K. Sack

Influence of fosfomycin and tobramycin on vancomycin-induced nephrotoxicity

SummarySince combinations of fosfomycin and vancomycin or tobramycin and vancomycin could be of advantage in the therapy of staphylococcal infections, we studied renal tolerance of both combinations. The experimental animal was the rat and the parameters of nephrotoxicity were cyturia and enzymuria. The experiments showed that fosfomycin at dosages of 50 and 250 mg/kg protected against nephrotoxicity caused by vancomycin (dose: 50 mg/kg), whereas the administration of both tobramycin (dose: 2.5 mg/kg) and vancomycin (dose: 50 mg/kg) resulted in an increase of cyturia and enzymuria. However, repeated dosing of vancomycin (single dose: 50 mg/kg) led to renal accumulation when combined with fosfomycin (single dose: 250 mg/kg); renal vancomycin concentrations were lower. This study suggests similarities in the renal handling of vancomycin and aminoglycosides and demonstrates the possibility of reducing drug-associated nephrotoxicity.ZusammenfassungDa Kombinationen von Fosfomycin und Vancomycin oder Tobramycin und Vancomycin vorteilhaft für die Therapie von Staphylokokken-Infektionen sein könnten, wurde die Nierenverträglichkeit beider Kombinationen tierexperimentell an der Ratte untersucht. Parameter der Nephrotoxizität waren Zyturie und Enzymurie. Die Experimente ergaben, daß Fosfomycin (Dosis: 50 und 250 mg/kg) gegen die Vancomycin-induzierte Nephrotoxizität (Dosis: 50 mg/kg) schützte, während Tobramycin (Dosis: 2,5 mg/kg) zu einer Zunahme der Zell- und Enzymausscheidung bei Kombination mit Vancomycin führte. Die renale Kumulation von Vancomycin verringerte sich bei Kombination mit Fosfomycin. Diese Studie zeigte Ähnlichkeiten zwischen Vancomycin und Aminoglykosiden bezüglich ihrer Wirkung auf die Niere und ergab Hinweise auf die Möglichkeit, die Tobramycin- und Vancomycin-induzierte Nephrotoxizität zu reduzieren.

