Efficacy of rifabutin in the treatment of disseminated infection due to Mycobacterium avium complex. The Rifabutin Treatment Group

Exploring the synthetic approaches and clinical prowess of established macrocyclic pharmaceuticals

Macrocyclic compounds, characterized by cyclic structures, often originate from either modified forms of unicyclic canonical molecules or natural products. Within the field of medicinal chemistry, there has been a growing fascination with drug-like macrocycles in recent years, primarily due to compelling evidence indicating that macrocyclization can significantly influence both the biological and physiochemical properties, as well as the selectivity, when compared to their acyclic counterparts. The approval of contemporary pharmaceutical agents like Lorlatinib underscore the notable clinical relevance of drug-like macrocycles. Nonetheless, the synthesis of these drug-like macrocycles poses substantial challenges, primarily stemming from the complexity of ring-closing reactions, which are inherently dependent on the size and geometry of the bridging linker, impacting overall yields. Nevertheless, macrocycles offer a promising avenue for expanding the synthetic toolkit in medicinal chemistry, enabling the creation of bioactive compounds. To shed light on the subject, we delve into the clinical prowess of established macrocyclic drugs, spanning various therapeutic areas, including oncology, and infectious diseases. Case studies of clinically approved macrocyclic agents illustrate their profound impact on patient care and disease management. As we embark on this journey through the world of macrocyclic pharmaceuticals, we aim to provide a comprehensive overview of their synthesis and clinical applications, shedding light on the pivotal role they play in modern medicine.

Role of ethambutol and rifampicin in the treatment of Mycobacterium avium complex pulmonary disease

Background

A three-drug regimen (macrolide, ethambutol, and rifampicin) is recommended for the treatment of Mycobacterium avium complex pulmonary disease (MAC-PD). Although macrolide has proven efficacy, the role of ethambutol and rifampicin in patients without acquired immune deficiency syndrome is not proven with clinical studies. We aimed to clarify the roles of ethambutol and rifampicin in the treatment of MAC-PD.

Methods

Patients treated for MAC-PD between March 1st, 2009 and October 31st, 2018 were reviewed retrospectively. Rates of culture conversion, microbiological cure, treatment failure, and recurrence were compared according to the maintenance (≥6 months) of ethambutol or rifampicin with macrolide.

Results

Among the 237 patients, 122 (51.5%) maintained ethambutol and rifampicin with macrolide, 58 (24.5%) maintained ethambutol and macrolide, 32 (13.5%) maintained rifampicin and macrolide, and 25 (10.6%) maintained macrolide only. Culture conversion was reached for 190/237 (80.2%) patients and microbiological cure was achieved for 129/177 (72.9%) who completed the treatment. Treatment failure despite ≥12 months of treatment was observed in 66/204 (32.4%), and recurrence was identified in 16/129 (12.4%) who achieved microbiological cure. Compared with maintenance of macrolide only, maintenance of ethambutol, rifampicin or both with macrolide were associated with higher odds of culture conversion [odds ratio (OR), 95% confidence interval (CI): 18.06, 3.67–88.92; 15.82, 2.38–105.33; and 17.12, 3.93–74.60, respectively]. Higher odds of microbiological cure were associated with maintenance of both ethambutol and rifampicin with macrolide (OR, 95% CI: 5.74, 1.54–21.42) and macrolide and ethambutol (OR, 95% CI: 5.12, 1.72–15.24) but not macrolide and rifampicin. Maintenance of both ethambutol and rifampicin with macrolide was associated with lower odds of treatment failure (OR, 95% CI: 0.09, 0.01–0.53) compared with macrolide only, while maintenance of one of these with macrolide was not. Maintenance of both ethambutol and rifampicin or one of these with macrolide did not decrease the probability of recurrence when compared with macrolide only.

