In vitro dynamic model for determining the comparative pharmacology of fluoroquinolones

An in vitro model for determining the comparative pharmacology of fluoroquinolones is presented. The true therapeutic potential of fluoroquinolones against bacterial pathogens may be best understood before clinical testing with the use of in vitro dynamic models. These models simulate pharmacokinetics in humans and can be used to compare different drugs in the same class over a wide range of dosages with respect to the antimicrobial effect (AME). Two models for evaluating AME are described. In one (a two-compartment model), a simple bacterial killing curve is generated after exposure to simulated clinical doses of antimicrobial. In the other (a one-compartment model), AME is defined as the area between the control bacterial growth curve in the absence of drug and the curve that represents bacterial killing and regrowth. This area can be readily measured and is referred to as the intensity of the effect (I(e)). In general, AME is correlated with drug exposure, as simulated in the model at different ratios of the area under the concentration-time curve (AUC) to the minimum inhibitory concentration (MIC) for the organism under study. With this in vitro dynamic model, several fluoroquinolones were tested over a range of AUC/MIC ratios for their AMEs against Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae. The data generated illustrate the usefulness of in vitro dynamic models for comparing AMEs of different fluoroquinolones. Because the model incorporates pharmacokinetic variables, it provides a method for comparing various dosage regimens or schedules of administration and is useful in preclinical drug development.

Changing epidemiology of infections in patients with neutropenia and cancer: emphasis on gram-positive and resistant bacteria

Over the past 3 decades, considerable changes have occurred in the types of bacteria causing infection in febrile patients with neutropenia and cancer. Twenty years ago, gram-negative bacteria caused approximately 70% of bloodstream infections. As a probable consequence of long-dwelling intravascular devices, fluoroquinolone prophylaxis, and high-dose chemotherapy-induced mucositis, there has been a shift toward gram-positive coccal bacteremia. In most centers today, approximately 70% of bacteremic isolates are gram-positive cocci. Of potential concern is that antimicrobial-resistant gram-positive organisms are becoming increasingly frequent in patients with neutropenia. Fluoroquinolone-resistant Escherichia coli are being isolated from several cancer centers. Several "new" organisms, such as Stomatococcus mucilaginosus, Bacillus cereus, Leuconostoc species, Corynebacterium jeikeium, Rhodococcus species, Stenotrophomonas maltophilia, Moraxella catarrhalis, Burkholderia cepacia, and Bartonella species, now cause infections in these patients. Careful application of infection-control principles, judicious prophylaxis, appropriate evaluation of new antibiotics, and prompt effective therapy will maximize benefits for these patients.

Prediction of the antimicrobial effects of trovafloxacin and ciprofloxacin on staphylococci using an in-vitro dynamic model

To compare the pharmacodynamics of trovafloxacin and ciprofloxacin, three clinical isolates of Staphylococcus aureus with different MICs (0.03, 0.15, 0.6 and 0.1, 0.25, 1.25 mg/L, respectively) were exposed to decreasing concentrations of the quinolones according to their half-lives of 9.25 and 4 h, respectively. With each organism, single doses of trovafloxacin and twice-daily doses of ciprofloxacin were designed to provide 8-fold ranges of the ratio of area under the concentration-time curve (AUC) to the MIC, 58-466 and 116-932 (mg x h/L)/(mg/L), respectively. The antimicrobial effect was expressed by its intensity: the area between the control growth in the absence of antibiotics and the antibiotic-induced time-kill/regrowth curves (I(E)). Linear relationships established between I(E) and log AUC/MIC were bacterial strain-independent but specific for the quinolones (r2 = 0.99 in both cases). At a given AUC/MIC ratio, the I(E)s of trovafloxacin were greater than those of ciprofloxacin, suggesting that the antimicrobial effect of trovafloxacin compared with ciprofloxacin against staphylococci may be even greater than might be expected from the difference in their MICs. These data were combined with previous results obtained with three Gram-negative bacteria. Again, I(E) correlated well with the log AUC/MIC of trovafloxacin and ciprofloxacin in a strain- and species-independent fashion (r2 = 0.94 and 0.96, respectively). On this basis, a value of the AUC/MIC of trovafloxacin which might be equivalent to Schentag's AUC/MIC = 125 (mg x h/L)/(mg/L) reported as the breakpoint value for ciprofloxacin was estimated at 71 (mg x h/L)/(mg/L) with the respective MIC breakpoint of 0.27 mg/L. Based on the I(E)-log AUC/MIC relationships, the I(E)s were plotted against the logarithm of trovafloxacin and ciprofloxacin dose (D) for hypothetical representatives of S. aureus, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa with MICs corresponding to the MIC50s. These I(E)-log D relationships allow prediction of the effect of a given quinolone on a representative strain of the bacterial species.

