Influence of probenecid on serum levels and urinary excretion of cinoxacin

Renal handling of fleroxacin in rabbits, dogs, and humans

The renal handling of fleroxacin was studied by renal clearance and stop-flow techniques in rabbits and dogs and by analyzing the pharmacokinetics with and without probenecid in humans. In rabbits the excretion ratios (fleroxacin intrinsic renal clearance/glomerular filtration rate) were greater than unity (2.01) without probenecid and were decreased to a value below unity (0.680) with probenecid. In dogs, on the other hand, the excretion ratios were less than unity (0.608 and 0.456) both without and with probenecid, and so were not affected by probenecid. This fact suggested that fleroxacin was excreted into urine by both glomerular filtration and renal tubular secretion in rabbits, but only by glomerular filtration in dogs, accompanied by partial renal tubular reabsorption in both species; these mechanisms were also supported by stop-flow experiments. In humans probenecid treatment induced increases in the elimination half-life and area under the serum concentration-time curve and decreases in apparent serum clearance, renal clearance, and urinary recovery of fleroxacin. The excretion ratio without probenecid was 1.13, which was significantly decreased to 0.750 with probenecid. These results indicated that both renal tubular secretion and reabsorption contributed to renal excretion of fleroxacin in humans. The contribution of tubular secretion was species dependent and was extensive in rabbits, minimal in dogs, and moderate in humans. Renal tubular reabsorption was commonly found in every species. The long elimination half-life of fleroxacin in humans might be explained by its small total serum clearance and small renal clearance, which are attributed to less tubular secretion and more tubular reabsorption.

Pharmacokinetics: metabolism and renal excretion of quinolones in man

The quinolones are relatively poorly absorbed from the gastrointestinal tract. The elimination proceeds mainly by renal excretion. The half-life of elimination depends on the molecular structure and varies between 2 and 10 h. Impaired kidney function is expected to increase the half-life of elimination, though this effect is not always observed. Since the 4-oxo-metabolites show a higher renal clearance than the parent drug, renal impairment will result in a cumulation of the metabolites in the body.

Time-dependent elimination of cinoxacin in rats

The effect of the variation of urinary pH on the pharmacokinetics of the acidic antibacterial agent, cinoxacin (pKa 4.60), was examined. Urinary pH of 24-h fasted rats remained at about pH 6 during the daytime, while that of nonfasted rats was high (about pH 7.5) in the morning and gradually decreased to a pH similar to that of the fasted rat in the afternoon. The free fraction of cinoxacin in fasted rat sera in the morning was similar to that in nonfasted rats despite the longer half-life of cinoxacin in fasted rats. In the afternoon the free fraction was slightly different despite similar cinoxacin elimination in fasted and nonfasted rats. These findings seemed to exclude the contribution of protein binding from the causes of increased cinoxacin elimination in nonfasted rats in the morning. Elimination rate constants of cinoxacin obtained with a one-compartment open model correlated well with urinary pH 30 min after injection, suggesting that the urinary pH plays a more important role in cinoxacin elimination. When cinoxacin was orally administered to fasted rats at 11:00, the area under the plasma concentration-time curve was threefold larger than in nonfasted rats. As found with the intravenous administration, this difference may be explained by the prolonged half-life caused by decreased urinary pH after fasting. This study revealed the time-dependent elimination of cinoxacin in nonfasted rats, which is related to physiological change of urinary pH caused by food intake.

Comparative pharmacokinetic profiles of cinoxacin and pipemidic acid in humans

Serum and urinary levels of Cinoxacin and pipemidic acid were determined at 7-day intervals in the same 10 healthy volunteers after a single oral dose of respectively 500 and 400 mg of the drugs. Comparison of results shows that Cinoxacin was absorbed faster (absorption half-life, ta 1/2cin = 0.25 h) than pipemidic acid (ta 1/2pip = 0.37 h) and distributed in a smaller apparent volume (AVDcin = 23.5 1/1.73 m2; AVDpip = 60.1 1/1.73 m2). Biological half-lives were identical (tb 1/2cin = 2.10 h; tb 1/2pip = 2.15 h). On the other hand, serum levels for Cinoxacin at 1, 2 and 4 hours (8.1 +/- 1.5 micrograms/ml, 10.6 +/- 1.5 micrograms/ml, 5.6 +/- 1.3 micrograms/ml respectively) were higher than those for pipemidic acid (3.3 +/- 0.3 micrograms/ml, 3.4 +/- 0.5 micrograms/ml, 2.1 +/- 0.5 micrograms/ml respectively). Urinary excretion of the two derivatives during the 12 hours following their administration was similar (Ucin0-12h = 86%; Upip0-12h = 83%). Mean urinary concentrations were particularly high, still attaining respectively 90 +/- 29 micrograms/ml and 131 +/- 38 micrograms/ml in samples collected between the 9th and the 12th hours; these levels were well above the M.I.C. for the Gram-negative organisms included within the spectrum of activity of these two quinolones. In addition, predictive calculations of serum levels reached after multiple dosing indicate that at an administration rate of 500 mg every 6 or preferably every 4 hours, Cinoxacin concentrations should be sufficiently high to be of interest in the treatment of systemic infections by sensitive organisms.

