Efficacy and safety of amikacin in systemic infections when given as a single daily dose or in two divided doses. Scandinavian Amikacin Once Daily Study Group

Once-Daily Intraperitoneal Gentamicin is Effective Therapy for Gram-Negative Capd Peritonitis

Objective

To report our 3-year experience with the use of once-daily intraperitoneal (IP) gentamicin in the treatment of gram-negative continuous ambulatory peritoneal dialysis (CAPD) peritonitis.

Design

A prospective cohort study in prevalent CAPD patients.

Setting

A tertiary care institution.

Patients

All CAPD patients who presented with new episodes of peritonitis were studied. At presentation with peritonitis, IP vancomycin and gentamicin were administered as empirical therapy. IP gentamicin was given at a single daily dose of 40 mg/2 L in the overnight bag. The antimicrobial agents were reviewed when the culture results became available. Intraperitoneal ceftazidime was added for the treatment of pseudomonas peritonitis.

Main Outcome Measures

Results of microbiological cultures and clinical outcomes of peritonitis were analyzed.

Results

Over a 36-month period, 190 episodes of peritonitis were recorded, of which 62/190 episodes (32.6%) isolated gram-negative organisms. The gram-negative organisms isolated were Escherichia coli, 15/62 episodes (24.1%); Pseudomonas aeruginosa, 12/62 episodes (19.4%); Acinetobacter spp, 12/62 episodes (19.4%); Klebsiella spp, 10/62 episodes (16.1%); and others, 13/62 episodes (21.0%). The overall treatment success rate was 66.1%. The treatment success rates were 74.0% if pseudomonas infections were excluded, 76.1% if gentamicin-resistant pathogens were excluded, and 80.5% if both pseudomonas infections and gentamicin-resistant pathogens were excluded.

Conclusions

Once-daily IP gentamicin appears to be effective in the treatment of gram-negative CAPD peritonitis.

Once-Daily Aminoglycosides: A Meta-Analysis of Nonneutropenic and Neutropenic Adults

Objective:

To compare the efficacy, nephrotoxicity, and ototoxicity of once-daily dosing of aminoglycosides versus conventional dosing.

Design:

Meta-analysis of 14 randomized trials identified through a MEDLINE search (January 1965-May 1996).

Patients:

Neutropenic and nonneutropenic adults.

Interventions:

Patients were randomly selected to receive an aminoglycoside once daily or in multiple daily doses.

Measurements and Main Outcomes:

The outcomes considered were clinical cure, bacteriologic cure, nephrotoxicity, auditory toxicity, and vestibular toxicity. The data were analyzed in the following subgroups: (1) all trials, (2) nonneutropenic patients, (3) neutropenic patients, and (4) patients with undefined neutrophil status. For all trials the pooled risk ratio was 1.268 (95% CI 0.828 to 1.939) for clinical cure, and was 1.390 (95% CI 1.350 to 1.392) for bacteriologic cure. Nephrotoxicity had a pooled risk ratio of 0.765 (95% CI 0.468 to 1.252), that for auditory toxicity was 1.117 (95% CI 0.151 to 5.636), and that for vestibular toxicity was 1.155 (95% CI 0.221 to 6.039). Analysis of the subgroups, including a separate analysis of neutropenic patients, demonstrated similar results.

Conclusions:

When all trials were considered, once-daily administration of aminoglycosides had similar efficacy and no increase in nephrotoxicity or ototoxicity compared with conventional aminoglycoside dosing.

Safety of IV amikacin in the treatment of pulmonary non-tuberculous mycobacterial disease

BACKGROUND AND OBJECTIVE

Pulmonary non-tuberculous mycobacterial (NTM) disease has a high mortality rate and often requires treatment with intravenous amikacin. We report on safety data in patients treated with intravenous amikacin for pulmonary.

METHODS

A retrospective observational study (2002-2012) was performed including 45 patients that met American Thoracic Society criteria for pulmonary NTM disease and were treated with intravenous amikacin at three hospitals in Brisbane, Australia. The aim was to define the rates of common adverse effects, the patient and regimen factors associated with these adverse effects and describe the rates of treatment success and associated factors.

