Clark B. Inderlied

Imipenem/cilastatin treatment of bacterial meningitis in children.

The safety and efficacy of imipenem/cilastatin were evaluated in 21 children, ages 3 to 48 months, with bacterial meningitis. Eradication of bacteria from the cerebrospinal fluid was demonstrated within 24 hours of antibiotic therapy in all but 2 patients who had Haemophilus influenzae type b meningitis and ultimately achieved bacteriologic cure after 2 to 3 days of imipenem/cilastatin therapy. Cerebrospinal fluid penetrations of imipenem and cilastatin were determined at various times after drug administration with mean cerebrospinal fluid: serum ratios of 14 and 10% for imipenem and cilastatin, respectively. The study was terminated when 7 (33%) patients developed seizure activity after antibiotic therapy was administered. The usefulness of imipenem/cilastatin for the treatment of bacterial meningitis in children may be limited by a possible increased incidence of drug-related seizure activity.

Azithromycin for treatment of Mycobacterium avium-intracellulare complex infection in patients with AIDS

Mycobacterium avium complex infection is common in patients with AIDS. Experimentally infected mice have been treated successfully with azithromycin, a macrolide antibiotic. We report an uncontrolled phase I study in which male homosexuals with AIDS and M avium complex disease were given 500 mg azithromycin per day orally for 10, 20, or 30 days. Quantitative blood cultures showed a mean reduction in mycobacteraemia from 118 colony forming units (cfu)/ml to 43 cfu/ml in 3 patients treated for 10 days, and from 2028 cfu/ml to 136 cfu/ml in 21 patients treated for 20 or 30 days. Of the patients treated for 20 or 30 days, 15 of 21 with fever pretreatment and 12 of 18 with night sweats pretreatment reported resolution of these symptoms. The principal side-effects were loose stools or diarrhoea, but these did not result in cessation of therapy. Azithromycin, as a single oral agent, safely reduced M avium complex bacteraemia and associated symptoms in almost 75% of patients treated for at least 20 days. Further studies are needed to assess emergence of resistance.

Stimulation with cytokines enhances penetration of azithromycin into human macrophages.

An effective intracellular concentration of an antimicrobial agent is essential for therapy of infections caused by organisms of the Mycobacterium avium complex. We previously reported on the effect of the combination of azithromycin and tumor necrosis factor (TNF) against M. avium infection in macrophages. We now report that stimulation of macrophages either with recombinant human gamma interferon (IFN-gamma, 10(2) U/ml) or with recombinant human TNF-alpha (10(2) U/ml) resulted in an increase in the intracellular concentration of azithromycin by approximately 200% within 3 h, compared with the concentration in unstimulated macrophages. Infection of macrophages with M. avium complex led to a decrease in the uptake of [14C]azithromycin by infected cells, compared with that by uninfected controls. Stimulation of infected macrophages with recombinant IFN-gamma or TNF-alpha overcame the inhibitory effect associated with infection. These results suggest that the increased bactericidal activity of the TNF-alpha-azithromycin or IFN-gamma-azithromycin combination against M. avium is related to enhanced uptake of the antibiotic by the stimulated phagocyte.

Activity of Moxifloxacin by Itself and in Combination with Ethambutol, Rifabutin, and Azithromycin In Vitro and In Vivo against Mycobacterium avium

ABSTRACT Moxifloxacin activity against Mycobacterium aviumcomplex (MAC) was evaluated in vitro against 25 strains. The MIC was determined to range from 0.125 to 2.0 μg/ml. In addition, U937 macrophage monolayers infected with MAC strain 101 (serovar 1) were treated with moxifloxacin (0.25 to 8 μg/ml) daily, and the number of intracellular bacteria was quantitated after 4 days. Moxifloxacin showed inhibitory activity at 0.5 μg/ml and higher. To assess the activity of moxifloxacin containing regimens in vivo, we infected C57BLbg+/bg+ mice with 3 × 107 MAC strain 101 bacteria intravenously. One week later treatment was begun with the following: (i) moxifloxacin (50 mg/kg/day or 100 mg/kg/day), ethambutol (100 mg/kg/day), or a combination of moxifloxacin and ethambutol; or (ii) moxifloxacin (100 mg/kg/day), azithromycin (200 mg/kg/day), or rifabutin (40 mg/kg/day) as oral monotherapy; or (iii) all permutations of two-drug therapy or all three drugs in combination. All groups contained at least 14 animals, and the control group received the drug vehicle. After 4 weeks, quantitative blood cultures were obtained and the number of bacteria in liver and spleen was quantitated. Moxifloxacin, ethambutol, and azithromycin were active as single agents in liver, spleen, and blood. Rifabutin showed inhibitory activity only in the blood. Two-drug combinations containing azithromycin were no more active than azithromycin alone. Similarly, the three-drug combination was not more active than azithromycin alone in the spleen. Rifabutin did not add to the activity of any other single agent or two-drug combination. Moxifloxacin at both concentrations in combination with ethambutol was significantly more active than each drug alone.

