Intrarenal concentrations of ampicillin in acute pyelonephritis

Effect of Enterococcus faecalis pyelonephritis on the intracortical accumulation kinetics of gentamicin in rats

The role of serum levels on the intracortical accumulation kinetics of gentamicin was evaluated in normal and Enterococcus faecalis-infected kidneys using a short term infusion model in conscious rats. Female Sprague-Dawley rats were infused over a period of 6 h with gentamicin achieving individual steady-state serum levels ranging from 0.5 to 20 μg/mL. Pyelonephritis was induced by a direct inoculation of the left kidney with a suspension of E faecalis. This model resulted in severe infection of the left kidney and mild infection of the right kidney. Gentamicin cortical concentrations were analyzed as a function of serum levels by linear regression (least squares regression analysis). Steady-state elevation of serum concentrations of gentamicin was associated with a linear increase of cortical concentrations in normal, and in both left and right infected kidneys. No significant difference in the kinetics of gentamicin uptake was observed between normal and right and left infected kidneys. Therefore, E faecalis pyelonephritis does not modify the intracortical accumulation kinetics of gentamicin.

Species-specific uncertainty factors for compounds eliminated principally by renal excretion in humans

An uncertainty factor of 100 is used to derive health-based guidance values for human intakes of chemicals based on data from studies in animals. The 100-fold factor comprises 10-fold factors for species differences and for interindividual differences in response. Each 10-fold factor can be subdivided into toxicokinetic and toxicodynamic aspects with a 4.0-fold factor to allow for kinetic differences between test species and humans. The current work determined the extent of interspecies differences in the internal dose (toxicokinetics) of compounds which are eliminated primarily by renal excretion in humans. An analysis of the published data showed that renal excretion was also the main route of elimination in the test species for most of the identified probe substrates. Interspecies differences were apparent for both the mechanism of renal excretion (glomerular filtration, tubular secretion and/or reabsorption) and the extent of plasma protein binding, both of which may affect renal clearance and therefore the magnitude of species differences in the internal dose. For compounds which are eliminated unchanged by both humans and the test species, the average differences in the internal doses between humans and animals were 1.6 for dogs, 3.3 for rabbits, 5.2 for rats and 13 for mice. This suggests that for renal excretion, the differences between humans and the rat and especially the mouse may exceed the 4.0-fold default factor for toxicokinetics.

Pharmacologic Basis for the Treatment of Pyelonephritis

Urinary tract infections (UTIs) are among the most common bacterial infections in humans. Even though physicians have been treating UTIs for 60 years, there has been no standardized approach regarding the rational choice of antimicrobial agents and optimal treatment duration for these infections. This review discusses the pharmacologic basis for the treatment of UTIs. Although most antibiotics concentrate well in the urine and can eradicate most of the sensitive uropathogens that cause lower UTI, antibiotics given for the treatment of pyelonephritis must concentrate and kill bacteria embedded within the renal parenchyma. Investigators once believed that antibiotics must concentrate in sufficient amounts in the urine of infected patients to be effective in treating pyelonephritis. In fact, the efficacy of an antibiotic in the treatment of pyelonephritis is proportional to its capacity to converge in high concentration not only in urine but also in the renal parenchyma because serum and urine levels of antibiotics are poor predictors of the intrarenal levels. Other factors should also be taken into consideration in the management of UTIs, such as the time of day antibiotics are given because significant time-dependent differences have been observed in the pharmacokinetics and rate of excretion in urine of several antibiotics. Finally, the authors review the recent development in the inflammatory response in the urinary tract that may explain the clinical features of UTI and may be useful in the diagnosis as well as better management of UTI.

Treatment of pyelonephritis in adults

Although prescribing an antibiotic for the treatment of pyelonephritis seems to be a relatively easy task, a close look at the available data is disturbing. Optimal therapies for the different clinical syndromes of pyelonephritis have not yet been defined. The high failure rate suggests that in pyelonephritis (bacteria protected in the medulla) as well as in bacterial endocarditis (bacteria sequestered in vegetations) and in infections in neutropenic patients (host defenses not necessarily operating in conjunction with antibiotics), it may be necessary to maintain bactericidal levels at the site of infection (infected medulla) to achieve cure. Pharmacodynamic studies suggest that TMP/SMX, quinolones, and aminoglycosides, which penetrate well the infected renal parenchyma and are not impaired by the local inflammatory process, should, with the exception of pyelonephritis in pregnancy, be preferred to beta-lactams as first-choice agents for the therapy of gram-negative pyelonephritis.

Management of acute pyelonephritis in an emergency department observation unit

STUDY OBJECTIVES

To determine whether moderately to severely ill patients with acute pyelonephritis can be treated successfully on an outpatient basis, and whether any aspect of history, physical examination, or initial laboratory data predicts failure of outpatient therapy and the need for hospitalization.