Cinoxacin. A review of its pharmacological properties and therapeutic efficacy in the treatment of urinary tract infections

Cinoxacin is a urinary antibacterial drug closely related structurally to nalidixic acid. It has a spectrum of in vitro antibacterial activity which qualitatively resembles that of the latter agent, covering most common Gram-negative pathogens, excluding Pseudomonas. In acute or recurrent urinary tract infections it has been shown to be at least as effective as nalidixic acid or co-trimoxazole, and in a few studies was as effective as amoxycillin or nitrofurantoin. Cinoxacin appears to be well tolerated and may have a low propensity to induce bacterial resistance during clinical use, although the latter needs further confirmation. Thus, cinoxacin is an effective alternative for treating urinary tract infections due to common Gram-negative pathogens, and its apparently low incidence of adverse effects may offer worthwhile advantages over the related compounds nalidixic and oxolinic acids. Its use as prophylactic therapy in patients with recurrent urinary tract infections is not yet well established, although this appears a worthwhile area for further study.

Effect of probenecid on the pharmacokinetics of aminophylline

The authors investigated the effect of probenecid on the pharmacokinetics of aminophylline. Seven normal volunteers served as their own controls in a crossover study. In the first phase, subjects received an oral dose of aminophylline after an overnight fast. In the second phase, probenecid was given orally 30 minutes prior to the administration of aminophylline. Serum and urine theophylline levels were determined by high performance liquid chromatography. Statistical analysis showed that probenecid had no significant effect on any of the pharmacokinetic parameters measured. Probenecid appears to have little or no influence on the liver metabolism of theophylline.

Mechanism of renal excretion of AM-715, a new quinolonecarboxylic acid derivative, in rabbits, dogs, and humans

The mechanisms of the renal excretion of AM-715, a synthetic antimicrobial agent, were studied in rabbits, dogs, and humans. In both rabbits and humans, AM-715 clearance was greater than creatinine clearance and was profoundly decreased by the administration of probenecid. Thus, in these subjects, AM 715 was cleared by both tubular secretion and glomerular filtration. In dogs, however, the excretion ratio (close to unity), biological half-life, and stop-flow pattern of AM-715 were not affected by probenecid, indicating that the renal excretion of AM-715 took place mostly through glomerular filtration. These results suggest that renal excretion of AM-715 differs with animal species.

Effect of cinoxacin on cellular metabolism and p-aminohippurate transport in kidney cortical slices in terms of its nephrotoxic action

Cinoxacin is a drug which, at very high doses, causes renal damage only in rats. This study compared the in vitro effects of cinoxacin and nalidixic acid on cellular metabolism and p-aminohippurate (PAH) transport in renal cortical slices. Cinoxacin had no effect on Na+ transport, ATP content, oxygen consumption, inulin space and tissue water content, in rat renal cortical slices in vitro, while nalidixic acid affected most of the parameters tested. PAH uptake by slices from rats pre-treated with a nephrotoxic dose of cinoxacin was decreased. This renal damage appeared to be due to physical trauma resulting from deposition of cinoxacin crystals in the urinary tract.

Cinoxacin (Cinobac, Eli Lilly & Co.)

Cinoxacin, a synthetic organic acid antibacterial agent, related structurally to nalidixic and oxolinic acid, has been approved for the treatment of initial and recurrent urinary tract infections (UTIs) caused by susceptible gram-negative microorganisms. The role of cinoxacin in the treatment of UTIs, compared with the usual first-line agents, is uncertain at this time. The efficacy of cinoxacin in the treatment of pyelonephritis, compared with these proven agents, has been examined in only small numbers of patients, and cinoxacin is more expensive than these agents. Cinoxacin may prove valuable in the treatment of prostatitis and in the prophylaxis of recurrent UTIs; further study in these areas is warranted. In the routine treatment of acute UTIs, cinoxacin perhaps should be reserved only for those patients with organisms resistant to usual first-line agents or those who fail to respond to therapy with these agents. In this respect, cinoxacin may, in the future, replace nalidixic acid.

