Saturday, 9 June 2018

Anti-tubercular drugs

·         Tuberculosis is one of the most communicable diseases in the developing nations caused by the mycobacterium tuberculosis.
·         The lipid rich mycobacterium cell wall is resistant to the penetration to most of the antibiotics.
·         They have high tendency to develop multi drug resistance.
·         For the treatment of Tuberculosis, DOTS (Directly observed treatment short course) were introduced in 1995 in India.
·         According to the clinical utility, the anti-tubercular drugs can be divided into two groups:
A.      First line TB drugs: these drugs are highly efficacious and less toxic.
B.      Second line Tb drugs: These are less efficacious and are used only where high resistance is developed for the first line drugs.

First Line anti-tubercular drugs

·         In the first line treatment, drugs which are used includes: Pyrizinamide, Rifampicin, Isoniazide, Ethambutol and Streptomycin.
A.      Pyrazinamide: Pyrazinamide is converted into Pyrazonic acid inside the body Pyrazonimidase.
  • It acts by inhibiting the mycolic acid synthesis and hence resulting in the death of mycobacterium..
  • Main side effects include hepatotoxicity & Arthalgiia.

B.      Rifampicin: It is semisynthetic derivative of Rifamycin obtained from Streptomyces Mediterrani.
  • It acts by inhibiting the DNA dependent RNA polymerase inside the mycobacterium.
  • Main side effects include hepatotoxicity and Hemolytic anemia.
  • Being an enzyme inducer it also results in contraceptive failure.

C.      Isoniazide: Isoniazide (INH) acts by inhibiting the mycolic acid synthesis.
  • It’s responsible for peripheral neuropathy and pyridoxine is given to counteract this adverse affect of INH.
  • INH is microsomal enzyme inhibitor.
  • Para Amino Salicylic acid inhibits INH metabolism.

D.      Ethambutol: Ethambutol acts by inhibiting Arabinosyl transerfase required for the synthesis of Arabinogalactose.
  • Optical neuropathy is the major side effect of the ethambutol.

E.       Streptomycin: Use of streptomycin is obsolete nowadays as first line treatment of the TB.
  • Major side effects include ototoxicity and nephrotoxicity.

Second-Line anti-tubercular drugs

·         Second line drugs are used only in the highly resistant cases where first line drugs are not effective any longer.
·         Second line drugs include following drugs:
A.      Aminoglycoside: Amikacin & Kanamycin are two aminoglycosides used.
B.      Capreomycin: Capreomycin is a cyclic peptide and also used in the Mycobacterium Avium Complex (MAC) infections.
C.      Fluroquinolones: Levofloxacin, Ciprofloxacin, Ofloxacin & Moxifloxacin are the fluroquinolones used as second line treatment for TB.
D.      Rifabutin
E.       Ethionamide & Prothionamide
F.       Cycloserine: It is obtained from Streptomyces Orchidaceous.
Cycloserine is single amino acid containing antibiotic (D-alanine).
G.     Terizidone
H.      Para Amino Salicylic acid (PAS): It inhibits folate synthtase.

·         For the prophylaxis of MAC infection Azithromycin (1200mg/week) or Clarithromycin (500 mg) is used.

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5.  Miscellaneous topics for GPAT

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