A four-year follow-up of patients with quiescent pulmonary tuberculosis at the end of a year of chemotherapy with twice-weekly isoniazid plus streptomycin or daily isoniazid plus pas

Comparative pharmacokinetics and pharmacodynamics of the rifamycin antibacterials

The rifamycin antibacterials, rifampicin (rifampin), rifabutin and rifapentine, are uniquely potent in the treatment of patients with tuberculosis and chronic staphylococcal infections. Absorption is variably affected by food; the maximal concentration of rifampicin is decreased by food, whereas rifapentine absorption is increased in the presence of food. The rifamycins are well-known inducers of enzyme systems involved in the metabolism of many drugs, most notably those metabolised by cytochrome P450 (CYP) 3A. The relative potency of the rifamycins as CYP3A inducers is rifampin > rifapentine > rifabutin; rifabutin is also a CYP3A substrate. The antituberculosis activity of rifampicin is decreased by a modest dose reduction from 600 to 450mg. This somewhat surprising finding may be due to the binding of rifampicin to serum proteins, limiting free, active concentrations of the drug. However, increasing the administration interval (after the first 2 to 8 weeks of therapy) has little effect on the sterilising activity of rifampicin, suggesting that relatively brief exposures to a critical concentration of rifampicin are sufficient to kill intermittently metabolising mycobacterial populations. The high protein binding of rifapentine (97%) may explain the suboptimal efficacy of the currently recommended dose of this drug. The toxicity of rifampicin is related to dose and administration interval, with increasing rates of presumed hypersensitivity with higher doses combined with administration frequency of once weekly or less. Rifabutin toxicity is related to dose and concomitant use of CYP3A inhibitors. The rifamycins illustrate the complexity of predicting the pharmacodynamics of treatment of an intracellular pathogen with the capacity for dormancy.

The value of in vitro drug activity and pharmacokinetics in predicting the effectiveness of antimycobacterial therapy: a critical review

Marked increases in case rates of drug-resistant tuberculosis and nontuberculous mycobacterial infections have brought renewed urgency to the development of new treatment regimens for mycobacterial infections. Preclinical data, such as in vitro measures of drug activity and pharmacokinetics, are used in the design of new treatment regimens. This review surveys the extensive published clinical experience concerning the treatment of drug-susceptible tuberculosis to evaluate the use of these preclinical measures in predicting clinical outcomes of antimycobacterial therapy. In vitro measures of drug activity predict the potency of a drug to prevent the emergence of resistance to other antimycobacterial drugs but do not predict the sterilizing activity of a drug or the activity of drug combinations. In vitro measures of drug activity do not allow reliable predictions of the level at which an organism should be considered resistant. Assays of drug penetration in tissues and activity against intracellular bacilli add modestly to the predictive value of in vitro measures of drug activity but still do not predict sterilizing activity. In contrast, animal models of tuberculosis have predicted relative drug potency (including sterilizing activity), the efficacy of multidrug regimens, and the duration of therapy needed. Despite pharmacokinetic parameters that would suggest the need for multiple doses per day, all of the first-line antituberculous drugs are active when given as infrequently as twice weekly. It is difficult to predict the efficacy of therapy for an intracellular pathogen that has the capacity for dormancy. Better in vitro models are needed, particularly ones that predict sterilizing activity.

False-positive cultures of Mycobacterium tuberculosis

During a single week in April 1982, cultures for Mycobacterium tuberculosis were reported positive from nine patients who did not appear clinically to have active infection. Each of the patients had only one positive culture out of multiple specimens cultured. At the time of investigation, five specimens were available and were found to be all of the same phage type which strongly suggested cross-contamination. Four patients received antituberculosis chemotherapy. In one year of follow-up of the five who did not receive chemotherapy, none developed clinical disease. The contamination was probably due to faulty laboratory technique, but the source of the contaminant is uncertain. This investigation suggests that patients without clinical evidence of active infection and with isolated positive cultures for Mycobacterium tuberculosis should be carefully evaluated before they are subjected to a prolonged, potentially toxic, and expensive course of chemotherapy.

Ethambutol plus isoniazid for the treatment of pulmonary tuberculosis--a controlled trial of our regimens

