Mexiletine hydrochloride in 150-mg capsules came back on the market last week after spending six months on backorder, yet veterinarians might have a tough time acquiring the drug through traditional distributor channels.

Most distributors serving the veterinary profession do not have wholesale agreements with Teva Pharmaceuticals USA, now the sole maker of mexiletine hydrochloride in America. MWI Veterinary Supply is the only veterinary distributor with an agreement to buy from Teva Pharmaceuticals, and it does not carry the orally active antiarrhythmic agent.

Teva Pharmaceuticals became the country's only producer of mexiletine hydrochloride last year when Boehringer Ingelheim Pharmaceuticals announced that it stopped manufacturing Mexitil, the name-brand version of the drug. Two generics makers also abandoned production of mexiletine hydrochloride due to slow sales.

That exodus from the market created a shortage that came to light last fall and particularly affected the availability of 150-mg capsules, the most commonly prescribed veterinary dose. Teva Pharmaceuticals offers mexiletine hydrochloride capsules in 150-mg, 200-mg and 250-mg strengths. 

Teva customer services confirms that the company is filling open orders for the drug, yet a secondary supply crunch is expected after the current stock is distributed. Licensed only for human use, the popularity of mexiletine hydrochloride has waned in recent years due to its known proarrhythmic properties and potential to cause sudden death, explains Dr. Mark Kittleson, a Veterinary Information Network consultant and board-certified cardiologist at the University of California, Davis School of Veterinary Medicine. Automatic implantable cardioverter defibrillators are replacing the need for the drug in human patients.

That alternative has not taken off in veterinary medicine, where mexiletine hydrochloride is prescribed off-label to treat ventricular arrhythmias in canine patients. During the past few months, some veterinarians have turned to compounders like Wedgewood Pharmacy, which sells the drug in eight formulations including seven capsules and an oral suspension. With the shortage now abated, veterinarians presumably can write prescriptions for mexiletine hydrochloride to be filled at local pharmacies.

A Teva customer services representative who identified himself as "Keith" but did not give his last name reported that he could not reveal names of distributors carrying the company's brand of mexiletine hydrochloride. He hinted that veterinarians who want to stock the drug should try one of the “big three” wholesalers serving human medicine.

Cardinal Health Inc., McKesson Corp. and AmerisourceBergen Corp. are widely identified as controlling up to 95 percent of the human medicine supply chain.