High failure rate of the dissolution tests for 500-mg amoxicillin capsules sold in Cambodia: is it because of the product or the test method?

OBJECTIVES: During the survey of substandard medicines in Cambodia in 2007, it was found that more than 90% of 500-mg amoxicillin (AMPC) capsules failed the United States Pharmacopeia (USP) 30 TEST 1 dissolution test. In the USP, several monographs provide multiple methods for performing the dissolution test. By using the 500-mg AMPC capsule as an example, we aimed to identify the problems and implications of the USP methods adopted for the dissolution test as a global standard.
METHODS: All AMPC samples were collected from the Cambodian market in 2007. For the quantitative test, we referred to USP 30. We performed the USP 28 and USP 30 TEST 2 dissolution tests and compared these results with those of the USP 30 TEST 1.
RESULTS: All 500-mg AMPC capsules used for the comparison passed the quantitative test. Samples that passed the USP 28 and USP 30 TEST 2 dissolution tests were identical, and the pass rate was 97.1% (34/35), whereas the pass rate with the USP 30 TEST 1 was 8.6% (3/35). The difference in the dissolution results between the three methods was significant (P<0.0001).
CONCLUSION: This study revealed that many users would select the most stringent method when multiple methods exist in the USP. This may lead to a high failure rate of the tests. Because USP is a global standard, we recommend that it take into consideration the developing countries and create a more detailed user-friendly manual for selection for appropriate methods.