A controlled clinical trial of 4 regimens was undertaken in patients with bacteriologically positive, newly-diagnosed pulmonary tuberculosis. The regimens were: ethambutol 15 mg/kg plus isoniazid 400 mg, daily (E7H7); ethambutol 45 mg/kg plus isoniazid 15 mg/kg, twice a week (E2H2); ethambutol 90 mg/kg plus isoniazid 15 mg/kg, once a week plus isoniazid 15 mg/kg, mid-way between the weekly doses (E1H2); and ethambutol 90 mg/kg plus isoniazid 15 mg/kg, once a week (E1H1). All patients received streptomycin 1 g plus ethambutol 25 mg/kg body-weight plus isoniazid 400 mg daily for the first 2 weeks. The total duration of treatment was 12 months for all patients. There were 484 patients admitted to the study. After excluding 60 (41 with initial drug resistance to isoniazid), there remain 424 patients (107 E7H7, 101 E2H2, 107 E1H2, 109 E1H1) in the main analyses. The pretreatment characteristics of the 4 groups were broadly similar. A favourable response at 12 months was observed in 96%, 88%, 93% and 75% of patients respectively: the differences between the E1H1 regimen and the other 3 regimens were all significant (P less than or equal to 0.03) as was that between the E7H7 and E2H2 regimens (P = 0.05). Among the slow inactivators of isoniazid, the proportions with a favourable response at one year were similar in the 4 groups (range 95--91%). However, among the rapid inactivators, the proportion with a favourable response in the E1H1 group was only 57%. There was suggestive evidence that the E1H2 regimen was superior to the E2H2 regimen. Of the patients with bacteriologically quiescent disease at 1 year, approximately a half, at random, had no further chemotherapy and were followed up for a 4-year period. Bacteriological relapse requiring retreatment occurred in 15% of 54 E7H7 patients, 26% of 38 E2H2, 33% of 43 E1H2 and 54% of 37 E1H1 patients, a significant difference (P less than 0.001). A final evaluation of long-term (5-year) favourable response achieved by the 12-month regimens was 83% for the E7H7, 63% for the E2H2, 63% for the E1H2 and 33% for the E1H1 regimens. In general, the regimens were well tolerated and the incidence of adverse reactions to the drugs was low. Of the 424 patients, 6 (1.4%) developed a visual disturbance during the year of chemotherapy.

Quality control in tuberculosis bacteriology. 2. The origin of isolated positive cultures from the sputum of patients in four studies of short course chemotherapy in Africa

During intensive bacteriological follow-up of 2123 patients who had received short course chemotherapy regimens in 4 controlled clinical trials in Africa and had not had a bacteriological relapse, 405 isolated positive cultures were obtained from 37 429 sputum specimens in 3 East African laboratories. These cultures might have arisen as a result of clerical error, of transfer of bacilli from positive to negative specimens in the laboratory or from the lesions of the patients. Clerical error in the labelling of specimens or the recording of results did not seem a frequent cause, since isolated positive cultures contained many fewer colonies than cultures from other positive specimens being processed at the same time. Several of evidence suggested that some isolated positive cultures arose from the lesions of patients: a decrease in their incidence occurred in successive time periods after chemotherapy; the number of isolated positives per patient departed significantly from the Poisson distribution; they were more often drug resistant than other cultures processed at the time; positive cultures were obtained less frequently from known autoclaved specimens inserted among the the study specimens than from the study specimens themselves; no association was found between the incidence of isolated positive and of specimens containing numerous viable M. tuberculosis being processed at the same time. Nevertheless some of these cultures probably arose by transfer in the laboratory, since the rates at which transfer were known to occur differed in the 3 laboratories and corresponded to the rates of obtaining isolated positive cultures.

Quality control in tuberculosis bacteriology. 1. Laboratory studies on isolated positive cultures and the efficiency of direct smear examination

Sputum specimens unlikely to contain M. tuberculosis or specimens artificially created as methylcellulose/egg solution were autoclaved and distributed in batches together with sputum specimens containing viable M. tuberculosis marked with an unusual drug-sensitivity pattern. These specimens were prepared in 1 East African laboratory, divided into aliquots and examined by direct smear and culture in 3 East African laboratories. Independent batches were also prepared and cultured in London. Scanty colonies of M. tuberculosis, always with the characteristic marker sensitivity pattern, were obtained from a proportion of the autoclaved specimens, ranging from 0% of 825 specimens in London to 1.3% of 2165 specimens in Kampala. Transfer of bacilli from positive to negative specimens could therefore account for some of the isolated positive cultures that occur in clinical trials. The occurrence of transfer seemed to be related more to the quality of the technician than to the detail of the technical methods. The African laboratories could be graded in their overall efficiency in smear and culture examination.

An investigation of the accuracy of the home address given by patients in an urban community in South India

Studies were undertaken in three tuberculosis clinics in Madras, a large Indian city with a good civic organization, to assess the accuracy of address recorded routinely by registry clerks at the patient's first clinic attendance. The accuracy was poor, with 20% to 30% of the letters posted not reaching the patients. It was appreciably improved, by 10% to 20%, by supplementing the clerk's efforts with questioning by a motivated, experienced health visitor. An address card, a card on which the patient's address was recorded by the local postman or a literate neighbour, relative or friend, was returned by 90% to 94% of the patients, and the accuracy of addresses was found to be at least as good as that obtained with the health visitor. Even when all three sources of information were considered, the patient's home could not be traced in 3% of cases and was found with difficulty in 4%.

