The U.S. FDA withheld approval of Amphastar Pharmaceuticals Inc.'s over-the-counter asthma inhaler, Primatene Mist.

The regulator, in a complete response letter, asked the pharmaceutical company to make further changes to the inhaler's label and packaging followed by a study to evaluate patients' ability to use the product without professional guidance.

Amphastar plans to address these concerns by mid-2017.

The original Primatene Mist was discontinued because it contained chlorofluorocarbons, which are harmful to the ozone layer. The new version of the inhaler uses the same active ingredient as the old one but uses a different delivery system.