Conclusions

Maintenance (≥6 months) of ethambutol and rifampicin with macrolide was associated with the most favorable treatment outcomes among patients with MAC-PD. Given the association between ongoing ethambutol use and microbiological cure, clinicians should maintain ethambutol unless definite adverse events develop.

Rifabutin: where do we stand in 2016?

Rifabutin is a spiro-piperidyl-rifamycin structurally closely related to rifampicin that shares many of its properties. We attempted to address the reasons why this drug, which was recently recognized as a WHO Essential Medicine, still had a far narrower range of indications than rifampicin, 24 years after its launch. In this comprehensive review of the classic and more recent rifabutin experimental and clinical studies, the current state of knowledge about rifabutin is depicted, relying on specific pharmacokinetics, pharmacodynamics, antimicrobial properties, resistance data and side effects compared with rifampicin. There are consistent in vitro data and clinical studies showing that rifabutin has at least equivalent activity/efficacy and acceptable tolerance compared with rifampicin in TB and non-tuberculous mycobacterial diseases. Clinical studies have emphasized the clinical benefits of low rifabutin liver induction in patients with AIDS under PIs, in solid organ transplant patients under immunosuppressive drugs or in patients presenting intolerable side effects related to rifampicin. The contribution of rifabutin for rifampicin-resistant, but rifabutin-susceptible, Mycobacterium tuberculosis isolates according to the present breakpoints has been challenged and is now controversial. Compared with rifampicin, rifabutin's lower AUC is balanced by higher intracellular penetration and lower MIC for most pathogens. Clinical studies are lacking in non-mycobacterial infections.

EDP-420, a bicyclolide (bridged bicyclic macrolide), is active against Mycobacterium avium

Infection caused by Mycobacterium avium complex (MAC) is common in patients with immunosuppression, such as AIDS, and deficiencies of gamma interferon and interleukin-12, as well as patients with chronic lung diseases. Treatment of MAC disease is limited since few drugs show in vivo activity. We tested a new bridged bicyclic macrolide, EDP-420, against MAC in vitro and in beige mice. EDP-420 was inhibitory in vitro at a concentration ranging from 2 to 8 microg/ml (MIC(50) of 4 microg/ml and MIC(90) of 8 microg/ml). In macrophages, EDP-420 was inhibitory at 0.5 microg/ml, suggesting that the drug concentrates intracellularly. Mice infected with macrolide-susceptible MAC strain 101 were given 100 mg of EDP-420/kg of body weight daily for 4 weeks and showed a significant reduction in the number of bacteria in both liver and spleen which was greater than the reduction observed with clarithromycin treatment at the same dose (P < 0.05). However, macrolide-resistant MAC 101 did not respond to EDP-420 treatment. A combination of EDP-420 with mefloquine was shown to be indifferent; mefloquine alone was active against macrolide-resistant MAC. The frequency of resistance to EDP-420 in MAC 101 was 10(-9), which is significantly less than the emergence of resistance to clarithromycin, approximately 10(-7) (P < 0.05). Further evaluation of EDP-420 in the treatment of MAC disease is warranted.

[Usefulness of chemotherapy associated with surgery in the management of nontuberculous mycobacterial adenitis]

BACKGROUND

In recent years, lymphadenitis caused by atypical mycobacteria (also called nontuberculous mycobacteria [NTMB] or, more recently, environmental) have played a significant role in the differential diagnosis of adenitis in non-immunocompromised children.

OBJECTIVES

To describe the clinical and pathological findings in childhood NTMB adenitis and study the possible usefulness of antimicrobial therapy in addition to surgery.

METHODS

We present eight cases of neck lymphadenitis occurring over a 5-year period. All of the children received combined chemotherapy, and six also underwent surgery. Of the two remaining patients, the parents of one child refused surgery and a watchful approach was adopted in the other.

RESULTS

Complete clinical recovery was achieved in all patients except one who did not undergo surgery.

