Shelf-life at time of delivery at GMS
All study drugs were received with adequate shelf-life with very few exceptions: two batches of ergometrine injection (foreign manufacturer), one batch of ampicillin injection (local manufacturer) and one batch of doxycycline capsules (local manufacturer). This is a direct benefit from the capability to manufacture pharmaceuticals in Zimbabwe.
Extent of the expiry problem
Although a significant proportion (5%) of samples were expired, it should be noted that the sampling method specifically aimed at obtaining the "worst case"; the actual proportion of expired drugs in the system is likely to be much lower. These expired samples were found in the "working stock" and consequently could be dispensed. However, there is the possibility that they may have been discarded before use if an alternative stock was obtained or alternative drugs prescribed. With epinephrine injection, virtually all stock in the supply system was expired and facility staff had no alternative but to use the expired stock. A separate interpretation of expired samples of epinephrine injection showed inconsistent quality which was no different from the unexpired stock.
Approved shelf-life in Zimbabwe
The problem of expiration may be considered in relation to the approved shelf-life as shown in Table 2 (page 11). The drug regulatory authority in Zimbabwe assigns a provisional two year shelf-life limit and considers extension on the basis of stability data submitted by the manufacturer. One long-standing manufacturer of amoxicillin capsules, ampicillin capsules, ferrous sulfate tablets and doxycycline capsules supplied these products with only a two year shelf-life. Slow turnover resulted in some expiration in three out of these four products. An extension to three years was recently obtained for amoxicillin capsules and doxycycline capsules. However, the arbitrary two year shelf-life remains for ampicillin capsules and ferrous sulfate tablets.
A summary on the range of product shelf-life available on the international market is included in Table 2. All the study drugs are considered as degradable. A comparison with approved shelf-life in Zimbabwe is also included in Table 1. For most drugs, the Zimbabwe approved shelf-life is low, with the exception of phenoxymethylpenicillin tablets and benzylpenicillin injection. This study and other field studies suggest that penicillins are stable in dry powder or solid dose forms and justify the longer shelf-life approved in Zimbabwe. The international average of two to three years for ergometrine injection is out of date in view of recent field data which proves its instability in topical climates.
In reality, many countries face the problem of drugs reaching their expiration date before use. In some cases, the regulatory authority authorizes extending the expiry date on the basis of laboratory testing. This is an expensive, time-consuming exercise which could be avoided. Manufacturers have the responsibility to formulate stable products, carry out stability studies and ensure adequate shelf-life. Furthermore, it is in the interests of the procurement organization to specify a minimum acceptable shelf-life at the time of tendering and purchase.