The regimen most highly recommended by ATS and CDC (based on nonrandomized clinical trials) involves 9 months of daily or twice-weekly doses of isoniazid. The twice-weekly regimen is recommended only if the taking of the medication is directly observed (ATS/CDC, 2000b). An “acceptable,” shorter isoniazid regimen for those without other risk factors involves 6 months of daily or twice-weekly doses of the drug (the latter only with direct observation). The shortest, currently acceptable regimen involves two drugs, rifampin and pyrazinamide, taken daily for 2 months.
The major concern about treatment of latent tuberculosis infection has been the potential for liver damage. A recent analysis of 7 years of experience at a Seattle public tuberculosis clinic suggests that the risk of liver damage form the most widely used drug (isoniazid) is lower than previously thought—less than 0.2 percent, compared with the 0.5 to 2.0 percent reported from earlier studies (Nolan et al., 1999). Other analyses (Salpeter, 1993; Garcia Rodriguez et al., 1997) have also suggested risks of adverse treatment effects that are lower than assessed earlier. Those at possible increased risk of liver damage include those who use alcohol daily, those with preexisting liver disease, older people, and pregnant or postpartum women (ATS/CDC, 2000b). Liver damage is also a concern with the rifampin-pyrazinamide treatment regimen, which is being closely monitored as more experience with the regimen accumulates (CDC, 2000c).
Careful screening, patient education about signs and symptoms of hepatitis, and prompt discontinuation of drugs when symptoms occur can reduce or eliminate the potential for adverse effects (ATS/CDC, 2000b). Baseline testing of liver function is recommended for patients at risk for liver disorders and for patients who have a history of liver disease, are infected with HIV, use alcohol regularly, or are pregnant or within 3 months of having given birth. In addition, monthly laboratory monitoring of liver function is advised for patients who have abnormal results on baseline liver function tests or who are otherwise at risk for hepatic disease. Nonetheless, for people with an infection that produces no symptoms and that usually has a fairly small chance of progressing to active disease (which usually can be successfully treated), even a very small possibility of liver damage or death may dissuade them from treatment of latent infection. Depending on the drug, less serious adverse reactions include rashes, gastrointestinal upsets, fever, and joint pain (ATS/CDC, 2000b). Some of these reactions may be bothersome enough to prompt a switch to another drug—or abandonment of therapy altogether. As with other treatments, careful communication of risks