Nursing care
Antitubercular Drugs: what to check before you give it
Written and reviewed by Dana Whitfield, RN, MSN · 5 min read · Updated September 2026
Short answer
Antitubercular drugs work in combination to kill or suppress Mycobacterium tuberculosis and prevent resistance developing to any single agent. The teaching point patients ask about most is rifampin turning urine, sweat, and tears orange — a harmless, expected effect that alarms patients if nobody warns them first.
Mechanism, simply
First-line antitubercular therapy combines isoniazid, rifampin, pyrazinamide, and ethambutol, each attacking the bacterium in a different way so resistance cannot easily develop to the regimen as a whole. Isoniazid inhibits synthesis of mycolic acid in the bacterial cell wall, rifampin blocks bacterial RNA synthesis, pyrazinamide works best in the acidic environment inside macrophages where dormant organisms hide, and ethambutol interferes with cell wall formation.
Because TB bacteria divide slowly and can persist in a dormant state, treatment runs for months rather than days, typically an intensive phase of four drugs for two months followed by a continuation phase of two drugs for four to seven months. Using drugs in combination for the full course is what prevents the emergence of multidrug-resistant TB, so gaps in adherence carry consequences well beyond the individual patient.
Indications you will see on the ward
Active pulmonary TB is the primary indication, confirmed by a positive sputum smear or culture, chest imaging showing infiltrates or cavitation, and clinical findings such as productive cough, night sweats, weight loss, and low-grade fever. Isoniazid alone is also used for latent TB infection, identified by a positive tuberculin skin test or interferon-gamma release assay without active disease.
You will see these drugs used in patients who are immunocompromised, in congregate settings such as shelters or correctional facilities, and in anyone with recent close contact to an active case. Extrapulmonary TB, affecting bone, the CNS, or the genitourinary tract, is treated with the same core regimen, sometimes extended in duration depending on the site involved.
Assessment before administration
Obtain baseline liver function tests before starting therapy, since isoniazid, rifampin, and pyrazinamide are all hepatotoxic and the combination increases that risk further. Ask about alcohol use, existing liver disease, and current medications, and get a baseline visual acuity and colour vision assessment before starting ethambutol, since it can cause optic neuritis.
Confirm the patient is not pregnant or planning pregnancy without discussing it with the prescriber, as some regimens are adjusted in pregnancy, and screen for peripheral neuropathy risk factors such as diabetes, alcohol use, or malnutrition before starting isoniazid, since these increase the likelihood of neuropathy without pyridoxine supplementation. Document baseline weight, since pyrazinamide dosing is weight-based.
Toxicity and the antidote
Isoniazid can cause peripheral neuropathy by depleting pyridoxine (vitamin B6), presenting as numbness, tingling, or burning in the hands and feet; pyridoxine is given prophylactically alongside isoniazid in patients at higher risk, including those with diabetes, alcohol use disorder, or malnutrition, and pyridoxine is also the treatment if neuropathy develops. Hepatotoxicity is the toxicity that matters most across the regimen, and it presents as jaundice, dark urine, right upper quadrant pain, or unexplained fatigue.
Ethambutol toxicity centres on the eye: optic neuritis presents as blurred vision, loss of red-green colour discrimination, or decreased visual acuity, and it is usually reversible if the drug is stopped promptly, so any visual complaint needs urgent reporting rather than a wait-and-see approach. Liver enzymes should be checked periodically through treatment, and any of these drugs is held if liver function tests climb significantly or the patient develops signs of hepatitis.
Interactions that matter
Rifampin is a potent inducer of hepatic cytochrome P450 enzymes, which speeds the metabolism of a long list of other drugs and reduces their effectiveness — oral contraceptives, warfarin, and many antiretrovirals among them. Patients on hormonal contraception need to be told it may fail during rifampin therapy and to use a backup method.
Isoniazid inhibits some of those same enzymes, working in the opposite direction and raising levels of drugs like phenytoin, so combination regimens require careful attention to concurrent medications rather than assuming the effects cancel out. Alcohol increases hepatotoxicity risk with isoniazid and rifampin both, and patients should be counselled to avoid it for the duration of treatment.
What the patient must be told
The teaching point patients ask about most is that rifampin turns urine, sweat, and tears orange-red, and it can permanently stain soft contact lenses, so they should switch to glasses during treatment. This is expected and harmless, but if nobody mentions it in advance, patients understandably panic and some stop the drug thinking something has gone wrong.
Tell patients to report any visual changes immediately if they are taking ethambutol, and any numbness or tingling in the hands or feet if they are taking isoniazid. Emphasise that the full course must be completed even once they feel better, since stopping early is how resistant TB develops, and reinforce that alcohol should be avoided and any yellowing of the skin or eyes reported without delay.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our respiratory practice questions are the closest set to what this page covers.
Common questions
Why does rifampin turn body fluids orange?
Rifampin itself is orange-red in colour, and as it is excreted it tints urine, sweat, tears, and saliva the same shade. It is harmless and expected, but soft contact lenses can be permanently stained, so patients should switch to glasses during treatment.
Why is pyridoxine given with isoniazid?
Isoniazid depletes vitamin B6, which can cause peripheral neuropathy. Pyridoxine is given prophylactically in patients at higher risk and is also the treatment if numbness or tingling develops.
What is the earliest sign of ethambutol toxicity?
Visual changes, particularly loss of red-green colour discrimination or blurred vision, signal optic neuritis. It is usually reversible if the drug is stopped promptly, so any visual complaint needs same-day reporting.
Why are multiple TB drugs given together instead of one?
Combination therapy attacks the bacterium through different mechanisms at once, which prevents resistance from developing to any single agent. Using fewer drugs, or stopping early, is how multidrug-resistant TB emerges.
Does rifampin affect birth control pills?
Yes. Rifampin induces liver enzymes that speed up the metabolism of oral contraceptives, reducing their effectiveness. Patients on hormonal birth control should use a backup method for the duration of therapy.