The erythromycin breath test (ERMBT) is a method used to measure metabolism (oxidation and elimination from the system) by a part of the cytochrome P450 system. Erythromycin is tagged with carbon-14 and given as an intravenous injection; after 20 minutes the subject blows up a balloon and the carbon dioxide exhaled that is tagged with carbon-14 shows the activity of the CYP3A4 isoenzyme on the erythromycin. Therefore, this activity can predict how other drugs that are metabolized by the CYP3A4 part of the cytochrome P450 system will be acted upon by a particular person.
The test allows doctors to determine or predict an individual’s drug treatment outcome. Will a patient develop serious or fatal side effects from a certain drug? Which foods and drugs should not be taken together? With this and other tests a physician may determine treatment outcomes in advance or study the effects of new drugs.
Some patients have a congenital inability to synthesize certain enzymes, so drugs may build up to toxic levels in their system or other drugs and foods a patient is taking may consume all of their ability to metabolize certain foods and drugs. An example is: when a person taking a cholesterol-lowering statin drug then drinking grapefruit juice, they may have a poor treatment outcome (adverse drug reaction) and sustain liver damage or kidney failure due to drug induced rhabdomyolysis (the breaking up of muscle tissue).