DESIGN

Retrospective chart review of all patients with a diagnosis of acute pyelonephritis seen during a three-year period.

SETTING

Emergency department observation unit of an urban teaching hospital serving residents of the city and county of Denver.

TYPE OF PARTICIPANTS

Women between the ages of 15 and 50 with symptoms, physical examination, and initial laboratory data consistent with a diagnosis of pyelonephritis.

INTERVENTIONS

Patients received IV antibiotics, rehydration, analgesics, and antiemetics in an observation unit for up to 12 hours, when they were either admitted to the hospital or discharged home on oral antibiotics.

MEASUREMENTS AND MAIN RESULTS

Sixty-three of 87 patients (72%) with acute pyelonephritis were managed successfully as outpatients, nine (22%) were hospitalized directly from the observation unit because they were considered to be too ill to go home, and five (6%) returned with persistent symptoms after ED therapy and were hospitalized. No clinical or laboratory variable predicted success or failure of ED observation unit therapy at the time of initial presentation.

CONCLUSION

In selected patients, the observation unit may be used to initiate therapy for acute pyelonephritis. Those with an adequate clinical response to initial treatment may be discharged on oral antibiotic therapy with appropriate follow-up.

Significance of tissue levels for prediction of antibiotic efficacy and determination of dosage

Determination of tissue levels is widely thought to provide useful information in the investigation of a new antibiotic, however this assumption is not fully justified. In this paper the following questions are covered. Firstly, the methodological problems encountered in the measurement of antibiotic levels in solid tissues and extravascular fluids are described. Secondly, the difficulties encountered in interpreting tissue concentrations are discussed, given the heterogeneity of distribution of drugs, potential intracellular penetration, binding to tissue proteins and local factors reducing antibacterial activity. Thirdly, the respective importance of animal and human data on tissue levels for prediction of efficacy is analysed. In some animal models it is possible to study the conditions affecting antibacterial activity and to obtain data relevant to the clinical situation. However, the inoculum effect, the metabolism of bacteria, the mechanism of the bactericidal action of drugs and the type of infected tissue are important factors to be taken into account. In humans, data obtained from infected tissue is sparse and contributes little to knowledge. Knowledge of tissue levels may be important for establishing whether data obtained in animals can be applied to humans or not. Fourthly, the importance of tissue levels in determining antibiotic dosages is evaluated. In humans, tissue levels are of limited value in the determination of unitary dose and dosage intervals in relation to the clinical response. Trough serum levels of free drug, half-life at the beta-phase and rate of in vitro killing are the most important parameters to be considered. Their relative importance depends mainly on the mode of action of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal pharmacokinetic changes of gentamicin during enterococcal pyelonephritis

In the present study, the renal pharmacokinetics of gentamicin was investigated in pyelonephritic rats infected with Streptococcus (Enterococcus) faecalis. Four days after the induction of infection, animals were given either a single dose of gentamicin or two daily injections for 7 days. The treated animals were evaluated from 1 h to 6 months posttreatment. After a single injection, limited pharmacokinetic variations were observed, whereas after 14 injections infected kidneys demonstrated significantly higher concentrations and a more extended renal elimination phase of the antibiotic. Analysis of the area under the curve of the concentration in kidney versus time showed more marked renal accumulation by the infected and long-term treated animals than by normal animals or those receiving only one injection of aminoglycoside. Renal function remained normal in both the infected and normal animals treated with this aminoglycoside. These results demonstrate that S. faecalis pyelonephritis disturbs the renal handling of gentamicin and may increase the susceptibility of the kidney to aminoglycosides.

Continuous-infusion ampicillin therapy of enterococcal endocarditis in rats

Intermittent administration of ampicillin alone has resulted in high failure rates in previously described animal models of enterococcal endocarditis. We developed a rat model of enterococcal endocarditis which permits comparison of continuous intravenous infusion of ampicillin with intramuscular therapy. Continuous low-dose ampicillin infusion (450 mg/kg [body weight] per day) was compared with the same dose given intramuscularly in three divided doses and with high-dose infusion (4.5 g/kg per day) of the drug. For the infecting strain of Streptococcus faecalis, the MIC and MBC were 1 microgram/ml. Mean ampicillin levels in serum were 53.9 +/- 4.8 (peak) and less than 1 (trough), 8.7 +/- 1.4, and 244 +/- 29 micrograms/ml for intramuscular, low-dose, and high-dose regimens, respectively. Ampicillin infusion therapy significantly increased the survival rate and sterilization of blood cultures. Continuous infusions were superior to intermittent therapy in eradicating bacteremia. After 5 days of treatment, low-dose ampicillin infusion was more effective than intermittent therapy in sterilizing cardiac vegetations (P less than 0.01). Continuous-infusion therapy at either dose was significantly more effective than intramuscular injection in reducing bacterial titers in cardiac vegetations (5.4 +/- 1.0 log10 CFU/g [low dose], 4.8 +/- 0.3 log10 CFU/g [high dose], and 7.7 +/- 0.3 log10 CFU/g [intramuscular]). However, no statistically significant advantage was found for high-dose compared with low-dose ampicillin infusion in lowering bacterial titers in vegetations (P greater than 0.3).