Prediction of the effects of inoculum size on the antimicrobial action of trovafloxacin and ciprofloxacin against Staphylococcus aureus and Escherichia coli in an in vitro dynamic model

The effect of inoculum size (N0) on antimicrobial action has not been extensively studied in in vitro dynamic models. To investigate this effect and its predictability, killing and regrowth kinetics of Staphylococcus aureus and Escherichia coli exposed to monoexponentially decreasing concentrations of trovafloxacin (as a single dose) and ciprofloxacin (two doses at a 12-h interval) were compared at N0 = 10(6) and 10(9) CFU/ml (S. aureus) and at N0 = 10(6), 10(7), and 10(9) CFU/ml (E. coli). A series of pharmacokinetic profiles of trovafloxacin and ciprofloxacin with respective half-lives of 9.2 and 4 h were simulated at different ratios of area under the concentration-time curve (AUC) to MIC (in [micrograms x hours/milliliter]/[micrograms/milliliter]): 58 to 466 with trovafloxacin and 116 to 932 with ciprofloxacin for S. aureus and 58 to 233 and 116 to 466 for E. coli, respectively. Although the effect of N0 was more pronounced for E. coli than for S. aureus, only a minor increase in minimum numbers of surviving bacteria and an almost negligible delay in their regrowth were associated with an increase of the N0 for both organisms. The N0-induced reductions of the intensity of the antimicrobial effect (IE, area between control growth and the killing-regrowth curves) were also relatively small. However, the N0 effect could not be eliminated either by simple shifting of the time-kill curves obtained at higher N0s by the difference between the higher and lowest N0 or by operating with IEs determined within the N0-adopted upper limits of bacterial numbers (IE's). By using multivariate correlation and regression analyses, linear relationships between IE and log AUC/MIC and log N0 related to the respective mean values [(log AUC/MIC)average and (log N0)average] were established for both trovafloxacin and ciprofloxacin against each of the strains (r2 = 0.97 to 0.99). The antimicrobial effect may be accurately predicted at a given AUC/MIC of trovafloxacin or ciprofloxacin and at a given N0 based on the relationship IE = a + b [(log AUC/MIC)/(log AUC/MIC)average] - c [(log N0)/(log N0)average]. Moreover, the relative impacts of AUC/MIC and N0 on IE may be evaluated. Since the c/b ratios for trovafloxacin and ciprofloxacin against E. coli were much lower (0.3 to 0.4) than that for ampicillin-sulbactam as examined previously (1.9), the inoculum effect with the quinolones may be much less pronounced than with the beta-lactams. The described approach to the analysis of the inoculum effect in in vitro dynamic models might be useful in studies with other antibiotic classes.

