Varidans streptococci in the oral flora of the patients at risk for infective endocarditis: species and penicillin susceptibilities

This study examined viridans streptococci (SV) in oral flora of patients at risk of infective endocarditis (IE) by obtaining 57 isolates from gum-tooth margin swabs of 3 groups of patients. Penicillin minimal inhibitory concentrations (MICs) were determined by E test. Group 1 was from 30 patients with prosthetic heart valves who did not receive antimicrobial agents within 3 months prior to recruitment. Group 2 consisted of 21 patients with known rheumatic heart diseases who regularly received penicillin prophylaxis. Group 3 was 2 patients with IE caused by SV in whom dental swabs were performed before and on the third day of treatment. Streptococcus mitis was found most frequently (49% among 51 oral isolates of SV from patients in group 1 and 2) and in both blood cultures of IE patients. Ninety-four per cent of the isolates were penicillin-susceptible and the rest were intermediate-resistant (IR) equally distributed in both groups 1 and 2. In 2 patients with IE, oral SV obtained after 3 days of penicillin therapy had MICs rising 3 and 5 folds of the baselines. It is suggested that surveillance of susceptibilities of oral SV in patients at risk for IE should be kept up since this will affect the dose and type of antimicrobial agents in IE prophylaxis.

Distribution of azithromycin into brain tissue, cerebrospinal fluid, and aqueous humor of the eye

To measure the concentrations of azithromycin in the central nervous system, 20 patients with brain tumors (group I) received a single 500-mg oral dose of azithromycin either 24, 48, 72, or 96 h prior to the tumor removal operation and 10 patients with cataracts undergoing surgery (group II) and 7 patients scheduled to undergo lumbar puncture (group III) received the same dose of azithromycin 24 h prior to the operation or procedure. Serum from all patients, brain tissue from group I, aqueous humor from group II, and cerebrospinal fluid from group III were assayed for azithromycin concentration. The mean concentrations of azithromycin in brain tissue 24, 48, 72, and 96 h after administration were 2.63 +/- 2.58, 3.64 +/- 3.81, 0.74 +/- 0.37, and 0.41 micrograms/g, respectively. In contrast, the concentrations of azithromycin in cerebrospinal fluid and aqueous humor of the eye were very low or undetectable. Therefore, these data show that azithromycin appears to be widely distributed into brain tissue but not into cerebrospinal fluid or aqueous humor of the eye.

The inhibitory effect of amiodarone and desethylamiodarone on dextromethorphan O-demethylation in human and rat liver microsomes

Amiodarone has been shown in-vitro to inhibit the activity of cytochrome P4502D6 (CYP2D6) in nonhuman primates. However, the influence of its major metabolite, desethylamiodarone, on this isozyme activity has not been studied. To determine the effect of these drugs on dextromethorphan O-demethylation, we carried out studies in 10 human and 10 rat liver microsomal preparations. In human microsomal studies, amiodarone and the metabolite competitively inhibited dextromethorphan metabolism with mean Ki values of 52.70 +/- 5.27 and 34.40 +/- 3.30 microM, respectively. Similar studies in rat microsomes showed a competitive inhibitory effect of amiodarone and its metabolite on dextromethorphan metabolism. These data suggest that amiodarone and desethylamiodarone have an inhibitory effect on CYP2D6 in man and CYP2D1 in rats. However, it cannot be concluded that both of them are substrates of this isozyme activity.