CONCLUSIONS

Prolonged administration of two antibiotics (of which one must be clarithromycin) in addition to surgery was well-tolerated and could be useful in patients with NTMB neck lymphadenitis.

Mycobacterium avium complex in patients with HIV infection in the era of highly active antiretroviral therapy

Disseminated Mycobacterium avium complex (MAC) infection is a common complication of late-stage HIV-1 infection. Since the advent of highly active antiretroviral therapy (HAART), the rate of MAC infection has declined substantially, but patients with low CD4 cell counts remain at risk. Among patients in the Johns Hopkins cohort with advanced HIV disease, the proportion developing MAC has fallen from 16% before 1996 to 4% after 1996, with a current rate of less than 1% per year. Factors associated with developing MAC include younger age, no use of HAART, and enrollment before 1996. Prophylaxis with azithromycin or clarithromycin is recommended for all patients with CD4 counts less than 50 cells/mL. Optimum treatment for disseminated MAC includes clarithromycin and ethambutol, and another investigation suggests that the addition of rifabutin might reduce mortality. Both prophylaxis and treatment of disseminated MAC can be discontinued in patients who have responded to HAART, and specific guidelines for withdrawing treatment have been published. Although HAART has altered the frequency and outcome of MAC infection, it remains an important complication of AIDS.

Activity of capuramycin analogues against Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium intracellulare in vitro and in vivo

OBJECTIVES

The antimycobacterial activities of RS-112997, RS-124922 and RS-118641, three capuramycin analogues that inhibit phospho-N-acetylmuramyl-pentapeptide translocase, were tested against clinical isolates of Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium intracellulare.

METHODS AND RESULTS

MICs were determined by the broth microdilution method using a modified Middlebrook 7H9 broth. RS-118641 was the most potent compound overall. The MIC50/90 (mg/L) results for RS-118641 were: M. tuberculosis, 1/2; multidrug-resistant (MDR) M. tuberculosis, 0.5/2; M. avium, 4/8; and M. intracellulare, 0.06/0.5. No statistically significant differences in MIC distributions were observed between non-MDR and MDR M. tuberculosis for any of the capuramycin analogues tested. In order to evaluate the therapeutic efficacy of RS-112997 and RS-124922 in a murine lung model of tuberculosis, both compounds were administered intranasally at 0.1 or 1 mg/mouse/day for 12 days. The mycobacterial load in the lungs was significantly lower in all treatment groups than in the untreated controls. Additional experiments were performed to evaluate the therapeutic efficacy of the three compounds against the M. intracellulare infection in mice. All compounds were administered intranasally at 0.1 mg/mouse/day for 21 days. The mycobacterial load in the lungs was significantly lower in all treatment groups than in the untreated controls.

CONCLUSIONS

These results suggest that capuramycin analogues exhibit strong antimycobacterial potential and should be considered for further evaluation in the treatment of M. tuberculosis and M. avium-M. intracellulare complex infections in humans.

Telithromycin is active against Mycobacterium avium in mice despite lacking significant activity in standard in vitro and macrophage assays and is associated with low frequency of resistance during treatment

The activity of telithromycin, a new ketolide, was evaluated in vitro and in vivo against Mycobacterium avium complex (MAC) strains. The MIC of telithromycin for several M. avium isolates obtained from the blood of AIDS patients ranged from 16 to >128 microg/ml (MIC at which 90% of isolates are inhibited, >128 microg/ml), and the compound did show activity in the macrophage system at concentrations greater than 8 or 16 microg/ml, but this was dependent on the MAC strain used. Telithromycin was then administered to mice infected with MAC strain 101 for 4 weeks at doses of 100, 200, or 400 mg/kg of body weight/day. Treatment with 100 and 200 mg/kg/day was bacteriostatic, but at 400 mg/kg/day telithromycin was bactericidal for MAC strains. The frequency of the emergence of resistance to telithromycin was low despite prolonged usage (12 weeks). This study demonstrates that telithromycin is active in vivo against MAC and warrants further evaluation.

