Influence of in-feed virginiamycin on the systemic and mucosal antibody response of chickens.

Subtherapeutic and prophylactic doses of virginiamycin are capable of altering the intestinal microbiota as well as increasing several growth parameters in chickens. In spite of the fact that the microbiota plays a role in shaping the host's immune system, little information is available on the effects of in-feed antibiotics on the chicken immune system. The objective of this study was to examine the effects of an antibiotic, virginiamycin, on the development of antibody responses. Chickens were fed diets containing no antibiotics, along with either subtherapeutic (11 ppm) or prophylactic (22 ppm) doses of virginiamycin. Chickens were then immunized with keyhole limpet hemocyanin (KLH) and sheep red blood cells systemically, and with BSA and KLH orally. Although antibodies were detected against BSA in the intestinal contents of birds that were orally immunized, there was no difference among different treatment groups. Systemic IgG, and to a lesser extent IgM, antibody responses to KLH were greater (P < 0.05) in birds fed a diet containing 11 or 22 ppm of virginiamycin compared with control birds fed no antibiotic. No treatment effect was found in the sheep red blood cell-immunized birds. Results of the present study implicate virginiamycin in enhancing antibody responses to some antigens in chickens. Further studies are required to determine to what extent these effects on antibody response are mediated through changes in the composition of the microbiota.

Risk factors for arthralgias or myalgias associated with quinupristin-dalfopristin therapy.

STUDY OBJECTIVE: To evaluate risk factors for the development of arthralgias or myalgias associated with quinupristin-dalfopristin. DESIGN: Retrospective chart review and case-control analysis. SETTING: An 850-bed tertiary care medical center. PATIENTS: All adult and pediatric patients who had received quinupristin-dalfopristin through either a compassionate-use protocol (February 1996-October 1999) or in the year after quinupristin-dalfopristin was added to the hospital formulary (November 1999-October 2000) were included in this study. Case patients were those who developed arthralgias or myalgias while receiving quinupristin-dalfopristin therapy; control patients were those who received quinupristin-dalfopristin but did not develop arthralgias or myalgias. INTERVENTION: Medical records, pharmacy dispensing information, and microbiology data were reviewed by a physician and a pharmacist, both of whom specialized in infectious diseases. Presence or absence of arthralgias or myalgias was the primary outcome assessed. MEASUREMENTS AND MAIN RESULTS: Quinupristin-dalfopristin was administered to 68 patients during the period defined by the study. Arthralgias and myalgias could not be assessed in 18 of the 68 patients because they were sedated and paralyzed, or they were young children who could not communicate the presence of pain. Univariate analysis demonstrated that significant risk factors for arthralgias or myalgias associated with quinupristin-dalfopristin were female sex, chronic liver disease, receipt of liver transplant, elevated bilirubin level at baseline, major surgery, and receipt of either mycophenolate or cyclosporine. Multivariate analysis demonstrated a strong association with chronic liver disease, receipt of liver transplant, elevated bilirubin level at baseline, and receipt of either cyclosporine or mycophenolate. Of 50 evaluable patients receiving quinupristin-dalfopristin, 25 had pain that may have been associated with this antimicrobial agent. CONCLUSION: The mechanism for development of arthralgias or myalgias associated with quinupristin-dalfopristin remains unknown, but these adverse events are more likely to occur in patients with chronic liver disease and those who have received a liver transplant or are receiving cyclosporine or mycophenolate.

Combination of quinupristin-dalfopristin and gentamicin against methicillin-resistant Staphylococcus aureus: experimental rabbit endocarditis study.

The combination of quinupristin-dalfopristin (Q-D) and gentamicin was tested against two strains of gentamicin- and dalfopristin-susceptible methicillin-resistant Staphylococcus aureus (MRSA). One strain was susceptible to macrolides, lincosamides, and streptogramin B type antibiotics (MLS(B)), and the other was constitutively resistant to these antibiotics by virtue of the ermA gene. The checkerboard method and time-kill curves showed that the combination of Q-D and gentamicin was indifferent. A rabbit endocarditis model simulated the pharmacokinetics achieved in humans receiving intravenous injections of Q-D (7.5 mg/kg of body weight three times a day) and gentamicin (3 mg/kg once daily). For the MLS(B)-susceptible strain, a 4-day regimen reduced mean bacterial titers (MBT) in vegetations from 8.5 +/- 0.8 log CFU/g (control group) to 4.1 +/- 2.6 (gentamicin), 3.0 +/- 0.9 (Q-D), and 2.6 +/- 0.5 log CFU/g (Q-D plus gentamicin). For the strain constitutively resistant to MLS(B), a 4-day regimen reduced MBT in vegetations from 8.7 +/- 0.9 log CFU/g (control group) to 5.0 +/- 2.2 (gentamicin), 5.2 +/- 2.2 (Q-D), and 5.1 +/- 2.4 log CFU/g (Q-D plus gentamicin). The differences between control and treatment groups were significant for both strains (P < 0.0001), although there was no significant difference between treatment groups. No resistant variant was isolated from vegetations, and no significant difference in MBT in vegetations of treatment groups after 1-day regimens was observed. This experimental study found no additive benefit in combining Q-D and gentamicin against dalfopristin- and gentamicin-susceptible MRSA.

