Drugs

Antitubercular Drugs (Drugs for Mycobacterium tuberculosis)

Antitubercular Drugs

  • Antitubercular Drugs (anti-TB drugs) are agents used to manage tuberculosis caused by Mycobacterium tuberculosis.

According to their clinical utility the anti-TB drugs can be divided into :

1. First line drugs :

  • These drugs have high antitubercular efficacy as well as low toxicity; are used routinely.
  • e.g.
  • First line drugs
    Isoniazid (H) / lsonicotinic acid hydrazide (INH)
    Rifampicin / Rifampin(R)
    Pyrazinamide (Z)
    Ethambutol (E)
    Streptomycin (S)

2. Second line drugs

  • These drugs are typically less effective, more toxic, and less extensively studied.
  • They are used for patients who cannot tolerate the first-line drugs or who are infected with resistant TB.
  • No drugs are specifically developed for NTM infections. Macrolides, rifamycins, and aminoglycosides are frequently included, but NTM regimens vary widely by organism.
  • e.g.
  • Second line drugs
    Thiacetazone / Amithiozone (Tzn)
    p-Aminosalicylic acid (PAS)
    Ethionamide (Etm)
    Cycloserine (Cys)
    Aminoglycosides {Amikacin (Am)Kanamycin (Kmc)}
    Capreomycin (Cpr)
    Fluoroquinolones (Ciprofloxacin, Ofloxacin, Moxifloxacin)
    Macrolides (Clarithromycin, Azithromycin)
    Rifabutin

M. tuberculosis is slow growing and requires treatment for months to years.

  • LTBI can be treated for 9 months with isoniazid (INH) monotherapy or with 12 once-weekly doses of INH (900 mg) and rifapentine (900 mg).
  • In contrast, active TB disease must be treated with several drugs.
  • Treatment for drug-susceptible TB lasts for at least 6 months, while treatment of multidrug-resistant TB (MDR-TB) typically lasts for about 2 years.

The goals of antitubercular chemotherapy are :

  • Kill dividing bacilli : Drugs with early bactericidal action rapidly reduce bacillary load in the patient and achieve quick sputum negativity so that the patient is non-contagious to the community: transmission of TB is interrupted. This also affords quick symptom relief.
  • Kill persisting bacilli : To effect cure and prevent relapse. This depends on sterilizing capacity of the drug.
  • Prevent emergence of resistance : So that the bacilli remain susceptible to the drugs.

Recommended doses of antitubercular drugs are as following :

For <50 kg

  • Drug Daily dose (mg/kg) 3 x per week dose (mg/kg)
    Isoniazid (H)  5 (4-6) mg/kg  10 (8-12) mg/kg
    Rifampin (R)  10 (8-12) mg/kg  10 (8-12) mg/kg
    Pyrazinamide (Z)  25 (20-30) mg/kg  35 (30-40) mg/kg
    Ethambutol (E)  15 (15-20) mg/kg  30 (25-35) mg/kg
    Streptomycin (S)  15 (12-18) mg/kg  15 (12-18) mg/kg

For >50 kg

  • Drug Daily dose (mg) 3 x per week dose (mg)
    Isoniazid (H)  300 mg  600 mg
    Rifampin (R)  600 mg  600 mg
    Pyrazinamide (Z)  1500 mg  2000 mg
    Ethambutol (E)  1000 mg  1600 mg
    Streptomycin (S)  1000 mg*  1000 mg

The WHO guidelines also describe a twice weekly dosage schedule, but do not recommend it.

* Dose to be reduced to 750 mg above 50 yr age and to 500 mg above 65 yr age; also in patients with renal Impairment

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