Tolerance and pharmacokinetic interactions of rifabutin and azithromycin

This multicenter study evaluated the tolerance and potential pharmacokinetic interactions between azithromycin and rifabutin in volunteers with or without human immunodeficiency virus infection. Daily dosing with the combination of azithromycin and rifabutin was poorly tolerated, primarily because of gastrointestinal symptoms and neutropenia. No significant pharmacokinetic interactions were found between these drugs.

Mefloquine is active in vitro and in vivo against Mycobacterium avium complex

Despite the development of several agents, new classes of antimicrobials with activity against the Mycobacterium avium complex (MAC) are needed. Based on a broad screening of compounds, we found that mefloquine has MICs of 8 to 16 microg/ml by the BACTEC system and 16 microg/ml by broth microdilution for five MAC strains tested. An expansion of the screening with broth microdilution to 24 macrolide-susceptible strains and 6 macrolide-resistant strains determined that the MIC for all strains was 16 microg/ml. To determine the intracellular activity of mefloquine, U937 macrophage monolayers infected with MAC strain 101, 100, or 109 (serovars 1, 8, and 4) were treated with mefloquine daily, and the number of intracellular bacteria was quantitated after 4 days. Significant growth inhibition against the three MAC strains at concentrations greater than or equal to 10 microg/ml (P < 0.05) was obtained. Due to the encouraging anti-MAC activity, in vivo efficacy in beige mice infected with MAC 101 was evaluated. Animals were treated with 5, 10, 20, or 40 mg/kg of body weight daily, three times a week, twice a week, or once a week for 4 weeks, and bacteria were quantitated in blood, liver, and spleen. No toxicity was observed with any of the treatment regimens. Mefloquine had borderline bactericidal activity at a dosage of 40 mg/kg daily (100% inhibition compared with a 1-week control), and significant inhibition was obtained at dosages of 40 mg/kg three times a week, as well as 20 mg/kg daily. Mefloquine had no significant effect on bacteremia. A combination of mefloquine and ethambutol showed significantly more activity than did either drug alone in liver, spleen, and blood; the combination was also bactericidal against M. avium. Although safety is a potential concern, mefloquine and related compounds deserve further investigation as anti-MAC therapies.

[Disseminated infection with Mycobacterium avium complex (MAC) in HIV infection]

EPIDEMIOLOGY

Disseminated MAC-infection is one of the most frequent opportunistic infections occurring in HIV-infected patients. Severely immunocompromised patients with CD4-counts < 50/microliter are at greatest risk for the disease. Survival of untreated infection is very poor (5 to 6 months). With therapy survival is prolonged by about 4 months. CLINICAL PRESENTATION AND DIAGNOSTIC PROCEDURES: The leading symptom of MAC-infection is fever eventually accompanied by weight lost, night sweats, enlarged lymph nodes, hepatosplenomegaly, abdominal pain and anemia. Blood cultures are very sensitive and the most appropriate examination. Other diagnostic procedures include bone marrow cultures, biopsies of the gastrointestinal tract, lymph nodes and the liver. Detection of MAC in sputum and stool samples only proves colonisation but not dissemination. However, colonisation of the gastrointestinal tract frequently precedes disseminated disease.

THERAPY

Combination of clarithromycin, rifabutin and ethambutol has proven to be the most efficacious therapy and therefore has to be considered as standard therapy for disseminted MAC-infection. Problems most frequently encountered with this medication include uveitis (rifabutin) gastrointestinal disturbances (clarithromycin) and leucopenia (rifabutin) as well as drug interactions with protease-inhibitors (rifabutin).

PROPHYLAXIS

Clarithromycin, rifabutin and azithromycin given as primary prophylaxis can diminish the risk of disseminated MAC-infection. Although a survival benefit has been seen with clarithromycin, primary prophylaxis of MAC-infection is not standard care in many centers. Reasons to withhold MAC-prophylaxis include lower incidence rates in some countries as well as possible side effects and drug interactions.

