About

The Dofetilide Initiation Dose Calculator helps determine the appropriate starting dose of dofetilide for patients with atrial fibrillation or atrial flutter. Dofetilide is a class III antiarrhythmic agent that requires careful dosing based on renal function and the baseline QTc interval to minimize the risk of proarrhythmia, specifically Torsades de Pointes (TdP).

Outputs

The calculator provides one of two primary outputs:

• Recommended Starting Dose: A specific dose in micrograms (mcg) to be administered twice daily (e.g., 500 mcg, 250 mcg, or 125 mcg BID), based on the patient’s calculated creatinine clearance (CrCl).
• Contraindication Alert: A clear warning if dofetilide is contraindicated due to either poor renal function (CrCl < 20 mL/min) or a baseline QTc interval that exceeds the safety thresholds (>440 msec, or >500 msec in patients with a ventricular conduction abnormality).

How to use

To use the calculator, provide the following patient data:

• Age, Weight, and Sex: Used to calculate creatinine clearance via the Cockcroft-Gault equation.
• Serum Creatinine (SCr): A key variable for assessing renal function.
• Baseline QTc Interval: The QTc from a 12-lead ECG prior to the first dose. This is critical for assessing the risk of TdP.
• Ventricular Conduction Abnormality (VCA): Check this box if the patient has a condition like a bundle branch block (BBB), as this changes the QTc cutoff for contraindication.

Dosing Overview

The initial dosing of dofetilide is stratified by renal function, which is estimated using the Cockcroft-Gault formula to calculate creatinine clearance (CrCl).

Initial Dosing Tiers

• CrCl > 60 mL/min: 500 mcg twice daily
• CrCl 40-60 mL/min: 250 mcg twice daily
• CrCl 20-39 mL/min: 125 mcg twice daily

Contraindications

• Renal Impairment: Dofetilide is contraindicated if CrCl is less than 20 mL/min.
• QTc Interval: Dofetilide is contraindicated if the baseline QTc is >440 msec (or >500 msec for patients with ventricular conduction abnormalities).

Switching

When switching a patient to dofetilide from other antiarrhythmic drugs, an adequate washout period is necessary to prevent additive cardiac effects, especially QTc prolongation. If switching from amiodarone, a prolonged washout is required, and QTc must be closely monitored due to amiodarone’s long half-life. Consult official prescribing information for specific guidance on washout periods.

Missed Dose

If a dose of dofetilide is missed, the patient should take the next scheduled dose at its regular time. The patient should not double the dose to make up for the missed one, as this can increase the risk of adverse effects.

Safety Alerts

Continuous ECG monitoring is required for a minimum of 3 days or until 12 hours after cardioversion to sinus rhythm, whichever is longer. Dose adjustments are based on follow-up QTc measurements taken 2–3 hours after each dose.

FAQ

Why is creatinine clearance (CrCl) essential for dofetilide dosing?

Dofetilide is primarily eliminated by the kidneys. Impaired renal function leads to drug accumulation, which significantly increases plasma concentrations and the risk of Torsades de Pointes. The dose must be adjusted based on CrCl to ensure safety.

Why does a ventricular conduction abnormality (VCA) change the QTc cutoff?

Conditions like a bundle branch block (BBB) widen the QRS complex, which can artificially lengthen the calculated QTc interval. A higher cutoff of 500 msec is used in these patients to account for this baseline QRS widening.

Should I use calculated CrCl or estimated GFR (eGFR)?

The original clinical trials and the FDA-approved prescribing information for dofetilide specify using the Cockcroft-Gault equation to calculate CrCl for dosing. Therefore, CrCl, not eGFR, should be used.

What happens if the QTc increases significantly after starting dofetilide?

If at any time after the first dose the QTc rises to >500 msec (or >550 msec with VCA), the dose must be reduced. If the QTc remains prolonged after dose reduction, dofetilide should be discontinued.

Can this calculator be used for pediatric patients?

No. The safety and effectiveness of dofetilide have not been established in patients under 18 years of age.

How should weight be entered for obese patients?

The Cockcroft-Gault formula may overestimate CrCl in obese patients when using actual body weight. Clinical judgment is advised, and some institutions use ideal or adjusted body weight in this scenario. Always follow institutional policy.

Does this tool account for drug interactions?

No. This tool only calculates the initial dose. Numerous drugs are contraindicated with dofetilide as they can inhibit its metabolism (e.g., ketoconazole, verapamil, cimetidine) or have additive QTc-prolonging effects. Always perform a thorough medication review.

Why is the starting dose for CrCl 40-60 mL/min half of the top dose?

This dose reduction is based on pharmacokinetic studies showing that moderate renal impairment leads to a significant increase in drug exposure. Halving the dose helps maintain a similar safety profile to patients with normal renal function.

References

• Dofetilide (Tikosyn) Prescribing Information. U.S. Food and Drug Administration.
• Pfizer Medical Information – Tikosyn (dofetilide). Pfizer Inc.
• Roden DM. Dofetilide. In: LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. National Institute of Diabetes and Digestive and Kidney Diseases; 2020.
• January CT, et al. 2019 AHA/ACC/HRS Focused Update of the 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation. Circulation. 2019;140(2):e125-e151.