Converting systemic corticosteroids

Let’s start with a patient case.  A patient is being treated with methylprednisolone 20 mg IV q6 hours for some inflammatory process and is clinically improving.  She can now tolerate oral medication and we would like to simplify her dosing regimen to transition to outpatient care. How can we manage her methylprednisolone dosing?

One issue that comes up frequently on the internal medicine service is the potency of different corticosteroids relative to each other and the correct way to convert the doses. Below is the chart that shows the equivalent dose of the various agents we commonly use.

• It’s noteworthy that “equivalent”, in this case, is referring to glucocorticoid potencies. This glucocorticoid potency generally parallels the anti-inflammatory potency of the medication. The glucocorticoid potency is not necessarily related to the mineralocorticoid potency which varies among these agents. The mineralocorticoid effects of these agents are generally mild and may not be adequate if you were attempting to give an entire replacement dose in someone with adrenal insufficiency (except for fludrocortisone).

Relative potencies and equivalent doses of corticosteroids
Agent	Anti-inflammatory potency	Duration	Equivalent dose (mg)
Cortisol (hydrocortisone)	1	Short	20
Fludrocortisone	10	Intermediate	*
Prednisone	4	Intermediate	5
Prednisolone	4	Intermediate	5
Methylprednisolone	5	Intermediate	4
Dexamethasone	25	Long	0.75

*Not used for glucocorticoid effects

Back to the patient case:

• 20 mg methylprednisolone IV q6 hours = 80 mg methylprednisolone IV per day
• IV is equal to po (as in 100% bioavailability)
• Switch to prednisone because methylprednisolone is only available as 4 mg, 8 mg, 16 mg, and 32 mg tablets. The 16 mg and 32 mg tablets are not commonly prescribed so the patient’s pharmacy might have to order them. So by staying with methylprednisolone the patient could either take ten 8 mg tablets per day or might have to wait for the pharmacy to order the 16 mg tablets and then still take five a day.
• Using the chart, 80 mg methylprednisolone (4:5 ratio with prednisone) = 100 mg prednisone per day

• Correct conversion would be:

o   Prednisone 100 mg po qday or 50 mg po bid (since prednisone is available as 50 mg tablets but not 100 mg tablets)

Take home points:

• Our most commonly used medications – methylprednisolone, prednisone, and hydrocortisone have the potency of 4mg, 5mg, and 20mg, respectively (easy to remember that 4x5=20)
• Oral absorption of hydrocortisone, methylprednisolone, prednisone, and dexamethasone is nearly 100% so convert IV to po on a 1:1 ratio.
• Note the duration of action above – dexamethasone has a long half-life and doesn’t need to be dosed more than once a day
• Though the dexamethasone mineralocorticoid potency is often listed as zero (and some charts will list methylprednisolone also as zero) fluid retention may occur with these agents when used in clinical settings
• See more about using steroids for COPD exacerbations which was updated here or for treating acute gout which was updated here.

References:

Schimmer BP, Funder JW. Chapter 42. ACTH, Adrenal Steroids, and Pharmacology of the Adrenal Cortex. In: Brunton LL, Chabner BA, Knollmann BC, eds. Goodman & Gilman's The Pharmacological Basis of Therapeutics. 12nd ed. New York: McGraw-Hill; 2011.

Dexamethasone. Micromedex. Available at: www.micromedexsolutions.com. Accessed October, 2013.

photo by denn