CONCLUSION

Disseminated MAC-infection is a frequent opportunistic disease in HIV-infected persons who are severely immunocompromised. Antibiotic combination therapy with clarithromycin, rifabutin and ethambutol improves clinical symptoms and survival. Primary prophylaxis with different regimens is efficacious but the specific epidemiologic situation in each country has to be considered.

Treatment and prophylaxis of disseminated Mycobacterium avium complex in HIV-infected individuals

OBJECTIVE

To review the pathophysiology, epidemiology, treatment, and prophylaxis of disseminated Mycobacterium avium complex (MAC) infection in HIV-infected individuals.

DATA SOURCES

A MEDLINE (January 1966-July 1997) and AIDSLINE (January 1980-July 1997) search of basic science articles pertinent to the MAC infection in HIV-infected patients.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Pertinent information, as judged by the authors, was selected for discussion.

DATA SYNTHESIS

The organism, epidemiology, and pathophysiology of disseminated MAC are discussed for background. A review of clinical trials for the treatment and prophylaxis of disseminated MAC are presented, along with unresolved issues concerning these topics.

CONCLUSIONS

The incidence of disseminated MAC has increased dramatically with the AIDS epidemic. The infection can lead to increased morbidity and mortality in HIV-infected patients. Treatment regimens for patients with a positive culture for MAC from a sterile site should include two or more drugs, including clarithromycin. Prophylaxis against disseminated MAC should be considered for patients with a CD4 cell count of less than 50/mm3.

Evaluation of a disk diffusion method for determining susceptibility of Mycobacterium avium complex to clarithromycin

We evaluated an agar disk diffusion method for determining the susceptibility of Mycobacterium avium complex to clarithromycin. Isolates were inoculated onto the surface of a Middlebrook 7H11 plate, followed by the application of a 15-microgram clarithromycin disk. Zone sizes were read after 5-7 days of incubation. Zone sizes had a bimodal distribution; 40 isolates (10%) had no zone of inhibition, whereas the zone sizes for the remaining isolates ranged from 11 to 60 mm. Most isolates (37/40) having no zone of inhibition came from patients who had been treated previously with clarithromycin. Fifty-one isolates were also tested for clarithromycin susceptibility using a microdilution broth method. Defining susceptibility as a zone size of > 10 mm, disk diffusion test results agreed with the results by the microdilution broth method for 50 of 51 (98%) isolates tested by both methods. Agar disk diffusion is a promising method for the determination of clarithromycin susceptibility testing for M. avium complex.

Prophylaxis for disseminated Mycobacterium avium complex (MAC) infection in patients with AIDS: a cost-effectiveness analysis

OBJECTIVE

To determine the effectiveness and costs of prophylaxis for disseminated Mycobacterium avium complex (MAC) infection in patients with AIDS.

DESIGN

A decision analysis model was constructed to compare rifabutin (300 mg/day), azithromycin (1200 mg/week), and clarithromycin (500 mg twice per day) with no prophylaxis. Sensitivity analysis was done on all model parameters, including initial CD4 count for beginning prophylaxis.

SETTING

The setting was hypothetical for the cost-effectiveness model. Clinical data were taken from published prospective randomized controlled trials.

MAIN OUTCOME MEASURES

Outcomes were measured in terms of projected life expectancy, quality-adjusted life expectancy, direct medical costs, and cost-effectiveness in U.S. dollars per quality-adjusted life-year saved ($/QALY).

