Fludrocortisone

Pharmacodynamics:

Fludrocortisone acts on the distal renal tubule to enhance the reabsorption of sodium and to increase the urinary excretion of both potassium and hydrogen ions. In small oral doses, the mineralocorticoid effects of fludrocortisone predominate; urinary excretion of potassium, marked sodium retention, and a rise in blood pressure as a result of the physiologic effects of these electrolytes levels. Larger doses result in predominance of glucocorticoid effects such as endogenous adrenal cortical secretion, thymic activity, and corticotropin excretion.

Contraindications and Precautions:

Fludrocortisone hypersensitivity, systemic fungal infections, and conditions not requiring intense mineralocorticoid activity are contraindications to use. It is a pregnancy category C drug, and it should be used cautiously during lactation because it is secreted into breast milk. Safety and efficacy are not established in children. It should also be used cautiously in patients with cardiovascular disease because it can elevate sodium and fluid levels.

Drug Interactions:

Fludrocortisone interacts with many of the same drugs as prednisone because of its high glucocorticoid activity.The drugs with which fludrocortisone interacts includes barbiturates, hydantoins, rifampin, anticholinesterases, and salicylates.

Pharmacotherapeutics:

Fludrocortisone is used for partial replacement therapy for primary and secondary adrenocortical insufficiency in Addison's disease and for treating self-losing adrenogenital syndrome.

Adverse Effects:

In small oral doses, marked sodium retention and increased urinary excretion of potassium, causing a rise in blood pressure. In larger doses, fludrocortisone inhibits endogenous adrenal cortical secretion and pituitary corticotropin excretion. It promotes the deposition of liver glycogen. It induces negative nitrogen balance when protein intake is inadequate. Adverse effects usually occur when the dosage is too high or when the drug is withdrawn too rapidly. Cardiovascular adverse effects may include edema, hypertension, chronic heart failure, and cardiomegaly. Dermatologic adverse effects may include bruising, diaphoresis, urticaria, or allergic skin rash. Hypokalemia alkalosis may occur. Additionally, fludrocortisone may cause adverse effects similar to those seen with the glucocorticoids.

Pharmacokinetics:

It is administered orally. It is absorbed readily from the GI tract, with peak concentration in 1.7 hours. It is metabolized in the liver and excreted by the kidney. Plasma half-life is approximately 3.5 hours, but biologic half-life ranges from 18-36 hours. Fludrocortisone crosses the placenta and is secreted in breast milk. The usual adult dosage is 0.1mg/day.