posted
So I know that some medications like Topamax (I think) will somehow affect the way the Pill works...does the same go for the patch? And why do they make a difference, anyway? And how bad are the side effects of the patch compared to the pill?
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posted
BtL quick 30 second answer while on the job: Topamax (as well as other drugs to treat epilepsia such as phenytonin, drugs for tuberculosos like rifampicin or those for fungal infections such as ketoconazole) is a substrate of an enzyme in the body called CYP3A4. CYP3A4 is always present in the body to some degree and participates in the conversion of over 50% of drugs that get metabolized (and subsequently excreted). Normally CYP3A4 is only present in small amounts but gets induced when one of its substrate enters the cell. So Topamax enters the cell, CYP3A4 increases, Topamax gets metabolized and excreted.
Now, synthetic steroid hormones like those used in oral contraception are also substrates of CYP3A4. Like Topamax they induce the production of CYP3A4 in the cell, which leads to the modification of the steroid and excretion. When both Topamax and synthetic steroids are present the amount of CYP3A4 increases dramatically. The reaction between CYP3A4 and oral contraceptives is very fast compared to CYP3A4 and Topamax so the contraceptives get metabolized first. Because there’s so much more CYP3A4 produced when both contraceptive steroids and Topamax are present compared to when there’s only contraceptive steroids present, the contraceptives get metabolized so quickly they stop working.
posted
Awesome answer, BtL! But does this also mean that taking BCPs might result in Topamax toxicity? I know antibiotics carry a warning that they can make BCPs less effective.
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posted
There's two mechanisms that interfere - some medications cause problems absorbing hormones in the digestive tract. These, I suppose, would not effect the patch so much.
The other mechanism is the one Bob described.
Short answer, maybe. Long answer, you have to read the labels and talk to your doctor.
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Good point, Dagonee. I do believe the digestion is the route by which antibiotics interfere with BCPs. Because they destroy all the flora in the gut. I'm not sure what happens nexts, but it causes yeast infections as well. Posts: 11017 | Registered: Apr 2003
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posted
Hey, pH, I just realized that I didn't completely answer your question. In this case, I can assure you that Topamax *does* inhibit the action of birth control pills by enzyme induction. You'd have the same problem with the patch. It isn't the rate of uptake that matters, it's the fact that Topamax and drugs like it decrease the bioavailability of progesterone and estrogen. You'd be better of with a valproate like Depakote or felbamate like Felbatol if you were looking into some form of chemical birth control. But, like Dag said, definitely talk to your doctor about all of this.
pooka, no, there wouldn't be an increase in Topamax toxicity. The hormone levels in birth control pills are minute compared to the levels of topiramate in Topamax (which is, I believe, the active ingredient). So while the increase of CYP3A4 caused by Topamax is detrimental to the hormones the loss of CYP3A4 to the hormones is insignificant to the rate of topiramate metabolism.
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posted
I'm not on Topamax; it was just the first thing that came to mind in terms of drugs that interfere with birth control.
The side effects thing I was wondering about because I've heard that the patch really does make a difference so far as those are concerned...but maybe that could be because it goes to the bloodstream and not through the stomach? Posts: 9057 | Registered: Nov 2000
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The patch would make a difference with drugs like Dag mentioned. Ones that inhibit the uptake of the hormones through the gut. But both modes of entry will be metabolized the same way (though the patch would probably introduce lower levels to the blood the the pill introduces to the stomach).
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