. Dabigatran plasma levels fall and anticoagulant effect weakens – stroke risk in atrial fibrillation rises.

Symptoms

The patient feels nothing. Stroke, deep vein thrombosis, and pulmonary embolism risks rise.

Management

Avoid the combination. Alternative anticoagulants: warfarin with INR monitoring or low molecular weight heparin for short courses. Alternative anticonvulsants without induction: levetiracetam, lamotrigine.

Mechanism

Clarithromycin inhibits P-glycoprotein (P-gp), the efflux transporter for dabigatran. In healthy volunteers, clarithromycin 500 mg twice daily increased dabigatran AUC about 1.19-fold and Cmax about 1.15-fold (EMA SmPC). The increase alone is small, but P-gp inhibition and impaired renal function are the two major independent factors that raise dabigatran exposure (FDA label), and their effects add up.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, blood in urine or stool, menorrhagia. Severe cases include gastrointestinal or intracranial haemorrhage. Risk rises in patients over 65 and with prior peptic ulcer disease.

Management

With creatinine clearance (CrCl) of 50 mL/min or more, keep the dabigatran dose. In atrial fibrillation the dose also stays the same at CrCl 30–50 mL/min: the FDA label lists clarithromycin among P-gp inhibitors that need no dabigatran dose adjustment. Per the FDA label, avoid the combination in two cases: CrCl below 50 mL/min when dabigatran is used to treat or prevent deep vein thrombosis and pulmonary embolism, and CrCl 15–30 mL/min in atrial fibrillation. Calculate CrCl with the Cockcroft–Gault formula before the course. During the course, watch for signs of bleeding and anaemia, especially with reduced renal function (EMA SmPC). If the combination is unsuitable, choose an antibiotic that is not listed as a P-gp inhibitor in the dabigatran label.

Mechanism

Dabigatran inhibits thrombin while ibuprofen damages gastric mucosa and blocks platelet aggregation, so two bleeding pathways add up. The label separates two scenarios: short-term NSAID analgesia was not linked to more bleeding, whereas with chronic use in the RE-LY study NSAIDs raised bleeding risk by about 50 % with both dabigatran and warfarin.

Symptoms

Black stools, coffee-ground vomit, gum or nose bleeding that is slow to stop, large bruises without trauma, pink urine. Fatigue and pallor point to anaemia from slow bleeding. Impaired renal function multiplies the risk, since dabigatran is cleared by the kidneys.

Management

For occasional pain, paracetamol replaces ibuprofen without touching coagulation. If an NSAID is needed, use the shortest course with gastric protection, watching stools and haemoglobin. Continuous ibuprofen alongside dabigatran should be reconsidered: that is exactly the scenario with the extra 50 % risk.

Mechanism

Rifampicin strongly induces P-glycoprotein, the main dabigatran clearance route. Dabigatran plasma levels fall by 66%; stroke prevention in atrial fibrillation or VTE treatment fails.

Symptoms

The patient feels nothing. Stroke risk in atrial fibrillation rises, as do deep vein thrombosis and pulmonary embolism risks.

Management

The combination is not prescribed. Alternative anticoagulants: warfarin with INR monitoring or low molecular weight heparin for short courses. Induction persists for 2 weeks after rifampicin stops.