Posted by medlib on April 12, 2002, at 10:53:38
In reply to slow metabolism and med sensitivity, posted by beardedlady on April 11, 2002, at 14:17:14
Hi beardy--
I think that your post may be referring to 3 (or more) different mechanisms of action. With the caveats that I'm no Cam, and my explications often come packaged with liberal amounts of shoe leather:
--A true allergic reaction (not a side effect) is a histamine-mediated response to a specific substance that has entered the blood stream. If that allergen is a drug, the allergic response is not affected by the presence of other drugs (unless they are antihistamines). This result also is independent of liver metabolism and of the drug's half-life. If you've encountered a drug (or its very close cousin) at least twice, you are not likely to become allergic to it with repeated or prolonged exposures. However, a drug which causes a mild allergic reaction at first *can* cause more severe reactions in subsequent contacts.
MDs will swear that it's not possible to have an allergic reaction to a drug on first exposure (because the body has not had an opportunity to develop allergen-specific antigens). But, I've had anaphylactic (potentially life-threatening allergic) reactions to 2 new antibiotics, neither of which I'd taken before; neither is closely related to an Ab I'm already allergic to, either. That's one reason (among many) that I consider *all* medical explanations hypotheses, not facts.
--How long effects of a drug last is influenced by a number of factors, the greatest of which is the nature of the drug itself. Even within the same drug category, variations can be substantial. (The half-life of Effexor is measured in hours; Prozac's can be measured in days.) Thus, your lengthy pupillary dilation may be related more to the type of drug used than to your individual rate of metabolism. Other important factors include the route of delivery (IV, oral, under or through the skin, etc.) and the body system affected. To illustrate, the atropine Mitch mentioned is not as useful for adult eye exams as some other agents because of its slow onset and long duration. But, the same drug administered by IV (during CPR, for example) increases a slow heart rate (bradycardia) in seconds.
--Most drugs are metabolized (broken down) in the liver by enzymes (called cytochromes) which collectively are designated P450. One of these enzymes (3C4) metabolizes several ADs, including Serzone and Prozac. When 2 drugs are taken which are metabolized by the same enzyme, they compete with one another for its use. The losing competitor must stick around in the body longer waiting for its turn; so, less of it is needed to achieve the same therapeutic effect. (I'm not sure what factors determine which drug wins in such competitions.) And, yes, several antibiotics utilize the 3C4 enzyme (like the myacin family). This slowed metabolism in the presence of pharmacological competitors plays a much smaller role in overall drug variability than the factors mentioned above, though.
Btw, posting to a teacher of writing is intimidating, at least to me.
Not a poet, either---medlib
poster:medlib
thread:102772
URL: http://www.dr-bob.org/babble/20020408/msgs/102859.html