Antibiotic penetrance of ascitic fluid in dogs

Principles of antimicrobial therapy

It has been 2500 years since the Chinese began applying moldy soybean curd to cure skin infections. Technology today has refined the benefits of antibiotic-forming molds and bacteria and has greatly increased the number of antimicrobial drugs available to combat infection. Understanding the principles fundamental to rational therapy with these drugs will ensure the best of possible outcomes.

Oral pharmacokinetics and ascitic fluid penetration of ofloxacin in cirrhosis

Plasma and ascitic fluid concentrations of ofloxacin were determined in 12 cirrhotic patients after a single dose and repeated 200 mg oral doses. The single dose kinetics were compared to those obtained in 12 healthy volunteers. Mean plasma elimination half-life was 11.6 h in cirrhotics and 7.0 h in controls. Mean total clearance was 2.3 times lower in patients than in controls, due to a significant decrease of renal clearance of the drug, unrelated to creatinine clearance. Mean apparent volume of distribution was 1.2 l/kg in patients and 1.8 l/kg in controls. Estimated by the ratio of AUC in peritoneal fluid and plasma, ascitic fluid penetration was 80% after the first oral dose. Ascitic fluid concentrations equaled corresponding plasma concentrations after 10 h, without pronounced accumulation of ofloxacin in ascites. We may conclude that, in cirrhotic patients with normal serum creatinine, a significant impairment of renal tubular handling of ofloxacin could be observed and led to a delayed elimination half-life of the drug. Because of its broad spectrum of activity, low side-effect profile, and large ascitic fluid penetration after oral administration, ofloxacin appears to be a new therapeutic approach of severe infections in cirrhotic patients, in particular spontaneous bacterial peritonitis.

Management of anaerobic infections

Successful management of anaerobic infection first requires an accurate diagnosis. Cytologic examination of wound exudates and inspection for characteristic clinical clues greatly facilitates an accurate initial diagnosis of anaerobic infection. Knowledge of antimicrobial activity against specific anaerobic pathogens is essential, since antibiotic susceptibility information is not routinely available. Whenever possible, antimicrobial and surgical therapy should be combined in managing anaerobic infections. Chloramphenicol, clindamycin, and metronidazole provide the most consistently reliable activity against pathogenic anaerobes, including Bacteroides. Penicillins are also generally effective, except for treatment of infections caused by penicillinase-producing strains of Bacteroides. Cephalosporins are not considered drugs of choice for anaerobic infections, although cefoxitin may in some instances be useful as monotherapy of mixed infections containing obligate anaerobes and coliform bacteria. Aminoglycosides and sulfonamides are ineffective and should be avoided for treatment of anaerobic infection.

The clinical relevance of protein binding and tissue concentrations in antimicrobial therapy

The relevance of protein binding, molecular size and lipophilicity to tissue penetration of antimicrobials is discussed, and the clinical relevance of tissue penetration of these agents is assessed. In order to assess the relevance of any factor on the clinical outcome of a group of infections it is necessary to obtain some form of dose response; i.e. the dose has to be (intentionally or otherwise) titrated down until negative responses are seen. Information on clinical failures tends not to be reported, hence useful data are difficult to obtain. The relevance of protein binding to the microbiological activity of a drug is important and the use of some highly bound agents in readily assessable diseases is illustrated with a few examples: the poor efficacy of fusidic acid in gonorrhoea, when high failure rates are found with doses of 2g; ceftriaxone in gonorrhoea, at doses (25mg) with which one would expect cures, is associated with significant failures; the failure of cefoperazone in serious illness can be related to the degree of protein binding. The degree of tissue penetration (protein binding apart) is related to clinical efficacy in urinary tract infections (where ample evidence is available), chest infections (where the data are somewhat fewer but probably convincing) and meningitis where experimental data are firm but clinical information less readily available.

