Sometimes medications come to market with a lot of fanfare and Horizant®, a newly formulated pro-drug of the commonly used gabapentin, which was released with FDA approval for restless leg syndrome in April 2011 seems to be one of these. I’d never heard of Horizant until it received FDA approval yesterday for treatment of postherpetic neuralgia in adults.
As a treatment for restless leg syndrome Horizant is almost certainly a niche drug because numerous generic options are available they tend be pretty effective. Examples include generic Requip, and Mirapex, along with clonazepam and tramadol. For the treatment of postherpetic neuralgia traditional gabapentin is a suboptimal choice because of the need to gradually taper the gabapentin up to effective dose in patients who really want pain relief much quicker. At the retail online price of about two or $220 per month for the typical 600 mg twice a day dosing Horizant remains higher in price than Lyrica, his primary competition which almost expensive costs in the $170 $180 per month for the 50 to 75 mg twice a day dose.
I’m not sure why using Horizant would be chosen over Lyrica, a medication with a somewhat longer track record and a slightly lower price, but it is good to have another alternative available. Horizant has a generic name gabapentin enacarbil, and is sold as a extended-release 600 mg tablet that is felt to be absorbed through the gastrointestinal tract and subsequently converted to gabapentin. The manufacturer takes care to note that Horizant is not equal to gabapentin on the milligram for milligram conversion and that the dosage of Horizant may not result in the same plasma gabapentin concentrations as with the use of gabapentin.
The efficacy of Horizant in treatment of restless leg syndrome was evaluated in a 12 week trial along with two supportive studies and the three studies combined only included 574 patients in three countries. This is a relatively small trial and in my opinion the use Horizant for restless leg syndrome is not likely to be frequently utilized.
For postherpetic neuralgia Horizant was assessed in a 12 week control study and the side effects of Horizant were fairly modest. The most common Horizant side effects were somnolence, dizziness, headache, and nausea all of which were slightly more frequent with Horizant then with placebo. Fatigue was noted in 6% of treated patients versus 1% of placebo patients making it a little bit more frequent when compared to placebo than the other side effects mentioned.
In summary don’t anticipate Horizant to leap to the front as the market leader in treatment of postherpetic neuralgia, but I do expect it to be an considered as option for patients who various reasons might not tolerate or cannot use Lyrica, and for whom gabapentin is anticipated take too long to get to therapeutic dosage to be chosen.