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2.3.6 Why are so many asthma drugs taken via inhaler?




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This article is from the Asthma FAQ, by Patricia Wrean and Marie Goldenberg mwg@radix.net with numerous contributions by others.

2.3.6 Why are so many asthma drugs taken via inhaler?


Medications taken orally almost always have a much higher
systemic concentration (concentration in your entire body)
than inhaled medications. So if the side effects are due
to systemic concentrations, then an inhaled drug is less
likely to have these side effects, or may have them much
less severely.

The idea behind an inhaler is that the full dose is delivered to
the lungs, where it is immediately absorbed by the lung tissue,
and starts to take effect locally. Excess drug may be absorbed
by the bloodstream and delivered to the rest of your body, but
this amount tends to be minimal. So your lungs receive an
immediate, high concentration of the drug, and the rest of your
body receives very little.

If you take the drug orally in tablet or capsule form, then you
need a much higher dose. The reason is that for the same amount
of drug to reach the lungs through the bloodstream, you need the
same concentration of drug in the rest of your body. For example,
most people take one or two puffs of albuterol (Ventolin or
Proventil) every four to six hours, and each puff is 90 micrograms
of albuterol. The usual dosage of Ventolin in tablets is 2-4
milligrams three or four times a day, which is something like 200
times the amount inhaled.

However, one advantage that tablets have is that the medication
may be available in a time-release format. So for a short-acting
medication like albuterol, the inhaled version might need to be
taken every four to six hours, while a extended-release tablet
such as Volmax would need to be taken only every twelve hours.

 

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