Discussions that mention quinidine

Pain Management board

St. John's Wort causes a significant DECREASE in methadone serum levels.

St. John's Wort is a potent inducer of CYP3A4, methadone's primary metabolozing enzyme. Basically, if you induce CYP3A4, you will reduce methadone serum levels, if you INHIBIT CYP3A4, you increase methadone levels.

I've searched but have not found any data that St. John's Wort affects levels of opioids other than methadone.

You can figure out most interactions with a CYP450 table.


Oxycodone uses CYP450-2D6, so I don't think it would interact with St. John's Wort (which induces 3A4).

Oxycodone is metabolized in part by cytochrome P450 2D6 to oxymorphone which represents less than 15% of the total administered dose. This route of elimination may be blocked by a variety of drugs (e.g., certain cardiovascular drugs including amiodarone and quinidine as well as polycyclic anti-depressants). However, in a study involving 10 subjects using quinidine, a known inhibitor of cytochrome P450 2D6, the pharmacodynamic effects of oxycodone were unchanged.

Oxycodone is metabolized in part to oxymorphone via cytochrome P450 2D6. While this pathway may be blocked by a variety of drugs (e.g., certain cardiovascular drugs including amiodarone and quinidine as well as polycyclic antidepressants), such blockade has not yet been shown to be of clinical significance with this agent. Clinicians should be aware of this possible interaction, however.

from www.rxlist.com/cgi/generic3/oxycontin_cp.htm

White Grapefruit juice (and only the white, not the pink) inhibits CYP3A4 and does indeed increase methadone serum levels. White grapefruit juice is contraindicated with some medications (e.g. xanax, valium) due to increased potency, and sometimes you will see a warning label on these meds.

What's Wrong with Grapefruit Juice?
www.dr_weil.com/u/QA/QA236820/ [It won't let me spell D R W E I L; remove the _ from the address.]

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