RESULTS

For patients with AIDS and those having CD4 counts <75 cells/mm3, azithromycin, clarithromycin, and rifabutin prophylaxis increased lifetime per person MAC-related costs by $994, $2,117, and $2,185 U.S., respectively. Quality-adjusted life expectancy increased from 1.6068 QALYs to between 1.6186 and 1.6255 QALYs. The cost-effectiveness ratios were $58,200, $116,000, and $179,100/QALY saved for azithromycin, clarithromycin, and rifabutin prophylaxis, respectively, each compared with no prophylaxis. Results were most dependent on the annual cost of prophylaxis, the initial CD4 count when starting prophylaxis, and any survival benefit with prophylaxis. For each type of prophylaxis, strategies beginning with CD4 counts <25 or 50 cells/mm3 were substantially more cost-effective than those beginning in patients with higher CD4 counts.

CONCLUSIONS

MAC prophylaxis is likely to cost society an additional $99 to $219 million U.S. per 100,000 patients treated. In the context of Centers for Disease Control and Prevention (CDC) recommendations to use prophylaxis in patients with CD4 counts <75 cells/mm3, azithromycin represents the best value and is most cost-effective when used in patients with CD4 counts <25 cells/mm3.

Diagnosis and treatment of disease caused by nontuberculous mycobacteria. This official statement of the American Thoracic Society was approved by the Board of Directors, March 1997. Medical Section of the American Lung Association

Diagnostic criteria of nontuberculous mycobacterial lung disease in HIV-seropositive and -seronegative hosts. The following criteria apply to symptomatic patients with infiltrate, nodular or cavitary disease, or a high resolution computed tomography scan that shows multifocal bronchiectasis and/or multiple small nodules. A. If three sputum/bronchial wash results are available from the previous 12 mo: 1. three positive cultures with negative AFB smear results or 2. two positive cultures and one positive AFB smear B. If only one bronchial wash is available: 1. positive culture with a 2+, 3+, or 4+ AFB smear or 2+, 3+, or 4+ growth on solid media C. If sputum/bronchial wash evaluations are nondiagnostic or another disease cannot be excluded: 1. transbronchial or lung biopsy yielding a NTM or 2. biopsy showing mycobacterial histopathologic features (granulomatous inflammation and/or AFB) and one or more sputums or bronchial washings are positive for an NTM even in low numbers.

COMMENTS

these criteria fit best with M. avium complex, M. abscessus, and M. kansasii. Too little is known of other NTM to be certain how applicable these criteria will be. At least three respiratory samples should be evaluated from each patient. Other reasonable causes for the disease should be excluded. Expert consultation should be sought when diagnostic difficulties are encountered.

TB or not TB?

These 3 cases illustrate what we believe to be unusual presentations of tuberculosis. In no case was there conclusive proof of infection with Mycobacterium tuberculosis using histological, microbiological or radiological techniques. All were treated empirically with anti-tuberculous medication, with complete recovery. With the re-emergence of tuberculosis, there may be a rise in such cases, and the importance of their recognition and empirical treatment is discussed.

Nontuberculous mycobacterial infections

The acquired immunodeficiency syndrome (AIDS) pandemic has led to greater understanding and respect for the pathogenic potential of non-tuberculous mycobacteria. Mycobacterium avium complex (MAC) has emerged as the most common systemic bacterial infection in AIDS, causing debilitating disseminated disease in late-stage HIV-infected patients. With the release of the macrolide antibiotics, clarithromycin and azithromycin, effective and well-tolerated therapeutic regimens for MAC have been developed which prolong survival and increase quality of life. The macrolides and rifabutin are also effective as preventive therapy for MAC in patients with AIDS. Mycobacterium kansasii, which causes pulmonary disease similar to tuberculosis as well as disseminated disease in AIDS, is treatable with isoniazid, rifampin and ethambutol. Clinical syndromes and therapeutic options for other non-tuberculous mycobacteria in AIDS are also reviewed.

