Lab on paper: assay of beta-lactam pharmaceuticals by redox titration

Field tests to detect substandard antibiotics are sorely needed in many low and middle-income countries (LMICs). We created a field screening test for amoxicillin capsules and ampicillin tablets based on USP method . To measure the amount of antibiotic, the user dissolves the contents of the capsule in water, carries out a simple chemical degradation, and adds drops of the sample to a paper test card. The test card performs a titration and displays a series of blue dots for visual comparison to standard images. Pharmaceutical samples were collected in western Kenya and analyzed using a blinded methodology to validate the test card's quantitative performance against HPLC assay. Within the quantification range of the test card, the absolute assay error for dosage forms was 4.4% for amoxicillin and 5.3% for ampicillin, and inter-operator precision was 2%. Users correctly categorized 94% of amoxicillin ( n = 84) and 88% of ampicillin ( n = 56) samples as either containing less than or greater than 90% of the expected amount of antibiotic, which is the lower regulatory limit. The test card detected several lot numbers of a substandard amoxicillin product, confirmed by HPLC analysis to contain only 40-60% of the stated amoxicillin content. IR, PXRD, and gravimetric analysis revealed that talc made up the remainder of the adulterated medications. This paper test card can identify ampicillin or amoxicillin formulations that contain