There are five drugs in first line attack against tuberculosis. The durgs differ in their mechanism of action; whether they are bactericidal i.e. kill bacteria rapidly or bacteriostatic i.e. inhibits the multiplication and growth of bacteria but do not kill them. They also differ in their action against intracellular bacilli (those mycobacteria that are in the cell), extracellular bacilli (those mycobacteria that are outside the cell) and the bacilli in the lesion itself.
No single drug is effective in treating the disease but when used in combination, they can cure the disease. Here are the first line drugs used in treatment of tuberculosis.
All except streptomycin are given orally.
Isoniazid
It is bacteriostatic for resting bacilli but kills those which divide actively. It is active against intracellular bacilli, extracellular bacilli and bacilli at lesion. It has good penetration in cerebrospinal fluid and possesses good overall activity. Along with rifampicin, it is the main drug in treatment of tuberculosis.
It inhibits cell wall mycotic acid synthesis.
Side Effects
- Gastrointenstinal disturbances
- Hepatotoxicity- elevation of liver enzymes, hepatic failure
- Hypersenstivity reactions- fever, rashes, purpura, vasculitis, drug induced lupus
- Agranulocytosis
- Pellagra
- Neurotoxicity,
- Peripheral neuropathy, optic neuritis
- Convulsions
- Psychoses
- Gynecomastia
It should be used along with pyridoxine 10 mg daily to prevent neurotoxicity. Liver function should be monitored regularly. The resistance against drug may develop due to failure of penetration into bacillus.
Rifampicin
Rifampicin is a bactericidal drug and active against all kind of bacteria. It inhibits DNA dependent RNA polymerase. It has following side effects-
- Gastrointenstinal disturbances
- Pseudomembranous colitis
- Hepatotoxicity (transient elevation enzymes)
- Shortness of breath
- Collapse and shock
- Thrombocytopenic purpura
- Hemolytic anemia
- Renal failure
- Hhypersensitivity reactions
The drug should be used on empty stomach and causes orange discoloration of the urine. This feature is used to evaluate compliance of the patient with the treatment. Liver function and blood counts should be monitored. The drug has wide range of activity and is used in leprosy, resistant staphylococcal infections, Legionnaire’s disease and prophylaxis of meningococcal meningitis.
Pyrazinamide
It is a and active against intracellular bacilli only. Exact mechanism of action is unknown. Side effects include
- Gastrointenstinal disturbances
- Hepatotoxicity- elevation of liver enzymes, hepatic failure
- Hypersenstivity reactions- fever, rashes
- Sideroblastic anaemia
- Hyperuricemia – increase in serum uric acid levels
It requires regular monitoring of serum uric acid and liver function test.
Ethambutol
Ethambutol is bacteriostatic and active against intra as well extracellular bacteria and also shows activity against bacilli in caseous lesion. It is more active against dividing bacilli. It is supposed to act by inhibiting bacterial cell wall synthesis.
It has follwing side effects
- Optic neuritis – reduced visual acuity
- Loss of red-green discrimination
- Peripheral neuropathy
- Hyperuricemia
It is not recommended in children below six years as they cannot report visual symptoms.
Streptomycin
It is a bactericidal drug and is mostly active against extracellular bacteria. It is given by intra muscular route.
As side effect it can cause
- Ototoxicity (vestibular more than cochlear)
- Nephrotoxicity
- Rash and fever
It is not prescribed in fresh cases as per new regime of WHO. It has traditionally be used locally in cold abcesses formed in tuberculosis.
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