Activities of the combination of quinupristin-dalfopristin with rifampin in vitro and in experimental endocarditis due to Staphylococcus aureus strains with various phenotypes of resistance to macrolide-lincosamide-streptogramin antibiotics.

We evaluated the activities of quinupristin-dalfopristin (Q-D), alone or in combination with rifampin, against three strains of Staphylococcus aureus susceptible to rifampin (MIC, 0.06 microg/ml) and to Q-D (MICs, 0.5 to 1 microg/ml) but displaying various phenotypes of resistance to macrolide-lincosamide-streptogramin antibiotics: S. aureus HM1054 was susceptible to quinupristin and dalfopristin (MICs of 8 and 4 microg/ml, respectively); for S. aureus RP13, the MIC of dalfopristin was high (MICs of quinupristin and dalfopristin for strain RP13, 8 and 32 microg/ml, respectively); and S. aureus HM1054R was obtained after conjugative transfer of macrolide-lincosamide-streptogramin B constitutive resistance to HM1054, and the MIC of quinupristin for this strain was high (MICs of quinupristin and dalfopristin, 64 and 4 microg/ml, respectively). In vitro time-kill curve studies showed an additive effect [corrected] between Q-D and rifampin, at a concentration of four times the MIC, against the three strains. Rabbits with aortic endocarditis were treated 4 days with Q-D, rifampin, or their combination. In vivo, the combination was highly bactericidal and synergistic against strains susceptible to quinupristin (HM1054 and RP13) and sterilized 94% of the animals. In contrast, the combination was neither synergistic nor bactericidal against the quinupristin-resistant strain (HM1054R) and did not prevent the emergence of mutants resistant to rifampin. We conclude that the in vivo synergistic and bactericidal activity of the combination of Q-D and rifampin against S. aureus is predicted by the absence of resistance to quinupristin but not by in vitro combination studies.

Quinupristin-dalfopristin combined with beta-lactams for treatment of experimental endocarditis due to Staphylococcus aureus constitutively resistant to macrolide-lincosamide-streptogramin B antibiotics.

Quinupristin-dalfopristin (Q-D) is an injectable streptogramin active against most gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). In experimental endocarditis, however, Q-D was less efficacious against MRSA isolates constitutively resistant to macrolide-lincosamide-streptogram B (C-MLS(B)) than against MLS(B)-susceptible isolates. To circumvent this problem, we used the checkerboard method to screen drug combinations that would increase the efficacy of Q-D against such bacteria. beta-Lactams consistently exhibited additive or synergistic activity with Q-D. Glycopeptides, quinolones, and aminoglycosides were indifferent. No drugs were antagonistic. The positive Q-D-beta-lactam interaction was independent of MLS(B) or beta-lactam resistance. Moreover, addition of Q-D at one-fourth the MIC to flucloxacillin-containing plates decreased the flucloxacillin MIC for MRSA from 500 to 1,000 mg/liter to 30 to 60 mg/liter. Yet, Q-D-beta-lactam combinations were not synergistic in bactericidal tests. Rats with aortic vegetations were infected with two C-MLS(B)-resistant MRSA isolates (isolates AW7 and P8) and were treated for 3 or 5 days with drug dosages simulating the following treatments in humans: (i) Q-D at 7 mg/kg two times a day (b.i.d.) (a relatively low dosage purposely used to help detect positive drug interactions), (ii) cefamandole at constant levels in serum of 30 mg/liter, (iii) cefepime at 2 g b.i.d., (iv) Q-D combined with either cefamandole or cefepime. Any of the drugs used alone resulted in treatment failure. In contrast, Q-D plus either cefamandole or cefepime significantly decreased valve infection compared to the levels of infection for both untreated controls and those that received monotherapy (P < 0.05). Importantly, Q-D prevented the growth of highly beta-lactam-resistant MRSA in vivo. The mechanism of this beneficial drug interaction is unknown. However, Q-D-beta-lactam combinations might be useful for the treatment of complicated infections caused by multiple organisms, including MRSA.

