Pharmacokinetics of sparfloxacin and serum bactericidal activity against pneumococci

Comparative pharmacokinetics and pharmacodynamics of the newer fluoroquinolone antibacterials

A number of new fluoroquinolone antibacterials have been released for clinical use in recent years. These new agents exhibit enhanced activity against Gram-positive organisms while retaining much of the Gram-negative activity of the earlier agents within the same class. The pharmacokinetics of most of these agents are well described including serum pharmacokinetics, tissue and fluid distribution, and pharmacokinetics in renal and hepatic disease. When compared with earlier agents within this class (i.e. ciprofloxacin), the newer agents retain the wide distribution characteristics; however, they exhibit a more prolonged elimination, which, in part, supports single daily administration for these agents. Based on their predominant renal elimination, dosage adjustment is necessary in the presence of renal disease for ciprofloxacin, levofloxacin, gatifloxacin and sitafloxacin. Drug interactions, particularly with multivalent cations (calcium/aluminium-containing antacids and iron products), remain a problem for the newer agents, resulting in reduced absorption requiring separate administration times to maximise bioavailability. However, the newer agents do not appear to interfere significantly with the cytochrome P450 system, thus minimising the potential for interactions with other drugs metabolised by this system. The pharmacodynamic properties of the fluoroquinolones have been well described. The bactericidal activity is maximised when the ratios of peak plasma drug concentration (Cmax): minimum inhibitory concentrations (MIC) or area under the concentration-time curve (AUC): MIC exceed specific threshold values. Knowledge of the pharmacodynamic relationships allows for appropriate drug selection and enables design of dosage regimens to maximise the bactericidal activity. Therapeutic drug monitoring of the fluoroquinolones may provide a means of optimising the dosage regimen in certain clinical situations (that is, meningitis and hospitalised pneumonias) with the goals of achieving a more predictable therapeutic response and minimising the potential for the development of resistance.

Influence of diminished susceptibility of Streptococcus pneumoniae to ciprofloxacin on the serum bactericidal activity of gemifloxacin and trovafloxacin after a single dose in healthy volunteers

The serum bactericidal activity against 2 Streptococcus pneumoniae strains (ciprofloxacin MIC 1 and 4 mg/l) was measured in 12 volunteers who received oral single doses of gemifloxacin 320 mg and trovafloxacin 200 mg in a crossover fashion. The 4-fold increase in ciprofloxacin MIC from the susceptible to the resistant strain resulted in a 2-fold increase in MIC (from 0.015 to 0.03 mg/l), a 2-fold decrease in C(max)/MIC (104 vs 52) and in AUC(0-24 h)/MIC (532 vs 266), but a 5.6-fold decrease in area under the bactericidal curve (AUBC: 168 vs 30) for gemifloxacin. Trovafloxacin showed a 4-fold higher MIC (0.25 vs 0.06 mg/l), a 4-fold lower C(max)/MIC (8.6 vs 36), a 4-fold lower AUC(0-24 h)/MIC (85 vs 356) and a 11-fold lower AUBCs (2 vs 22) against the resistant isolate compared with the susceptible one. Trovafloxacin serum bactericidal titres against the ciprofloxacin-resistant strain were measurable generally only at 1 h after dosing (median titre=2). Gemifloxacin showed similar ex vivo bactericidal activity against the ciprofloxacin-resistant strain to that of trovafloxacin against the ciprofloxacin-susceptible strain.

Activities of trovafloxacin, gatifloxacin, clinafloxacin, sparfloxacin, levofloxacin, and ciprofloxacin against penicillin-resistant Streptococcus pneumoniae in an in vitro infection model

We adapted an in vitro pharmacodynamic model of infection to incorporate infected fibrin clots. The bactericidal activities of various fluoroquinolones against two strains of penicillin-resistant Streptococcus pneumoniae were studied over a 48-h period. Bacteria were prepared in Muller-Hinton broth by using colonies from a 24-h tryptic soy agar plus 5% sheep blood plate and were added to a mixture of cryoprecipitate (80%) and thrombin (10%) to achieve approximately 10(6) CFU of organism per fibrin clot. The fibrin clots were suspended into the models and removed, in triplicate, at various time points over 48 h. Control models were also conducted to characterize the growth of S. pneumoniae in the growth medium without antibiotic. Trovafloxacin, gatifloxacin, clinafloxacin, sparfloxacin, levofloxacin, and ciprofloxacin were administered to simulate their pharmacokinetic profiles in humans. Fibrin clot samples were also plated onto antibiotic-containing tryptic soy agar plus 5% lysed horse blood to detect resistance. The newer fluoroquinolones demonstrated better activity than ciprofloxacin against both isolates. In conclusion, the newer quinolones demonstrated significant activity against penicillin-resistant S. pneumoniae, with standard dosing resulting in area under the concentration-time curve/MIC ratios and peak concentration/MIC ratios that resulted in 99.9% killing against these isolates.

