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

From the Guidelines

Intravenous (IV) and oral dexamethasone are bioequivalent, allowing for seamless transition between routes of administration without dose adjustment, as supported by the high oral bioavailability of dexamethasone 1. When considering the equivalence between IV and oral dexamethasone, it's crucial to understand that the oral form is nearly 100% bioavailable, meaning a 4 mg IV dose is equivalent to a 4 mg oral dose. The onset of action for oral dexamethasone is slightly delayed compared to IV, but the duration of action remains the same due to dexamethasone's long half-life of 36-72 hours. This high bioavailability occurs because dexamethasone is lipophilic, readily crosses cell membranes, and bypasses significant first-pass metabolism in the liver. Some key points to consider include:

• The bioequivalence of IV and oral dexamethasone allows for flexibility in administration routes, which can be beneficial in clinical practice, especially when patients are transitioning from IV to oral therapy 1.
• The high oral bioavailability of dexamethasone means that patients can be switched from IV to oral therapy without needing a dose adjustment, making it more convenient and less invasive 1.
• Dexamethasone's long half-life contributes to its effectiveness in preventing nausea and vomiting, as it provides a prolonged duration of action, which is beneficial for patients undergoing chemotherapy 1.
• The only exceptions where IV administration might be preferred over oral are in patients with malabsorption disorders, severe gastrointestinal disease, or those who cannot take oral medications, as these conditions may affect the absorption of oral dexamethasone 1. Overall, the equivalence between IV and oral dexamethasone, supported by its high oral bioavailability and long half-life, makes it a versatile and effective option for preventing nausea and vomiting in patients undergoing chemotherapy.

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.
• The results showed that the bioavailability of oral dexamethasone was 81% (95% CI 54,121) after correction for differences in dexamethasone dose, making oral dexamethasone an appropriate alternative for intravenous administration in these patients.
• The AUC ratio of 6 mg oral and 4 mg intravenous dexamethasone was 1.22 (95% confidence interval (CI) 0.81,1.82), indicating similar systemic exposure between the two routes of administration.

Comparison of Dexamethasone Formulations

• The study 4 compared the cytotoxicity of different corticosteroid preparations, including dexamethasone, on human mesenchymal stem cells.
• The results showed that dexamethasone was the most gentle on MSCs, with a curvilinear dose-response pattern, while betamethasone was the most toxic.
• The study suggests that choosing dexamethasone may result in less harmful effects when compared with other injectable steroids.

Clinical Use of Dexamethasone

• The study 5 evaluated the efficacy of IV dexamethasone as adjuvant therapy for patients presenting to an emergency department with acute migraine.
• The results showed that a moderate dose of IV dexamethasone should not be administered routinely for the emergency department-based treatment of acute migraine, although it might be useful for patients with migraine lasting longer than 72 hours.
• The study 6 reviewed the role of dexamethasone and methylprednisolone in coronavirus disease 2019 (COVID-19) hospitalized patients, highlighting their anti-inflammatory, analgesic, and anti-allergic characteristics.
• The study 7 evaluated the association between the dose and duration of dexamethasone and serious adverse events in cancer patients, showing that greater dexamethasone exposure was associated with more serious adverse events.