Rifampicin is a semi-synthetic antibiotic chemical and belongs to the Rifampicin group characterised by a long aliphetic bridge connecting two non-adjacent positions of an aromatic nucleus. Rifampicin is active in vitro against tubercle bacilli and a variety of gram-positive and gram-negative microorganisms. The sensitive organisms include Mycobacterium tuberculosis, Mycobacterium leprae and Neisseria meningitidis. No cross resistance has been shown between rifampicin and other anti-tuberculosis drugs. In adults an oral dose of 450-600 mg rifampicin produces therapeutically effective levels in the blood with the peak being observed approximately 2 hours after administration. After absorption, rifampicin is rapidly eliminated in the bile, and an enterohepatic circulation ensues.
Rifampicin is a semisynthetic antibiotic derived from Rifamycin. The antibiotic affects mainly gram-positive bacteria. Gram-negative bacteria are much less sensitive to Rifampicin. Gram-negative bacteria possess an outer membrane that is probably too great a barrier for the transport of Rifampicin into the cell. Rifampicin's bactericidal effect is caused by the inhibition of RNA synthesis in bacteria. The antibiotic interacts with RNA polymerase, thus inhibiting the synthesis for long RNA strands. Rifampicin's binding site lies on the beta-subunit of the enzyme. The antibiotic, however, does not bind to the isolated subunit but only to the complete holo-enzyme. Rifampicin does not interact with eukaryotic RNA polymerases. It is, however, active against RNA polymerases present in chloroplasts and mitochondria. This makes Rifampicin a toxic agent for plant and mammal cells. Resistance to Rifampicin can be built up rapidly and is based on a change in the bacterial RNA polymerases. In plant cell tissue cultures Rifampicin is used together with Trimethoprim. This combination, however, is toxic for most plant cells and resistance to it is developed rapidly. In view of this a Cefotaxime and Vancomycin combination is more suitable for the desired purpose. This combination has a stronger bacterial effect, induces resistance very slowly and has a broader spectrum of activity.
Rifampicin has assumed importance because of its superior in vivo activity against mycobacterial tuberculosis, making it very effective in the treatment of this dreaded disease. Significantly it is also active against a large number of gram positive and gram negative microorganism. The drug has also been used in the treatment of leprosy, with encouraging results, particularly in cases where there is growing resistance to Dapsone, another drug.
Rifampicin and isoniazid are active bactericidal anti-tuberculosis drugs. Rifampicin and isoniazid are particularly active against the rapidly growing extracellular organisms. Rifampicin and isoniazid also have bactericidal activity intracellularly.