快樂小藥師 Im pharmacist nichts glücklich

Nancy H. Hope, PharmD

Question:

Can an amiodarone drip be converted to twice-daily IV bolus dosing if the patient is unable to take anything by mouth or nasogastric tube?

Amiodarone injection is approved for patients with recurrent ventricular fibrillation and hemodynamically unstable ventricular tachycardia. Amiodarone is used off-label for atrial fibrillation.^[1,2] Initial amiodarone loading is often achieved by intravenous (IV) bolus dosing followed by IV infusion. Conversion to oral therapy is recommended for maintenance; however, oral therapy is dependent on the patient's ability to take medication either by mouth or by enteral feeding tube. But what if the patient is unable to take medications enterally? This requires a look into the pharmacokinetics of IV vs oral amiodarone therapy.

IV amiodarone is rapidly distributed in the body and quickly reaches peak serum concentrations. Secondary to these pharmacokinetic properties, discontinuation of infusion causes the serum concentration to decrease to approximately 10% of the peak serum concentration within 30-45 minutes.^[1] Oral amiodarone, however, has a much slower onset of action (2-3 days) and a half-life of anywhere from 60 to 120 days.^[1,2]

Use of IV amiodarone has not been studied in patients for more than 3-6 weeks and therefore only carries the indication for initial loading of the drug.^[1,2] IV amiodarone bolus dosing has been studied in patients who are started on infusion but require additional dosing for rhythm control,^[1] patients receiving perioperative coronary artery bypass management,^[3] patients requiring immediate slowing of atrial fibrillation with a high ventricular rate,^[4] and patients in ventricular arrhythmia requiring advanced cardiac life support.^[5]

In conclusion, on the basis of the pharmacokinetic properties of IV amiodarone and all recommendations in clinical studies and guidelines, it is not appropriate to substitute oral maintenance therapy with IV bolus dosing after discontinuation of infusion. Of note, if oral therapy is interrupted it is appropriate to use a short-term IV infusion without the loading dose to maintain sinus rhythm.^[2]

References

1. Amiodarone hydrochloride injection [package insert]. Bedford, Ohio: Bedford Laboratories; 2005.
2. Goldschlager N, Epstein AE, Naccarelli G, Olshansky B, Singh B, for the Practice Guidelines Subcommittee, North American Society of Pacing and Electrophysiology. Practical guidelines for clinicians who treat patients with amiodarone. Arch Intern Med. 2000;160:1741-1748. Abstract
3. Vassallo P, Trohman RG. Prescribing amiodarone: an evidence-based review of clinical indications. JAMA. 2007;298:1312-1322. Abstract
4. Hofmann R, Steinwender C, Kammler J, Kypta A, Leisch F. Effects of a high dose intravenous bolus amiodarone in patients with atrial fibrillation and a rapid ventricular rate. Int J Cardiol. 2006;110:27-32. Abstract
5. Siddoway LA. Amiodarone: guidelines for use and monitoring. Am Fam Physician. 2003;68:2189-2196. Abstract