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Healthcare Communications

Antituberculosis
Chemotherapy

 

 

Older “Standard” Chemotherapy
(Streptomycin, INH, PAS x 18-24 months)

- Inconveniently long regimen
- Poor compliance
- Low overall success (estimated to be 8% in Indian conditions)

 

 

 

In India, it is estimated that only 30% of cases in the community are diagnosed to start with, and of this, only 35% remain under treatment for an adequate period of time. Further, only 75% of these patients who complete the treatment are finally cured. This means that out of every 100 cases in the community, the overall level of success is only 8%.

- Fox W., Lung India, 1984, II, 161-174

 

Newer Short Course Chemotherapy

- Based on improving compliance to achieve better overall success
- Drugs must inhibit actively multiplying organisms as well as persisters
- Main drugs include rifampicin, INH and pyrazinamide, each having actions against particular populations of Mycobacterium tuberculosis

 

 

 

  Cavitary lesions Caseous lesions Macrophages
1. Location of bacilli Extracellular Extracellular Intracellular
2. Population of bacilli +++ ++ ++
3. Oxygen tension high low low
4. Medium Neutral
/Alkaline
Neutral Acidic
5. Resistant mutants Common Uncommon Uncommon

 

 

 

 

Usual Anti TB Regimen

6 months regimen:

First 2 months (Intensive phase) : EHRZ
Next 4 months (Continuation phase) : HR

(H = Isoniazid; R = Rifampicin; Z = Pyrazinamide
E = Ethambutol)

* Ethambutol is optional; another drug may be used in its place
* Regimens of longer duration and/or with 3 or 5 drugs in intensive phase may be used

Cardinal Anti TB drugs- Important features

Rifampicin
- Active against various mycobacterial populations, hence mainstay of treatment
- Very rapid bactericidal action Isoniazid
- Active against various mycobacterial populations, hence mainstay of treatment
- Bactericidal

 

Anti TB drugs - Important features (contd.)

Pyrazinamide
- Active against intracellular organisms in acidic pH
- Bactericidal

Ethambutol
- Bacteriostatic drug, added to regimen to take care of resistance

Other drugs
- May need to be added to regimen especially in cases of relapse, because of multi drug resistance (MDR)

 

 

 

Daily Dosages

 
Adults
Children
Rifampicin
400-600 mg
10-20 mg/kg
Isoniazid
300 mg
5-20 mg/kg
Pyrazinamide
1.5 - 2 g
20-35 mg/kg
Ethambutol
15-25 mg/kg
15-25 mg/kg

 

 

Some Adverse Effects of the Main Anti TB drugs

Rifampicin : brownish discolouration of urine, hepatoxicity Isoniazid : hepatotoxicity, peripheral neuropathy Pyrazinamide : hepatotoxicity, hyperuricaemia
Ethambutol : optic neuritis

 

Some Other Anti TB drugs

Capreomycin
Dosage : 1 g daily (15-20 mg/kg/day) given IM for 60-120 days; then 2-3 times weekly upto 18-24 months

Cycloserine
Dosage : 250 mg 12 hourly for 2 weeks, increased to 500 mg 12 hourly. Children 10 mg/kg/day

Ethionamide
Dosage : 15-20 mg/kg o.d. (max 1 g daily)

Prothionamide
Dosage :15-20 mg/kg/day (max 1 g daily)

Streptomycin
Dosage : Adults 0.75-1 g daily. Children 15-20 mg/kg/day. Daily for 1st 2 months; thrice weekly for next 2-6 month
s