Comprehensive Nursing Pharmacology Q 139
Which of the following groups of antitubercular agents includes first-line agents?
A. INH, PZA, RIF
B. SM, PAS, INH
C. EMB, PAS, INH
D. INH, cycloserine, RIF
Correct Answer: A. INH, PZA, RIF
INH, PZA, and RIF are used as combination first-line agents. Antitubercular medications: rifampin, isoniazid, pyrazinamide, and ethambutol are FDA approved for the treatment of Mycobacterium tuberculosis infections. The combination and duration on which medications to use for therapy rely on whether the patient has an active or latent disease.
Option B: Rifampin exerts its effects by reversibly inhibiting DNA-dependent RNA polymerase, which further inhibits bacterial protein synthesis and transcription. Isoniazid is a pro-drug that is converted to its active form metabolite by catalase-peroxidase and exerts its action by further inhibiting the biosynthesis of mycolic acid. Pyrazinamide’s mechanism of action remains unknown and not fully understood. Pyrazinamide is converted to its active form pyrazinoic acid and exerts its effect by inhibiting trans-translation and possibly coenzyme A synthesis needed for the bacteria to survive.
Option C: Ethambutol inhibits the enzyme arabinosyl transferases and prevents the biosynthesis of the mycobacterial cell wall. Aminoglycosides exert their action by binding to the 30S subunit of ribosomes and inhibiting the protein synthesis of the mycobacteria. Fluoroquinolones exert their effects by inhibiting DNA gyrase and topoisomerase IV, further inhibiting DNA synthesis within the bacteria.
Option D: During active disease, there are two phases for treatment: the initiation phase and the continuation phase. The initiation phase consists of two months of rifampin, isoniazid, pyrazinamide, and ethambutol therapy. This regimen is administered orally daily for eight weeks for a total of 56 doses. Once completed, isoniazid and rifampin are continued for an additional four-month for the continuation phase. This regimen is administered orally daily for 18 weeks for a total of 126 doses. For patients that cannot tolerate ethambutol, streptomycin can be substituted.