RESULTS

Forty-five patients (34 women; median age 63 years) were treated for Mycobacterium intracellulare (25), Mycobacterium abscessus (13), Mycobacterium avium (6) and Mycobacterium fortuitum (1) using multi-drug therapy that included IV amikacin. Transient ototoxicity was seen in eight (18%) but long-term ototoxicity was seen in only three (7%). There were no cases of nephrotoxicity and no long-term vestibulotoxicity. Sustained culture conversion at 6 months was only found in 17 (38%), however, the majority (34 patients, 76%) had a clinical response to treatment determined by an improvement in symptoms.

CONCLUSION

Carefully selected and closely monitored patients with pulmonary NTM can be treated using IV amikacin safely with low rates of toxicity. No pretreatment patient or regimen factors were predictive of toxicity or treatment success in this small cohort. Lower treatment success rates were found than previous trials suggest there is a difficult balance in this patient group between treatment success and toxicities.

Gentamicin extended interval regimen and ototoxicity in neonates

OBJECTIVES

To assess the extended interval regimen gentamicin associated ototoxicity in neonatal intensive care unit using hearing tests.

METHODS

Two hundred and twenty neonates admitted to neonatal intensive care were assessed; 110 neonates who had received gentamicin and 110 neonates who had not received gentamicin served as control group. Gentamicin group were further subdivided according to the duration of treatment into 50 neonates who had received gentamicin for 5 days or less and 60 neonates who had received gentamicin for more than 5 days. TEOAEs were used for hearing screening. Auditory brain response was performed 3 months later for failed cases to confirm the hearing impairment.

RESULTS

Three neonates failed TEOAEs screening in each group but hearing impairment was confirmed in one neonate only (0.9%) in each group (gentamicin and control groups). Neonates who received gentamicin for more than 5 days showed comparable results as regard TEOAEs or ABR results with those who received gentamicin for 5 days or less, and control group.

CONCLUSIONS

Extended interval dosing of gentamicin therapy in neonates does not increase the incidence of hearing loss. This suggests that hearing loss in neonatal intensive care unit may be attributed to factors other than gentamicin treatment.

Beta lactam antibiotic monotherapy versus beta lactam-aminoglycoside antibiotic combination therapy for sepsis

BACKGROUND

Optimal antibiotic treatment for sepsis is imperative. Combining a beta lactam antibiotic with an aminoglycoside antibiotic may provide certain advantages over beta lactam monotherapy.

OBJECTIVES

Our objectives were to compare beta lactam monotherapy versus beta lactam-aminoglycoside combination therapy in patients with sepsis and to estimate the rate of adverse effects with each treatment regimen, including the development of bacterial resistance to antibiotics.

SEARCH METHODS

In this updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2013, Issue 11); MEDLINE (1966 to 4 November 2013); EMBASE (1980 to November 2013); LILACS (1982 to November 2013); and conference proceedings of the Interscience Conference of Antimicrobial Agents and Chemotherapy (1995 to 2013). We scanned citations of all identified studies and contacted all corresponding authors. In our previous review, we searched the databases to July 2004.

SELECTION CRITERIA

We included randomized and quasi-randomized trials comparing any beta lactam monotherapy versus any combination of a beta lactam with an aminoglycoside for sepsis.

DATA COLLECTION AND ANALYSIS

The primary outcome was all-cause mortality. Secondary outcomes included treatment failure, superinfections and adverse events. Two review authors independently collected data. We pooled risk ratios (RRs) with 95% confidence intervals (CIs) using the fixed-effect model. We extracted outcomes by intention-to-treat analysis whenever possible.