MIC-based interspecies prediction of the antimicrobial effects of ciprofloxacin on bacteria of different susceptibilities in an in vitro dynamic model

Multiple predictors of fluoroquinolone antimicrobial effects (AMEs) are not usually examined simultaneously in most studies. To compare the predictive potentials of the area under the concentration-time curve (AUC)-to-MIC ratio (AUC/MIC), the AUC above MIC (AUCeff), and the time above MIC (Teff), the kinetics of killing and regrowth of four bacterial strains exposed to monoexponentially decreasing concentrations of ciprofloxacin were studied in an in vitro dynamic model. The MICs of ciprofloxacin for clinical isolates of Staphylococcus aureus, Escherichia coli 11775 (I) and 204 (II), and Pseudomonas aeruginosa were 0.6, 0.013, 0.08, and 0.15 microg/ml, respectively. The simulated values of AUC were designed to provide similar 1,000-fold (S. aureus, E. coli I, and P. aeruginosa) or 2, 000-fold (E. coli II) ranges of the AUC/MIC. In each case except for the highest AUC/MIC ratio, the observation periods included complete regrowth in the time-kill curve studies. The AME was expressed by its intensity, IE (the area between the control growth and time-kill and regrowth curves up to the point where the viable counts of regrowing bacteria are close to the maximum values observed without drug). For most AUC ranges the IE-AUC curves were fitted by an Emax (maximal effect) model, whereas the effects observed at very high AUCs were greater than those predicted by the model. The AUCs that produced 50% of maximal AME were proportional to the MICs for the strains studied, but maximal AMEs (IEmax) and the extent of sigmoidicity (s) were not related to the MIC. Both Teff and log AUC/MIC correlated well with IE (r2 = 0.98 in both cases) in a species-independent fashion. Unlike Teff or log AUC/MIC, a specific relationship between IE and log AUCeff was inherent in each strain. Although each IE and log AUCeff plot was fitted by linear regression (r2 = 0.97 to 0.99), these plots were not superimposed and therefore are bacterial species dependent. Thus, AUC/MIC and Teff were better predictors of ciprofloxacin's AME than AUCeff. This study suggests that optimal predictors of the AME produced by a given quinolone (intraquinolone predictors) may be established by examining its AMEs against bacteria of different susceptibilities. Teff was shown previously also to be the best interquinolone predictor, but unlike AUC/MIC, it cannot be used to compare different quinolones. AUC/MIC might be the best predictor of the AME in comparisons of different quinolones.

A new approach to in vitro comparisons of antibiotics in dynamic models: equivalent area under the curve/MIC breakpoints and equiefficient doses of trovafloxacin and ciprofloxacin against bacteria of similar susceptibilities

Time-kill studies, even those performed with in vitro dynamic models, often do not provide definitive comparisons of different antimicrobial agents. Also, they do not allow determinations of equiefficient doses or predictions of area under the concentration-time curve (AUC)/MIC breakpoints that might be related to antimicrobial effects (AMEs). In the present study, a wide range of single doses of trovafloxacin (TR) and twice-daily doses of ciprofloxacin (CI) were mimicked in an in vitro dynamic model. The AMEs of TR and CI against gram-negative bacteria with similar susceptibilities to both drugs were related to AUC/MICs that varied over similar eight-fold ranges [from 54 to 432 and from 59 to 473 (microg . h/ml)/(microg/ml), respectively]. The observation periods were designed to include complete bacterial regrowth, and the AME was expressed by its intensity (the area between the control growth in the absence of antibiotics and the antibiotic-induced time-kill and regrowth curves up to the point where viable counts of regrowing bacteria equal those achieved in the absence of drug [IE]). In each experiment monoexponential pharmacokinetic profiles of TR and CI were simulated with half-lives of 9.2 and 4.0 h, respectively. Linear relationships between IE and log AUC/MIC were established for TR and CI against three bacteria: Escherichia coli (MIC of TR [MICTR] = 0.25 microg/ml; MIC of CI [MICCI] = 0.12 microg/ml), Pseudomonas aeruginosa (MICTR = 0.3 microg/ml; MICCI = 0.15 microg/ml), and Klebsiella pneumoniae (MICTR = 0.25 microg/ml; MICCI = 0.12 microg/ml). The slopes and intercepts of these relationships differed for TR and CI, and the IE-log AUC/MIC plots were not superimposed, although they were similar for all bacteria with a given antibiotic. By using the relationships between IE and log AUC/MIC, TR was more efficient than CI. The predicted value of the AUC/MIC breakpoint for TR [mean for all three bacteria, 63 (microg . h/ml)/(microg/ml)] was approximately twofold lower than that for CI. Based on the IE-log AUC/MIC relationships, the respective dose (D)-response relationships were reconstructed. Like the IE-log AUC/MIC relationships, the IE-log D plots showed TR to be more efficient than CI. Single doses of TR that are as efficient as two 500-mg doses of CI (500 mg given every 12 h) were similar for the three strains (199, 226, and 203 mg). This study suggests that in vitro evaluation of the relationships between IE and AUC/MIC or D might be a reliable basis for comparing different fluoroquinolones and that the results of such comparative studies may be highly dependent on their experimental design and datum quantitation.