Benefit from high intrarenal levels of gentamicin in the treatment of E. coli pyelonephritis

The importance of high intrarenal levels of gentamicin on the outcome of experimental pyelonephritis was studied in rats receiving either a short course (three days) of gentamicin (G) alone or combined with a longer course (14 days) of ampicillin (A), cephalothin (C), or trimethoprim (T), or two weeks of therapy with ampicillin, cephalothin, trimethoprim and gentamicin given alone. While ampicillin, cephalothin and trimethoprim were undetectable in the medulla within six hours of cessation of therapy, gentamicin was still detectable in levels six folds above the MIC up to six months after treatment had ceased. Six months after the end of treatment, the percentage of sterile left kidneys in animals treated with ampicillin (50%), cephalothin (15%), trimethoprim (20%) was lower than the percentage of animals receiving 14 days of gentamicin (100%), or the combinations AG:89%, CG:67% and TG:60%, P less than 0.01. Following three days of gentamicin, 50% of the left kidneys were sterilized. When compared to ampicillin, cephalothin or trimethoprim alone, combined therapies significantly reduced the number of CFU in the kidneys P less than 0.01. These combinations were almost as effective as two weeks of therapy with gentamicin. Short-term therapy (three days) with an aminoglycoside which concentrates in the renal parenchyma, combined with an antibiotic which will accumulate in other parts of the nephron, may result in "pharmacological synergy". This new approach to therapy of pyelonephritis may be promising.

Tissue penetration of antibiotics

To be effective, antibiotics must be active against the offending pathogen(s) and must reach sufficient concentrations at the site of infection where microorganisms have induced severe inflammation. Such inflammation may, depending on the infected tissue, increase or decrease antibiotic penetration. Once it has reached the infected site an antibiotic may be inactivated locally. In this work, we have reviewed: 1. Factors modulating the penetration of antibiotics in tissues of normal and infected humans and animals; 2. The relationship between concentrations and efficacy of antimicrobials in experimental and human infections; 3. The mechanisms by which high tissue levels of antibiotics may be toxic; 4. New antibiotic targetting delivery systems which may increase tissue concentrations of antibiotics. To better understand the interaction between antimicrobial agents, pathogens in specific infected sites and the host, more experimentation dealing simultaneously with tissue penetration and antibiotic efficacy in acute and chronic infection is required. Innovative approaches to the therapy of human infections are needed.

Intrarenal concentration-time profile of ampicillin after administration of bacampicillin to patients before nephrectomy

Nineteen patients with renal cancer who were to undergo nephrectomy received a single oral dose of bacampicillin 800 mg at approximately three (N = 5), six (N = 7), or nine (N = 7) hours before nephrectomy. Serum samples were taken at 30, 60, and 90 minutes after administration and at nephrectomy. Urine was collected immediately before operation. Samples of medulla and cortex tissues were immediately and carefully dissected from a healthy part of the removed kidney and homogenized with a buffer solution. All concentrations were determined by bioassay. Bacampicillin was well absorbed, with a mean +/- SD serum concentration of 16.0 +/- 11.4 mg/L at one hour. The concentrations in renal tissues were higher than the serum levels taken at the same time, and the highest concentrations were found in the urine. the mean ampicillin elimination half-life was approximately the same in the cortex, medulla, and urine, (2.7, 2.3, and 2.4 hr, respectively) but it was shorter in the serum (1.4 hr). Bacampicillin 800 mg produced concentrations in the renal tissues that were higher and more sustained than in the serum and were well above the minimum inhibitory concentrations for common urinary pathogens even ten hours after the dose.

Intrarenal distribution of ampicillin in the healthy and the infected rat kidney: a comparison of methods

The ampicillin concentration in the cortex of the normal and the infected rat kidney was determined by means of three different methods: tissue homogenate analysis, renal lymph analysis, and autoradiography. Both tissue homogenate analysis and autoradiography revealed that the cortical ampicillin concentration was about five times as high as the serum concentration. Renal lymph analysis disclosed that the ampicillin concentration in this fluid amounted to about 93% of the serum concentration. The discrepancy between these results can be explained on the basis of the binding of ampicillin to cellular components in the cortex. The results of the study of ampicillin distribution in infected rat kidneys with the aid of tissue homogenate analysis and autoradiography indicate that the ampicillin concentration was lower in the affected than in the intact tissue. Renal lymph analysis showed that the ampicillin concentration in the lymph was not affected by the presence of the infection. Quantitative autoradiography demonstrated that the ampicillin concentration in the cortical foci of infection was of the same order of magnitude as the serum concentration. For this kind of study autoradiography together with lymph analysis are recommended.