MAIN RESULTS

We included 69 trials that randomly assigned 7863 participants. Twenty-two trials compared the same beta lactam in both study arms, while the remaining trials compared different beta lactams using a broader-spectrum beta lactam in the monotherapy arm. In trials comparing the same beta lactam, we observed no difference between study groups with regard to all-cause mortality (RR 0.97, 95% CI 0.73 to 1.30) and clinical failure (RR 1.11, 95% CI 0.95 to 1.29). In studies comparing different beta lactams, we observed a trend for benefit with monotherapy for all-cause mortality (RR 0.85, 95% CI 0.71 to 1.01) and a significant advantage for clinical failure (RR 0.75, 95% CI 0.67 to 0.84). No significant disparities emerged from subgroup and sensitivity analyses, including assessment of participants with Gram-negative infection. The subgroup of Pseudomonas aeruginosa infections was underpowered to examine effects. Results for mortality were classified as low quality of evidence mainly as the result of imprecision. Results for failure were classified as very low quality of evidence because of indirectness of the outcome and possible detection bias in non-blinded trials. We detected no differences in the rate of development of resistance. Nephrotoxicity was significantly less frequent with monotherapy (RR 0.30, 95% CI 0.23 to 0.39). We found no heterogeneity for all these comparisons.We included a small subset of studies addressing participants with Gram-positive infection, mainly endocarditis. We identified no difference between monotherapy and combination therapy in these studies.

AUTHORS' CONCLUSIONS

The addition of an aminoglycoside to beta lactams for sepsis should be discouraged. All-cause mortality rates are unchanged. Combination treatment carries a significant risk of nephrotoxicity.

Ototoxicity caused by once- and twice-daily administration of amikacin in rabbits

OBJECTIVE

The cochleotoxic effects of aminoglycosides, such as amikacin, are well-established. The aim of the present study was to investigate the possible differences in cochleotoxic effects between once-daily administration (ODA) and twice-daily administration (TDA) of amikacin simulating pediatric dosing.

METHODS

Twenty-one rabbits were used. Seven animals received intramuscularly amikacin once daily (ODA-group) and seven received the drug twice daily (TDA-group), for a total time period of 2 weeks. All the animals were subjected to Distortion Product Otoacoustic Emissions (DPOAEs) every 3 days since beginning of the experiment. The rest 7 animals did not receive any medication and served as controls (Control group). Two measurements (7 and 14 days) were obtained following the cease of drug administration.

RESULTS

Reduced cochlear activity (as depicted in the respective reduced DPOAE-amplitudes) compared to the pre-treatment state was found in both ODA- and TDA-groups. Cochlear activity was reduced at a wider range of frequencies (from 593 to 4031Hz in TDA-group and from 593 to 1093Hz in ODA-group) and to a higher degree in group B than in group A. Cochlear activity was reduced earlier in ODA-group than in TDA-group. No differences to the pre-treatment state were observed in the control group.

CONCLUSIONS

The above findings suggest that less frequent administration in higher dose of amikacin is associated with minimal cochleotoxicity.

Dosing Regimes for Antimicrobials during Continuous Veno-Venous Haemofiltration (CVVH)

The pharmacokinetic profile of antibiotics used in critically ill patients during continuous haemofiltration is different both from healthy people and from stable patients on long-term dialysis. This article reviews the patient-related, drug-related and haemofiltration-related variables influencing drug elimination in this group of patients, and provides specific recommendations for antibiotic dosing for different classes of antibiotics. Loading doses do not need to be altered. Subsequent dose adjustment should be based on the estimated ultrafiltration capacity of the renal replacement technique and the degree of extracorporeal clearance. A table of recommended doses is provided.

Principles of Antimicrobial Therapy

The most compelling reason for practicing judicious antimicrobial use is to facilitate therapeutic success. The definition of therapeutic success has changed in recent years, however; not only does success include eradication of infection, but it must now include avoidance of resistance. If the goal of antimicrobial therapy is to achieve sufficient concentrations at the site of infection such that the infecting organism is killed, therapy should be successful.

