Switching from Diltiazem ER to Cartia XT
You can switch directly from diltiazem ER to Cartia XT on a milligram-for-milligram basis without any tapering or dose adjustment, as both are extended-release formulations of the same drug (diltiazem) designed for once-daily dosing. 1, 2
Understanding the Formulations
- Cartia XT is simply a brand name for diltiazem extended-release capsules, identical in mechanism and dosing to generic diltiazem ER formulations 1
- Both formulations are designed for controlled delivery over 24 hours with once-daily administration 1
- The therapeutic range for both formulations is 120-360 mg daily, with some studies supporting doses up to 540 mg daily for hypertension 1, 3
Direct Conversion Protocol
- Convert directly on a 1:1 milligram-for-milligram basis - if the patient is taking diltiazem ER 240 mg daily, switch to Cartia XT 240 mg daily 2
- If the exact dose is not available in the Cartia XT formulation, round up to the next higher available 120 mg increment 2
- No tapering period is required, as diltiazem does not cause withdrawal syndrome or rebound phenomena like beta-blockers 4
- Make the switch immediately - the patient can take their first dose of Cartia XT the day after their last dose of diltiazem ER 4, 2
Post-Conversion Monitoring
- Monitor blood pressure and heart rate within 1-2 weeks after switching to assess for return of symptoms or inadequate control 1, 4
- Watch for the indication-specific response: elevated blood pressure if treating hypertension, angina if treating coronary disease, or rapid heart rate if treating atrial fibrillation 1
- No ECG monitoring is required for the conversion itself unless the patient has underlying conduction system disease 1
Common Pitfalls to Avoid
- Do not attempt to split or crush either extended-release formulation - these cannot be divided and must be swallowed whole 4
- Do not confuse this conversion with switching between immediate-release and extended-release formulations, which may require dose adjustments 2
- Do not treat this like a beta-blocker switch - diltiazem requires no gradual tapering or overlap period 4
- Avoid unnecessary "bridging" strategies or dose reductions, as the bioavailability and pharmacokinetics are equivalent between extended-release diltiazem formulations 1, 2