Rivaroxaban

Mechanism

Apixaban and rivaroxaban are both direct factor Xa inhibitors. Their effects are additive without therapeutic gain. Risk of major bleeding rises sharply.

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 between DOACs, stop the first agent and start the second at the time of the next scheduled dose, with no overlap. If a patient inadvertently takes both, observe in hospital for at least 24 hours with haemoglobin and creatinine monitoring.

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

Phenytoin is a strong inducer of the CYP3A4 enzyme and the P-glycoprotein transporter (rivaroxaban label of the US Food and Drug Administration, FDA), and rivaroxaban is cleared through both routes. Rivaroxaban blood levels fall and protection against clots weakens. For rifampicin, another strong inducer, the SmPC of the European Medicines Agency (EMA) reports about a 50% fall in rivaroxaban area under the curve (AUC) with a parallel loss of effect. There are no figures for phenytoin; the SmPC states that it can also lower rivaroxaban levels (rivaroxaban SmPC, EMA).

Symptoms

Stroke or recurrent venous thrombosis.

Management

The combination is contraindicated in the 2021 practical guide of the European Heart Rhythm Association (EHRA): its antiepileptic drug table marks this pair as contraindicated because of reduced rivaroxaban levels (EHRA 2021). The rivaroxaban labels require avoiding it: the European Medicines Agency (EMA) allows it only if the patient is closely monitored for signs of thrombosis (rivaroxaban SmPC, EMA), and the US Food and Drug Administration (FDA) advises avoiding it (FDA rivaroxaban label). The European Society of Cardiology (ESC) advises avoiding the combination where possible (ESC 2024). If it cannot be avoided, monitor the patient closely for signs of thrombosis (rivaroxaban SmPC, EMA): leg swelling and pain, sudden breathlessness and chest pain, sudden weakness or numbness of an arm, a leg or one side of the face, speech problems.

Mechanism

Warfarin blocks vitamin K-dependent clotting factor synthesis; rivaroxaban directly inhibits factor Xa. Effects are additive with 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. Switching from warfarin to rivaroxaban: stop warfarin, wait for INR below 3.0, then start rivaroxaban. Reverse switch: overlap with INR monitoring, stop rivaroxaban once INR exceeds 2.0.

Mechanism

Aspirin irreversibly blocks platelet cyclooxygenase; rivaroxaban directly inhibits factor Xa. No clinically significant pharmacokinetic or pharmacodynamic interaction was found with acetylsalicylic acid 500 mg. But the EMA SmPC lists acetylsalicylic acid among drugs that typically increase bleeding risk, and the effects on haemostasis 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

The combination itself is an approved use of rivaroxaban. Rivaroxaban 2.5 mg twice daily with acetylsalicylic acid 75–100 mg daily is given after acute coronary syndrome (EMA SmPC). The same regimen is used in coronary artery disease or peripheral artery disease at high risk of ischaemic events (EMA SmPC and FDA label). The EMA SmPC contraindicates the combination in two groups: acute coronary syndrome in patients with prior stroke or transient ischaemic attack, and coronary or peripheral artery disease in patients with prior haemorrhagic or lacunar stroke or any stroke within the past month. On full-dose rivaroxaban (atrial fibrillation, deep vein thrombosis), add aspirin only for a separate indication and with caution. Patients at risk of peptic ulcer may receive gastric prophylaxis (EMA SmPC). Add NSAIDs to this pair only if the benefit outweighs the bleeding risk.

Mechanism

Amiodarone moderately blocks CYP3A4 and P-glycoprotein – two rivaroxaban clearance routes. Rivaroxaban plasma levels rise by about 50%; bleeding risk rises moderately.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, black stools, blood in urine. Severe cases include gastrointestinal or intracranial haemorrhage.

Management

The combination is acceptable in patients with preserved renal function (creatinine clearance above 50 mL/min) and atrial fibrillation. In renal impairment, switch to warfarin or apixaban.

Mechanism

As with apixaban, carbamazepine induces CYP3A4 and P-glycoprotein, and rivaroxaban levels fall. Rifampicin, an inducer of the same strength, lowers rivaroxaban AUC by about 50%. Anticoagulation loses effect, with a higher risk of stroke and recurrent thrombosis.