Evaluation of aztreonam in the treatment of spontaneous bacterial peritonitis in patients with cirrhosis

To determine the efficacy of aztreonam in the treatment of spontaneous bacterial peritonitis in patients with hepatic cirrhosis, 14 patients (7 males, 7 females) with 16 Gram-negative infective episodes (12 Escherichia coli and 4 Klebsiella pneumoniae) were treated with aztreonam infusions at doses of 1 gm per 8 hr for a planned 14-day period. Ages ranged from 40 to 75 years with a mean of 57 +/- 10 years. All organisms were highly susceptible to aztreonam (minimal inhibitory concentration less than or equal to 0.06 to 0.12 micrograms per ml). Serum antibiotic levels were 61.9 +/- 25.5 micrograms per ml (peak) and 27 +/- 18.5 micrograms per ml (trough). Ascitic fluid antibiotic levels were 33.6 +/- 22.5 micrograms per ml (peak) and 32.7 +/- 16.8 micrograms per ml (trough). Although the symptoms of infection were controlled within 3 days and ascitic fluid cultures became negative after 48 hr, 10 patients (62.5%) died, with hepatorenal syndrome and digestive tract hemorrhage as the principal causes of death. Three patients developed streptococcal superinfections during treatment; Streptococcus faecalis peritonitis in one case and spontaneous bacteremia due to Streptococcus equinus and Streptococcus mutans in the other two. Aztreonam was well tolerated and clinically and bacteriologically efficacious in controlling the infection. Serum and ascitic fluid levels were considerably higher than the minimal inhibitory concentration for the causative organisms, suggesting that lower doses may achieve suitable therapeutic levels. A negative aspect of the antibiotic therapy was the superinfections. The high mortality rate was attributable to the generally poor underlying condition of the patients.

Penetration and clearance of cefoperazone and moxalactam in pleural fluid

The penetration of cefoperazone and moxalactam into pleural fluid was studied in 11 patients after intravenous infusion of 2-g doses of these agents. Clearance of these agents from pleural fluid was studied in seven patients after instillation of 1-g doses into the pleural space. The concentrations in pleural fluid after intravenous infusion of 2-g doses reached a peak of 7 to 25 micrograms/ml for cefoperazone and 9 to 35 micrograms/ml for moxalactam at 4 to 6 h after administration. These levels exceeded reported MICs for most susceptible organisms. The elimination half-life of both agents was about two to five times longer in pleural fluid than in serum. These prolonged elimination rates of both agents might be of great advantage for killing bacteria in the pleural space.

Influence of ascites on tobramycin pharmacokinetics

The influence of ascites on the disposition of tobramycin was examined in eight subjects with cirrhosis of the liver. Five of these subjects had resolution of ascites so they could be used as their own controls. While there was no significant effect of ascites on the clearance and half-life of tobramycin, the volume of distribution of tobramycin was significantly larger when ascites was present, 0.32 versus 0.26 liter/kg (P less than 0.01). There was a trend for the volume of distribution to be larger in those patients with larger ascitic fluid volume.

Plasma concentration and disposition of antimicrobial agents in the dog

Although there is sufficient information on the pharmacology and therapeutic application of the antimicrobial drugs to permit their effective use, they are still often misused in canine practice. This paper collates the data on drug dose rate/plasma concentration relationships observed in dogs after the administration of specific members of the major antimicrobial drug groups and on the possible impact of drug disposition (distribution and elimination) on therapeutic effect. Some information gleaned from studies in other animal species is added.

Peritoneal fluid concentrations of gentamicin in patients with spontaneous bacterial peritonitis

Simultaneous peritoneal fluid and serum gentamicin assays were performed at 1- or 4-h intervals after the intravenous administration of gentamicin (3 to 5 mg/kg per day) during nine episodes of spontaneous bacterial peritonitis in cirrhotic patients. Mean peritoneal fluid levels were 4.2 micrograms/ml, whereas simultaneous mean serum levels were 6.1 micrograms/ml (mean percent diffusion into ascites of 67.8%). Three additional patients with uninflamed ascites demonstrated lower levels of diffusion. Regression analysis revealed a positive correlation between simultaneous serum and peritoneal fluid levels. We conclude that diffusion of gentamicin from serum into peritoneal fluid during spontaneous peritonitis is therapeutically adequate if sufficient serum levels are maintained.

