The quality control of tuberculin PPD products from seven Latin American laboratories

Abstract

The Pan American Health Organization, through its Pan American Zoonoses Center (CEPANZO), distributes the concentrated stock solution of PPD batch RT23 (1 mg ml⁻¹ = 50 000 TU ml⁻¹) to national central laboratories. In the laboratories the stock solution is diluted to 2 TU/0·1 ml and dispensed with the addition of Tween 80 and either chinosol or phenol as preservatives in rubber-stoppered vials for use in the Mantoux test. The expiry date is usually fixed at six months after filling. Samples of nine lots of PPD 2 TU from seven countries (Argentina, Brazil, Colombia, Dominican Republic, Ecuador, Paraguay and Uruguay) were received by CEPANZO for quality control. The biological activity and phenol concentrations of these samples were assayed periodically after storage at 4, 25 or 37 °C either unopened or opened and re-used in a manner simulating extreme field conditions of use and storage. The object of the study was to determine the stability of the biological activity as well as the maintenance of sterility in these conditions with a view to assessing the need for stricter requirements for the labelling of tuberculin.

The results obtained showed that PPD 2 TU with 0·4–0·5% ($\text{w}\text{v}$) phenol added, and dispensed in vials, was stable in its biological activity and maintained its sterility. Therefore, it seems unnecessary to issue stricter requirements than those currently applied. PPD 2 TU can be used for six months after dilution provided that it has been stored at 5 ± 3 °C, protected from sunlight, and held in vials or ampoules filled to capacity provided that containers used twice with a remaining volume of half or less of the original volume were discarded.