Difference in CYP P450 taxation of drugs

[Solipsis]

While the more general title is what my core question revolves around, this is actually about a more specific case:

Someone I know (no really :D ) is a frequent drinker and has recently tried prescribed alprazolam for incidental use. Other options - even temporary - haven't been tried in the sedative department. There is some reliance / dependence on sedatives you could say.
This person wants to undergo treatment lasting a week of an antibiotic that is contraindicated with alcohol and inducers or inhibitors of CYP P450, not exactly sure if multiple subtypes or which.

Certainly CYP P450 enzymes metabolize MANY compounds, but not all drugs preoccupy the enzymes or induce / inhibit the same way. I assume that this would depend on dose amounts of the drug combined with how strongly / long they bind? So how exactly does one proceed to find out which drugs would be relatively harmless to ward off serious anxiety, etc without being significantly contraindicated?

Would you agree that that would be the sedative with the optimal ratio of efficacy of action vs. whatever determines CYP P450 taxing?

(P.S. There is also a prescription of an SSRI, seems strange cause that would also be a contraindication? Is her medical professional already pushing it, allowing little room left for say alprazolam use during the treatment with a week's duration?)

I am interested in both insight into such a situation, not actual medical advice mind you... as well as the general theory for furure reference.. Thanks!!

 

[St3ve]

I'm guessing we're talking about the 3A4 subunit here as alprazolam is known to inhibit its action. 3A4 is the most important one as it alone is responsible for the metabolism of about 50% of the drugs out there. The other CYP P450 enzymes metabolise a much smaller number of drugs each. 2D6 is another important one to keep an eye as it is polymorphic. Ie. some people produce large amounts of it, others next to none and most people will find themselves somewhere in the middle. Depending on the drug 2D6 hypermetabolisers might need to medicate more often, whereas hypometabolizers will need lower doses and need to dose less often.

I'm not sure where you'd be able to find how much of the 3A4 subunit a given dose of alprazolam would inhibit, and I'm guessing there'd still be differences between different people. Usually warnings will be noted for drug interactions if there is a "significant" amount of CYP inhibition caused by a certain drug. My guess would be that in low doses alprazolam and the antibiotic shouldn't cause too many problems if combined, other than increasing eachother's duration... For HR reasons your friend should probably not attempt this .

The SSRI might not be contraindicated, fluoxetine for instance isn't an inhibitor or substrate for 3A4 and should be ok to combine with alprazolam and the antibiotic.

It'd probably be helpful if you could find out which antibiotic and SSRI (and doses) she's being prescribed. In any case, my advice would be to temporarily switch from alprazolam to another benzodiazepeine (like lorazepam) that doesn't act on CYP 3A4 for the duration of the antibiotic treatment...