Controversies in the management of Mycobacterium avium complex infection in AIDS patients

OBJECTIVE

To update readers on the clinical management of infections secondary to Mycobacterium avium complex (MAC) in patients with AIDS. A general description of the organism, culture and susceptibility testing, and clinical manifestations of the disease is provided. Several aspects of the treatment of the disease, including an historical perspective, current approaches, and future research opportunities, are described.

DATA SOURCES

Current medical literature, including abstracts presented at international meetings, is reviewed. References were identified through MEDLINE, Current Contents, and published meeting abstracts.

STUDY SELECTION

Data regarding the epidemiology, clinical manifestations, culture and susceptibility testing, and treatment of MAC are cited. Specific attention is given to the management of patients with MAC infection.

DATA EXTRACTION

Information contributing to the discussion of the topics selected by the author is reviewed. Data supporting and disputing specific conclusions are presented.

DATA SYNTHESIS

Disseminated MAC infection is diagnosed antemortem in approximately 30 percent of patients with AIDS; postmortem rates of isolation exceed 50 percent. The incidence of MAC may increase as attempts at isolating the organism become more aggressive. The traditional approach to the isolation, susceptibility testing, and treatment of MAC has been derived from the management of Mycobacterium tuberculosis, with disappointing results. Newer radiometric in vitro methods of susceptibility testing appear to show more promise. Current mouse models of MAC are not true AIDS models; new CD4-deficient mouse models are being developed. Clinical mycobacteriologic and pharmacokinetic laboratory support have been underused, with treatment generally proceeding empirically. New agents that may contribute to the management of disseminated MAC infection include the macrolide derivatives clarithromycin and azithromycin. Research also continues with new rifamycins (including rifabutin) and fluoroquinolones (ciprofloxacin, sparfloxacin). Preliminary results suggest a central role for macrolides in the treatment of disseminated MAC; effective companion drugs are needed to prevent the rapid emergence of macrolide-resistant MAC.

CONCLUSIONS

Treatment results for disseminated MAC infection remain poor. Therapy may be improved by selecting drugs on the basis of susceptibility data for each isolate, rather than by using empiric regimens based on susceptibility trends. Significant antimycobacterial drug malabsorption has been documented, and may contribute to poor outcomes. More-potent agents are needed to improve the clinical outcome in AIDS patients with MAC.

Antibiotic tissue penetration and its relevance: models of tissue penetration and their meaning

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Kinetics and dynamics of tobramycin action in patients with bacteriuria given single doses

We studied the effect of a single intravenous dose of tobramycin on the rate of bacterial eradication from urine in 10 patients with bladder catheters. The catheter was replaced 4 to 6 h after the tobramycin dose. Pseudomonas aeruginosa was found in 7 of the 10 patients, while members of the family Enterobacteriaceae accounted for the remaining pathogens. The MIC for each bacterium was determined in both broth and urine. Tobramycin eradicated the bacteria from eight patients. Bacteriuria resolved in 21.8 +/- 18.0 h, and urine bactericidal activity persisted for 43.4 +/- 20.3 h after the dose of tobramycin. Most patients were recolonized by another bacterial species if use of Foley catheters was resumed on a continuous basis. Two patients required additional doses of tobramycin to eradicate the original pathogen. There were significant temporal relationships between the pharmacokinetics of tobramycin and the change in colony count of bacteria in urine.

Improved high-performance liquid chromatographic assay for the determination of ethionamide in serum

A solid-phase extraction (SPE) method was developed to simplify the preparation of human serum prior to high-performance liquid chromatography of ethionamide (ETA). Octadecyl SPE columns were used. Serum constituents were removed from the column with water, and ETA was eluted with methanol. Samples were evaporated to dryness, reconstituted in mobile phase, and assayed. The method is reproducible, with a recovery of ETA of 64%, comparable to the more tedious liquid-liquid extraction method for ETA.

Dual individualization of intravenous ciprofloxacin in patients with nosocomial lower respiratory tract infections

Dual individualization is the integration of patient-specific pharmacokinetic parameters with the pharmacodynamics (concentration versus response) of the infecting pathogen. This technique allows description of the time of in vivo bacterial eradication, and allows estimation of optimal dosages using small numbers of seriously ill patients. In an ongoing study, 11 patients with nosocomial lower respiratory tract infections were given 200 mg of intravenous ciprofloxacin every 12 hours. Ten blood samples were taken after the first dose, with additional peaks and troughs measured on Day 4 and at the end of treatment. Bacterial isolates had minimal inhibitory concentrations (MICs) determined by standard microdilution techniques. In the 11 patients, there were 14 bacterial isolates, of which seven were Pseudomonas aeruginosa and the remainder were other pathogens. Ciprofloxacin MICs ranged from 0.008 to 1.0 microgram/ml. The pharmacokinetics of ciprofloxacin in these patients varied with renal function, and average peak serum concentrations ranged from 1.7 to 4.9 micrograms/ml. Eradication of bacteria from tracheal aspirates occurred between Days 1 and 7, except in four patients in whom the organism persisted. Correlations were observed between the day of eradication and the length of time ciprofloxacin concentrations remained above the minimal inhibitory concentration (MIC). Essentially all bacteria with MICs of less than 0.25 were eradicated. Of the non-eradicated bacteria, most had either MICs of more than 0.25, or less than 100 percent time above the MIC. The clinical response was satisfactory. It is concluded that 200 mg of intravenous ciprofloxacin every 12 hours is highly effective for bacteria with MICs less than 0.25 microgram/ml, but higher dosages may be required to eradicate organisms with higher MICs.