Shorting your meds

A friend to this blog -- call him W (no, not that W) -- sent in the following report. I publish his words below the asterisks, with permission:

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Yesterday, I had a rather intriguing conversation with a pharmacist, the upshot of which you might find interesting.

I have a serious autoimmune illness that requires I be on a low maintenance dose of a fairly powerful immunosuppressant called methotrexate.

Recently, the drug store I use decided for some reason or other to change the brand of generic mexthotrexate they sell. My dosage remained exactly the same, the only thing that changed was the manufacturer of the drug.

Soon after, I started having a flare up of symptoms that had been in remission for quite a long time.

After a while, it occurred to me that possibly there might be a connection between my flare up and the change of brand. Might the new brand of methotrexate be of an inferior quality? I consulted with a pharmacist acquaintance of mine.

I was shocked to learn from him that current federal regulations allow -- now get this -- that a given prescription medication only has to be within twenty percent (20%) of its stated strength!

This regulation governs drug potency, not quantity. I want to be clear that this is all about the strength of the actual compound itself, and not the units of compound being sold. In other words, it's not OK with the FDA to put 20% fewer pills in the bottle than called for (at least not yet anyway). But it is hunky-dory with them if the pills in the bottle are up to 20% weaker than what they're being sold as.

In medical terms, it means when your doctor carefully prescribes a specific course of treatment, it's perfectly legal for a pharmaceutical manufacturer, in collusion with the pharmacy, to reduce your doctor's instructions by up to 20%.

Now while he tells me a deviation of 20% is not so common, my pharmacist chum also said that significant variability in strength from one brand to another is looked upon as normal.

In fact, in the wonderfully footloose and fancy free world of pharmaceuticals, it is apparently considered routine for there to be a significant variation in potency within a single brand from one batch of a drug to the next batch. So even without switching brands, you can never have any longterm confidence in the consistency of the dosage that you're ingesting, as it may well fluctuate substantially from refill to refill.

Sheez, talk about "liberal permissiveness"!

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Cannon again: W sent a follow-up note:

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I decided to ring up Pike my veterinarian and pick his brain regarding this whole strength of prescription medication business. We've been good friends for nigh on 14 years. He and his wife are both vets and they are not only brilliant animal internists and surgeons, they are also two of the finest, most honorable people I've ever had the privilege to know personally.

While Pike isn't a cynic, he is a healthy skeptic. He hadn't specifically heard that there is an official 20% leeway granted on prescription medication strength, although he freely allowed that it sounded entirely plausible to him.

What he did know for sure is that with respect to all prescription meds whether for humans or animals, bioavailability plays an enormous role in determining what the real-world potency of a specific drug actually turns out to be.

Essentially, bioavailability refers to how well a drug or other substance is absorbed and goes into effect.

All else being equal, quality of manufacture is the single most important factor influencing bioavailability.

As an example Pike told me about a branded canine thyroid supplement called Soloxine. The company that makes Soloxine adheres to a high standard of quality. Consequently, he finds that Soloxine can always be trusted to rapidly go to work in a dog's system. But unfortunately, Soloxine is also kind of expensive compared with a the same thyroid supplement in non-branded generic form. When switching a pooch from Soloxine to an inexpensive generic version of the same drug, he always has to be careful to substantially increase the dosage of the generic, even though it is technically the exact same chemical compound, because the generics are much "weaker" than Soloxine, because the bioavailability of the generics is so much lower.

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Cannon here: I was always under the impression that generics were truly equal to the non-generic drugs. Was that presumption mistaken?