In vivo pharmacodynamic activities of two glycylcyclines (GAR-936 and WAY 152,288) against various gram-positive and gram-negative bacteria

Abstract

The in vivo pharmacodynamic activities of two glycylcyclines (GAR-936 and WAY 152,288) were assessed in an experimental murine thigh infection model in neutropenic mice. Mice were infected with one of several strains of Streptococcus pneumoniae, Staphylococcus aureus, Escherichia coli, or Klebsiella pneumoniae. Most infections were treated with a twice-daily dosing schedule, with administration of 0.75 to 192 mg of GAR-936 or WAY 152,288 per kg of body weight. A maximum-effect dose-response model was used to calculate the dose that produced a net bacteriostatic effect over 24 h of therapy. This dose was called the bacteriostatic dose. More extensive dosing studies were performed with S. pneumoniae 1199, E. coli ATCC 25922, and K. pneumoniae ATCC 43816, with doses being given as one, two, four, or eight equal doses over a period of 24 h. The dosing schedules were designed in order to minimize the interrelationship between the various pharmacokinetic and pharmacodynamic parameters studied. These parameters were time above 0.03 to 32 times the MIC, area under the concentration-time curve (AUC), and maximum concentration of drug in serum (C(max)). The bacteriostatic dose remained essentially the same, irrespective of the dosing frequency, for S. pneumoniae 1199 (0.3 to 0.9 mg/kg/day). For E. coli ATCC 25922 and K. pneumoniae ATCC 43816, however, more frequent dosing led to lower bacteriostatic doses. Pharmacokinetic studies demonstrated dose-dependent elimination half-lives of 1.05 to 2.34 and 1.65 to 3.36 h and serum protein bindings of 59 and 71% for GAR-936 and WAY 152,288, respectively. GAR-936 and WAY 152,288 were similarly effective against the microorganisms studied, with small differences in maximum effect and 50% effective dose. The glycylcyclines were also similarly effective against tetracycline-sensitive and tetracycline-resistant bacteria. Time above a certain factor (range, 0.5 to 4 times) of the MIC was a better predictor of in vivo efficacy than C(max) or AUC for most organism-drug combinations. The results demonstrate that in order to achieve 80% maximum efficacy, the concentration of unbound drug in serum should be maintained above the MIC for at least 50% of the time for GAR-936 and for at least 75% of the time for WAY 152,288. The results of these experiments will aid in the rational design of dose-finding studies for these glycylcyclines in humans.

FIG. 1

Effects of various GAR-936 (a), WAY 152,288 (b), and minocycline (c) dosage regimens on the number of S. pneumoniae ATCC 10813 organisms in the neutropenic mouse thigh muscle infection model after 48 h of treatment. The dashed horizontal line represents the number of CFU per thigh at the start of treatment. ●, single dose; ○, once-daily dose; ▾, twice-daily dose; ▿, four-times-daily dose; ——, single dose; ······, once-daily dose; –––, twice-daily dose; —··, four-times-daily dose; —–, log CFU at start of treatment.

FIG. 2

Dose-effect relationship of the glycylcyclines GAR-936 (a) and WAY 152,288 (b) in an experimental thigh muscle infection with S. pneumoniae 1199 in neutropenic mice. Each point represents the results for a single mouse. The sigmoid curve represents the dose-effect curve established according to the Hill equation.

FIG. 3

In vivo PAE of GAR-936 after administration of 3 mg/kg subcutaneously to neutropenic mice infected with S. pneumoniae ATCC 10813 (a) and E. coli ATCC 25922 (b). t>MIC, period when an active concentration of GAR-936 is present; ●, untreated mice; ○, GAR-936-treated mice.

FIG. 4

Relationship between pharmacokinetic-pharmacodynamic parameters and therapeutic efficacy of GAR-936 (free drug) against S. pneumoniae 1199 in the neutropenic mouse thigh muscle infection model (R² = 0.82, 0.83, and 0.54 for panels a, b, and c, respectively). (a) time above the 0.5 × MIC versus effect. (b) Log AUC versus effect. (c) Log C_max versus effect.

FIG. 5

Relation between effect of GAR-936 on number of CFU in the thigh after 24 h of therapy in a thigh muscle infection caused by S. pneumoniae ATCC 10813 in neutropenic mice and percent survival after 5 days (2) of treatment. The sigmoid curve represents the dose-effect curve according to the Hill equation. ●, mice for which the effect on the number of CFU was established; each point in the curve represents an individual mouse; ○, mice for which the survival percentage was established (five mice per group).