Inter- and intraquinolone predictors of antimicrobial effect in an in vitro dynamic model: new insight into a widely used concept

Earlier efforts to search for pharmacokinetic and bacteriological predictors of fluoroquinolone antimicrobial effects (AMEs) have resulted in conflicting findings. To elucidate whether these conflicts are real or apparent, several predictors of the AMEs of two pharmacokinetically different antibiotics, trovafloxacin (TRO) and ciprofloxacin (CIP), as well as different dosing regimens of CIP were examined. The AMEs of TRO given once daily (q.d.) and CIP given q.d. and twice daily (b.i.d.) against Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae were studied in an in vitro dynamic model. Different monoexponential pharmacokinetic profiles were simulated with a TRO half-life of 9.2 h and a CIP half-life of 4.0 h to provide similar eightfold ranges of the area under the concentration-time curve (AUC)-to-MIC ratios, from 54 to 432 and from 59 to 473 (microg x h/ml)/(microg/ml), respectively. In each case the observation periods were designed to incorporate full-term regrowth phases in the time-kill curves, and the AME was expressed by its intensity (IE; the area between the control growth and time-kill and regrowth curves up to the point at which the viable counts of regrowing bacteria are close to the maximum values observed without drug). Species-independent linear relationships were established between IE and log AUC/MIC, log AUC above MIC (log AUCeff), and time above the MIC (Teff). Specific and nonsuperimposed IE versus log AUC/MIC or log AUCeff relationships were inherent in each of the treatments: TRO given q.d. (r2 = 0.97 and 0.96), CIP given q.d. (r2 = 0.98 and 0.96), and CIP given b.i.d. (r2 = 0.95 and 0.93). This suggests that in order to combine data sets obtained with individual quinolones to examine potential predictors, one must be sure that these sets may be combined. Unlike AUC/MIC and AUCeff, the IE-Teff relationships plotted for the different quinolones and dosing regimens were nonspecific and virtually superimposed (r2 = 0.95). Hence, AUC/MIC, AUCeff and Teff were equally good predictors of the AME of each of the quinolones and each dosing regimen taken separately, whereas Teff was also a good predictor of the AMEs of the quinolones and their regimens taken together. However, neither the quinolones nor the dosing regimens could be distinguished solely on the basis of Teff whereas they could be distinguished on the basis of AUC/MIC or AUCeff. Thus, two types of predictors of the quinolone AME may be identified: intraquinolone and/or intraregimen predictors (AUC/MIC, AUCeff and Teff) and an interquinolone and interregimen predictor (Teff). Teff may be able to accurately predict the AME of one quinolone on the basis of the data obtained for another quinolone.

