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The gabapentinoids are a class of drugs vaguely resembling the neurotransmitter GABA. Although they were developed to imitate GABA’s action, later research discovered they acted on a different target, the A2D subunit of calcium channels. Two gabapentinoids are approved by the FDA: gabapentin (Neurontin®) and pregabalin (Lyrica®).

Gabapentin has been generic since 2004. It’s commonly used for seizures, nerve pain, alcoholism, drug addiction, itching, restless legs, sleep disorders, and anxiety. It has an unusually wide dose range: guidelines suggest using anywhere between 100 mg and 3600 mg daily. Most doctors (including me) use it at the low end, where it’s pretty subtle (read: doesn’t usually work). At the high end, it can cause sedation, confusion, dependence, and addiction. I haven’t had much luck finding patients a dose that works well but doesn’t have these side effects, which is why I don’t use gabapentin much.

Pregabalin officially went generic last month, but isn’t available yet in generic form, so you’ll have to pay Pfizer $500 a month. On the face of things, pregabalin seems like another Big Pharma ploy to extend patents. The gabapentin patent was running out, so Pfizer synthesized a related molecule that did the same thing, hyped it up as the hot new thing, and charged 50x what gabapentin cost. This kind of thing is endemic in health care and should always be the default hypothesis. And a lot of scientists have analyzed pregabalin and said it’s definitely just doing the same thing gabapentin is.

But some of my anxiety patients swear by pregabalin. They call it a miracle drug. They can’t stop talking about how great it is. I can’t use it too often, because of the price, but I’m really excited about the upcoming generic version coming out so I can use it more often.

Still, I have to wonder – why am I sitting around waiting when I could just give people gabapentin? Confirmed pharmacodynamically-identical, generic, and cheap? The answer is, gabapentin doesn’t seem to work that well. I’ve never had patients with more than minimal anxiety happy on gabapentin alone. Am I imagining a difference betwee these two supposedly-similar medications? I don’t know. Although studies confirm pregabalin is great for anxiety, nobody has done the studies on gabapentin that would let me compare it. For now, the apparent difference between pregabalin and gabapentin is one of the great mysteries of life, one of the things that makes me doubt my own sanity.

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