Pharmacodynamics of antimicrobials: treatment optimisation

As bacterial resistance continues to increase, optimising the potential for successful clinical outcomes with antimicrobial therapy requires consideration of pharmacodynamic concepts in order to maximise bacterial eradication and minimise the potential for further resistance. Based on the pharmacodynamic characteristics of specific antibiotics, dosage modifications can be implemented to improve the likelihood of bactericidal exposure. Considering their concentration-dependent bactericidal activity, aminoglycosides benefit from increased dosages and infrequent administration, so as to achieve a maximum concentration/minimum inhibitory concentration (MIC) of 10-12. In contrast, beta-lactams are concentration-independent killers and benefit greatest by increasing the time above the MIC (T > MIC). This can be accomplished with the use of prolonged or continuous infusion. By optimising pharmacodynamic parameters with these methodologies, successful treatment of pathogens may be possible in patient populations for whom standard dosing regimens are not effective.

Beta lactam antibiotic monotherapy versus beta lactam-aminoglycoside antibiotic combination therapy for sepsis

BACKGROUND

Optimal antibiotic treatment for sepsis is imperative. Combining a beta-lactam antibiotic with an aminoglycoside antibiotic may have certain advantages over beta-lactam monotherapy.

OBJECTIVES

We compared clinical outcomes for beta lactam-aminoglycoside combination therapy versus beta lactam monotherapy for sepsis.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), (The Cochrane Library, Issue 3, 2004); MEDLINE (1966 to July 2004); EMBASE (1980 to March 2003); LILACS (1982 to July 2004); and conference proceedings of the Interscience Conference of Antimicrobial Agents and Chemotherapy (1995 to 2003). We scanned citations of all identified studies and contacted all corresponding authors.

SELECTION CRITERIA

We included randomized and quasi-randomized trials comparing any beta-lactam monotherapy to any combination of one beta-lactam and one aminoglycoside for sepsis.

DATA COLLECTION AND ANALYSIS

The primary outcome was all-cause fatality. Secondary outcomes included treatment failure, superinfections, colonization, and adverse events. Two authors independently collected data. We pooled relative risks (RR) with their 95% confidence intervals (CI) using the fixed effect model. We extracted outcomes by intention-to-treat analysis whenever possible.

MAIN RESULTS

We included 64 trials, randomizing 7586 patients. Twenty trials compared the same beta-lactam in both study arms, while the remaining compared different beta-lactams using a broader spectrum beta-lactam in the monotherapy arm. In studies comparing the same beta-lactam, we observed no difference between study groups with regard to all-cause fatality, RR 1.01 (95% CI 0.75-1.35) and clinical failure, RR 1.11 (95% CI 0.95-1.29). In studies comparing different beta-lactams, we observed an advantage to monotherapy: all cause fatality RR 0.85 (95% CI 0.71-1.01), clinical failure RR 0.77 (95% CI 0.69-0.86). No significant disparities emerged from subgroup and sensitivity analyses, including the assessment of patients with Gram-negative and Pseudomonas aeruginosa infections. We detected no differences in the rate of resistance development. Adverse events rates did not differ significantly between the study groups overall, although nephrotoxicity was significantly more frequent with combination therapy, RR 0.30 (95% CI 0.23-0.39). We found no heterogeneity for all comparisons. We included a small subset of studies addressing patients with Gram-positive infections, mainly endocarditis. We identified no difference between monotherapy and combination therapy in these studies.

AUTHORS' CONCLUSIONS

The addition of an aminoglycoside to beta-lactams for sepsis should be discouraged. All-cause fatality rates are unchanged. Combination treatment carries a significant risk of nephrotoxicity.

The effect of vecuronium is enhanced by a large rather than a modest dose of gentamicin as compared with no preoperative gentamicin