Renal tolerance of impienem/cilastatin and other beta-lactam antibiotics in rats

SummaryImipenem is inactivated by the renal dehydropeptidase I, which can be inhibited by cilastatin. Therefore, both compounds are administered in combination. According to the manufacturers, they are not nephrotoxic in rats. 70 female Wistar rats (n=10 /test series) were treated over five days at dosage intervals of 12 hours with intraperitoneal injections (injection volume: 10 ml/200 g body weight) of isotonic 0.9% NaCl, cilastatin (1000 mg/kg/day), imipenem (500 and 1000 mg/kg/day), cilastatin + imipenem (500 or 1000 mg/kg/day each) and cefsulodin (1000 mg/kg/day). The nocturnal excretion of renal tubular cells was determined. Furthermore, three rats in each test were treated intraperitoneally with 150 mg/kg imipenem or with the combination of imipenem and cilastatin (150 mg/kg each). Imipenem concentrations were measured over four hours in the blood of the tail vein. Commencing on the second day of study, cilastatin, imipenem and the combination of both substances induced significant surplus excretion of tubular cells compared to the control group. The tubulotoxic effects of imipenem and imipenem + cilastatin in combination were dose-dependent. The toxic effects of imipenem, imipenem + cilastatin and cefsulodin did not significantly differ. Cilastatin prolonged the half-life of imipenem in the blood from 0.4 to 0.9 h and increased the AUC of imipenem from 156 to 325 mg/l/h. Thus, the tubulotoxic potency of imipenem and imipenem + cilastatin in combination can be considered similar to that of pyridinium-substituted cephalosporins. Cilastatin increases the bioavailability of imipenem, probably as a result of competitive displacement at the renal tubular cell. However, it is not possible to measure to what extent the renal tubular cell is protected by cilastatin from the toxic effect of imipenem as cilastatin itself is also tubulotoxic.ZusammenfassungImipenem, (das erste verfügbare Thienamycin-Derivat, ein Betalactam-Antibiotikum mit breitem Spektrum,) wird durch die renale Dehydropeptidase I inaktiviert, die durch Cilastatin gehemmt werden kann. Daher werden beide Substanzen kombiniert verabfolgt. Sie sollen bei der Ratte, nach Angaben des Herstellers, nicht nephrotoxisch sein. 70 weibliche Wistar-Ratten (n=10/Serie) wurden über fünf Tage bei einem 12-Stunden-Dosierungsintervall i.p. behandelt (injiziertes Volumen: 10 ml/200 g Körpergewicht) mit 0,9% NaCl, Cilastatin (1000 mg/kg/Tag), Imipenem (500, 1000 mg/kg/Tag), Imipenem + Cilastatin (je 500 oder 1000 mg/kg/Tag) und Cefsulodin (1000 mg/kg/Tag) und die nächtliche Ausscheidung an Tubuluszellen bestimmt. Je drei Ratten wurden i.p. mit 150 mg/kg Imipenem bzw. je 150 mg/kg Imipenem + Cilastatin behandelt und die Imipenem-Konzentrationen im Schwanzvenenblut über vier Stunden gemessen. Cilastatin, Imipenem und Cilastatin + Imipenem führen vom zweiten Versuchstag an zu einer im Vergleich zur Kontrolle signifikanten Mehrausscheidung an Tubuluszellen. Die tubulotoxischen Wirkungen von Imipenem und Cilastatin + Imipenem sind dosisabhängig. Die toxischen Effekte von Imipenem, Cilastatin + Imipenem und Cefsulodin unterscheiden sich nicht signifikant voneinander. Cilastatin verlängert die Halbwertszeit von Imipenem von 0,4 auf 0,9 Stunden im Blut und vergrößert die AUC von Imipenem von 156 auf 325 mg/l/Stunde. Demnach ist die tubulotoxische Potenz von Imipenem und Cilastatin + Imipenem ähnlich einzuschätzen wie die von Pyridinium-substituierten Cephalosporinen. Cilastatin erhöht die Bioverfügbarkeit von Imipenem, wahrscheinlich aufgrund einer kompetitiven Verdrängung am Tubulus. Die infolgedessen zu erwartende Protektion des Tubulus durch Cilastatin vor der toxischen Wirkung von Imipenem wird jedoch nicht meßbar, da Cilastatin ebenfalls tubulotoxisch wirkt.