Influence of resistance to streptogramin A type antibiotics on the activity of quinupristin-dalfopristin in vitro and in experimental endocarditis due to Staphylococcus aureus.

We evaluated the activity of quinupristin-dalfopristin (Q-D) against three clinical strains of Staphylococcus aureus susceptible to Q (MIC, 8 microg/ml) and Q-D (MICs, 0.5 to 1 microg/ml) but displaying various levels of susceptibility to D. D was active against S. aureus HM 1054 (MIC, 4 microg/ml) and had reduced activity against S. aureus RP 13 and S. aureus N 95 (MICs, 32 and 64 microg/ml, respectively). In vitro, Q-D at a concentration two times the MIC (2xMIC) produced reductions of 4.3, 3.9, and 5.8 log(10) CFU/ml after 24 h of incubation for HM 1054, RP 13, and N 95, respectively. Comparable killing was obtained at 8xMIC. Q-D-resistant mutants were selected in vitro at a frequency of 2 x 10(-8) to 2 x 10(-7) for the three strains on agar containing 2xMIC of Q-D; no resistant bacteria were detected at 4xMIC. Rabbits with aortic endocarditis were treated for 4 days with Q-D at 30 mg/kg of body weight intramuscularly (i.m.) three times a day (t.i.d.) or vancomycin at 50 mg/kg i.m. t.i.d. In vivo, Q-D and vancomycin were similarly active and bactericidal against the three tested strains compared to the results for control animals (P < 0.01). Among animals infected with RP 13 and treated with Q-D, one rabbit retained Q-D-resistant mutants that were resistant to Q and to high levels of D (MICs, 64, >256, and 8 microg/ml for Q, D, and Q-D, respectively). We conclude that the bactericidal activity of Q-D against strains with reduced susceptibility to D and susceptible to Q-D is retained and is comparable to that of vancomycin. Acquisition of resistance to both Q and D is necessary to select resistance to Q-D.

Pharmacokinetics of quinupristin-dalfopristin in continuous ambulatory peritoneal dialysis patients.

Quinupristin-dalfopristin may be useful for treatment of organisms causing peritoneal dialysis-related peritonitis, including methicillin-resistant coagulase-negative staphylococci, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci. The pharmacokinetic profiles of single intravenous doses of this combination streptogramin antibiotic of 7.5 mg/kg of body weight were characterized for eight noninfected patients receiving continuous ambulatory peritoneal dialysis. Comparison was made to pharmacokinetic profiles determined for eight healthy volunteers matched by age, sex, and race. Drug was measured in dialysate up to 6 h following the dose. Plasma and dialysate were assayed for parent compounds and metabolites. Mean pharmacokinetic parameters were compared between groups. No statistically significant differences were observed between groups for maximal concentrations in plasma, times to maximal concentration, areas under the curve, distribution volumes, rates of total body clearance, or half-lives in plasma for quinupristin and dalfopristin. No statistically significant differences were observed in maximal concentrations in plasma, times to maximal concentration, areas under the curve, or half-lives for cysteine, the glutathione conjugates of quinupristin, or the pristinamycin IIA metabolite of dalfopristin. The measurements in dialysate of the parent and most metabolites were below the expected MICs. Dialysis clearance was insignificant. Quinupristin-dalfopristin was well tolerated in both groups, causing only mild adverse events that resolved prior to discharge from the study. The disposition of quinupristin, dalfopristin, or their primary metabolites following a single dose was unaltered in patients receiving peritoneal dialysis. Intravenous dosing of this antibiotic combination is unlikely to be adequate for the treatment of peritonitis associated with peritoneal dialysis.

Simultaneous high-performance liquid chromatographic determination of quinupristin, dalfopristin and their main metabolites in human plasma.

Quinupristin-dalfopristin (30:70, w/w) is a new streptogramin, which has been developed for intravenous use. A specific and sensitive HPLC method was developed to measure simultaneously quinupristin (RP 57669) and dalfopristin (RP 54476) and their main metabolites in human plasma. The metabolites measured by this method were RP 69012 (glutathione-conjugated) and RPR 100391 (cysteine-conjugated) from quinupristin and RP 12536 (natural pristinamycin IIA), from dalfopristin. Solid-phase extraction with disposable cartridges was combined with reversed-phase HPLC and fluorimetric detection for RP 57669, RP 69012 and RPR 100391 and UV detection for RP 54476 and RP 12536. The method provided good recovery and low limits of quantitation (0.025 mg l(-1) for RP 57669, RP 54476 and RP 12536, and of 0.010 mg l(-1) for RP 69012 and RPR 100391). The validated range of concentrations of the method was: 0.025-5000 mg l(-1) for RP 57669, RP 54476 and RP 12536 and 0.010-0.750 mg l(-1) for RP 69012 and RPR 100391.

