Aceto Corp. has begun selling a generic medicine to treat conjunctivitis.

The Port Washington-based manufacturer of drugs and chemicals said on Monday it has launched olopatadine hydrochloride 0.1 percent ophthalmic solution, a generic version of Patanol from Alcon Inc.

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The drug introduction, by Aceto’s Rising Pharmaceuticals division, comes as the patent expires on Patanol.

Sales of the medicine from all manufacturers totaled about $223 million per year, according to data provider IMS Health.

Aceto executives said they expect “six or more generic competitors will enter the market at or around the same time as Rising.”