13. Relative potencies and equivalent doses of corticosteroids __________________________________________________________________________________________________________________________ RELATIVE ANTI- RELATIVE APPROXIMATE INFLAMMATORY Na+- DURATION OF EQUIVALENT COMPOUND POTENCY RETAINING ACTION* DOSE † POTENCY (mg) __________________________________________________________________________________________________________________________ Cortisol (Hydrocortisone) 1 1 S 20 Tetrahydrocortisol 0 0 - - Prednisone (∆ 1 -Cortisone) 4 0.8 I 5 Prednisolone (∆ 1 -Cortisol) 4 0.8 I 5 6 -Methylprednisolone 5 0.5 I 4 Fludrocortisone (9 -Fluorocortisol) 10 125 S - 11-Desoxycortisol) 0 0 - - Cortisone (11-Dehydrocortisol) 0.8 0.8 S 25 Corticosterone 0.35 15 S - Triamcinolone (9 -Fluoro-16 -hydroxyprednisolone) 5 0 I 4 Paramethasone (6 -Fluoro-16 -methylprednisolone) 10 0 L 2 Betamethasone (9 -Fluro-16 -methylprednisolone) 25 0 L 0.75 Dexamethasone (9 -Fluoro-16 -methylprednisolone) 25 0 L 0.75 _________________________________________________________________________________________________________________________ *S=Short, or 8 to 12 hour biological half-life; I=intermediate, or 12 to 36 hour biological half-life; L=long, or 36 to 72 hour biological half-life. † These dose relationships apply only to oral or intravenous administration; relative potencies may differ greatly when injected intramuscularly or into joint spaces.
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20. Drug interactions of glucocorticoids Glucocorticoid dosage is decreased: Antibiotics (erythromycin, trioleandomycin), cyclosporin, isoniazid and ketoconazole reduce the metabolic clearance of glucocorticoids. Estrogens increase the levels of corticosteroid binding protein and thus reduce the free fraction; they also reduce the clearance. Cholestyramine decreases the intestinal absorption. Antiepileptic drugs(barbiturates, phenytoin, carbamazemine), rifampicin,, aminoglutethimide increase the metabolism by inducing hepatic microsomal enzymes. Antianxiety and antipsychotic drugs: Recurrent or poor control of CNS symptoms due to inherent glucocorticoid effects. Glucocorticoid dosage is increased: Glucocorticoid dosage needs adjustment: Anticholinesterases: May precipitate myasthenic crisis Anticoagulants: Effectiveness of anticoagulants decreases Antihypertensives: Their effectiveness decreases Oral hypoglycemics: Their effectiveness decreases Sympathomimetics: Their effectiveness increases Salicylates: Their clearance is increased
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