Chemotherapy and its implication in TB control

Chemotherapy for TB is the use of an anti-TB drugs to kill, or prevent the replication of, TB mycobacteria in the patient’s body. Effective anti-TB chemotherapy renders the patient non-contagious and cures the patient, thereby interrupting the chain of transmission. Mortality rates of TB range from 50-80% in untreated smear-positive individuals and drop to lower than 5% under chemotherapy.

Most of the bacteria are killed during the first 8 weeks of treatment; however, there are persistent organisms that require longer treatment. TB disease must be treated for at least 6 months and in some cases even longer. The use of multi-drug therapy reduces the incidence of drug-resistance  and increases the overall effectiveness of treatment.

If treatment is interrupted, any surviving bacteria may cause the patient to later become ill and infectious again, potentially with drug-resistant disease.

How infectious are tuberculosis patients under chemotherapy?

Under effective chemotherapy, there is a substantial decline in infectiousness in two weeks time, and may not be a major source of risk to any contact persons. This decline is indicated by the rapid fall in the number of viable organisms in the sputum, and reduced frequency of coughing.  

Types of Chemotherapy in TB

1. Preventive Chemotherapy: Regimen for healthy but TB infected persons with a high risk of developing TB, in order to prevent them from developing TB.
2. Standard Chemotherapy: Two-phased chemotherapy for an average of 6-8 months based on the combination of at least four major drugs (HRZE) given for 2 months during the initial intensive phase of treatment and followed by a combination of at least 2 drugs given for at least 4 months during the continuation phase of treatment.
3. Chemotherapy for Drug-resistant TB: Two-phased chemotherapy varying from 9 - 24 months in patients having demonstrated resistance to drugs used in standard chemotherapy. The regimen varies with the drug to which the resistance is present, however, each regimen contains a mix of second-line anti-TB drugs including injectables.   

Resources

• Training Modules (1-4) for Programme Managers and Medical Officers, 2020.
• Tuberculosis Infectiousness and Host Susceptibility, The Journal of Infectious Diseases, Vol. 216, suppl_6, 2017.
• Tuberculosis chemotherapy: Current Drug Delivery Approaches, Respiratory Research 7, Article no. 118, 2006.
• Tuberculosis Case-finding and Chemotherapy: Questions and Answers, K. Toman.

 Assessment