The standard regimen for bacteriologically confirmed, drug-susceptible pulmonary tuberculosis consists of an intensive phase followed by a continuation phase. The intensive phase lasts
2 months and includes
four drugs: isoniazid, rifampicin, pyrazinamide, and ethambutol. The continuation phase lasts
4 months and includes
two drugs: isoniazid and rifampicin. This is commonly abbreviated as
2HRZE/4HR.
The intensive phase aims to rapidly kill actively multiplying bacilli and reduce the bacterial load, while the continuation phase eliminates remaining dormant or slowly replicating organisms to prevent relapse. Pyrazinamide is particularly active in the acidic environment of macrophages and is most effective during the early phase, which is why it is stopped after 2 months. Ethambutol is included initially to protect against unrecognized isoniazid resistance until drug susceptibility testing confirms the isolate is fully susceptible.
The four-drug intensive phase is critical because even in drug-susceptible TB, a small subpopulation of bacilli may harbor spontaneous mutations conferring resistance to a single drug. Using multiple agents with different mechanisms of action reduces the probability that any mutant survives.
Once susceptibility is confirmed and the bacterial burden is substantially reduced, two drugs are sufficient for the continuation phase.
In the National Tuberculosis Program setting, these drugs are typically provided as
fixed-dose combination tablets, which simplify administration, reduce pill burden, and lower the risk of monotherapy or incorrect dosing. A treatment supporter from the barangay directly observes intake, which is a core component of the program.
| Phase | Duration | Drugs | Purpose |
|---|
| Intensive phase | 2 months | Isoniazid, rifampicin, pyrazinamide, ethambutol (4 drugs) | Rapidly reduce bacillary load; cover possible initial drug resistance |
| Continuation phase | 4 months | Isoniazid, rifampicin (2 drugs) | Eliminate persisting bacilli; prevent relapse |
Key point! The total treatment duration is
6 months, not 4 months. Some newer rifapentine-based regimens can shorten treatment to 4 months in selected patients, but this woman is starting the standard regimen under the NTP, so the classic 2HRZE/4HR schedule applies.
Watch out! Ethambutol is stopped after the intensive phase, so the continuation phase contains only two drugs, not three. The option listing three drugs in the continuation phase is incorrect.
For this patient, additional considerations include her use of combined oral contraceptive pills. Rifampicin is a potent inducer of hepatic cytochrome P450 enzymes, which accelerates the metabolism of estrogen and progestin, reducing contraceptive efficacy. The nurse should counsel her about using a barrier method or an alternative non-hormonal contraceptive during treatment and for a period after completion. Her children aged 3 and 8 should be screened for TB infection and disease, as household contacts of a bacteriologically confirmed pulmonary TB case are at high risk. The 3-year-old is especially vulnerable to progression to active disease if infected.