Synergistic activity of ceftriaxone combined with netilmicin administered once daily for treatment of experimental streptococcal endocarditis

Tedizolid as Step-Down Therapy following Daptomycin versus Continuation of Daptomycin against Enterococci and Methicillin- and Vancomycin-Resistant Staphylococcus aureus in a Rat Endocarditis Model

Tedizolid (TZD) and daptomycin (DAP) were assessed in a rat endocarditis model against Enterococcus faecalis, Enterococcus faecium (resistant to vancomycin and ampicillin), and Staphylococcus aureus As a monotherapy, TZD for 5 days was not effective in a comparison with no-treatment controls, while DAP for 5 days was significantly effective against these bacteria. Step-down therapy (DAP for 3 days followed by TZD for 2 days) was as effective as DAP for 5 days and was comparable to 3 days of DAP plus ceftriaxone against all bacteria and to 3 days of DAP plus gentamicin against E. faecalis OG1RF.

Efficacy of Telavancin Alone and in Combination with Ampicillin in a Rat Model of Enterococcus faecalis Endocarditis

We first assessed telavancin (TLV) pharmacokinetics in rats after a single subcutaneous dose of 35 mg/kg of body weight. The pharmacokinetic data were used to predict a TLV dose that simulates human exposure, and the efficacy of TLV was then evaluated using a TLV dose of 21 mg/kg every 12 h against Enterococcus faecalis OG1RF (TLV MIC of 0.06 μg/ml) in a rat endocarditis model with an indwelling catheter. Therapy was given for 3 days with TLV, daptomycin (DAP), or ampicillin (AMP) monotherapy and with combinations of TLV plus AMP, AMP plus gentamicin (GEN), and AMP plus ceftriaxone (CRO); rats were sacrificed 24 h after the last dose. Antibiotics were given to simulate clinically relevant concentrations or as used in other studies. TLV treatment resulted in a significant decrease in bacterial burden (CFU per gram) in vegetations from 6.0 log₁₀ at time 0 to 3.1 log₁₀ after 3 days of therapy. Bacterial burdens in vegetations were also significantly lower in the TLV-treated rats than in the AMP (P = 0.0009)- and AMP-plus-GEN (P = 0.035)-treated rats but were not significantly different from that of the AMP-plus-CRO-treated rats. Bacterial burdens from vegetations in TLV monotherapy and TLV-plus-AMP-and-DAP groups were similar to each other (P ≥ 0.05). Our data suggest that further study of TLV as a therapeutic alternative for deep-seated infections caused by vancomycin-susceptible E. faecalis is warranted.

Bactericidal activity of penicillin, ceftriaxone, gentamicin and daptomycin alone and in combination against Aerococcus urinae

Aerococcus urinae can cause severe infections (bacteraemia and endocarditis) that are associated with high mortality. However, data on the bactericidal and synergistic activity for clinically implemented antibiotics are scarce. Time-kill analyses were performed on two clinical isolates (AU1 and AU2) and the reference strain ATCC 700306 for penicillin (PG), ceftriaxone (CRO), gentamicin (GEN), daptomycin (DAP) and their combinations. AU1 and AU2 were CRO-resistant (MICs, 2 µg/mL) and ATCC 700306 was high-level GEN-resistant (MIC, 512 µg/mL), whereas all strains were PG- and DAP-susceptible (MICs, ≤0.125 and ≤1 µg/mL, respectively). CFU counts were determined at various time points from 0 to 48 h. All experiments were performed at 0.5×, 1×, 2× and 4× MIC. PG and CRO were not bactericidal for all strains, whereas DAP exhibited bactericidal activity at all concentrations for AU2 and ATCC 700306. The combination of PG or CRO with GEN was bactericidal for AU1 and AU2 at antibiotic concentrations ≥1× MIC. Bactericidal synergism was detected for PG or CRO combined with GEN in the two clinical isolates. PG plus CRO showed non-bactericidal synergism for ATCC 700306. DAP with GEN was synergistic at 1× MIC for AU1, whereas the killing activity of DAP was too pronounced to detect potential synergism in AU2. The combination of PG or CRO with GEN is synergistic and bactericidal. Moreover, these in vitro data suggest that DAP may represent a potential bactericidal treatment alternative against A. urinae. This finding could be important for the treatment of patients with a β-lactam allergy or renal insufficiency.

