Fludrocortisone Phenytoin

In two patients with adrenal insufficiency, phenytoin increased fludrocortisone dosage requirements (4). 

Keilholz U, Guthrie GP Jr. Adverse effect of phenytoin on mineralocorticoid replacement with fludrocortisone in adrenal insufficiency. Am J Med Sci 1986 291(4) 280-3. 

The therapeutic effects of dexamethasone, methylprednisolone, prednisolone, prednisone (and probably other glucocorticoids) and fludrocortisone can be markedly reduced by phenytoin. One study su ested that dexamethasone may modestly increase serum phenytoin levels, but another study and two case reports of patients with brain metastases suggest that an important decrease can occur. The results of the dexamethasone adrenal suppression test may prove to be unreliable in those taking phenytoin. 

The fludrocortisone dosages of two patients required 4-fold and 10- to 20-fold increases, respectively, in the presence of phenytoin. ... 

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See also in sourсe #XX -- [ ]

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