Nebenwirkungen von Aminoglykosiden: Nephrotoxizität

ZusammenfassungMorphologische Untersuchungen am Versuchstier zeigen, daß alle Aminoglykoside qualitativ ähnliche tubulotoxische und glomerulotoxische Eigenschaften haben. Quantitative Unterschiede in der tubulotoxischen Potenz der Substanzen Gentamicin, Tobramycin, Sisomicin, Kanamycin, Kanendomycin, Amikacin und Butirosin sind experimentell mittels Analysen der Exkretionsraten für Nierenepithelien und Harnenzyme an der Ratte nachzuweisen. Diese Parameter beschreiben die toxischen Wirkungen der Aminoglykoside in Dosis-Wirkungsbeziehungen, erlauben daher die Bestimmung von toxischen Schwellendosen und somit die Einordnung jeder Substanz in ein Nierenverträglichkeitsspektrum. Ferner unterscheiden sich Aminoglykoside in ihrer Affinität zum Nierengewebe und damit in der renal-kumulativen Potenz bei repetierter Applikation. Diese Tatsache wirkt sich modifizierend auf den Verlauf der toxikologischen Zeit-Wirkungsbeziehungen aus. Vergleichende Untersuchungen an Ratte und Meerschweinchen führen zu weitgehend ähnlichen Ergebnissen der Harnanalysen. Auch erste vergleichende Prüfungen am Menschen weisen darauf hin, daß die experimentell gewonnenen Resultate keine Spezies-immanenten Besonderheiten darstellen. Abschließend ist zu folgern, daß — verglichen mit Gentamicin — im klinischen Umgang mit den neuen Aminoglykosiden eine eher noch größere Vorsicht angebracht ist, um nephrotoxische Komplikationen zu vermeiden.SummaryAnimal experiments showed that all aminoglycosides cause similar toxic tubular and glomerular damage when investigated by qualitative morphology. Quantitative differences in the tubular nephrotoxicity of gentamicin, tobramycin, sisomicin, kanamycin, kanendomycin, amikacin, and butirosin can be demonstrated experimentally by evaluation of the excretion rates of tubular cells and urinary enzymes in rats. By this means dose-effect relationships were established resulting in varying reproduceable toxic threshold doses for each antibiotic, and thus in a scale of increasing nephrotoxicity. The aminoglycosides differed in their affinity to kidney tissue as measured by determination of the accumulating renal concentrations of the drugs at different times during multiple-dose administration. This had a modifying influence on excretion rates of cells and enzymes affecting the scale of toxicity in long-term studies. Comparative investigations on nephrotoxicity in rats and guinea pigs gave similar results. In addition, a study in man suggested that the test results of nephrotoxicity are not species-specific. For human therapy it is concluded that even more caution should be practised with the new aminoglycosides than with gentamicin in order to avoid renal damage.Animal experiments showed that all aminoglycosides cause similar toxic tubular and glomerular damage when investigated by qualitative morphology. Quantitative differences in the tubular nephrotoxicity of gentamicin, tobramycin, sisomicin, kanamycin, kanendomycin, amikacin, and butirosin can be demonstrated experimentally by evaluation of the excretion rates of tubular cells and urinary enzymes in rats. By this means dose-effect relationships were established resulting in varying reproduceable toxic threshold doses for each antibiotic, and thus in a scale of increasing nephrotoxicity. The aminoglycosides differed in their affinity to kidney tissue as measured by determination of the accumulating renal concentrations of the drugs at different times during multiple-dose administration. This had a modifying influence on excretion rates of cells and enzymes affecting the scale of toxicity in long-term studies. Comparative investigations on nephrotoxicity in rats and guinea pigs gave similar results. In addition, a study in man suggested that the test results of nephrotoxicity are not species-specific. For human therapy it is concluded that even more caution should be practised with the new aminoglycerides than with gentamicin in order to avoid renal damage.

Standardization of a model of E. coli-pyelonephritis in rats

The validity of preclinical testing of antibiotics in animal experiments is highly dependent on the quality and, especially, the standardizability of the infection model. Some of the factors associated with standardization of the acute phases of infection are demonstrated for experimental pyelonephritis in female albino Wistar rats after transuretheral infection. The renal bacterial count and infection rate are correlated to the volume and bacterial concentration of the instilled E. coli suspension. Strains of albino Wistar rats from different breeding institutions show differing resistance to the infection. E. coli pyelonephritis establishes more easily in female Wistar rats of strain Han: WIST than in strain Bor: WIST. Following dissection of the animals, the infected kidneys can be stored for at least 4 weeks at -30 degrees C or in liquid nitrogen, because the bacterial counts remain constant. However, in frozen renal homogenates the bacterial counts fall rapidly. During the first 4 post-infection days the bacterial content of the kidneys is relatively constant. The period 30-72 h post infection is especially suitable for therapeutic studies.

