What is the equivalence between intravenous (IV) and oral dexamethasone (a corticosteroid)?

From the Guidelines

Oral and intravenous (IV) dexamethasone are considered bioequivalent, with a 1:1 dose conversion ratio, as supported by the most recent and highest quality study 1. For most clinical situations, the same dose of oral and IV dexamethasone can be used interchangeably. Dexamethasone has excellent oral bioavailability, meaning that when taken orally, most of the drug reaches systemic circulation. The onset of action is slightly faster with IV administration compared to oral, which may be clinically relevant in emergency situations requiring immediate anti-inflammatory effects. However, for most non-urgent indications such as chronic inflammatory conditions, outpatient management of COPD exacerbations, or chemotherapy-induced nausea and vomiting prophylaxis, oral administration is equally effective and more convenient. Some key points to consider when using dexamethasone include:

• The dose of dexamethasone can be adjusted based on the specific clinical situation, such as the type of chemotherapy being used 1.
• The use of dexamethasone in combination with other antiemetic agents, such as 5-HT3 receptor antagonists and NK1 receptor antagonists, can provide improved efficacy in preventing chemotherapy-induced nausea and vomiting 1.
• The oral route is generally preferred when feasible due to lower costs, greater convenience, and reduced risk of complications associated with IV access. When switching from IV to oral dexamethasone, no dose adjustment is typically needed, as shown in studies such as 1. This high bioequivalence makes dexamethasone different from some other corticosteroids, which require dose adjustments when converting between routes. In terms of specific dosing, a study from 2017 1 recommends the following doses for dexamethasone in the prevention of chemotherapy-induced nausea and vomiting:
• 8 mg oral or IV on the day of chemotherapy
• 8 mg oral or IV on subsequent days, as needed. It's also important to note that the use of dexamethasone should be guided by the specific clinical situation and the patient's individual needs, as outlined in studies such as 1 and 1.

From the FDA Drug Label

When the intravenous route of administration is used, dosage usually should be the same as the oral dosage The equivalence between IV and oral dexamethasone is suggested to be 1:1, as the dosage for intravenous administration is usually the same as the oral dosage 2.

• This means that the dose of dexamethasone given intravenously is typically equivalent to the dose given orally.
• However, in certain situations, such as overwhelming, acute, life-threatening conditions, higher doses may be used, and the dosage may be in multiples of the oral dosages.

From the Research

Equivalence between IV and Oral Dexamethasone

• The study 3 compared the pharmacokinetics of oral vs. intravenous dexamethasone in patients hospitalized with community-acquired pneumonia, finding that the bioavailability of oral dexamethasone was 81% after correction for differences in dexamethasone dose.
• The AUC ratio of 6 mg oral and 4 mg intravenous dexamethasone was 1.22, indicating that oral dexamethasone can be an appropriate alternative for intravenous administration in these patients.
• Other studies, such as 4, 5, and 6, focused on the effects of corticosteroids, including dexamethasone, in various conditions like COVID-19 and migraine, but did not directly compare IV and oral dexamethasone equivalence.
• Study 7 examined the impact of dosing and duration of dexamethasone on serious corticosteroid-related adverse events, but did not address the equivalence between IV and oral administration.

Key Findings

• Oral dexamethasone has a bioavailability of 81% compared to intravenous administration in patients with community-acquired pneumonia 3.
• The AUC ratio of oral to intravenous dexamethasone was 1.22, suggesting that oral administration can be a suitable alternative 3.
• Other studies did not provide direct comparisons of IV and oral dexamethasone equivalence, but highlighted the importance of considering dosing and duration when using dexamethasone 7.