Symptoms

Ischemic stroke in atrial fibrillation patient or recurrent venous thrombosis on apparently active anticoagulant.

Management

Avoid the combination: this is what the rivaroxaban labels say (AEMPS, FDA), and the carbamazepine label calls for close watch for signs of thrombosis if the pair cannot be avoided. If carbamazepine cannot be replaced, switch to warfarin with a target INR of 2.0–3.0. Alternative anticonvulsant: levetiracetam.

Mechanism

Clopidogrel blocks the platelet P2Y12 receptor; rivaroxaban directly inhibits factor Xa. The two antithrombotic mechanisms add up, roughly doubling major bleeding risk.

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

Dual therapy is used after acute coronary syndrome or stenting in atrial fibrillation, generally for no more than 1–6 months. Rivaroxaban dose is adjusted to age and renal function. PPI cover with pantoprazole is mandatory.

Mechanism

Additive GI bleeding risk: anticoagulant (rivaroxaban) + ulcerogenic NSAID (diclofenac). Diclofenac additionally raises cardiovascular risk.

Symptoms

Black or tarry stools (melena), vomiting blood or coffee-ground material, epigastric pain. Risk multiplies in older patients and with prior peptic ulcer disease.

Management

Avoid prolonged combination. If diclofenac is needed for a short course, use the minimum effective dose for 5–7 days under pantoprazole cover. For chronic analgesia: paracetamol, celecoxib (less GI toxicity), or topical NSAIDs.

Mechanism

Additive GI bleeding risk: anticoagulant (rivaroxaban) + ulcerogenic NSAID with antiplatelet effect (ibuprofen).

Symptoms

Black or tarry stools (melena), vomiting blood or coffee-ground material, epigastric pain. Risk multiplies in older patients and with prior peptic ulcer disease.

Management

Avoid prolonged combination. If ibuprofen is needed for a short course, use the minimum effective dose for 5–7 days under pantoprazole cover. For chronic analgesia: paracetamol, celecoxib, or topical NSAIDs.

Mechanism

Ketoconazole strongly inhibits CYP3A4 and P-glycoprotein, both clearance routes of rivaroxaban. Ketoconazole 400 mg daily raised rivaroxaban AUC 2.6-fold and peak concentration 1.7-fold. The EU SmPCs of rivaroxaban and oral ketoconazole do not recommend the combination, and the FDA labels say to avoid it. No label lists the pair as a 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

Avoid the combination. For dermatophytosis, terbinafine is the usual choice instead of oral ketoconazole; for systemic mycoses, echinocandins. If a short course of oral ketoconazole is needed, switch rivaroxaban to a parenteral anticoagulant for that period.

Mechanism

Ketorolac inhibits platelet aggregation, prolongs bleeding time and damages the gastric mucosa; according to its SmPC it causes serious gastrointestinal toxicity more often than equivalent doses of other NSAIDs. Rivaroxaban is a direct factor Xa inhibitor, and its SmPC notes that NSAIDs increase bleeding risk on their own, so the risks add up.

Symptoms

Black or tarry stools (melena), vomiting blood or coffee-ground material, epigastric pain. Risk is higher in older patients and with a history of peptic ulcer disease.

Management

Spanish ketorolac SmPCs list anticoagulants among combinations that are not recommended, and for patients on full (therapeutic) doses of anticoagulants the interaction section calls the combination contraindicated (ketorolac 10 mg and 30 mg/ml SmPCs). Ketorolac is therefore not given to patients on a therapeutic dose of rivaroxaban. At any anticoagulant dose, the FDA allows the combination only after weighing benefits against risks, with extreme caution and close monitoring (US ketorolac label). The rivaroxaban SmPC asks for caution with any NSAID and allows ulcer prophylaxis in patients at risk of peptic ulcer disease (rivaroxaban SmPC, EMA). In older patients and those at high risk of gastrointestinal complications, start ketorolac at the lowest dose and consider gastroprotection with misoprostol or a proton pump inhibitor; oral treatment lasts no more than 7 days (ketorolac 10 mg SmPC). Stop ketorolac at once if bleeding is suspected (ketorolac SmPCs).

Mechanism

Direct oral anticoagulant (rivaroxaban) + NSAID (meloxicam) – additive GI bleeding risk via combined anticoagulation, mucosal injury, and platelet dysfunction.