Drug treatment of HIV-related opportunistic infections

The AIDS epidemic has led to the emergence of several disease entities which in the pre-AIDS era were rare or seemingly innocuous. Experience of treating these diseases varies. In some instances, such as Pneumocystis carinii pneumonia, there is an abundance of published literature to direct our course of action. However, for many of these newly recognised diseases our treatment experience is limited. Furthermore, in many instances, well controlled trials evaluating treatment modalities in the AIDS population are lacking. We have identified 13 disease entities (P. carinii pneumonia, toxoplasmosis, cryptococcosis, histoplasmosis, Mycobacterium tuberculosis, Mycobacterium avium complex, cytomegalovirus, coccidioidomycosis, isosporiasis, candidosis, Kaposi's sarcoma, herpes simplex virus, and varicella zoster virus) and have reviewed the current literature with regard to their treatment.

The use of rifabutin in Europe for the treatment of mycobacterial infection in AIDS patients

The MICs of rifabutin on Mycobacterium avium are compatible with its efficacy in clinical infections. Two North American trials established the prophylactic effect of rifabutin in disseminated M. avium disease in AIDS patients. Several prospective non-randomized trials show the clinical and bacteriological efficacy of rifabutin. A large European study conducted from 1990 to 1993 randomized 382 patients, selected on a clinical basis, to receive a combination of ethambutol + clofazimine + isoniazid + placebo or rifabutin for 12 weeks. Of these, 200 were eligible, i.e. had a positive blood culture at day 0. The percentage of patients with fever decreased from 78% to 23% in the rifabutin arm and from 76% to 11% in the placebo group (difference statistically not significant). The percentage of positive blood cultures decreased from 100% to 70% and 29% in the placebo group and from 100% to 45% and 18% in the rifabutin group at weeks 0, 6 and 12 respectively. The rate of adverse events was 35% in the placebo and 30% in the rifabutin group (difference statistically not significant). Two other French randomized trials are being analysed: the first one compares a 14-day regimen of rifabutin to placebo. It shows a 70% success rate in the rifabutin arm and a 8% success rate in the control group. The second trial demonstrates that when given in addition to clarithromycin, unlike clofazimine a combination of rifabutin + ethambutol is effective in decreasing the relapse rate with acquired resistance to clarithromycin. After clarithromycin, rifabutin is the second drug which was proven to be active against disseminated M. avium disease in a controlled placebo trial.

A comparison of two regimens for the treatment of Mycobacterium avium complex bacteremia in AIDS: rifabutin, ethambutol, and clarithromycin versus rifampin, ethambutol, clofazimine, and ciprofloxacin. Canadian HIV Trials Network Protocol 010 Study Group

BACKGROUND

Bacteremia with the Mycobacterium avium complex is common in patients with the acquired immunodeficiency syndrome (AIDS), but the most effective treatment for this infection remains unclear.

METHODS

We randomly assigned 229 patients with AIDS and M. avium complex bacteremia to receive either rifampin (600 mg daily), ethambutol (approximately 15 mg per kilogram of body weight daily), clofazimine (100 mg daily), and ciprofloxacin (750 mg twice daily) (the four-drug group) or rifabutin (600 mg daily), ethambutol (as above), and clarithromycin (1000 mg twice daily) (the three-drug group). In the three-drug group the dose of rifabutin was reduced by half after 125 patients were randomized, because 24 of 63 patients had uveitis.

RESULTS

Among 187 patients who could be evaluated, blood cultures became negative more often in the three-drug group than in the four-drug group (69 percent vs. 29 percent, P<0.001). Among patients treated for at least four weeks, the bacteremia resolved more frequently in the three-drug group (78 percent vs. 40 percent, P<0.001). In the three-drug group, bacteremia resolved more often with the 600-mg dose of rifabutin than with the 300-mg dose (P=0.025), but the latter regimen was more effective than the four-drug regimen (P<0.05). The median survival was 8.6 months in the three-drug group and 5.2 months in the four-drug group (P = 0.001). The median Karnofsky performance score was higher in the three-drug group than in the four-drug group from week 2 to week 16 (P<0.05). Mild uveitis developed in 3 of the 53 patients receiving the 300-mg dose of rifabutin, an incidence about one quarter that observed with the 600-mg dose (P<0.001).