The pharmacokinetics of quinupristin/dalfopristin in laboratory animals and in humans.

The pharmacokinetics of quinupristin/dalfopristin have been studied in rats, monkeys and humans following intravenous infusion of radiolabelled and unlabelled drug. In rats and monkeys quinupristin and dalfopristin undergo rapid elimination from the blood and wide tissue distribution. Nevertheless, they do not penetrate the central nervous system or cross the placenta to any significant degree and they do not appear to be subject to significant body retention following cessation of administration. The blood elimination half-life of quinupristin was approximately 0.6 h in rats and 0.5 h in monkeys, and that of dalfopristin was approximately 0.6 h and 0.2 h, respectively. Both compounds are primarily eliminated through the bile into the faeces; quinupristin is mainly excreted unchanged whereas dalfopristin is extensively metabolized beforehand. The metabolites include the microbiologically active pristinamycin PIIA for dalfopristin and the microbiologically active glutathione- and cysteine-conjugated derivatives for quinupristin. Quinupristin and dalfopristin appear to be handled in a similar manner by humans. Following intravenous administration both compounds are rapidly cleared from the blood with elimination half-lives of approximately 1 h for quinupristin and 0.4-0.5 h for dalfopristin. The pharmacokinetic profile of quinupristin is dose-independent and so is that of dalfopristin and RP 12536 when considered together. Extravascular diffusion of quinupristin/dalfopristin has been assessed in human non-inflammatory interstitial fluid.

Treatment of experimental endocarditis due to erythromycin-susceptible or -resistant methicillin-resistant Staphylococcus aureus with RP 59500.

RP 59500 is a new injectable streptogramin composed of two synergistic components (quinupristin and dalfopristin) which are active against erythromycin-susceptible and -resistant gram-positive pathogens. The present experiments compared the therapeutic efficacy of RP 59500 with that of vancomycin against experimental endocarditis due to either of two erythromycin-susceptible or two constitutively erythromycin-resistant isolates of methicillin-resistant Staphylococcus aureus. RP 59500 had low MICs for the four test organisms as well as for 24 additional isolates (the MIC at which 90% of the isolates were inhibited was < 1 mg/liter) which were mostly inducibly (47%) or constitutively (39%) erythromycin resistant. Aortic endocarditis in rats was produced with catheter-induced vegetations. Three-day therapy was initiated 12 h after infection, and the drugs were delivered via a computerized pump, which permitted the mimicking of the drug kinetics produced in human serum by twice-daily intravenous injections of 7 mg of RP 59500 per kg of body weight or 1 g of vancomycin. Both antibiotics reduced vegetation bacterial titers to below detection levels in ca. 70% of animals infected with the erythromycin-susceptible isolates (P < 0.05 compared with titers in controls). Vancomycin was also effective against the constitutively resistant strains, but RP 59500 failed against these isolates. Further experiments proved that RP 59500 failures were related to the very short life span of dalfopristin in serum (< or = 2 h, compared with > or = 6 h for quinupristin), since successful treatment was restored by artificially prolonging the dalfopristin levels for 6 h. Thus, RP 59500 is a promising alternative to vancomycin against methicillin-resistant S. aureus infections, provided that pharmacokinetic parameters are adjusted to afford prolonged levels of both of its constituents in serum. This observation is also relevant to humans, in whom the life span of dalfopristin in serum is also shorter than that of quinupristin.

RP 59500 prophylaxis of experimental endocarditis due to erythromycin-susceptible and -resistant isogenic pairs of viridans group streptococci.

