Aceto Corp. on Thursday reported its profit for the January-March period was 46 percent lower than the same period a year earlier because of competition among rival producers of generic drugs.

The Port Washington-based manufacturer of drugs and chemicals said its profit was $5.6 million in the three months ended March 31. A year earlier, the company had a profit of $10.4 million.

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Sales rose 20 percent in the quarter to $190 million, year over year.

Executives attributed the sales gain to a larger product portfolio because of a recent acquisition.

“The expansion of our product portfolio also brought us one step further along in our strategic transition towards human health, with our human health and pharma ingredients business segments collectively accounting for over 75 percent of total sales for the first time ever,” Aceto CEO Sal Guccione said in a statement.

The earnings announcement came after the stock market close. In after-hours trading, Aceto shares were down $2.46, or 16 percent, to $13.15 on the Nasdaq Stock Market.