fludrocortisone
Meaning of fludrocortisone: Salt handling rather than swelling: this is the steroid given for what the kidney does with sodium, and it rarely works alone.
Definition of fludrocortisone
Fludrocortisone is a synthetic steroid that copies the action of aldosterone, the adrenal hormone directing the kidney to hold on to sodium and water while shedding potassium. It is given to replace that hormone when the adrenal glands cannot produce enough of it, and to raise blood pressure in certain causes of persistent lightheadedness on standing.
What does it do in the body?
It acts on the tubules of the kidney, the tiny channels where filtered fluid is processed before it becomes urine. There it switches on the receptor aldosterone normally uses, and sodium is pulled back into the bloodstream instead of being lost. Water follows the sodium, so the circulating volume rises and with it the blood pressure. Potassium and acid move the other way, into the urine. This is a different job from the one most steroid medicines are known for. The familiar members of the family calm inflammation and alter how the body handles sugar, fat and protein, while this one is used almost entirely for its grip on salt and fluid.
| Medicine | Dominant effect |
|---|---|
| Fludrocortisone | Salt and water retention |
| Hydrocortisone | Broad steroid replacement, with some salt effect |
| Prednisone or dexamethasone | Suppression of inflammation, with little or no salt effect |
Where is it used?
Chiefly in primary adrenal insufficiency, where the adrenal cortex itself has failed and both classes of hormone are missing, which is why this drug is normally paired with a second one supplying the rest. The salt losing form of congenital adrenal hyperplasia calls for it from infancy. It is not usually needed when the failure lies in the pituitary gland instead, because aldosterone production is governed by a signaling system in the kidney rather than by the pituitary, so it carries on despite that failure. A separate use is in some forms of lightheadedness on standing caused by faulty nerve control of the vessels, where expanding blood volume props up the pressure.
What is followed during treatment?
Exactly what the drug moves. Potassium can fall too low, sodium can rise, and holding on to fluid can swell the ankles, drive blood pressure up or overload someone whose heart already struggles. Blood pressure lying and standing, along with sodium and potassium levels, is the usual way the dose is judged, and a blood measure of the kidney signal that would normally call for aldosterone gives a further guide to whether replacement is adequate. Too little produces salt craving, dizziness and fatigue, and too much produces swelling and raised pressure, so the useful range sits between two recognizable pictures rather than at a single number.
Used in a sentence
Fludrocortisone was added to the patient's hydrocortisone regimen to manage persistent low blood pressure from adrenal insufficiency.
Good to know
Fludrocortisone provides mainly mineralocorticoid replacement rather than the glucocorticoid effect supplied by medications such as hydrocortisone, which is why the two are often prescribed together in adrenal insufficiency.