The prevalence of fluoroquinolone resistance among clinically significant respiratory tract isolates of Streptococcus pneumoniae in the United States and Canada--1997 results from the SENTRY Antimicrobial Surveillance Program

As part of the SENTRY antimicrobial resistance surveillance program, a total of 1100 clinically significant respiratory tract isolates of Streptococcus pneumoniae were tested for susceptibility to six fluoroquinolone antimicrobial agents: ciprofloxacin, levofloxacin, gatifloxacin, grepafloxacin, sparfloxacin, and trovafloxacin. Isolates were obtained during the 5-month period, February to June, 1997 from 27 United States medical center laboratories and seven laboratories in Canadian health care institutions. All testing was performed in a single center. Of 1100 test strains, 3 (0.3%), all from different U.S. centers, were fluoroquinolone resistant. Among the remaining 1097 fluoroquinolone-susceptible isolates, the rank order of activity among the six agents tested in this study was grepafloxacin (modal MIC = 0.25 microgram/mL) = trovafloxacin (modal MIC = 0.25 microgram/mL) = sparfloxacin (0.25 microgram/mL) > gatifloxacin (0.5 microgram/mL) > levofloxacin (1 microgram/mL) = ciprofloxacin (1 microgram/mL). Fluoroquinolone resistance is currently uncommon among respiratory tract isolates of S. pneumoniae in North America, but there exist clear differences between the in vitro activities of different fluoroquinolones for this organism.

Comparative in vitro activities of four new fluoroquinolones against Streptococcus pneumoniae determined by Etest

Clinafloxacin, levofloxacin, sparfloxacin and trovafloxacin were tested by Etest against 188 Streptococcus pneumoniae isolates. Clinafloxacin and trovafloxacin were 2-4-fold more potent than sparfloxacin and 8-fold more than levofloxacin. Two isolates, both serotype 6, with high-level quinolone resistance (> or = 8 micrograms/ml) were detected. The Etest is a practical means for determining S. pneumoniae susceptibilities to new fluoroquinolones.

Pharmacodynamic effects of amoxicillin versus cefotaxime against penicillin-susceptible and penicillin-resistant pneumococcal strains: a phase I study

Serum bactericidal activity against a penicillin-susceptible strain and a penicillin-resistant strain of Streptococcus pneumoniae (amoxicillin and cefotaxime MICs, 0.001 and 1 microg/ml, respectively, and MBCs, 0.01 and 2 microg/ml, respectively) was measured in 12 healthy volunteers who each received an oral 875-mg dose of amoxicillin and an intramuscular 1-g dose of cefotaxime in a crossover fashion. The areas under the bactericidal activity-time curves for the two strains were found to be similar for both antibiotics despite the significantly higher (P < 0.002) AUC/MIC and peak level/MIC values for cefotaxime.

Suspicion of quinolone active metabolite following discrepancy between predicted and experimental urine bactericidal activities

The prediction of urine antibacterial activity from pharmacological and microbiological parameters was assessed by using experimental urine levels and urine bactericidal titers determined up to 72 h after a 400-mg single dose of two quinolones in a phase I study. The area under the bactericidal curve (AUBC) was accurately predicted for norfloxacin but significantly (P < 0.001) underestimated for rufloxacin (actual value was four times higher than the predicted value against Escherichia coli and two times higher against Staphylococcus aureus). In vitro susceptibility differences between the two strains predicted the ex vivo AUBC differences for norfloxacin but not for rufloxacin, where ex vivo differences were greater than expected. Urine bactericidal titers for up to 72 h were accurately predicted for norfloxacin against E. coli and S. aureus and for rufloxacin against S. aureus, but experimental activity for up to 48 h was four times higher (P < 0.001) than the predicted activity for rufloxacin against E. coli. In the case of norfloxacin, the duration of adequate urine antibacterial activity against S. aureus was overestimated. Inaccurate estimations of ex vivo antibacterial activity of a suspected active metabolite (as with rufloxacin) when an adequate cutoff is not established may have dosing implications.

Sparfloxacin. A review of its antibacterial activity, pharmacokinetic properties, clinical efficacy and tolerability in lower respiratory tract infections

Sparfloxacin is a fluoroquinolone antibacterial agent with activity against a broad range of Gram-negative and Gram-positive organisms including Streptococcus pneumoniae, one of the main pathogens in community-acquired pneumonia. In this infection, sparfloxacin has shown efficacy similar to that of amoxicillin, erythromycin, roxithromycin, amoxicillin/clavulanic acid and amoxicillin plus ofloxacin, producing clinical cure rates of 80 to 84% assessed by intention-to-treat analyses in European or multinational trials. US studies showed similar results for sparfloxacin to those for erythromycin and cefaclor. Sparfloxacin was also as effective as all other comparator drugs in patients with other lower respiratory tract infections, usually acute exacerbations of chronic obstructive pulmonary disease (COPD). The profile of adverse effects for sparfloxacin is generally similar to that of other quinolones: gastrointestinal discomfort and CNS effects are the most common in clinical trials. Sparfloxacin causes fewer gastrointestinal disturbances than agents such as amoxicillin and erythromycin and doses not interact with theophylline, an important consideration when treating patients with respiratory disease. Its long elimination half-life permits once-daily dosage regimens. On the other hand, there are infrequent reports of prolonged QTc interval (3% increase) during sparfloxacin therapy. Photosensitivity occurs more frequently than with the other fluoroquinolones (2% of patients in an ongoing postmarketing study and 7.9% of those in US trials), and requires ongoing surveillance. In summary, the good activity of sparfloxacin against S. pneumoniae and other respiratory pathogens supports its use in lower respiratory tract infections, particularly community-acquired pneumonia. Its profile of good efficacy, once-daily dosage, good gastrointestinal tolerability and lack of interaction with theophylline are advantageous, but clinicians and patients must be alert to the possibility of photosensitivity reactions. On this basis, sparfloxacin, when appropriately prescribed, can provide the clinician with a useful alternative treatment option for these common infections.