What is the half-life of dexamethasone?

Half-Life of Dexamethasone

The plasma elimination half-life of dexamethasone is approximately 36-72 hours in humans, which is substantially longer than other commonly used corticosteroids like hydrocortisone (90 minutes) or prednisolone (12-36 hours). 1

Pharmacokinetic Parameters

Plasma Half-Life

• The biological half-life of dexamethasone ranges from 36 to 72 hours, making it a long-acting corticosteroid suitable for once-daily or less frequent dosing 1, 2
• Clinical pharmacokinetic studies have demonstrated terminal half-life values ranging from 3.0 to 8.2 hours for the initial elimination phase, with the longer biological activity extending well beyond this due to tissue distribution and receptor binding 3
• The extended duration of action allows dexamethasone to be dosed less frequently than shorter-acting corticosteroids 4

Clinical Implications of Extended Half-Life

Due to its prolonged half-life, dexamethasone should not be administered at intervals less than one week when used in extended-release formulations or for certain indications 1

• A single 8 mg dose of dexamethasone provides glucocorticoid coverage equivalent to approximately 200 mg of hydrocortisone for up to 24 hours 1
• The long half-life enables single-dose or two-day treatment regimens to be as effective as five-day courses of shorter-acting corticosteroids like prednisone 4
• In acute asthma exacerbations, two days of dexamethasone (16 mg daily) demonstrated equivalent efficacy to five days of prednisone (50 mg daily), with 90% of patients returning to normal activities within three days 4

Comparative Pharmacology

Dexamethasone is approximately 25-30 times more potent than hydrocortisone on a milligram-per-milligram basis 1

• 10 mg hydrocortisone ≈ 2.0 mg prednisolone ≈ 0.1 mg dexamethasone 1
• All three agents have excellent oral bioavailability and are rapidly absorbed 1
• Unlike hydrocortisone, dexamethasone has no mineralocorticoid activity, making it inadequate as sole therapy for primary adrenal insufficiency 1

Important Clinical Caveats

• The plasma elimination half-life may be shorter in patients taking CYP3A4 inducers or those with hyperthyroidism 1
• The half-life may be prolonged in critically ill patients 1
• The volume of distribution may be increased in certain clinical scenarios, affecting overall drug exposure 1
• Obese patients may require higher doses due to altered pharmacokinetics, though definitive evidence is limited 1

Tissue-Specific Considerations

• In cerebrospinal fluid, when formulated as liposomal cytarabine with dexamethasone co-administration, the dexamethasone provides sustained anti-inflammatory effects over the dosing interval 1
• Dexamethasone 4 mg twice daily for 5 days is commonly used with certain chemotherapy regimens, suggesting a clinical duration of approximately 12 hours for specific antiemetic effects despite the longer plasma half-life 5