We compared the effect of two doses of gentamicin versus no gentamicin (NG) given before surgery on the neuromuscular relaxant effect of vecuronium. Seventy patients (intraabdominal procedures) were randomly allocated to receive preoperative large-dose (4 mg/kg) gentamicin (LD), a modest dose (1.2 mg/kg) of gentamicin (MD), or NG. No more than one dose of gentamicin was given before the vecuronium administration. Serum gentamicin levels, the time for 25% recovery of the first twitch in the train-of-four after a bolus of vecuronium, and the time from cessation of the vecuronium infusion to extubation of the trachea were estimated. Serum gentamicin levels were higher (P < 0.001) for LD than MD. The time for 25% recovery of the first twitch after the vecuronium bolus was slightly longer with LD than MD (P = 0.06) and longer in LD than NG (P = 0.001) (42.9 +/- 23.6 min versus 36.2 +/- 17 min and 27.4 +/- 9 min, respectively). The time to extubation was similar with LD and MD and longer for LD than NG (P = 0.008) (34.7 +/- 19.2 min versus 27.4 +/- 19.3 min and 19.4 +/- 10.1 min, respectively). The differences in these times were insignificant between MD and NG. Gentamicin administered as a LD rather than MD enhanced the neuromuscular blockade of vecuronium as compared with NG given before surgery.

IMPLICATIONS

We demonstrated that the neuromuscular relaxant effect of vecuronium is enhanced by a large (4 mg/kg) rather than a modest (1.2 mg/kg) dose of gentamicin as compared with no gentamicin given before surgery.

Gentamicin for the practicing urologist: review of efficacy, single daily dosing and "switch" therapy

PURPOSE

We review the literature on gentamicin, including single daily dosing and "switch" therapy.

MATERIALS AND METHODS

We used MEDLINE to search the literature from 1966 to June 1997, and then manually searched bibliographies to identify studies that our initial search might have missed.

RESULTS

Gentamicin has attractive characteristics, including wide spectrum, infrequent resistance, economy and familiarity. Although limited by well known toxicities, gentamicin remains a drug of choice for serious Gram-negative infections. Dosing strategies, such as single daily dosing and switch therapy, have renewed enthusiasm for this time-honored drug.

CONCLUSIONS

Gentamicin remains a valuable drug in urology. Once daily dosing and switch therapy offer the potential to increase effectiveness and convenience while decreasing toxicity and costs.

Prospective evaluation of the effect of an aminoglycoside dosing regimen on rates of observed nephrotoxicity and ototoxicity

The nephrotoxicity and ototoxicity associated with once-daily versus twice-daily administration of aminoglycosides was assessed in patients with suspected or proven gram-negative bacterial infections in a randomized, double-blind clinical trial. Patients who received therapy for >/=72 h were evaluated for toxicity. Patients also received concomitant antibiotics as deemed necessary for treatment of their infection. Plasma aminoglycoside concentrations, prospective aminoglycoside dosage adjustment, and serial audiologic and renal status evaluations were performed. The probability of occurrence of a nephrotoxic event and its relationship to doses and daily aminoglycoside exposure served as the main outcome measurement. One hundred twenty-three patients were enrolled in the study, with 83 patients receiving therapy for at least 72 h. For 74 patients plasma aminoglycoside concentrations were available for analysis, and the patients formed the group evaluable for toxicity. The primary infectious diagnosis for the patients who were enrolled in the study were bacteremia or sepsis, respiratory infections, skin and soft tissue infections, or urosepsis or pyelonephritis. Of the 74 patients evaluable for toxicity, 39 received doses twice daily and 35 received doses once daily and a placebo 12 h later. Nephrotoxicity occurred in 6 of 39 (15.4%) patients who received aminoglycosides twice daily and 0 of 35 patients who received aminoglycosides once daily. The schedule of aminoglycoside administration, concomitant use of vancomycin, and daily area under the plasma concentration-time curve (AUC) for the aminoglycosides were found to be significant predictors of nephrotoxicity by multivariate logistic regression analysis (P Collapse

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MESH Headings

• Adult
• Aged
• Aged, 80 and over
• Aminoglycosides
• Anti-Bacterial Agents/administration & dosage
• Anti-Bacterial Agents/adverse effects
• Anti-Bacterial Agents/pharmacokinetics
• Double-Blind Method
• Drug Administration Schedule
• Female
• Hearing/drug effects
• Humans
• Kidney/drug effects
• Male
• Middle Aged
• Prospective Studies

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Grants Collapse

Affiliation(s)