Swedish guidelines for diagnosis and treatment of infective endocarditis

Swedish guidelines for diagnosis and treatment of infective endocarditis (IE) by consensus of experts are based on clinical experience and reports from the literature. Recommendations are evidence based. For diagnosis 3 blood cultures should be drawn; chest X-ray, electrocardiogram, and echocardiography preferably transoesophageal should be carried out. Blood cultures should be kept for 5 d and precede intravenous antibiotic therapy. In patients with native valves and suspicion of staphylococcal aetiology, cloxacillin and gentamicin should be given as empirical treatment. If non-staphylococcal etiology is most probable, penicillin G and gentamicin treatment should be started. In patients with prosthetic valves treatment with vancomycin, gentamicin and rifampicin is recommended. Patients with blood culture negative IE are recommended penicillin G (changed to cefuroxime in treatment failure) and gentamicin for native valve IE and vancomycin, gentamicin and rifampicin for prosthetic valve IE, respectively. Isolates of viridans group streptococci and enterococci should be subtyped and MIC should be determined for penicillin G and aminoglycosides. Antibiotic treatment should be chosen according to sensitivity pattern given 2-6 weeks intravenously. Cardiac valve surgery should be considered early, especially in patients with left-sided IE and/or prosthetic heart valves. Absolute indications for surgery are severe heart failure, paravalvular abscess, lack of response to antibiotic therapy, unstable prosthesis and multiple embolies. Follow-up echocardiography should be performed on clinical indications.

Efficacy of ceftriaxone and gentamicin given once a day by using human-like pharmacokinetics in treatment of experimental staphylococcal endocarditis

We compared the efficacy of ceftriaxone combined with gentamicin, both given once a day, with that of cloxacillin given every 4 h plus gentamicin given once a day or in three daily doses (t.i.d.) for the treatment of experimental methicillin-susceptible staphylococcal endocarditis. The antibiotics were administered by using human-like (H-L) pharmacokinetics that simulated the profiles of these drugs in human serum. Animals with catheter-induced endocarditis were infected intravenously with 10(5) CFU of Staphylococcus aureus S5 (MICs and minimal bactericidal concentrations of cloxacillin, ceftriaxone, and gentamicin, 0.5 and 2 microg/ml, 4 and 8 microg/ml, and 0.5 and 1 microg/ml, respectively). The animals were then treated for 24 h with cloxacillin at a dose of 2 g that simulated H-L pharmacokinetics (H-L 2 g) every 4 h alone or combined with gentamicin (administered at doses of H-L 1 mg/kg of body weight every 8 h or H-L 4.5 mg/kg every 24 h) or with ceftriaxone at H-L 2 g every 24 h alone or combined with gentamicin (administered at doses of H-L 1 mg/kg every 8 h or H-L 4.5 mg/kg every 24 h). The results of therapy for experimental endocarditis due to the S5 strain showed that (i) cloxacillin alone is more effective than ceftriaxone alone in reducing the bacterial load (P < 0.01), (ii) the combination of cloxacillin or ceftriaxone with gentamicin is more effective than each of these drugs alone (P < 0.01), and (iii) Ceftriaxone H-L plus gentamicin H-L 4.5 mg/kg, both administered every 24 h, showed efficacy similar to that of the "gold standard," cloxacillin H-L plus gentamicin H-L 1 mg/kg t.i.d. (P > 0.05). An increase in the interval of administration of gentamicin to once daily resulted in a reduction in the numbers of bacteria in the vegetations equivalent to that achieved with the recommended regimen of cloxacillin plus gentamicin t.i.d. in the treatment of experimental endocarditis due to methicillin-susceptible S. aureus. Ceftriaxone plus gentamicin, both administered once a day, may be useful for home-based therapy for selected cases of staphylococcal endocarditis.

Aminoglycoside nephrotoxicity: do time and frequency of administration matter?