CONCLUSIONS

In patients with AIDS and M. avium complex bacteremia, treatment with the three-drug regimen of rifabutin, ethambutol, and clarithromycin leads to resolution of the bacteremia more frequently and more rapidly than treatment with rifampin, ethambutol, clofazimine, and ciprofloxacin, and survival rates are better.

Early bactericidal activity of rifabutin versus that of placebo in treatment of disseminated Mycobacterium avium complex bacteremia in AIDS patients

Rifabutin, 600 mg/day, was compared with a placebo in the early treatment of culture-proven Mycobacterium avium bacteremia in patients with AIDS. Following 14 days' treatment, bacteriological success, defined as a negative culture or a reduction in the number of CFU of M. avium organisms per milliliter of blood by a factor of > or = 0.5 log from the baseline, was observed in 7 of 10 (70%) evaluable rifabutin patients and in 1 of 13 (8%) evaluable placebo patients (P = 0.002). Rifabutin is active against M. avium as a single agent and can make a significant contribution to combination regimens for the treatment of disseminated M. avium infection in AIDS patients.

In vitro activities of rifabutin, azithromycin, ciprofloxacin, clarithromycin, clofazimine, ethambutol, and amikacin in combinations of two, three, and four drugs against Mycobacterium avium

Multidrug therapy is recommended for treatment of Mycobacterium avium complex (MAC) bacteremia in patients with AIDS. Azithromycin, clarithromycin, rifabutin, ciprofloxacin, ethambutol, clofazimine, and amikacin have all been suggested for use in treating MAC bacteremia, but the most active combinations of these drugs have not been identified, nor has the minimum number of drugs needed for effective therapy been determined. To address the former, the in vitro bactericidal activities of all two-, three-, and four-drug combinations of these seven agents was determined by using 10 blood-derived strains of MAC isolated from patients with AIDS. The activities of the 132 drug combinations were compared by statistical analysis of survival means (analysis of variance) and further evaluated by determining the percentage of strains considered susceptible to each combination. When susceptibility was defined as a decrease in CFU of > or = 2 log10, no two- or three-drug combination and only two four-drug combinations were active against all 10 MAC strains. When a less stringent definition was applied (> or = 1 log10 decrease in CFU), 1 two-drug combinations, 9 three-drug combinations, and 31 four-drug combinations showed activity against all 10 strains. Eighteen selected drug combinations were also tested for intracellular activity in MAC-infected J774 cells. Combinations which contained amikacin as a component were considerably less active against intracellular MAC organisms than against organisms in broth. The opposite result was obtained for the combination of clarithromycin plus clofazimine.

Treatment of nontuberculous mycobacterial lymphadenitis with clarithromycin plus rifabutin

Treatment with clarithromycin plus rifabutin in children with nontuberculous mycobacterial lymphadenitis was associated with resolution of chronic sinus formation and discharge after incomplete excision in five of five cases, and involution of the enlarged lymph nodes in two of three cases treated without surgery.

Activities of rifabutin, clarithromycin, and ethambutol against two virulent strains of Mycobacterium avium in a mouse model

Rifabutin, clarithromycin, and ethambutol, which were administered at concentrations similar to those used in clinical trials that are now under way, were tested for their capacities to inhibit the growth of two highly virulent isolates of Mycobacterium avium in inbred C57BL/6 mice and in vitro in a bone marrow-derived murine macrophage model. In the latter model rifabutin and clarithromycin had modest activities against strain 101 and somewhat better activities against strain 2-151. When they were tested in vivo, however, the best results, against strain 101 were seen when the three drugs were given in combination, whereas against strain 2-151 the combination therapy showed no significant improvement over that of clarithromycin given alone. It will be of interest to note to what degree the eventual outcomes of the current trials correlate with the predictions of these animal model systems.