Rapid litmus-like test checks antibiotic integrity

Researchers at Colorado State University have developed a paper-based test that can quickly determine whether an antibiotic sample is authentic and unadulterated.

The litmus-like test can detect if an antibiotic has an appropriate strength, or if it is diluted with filler substances and takes just 15 minutes to deliver a read-out.

In the test, the antibiotic is dissolved in water, and the resulting solution is tested using a paper that contains a molecule – called nitrocefin – which changes colour when it reacts with the enzyme beta-lactamase. Beta-lactamase is naturally produced by bacteria to give them resistance to antibiotics by chemically binding to portions of the drug molecule.

The antibiotic and nitrocefin are in a competition to bind with the enzyme during the test, and the tester includes a pH indicator which determines the acidity or alkalinity, and whether a sample has been adulterated.

With a strong antibiotic dose, there is little colour change to yellow, as the antibiotic outcompetes the nitrocefin – due to there being much more of it to bind to the enzyme. With a substandard or counterfeit antibiotic, the nitrocefin will instead react with the enzyme, giving a red tint to the paper.

To test the paper device and determine its usability, the researchers included a blind test with five participants who were unfamiliar with both the device or the intent behind it. They successfully identified 29 out of 32 samples as either genuine or counterfeit.

The one failure for the test was with acetylsalicylic acid – or aspirin as it is more commonly known – which did not turn as vivid a red as the other false samples, as its pH destabilised the reaction. This means further refinement of the test is needed, although it is effective for a broad variety of beta-lactam antibiotics.

“In this country, we take for granted that our antibiotics are good - we don't even think twice,” said Kat Boehle, one of the team behind the work which is published in the journal ACS Sensors.

“But counterfeit and substandard antibiotics are an extremely common thing in other parts of the world. The goal of this project has been to make a cheap detection device that is easy to use; our device costs literally a quarter to make.”