E-drug: Antiobiotic prescribing
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Hi:
I have just finished conducting a compliance study on the use of erythromycin
in the cure of a common STD (C. trachomatis). The protocol called for 500
mg of
erythromycin to be self administered by the patient QID for 10 days. I have
made the assumption that prescribing erythromycin QID implies adequate
therapeutic coverage for 6 hours per dose. By therapeutic coverage I mean
achieving serum levels of the antibiotic such that the antibiotic will remain
effective over the course of the 6 hour interval between doses.
My results indicate that patients had an average compliance rate of less than
60% (range 29 to 91%) but we observed a 100% cure rate. My concern is that
Physicians are over-prescribing given these results.
I am wondering whether erythromycin is a "very forgiving" drug when is comes
to maintaining therapeutic blood levels vs the timing of the dose taken, or
whether my assumption of adequate serum levels of 6 hours per dose is
incorrect.
My questions are therefore as follows:
1. Where does the standard 10 day course of therapy come from (What is it
based on)?
2. Is erythromycin an especially 'forgiving' antibiotic in that therapeutic
coverage is longer than 6 hours?
3. Are we prescribing too much?
Any comments will be greatly appreciated
Jay
Jay M. Fleisher Ph.D.
Department of Preventive Medicine
SUNY Health Science Center at Brooklyn
Box 43
450 Clarkson Avenue
Brooklyn, New York 11203
TELEPHONE 718-270-1075 FAX 718-270-2533
WEB http://www.netcom.com/~fleishe1
Email fleishe1@ix.netcom.com
"If one lives alone in a mountainous wilderness,
the only thing close to fame one could create,
would be a simple echo"
[Note from moderator: The dosing interval is generally set based on the
serum halflife of the drug and the intention to keep that above a certain
level (within the therapeutic window) at any time. For antibiotics I think
the issue is not as simple as using serum levels alone. The therapeutic
result is also dependent on other factors such as achieving a high peak
and/or keep the serum concentration above the MIC (minimum inhibitory
concentration) all the time. There is some controversy as to whether plasma
levels should be above MIC all the time or whether it is the peak that is
important. That's why e.g. for Penicillin V some will recommend 2 times a
day, others use 4 times a day. Further, some will recommend giving iv
antibiotics by continuous infusion, others by bolus. Some antibiotics also
have so called postantibiotic effect which means that they inhibi microbial
growth for a period after plasmalevels have dropped below MIC. Also, the
penetration to the focus of the infection is important, and lastly the
sensitivity towards the microbe in question.
Very often we are prescribing too much, cf. historical development in
treatment of UVI. Here in Norway we even recommend 14 days for C
trachomatis, I have no idea where it comes from. Kirsten Myhr]
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