Transmission of tubercle bacilli: The effects of chemotherapy

The important differences in the infectivity of the various forms of tuberculosis can be explained by quantitative data concerning the behaviour of the tubercle bacillus in man and the number of bacilli in the lesions and sputum. Patients in whom tubercle bacilli can be detected by direct examination of the sputum smear are the main sources of transmission. Moreover the individuals infected by them break down more often with the disease. In the individual patient, the use of antibacterial drugs completely changes the natural history of the disease: not only do patients no longer die but they are cured; their period of infectivity is considerably reduced, relapses are avoided, chronicity disappears. The drugs used prophylactically in individuals of high risk groups prevent development of the disease. The impact of chemotherapy is reflected by a two-to-three-fold increase in the speed of decline of the risk of infection, a decline which had started before the introduction of the drugs. While patients given the right combination of drugs lose their infectivity in a few weeks (probably most often in less than two weeks), treatment must of course be continued much longer and regularly in order to ensure the maintenance of conversion and the absence of relapse. This stresses the importance of providing means to ensure the taking of the drugs by all patients. The future reduction of transmission will essentially depend on the maintenance of an adequate system ensuring the early diagnosis and correct treatment of cases, which will inevitably continue to appear among the already infected portion of the population. Epidemiological surveillance is mandatory as well as the surveillance of the delivery of services, particularly of the quality of diagnosis and therapeutic services. The roles of public health authorities and perhaps still more that of the practising physician, specialized and not specialized, remain considerable both from an epidemiological point of view and from the point of view of the relief of all the suffering still created by the disease.

A tuberculosis treatment survey in Singapore: results at five-years

A National Tuberculosis Treatment Survey was instituted in the Republic of Singapore in 1969 with the aim of evaluating the Tuberculosis Treatment Services in Singapore. This five-year follow-up study of the 1969 survey was based on the assessment of the first 1000 consecutive patients who were registered for treatment during the year. Two hundred and forty-six cases were excluded for various reasons, leaving 754 cases for analysis. At the end of 5 years, only 2 (0.3%) were culture positive, 677 (89.8%) were culture negative, 48 cases (6.4%) had died from tuberculosis and 27 cases (3.6%) were lost. The most notable factor which influenced bacteriological positivity was lack of co-operation leading to interruption of chemotherapy. It is concluded that with an efficient organisation highly satisfactory results can be achieved by routine treatment services and prolonged observation of adequately treated patient is not necessary.

Potentially serious side-effects of high-dose twice-weekly rifampicin

Daily rifampicin in a single dose of 600 mg, combined with other drugs, usually streptomycin and isoniazid, was given to forty-nine patients for 3 months. It was planned to continue for another 15 months with twice-weekly rifampicin 1200 mg plus isoniazid 900 mg, but the high incidence of side effects led to cessation of the intermittent regimen when only two patients had completed 18 months.

Though there was no serious problem with daily treatment, eleven patients (22%) were unable to continue rifampicin on the intermittent regimen. In eight (16%) a pyrexial syndrome occurred. In one of these patients there was also temporary renal failure and in another, precipitous thrombocytopenia led to epistaxis and bleeding into the tongue and lips. Symptomless thrombocytopenia developed in two other patients, making three cases (6%) of thrombocytopenia in all.

In sixteen (33%) of the forty-nine patients antibodies to rifampicin were detected in the blood. Side-effects occurred in nine (56%) of these, including the three developing thrombocytopenia, but in only two (6%) of the thirty-three patients with no antibodies detected. This association of toxic reactions with antibodies is highly significant (P < 0·001).

Potentially serious side effects of high-dose twice-weekly rifampicin

Daily rifampicin in a single dose of 600 mg, combined with other drugs, usually streptomycin and isoniazid, was given to 49 patients for three months. It was planned to continue for another 15 months with twice-weekly rifampicin 1,200 mg plus isoniazid 900 mg, but the high incidence of side effects led to cessation of the intermittent regimen when only two patients had completed 18 months.Though there was no serious problem with daily treatment 11 patients (22%) were unable to continue rifampicin on the intermittent regimen. In 8 (16%) a pyrexial syndrome occurred. In one of these patients there was also temporary renal failure, and in another precipitous thrombocytopenia led to epistaxis and bleeding into the tongue and lips. Symptomless thrombocytopenia developed in two other patients, making three cases (6%) of thrombocytopenia in all.In 16 (33%) of the 49 patients antibodies to rifampicin were detected in the blood. Side effects occurred in 9 (56%) of these, including the three developing thrombocytopenia, but in only 2 (6%) of the 33 patients with no antibodies detected. This association of toxic reactions with antibodies is highly significant (P<0.001).