Para-aminosalicylic acid (PAS) has received orphan drug designation for use in the combination therapy of multi-drug resistant tuberculosis. PAS was first used in the 1940s, but was quickly replaced by more potent and less toxic antibiotics. However, as the rate of multi-drug resistant tuberculosis in Australia is currently 3.5% and rising, so too is the need for additional treatment options.
PAS rapidly degrades to a hepatotoxic metabolite in acidic conditions. It is therefore formulated as small, acid resistant granules. Their size enables rapid transit through the acidic environment of the stomach and dissolution then occurs in the neutral to alkaline conditions of the small intestine. To maintain the integrity of the acid resistant coating, the granules must be taken with an acidic medium, e.g. orange juice or yoghurt.
Gastrointestinal side effects are commonly experienced with PAS. Patients should also be monitored for the possibility of drug-induced hepatitis.
- Granupas® (para-aminosalicylic acid) European Medicines Agency summary of product characteristics. Paris: Lucane Pharma. Approved 07 April 2014.
- Lumb R, Bastian I, Carter R, Jelfs P, Keehner T, Sievers A. Tuberculosis in Australia: bacteriologically confirmed cases and drug resistance, 2010. Communicable Diseases Intelligence 2013; 37(1): E40-6.