Symptoms

Black or tarry stools, vomiting blood, epigastric pain. Risk multiplies in older patients and with prior peptic ulcer disease.

Management

Avoid prolonged combination. If meloxicam is needed for a short course, use the minimum effective dose for 5–7 days under pantoprazole cover. For chronic analgesia: paracetamol or celecoxib.

Mechanism

Direct oral anticoagulant (rivaroxaban) + NSAID (naproxen) – additive GI bleeding risk.

Symptoms

Black or tarry stools, vomiting blood, epigastric pain. Risk multiplies in older patients and with prior peptic ulcer disease.

Management

Avoid prolonged combination. If naproxen is needed for a short course, use the minimum effective dose for 5–7 days under pantoprazole cover. For chronic analgesia: paracetamol or celecoxib.

Mechanism

Rifampicin is a strong CYP3A4 + P-gp inducer. Rivaroxaban falls 50% – anticoagulation lost.

Symptoms

Stroke or recurrent VTE.

Management

Avoid the combination unless the patient can be closely watched for signs of thrombosis, as the EU SmPC and the FDA label of rivaroxaban state. During the rifampicin course rivaroxaban can be replaced with low molecular weight heparin. Warfarin is affected too: the rifampicin SmPC reports a 74% fall in S-warfarin exposure, so the dose is titrated to INR, checked more often than usual, including after rifampicin is stopped.

Mechanism

Ritonavir strongly inhibits CYP3A4 and P-glycoprotein, both clearance routes of rivaroxaban. Ritonavir 600 mg twice daily raised rivaroxaban AUC 2.5-fold and peak concentration 1.6-fold. The EU SmPCs of rivaroxaban and ritonavir do not recommend the combination, and the FDA labels say to avoid it. None of these labels lists the pair as a 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

Avoid the combination. In a patient with HIV, choose a ritonavir-free antiretroviral regimen where possible or switch the anticoagulant. Warfarin is an option with frequent INR checks: ritonavir lowers R-warfarin levels, and the ritonavir SmPC advises INR monitoring. Another option is a short course of low molecular weight heparin. Nirmatrelvir with ritonavir for COVID-19 also contains ritonavir, and its SmPC does not recommend use with rivaroxaban.

Mechanism

Azithromycin is a weak P-glycoprotein inhibitor; rivaroxaban is a P-glycoprotein substrate. Rivaroxaban plasma levels may rise modestly, raising bleeding risk.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, black or tarry stools. Higher risk in older patients and chronic kidney disease.

Management

For short azithromycin courses (3–5 days), the combination is acceptable without dose change. In older patients and creatinine clearance below 50 mL/min: monitor for bleeding signs. Alternative antibiotics without P-glycoprotein effect: a cephalosporin, amoxicillin-clavulanate, doxycycline.

Mechanism

Rivaroxaban is cleared partly through the CYP3A4 enzyme and the P-glycoprotein (P-gp) transporter. The European Medicines Agency (EMA) classes clarithromycin as a strong CYP3A4 inhibitor and a moderate P-gp inhibitor: at 500 mg twice daily it raised the rivaroxaban area under the curve 1.5-fold and peak concentration 1.4-fold (rivaroxaban SmPC, EMA). In severe kidney impairment, rivaroxaban levels are higher even without interacting drugs, on average 1.6-fold (rivaroxaban SmPC, EMA).

Symptoms

Bleeding gums, nosebleeds, bruising without injury, blood in the urine or stool, heavy periods. In severe cases, gastrointestinal or intracranial bleeding. The risk is higher in patients aged 75 or over, with chronic kidney disease, previous bleeding or anaemia, and with concomitant antiplatelet drugs, non-steroidal anti-inflammatory drugs or systemic corticosteroids.

