Shining a light on drug concentrations

A new method for monitoring drug concentrations during treatment uses light to identify harmful overdosing or inefficient underdosing, according to research published online this week in Nature Chemical Biology. The simplicity of this method may be particularly valuable for monitoring drug treatment outside of diagnostic laboratories.

The optimal drug dosage, or the concentration of drug that is prescribed, can vary widely depending on the disease and the profile of the specific patient being treated. Some drugs have a very limited ‘treatment window’, meaning they have to be used at specific concentrations to effectively treat the disease without too much toxicity to the patient. Consequently, being able to confirm that the prescribed dose is at the right concentration is very important. However, identifying drug concentrations currently requires lengthy procedures or machines that are not readily used outside of doctors’ offices and clinical laboratories.

Kai Johnsson and colleagues now incorporate luminescent proteins, or proteins that give off light, as part of a larger sensor molecule made of both proteins and synthetic components and introduce these molecules into blood samples. In the absence of the drug molecule, this sensor system gives off red light. However, upon binding the drug, the sensor switches to blue light, with the ratio of red and blue light dependent on the drug concentration. The authors demonstrate the system works with six different commonly used drugs.

As the system gives off light, the signal can be detected from a single drop of blood with a commercially-available digital camera, suggesting the method could be extended for use in developing world regions with limited infrastructure or in patient homes.