Disposition of cefoxitin in patients with ascites

The pharmacokinetics of Cefoxitin was studied in 8 cirrhotic patients with ascites after i.v. administration of a single 30 mg/kg dose. Concentrations of cefoxitin in serum and in ascitic fluid were determined simultaneously and by a microbiologic plate diffusion method. The antibiotic followed a two-compartment open kinetic model. In ascitic fluid, Cefoxitin reached its maximum concentration of 32.80 +/- 13,78 micrograms/ml 2 h after administration. The mean elimination constant from ascitic fluid was 0.201 +/- 0.008 h(-1), significantly lower (p less than 0.05) than the slow disposition phase constant (beta = 0.556 +/- 0.17 h(-1)). At the dose studied and with a dosage interval of 8 h, the level of antibiotic in the ascitic fluid would be maintained at a value greater than the MIC of most cefoxitin-sensitive organisms.

Ascitic fluid modifying the distribution of sulphafurazole in rats with intestinal occlusion

In order to confirm our previous findings of increased sulphafurazole (sulfisoxazole, SF) inactivation by intestinal occlusion, SF was given intravenously 20 mg/kg to rats with a low small intestinal occlusion and to sham-operated controls 40-45 hours after the operation. Occlusion did not cause major changes in the distribution of SF to various tissues, but there were some indications of increased SF acetylation after occlusion. The occlusion rats produced ascitic fluid into the abdominal cavity and the total SF levels in the ascitic fluid were almost identical to those in blood, also after oral administration of SF, 50 mg/kg. After intraperitoneal administration of 2 ml of SF (60 microgram/ml) more SF accumulated into the small intestinal wall in occlusion rats than in controls, and the acetyl SF levels were increased in the small and large intestine. So, our previous suggestion of an increased excretory function of the large intestine in occlusion states may not be the only explanation for increased drug levels in the large intestine found after oral administration of SF. Part of the SF in the intestinal wall can also result from ascitic fluid SF, and ascites must be taken into account when considering drug pharmacokinetics.

Comparative penetration of various cephalosporins into inflammatory exudate

A rabbit sterile peritonitis model was used to determine the relative penetration of four cephalosporin antibiotics into exudate fluid. Male New Zealand white rabbits were given 120 ml of sterile saline intraperitoneally, and peritonitis developed over the following 8 h, with exudate fluid containing a mean of 17,188 granulocytes per mm(3) at 8 h. Each antibiotic was administered intramuscularly at a dose of 30 mg/kg 3 h after peritonitis was initiated, and serum and peritoneal concentrations were measured 0.5, 1, 2, and 4 h later. Cefamandole gave the highest mean peak serum level (26.8 mug/ml), and cephalothin, cephacetrile, and cephradine all gave peak serum levels between 13 and 15 mug/ml. When peak peritoneal exudate concentration was expressed as a percentage of peak serum concentration, cephradine developed 28.5% of the peak serum level, cephacetrile 27.7%, cephalothin 14.0%, and cefamandole 12.5%. These percentages of exudate penetration were inversely proportional to the degree of serum protein binding: cephradine 26.6%, cephacetrile 36.3%, cephalothin 50%, and cefamandole 88%.

Ascitic fluid cephalosporin concentrations: influence of protein binding and serum pharmacokinetics

Mongrel dogs with ascites created by inferior vena cava ligation were given cephalothin, cephaloridine, cefazolin, and cefamandole to evaluate the effect of protein binding and serum pharmacokinetics on the distribution of cephalosporins into ascitic fluid. Antibiotics were given intramuscularly (15 mg/kg) every 4 h for a total of eight doses. Antibiotic binding to dog serum and ascitic fluid was measured by ultracentrifugation. Binding of the cephalosporins to dog serum ranged from 31% for cephaloridine to 46% for cephalothin, considerably lower than human serum binding for cefazolin, cephalothin, and cefamandole. Antibiotic binding to ascitic fluid was only slightly lower than that to serum. Ascitic fluid antibiotic concentrations, which approached equilibrium at 16 to 28 h, were significantly higher for cefazolin and cephaloridine than for cephalothin and cefamandole. However, serum concentrations were also higher for cefazolin and cephaloridine, and percent penetration (ratio of serum peak to ascites peak x 100) was not statistically different among the four drugs. Binding of these cephalosporins to extravascular fluid protein was an important factor that determined the total ascitic fluid antibiotic level achieved. A formula utilizing the log mean serum level and binding to serum and extravascular fluid protein was used to accurately predict ascitic fluid drug levels at equilibrium.