Difference Between Cardizem CD and Tiazac
Both Cardizem CD and Tiazac are once-daily extended-release formulations of diltiazem, but they have significantly different pharmacokinetic profiles: Tiazac delivers higher daytime plasma concentrations (5-12 hours post-dose) while Cardizem CD provides more consistent 24-hour levels with less fluctuation between peak and trough. 1, 2
Key Pharmacokinetic Differences
Plasma Concentration Profiles
Tiazac produces 46% higher peak plasma concentrations (Cmax) after single doses compared to Cardizem CD, though the area under the curve (AUC) is only 19% higher 2
At steady-state, Tiazac delivers significantly higher diltiazem plasma levels between 5-12 hours post-dose compared to Cardizem CD, which may be clinically important for counteracting higher daytime blood pressures due to circadian variations 1
Cardizem CD maintains more stable 24-hour plasma levels with 21% higher minimum concentrations and 28% higher trough concentrations compared to Tiazac at steady-state 2
Tiazac exhibits 1.5-times greater fluctuation between maximum and minimum plasma concentrations compared to Cardizem CD, indicating less consistent drug delivery throughout the dosing interval 2
Bioavailability Considerations
The total steady-state AUC over 24 hours is similar between both formulations, but the timing and magnitude of drug delivery differs substantially 2
Both formulations produce similar pharmacokinetic profiles for the active metabolites desacetyldiltiazem and N-desmethyldiltiazem, following the pattern of the parent drug 2
Clinical Implications
Dosing Equivalence
Both formulations are dosed identically at 120-360 mg once daily for hypertension and angina, with typical starting doses of 120-180 mg daily 3
The American Heart Association recommends dosing ranges of 180-420 mg for both Cardizem CD and Tiazac for hypertension and angina 3
Therapeutic Considerations
Tiazac's higher daytime plasma concentrations may theoretically provide better coverage during the physiologic morning blood pressure surge, when cardiovascular events are most common 1
Cardizem CD's more consistent 24-hour levels may be preferable for patients requiring stable rate control or those sensitive to fluctuations in drug levels 2
Both formulations demonstrate nonlinear pharmacokinetics with dose escalation, with apparent oral clearance decreasing 35-51% over a 3-4 fold dose range 4
Practical Prescribing Guidance
When to Choose Each Formulation
Consider Tiazac when targeting daytime blood pressure control or angina symptoms that predominantly occur during waking hours, given its higher plasma levels between 5-12 hours post-morning dosing 1
Consider Cardizem CD when consistent 24-hour rate control is the primary goal (e.g., atrial fibrillation rate control), or when minimizing peak-to-trough fluctuation is important 2
Common Pitfalls
Do not assume therapeutic equivalence when switching between formulations - patients may experience different efficacy or tolerability despite identical dosing 1, 2
Monitor blood pressure and heart rate when switching formulations, as the different pharmacokinetic profiles may necessitate dose adjustment 3
Both formulations share identical contraindications: second/third-degree AV block without pacemaker, decompensated systolic heart failure, severe LV dysfunction, cardiogenic shock, and Wolff-Parkinson-White syndrome with atrial fibrillation/flutter 3, 5
Monitoring Requirements
Monitor blood pressure and heart rate at each visit during titration for both formulations 3
Assess for signs of heart failure in at-risk patients, particularly hypotension, bradycardia, peripheral edema, and worsening dyspnea 3
Perform ECG monitoring in patients with conduction system disease and liver function tests if clinically indicated 3