M J Rybak The Anti-Infective Research Laboratory, Department of Pharmacy Services, Detroit Receiving Hospital and University Health Center, College of Pharmacy and Allied Health Professions, Wayne State University, Detroit, Michigan 48201, USA.
B J Abate
S L Kang
M J Ruffing
S A Lerner
G L Drusano

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Once daily ceftriaxone plus amikacin vs. three times daily ceftazidime plus amikacin for treatment of febrile neutropenic children with cancer. Writing Committee for the International Collaboration on Antimicrobial Treatment of Febrile Neutropenia in Children

BACKGROUND

The combination of ceftazidime plus aminoglycoside is widely used for the treatment of febrile neutropenic patients but requires multiple daily administration. Because the frequency of Pseudomonas aeruginosa is low in many centers, there is a rationale to test other antibiotic regimens that provide appropriate antibacterial coverage with the advantage of reduced dosing frequency, such as once daily ceftriaxone plus amikacin.

METHODS

Febrile neutropenic children with leukemia, lymphoma or solid tumors after chemotherapy were included in an open, prospective, randomized, multinational study comparing once daily ceftriaxone plus amikacin vs. 8-hourly ceftazidime and amikacin. The response to antimicrobial therapy was defined as complete response, improvement or failure. Assessment of adverse events was supplemented by specific definitions of nephrotoxicity, ototoxicity, hepatotoxicity and hypokalemia. Costs were estimated from published values of acquisition costs, delivery costs and hospitalization costs.

RESULTS

Efficacy was evaluable in 364 of 468 episodes in 265 children. Response rates in ceftriaxone and amikacin vs. ceftazidime and amikacin-treated episodes were 119 of 181 (66%) vs. 121 of 183 (66%), 7 of 181 (4%) vs. 9 of 183 (5%) and 55 of 181 (30%) vs. 53 of 181 (29%) for complete response, improvement and failure, respectively. Safety profiles were similar with both treatment regimens. The acquisition and administration costs were lower for the ceftriaxone and amikacin regimen.

CONCLUSIONS

A once daily regimen of ceftriaxone and amikacin is as safe and clinically effective as that of three times daily ceftazidime and amikacin for the treatment of febrile neutropenic children with cancer and is more cost-effective. The once daily regimen of ceftriaxone and amikacin is suitable for outpatient treatment.

In vivo antibacterial effects of simulated human serum profiles of once-daily versus thrice-daily dosing of amikacin in a Serratia marcescens endocarditis experimental model

Once-daily dosage of aminoglycosides is currently under consideration. The lower toxicity of this regimen has been clearly established, but there are conflicting experimental and clinical data concerning its efficacy. It is inadvisable to optimize human therapy by extrapolation from experimental studies since animal and human pharmacokinetics differ. The simulation of human pharmacokinetics in experimental infectious models would seem to offer a more rational approach. We used computer-controlled infusion of amikacin at a variable flow rate to simulate human pharmacokinetics in a Serratia marcescens rabbit endocarditis model and to compare two therapeutic regimens (once-daily versus thrice-daily doses). The doses corresponded to simulations of 15 and 30 mg/kg of body weight per day in humans, and antibacterial activity was measured in vegetations (Veg) after 24 h of treatment. The results show that the dose corresponding to 15 mg/kg/day failed to produce a significant reduction of CFU (6.8 +/- 0.9 and 6.4 +/- 0.8 log10 CFU/g of Veg, respectively, for once-daily and thrice-daily doses versus 7.6 +/- 1.0 for controls). A significant reduction was observed only for the dose corresponding to 30 mg/kg/day in humans (5.2 +/- 1.5 and 5.4 +/- 1.1 log10 CFU/g of Veg, respectively, for the two regimens). With this model, the efficacy of amikacin was similar for both regimens after 24 h of treatment simulating human pharmacokinetics.

