TB Drugs: Second Line Drugs

Streptomycin (Strep):

Streptomycin is a bactericidal aminoglycoside given in a dose of 15 mg/kg IM for 5 to 7 days per week (use 10 mg/kg IM per day in patients over 59 years of age). It is nephrotoxic and neurotoxic.

An audiogram, vestibular testing, and a serum creatinine measurement should be obtained at baseline and questioning as to auditory (hearing loss) or vestibular symptoms(dizziness, falling to one side) must be asked at every visit.


Cycloserine is given in a dose of 10 to 15 mg/kg po per day in a divided dose. It has central nervous system toxicity ranging from restlessness to seizures which can be lessened by having the patient take 100 to 200 mgs po per day of pyridoxine.

Cycloserine should not be used in patients with a creatinine clearance of less than 50 ml/min. It is not hepatotoxic.


Ethionamide is given in a dose of 15 to 20 mg/kg po per day in a single or divided dose. Gastrointestinal toxicity includes nausea, metallic taste in mouth,and abdominal pain. It is hepatotoxic and should be use with care in patients with liver disease.

Endocrine manifestations include gynecomastia, alopecia, and hypothyroidism. Measure liver chemistries and thyroid stimulating hormone levels at baseline and monthly thereafter.


These are very nephrotoxic and ototoxic drugs which are given in a dose of 15 mg/kg per day IM or IV 5 to 7 days per week at first and 2 to 3 times per week after 2 to 4 months. These TB drugs require the same form of monitoring as streptomycin.


Capreomycin is given in a dose of 15 mg/kg per day at first and then 2 to 3 times per week after 2 to 4 months. Nephrotoxicity and ototoxicity are prominent side effects. It is monitored in the same way as streptomycin, but in addition monthly levels of potassium and magnesium should be measured.

Para-amino salicylic acid (PAS):

PAS is given in a dose of 8 to 12 grams per day in divided dosage.

Side effects include

  • hepatotoxicity (hepatitis)
  • gastrointestinal toxicity (nausea and vomiting)
  • malabsorption (steatorrhea and low folate levels)
  • endocrine toxicity (hypothyroidism)
  • coagulopathy (doubles the prothrombin time).

Monitor with baseline liver chemistries and thyroid stimulating hormone levels every 3 months.


Levofloxacin, gatifloxacin, or moxifloxacin are quinolones that target DNA gyrase. They can be given in a dose of 500 to 1000 mgs po qd. Levofloxacin is the preferred drug, especially in patients with drug resistant TB. Gatifloxacin and moxifoxacin must be used carefully especially at doses of greater than 400 mg per day.

Adverse effects of levofloxacin:

  • Gastrointestinal (nausea and bloating)
  • cutaneous (rash and photosensitivity)
  • neurological (dizziness and insomnia)
    problems are very uncommon

When giving patients fluoroquinolones these TB drugs should be given at least 2 hours before or after antacids and/or other medications containing divalent cations.

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