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Switching from generic to brand name


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Probably wondering why I'm doing this. Basically I applied for a patient assistance program and got it. They are sending Effexor XR to my Pdoc's office and I'm lucky to get this, very lucky indeed. They offered me Pristiq but I didn't want to change as I feel a bit stable

I was wondering if I should expect the two to be vastly different or if the change wont be noticed

Going from 300mg Venlafaxine XR to 300mg Effexor XR. I'm always a bit a shaky when it comes to med changes, i know some feel the same?

Anyhow has anyone tried both or switched between them?

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Probably not.. but it's possible. Generic only has to be 80% comparable, so it can act differently - even from one manufacturer to another. The majority of the time people are ok with the change, but sometimes a difference can be felt. You'll only know which will happen when you start taking it.

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Generic only has to be 80% comparable

Not exactly. The FDA's default definition of bioequivalence is this:

The 1992 guidancefurther recommended that statistical analysis for pharmacokinetic measures, such as area under the curve (AUC) and peak concentration (Cmax), be based on the two one-sided tests procedure to determine whether the average values for the pharmacokinetic measures determined after administration of the T and R products were comparable. This approach is termed average bioequivalence and involves the calculation of a 90% confidence interval for the ratio of the averages (population geometric means) of the measures for the T and R products. To establish BE, the calculated confidence interval should fall within a BE limit, usually 80-125% for the ratio of the product averages.

So, they collect the PK data for both the T (test, generic) and R (reference, brand) drugs, determine the geometric mean of each, and find the ratio of the test mean to the reference mean. Then they calculate a 90% confidence interval (the interval in which 90% of the observed data falls, i.e. if you repeated the experiment on any number of random people you would expect to get a value in that interval 90% of the time, with a 5% chance of getting a value below the interval's lower limit and a 5% chance of getting a value above the upper limit). If that confidence interval does not fall entirely between 80% and 125% of the ratio of the averages, the test product cannot be marketed.

This is a much narrower range then one would expect. Most of the time, the 90% CI lies between 90% and 115% of the ratio, if not less. Any product with a really broad confidence interval is not likely to pass, since this interval would probably lie at least partly outside the boundary range. The 80-125% range is only a default, and the FDA may have reason to impose different boundaries depending on the drug.

EDIT: I note that the exact same standard is used in drug interaction studies conducted by the brand company. The test drug just happens to be a combination of drugs, and a 90% CI outside of the boundaries indicates an interaction.

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Generic only has to be 80% comparable

Not exactly. The FDA's default definition of bioequivalence is this:

The 1992 guidancefurther recommended that statistical analysis for pharmacokinetic measures, such as area under the curve (AUC) and peak concentration (Cmax), be based on the two one-sided tests procedure to determine whether the average values for the pharmacokinetic measures determined after administration of the T and R products were comparable. This approach is termed average bioequivalence and involves the calculation of a 90% confidence interval for the ratio of the averages (population geometric means) of the measures for the T and R products. To establish BE, the calculated confidence interval should fall within a BE limit, usually 80-125% for the ratio of the product averages.

So, they collect the PK data for both the T (test, generic) and R (reference, brand) drugs, determine the geometric mean of each, and find the ratio of the test mean to the reference mean. Then they calculate a 90% confidence interval (the interval in which 90% of the observed data falls, i.e. if you repeated the experiment on any number of random people you would expect to get a value in that interval 90% of the time, with a 5% chance of getting a value below the interval's lower limit and a 5% chance of getting a value above the upper limit). If that confidence interval does not fall entirely between 80% and 125% of the ratio of the averages, the test product cannot be marketed.

This is a much narrower range then one would expect. Most of the time, the 90% CI lies between 90% and 115% of the ratio, if not less. Any product with a really broad confidence interval is not likely to pass, since this interval would probably lie at least partly outside the boundary range. The 80-125% range is only a default, and the FDA may have reason to impose different boundaries depending on the drug.

EDIT: I note that the exact same standard is used in drug interaction studies conducted by the brand company. The test drug just happens to be a combination of drugs, and a 90% CI outside of the boundaries indicates an interaction.

Sorry I'm not thinking too clearly. Can I get a translation?

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Thanks for your help a ton guys.

I haven't noticed too much of a difference, except it feels a bit stronger than the generic. I'll update in a few more days I'm only on day 2.

Well I'm doing pretty bad, I feel like I'm in withdrawals now. I'm going to have to go back to the generic as weird as it is. I was doing better on it. I hope my depression isn't getting worse, or effexor hasn't pooped out completely. I just know since i started this brand name i've felt worse.

This ever happen to anyone else here?

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Thanks for your help a ton guys.

I haven't noticed too much of a difference, except it feels a bit stronger than the generic. I'll update in a few more days I'm only on day 2.

Well I'm doing pretty bad, I feel like I'm in withdrawals now. I'm going to have to go back to the generic as weird as it is. I was doing better on it. I hope my depression isn't getting worse, or effexor hasn't pooped out completely. I just know since i started this brand name i've felt worse.

This ever happen to anyone else here?

Hqve you talked to your pdoc about tweaking your dosage a bit? If you're feeling like you're in withdrawals, it might make sense to increase a little, and see if that helps?

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Most generics have such close bio equivalency to the brand that it's very close or even better than a comparison of the BE between two tablets of the brand. It mostly matters with drugs like lithium that have such finicky dosing and such a narrow therapeutic window.

Source: CVS.com (lol I know)

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Thanks for your help a ton guys.

I haven't noticed too much of a difference, except it feels a bit stronger than the generic. I'll update in a few more days I'm only on day 2.

Well I'm doing pretty bad, I feel like I'm in withdrawals now. I'm going to have to go back to the generic as weird as it is. I was doing better on it. I hope my depression isn't getting worse, or effexor hasn't pooped out completely. I just know since i started this brand name i've felt worse.

This ever happen to anyone else here?

Hqve you talked to your pdoc about tweaking your dosage a bit? If you're feeling like you're in withdrawals, it might make sense to increase a little, and see if that helps?

I talk to my pdoc this week and she said she thinks there can be issues coming off the generic since the body gets used to whatever. In any case I'm going to stick with the brand for another week or so to see if I improve, if not I'm going to go back to what I know was working. I hate having to do all this.

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