Activity of trovafloxacin (with or without ampicillin-sulbactam) against enterococci in an in vitro dynamic model of infection

Antibiotic-resistant enterococci are being increasingly identified as causal agents of infection. Trovafloxacin is a new fluoronaphthyridone with enhanced activity against gram-positive cocci and variable activity reported against Enterococcus spp. Twenty-one strains of vancomycin-resistant Enterococcus faecium and two strains of Enterococcus faecalis (one vancomycin resistant) were studied at an initial inoculum of 10(6) CFU/ml in time-kill assays with trovafloxacin (3 mg/liter), ampicillin-sulbactam (100/50 mg/liter), and the combination. Six strains of E. faecium (five vancomycin resistant) also were studied in an in vitro two-compartment dynamic model that mimics human pharmacokinetics with trovafloxacin simulated at 300 mg every 12 h (q12h), ampicillin-sulbactam at 2/1 g q6h, and the combination. Peripheral compartments were sampled q2h for 30 h for bacterial counts. Trovafloxacin MICs ranged from 0.5 to 32 mg/liter, and the nine strains of vancomycin-resistant E. faecium for which MICs were < or =2 mg/liter were more likely to show a reduction of 2 log units or more in viable counts in time-kill assays than were strains for which MICs were higher. Synergism with ampicillin-sulbactam was found for only one strain (trovafloxacin MIC, 16 mg/liter). Similar results were obtained in the pharmacokinetic model, with 2- to 4-log-unit reductions in viable bacteria for trovafloxacin-susceptible strains. Although no convincing evidence of synergism was found, ampicillin-sulbactam in combination minimized late bacterial regrowth of two trovafloxacin-susceptible strains. These data suggest that this high dose of trovafloxacin (with or without ampicillin-sulbactam) might be useful against strains of vancomycin-resistant E. faecium for which MICs were < or =2 mg/liter.

Sexual behavior and contraceptive use. Changes from 1975 to 1995 in college women

OBJECTIVE

The objective of this study was to compare the sexual practices and contraceptive use in a sample of college women in 1995 with women surveyed in 1975, 1986 and 1989.

STUDY DESIGN

We surveyed 336 college women seen at a university student health service or on campus and compared their responses to those of women surveyed at the university in 1975, 1986 and 1989.

RESULTS

The proportions of women who were sexually experienced, number of life-time male sexual partners, number of male sexual partners in the past year and frequencies of specific sexual practices were similar over the four survey times. Condom use was reported as the usual method of contraception in 7% of sexually experienced women in 1975, 14% in 1986, 25% in 1989 and 46% in 1995 (P < .00001, linear trend).

CONCLUSION

We found little change in sexual practices in this college population over the four survey years, with the exception of an increase in the self-reported use of condoms. Increased educational efforts should emphasize safe sexual practices (barrier methods) to prevent sexually transmitted diseases and highly efficacious methods of contraception (hormonal contraception) to avoid unintended pregnancy.

Net effect of inoculum size on antimicrobial action of ampicillin-sulbactam: studies using an in vitro dynamic model

To examine the predictable effect of inoculum size on the kinetics of the antimicrobial action of ampicillin-sulbactam, five TEM-1 beta-lactamase-producing Escherichia coli strains were studied in an in vitro dynamic model at two different initial inocula (N0S). All bacteria were exposed to ampicillin-sulbactam in a simulated system reflecting the pharmacokinetic profiles in human tissue after the administration of a single intravenous dose of ampicillin (2 g) plus sulbactam (1 g). Each strain was studied at low (4.0 to 5.2 log CFU/ml) and high (5.0 to 7.1 log CFU/ml) N0S. Despite pronounced differences in susceptibilities, the patterns of the killing curves observed with a given strain at different N0S were similar. As expected, viable bacterial counts increased with inoculum size. Striking visual contrasts in the respective curves for each organism were reflected by the area under the bacterial count-time curve (AUBC) but not by the difference between the N0 and the lowest bacterial counts (Nmin) at the nadir of the killing curve: the N0-associated changes in the AUBC on average were 75%, versus 2.5% for log N0--logNmin. To examine qualitative differences in antimicrobial effects at different N0S (i.e., the net effect of the inoculum), the difference in the high and low N0S was subtracted from each point on the killing curve obtained at the higher N0 for each strain. These adjusted curves were virtually superimposable on the observed killing curves obtained at the lower N0. Moreover, by using adjusted data, the AUBC values were similar at the two inocula, although slight (average, 11%) but systematic increases in the AUBC occurred at high N0S. Thus, there was only a weak net effect of inoculum size on the antibacterial effect of ampicillin-sulbactam. Due to similar slopes of the AUBC-log N0 plots, the antibacterial action at different N0S may be easily predicted by an approximate equation; the predicted AUBCs were unbiased and well correlated with the observed AUBCs (r = 0.997). Compiled data obtained with normalized AUBCs for different strains at different N0S yielded a positive correlation (r = 0.963) between the N0-normalized AUBC and the MIC of ampicillin-sulbactam. The adjustment and normalization procedure described might be a useful tool for revealing the net effect of the inoculum and to predict the inoculum effect if there are no qualitative differences in antimicrobial action at different inocula.

