Drug resistance
All drugs used in the treatment of tuberculosis tend to produce resistant strains. Drug resistance means that certain strains of tuberculosis bacilli are not killed by the anti–tuberculosis drugs given during treatment. Between 50 to 100 million people worldwide are thought to be infected with strains of drug resistant tuberculosis.

Drug resistance is caused by inadequate treatment and poor tuberculosis control programs. The most common reasons for the development of resistance are:

1. Patient does not take the drugs regularly.
2. Irregular supply of drugs.
3. Incorrect prescription.
4. Lack of supervision and follow–up.
5. The emergence of infections like AIDS.

In all countries and especially those with rapidly rising number of cases of tuberculosis, development of resistant strains of the disease is a serious concern, due to its association with HIV. An accurate picture of drug resistance is not available because few countries have a reliable drug resistance surveillance system.

Drug resistance tuberculosis in India
The primary drug resistance in India is mostly to isonized, of a varying order but below 20%, followed by that to streptomycin below 10% and to rifampicin around 1%. Treatment of MDR (multiple drug resistant tuberculosis) tuberculosis can take at least two years.

Role of the BCG vaccine in the prevention of tuberculosis
There is a lot of on–going debate about the usefulness of the protective effect of the BCG vaccine. Since tuberculosis is not a health problem as it is in the developing countries, the BCG vaccination is no longer administered. BCG is the only widely used live bacterial vaccine. It consists of living bacteria derived from an attenuated (they have lost their ability to multiply and cause disease) strain of the tubercle bacilli.
Dosage
For vaccination, the usual strengths is 0.1 mg in 0.1 ml volume. The dosage to newborns aged below four weeks is about 0.05 ml.
Age
In countries where tuberculosis is prevalent and the risk of childhood infection is high (as in India), the national policy is to administer BCG very early in infancy either at birth (for institutional deliveries) or at six weeks of age simultaneously with other immunizing agents such as DPT and polio. BCG administered early in life provides a high level of protection, particularly against the severe forms of childhood tuberculosis and tuberculosis meningitis.
Side effects of the BCG vaccine
The vaccine commonly causes a reddish raised area to develop over the site of vaccination which can be present for a few weeks before it resolves.
If sterile precautions are not taken, the vaccine is not administered properly or the dose is incorrect, skin abscess or even pus can form at the site with enlargement of the lymph nodes. Very rarely, the infection can spread to the bones.
Duration of immunity provided by BCG vaccination: The duration of protection is usually from 15 to 20 years.

Tuberculosis and HIV
Of an estimated 1 million AIDS–related deaths in 1995, about one–third might have been due to tuberculosis.