Allergenic extracts have a defined expiration which is printed on the product label. The expiration dates assigned have been carefully determined to help minimize potency differences between older and newer lots.
As time passes, the allergenic proteins in solution begin to decay, which reduces the potency of the extract. This rate of decay is dependent on a number of factors including the formulation, the type of diluent used, the protein concentration, and the storage conditions.
To prevent supply shortages in your practice, inventory should be monitored regularly for expiring material and new supplies should be ordered proactively.
It is also important to consider expiration dates when mixing patient vials.