Monotherapy with meropenem versus combination therapy with ceftazidime plus amikacin as empiric therapy for fever in granulocytopenic patients with cancer. The International Antimicrobial Therapy Cooperative Group of the European Organization for Research and Treatment of Cancer and the Gruppo Italiano Malattie Ematologiche Maligne dell'Adulto Infection Program

Combinations of beta-lactams plus aminoglycosides have been standard therapy for suspected infections in granulocytopenic cancer patients, especially those with profound long-lasting granulocytopenia. With the advent of new broad-spectrum bactericidal antibiotics such as extended-spectrum cephalosporins or carbapenems, the need to combine beta-lactams with aminoglycosides became more controversial. The objective of this prospective randomized multicenter study was to compare the efficacy, safety, and tolerance of meropenem monotherapy with those of the combination of ceftazidime plus amikacin for the empirical treatment of fever in granulocytopenic cancer patients. Of 1,034 randomized patients, 958 were assessable in the intent-to-treat analysis for response to antibacterial therapy, including 483 in the meropenem group and 475 in the ceftazidime-plus-amikacin group. The median durations of neutropenia were 16 and 17 days, respectively. A successful outcome was reported in 270 of 483 (56%) patients treated with monotherapy compared with 245 of 475 (52%) patients treated with the combination group (P = 0.20). The success rates in the monotherapy group and the combination group were similar by type of infection (single gram-negative bacteremia, single gram-positive bacteremia, clinically documented infection, and possible infection). The occurrence of further infections assessed in patients for whom the allocated regimen was not modified did not differ between the two groups (12% in both groups). Mortality due to the presenting infection or further infection was relatively low (8 patients treated with the monotherapy compared with 13 patients treated with the combination). A total of 1,027 patients were evaluable for adverse events; the proportion of those who developed adverse effects was similar between the two groups (29% in both groups), and only 19 (4%) patients in the monotherapy group and 31 (6%) in the combination group experienced an adverse event related or probably related to the study drug. Allergic reactions were the only reason for stopping the protocol antibiotic(s) (3 and 5 patients, respectively). This study confirms that monotherapy with meropenem is as effective as the combination of ceftazidime plus amikacin for the empiric treatment of fever in persistently granulocytopenic cancer patients, and both regimens were well tolerated.

Predictors of effect of ampicillin-sulbactam against TEM-1 beta-lactamase-producing Escherichia coli in an in vitro dynamic model: enzyme activity versus MIC

