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

From the Guidelines

Dexamethasone has nearly 100% bioavailability when given orally, making oral and intravenous (IV) formulations essentially equivalent in terms of systemic exposure, and for most clinical situations, a 1:1 dose ratio can be used when converting between routes. This is supported by the high bioavailability of oral dexamethasone, which is well-absorbed from the gastrointestinal tract and undergoes minimal first-pass metabolism in the liver 1. The equivalence of oral and IV dexamethasone allows for convenient transition from IV to oral therapy as a patient's condition improves, facilitating earlier hospital discharge and reducing costs.

Some key points to consider when using dexamethasone include:

• The high bioavailability of oral dexamethasone makes it an effective alternative to IV administration in most cases
• A 1:1 dose ratio can be used when converting between oral and IV routes, meaning no dose adjustment is necessary when switching from IV to oral administration or vice versa
• Both oral and IV formulations have similar onset of action, though IV administration may have slightly faster initial effects
• In specific clinical scenarios, such as severe gastrointestinal disorders or critical illness, the IV route may be preferred initially

The most recent and highest quality study supporting this recommendation is from 2017, which provides guidance on antiemetic dosing for adults by chemotherapy risk category 1. This study, along with others, supports the use of dexamethasone as an effective antiemetic agent, with oral and IV formulations being equivalent in terms of systemic exposure.

In terms of specific dosing, the study recommends a dose of 8 mg oral or IV dexamethasone for low-emetic-risk agents, and 12 mg oral or IV dexamethasone when used with aprepitant or fosaprepitant 1. However, the key takeaway is that oral and IV dexamethasone are essentially equivalent, and a 1:1 dose ratio can be used when converting between routes.

Overall, the evidence supports the use of oral and IV dexamethasone as equivalent formulations, with a 1:1 dose ratio, in most clinical situations, allowing for convenient transition between routes and facilitating earlier hospital discharge and reducing costs.

From the Research

Equivalence between IV and Oral Dexamethasone

• The equivalence between IV and oral dexamethasone is not directly addressed in the provided studies, but some studies compare the effects of IV and oral dexamethasone in different contexts 2.
• A study comparing oral and IV dexamethasone premedication in the prevention of docetaxel-induced allergic reactions found that both routes were effective in preventing hypersensitivity reactions, but IV dexamethasone was preferred due to improved patient compliance and reduced risk of hypersensitivity reactions 2.
• Another study examined the impact of dosing and duration of dexamethasone on serious corticosteroid-related adverse events, but it did not specifically compare IV and oral routes 3.
• A study on the differential cytotoxicity of corticosteroids on human mesenchymal stem cells found that dexamethasone was the most gentle on MSCs compared to other corticosteroids, but it did not compare IV and oral routes 4.
• The study on the randomized trial of IV dexamethasone for acute migraine in the emergency department did not compare IV and oral routes, but it found that IV dexamethasone was not effective in achieving a headache-free state in the ED and maintaining it for 24 hours 5.
• The review on the role of dexamethasone and methylprednisolone corticosteroids in coronavirus disease 2019 hospitalized patients did not compare IV and oral routes, but it discussed the use of corticosteroids in COVID-19 patients 6.

Key Findings

• IV dexamethasone may be preferred over oral dexamethasone due to improved patient compliance and reduced risk of hypersensitivity reactions 2.
• Dexamethasone is the most gentle on MSCs compared to other corticosteroids 4.
• The effectiveness of IV dexamethasone in achieving a headache-free state in the ED and maintaining it for 24 hours is limited 5.
• Corticosteroids, including dexamethasone, have anti-inflammatory, analgesic, and anti-allergic characteristics, and are recommended for treating symptoms of multiple ailments 6.