RP 59500 is a new injectable streptogramin composed of two synergistic components (quinupristin and dalfopristin) which are active against a number of erythromycin-susceptible and -resistant gram-positive bacteria. The following experiments investigate the ability of RP 59500 to prevent experimental endocarditis due to either of two erythromycin-susceptible streptococcal isolates or their constitutively erythromycin-resistant Tn916 delta E transconjugants. RP 59500 had low MICs (0.125 to 0.5 mg/liter) for all four test organisms and was substantially bactericidal in vitro. Rats with catheter-induced aortic vegetations were given single-dose antibiotic prophylaxis 30 to 60 min before bacterial inoculation through a computerized pump system which permitted the simulation of drug kinetics for humans produced by either 7 mg of RP 59500 per kg of body weight or 1 g of vancomycin. Single-dose RP 59500 prophylaxis successfully prevented endocarditis due to both the erythromycin-susceptible parent strains and their erythromycin-resistant derivatives in rats challenged with the minimal inoculum infecting 90% of controls. In addition, RP 59500 also prevented infection in animals challenged with fivefold-larger inocula of the erythromycin-susceptible parent strains. Vancomycin successfully prevented endocarditis due to any of the four test organisms. These results underline the in vivo efficacy of RP 59500 against both erythromycin-susceptible and -resistant streptococci. Such good results against the resistant strains would not be expected with erythromycin or clindamycin, which are the standard macrolidelincosamide-streptogramin antibiotics used for endocarditis prophylaxis in humans. An oral form of RP 59500 which might advantageously replace some of the older prophylactic regimens is currently being developed.

Pharmacokinetics and suction blister fluid penetration of a semisynthetic injectable streptogramin RP 59500 (RP 57669/ RP 54476).

RP 59500 is a new semisynthetic injectable streptogramin with excellent activity against most gram-positive bacteria. In order to assess its potential for the treatment of tissue infections, the pharmacokinetics and penetration into suction blister fluid were studied in a pilot phase I study in six male volunteers following a single infusion of 12 mg/kg over 1 h. Plasma and suction blister fluid concentrations were determined by microbiological assay. The mean peak concentration in plasma was 8.65 mg/l at the end of infusion. The mean plasma elimination half-life was 1.48 h. The mean peak concentration in interstitial fluid was 2.41 mg/l and was reached after 1 h in two volunteers and after 2 h in the other four. The mean percentage penetration for the interval 0-6 h was 82.5%. RP 59500 was still detectable in interstitial fluid at 6 h at a mean concentration of 0.92 +/- 0.25 mg/l. The data of this pilot study demonstrate good penetration of RP 59500 into non-inflammatory interstitial fluid.

Single oral dose pharmacokinetics of the two main components of pristinamycin in humans.

A preliminary study of the pharmacokinetics of the two main components of pristinamycin, PIA and PIIA is reported. A single oral dose of 2 g of pristinamycin was administered to six patients with normal renal and hepatic function. The samples were withdrawn during 9.5 h and assayed by HPLC. PIA and PIIA plasma levels evolved in parallel in each subject and their kinetic parameters were comparable: Tmax of 3.25 +/- 1.80 h and 3.08 +/- 1.98 h, Cmax of 0.760 +/- 0.427 mg/l and 0.581 +/- 0.285 mg/l, elimination half-life of 4.03 +/- 2.77 h-1 and 2.83 +/- 0.75 h-1, respectively. The relative proportions of PIA and PIIA, which govern the antibacterial activity of the mixture, were maintained during the study in the range of values leading to 90-100% of optimal activity against Staphylococcus aureus. The sum of the plasma concentrations of PIA and PIIA, which can be considered to be equivalent to the concentration of total pristinamycin, was superior to the MICs for the most susceptible staphylococcal strains during the entire period of study. On the other hand, the sum of PIA and PIIA concentrations exceeded the MICs for the less susceptible strains for only 4 h. These results differ from the scanty pharmacokinetic data presently available, which were obtained by microbiological methods.

[Study of the bactericidal activity of pristinamycin ]. / Etude de l'activité bactéricide de la pristinamycine.

In vitro, the bacteriostatic activity of pristinamycin varies according to the relative proportion of its two components, P I and P II, following a bell-shaped curve reflecting their synergistic effect. In vivo, the pharmacological profile of both components could be different and their synergistic bacteriostatic effect may therefore vary. This led us to study the bactericidal activity of different concentrations of the two components. Strains of staphylococci of varying sensitivity to macrolides and to each of the two components, P I and P II, were tested in our laboratory. We studied the bactericidal effect of various relative concentrations of both components tested in nutrient broth and transferred on nutrient agar, using Millipore membranes (according to the modified Chabbert's technique of cellophane transfer). We showed that the synergistic bactericidal activity of the two components yields a curve quite different from that observed for their bacteriostatic activity: the bactericidal activity is excellent, irrespective of the relative proportions of P I and P II in the medium. For all tested strains and relative proportions of both components, the MIC/MBC ratio is equal to one. We can therefore conclude that the determination of the SBA is useless and can assume that, as far as the serum levels of both components are above the MIC for the pathogenic strains, the blood is bactericidal. We have previously shown that transient incubation of P II on its target (50 S ribosomal sub-unit) led to a binding strength which is high (bactericidal activity) and prolonged ("bacteriopause").