What baseline investigations and assessments are required before switching a patient from rivaroxaban to apixaban?

Baseline Investigations Before Switching from Rivaroxaban to Apixaban

Before switching a patient from rivaroxaban to apixaban, obtain renal function (creatinine clearance via Cockcroft-Gault), complete blood count, liver function tests (transaminases and bilirubin), and review all concomitant medications for drug interactions. 1

Essential Laboratory Tests

Renal Function Assessment

• Calculate creatinine clearance using the Cockcroft-Gault formula to determine appropriate apixaban dosing and assess drug elimination capacity. 1
• Measure serum creatinine as it is one of three criteria (≥1.5 mg/dL) that may require apixaban dose reduction when combined with other factors. 2
• Apixaban has 27% renal clearance compared to rivaroxaban's higher renal dependence, making renal function critical for both discontinuation timing and new drug dosing. 2, 3

Hematologic Assessment

• Obtain a complete blood count including platelet count to screen for thrombocytopenia and baseline hemoglobin before switching anticoagulants. 1
• Baseline hemoglobin establishes a reference point for detecting future bleeding complications, defined as a drop ≥2 g/dL. 1

Hepatic Function

• Measure transaminases (ALT/AST) and bilirubin to identify liver disease that may affect drug metabolism and increase bleeding risk. 1
• Both rivaroxaban and apixaban undergo hepatic metabolism, with rivaroxaban dependent on CYP3A4 and apixaban on both CYP3A4 and P-glycoprotein pathways. 1

Coagulation Testing Considerations

Baseline Coagulation Studies

• Obtain PT/aPTT and baseline coagulation parameters before initiating the new anticoagulant, though these are not required for routine DOAC monitoring. 1
• Standard coagulation tests show insufficient correlation with DOAC levels and should not be used to guide dosing decisions. 4

Drug-Specific Monitoring (If Available)

• Anti-Xa assays with drug-specific calibrators provide the most accurate assessment of rivaroxaban and apixaban plasma concentrations if measurement is needed. 4
• Heparin-calibrated anti-Xa assays generate different results across reagent systems and should not be used interchangeably without system-specific validation. 5

Medication Review

Drug Interaction Assessment

• Identify strong dual P-gp and CYP3A4 inhibitors (ketoconazole, itraconazole, ritonavir, clarithromycin) that require 50% apixaban dose reduction or complete avoidance if already on 2.5 mg twice daily. 3
• Avoid apixaban entirely with strong inducers (rifampin, carbamazepine, phenytoin, St. John's wort) as these markedly reduce plasma levels and increase thrombotic risk. 3
• Review antiplatelet agents (aspirin, clopidogrel, prasugrel, ticagrelor) as concomitant use increases bleeding risk and should be limited to situations where dual therapy is absolutely necessary. 3
• Moderate inhibitors like diltiazem increase apixaban levels by 40% but generally do not require dose adjustment unless combined with other risk factors. 3

Patient-Specific Factors for Dose Determination

Apixaban Dose Reduction Criteria

• Reduce apixaban from 5 mg to 2.5 mg twice daily only when at least 2 of these 3 criteria are present: age ≥80 years, body weight ≤60 kg, or serum creatinine ≥1.5 mg/dL. 2
• Measure body weight as it is one of the three dose-reduction criteria. 2
• Document patient age as ≥80 years qualifies as a dose-reduction criterion. 2

Bleeding Risk Assessment

• Calculate HAS-BLED score to identify modifiable bleeding risk factors (uncontrolled blood pressure, labile INRs if previously on warfarin, concomitant NSAIDs, alcohol use). 1
• A HAS-BLED score ≥3 indicates high bleeding risk requiring caution and regular review, but should not exclude patients from anticoagulation. 1

Timing of Switch

Rivaroxaban Washout Period

• For CrCl ≥80 mL/min, wait 24 hours after the last rivaroxaban dose before starting apixaban for low-risk procedures or switches. 1
• For CrCl 50-80 mL/min, wait 24 hours for low-risk scenarios and up to 36 hours if bleeding risk is elevated. 1
• For CrCl 30-50 mL/min, wait 24-48 hours depending on bleeding risk, as rivaroxaban half-life is prolonged. 1
• Rivaroxaban has a half-life of 7-11 hours in normal renal function but extends to 9-13 hours in severe renal impairment. 1

No Bridging Required

• Do not use LMWH or unfractionated heparin bridging when switching between DOACs, as continuous anticoagulation is maintained through appropriate timing. 1

Common Pitfalls to Avoid

• Do not use heparin-calibrated anti-Xa assays interchangeably across different reagent/instrument systems as they produce significantly different concentration estimates. 5
• Do not assume apixaban dosing is the same as rivaroxaban dosing—apixaban requires twice-daily administration and has different dose-reduction criteria. 2
• Do not overlook concomitant verapamil or clarithromycin when the patient was on rivaroxaban, as these interactions differ between the two drugs. 1
• Do not restart anticoagulation without confirming the indication remains valid and reassessing thrombotic versus bleeding risk. 1