Effect of oxidation on the stability of tuberculin purified protein derivative (PPD)

The purpose of the present work was two-fold: firstly, to collect data on the effect that air may have on the biological potency of a dilute solution of tuberculin PPD (5 TU/dose), and secondly, to find out whether or not the solubility of a tuberculin PPD preparation stored in powder form would be affected by air over a long period of time. It was shown that the presence of air in the headspace of multidose vials containing a dilute tuberculin PPD solution contributed to the lowering of its potency by approximately 50% over a period of 4 months at 5 degrees C, and that thereafter the potency remained constant for up to 12 months. It was also shown that approximately 55% of a PPD preparation, stored in powder form over a period of 7 years at 24 degrees C in containers closed with non-absorbent cotton plugs, allowing free access of air, became insoluble, whereas when an identical preparation was stored for the same length of time, at 24 degrees C or for at least 14 years at 5 degrees C, in tightly closed containers, it retained its solubility. The partial loss of potency and the loss of some solubility were attributed to the denaturation of PPD through the process of air oxidation. To reduce the loss of potency of tuberculin PPD products through the process of oxidation, it was suggested that: firstly, the vials be filled as fully as possible to minimize the amount of air trapped in the headspace, or the filling of vials be carried out under nitrogen so as to expel any air in the headspace.(ABSTRACT TRUNCATED AT 250 WORDS)