A yellow color indicates legitimate drugs, while a color change from yellow to red indicates falsified drugs. Source: Colorado State University

As one of the of the most widely prescribed families of medicines, antibiotics have saved millions of lives worldwide since the early 20th century. These drugs prove less effective and even dangerous in developing areas, where the production and sale of counterfeit medicine is widespread. The World Health Organization estimates that up to 10 percent of all drugs worldwide could be falsified, with up to 50 percent of those being some form of antibiotics. A ‘fake’ antibiotic can endanger patients and contribute to the wider problem of antimicrobial resistance.

A paper-based test that can identify substandard or counterfeit antibiotics was developed at Colorado State University to address this pharmaceutical problem. The simple 15-minute paper assay, which can be performed by untrained personnel, turns red if a fake antibiotic is detected.

The beta-lactamase enzyme produced by bacteria to impart resistance to antibiotics was tapped by the researchers to empower their device to detect the presence of antibiotics in a given sample. To conduct a test, the user dissolves the antibiotic in water, and adds the solution to a small paper device. The paper contains a molecule called nitrocefin that changes color when it reacts with the enzyme, located in a detection zone. The antibiotic and the nitrocefin compete to bind with the enzyme in the detection zone.

Little color change in the paper strip is observed if the antibiotic dose is acceptable because the drug outcompetes the nitrocefin and successfully binds with the beta-lactamase enzyme. In a falsified or weakened antibiotic, the paper turns red because the enzyme instead reacts with the nitrocefin. A yellow color signifies an appropriate strength antibiotic.

The device also includes a pH indicator to determine if a sample is acidic or alkaline. This extra information could further alert the user to whether a sample has been falsified with filler ingredients, which might otherwise confound the main test.

In a blind test with five users who were unfamiliar with the device or the science behind it, 29 out of 32 antibiotic samples were successfully identified as either legitimate or false.

The research is reported in ACS Sensors.