Animal studies on the reduction of aminoglycoside-induced nephrotoxicity by D-glucaro-1,5-lactam

SummaryWe studied the effect of D-glucaro-1,5-lactam on aminoglycoside-induced nephrotoxicity in rats. Parameters of nephrotoxicity were urinary excretion of tubule cells and malate dehydrogenase. When given in appropriate doses, either i. m. or via an oral tube, D-glucaro-1,5-lactam significantly reduced the excretion of cells and enzymes during the administration of gentamicin, tobramycin, dibekacin, netilmicin and ribostamycin. It did inot impair the therapeutic efficacy of ribostamycin in the experimental treatment of acute pyelonephritis in rats. The protective effect of D-glucaro-1,5-lactam could be ascribed to its inhibition of β-glucuronidase, an enzyme which is located in renal lysosomes and which is activated by aminoglycosides.ZusammenfassungEs wurde der Einfluß von D-Glukaro-1,5-Laktam auf die Aminoglykosid-induzierte Nephrotoxizität tierexperimentell an der Ratte untersucht. Parameter der Nephrotoxizität waren die Ausscheidung von Tubuluszellen und Malat-Dehydrogenase im Harn. Wenn D-Glukaro-1,5-Laktam in geeigneter Dosis entweder intramuskulär oder peroral gegeben wurde, reduzierte sich die Exkretion von Zellen und Enzymen während der Verabreichung von Gentamicin, Tobramycin, Dibekacin, Netilmicin und Ribostamycin signifikant. D-Glukaro-1,5-Laktam verminderte nicht die therapeutische Effektivität von Ribostamycin in der experimentellen Chemotherapie der akuten Pyelonephritis der Ratte. Der Schutzeffekt von D-Glukaro-1,5-Laktam könnte der Hemmung der Beta-Glukuronidase, einem Enzym, das sich in renalen Lysosomen befindet und von Aminoglykosiden aktiviert wird, zugeschrieben werden.

Ceftazidime, ceftizoxime, cefotaxime and HR 221 in experimental chronic Escherichia coli pyelonephritis in rats

SummaryThe therapeutic efficacy and pharmacokinetics of the cephalosporins ceftazidime, ceftizoxime, cefotaxime and HR 221 were studied in animal experiments. The animal model used was experimental estrogen-induced or non-induced chronicEscherichia coli pyelonephritis in rats. The animals were treated with 5 mg cephalosporin/kg twice daily for one week. Each of the cephalosporins tested led to a significant decrease in renal bacterial counts, in spite of the low doses given. Ceftazidime was significantly more active than HR 221 in both experimental models, although the serum levels of HR 221 were higher and were maintained for a longer period of time than those of ceftazidime. Differences in pharmacokinetic properties (influenced by metabolic stability and protein binding) could be the reason for the differences in therapeutic activity, since thein vitro antimicrobial activity of each of the cephalosporins tested was very similar against the test strain.ZusammenfassungDie therapeutische Effektivität und Pharmakokinetik der Cephalosporine Ceftazidim, Ceftizoxim, Cefotaxim und HR 221 wurde tierexperimentell untersucht. Tiermodell war die experimentelle östrogengebahnte und nicht-gebahnte chronischeE. coli-Pyelonephritis der Ratte. Die Tiere wurden für eine Woche 2× täglich mit 5 mg Cephalosporin/kg behandelt. Alle Cephalosporine führten zu einem signifikanten Abfall der renalen Keimzahlen trotz der niedrigen Dosierung. In beiden Tiermodellen war Ceftazidim signifikant wirksamer als HR 221, obwohl die Serumspiegel von HR 221 höher waren und länger andauerten als die von Ceftazidim. Unterschiede in der Pharmakokinetik (metabolische Stabilität, Proteinbindung) könnten der Grund für die unterschiedliche therapeutische Effektivität sein, da die antimikrobielleIn-vitro-Aktivität aller Cephalosporine gegenüber dem Testkeim sehr ähnlich war.

