With sales of its respiratory drugs doing well, GlaxoSmithKline has been spending hundreds of millions of dollars to expand manufacturing of several kinds of inhalers. But a glitch at one of its Ventolin inhaler plants has resulted in recalling nearly 600,000 units in the U.S.

According to an FDA Enforcement Report, GSK recently began recalling 593,088 Ventolin inhalers after discovering that an elevated number of the units were out of specification for leak rate, the company reported. The units were manufactured at its plant in Zebulon, North Carolina.

A GSK spokesperson pointed out this was not a consumer level recall, so patients can keep any Ventolin inhalers they have on hand. The voluntary recall is to the retail and wholesaler level so products are being removed from those channels. 

About 15 months ago, GSK recalled nearly 130,000 inhalers over concerns that some canisters might not contain sufficient propellant to deliver the 200 doses its label said it can provide through the end of its shelf life.

GSK has been adding capacity for a number of its respiratory products after doubling down on that business several years ago. Last year it opened an $80.5 million (£56 million), 4,500-square-meter plant in Ware in the U.K. that will allow it to double production of its Ellipta inhalers to 37 million a year. 

In February, the U.K.-based company informed local authorities it intended to build the $137 million four-story facility at its site in Scotland for the production of salbutamol, the API in Ventolin, a treatment for asthma and chronic obstructive pulmonary disease.