The duration of suppression of the pituitaryadrenal axis after single injections of three commonly used derivatives of 9-α-fluoroprednisolone was studied. Triamcinolone acetonide (TCA) in 40 mg doses decreased corticosteroid levels for as long as four weeks after injection, whereas 50 mg of triamcinolone diacetate (TCDA) and 9 mg of betamethasone acetate-phosphate mixture (BAP) had adrenal suppressive effects persisting for only one week. This correlates, to a great degree, with the duration of the therapeutic effect observed with each of these preparations. The data indicate that in selecting a depot corticosteroid preparation for intramuscular administration, it is essential to keep in mind the relatively prolonged adrenal suppression that occurs with TCA as compared to TCDA and BAP.
Mikhail GR, Livingood CS, Mellinger RC, Paige TN, Salyer HL. Effect of Long-Acting Parenteral Corticosteroids on Adrenal Function. Arch Dermatol. 1969;100(3):263-268. doi:10.1001/archderm.1969.01610270005001