Anti-TB drugs

What are antitubercular (anti TB) drugs?

Antitubercular drugs are medicines used for the treatment of any type of tuberculosis (TB) including extra pulmonary TB that affects organs other than lungs. Before these drugs became available, TB was an incurable disease. Vast majority of people who had TB died of the disease. The list includes famous people from all walks of life such as Vivien Leigh, Jane Austen and John Keats to name a very few.

The advent of anti-TB drugs completely changed the picture. Complete cure of tuberculosis is possible if the patient uses these drugs effectively. However, all antitubercular drugs have some side effects, which most patients have to endure during treatment.

The prognosis is excellent, when the patient is compliant and completes the treatment course. Patients who do not complete the course or relapse after treatment have a relatively less favorable outcome. Prognosis is not good in patients who are resistant to most of the anti-tubercular drugs, and those who have tuberculosis in organs other than the lungs.

What are the drugs used? 

• First line or primary drugs – The five first line anti-TB drugs are isoniazid, rifampin, pyrazinamide, ethambutol and streptomycin. They are the cornerstone of treatment of new cases of TB.
• Second line drugs - apart from the five primary drugs, all the other anti-TB drugs are called “second line”, reserve, or new drugs. The list includes levofloxacin, moxifloxacin, rifapentine, ethionamide, amikacin, cycloserine, capreomycin, rifabutin, clofazimine para aminosalicylic acid, bedaquiline.

For how long are anti-TB dugs needed?

Typically, the antitubecular drug treatment may last for 4 months to 18 months. The treatment duration varies according to the site of tubercular infection, the number of organisms that are present, the type of case like a primary case, or a relapsed patient, or a recurrent and resistant case of tuberculosis. For extra pulmonary tuberculosis, the treatment usually exceeds a year.

What are the goals of TB treatment?

To shorten the clinical course of the disease, to prevent complications, to ensure complete treatment, to prevent development of latency, to reduce relapses and recurrences of the disease, finally to decrease the likelihood of TB transmission.
Individual drugs and their potentially fatal side effects:

1. Isoniazid or INH is used in preventive therapy, and as one of the first line drugs in management of active TB. Potential side effect - peripheral neuritis.
2. Rifampicin has to be used in combination with at least one other anti-TB drug. Side effect – Hepatitis, shock like syndrome
3. Pyrazinamide is primarily a bacteriostatic drug against the TB bacilli. However, at higher concentrations it can act as bactericidial. Side effect – severe liver damage.
4. Ethambutol is bactericidal in action. Side effect - optic neuritis.

Special considerations:
Streptomycin should not be used in pregnant women.
Ethambutol is often avoided in young children
Dose adjustments may be necessary in HIV infected patients

Special terms in anti-TB treatment:
Multidrug resistance TB: MDR-TB is defined as resistance to isoniazid and rifampin, which are the 2 most effective first-line drugs for TB.
A rare type of MDR-TB, called extensively drug-resistant TB (XDR-TB), has been reported in Italy, Iran, and India. It is a rare type of multidrug-resistant tuberculosis (MDR TB) that is resistant to isoniazid and rifampin, plus any fluoroquinolone and at least one of three injectable second-line drugs (i.e., amikacin, kanamycin, or capreomycin).
Full resolution is generally expected with few complications in cases of non-MDR- and non-XDR-TB, when the drug regimen is completed. Poor prognostic markers include extra pulmonary involvement, an immune-compromised state, older age, and a history of previous treatment.