Aminoglycosides remains the mainstay in the treatment of gram-negative infections despite their potential oto-and nephrotoxicity although alternatives with equal or better efficacy are available. Several approaches were investigated to decrease aminoglycosides nephrotoxicity. Among them, only the once-daily dosing of aminoglycosides has been brought to the clinic and physicians are now increasingly adopting this approach to reduce the toxicity of these agents. The incidence of aminoglycoside nephrotoxicity can be further reduced in view of the recent data on the circadian variations of their nephrotoxicity. In fact, it has been clearly demonstrated in both experimental animals and humans that the toxicity is maximal when the drug is injected during the rest period compared with the activity period. Thus, injecting aminoglycosides once-daily at the time of the lowest toxicity is actually the most interesting and clinically applicable approach to reduce aminoglycosides toxicity.

Efficacy of teicoplanin-gentamicin given once a day on the basis of pharmacokinetics in humans for treatment of enterococcal experimental endocarditis

With the aim of investigating home therapy for enterococcal endocarditis, we compared the efficacy of teicoplanin combined with gentamicin given once a day or in three daily doses (t.i.d.) with the standard treatment, ampicillin plus gentamicin administered t.i.d., for treating experimental enterococcal endocarditis. The antibiotics were administered by using "human-like pharmacokinetics" (H-L), i.e, pharmacokinetics like those in humans, that simulated the profiles of these drugs in human serum. Animals with catheter-induced endocarditis were infected intravenously with 10(8) CFU of Enterococcus faecalis EF91 (MICs and MBCs of ampicillin, gentamicin, and teicoplanin, 0.5 and 32, 16 and 32, and 0.5 and 1 microg/ml, respectively) and were treated for 3 days with ampicillin H-L at 2 g every 4 h plus gentamicin H-L at 1 mg/kg every 8 h, or teicoplanin H-L at 10 mg/kg every 24 h, alone or combined with gentamicin, administered at dose of H-L at 1 mg/kg every 8 h or H-L at 4.5 mg/kg every 24 h. The results of therapy for experimental endocarditis due to EF91 showed that teicoplanin alone was as effective as ampicillin alone in reducing the bacterial load (P > 0.05). The combination of ampicillin or teicoplanin with gentamicin was more effective than the administration of both drugs alone in reducing the log(10)CFU/gram of aortic vegetation (P < 0.01 and P < 0.05, respectively). Teicoplanin plus gentamicin H-L at 4.5 mg/kg, both administered every 24 h, showed an efficacy equal to the "gold standard," ampicillin plus gentamicin H-L at 1 mg/kg t.i.d. (P > 0.05). Increasing the interval of administration of gentamicin to a single daily dose combined with teicoplanin resulted in a reduction of bacteria in the vegetations equivalent to that achieved with the recommended regimen of ampicillin plus thrice-daily gentamicin in the treatment of experimental endocarditis due to E. faecalis. Teicoplanin plus gentamicin, both administered once a day, may be useful home therapy for selected cases of enterococcal endocarditis.

Effectiveness and toxicity of gentamicin in an experimental model of pyelonephritis: effect of the time of administration

Temporal variations in the renal toxicity of aminoglycosides have been reported for experimental animals as well as for humans. In fact, maximal renal toxicity of aminoglycosides was observed when the drug was given during the rest period, while a lower toxicity was observed when the drug was injected during the activity period. The aim of the present study was to evaluate temporal variations in the effectiveness and renal toxicity of gentamicin in an experimental model of pyelonephritis in rats. The experiments were carried out with female Sprague-Dawley rats (185 to 250 g). They had free access to food and water throughout the study and were maintained on a 14-h light-10-h dark cycle. Animals were divided into four groups corresponding to the respective time of induction of pyelonephritis and treatment: 0700, 1300, 1900, and 0100 h. Pyelonephritis was induced by a direct inoculation of Escherichia coli (10(7) to 10(8) CFU) in the left kidney. Animals were treated for 3 and 7 days with a single daily dose of gentamicin (20 and 40 mg/kg of body weight, respectively) or saline (NaCl, 0.9%) at either 0700, 1300, 1900, or 0100 h. Animals treated at 0100 h for 3 days with gentamicin (20 mg/kg) showed a significantly lower number of bacteria in their kidneys than did all other groups (P < 0.01). After 7 days of treatment, the efficacy, evaluated by the log CFU per gram of tissue and by the percentage of sterilized kidneys, was also higher when gentamicin was administered at 0100 h. The beta-galactosidase and the N-acetyl-beta-D-glucosaminidase activities were significantly higher in urine of rats given gentamicin at 1300 h than in urine of rats treated at another time of day (P < 0.05). Gentamicin injected at 1300 h induced a significantly greater increase of [3H]thymidine incorporation into DNA of renal cortex (P < 0.01), a significantly greater inhibition of sphingomyelinase activity (P < 0.05), and significantly more histopathological lesions than the same dose injected at another time of the day. Creatinine and blood urea nitrogen levels in serum were significantly higher (P < 0.05) and the creatinine clearance was significantly lower (P < 0.05) when gentamicin was injected at 1300 h than when it was injected at another time of day. Our data suggest temporal variations in both the toxicity and the effectiveness of gentamicin, the drug being more effective and less toxic when injected during the activity period of the animals.