The clinical outcome in patients treated with ampicillin-sulbactam may not always be predictable by disc susceptibility testing or with the MIC as determined with a constant level (4 micrograms/ml) of the beta-lactamase inhibitor (MIC1). The enzyme activities (EA) and the MICs estimated at a constant ratio of ampicillin to sulbactam of 2:1 (MIC2) for 15 TEM-1 beta-lactamase-producing strains of Escherichia coli were examined as alternatives to MIC1 as predictors of the antibacterial effects of this combined drug as studied in an in vitro model which simulates ampicillin-sulbactam pharmacokinetic profiles observed in human peripheral tissues. Integral parameters describing the area under the bacterial count-time curve (AUBC), the area between the normal growth curve, and the killing curve of bacteria exposed to antibiotic (ABBC), and the second parameter expressed as a percentage of its maximal hypothetical value (ABBC/ABBCmax) were calculated. All three parameters correlated well with EA (AUBC, r = 0.93; ABBC, r = -0.88; ABBC/ABBCmax, r = -0.91) and with MIC2 (r = 0.94, -0.94, and -0.95, respectively) but not with MIC1. Both EA and MIC2 can be considered reliable predictors of the antibacterial effect of ampicillin-sulbactam in an in vitro model. These correlations suggest that in vitro kinetic-dynamic models might be useful to reexamine established susceptibility breakpoints obtained with data based on the MIC1 (MICs obtained with constant levels of beta-lactamase inhibitors). These data also suggest that quantitative determinations of bacterial beta-lactamase production and MICs based on the component concentration ratio observed in vivo might be useful predictors of the effect of ampicillin-sulbactam and other beta-lactam-inhibitor combinations.

New and unusual infections in neutropenic patients

Infections in immunocompromised patients with cancer are common and the primary risk factor is neutropenia, usually induced by chemotherapeutic agents. The spectrum of bacterial infection is shifting from gram-negative to gram-positive. The array of fungal infections in cancer patients is expanding to include organisms previously unknown as invasive human pathogens. New species are being defined to explain extant pathologies, and free living algae are now emerging as pathogens in immunocompromised patients. Physicians must remain alert to these emerging pathogens and to the need to evaluate optimal treatments for the usual and unusual infections in neutropenic and other compromised patients with cancer and allied diseases.

Pharmacodynamics of piperacillin alone and in combination with tazobactam against piperacillin-resistant and -susceptible organisms in an in vitro model of infection

The pharmacodynamics of dosage regimens of piperacillin alone or in combination with tazobactam against piperacillin-resistant or -susceptible bacteria were studied in an in vitro model of infection. Experiments were conducted by using a fixed daily exposure of 12 g of piperacillin, given as 3 g alone or in combination with tazobactam at 0.375 g every 6 h, or the same total dose of the combination given as 4 g of piperacillin plus 0.5 g of tazobactam every 8 h. The addition of tazobactam to piperacillin, irrespective of the dosing interval, did not alter the killing of piperacillin-susceptible organisms (Escherichia coli J53 and Pseudomonas aeruginosa ATCC 27853). In contrast, experiments with an isogenic TEM-3-containing transconjugant of E. coli J53 (E. coli J53.2-TEM-3) that was resistant to piperacillin (MIC, 128 micrograms/ml) showed that the addition of tazobactam resulted in bacterial killing similar to that observed with the wild-type strain. Although tazobactam concentrations fell to less than 4 mg/liter (the concentration associated with a reduction in the piperacillin MIC from 128 to 2 mg/liter) 2 to 3 h after a dose, a similar degree of bacterial killing was observed when the same total 24-h dose of piperacillin-tazobactam was fractionated into dosing intervals of every 6 or 8 h. Investigations with Staphylococcus aureus 7176 (piperacillin MIC, 128 micrograms/ml) showed that the addition of tazobactam, again irrespective of dosing interval, also resulted in net bacterial killing which was not seen with piperacillin alone. These data support the use of extended dosing intervals (every 8 h) of piperacillin-tazobactam in the treatment of infections caused by piperacillin-resistant bacteria.

The incidence of genitourinary infections in a cohort of healthy women

BACKGROUND AND OBJECTIVES

Few data are available on the incidence and frequency of occurrence of vaginitis and urinary tract infections in population-based groups.

GOAL OF THIS STUDY

To assess the incidence and frequency of occurrence of vaginitis and urinary tract infections among a population of healthy adult women.

