A batch of the asthma inhaler Respigen has been recalled as it might not have exactly the required quantity of active ingredient salbutamol.

The problem batch of the 100mcg inhalation aerosol, number 9F282A, has an expiry date of May 2012.

Distributor Mylan New Zealand said a small number of the blue, reliever-type inhalers, might have quantities of salbutamol that are "out of specification".

Patients are asked to return their inhaler to a pharmacy where they will be given a free replacement.