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PK Question
Started by RX CARE
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That is revisable metabolism where the metabolite can be converted back to the parent. That is also common with corticosteroids. I really can't think of a case where Phase II occurs before phase I.
Wait wait wait... are we doing your drug action homework for you?
Thanks for the input guys. I was just thinking out loud because after a brief review of PK I found out that there were some exceptions to the norm of phase I to phase 2, and that there is a reverse, but there wasn't any specific examples stated. I was looking at isoniazid, but the second reaction is a hydrolysis, which I am not sure if it really qualifies as phase I. I'm just thinking if any drug directly gets conjugated, without phase 1, that would qualify.....but still not sure...so any acetylations, methylations and stuff.....I am also looking at acetylcysteine. Thanks a lot though 🙂
Phase I does not ALWAYS precede phase II. There are some cases where it does not. Off the top of my head, I can't remember atm. I believe oxazepam is one of them- it only undergoes conjugation removal (phase II). But the OP wants a phase II THEN PHASE I...
Been a while since biochem/biopharmaceutics, but it doesn't seem like there would be any reason for this...The only purpose of nonsynthetic phase 1 reactions is to make synthetic phase 2 reactions possible. If the molecule is already setup for a phase 2 reaction, then there is no need for a phase 1.
The only thing I can think of is that you are thinking of active metabolites- in which case the parent drug would metabolize as phase 1 --> phase 2 (creation of metabolite) --> phase 1 --> phase 2 (inactivation of metabolite). Theoretically i suppose if you just pull out the middle of it, it would appear that a medication that has an active metabolite would have a step that goes from phase 2 --> phase 1, but that is just ultimately setting up the excretion of the active metabolite.
Otherwise, once phase 2 reaction has occurred you are now looking at a different compound because by definition a phase 2 reaction is a synthetic reaction, so a subsequent non-synthetic phase 1 reaction would not be on the parent drug
The only thing I can think of is that you are thinking of active metabolites- in which case the parent drug would metabolize as phase 1 --> phase 2 (creation of metabolite) --> phase 1 --> phase 2 (inactivation of metabolite). Theoretically i suppose if you just pull out the middle of it, it would appear that a medication that has an active metabolite would have a step that goes from phase 2 --> phase 1, but that is just ultimately setting up the excretion of the active metabolite.
Otherwise, once phase 2 reaction has occurred you are now looking at a different compound because by definition a phase 2 reaction is a synthetic reaction, so a subsequent non-synthetic phase 1 reaction would not be on the parent drug
