A very young patient is treated with an antibiotic at 2 mg every 4 hours, but the kid does not like the taste and rejects taking his drug, causing a "compliance" problem and a flare-up of his infection. His doctor decides to make use on a rectal preparation of the same drug and thus prescribes the same dose for this formulation and frequency of administration.
Do you see a problem with this or would you have done the same or what information would you require before proceeding in any way?
Please explain via a comment below!
The same dosage delivered as a rectal preparation would probably not be as effective as an oral preparation. My educated guess is that the dosage would have to be higher for a rectal preparation. I would have to know how the drug is metabolized and where it is metabolized to know whether it would still be effective as a rectal preparation.
ReplyDeleteI actually think the opposite of Courtney. The rectum has 2 blood supplies: systemic and portal whereas the oral admin (to the GI tract) has one. The bioavailability of the oral admin = ~50% due to 1st pass loss and the bioavailability of the rectal admin = ~75% since the systemic blood supply there has no 1st pass loss and the portal has a 50% 1st pass loss. Since the body would then technically be absorbing more of the drug after the rectal admin, the doctor should have prescribed a lower dose or for the drug to be given less fequently.
ReplyDeleteNatalie is closer to the probable truth: Half of the drug when given rectally will be bypassing the "first pass" effect and thus be fully bioavavilable: The rectal blood supply is 50% systemic. So, if the oral bioavavilability were to eb 50%, one might achieve the same result by giving about 3/4 of the dose. In practice, these considerations would only be important if dealing with a drug that has little tolerance in terms of peak concentrations (and adverse effects). All depends on the question of what the bioavailability is - if it is very low you should be more concerned... OK - thanks for trying! That way you learn more...
ReplyDelete