Pharmacodynamics of vancomycin alone and in combination with gentamicin at various dosing intervals against methicillin-resistant Staphylococcus aureus-infected fibrin-platelet clots in an in vitro infection model

We compared the pharmacodynamic activities of vancomycin with or without gentamicin in an in vitro infection model with methicilin-resistant Staphylococcus aureus-infected fibrin-platelet clots. Infected fibrin-platelet clots (FPCs) were prepared with human cryoprecipitate, human platelets, thrombin, and the organism (approximately 10[9] CFU of MRSA-494/g) and were suspended with monofilament line in an infection model capable of simulating human pharmacokinetics. Antibiotics were bolused to simulate vancomycin regimens of 2 g every 24 h (q24h), 1 g q12h, 500 mg q6h, and continuous infusion (steady-state concentration of 20 microg/ml) and gentamicin regimens of 1.5 mg/kg of body weight q12h and 5 mg/kg once daily (q.d.). Model experiments were performed in duplicate over 72 h. FPCs were removed from the models in quadruplicate at 0, 8, 24, 32, 48, 72 h, weighed, homogenized, diluted, and plated to determine colony counts. The inoculum density at 72 h was used to compare bactericidal activities between the regimens. All regimens containing vancomycin significantly decreased the bacterial inoculum compared to the growth control (P < 0.001). Vancomycin monotherapy regimens were similar in bacterial kill regardless of dosing frequency. The addition of gentamicin (either q12h or q.d.) significantly improved the bactericidal activity of the vancomycin q6h, q12h, and q24h regimens (P < 0.001). The greatest reduction in bacterial density at 72 h (P < 0.001) and the most rapid rate of kill (time to 99.9% killing) were achieved with the regimen consisting of 2 g of vancomycin q24h plus gentamicin (q.d. or q12h).

Effect of gentamicin dosing interval on efficacy of penicillin or ceftriaxone treatment of experimental endocarditis due to penicillin-susceptible, ceftriaxone-tolerant viridans group streptococci

The efficacy of ceftriaxone or penicillin alone or combined with gentamicin at different dosing intervals was evaluated in experimental endocarditis due to a penicillin-susceptible, ceftriaxone-tolerant strain of Streptococcus sanguis I. The difference between monotherapy with ceftriaxone and procaine penicillin approached statistical significance (P = 0.052). Ceftriaxone combined with gentamicin administered as a single daily dose was less effective than was procaine penicillin combined with gentamicin administered in a single daily dose or in three divided doses.

Monotherapy with meropenem versus combination therapy with ceftazidime plus amikacin as empiric therapy for fever in granulocytopenic patients with cancer. The International Antimicrobial Therapy Cooperative Group of the European Organization for Research and Treatment of Cancer and the Gruppo Italiano Malattie Ematologiche Maligne dell'Adulto Infection Program