The role of copper on ethambutol's antimicrobial action and implications for ethambutol-induced optic neuropathy

The principal side effect of the antimycobacterial agent ethambutol (EMB) is an optic neuropathy with clinical features very similar to a mitochondrial hereditary optic neuropathy (Lebers). The mechanism of EMB-induced optic neuropathy may be EMBs chelation of copper, thereby precluding normal cytochrome c oxidase activity and mitochondrial metabolism in the optic nerve. Before attempting to use therapeutic copper to replenish endogenous stores in an attempt to preclude EMB-induced optic neuropathy, we wished to determine whether EMB is still effective against mycobacteria in the presence of copper. EMB and copper, alone and in combination, were tested against six strains of Mycobacterium tuberculosis and five strains of Mycobacterium avium using a radiometric broth macrodilution assay. Copper did not effect EMBs antimicrobial actions against either species of mycobacteria. This in vitro study suggests that if copper were given to patients to prevent EMB-induced optic neuropathy, it would not compromise EMBs bacteriostatic properties.

Amikacin, ciprofloxacin, and imipenem treatment for disseminated Mycobacterium avium complex infection of beige mice.

The Mycobacterium avium complex (MAC) is a common cause of disseminated infection in patients with acquired immunodeficiency syndrome and is increasingly seen as a cause of infection in other immunocompromised patients. Traditional antimycobacterial therapy often is ineffective, and there is a clear need for antibiotics with proven activity against the MAC. Three agents, amikacin, ciprofloxacin, and imipenem, were tested in vitro for activity against MAC strain 101. Amikacin was bacteriostatic, with an MIC of 4.8 micrograms/ml, which is significantly lower than the concentration in serum obtained with standard dosing. Imipenem and ciprofloxacin had little or no activity alone (MICs, greater than 16 and 4.7 micrograms/ml, respectively), but when they were combined with amikacin there was bactericidal activity. Each agent was tested individually and in combination by using the beige mouse model of disseminated MAC infection. There was no mortality in a group of animals infected with MAC 101 and treated with amikacin alone; also, there was a significant decrease in the infection of the blood, liver, and spleen. There was no apparent improvement in therapeutic effectiveness when amikacin was combined with the other agents. Neither ciprofloxacin nor imipenem was active as a single agent, which was consistent with the in vitro activities of these agents. Amikacin in combination with traditional antimycobacterial agents warrants further study as potential therapy for disseminated MAC infections.

Thiosemicarbazole (Thiacetazone-Like) Compound with Activity against Mycobacterium avium in Mice

ABSTRACT In vitro screening of thiacetazone derivatives indicated that two derivatives, SRI-286 and SRI-224, inhibited a panel of 25 Mycobacterium avium complex (MAC) isolates at concentrations of 2 μg/ml or lower. In mice, SRI-224 and thiacetazone had no significant activity against the MAC in livers and spleens, but treatment with SRI-286 resulted in significant reduction of bacterial loads in livers and spleens. A combination of SRI-286 and moxifloxacin was significantly more active than single drug regimens in liver and spleen.

Multisite Reproducibility of Results Obtained by Two Broth Dilution Methods for Susceptibility Testing of Mycobacterium avium Complex