STUDY DESIGN

A questionnaire regarding genitourinary infections was sent to 500 women, 315 (63%) of whom responded.

RESULTS

A history of one or more urinary tract infections was reported by 199 (63.2%) of the women. Trichomoniasis was reported by 82 (26%) and bacterial vaginosis by 91 (29%) of the participants. A history of physician-diagnosed vulvovaginal candidiasis was noted by 210 (67%) of the respondents, 70 (22%) of whom had been treated for vulvovaginal candidiasis during the preceding year. Classical sexually transmitted conditions such as gonorrhea (4.8%), genital herpes (6.7%), and genital warts (7.6%) were reported less often than vaginal and urinary tract infections.

CONCLUSION

Urinary tract infections and vaginal infections, especially vulvovaginal candidiasis, are common events among healthy adult women.

Dose ranging and fractionation of intravenous ciprofloxacin against Pseudomonas aeruginosa and Staphylococcus aureus in an in vitro model of infection

The effect of dose or dose interval on the pharmacodynamics of simulated high-dose intravenous ciprofloxacin therapy on infection due to Pseudomonas aeruginosa and Staphylococcus aureus was studied in an in vitro hollow-fiber model of infection. Simulated doses of 1,200 mg of ciprofloxacin per day as either 400 mg every 8 h or 600 mg every 12 h against P. aeruginosa resulted in selection of ciprofloxacin-resistant bacteria. The results with one test strain that was isolated from a patient prior to administration of intravenous ciprofloxacin demonstrated selection of a gyrA mutant in the model, as had occurred in vivo. A single 1,200-mg dose every 24 h did not select for bacterial resistance; however, breakthrough regrowth of ciprofloxacin-susceptible bacteria occurred. Dosages of 400 or 600 mg of ciprofloxacin every 12 h effectively reduced bacterial counts of one strain each of methicillin-susceptible or -resistant S. aureus, with no bacterial resistance detected at the end of experiment; in contrast, 200 mg every 12 h resulted in bacterial regrowth due to the selection of drug-resistant bacteria. These data show the need for high-dose intravenous ciprofloxacin, particularly with regimens producing high peak levels, for treatment of infections where selection for bacterial resistance is a clinical problem.

2',3'-didehydro-3'-deoxythymidine (d4T) in patients with AIDS or AIDS-related complex: a phase I trial

2',3'-didehydro-3'-deoxythymidine (d4T) is a pyrimidine analogue and inhibitor of reverse transcriptase with potent in vitro activity against human immunodeficiency virus (HIV). A phase I trial of d4T was conducted in 41 HIV-infected patients, 12 with AIDS and 29 with AIDS-related complex (ARC). Thirty-six patients were evaluatable. The maximum tolerated dose was 2 mg/kg/day. The dose-limiting toxicity was sensory peripheral neuropathy, which occurred in 20 patients (55%). Four patients (11%) developed hepatotoxicity. Five (14%) developed anemia requiring a transfusion but not discontinuation of drug. The mean +/- SE plasma elimination half-life at all dose levels was 1.2 +/- 0.09 h. Increased or stable absolute CD4 counts were seen in most patients. The majority of patients with detectable serum p24 antigen levels had a persistent decrease by 6 months. d4T is a promising drug for patients with AIDS or ARC. This clinical trial is continuing to determine the minimal effective dose.

Management of urinary tract infections in pregnancy: a review with comments on single dose therapy

Most investigators agree that the adverse effects of urinary tract infections in pregnancy can be abrogated by effective early detection and treatment. However, the optimal methods for screening and treatment remain controversial. Although single-dose therapy has not been applied to pregnant women with acute pyelonephritis, most but not all studies which have compared single-dose with longer courses of beta-lactam or other antibiotics in pregnant asymptomatic bacteriuric women have shown no differences in outcome. This paper reviews recent trials of single-dose treatment of bacteriuria in pregnant women.