Tuesday, February 10, 2009

How Much More Steroids am I Getting from My Inhaler? The Relative Doses of Steroids for Asthma

I have a hard convincing many patients to take their daily inhaled corticosteroid for asthma. The reasons: it's a headache to remember to take their medicine twice per day, they're concerned about the short-term and long-term side effects, the price of the inhalers is high and going up annually, it's hard to see if the inhalers have any benefit on a daily, let alone month to month basis. All valid objections in my opinion. Let's run some numbers and compare the amounts of steroids a person actually receives depending on the circumstances.

I treat an ordinary exacerbation of asthma with oral prednisone 20 mg bid (twice per day) for 7 days. The total amount taken is 20 mg x 2/day x 7 days = 280 mg in 7 days.

(My partners give a "prednisone taper", which is 20 mg 2x/day x 5 days, then day 6 take 20 mg am + 10 mg pm, then day 7 take 20 mg am only, then day 8 take 10 mg am only. The total dose is 260 mg, less than 10% difference and longer by one day. There is no proof in a single study that this is necessary in short-term courses.)

Suppose you take Advair 250/50 1 puff twice per day for 1 year. The total amount of steroid taken is 250 micrograms x 2/day x 365 days/year x 1/1,000 mg units = 182.5 mg in 1 year.

You can see that the entire dose of Advair 250 for 1 year (365 days) is LESS than the 7 days worth of prednisone 20 by a ratio of roughly 2:3!

Here's other ways of looking at this:
1) one inhaler of Advair has 250 mcg x 2/day x 30 days = 15 mg.
2) Advair 250 mcg 2x/day x 80 days = 40 mg = prednisone 20 mg 2x/day x 1 day.
3) Advair 250 mcg 2x/day x 560 days = 280 mg = 18.67 inhalers of Advair = prednisone 20 mg 2x/day x 7 days (a typical course of prednisone for an exacerbation)

Let's introduce one wrinkle. If you get hospitalized for 3 days, you would typically get treated with SoluMedrol (steroid) intravenously 80 mg 3x/day x 3 days, for a total of 720 mg. This is why people get better so quickly. They have gotten the equivalent of 4 YEARS worth of Advair in just 3 days. Then the oral taper of prednisone that always follows, so there's even more steroid taken!

One other wrinkle: oral bioavailability is the fraction of inhaled corticosteroid that is actually swallowed, makes it through the liver without being deactivated and is systemically active. This fraction varies from less than 1% to 40%.

All of the means that there is a huge advantage in terms of preventing asthma exacerbations and avoiding side effects from excess doses of steroids when the inhaled steroids are taken daily.

The pattern of this analysis holds up even for other inhaled corticosteroids. Let's take Symbicort 160 mcg. 160 mcg 2 puffs 2x/day x 365 days x 1/1000 mg = 233.6 mg in 1 year. Still less than the amount of prednisone in a 7 day burst above. Do your own math!

The Expert Panel Report Guidelines for Asthma recommend the amount of daily inhaled corticosteroid medicine be increased if even 2 oral corticosteroids are taken in 6 months. Why again? The amounts of oral corticosteroids taken when ill are so much more than the doses taken daily by inhalation.

I hope this helps parents, family members, caregivers, and patients understand why asthma specialists emphasize so heavily, or should, the importance of taking daily inhaled corticosteroids.

1 comment:

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