ABSTRACT A multicenter study was conducted to assess the interlaboratory reproducibility of susceptibility testing of Mycobacterium avium complex (MAC) by broth microdilution using two different media (cation-adjusted Mueller-Hinton broth with 5% oleic acid-albumin-dextrose-catalase and 7H9 broth with casein) and by macrodilution using the BACTEC 460TB and 12B media at pH 6.8 and 7.3 to 7.4. Ten well-characterized strains of MAC (four macrolide susceptible, six macrolide resistant) were tested against clarithromycin and azithromycin (the latter only by BACTEC 460TB, pH 6.8). At each site, strains were tested against clarithromycin three times on each of three separate days (nine testing events per isolate) by using a common lot of microdilution trays and BACTEC 12B medium, pH 6.8; strains were tested once on three separate days against clarithromycin in 12B medium at pH 7.3 to 7.4 and against azithromycin. Agreement among MICs (i.e., mode ± 1 twofold dilution) was 100% for all strains and both drugs when BACTEC 460TB was used, regardless of the pH of the medium, but varied when microdilution with either medium was used, particularly with susceptible strains. Agreement based on interpretive category, with NCCLS-recommended breakpoints, was 100% for all strains with the BACTEC 460TB method (both drugs and both pH values) and with microdilution using 7H9 broth. With microdilution and Mueller-Hinton broth, agreement by interpretive category was 100% for eight isolates and >90% for two; errors occurred only in laboratories where personnel had minimal experience with this technique. MAC susceptibility testing may be performed by broth macrodilution or microdilution at either pH, with NCCLS-recommended interpretive breakpoints. However, because visual interpretation of broth microdilution end points is subjective, it is more prone to reader error; therefore, this method requires greater expertise than the BACTEC 460TB. Both techniques require appropriate validation and continued documentation of proficiency.

Activity of KRM 1648 alone or in combination with ethambutol or clarithromycin against Mycobacterium avium in beige mouse model of disseminated infection.

Rifamycins are active against slowly growing mycobacteria, such as Mycobacterium tuberculosis and Mycobacterium kansasii, but the majority of rifamycins thus far investigated both in vitro and in vivo are inactive or have only modest activity against the Mycobacterium avium complex (MAC). We investigated the activity of three doses of the semisynthetic benzoxazinorifamycin KRM 1648, alone or in combination with ethambutol or clarithromycin, in beige mice challenged with the MAC strain 101. Our results show the following. (i) KRM 1648 was significantly effective against MAC infection as determined by the reduction of the number of bacteria in the blood, liver, and spleen when administered at doses of 20 and 40 mg/kg of body weight per day but not at 10 mg/kg/day, compared with untreated controls. (ii) KRM 1648 (40 mg/kg/day) administered in combination with ethambutol (100 mg/kg/day) resulted in significant reduction in bacteremia compared with values for untreated controls (P 0.001), KRM 1648 alone (P = 0.019), and ethambutol alone (P = 0.003). Furthermore, the combination of KRM 1648 and ethambutol was associated with a significant decrease of the number of bacteria in the spleen and the liver compared with values for both untreated controls and each drug alone (P < 0.001 for all comparisons). (iii) KRM 1648 (40 mg/kg/day) administered in combination with clarithromycin (200 mg/kg/day) resulted in a significant decrease of the number of bacteria in the blood and the spleen compared with the number for untreated controls (P < 0.001 for all comparisons). In our experience, using MAC 101 as the challenging organism, KRM 1648 is the first the number of bacteria in the blood and spleen compared with the number for untreated controls (P >0.001 for all comparions). In our experience, using MAC 101 as the challenging organism, KRM 1648 is the first rifamycin with significant activity in vivo against MAC infection in beige mice.

Orally administered clarithromycin for the treatment of systemic Mycobacterium avium complex infection in children with acquired immunodeficiency syndrome

OBJECTIVE To determine the safety, tolerance, pharmacokinetics, and antimycobacterial activity of orally administered clarithromycin in children with acquired immunodeficiency syndrome and disseminated Mycobacterium avium complex (MAC) infection. DESIGN Phase I study with a 10-day pharmacokinetic phase followed by a 12-week continuation therapy phase. PATIENTS Twenty-five patients with a median age of 8.3 years were enrolled. Ten were receiving zidovudine and 13 were receiving didanosine at the time of enrollment. INTERVENTION Clarithromycin suspension was administered to each patient at one of three dose levels: 3.75, 7.5, and 15 mg/kg per dose every 12 hours. Clarithromycin and antiretroviral pharmacokinetics were measured during single-drug and concurrent-drug administration. Clinical and laboratory monitoring was performed biweekly. MEASUREMENTS AND MAIN RESULTS Clarithromycin was well tolerated at all dose levels. Plasma clarithromycin concentrations increased proportionately with increasing doses, and significant pharmacokinetic interactions were not observed during concurrent administration with zidovudine or didanosine. Decreases in mycobacterial load in blood were observed only at the highest clarithromycin dose level. Decreased susceptibility to clarithromycin developed rapidly (within 12 to 16 weeks) in the majority of MAC strains isolated from study patients.