[Effectiveness and problems of PZA-containing 6-month regimen for the treatment of new pulmonary tuberculosis patients]

M Wada
Kekkaku: [Tuberculosis] 2001, 76 (1): 33-43
One third of the world population has been infected with Mycobacterium tuberculosis, and the number of tuberculosis will increase worldwide without more effective programs of tuberculosis control. Despite of the presence of very potent anti-tuberculosis drugs the global tuberculosis situation is still very serious, and such gloomy feature are caused, at least partly, by the failures in the treatment of tuberculosis. The most important factor for the failure in chemotherapy is incompliance of the patients to the regimens. History of the chemotherapy of tuberculosis can be said as the history of the efforts to reduce such defaulters. Modern chemotherapy of tuberculosis has started from the discovery of streptomycin. Streptomycin monotherapy could improve temporally symptoms and bacteriological status, but could not cure the patients with moderately advanced pulmonary tuberculosis because of the emerge of drug-resistant tuberculosis. This problem was overcome by combining use of para-aminosalicylate and/or isoniazid developed later on. About 97% of patients with pulmonary tuberculosis became bacteriologically quiescent by the 12 months of streptomycin, para-aminosalicylate and isoniazid. Since 1950s through 1970s three drug combination of streptomycin, para-aminosalicylate and isoniazid had been the standard regimen for the treatment of tuberculosis. By the introduction of rifampicin, the duration of chemotherapy could be shortened to 9 months. Subsequent to the successful animal experiments carried out by Grosset which demonstrated that the addition of pyrazinamide for initial 2 months to the standard two-drug combination (isoniazid and rifampicin) could remarkably shorten the duration of chemotherapy, many clinical trials have been done all over the world to compare the efficacy and safety of pyrazinamide-containing intensified short-course regimen with those of standard regimen without pyrazinamide. Sputum negative conversion rates after 2 months of treatment with PZA-regimen was 70-95%, and the relapse rates after the completion of the treatment course were less than 4%. The incidence of adverse events was less than 4%. The pyrazinamide-containing 6 months short-course regimens has been established as a new standard regimen for the initial treatment of pulmonary tuberculosis worldwide. But, in Japan, this regimen had not been adapted as the standard until April 1996 because of undue fear for high incidence of liver toxicity induced by pyrazinamide. However, in many clinical trials carried out in various parts of the world did not show any causative relationship between the higher incidence of liver toxicity and pyrazinamide. According to our own experience in Fukujuji Hospital, Japan Anti-tuberculosis Association, the frequency of drug induced hepatitis among 632 patients with normal liver function at the onset of chemotherapy was 7.9 percent (50/632) when treated with pyrazinamide-containing regimens, and was similar to that among 412 patients treated with other regimens without pyrazinamide (7.3 percent 30/412). These figures were higher than those reported in the literatures. The risk factors of drug-induced hepatitis so far reported included elderly, positive hepatitis C virus antibody, low serum albumin and so on. Such known risk factors could not wholly explain the higher rate of liver dysfunction observed among our Japanese patients. We have examined additional factors affecting the frequency of drug-induced hepatitis in our hospital, and noticed that the past history of gastrectomy and over-dosing of isoniazid (> or = 7.5 mg/kg) and/or pyrazinamide (> or = 30 mg) were relating to the higher incidence of drug-induced hepatitis. Another important finding is that the relapse rate among patients complicated with diabetes mellitus is significantly higher than that of the patients without diabetes mellitus (6.31/100 person-years vs 0.90/100 person-years, P < 0.001). Further research will need whether the patients complicated with diabetes mellitus have any immunological deficient to kill Mycobacterium tuberculosis. WHO, CDC and ATS recommended that 4-drug regimen including pyrazinamide for the initial treatment of all cases of tuberculosis. Considering that the incidence of initial resistance to isoniazid is 4.4% in Japan, we should start to treat all cases of newly diagnosed tuberculosis with pyrazinamide-containing regimen (isoniazid, rifampicin, pyrazinamide, plus streptomycin or ethambutol). To do this, further studies on the risk factors of drug-induced hepatitis are urgently needed.

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