Combinations of beta-lactams plus aminoglycosides have been standard therapy for suspected infections in granulocytopenic cancer patients, especially those with profound long-lasting granulocytopenia. With the advent of new broad-spectrum bactericidal antibiotics such as extended-spectrum cephalosporins or carbapenems, the need to combine beta-lactams with aminoglycosides became more controversial. The objective of this prospective randomized multicenter study was to compare the efficacy, safety, and tolerance of meropenem monotherapy with those of the combination of ceftazidime plus amikacin for the empirical treatment of fever in granulocytopenic cancer patients. Of 1,034 randomized patients, 958 were assessable in the intent-to-treat analysis for response to antibacterial therapy, including 483 in the meropenem group and 475 in the ceftazidime-plus-amikacin group. The median durations of neutropenia were 16 and 17 days, respectively. A successful outcome was reported in 270 of 483 (56%) patients treated with monotherapy compared with 245 of 475 (52%) patients treated with the combination group (P = 0.20). The success rates in the monotherapy group and the combination group were similar by type of infection (single gram-negative bacteremia, single gram-positive bacteremia, clinically documented infection, and possible infection). The occurrence of further infections assessed in patients for whom the allocated regimen was not modified did not differ between the two groups (12% in both groups). Mortality due to the presenting infection or further infection was relatively low (8 patients treated with the monotherapy compared with 13 patients treated with the combination). A total of 1,027 patients were evaluable for adverse events; the proportion of those who developed adverse effects was similar between the two groups (29% in both groups), and only 19 (4%) patients in the monotherapy group and 31 (6%) in the combination group experienced an adverse event related or probably related to the study drug. Allergic reactions were the only reason for stopping the protocol antibiotic(s) (3 and 5 patients, respectively). This study confirms that monotherapy with meropenem is as effective as the combination of ceftazidime plus amikacin for the empiric treatment of fever in persistently granulocytopenic cancer patients, and both regimens were well tolerated.

Temporal variation in nephrotoxicity of low doses of isepamicin in rats

The temporal variation in the nephrotoxicity of low doses of isepamicin was studied in male Sprague-Dawley rats treated with a single daily intraperitoneal injection of saline (NaCl, 0.9%) or isepamicin (80 mg/kg of body weight) at either 0800, 1400, 2000, or 0200 h for 4 and 10 days. On day 10, the cellular regeneration (incorporation of [3H] thymidine into DNA of renal cortex) and cortical accumulation of isepamicin were significantly higher in animals treated at 1400 h than at 0200 h (P < 0.01). Immunogold labeling studies showed that isepamicin was essentially localized in the lysosomes of proximal tubular cells in all treated groups, but the density of the gold particles over the lysosomes was higher in animals treated at 1400 than at 0200 h. The results of the present study show that the renal toxicity of isepamicin was maximal at 1400 h (midlight period) and minimal at 0200 h (middark period).

In vitro activities of 22 beta-lactam antibiotics against penicillin-resistant and penicillin-susceptible viridans group streptococci isolated from blood

A total of 410 strains of viridans group streptococci isolated consecutively from blood were tested by the microdilution method for in vitro susceptibility to 22 beta-lactam antibiotics. One hundred thirty-eight strains (33.6%) were resistant to penicillin with a MIC range of 0.25 to 8 micrograms/ml. MICs of all beta-lactam agents tested were higher for penicillin-resistant strains than for susceptible strains. These antibiotics were classified into three groups according to their in vitro activities (MICs at which 50 and 90% of the isolates are inhibited). Beta-Lactams of the first group (these included imipenem, cefpirome, FK-037, cefditoren, cefotaxime, ceftriaxone, and cefepime) showed activities higher than or similar to that of penicillin against penicillin-resistant viridans group streptococci. However, 80% of highly penicillin-resistant Streptococcus mitis organisms required cefotaxime and ceftriaxone MICs of > or = 2 micrograms/ml (range, 2 to 16 micrograms/ml). Beta-Lactams of the second group (cefpodoxime, ampicillin, amoxicillin-clavulanate, piperacillin, and cefuroxime) showed lower activities than penicillin. Finally, antibiotics of the third group (cephalothin, oxacillin, ceftazidime, cefixime, cefaclor, cefetamet, cefadroxil, cephalexin, and ceftibuten) showed poor in vitro activities. Therefore, some of the beta-lactam agents included in the first group could be an acceptable alternative in the treatment of serious infections due to strains highly resistant to penicillin, although clinical experience is needed.

