The oral administration of therapeutic drugs is an easy and preferred route over other administration routes, however, there are certain aspects that need special attention. Bioavailability of oral drugs primarily depends on well-functioning digestive system and microbiota that colonize the digestive system. It has been proved that human microbiome composition plays an important role in drug and xenobiotic metabolism by means of various enzymatic reactions mediated by microbiota produced enzymes.
The occurrence of such interactions may have a complementary or opposite effect on the host’s enzymatic system ultimately affecting on pharmacological effects of administrated drugs. Some of the administrated drugs may be activated to its active form (in eg. Sulfasalazine can be transformed into 5-amino-5-salicylic acid in the course of gut inflammation disorders treating) or metabolically reactivated via bacterially expressed enzymes (like irinotecan by bacterial β-glucuronidase in cancer chemotherapy), whereas others may be inactivated (like digoxin) as a result of gut microbiota enzyme expression. While analyzing these connections, scientist has also noticed the occurrence of various enzyme competition. The most recognizable is the one between microbial p-cresol and host metabolites of administrated drug, like acetaminophen, for sulfotransferase 1A1 (SULT1 A1) that catalyze the conjugation of many hormones, drugs, and neurotransmitters.
The number of known interplays between gut microbiota and pharmaceutically active compounds has been described for more than 50 widely used drugs, and due to the extended research, the total number continues to grow. Gaining knowledge about these microbial enzymes and understanding molecular mechanism that undergoes in the intestine is essential for better control of the pharmacokinetic action of commonly prescribed pharmaceuticals, and thus improving the efficiency of pharmaceutical treatment.