Can dexamethasone be given intramuscularly (IM) for the dexamethasone suppression test?

From the Guidelines

Dexamethasone should not be given intramuscularly (IM) for the dexamethasone suppression test, as the standard protocol involves oral administration to ensure reliable and standardized test results. The dexamethasone suppression test is a crucial diagnostic tool for evaluating Cushing's disease and other disorders of the hypothalamic-pituitary-adrenal axis, and its accuracy depends on precise timing and dosing. According to the consensus guideline update published in The Lancet Diabetes and Endocrinology in 2021 1, the test involves oral administration of dexamethasone, and measuring dexamethasone level along with cortisol the morning after ingestion improves test interpretability.

The standard protocol for the low-dose test involves administering 1 mg of dexamethasone orally at 11 PM, followed by measurement of serum cortisol at 8 AM the next morning. The high-dose test involves administering 8 mg of dexamethasone orally, either as a single dose or divided into multiple doses over 24 hours. Administering dexamethasone via the intramuscular route would alter the pharmacokinetics of the drug, potentially affecting the reliability and standardization of the test results.

Key considerations for the dexamethasone suppression test include:

• Starting with either urinary free cortisol (UFC) and/or late-night salivary cortisol (LNSC) if Cushing's disease is suspected
• Using any test to confirm Cushing's disease, with UFC average 2–3 collections, LNSC ≥2 on consecutive days, or dexamethasone suppression test (DST)
• Measuring dexamethasone level along with cortisol the morning after 1 mg dexamethasone ingestion to improve test interpretability, as recommended by the guideline update 1.

In clinical practice, if a patient cannot take oral medication, the test should be postponed or alternative diagnostic approaches should be considered rather than substituting with IM administration, to ensure accurate and reliable test results.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Dexamethasone sodium phosphate injection, 4 mg per mL– For intravenous, intramuscular, intra-articular, intralesional, and soft tissue injection.

The FDA drug label does not answer the question about using dexamethasone given IM for the dexamethasone suppression test.

From the Research

Dexamethasone Administration for Suppression Test

• The provided studies do not specifically address the administration of dexamethasone via intramuscular (IM) injection for the dexamethasone suppression test 2, 3, 4, 5, 6.
• All the mentioned studies involve oral administration of dexamethasone, with varying doses and timing, to assess its suppressive effect on cortisol levels.
• There is no direct evidence in the given studies to support or refute the use of IM dexamethasone for the suppression test.

Oral Dexamethasone Administration

• The studies consistently show that oral dexamethasone administration is effective in suppressing cortisol levels, which is the primary goal of the dexamethasone suppression test 2, 3, 4, 5, 6.
• Different doses and timing of oral dexamethasone administration are explored in the studies, including the comparison of low-dose and high-dose tests, as well as the timing of administration 2, 4, 5.
• The results indicate that oral dexamethasone is a reliable method for assessing the hypothalamic-pituitary-adrenal axis response, but there is no information on the efficacy or safety of IM administration.

Conclusion on Available Evidence

• Based on the provided studies, there is no research evidence to assist in answering whether dexamethasone can be given intramuscularly for the dexamethasone suppression test.
• The existing research focuses on oral administration, and its findings cannot be directly applied to IM administration without further investigation.