The therapeutic response of cephalosporin-treated E. coli pyelonephritis of the rat, in relation to variations of the infection model

In the E. coli pyelonephritis, induced in female Wistar rats by retrograde infection (high pressure reflux), we investigated the influence of 1) the time of commencement of therapy, 2) the renal bacterial counts, i.e. the inflammatory activity of the pyelonephritis after endovesical instillation of cultures with different bacterial concentrations, and 3) the level of infection resistance of the experimental animal strain on the therapeutic response of the model infection with single doses of cefoxitin (150 mg/ml) and cefotaxime (5 mg/ml). Early commencement of therapy post inoculation was therapeutically advantageous provided the intrarenal multiplication of the infective organisms was not delayed or the initial bacterial concentrations were not too high. The mild form of pyelonephritis with lower renal bacterial concentrations and poor inflammatory activity after endovesical instillation of a low inoculum (10(4) cfu/ml) was less amenable to treatment than the inflammatory active pyelonephritis with high renal bacterial counts, using a high inoculum (10(7) cfu/ml). High renal bacterial counts after retrograde inoculation of an E. coli culture of 10(8) cfu/ml resulted in significant reduction of bacterial counts 48, 72 and 96 h post infectionem, with i.m. application of cefoxitin 12 h prior. For Wistar rat strain Bor:WIST, which showed a stronger infection resistance with lower renal bacterial concentrations and a stronger tendency to spontaneous healing, application of a single dose of cefotaxime (5 mg/ml) was therapeutically ineffective, whereas, in contrast, with Han: WIST rats the acute phase of E. coli pyelonephritis could be treated effectively.

Relationship between the bactericidal and bacteriolytic activity of cephalosporins and changes in the cell volumes of Escherichia coli cultures

SummaryThe bactericidal effect of cefoxitin and cefotaxime in relation to concentration and exposure time, as demonstrated by the killing curve diagrams ofEscherichia coli cultures, was compared with the degree of bacteriolysis and the cell volume increase measured by the coulter counter-channel analyser system. Human plasma ultrafiltrate was used as the growth medium. Cefoxitin has a higher bactericidal activity than cefotaxime. With increasing concentrations the bactericidal efficacy of cefoxitin increases more rapidly in the lower range of concentrations (2–10 mg/l) than in the higher range (10–40 mg/l). In contrast, the bactericidal effect of cefotaxime in the range 0.06–1.2 mg/l is virtually constant and can only be increased by high levels (10–40 mg/l). The morphometric effect of cefoxitin onE. coli cultures, as demonstrated by volume distribution curves, is characterized by intensive and rapidly appearing bacteriolysis 20 min after exposure to the antibiotic without a preceding increase in bacterial cell volume. Higher concentrations result in an earlier onset of bacteriolysis. In contrast, the application of cefotaxime reveals a massive increase in bacterial cell volume (more than five-fold) with a delayed (> 2 h) onset of bacteriolysis. High cefotaxime concentrations reduce the extent of bacterial cell volume increase, associated with an earlier and more intensive onset of bacteriolysis. With both cephalosporins, the bacterial cell alterations are particularly dependent on the exposure time. There is evidently a close correlation between bactericidal and bacteriolytic activity. This is valid both for the two cephalosporins and generally for the concentration-activity relationships.ZusammenfassungDer bakterizide, an Absterbekurven vonEscherichia coli-Kulturen gemessene Effekt von Cefoxitin und Cefotaxim in Abhängigkeit von der Konzentration und Einwirkzeit wurde mit dem Ausmaß der Bakteriolyse und Zellvolumenzunahme unter Verwendung des Coulter Counter-Channelanalyser-Systems verglichen. Wachstumsmedium war humanes Plasma-Ultrafiltrat. Cefoxitin besitzt eine höhere bakterizide Aktivität als Cefotaxim. Mit steigenden Konzentrationen nimmt die bakterizide Wirkung von Cefoxitin im niedrigen Konzentrationsbereich (2–10 mg/l) stärker zu als bei höheren Wirkspiegeln (10–40 mg/l). Im Gegensatz dazu ist der bakterizide Effekt von Cefotaxim im Bereich 0,06–1,2 mg/l nahezu konstant und erst durch hohe Spiegel (10–40 mg/l) zu steigern. Der anhand von Volumenverteilungskurven vonE. coli-Kulturen ermittelte morphometrische Effekt von Cefoxitin ist durch eine intensive, nach 20minütiger Antibiotikaexposition rasch einsetzende Bakteriolyse ohne vorherige Größenzunahme der Zellen gekennzeichnet. Höhere Spiegel haben einen frühzeitigeren Beginn der Lyse zur Folge. Dem gegenüber steht nach Applikation von Cefotaxim eine massive Volumenzunahme (> 5fach) der Bakterienzelle im Vordergrund mit verzögert (> 2 h) einsetzender Bakteriolyse. Durch hohe Cefotaxim-Konzentration vermindert sich die Volumenzunahme, gleichzeitig nehmen Intensität und Beginn der Lyse zu. Bei beiden Cephalosporinen hängen die Zellalterationen besonders von der Expositionszeit ab. Es besteht eine enge Korrelation zwischen bakterizider und bakteriolytischer Aktivität. Dies gilt sowohl für jedes einzelne Cephalosporin als auch allgemein für Konzentrations-Wirkungsbeziehungen.