Cinoxacin: mechanism of action, spectrum of activity, pharmacokinetics, adverse reactions, and therapeutic indications

Cinoxacin, a chemotherapeutic agent that inhibits bacterial DNA synthesis, has recently been approved for the treatment of initial and recurrent bacterial urinary tract infections. Although closely related to nalidixic acid, cinoxacin possesses some distinct characteristics: rapid attainment of therapeutic urinary concentrations and greater activity against strains of Enterobacteriaceae that cause urinary tract infections. Biopharmaceutical properties include serum protein binding of approximately 70%, 50-60% excretion of intact drug in the urine of patients with normal renal function, and an elimination half-life of approximately one hour. The elimination half-life is increased in patients with decreased renal function and when probenecid is coadministered. Adverse events occur infrequently and consist of nausea, vomiting, headache, dizziness, and hypersensitivity reactions. The drug compares favorably with standard therapies for the treatment of bacterial cystitis and recurrent urinary tract infections. Initial studies demonstrate that cinoxacin has substantial efficacy as a prophylactic agent for those women who experience recurrent, symptomatic urinary tract infections.

Cinoxacin in urinary tract infections. Theoretical and practical considerations

In dogs we found that cinoxacin concentrations in prostatic tissue, secretion, and interstitial fluid always were lower than the simultaneous serum concentrations, during constant infusion experiments. The cinoxacin concentrations in urethral and vaginal secretions were similar to those found in prostatic interstitial fluid, approximately one third to one fourth of the simultaneous serum concentrations. The concentrations of cinoxacin in human prostatic tissue after single or multiple doses of 500 mg. were found to be in the range of minimum inhibitory concentrations for most microorganisms found in urinary tract infections. Cinoxacin was found to have a half-life of 2.7 hours in patients with normal renal function, but increased to 8.5 hours in patients with impaired renal function. We found little or no drug accumulation during a seven-day treatment of patients with impaired renal function.

The effect of probenecid on the pharmacokinetics and distribution of cefoxitin in healthy volunteers

1 Cefoxitin was given by acute intravenous injection to six healthy volunteers, in a crossover study to investigate the effects of concurrent probenecid administration. 2 Serum antibiotic concentrations were determined by microbiological assay. Cefoxitin concentrations were simultaneously determined in the fluid of blisters produced by topical cantharides. All antibiotic was accounted for in the urine. 3 Cefoxitin was administered by intravenous infusion, subsequent to a loading dose, to produce steady state levels in the region of 10 microgram/ml, in one volunteer. The procedure was later repeated after prior administration of probenecid in the same subject. 4 Pharmacokinetic analyses indicated significant changes only in the parameters associated with renal excretion of drugs. Clearance was reduced by half. 5 The absolute and relative amounts of antibiotic in the central and peripheral compartments were calculated for both modes of administration. In the acute study probenecid produced a small change in distribution away from the peripheral or tissue compartment, towards the central compartment. 6 There was no elevation of initial serum concentrations and sustained levels of antibiotic could be accounted for principally by retarded excretion produced by probenecid, with little contribution by alteration in the disposition of antibiotic. 7 The sustained serum levels of cefoxitin that resulted from its decreased excretion were also reflected in blister fluid. It was concluded that the sustained cefoxitin levels produced by probenecid resulted in similar raised levels in the peripheral or "tissue' compartment, since the redistribution away from the peripheral compartment did not contribute materially to other changes in disposition of drug.

Effect of orally administered probenecid on the pharmacokinetics of cefoxitin

To characterize the effect of orally administered probenecid on the pharmacokinetics of cefoxitin in healthy male volunteers, we administered to one group of six subjects 2 g of cefoxitin by intravenous (i.v.) bolus either alone, with 1 g of probenecid concomitantly, or when 1 g of probenecid was administered 1 h previously by using a crossover design. Likewise, we administered to a second group of six subjects 2 g of cefoxitin intramuscularly (i.m.) together with 1 and 2 g of probenecid. Probenecid increased the mean terminal half-life and the area under the serum cefoxitin concentration-time curve (AUC0-24) and decreased renal clearance, but did not alter the volume of the central compartment or the total urinary recovery of i.v.-administered cefoxitin; pretreatment with probenecid produced a greater increase in cefoxitin AUC0-24 and a constant decrease in renal clearance compared to concomitant probenecid. The AUC0-24 after i.m.-administered cefoxitin was greater after 2 g than 1 g of probenecid; the AUC0-24 after i.v.-and i.m.-administered cefoxitin was similar after 1 g of probenecid was given concomitantly. Cefoxitin AUC0-24 was increased further when 1 g of probenecid was given before i.v.-administered cefoxitin or when 2 g of probenecid was given with i.m.-administered cefoxitin. The effect of probenecid was related to both timing and dose.