Effect of gentamicin dosing interval on therapy of viridans streptococcal experimental endocarditis with gentamicin plus penicillin

This study compares the effects of a total daily dose of gentamicin given once a day (q.d.) or three times a day (t.i.d.) in the therapy of experimental endocarditis in rabbits caused by penicillin-susceptible, penicillin-tolerant, or penicillin-resistant viridans streptococci. Four isolates were used in vivo: one penicillin susceptible (MIC < or = 0.03 microgram/ml), one penicillin tolerant (MBC/MIC, < or = 0.03/ > 32 micrograms/ml), and two penicillin resistant (MICs = 0.5 and 2 micrograms/ml). Animals were infected with one of the four isolates and assigned to one of the following treatment regimens: no treatment, procaine penicillin at 1.2 million IU intramuscularly (i.m.) t.i.d., procaine penicillin plus gentamicin at 1 mg/kg of body weight i.m. t.i.d., procaine penicillin plus gentamicin at 3 mg/kg i.m. q.d., or procaine penicillin plus gentamicin at 1 mg/kg i.m. q.d. (only animals infected with the penicillin-susceptible isolate). Serum drug concentrations measured 30 min after administration of 1.2 million IU of penicillin and 1 or 3 mg of gentamicin per kg were 22.6, 3.8, and 8.5 micrograms/ml, respectively. The reduced total daily dose of gentamicin was ineffective among animals infected with penicillin-susceptible viridans streptococci; treatment with 1 mg of gentamicin per kg per day plus penicillin was less effective (P < 0.05) than was treatment with 3 mg of gentamicin per kg per day plus penicillin. The 1-mg/kg/day gentamicin treatment regimen was not further studied. The gentamicin dosing interval did not significantly affect (q.d. versus t.i.d., P > 0.05) the relative efficacy of penicillin plus gentamicin for treatment of experimental endocarditis among animals infected with each of the four isolates tested.

Outpatient treatment of endocarditis in a clinic-based program in Argentina

The major cost in the treatment of infective endocarditis (IE) is the length of hospitalization required for the administration of intravenous antibiotics. This can be reduced by substituting shorter regimens and by the introduction of outpatient parenteral antibiotic therapy (OPAT). Careful selection of patients is vital for the success of OPAT in IE. The patients should be hemodynamically stable and without clinical complications. The delivery of OPAT for IE followed a clinical and home-based program involving an endocarditis team whose members included an infectious diseases physician, a microbiologist, a cardiologist and a nurse trained in intravenous techniques. Among the antimicrobial agents used in OPAT of IE, single-agent ceftriaxone for four weeks followed by a short course of amoxicillin or ceftriaxone in combination with an aminoglycoside for two weeks (short course) are effective modes of treatment for streptococcal endocarditis, the most common cause of IE. This treatment is also effective for carefully selected patients with other types of endocarditis, such as those due to the HACEK group (Haemophilus aphrophilus/paraphrophilis, Actinobacillus actinomycetem comitans, Caradiobacterium hominis, Eikenella corrodens and Kingella kingae). Staphylococcus aureus, enterococci and late prosthetic valve endocarditis associated with a streptococcus may also be treated on an outpatient basis after stabilization (approximately 2 weeks). As a result of their need for prolonged treatment periods, these patients are also very good candidates for OPAT. In conclusion, new regimens utilizing ceftriaxone once daily and short-term therapy on a clinical or home basis offer the potential benefits of cheaper safer and more convenient treatment for patients with IE.