Management

The combination can be used with caution. The European Medicines Agency (EMA) considers the interaction clinically irrelevant for most patients but potentially significant in high-risk patients (rivaroxaban SmPC, EMA). The US Food and Drug Administration (FDA) requires no special measures (rivaroxaban FDA label). Caution matters most in patients at high risk of bleeding (clarithromycin SmPC) and in those with reduced kidney function: rivaroxaban is used with caution in patients with renal impairment who take drugs that raise its levels (rivaroxaban SmPC, EMA), and the European Society of Cardiology (ESC) flags clarithromycin specifically when kidney function is impaired (ESC 2024). The European Heart Rhythm Association (EHRA) advises particular caution with polypharmacy and when two or more risk factors are present, such as age 75 or over, chronic kidney disease, antiplatelet drugs, non-steroidal anti-inflammatory drugs, systemic corticosteroids or previous bleeding; in that case, first consider whether another anticoagulant or antibiotic with fewer interactions is suitable (EHRA 2021). Watch the patient for signs of bleeding and stop rivaroxaban if severe bleeding occurs (rivaroxaban SmPC, EMA).

Mechanism

Rivaroxaban blocks coagulation factor Xa; etoricoxib selectively inhibits cyclooxygenase-2 (COX-2) and by itself causes upper gastrointestinal ulcers, perforations and bleeding, some of them fatal (etoricoxib SmPC, AEMPS, section 4.4). Etoricoxib has no antiplatelet effect (etoricoxib SmPC, 4.4), but it damages the mucosa, and on an anticoagulant such damage bleeds more. The rivaroxaban SmPC lists NSAIDs among drugs that affect haemostasis and asks for caution (EMA, 4.4 and 4.5). There is no kinetic conflict: etoricoxib does not affect CYP3A4 (etoricoxib SmPC, 4.5), the enzyme that clears rivaroxaban. Etoricoxib adds a second factor through the kidney: NSAIDs can impair renal function (etoricoxib SmPC, 4.4), and in renal impairment rivaroxaban concentrations rise (rivaroxaban SmPC, 4.4).

Symptoms

Above all gastrointestinal bleeding: black or bloody stools, vomiting blood, abdominal pain, weakness, a fall in haemoglobin. The rivaroxaban SmPC lists mucosal bleeding (nosebleeds, gums, gastrointestinal, genitourinary including heavier menstrual bleeding) and anaemia, and requires a search for the bleeding site after any unexplained fall in haemoglobin or blood pressure (EMA, 4.4). From etoricoxib separately: fluid retention, oedema, a rise in blood pressure, worsening renal function (etoricoxib SmPC, AEMPS, 4.4). Uncontrolled hypertension and renal impairment in a patient on rivaroxaban are also bleeding risk factors (rivaroxaban SmPC, 4.4).

Management

The combination is acceptable with caution; no label forbids it. The rivaroxaban SmPC asks for caution with concomitant NSAIDs because of the bleeding risk (EMA, 4.4 and 4.5), and the etoricoxib SmPC asks for caution with warfarin and other oral anticoagulants (AEMPS, 4.4). The EHRA 2021 practical guide advises weighing such a combination against the expected benefit in each clinical situation. First check the etoricoxib contraindications: active peptic ulcer or gastrointestinal bleeding, uncontrolled hypertension above 140/90 mmHg, congestive heart failure, ischaemic heart disease, peripheral arterial or cerebrovascular disease, creatinine clearance below 30 mL/min (etoricoxib SmPC, 4.3). Rivaroxaban is also contraindicated with an active or recent ulcer (rivaroxaban SmPC, 4.3). Give etoricoxib at the lowest effective dose for the shortest possible time (etoricoxib SmPC, 4.4), and in patients at risk of ulcer disease consider prophylactic treatment (rivaroxaban SmPC, 4.4). Monitoring: watch for signs of bleeding and anaemia; haemoglobin and haematocrit help to detect occult bleeding (rivaroxaban SmPC, 4.4); promptly evaluate any sign of blood loss in a patient on an NSAID (rivaroxaban FDA label, 7.4). The etoricoxib requirement to monitor the INR closely is written for warfarin. The INR does not measure the effect of rivaroxaban, routine monitoring is not needed, and a calibrated anti-Xa assay is reserved for exceptional situations (rivaroxaban SmPC, EMA, 4.4; FDA, 5.2). Check blood pressure during the first two weeks of etoricoxib and periodically afterwards (etoricoxib SmPC, 4.4). If renal function worsens, use rivaroxaban with caution at creatinine clearance 15–29 mL/min and do not use it below 15 mL/min (rivaroxaban SmPC, 4.4). Stop rivaroxaban in case of severe bleeding (EMA, 4.4).