Bactericidal Activity and Induction of Cell Volume Alterations of Cephalosporins in Escherichia coli

The bactericidal efficacy of cefuroxime and cephacetril on Escherichia coli cultures was measured by killing curves. Simultaneously bacterial cell volumes were analysed by electronic particle counting using a Coulter Counter Channelanalyser system in order to study the relationship between bactericidal activity and bacterial cell volume alterations. Various concentrations (2-120 mg/l cefuroxime and 16-120 mg/l cephacetril) and different exposure times (over a time period of 12 h) were used. Growth medium was human plasma ultrafiltrate. The bactericidal activity of cefuroxime, as measured by the rate of killing of the E. coli culture, was independent of the concentration and constant in the range 4-120 mg/l. The characteristic cefuroxime-induced change in bacterial cell volume was a marked volume increase up to a maximum of 5-fold after 160-200 min exposure with a low-grade bacteriolysis following. The cefuroxime-induced bacterial volume changes were, in accordance with the bactericidal testing, almost independent of the concentration. In contrast, the killing curves for cephacetril strongly depended on the drug concentration. However, this effect was short-lived and regrowth of the E. coli culture followed. The typical cephacetril-induced volume distribution curves were also highly concentration-dependent. With increasing drug levels bacterial cell volume increased up to 20-fold, and regrowth of a persisting bacterial population occurred at lower antibiotic concentrations. Bacteriolysis started earlier than with cefuroxime. The relationship between loss of viability and cell volume increase was more marked with cefuroxime than with cephacetril.

Analysis of cephalosporin-induced changes in the volume distribution of Escherichia coli cultures by an electronic counter-channelanalyser

The demonstration of morphological alterations of the bacterial cell together with bactericidal kinetics are of value for the description of the antibacterial activity of beta-lactam antibiotics. One of the indicators of antibiotic effect on bacterial morphology is the change in bacterial cell volume. This can be demonstrated graphically and numerically by means of electronic cell counting and volume distribution analysis using the Coulter Counter-Channelanalyser system connected to a computer. After registration of the distribution of the relative volume of the Escherichia coli population, the mean cell volume was calculated. The latter parameter increased more than 6 fold with increasing cefotaxim-exposure times. The onset of the delayed (2 h after cefotaxim administration) bacteriolytic effect was reorganized by the appearance of small cell breakdown particles and quantified by counting. In order to demonstrate the therapeutic process graphically the distribution curves were transformed to a common scale. Since a complete storage of the data per sample is performed normally within one minute, the Coulter Counter-Channelanalyser technique can be carried out simultaneously with the bactericidal kinetic experiment. The data demonstrate the speed and intensity of the morphological cell alterations induced by the beta-lactam antibiotic.