Ceftriaxone protects against tobramycin nephrotoxicity

The effect of ceftriaxone on tobramycin-induced nephrotoxicity was investigated. Female Sprague-Dawley rats were treated during 4 and 10 days with saline (NaCl, 0.9%), ceftriaxone at a dose of 100 mg/kg of body weight/12 h subcutaneously, tobramycin at doses of 40 and 60 mg/kg/12 h intraperitoneally, or the combination ceftriaxone-tobramycin. Creatinine levels in serum were significantly higher in animals treated with tobramycin alone given at 60 mg/kg/12 h during 10 days, compared with control animals (P < 0.01) or animals receiving the combination tobramycin-ceftriaxone (P < 0.01). After 10 days of treatment, ceftriaxone did not accumulate in renal tissue but did reduce the renal intracortical accumulation of tobramycin (P < 0.05). Tobramycin given alone at either 40 or 60 mg/kg/12 h induced a significant inhibition of sphingomyelinase activity compared with control animals (P < 0.05). However, this enzyme activity was significantly less inhibited when tobramycin was injected in combination with ceftriaxone (P < 0.05). Ceftriaxone alone had no effect on the activity of this enzyme. The [3H]thymidine incorporation into the DNA of renal cortex was also significantly lower in animals treated with tobramycin-ceftriaxone compared with animals receiving tobramycin alone (P < 0.05). The 24-h urinary excretion of beta-galactosidase was significantly reduced in animals treated with the combination tobramycin-ceftriaxone compared with the administration of tobramycin alone at 40 and 60 mg/kg/12 h after 5 and 10 days (P < 0.05). Histologically, ceftriazone induced very few cellular alterations and reduced considerably the presence of typical signs of tobramycin nephrotoxicity. This investigation demonstrated that ceftriaxone protects animals against tobramycin-induced nephrotoxicity.

Nephrotoxicity of low doses of tobramycin in rats: effect of the time of administration

The circadian and the circannual variations of the nephrotoxicity of tobramycin were studied in female Sprague-Dawley rats. Animals were maintained on a light-dark period of 14/10 hrs (light on: 06h00 to 20h00). They were injected once daily for 4 and 10 days with saline or tobramycin at a dose of 40 mg/kg/day i.p. at either 08h00, 14h00, 20h00 and 02h00, in April 1991, July 91, October 91, January 92. In April 91, tobramycin injected at 14h00 during 10 days induced a significant increase of [3H]-thymidine incorporation into DNA of renal cortex as compared to other groups (p < 0.01): toxicity was highest at 14h00 and lowest at 02h00. No temporal change was observed in the renal cortical accumulation of tobramycin, and in serum creatinine after the 4 or 10 days of treatment. In experiments done in April, July and October 1991 and in January 1992, no circannual variation was found in tobramycin cortical levels but peaks of toxicity were observed at 02h00 in April and October 1991 and at 14h00 in July 1991 and January 1992. There was no linear correlation between the toxicity and the tobramycin accumulation in the renal cortex (r = 0.21). The data suggest that the circadian changes in tobramycin toxicity are due to temporal changes in the susceptibility of renal cells to tobramycin.

Simulated human serum profiles of one daily dose of ceftriaxone plus netilmicin in treatment of experimental streptococcal endocarditis

We performed experiments in rats aimed at determining whether a combination of ceftriaxone (CRO) and netilmicin (NET), by using once-daily administration in rats, which simulated profiles of drug in human serum, was more effective than either agent alone in the treatment of endocarditis caused by viridans group streptococci. A programmable infusion pump system enabled the production of profiles of CRO in serum that simulate those found in humans after the intravenous administration of 2 g. The subcutaneous administration of 18 mg of NET per kg of body weight produced levels in the sera of rats comparable to those after the intravenous administration of a dose of 5 mg of NET per kg in humans. Rats with catheter-induced aortic vegetations were infected intravenously with two test strains, a CRO-susceptible Streptococcus sanguis strain (MICs of CRO and NET, 0.064 and 8 mg/liter, respectively) and a relatively CRO-resistant Streptococcus mitis strain (MICs of CRO and NET, 2 and 8 mg/liter, respectively). Against both strains, the combination of CRO and NET was synergistic in vitro as determined by time-kill curves. Treatment of rats was started 48 h postinfection and lasted for 3 days. CRO alone was effective against the susceptible strain (P < 0.001 compared with control animals) but was not effective against the resistant organism. A significantly enhanced antibacterial activity of the CRO-NET combination in reducing the valvular bacterial counts was observed with both test strains (P < 0.001). The synergistic effect was obtained with a single daily injection of NET which provided detectable levels in serum for only 8 h, suggesting that in vivo synergism in the treatment of infections caused by viridans group streptococci can be obtained without 24 h of aminoglycoside coverage. These experimental data might provide a rationale for clinical trials of a once-a-day dosing regimen in the treatment of streptococcal but nonenterococcal endocarditis.