Initial clarithromycin monotherapy for Mycobacterium avium-intracellulare complex lung disease.

Sputum conversion rates in Mycobacterium avium-intracellulare (MAI) complex lung disease have ranged from only 50 to 80% despite the use of three to five antituberculosis agents. We initiated a prospective, open, noncomparative trial of initial clarithromycin monotherapy at 500 mg twice a day for 4 months in HIV-negative patients with MAI lung disease. The primary study end point was microbiologic improvement. Of 30 patients enrolled, 20 completed therapy. This latter group was predominantly male (60%), smokers (70%), older than 45 yr of age (90%), infected with Mycobacterium intracellulare (70%) and with bilateral disease (85%). Of 19 patients with pretreatment minimum inhibitory concentrations (MIC) for clarithromycin < 16 micrograms/ml, 58% became sputum-negative, and 21% showed significant reductions in sputum positivity. Heavily positive sputum cultures (> 200 colonies) were reduced from 30 to 47 samples pretherapy (64%) to three of 54 (6%) post-therapy (p < 0.0001); 18 of 19 patients (95%) showed an improvement in sputum cultures, chest radiographs, or both. Only two patients (7%) discontinued the drug because of adverse events. Only three (16%) of 19 isolates developed clarithromycin resistance (MIC > 32 micrograms/ml). Clarithromycin-susceptible and -resistant MAI isolates from the same patient had identical DNA large-restriction fragment patterns. Clarithromycin is the first single agent to be shown efficacious in the treatment of MAI lung disease.

Acquired resistance of Nocardia brasiliensis to clavulanic acid related to a change in beta-lactamase following therapy with amoxicillin-clavulanic acid.

Previous studies have demonstrated that Nocardia brasiliensis is susceptible to amoxicillin-clavulanic acid and that its beta-lactamases are inhibited in vitro by clavulanic acid. A cardiac transplant patient with disseminated infection caused by N. brasiliensis was treated with this drug combination with good response, but relapsed while still on therapy. The relapse isolate was found to be identical to the initial isolate by using genomic DNA restriction fragment patterns obtained by pulsed field gel electrophoresis, but it was resistant to amoxicillin-clavulanic acid. On isoelectric focusing, the beta-lactamase from the relapse isolate exhibited a shift in the isoelectric point (pI) of its major band from 5.10 to 5.04 compared with the enzyme from the pretreatment isolate. As determined by using values of the amount of beta-lactamase inhibitor necessary to give 50 +/- 5% inhibition of beta-lactamase-mediated hydrolysis of 50 microM nitrocefin, the beta-lactamase of the relapse isolate was also 200-fold more resistant than the enzyme from the pretreatment isolate to clavulanic acid and was more resistant to sulbactam, tazobactam, cloxacillin, and imipenem. The beta-lactamase of the relapse isolate exhibited a 10-fold decrease in hydrolytic activity for cephaloridine and other hydrolyzable cephalosporins compared with that for nitrocefin. Acquired resistance to amoxicillin-clavulanic acid in this isolate of N. brasiliensis appears to have resulted from a mutational change affecting the inhibitor and active site(s) in the beta-lactamase.

Selecting drug combinations for treatment of drug-resistant mycobacterial diseases.

Mixtures of antituberculosis drugs were evaluated for their in vitro effects on drug-resistant isolates of Mycobacterium tuberculosis and M. avium-intracellulare. The response of individual isolates to representative drug combinations was not always predictable from the results of single-drug sensitivity assays. For the case of M. tuberculosis, combinations of drugs were often bactericidal even under conditions where two or more drugs were without effect when tested singly. The more widely drug-resistant M. avium-intracellulare demonstrated increased growth inhibition when subcultured in the presence of single drugs, particularly rifampin and streptomycin. However, these conditions favored the selection of highly resistant strains. Alternatively, multiple drugs were often bacteriostatic; and under conditions where isolates demonstrated growth inhibition, the selection of highly drug-resistant strains was delayed. These results suggest a role for multiple-drug sensitivity assays in selecting drug combinations to be used in the treatment of drug-resistant mycobacterioses.