Pharmacokinetics of once-daily amikacin in pediatric patients

OBJECTIVE: To study the pharmacokinetic parameters of a once-daily regimen of amikacin (15 mg/kg) in association with other antimicrobial agents in 35 children with severe Gram-negative infections. METHODS: A Bayesian approach was developed to optimize the amikacin regimen. The predictive performance was assessed by computing bias and precision. Each patient was evaluated for toxicity after 5 days of treatment. RESULTS: Peak amikacin concentrations on days 2 and 5 of therapy averaged 31.3 plus minus 9.0 mg/L and 32.4 plus minus 7.4 mg/L, respectively. To achieve peak serum concentrations between 30 and 40 mg/L, individualized dosage was necessary in 19 of 35 children. The pharmacokinetic parameters showed large interindividual variations, with a mean half-life of 2 h and a mean volume of distribution of 0.36 L/kg. No nephrotoxicity was observed in any of the children. After individualization of dosage on the basis of one measurement of peak concentration, no significant differences were observed between predicted and subsequently measured amikacin concentrations. CONCLUSIONS: Once-daily dosage of amikacin (15 mg/kg) is well tolerated in pediatric patients; however, a loading dose of 20 mg/kg is recommended to achieve a therapeutic peak value between 30 and 40 mg/L. Initial serum monitoring is essential in a population such as children, with wide interpatient variability. Using the Bayesian approach, the amikacin regimen in children can then be predicted with minimal bias and good precision.

Treatment of experimental endocarditis due to Enterococcus faecalis using once-daily dosing regimen of gentamicin plus simulated profiles of ampicillin in human serum

We compared the efficacy of ampicillin, both alone and in combination with gentamicin given once a day (q.d.) or three times a day (t.i.d.), in the treatment of experimental enterococcal endocarditis. Ampicillin was administered by using humanlike pharmacokinetics that simulated the profiles of this drug in human serum. An open one-compartment mathematical model developed in this study was used to estimate the decreasing doses administered with a computer-controlled infusion pump that simulated in rabbits the human serum pharmacokinetics after intravenous administration of 2 g of ampicillin every 4 h. Animals with catheter-induced endocarditis were infected intravenously with 10(8) CFU of Enterococcus faecalis J4 (MICs and MBCs of ampicillin and gentamicin, 2 and 128 and 16 and 64 micrograms/ml, respectively) and were treated for 3 days with ampicillin alone or in combination with gentamicin at 2 mg/kg of body weight subcutaneously t.i.d. or at 6 mg/kg subcutaneously q.d. The serum ampicillin levels and pharmacokinetic parameters of the humanlike pharmacokinetics of ampicillin in rabbits were similar to those found in humans treated with 2 g of ampicillin intravenously. The results of therapy for experimental endocarditis caused by E. faecalis J4 showed that the residual bacterial concentration in aortic valve vegetation was significantly lower in the animals treated with combinations of ampicillin plus gentamicin given q.d. or t.i.d. than in those treated with ampicillin alone (P < 0.01). The dosing interval of gentamicin did not significantly affect (q.d. versus t.i.d.; P = 0.673) the therapeutic efficacy of the combination of ampicillin plus gentamicin.

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.

Experience of once-daily aminoglycoside dosing using a target area under the concentration-time curve

BACKGROUND

Many centres are changing to once-daily aminoglycoside administration. However, proposed methods for this practice often have theoretical and practical difficulties. We have developed a method in which a target area under the concentration-time curve (AUC) is used instead of traditional peak and trough serum concentrations.

AIMS

To analyse our experience with the target AUC method in the first 100 courses of once-daily aminoglycoside administration in the Christchurch, New Zealand hospitals.

METHODS

Following a starting dose of 5-7 mg/kg, administered by 30-minute infusion, the AUC was calculated using two serum aminoglycoside concentrations taken at one and six-14 hours after the start of the infusion. Dose adjustment was made to correct for any difference between the calculated AUC and a target AUC (72-101 mg.1(-1).h). The method was assessed for practicality and precision in 100 courses of treatment. The incidence of aminoglycoside toxicity was documented.

RESULTS

The mean final dose of 6.68 mg/kg, and AUC of 92.8 mg.1(-1).h, were significantly different from the mean starting dose and AUC of 5.67 mg/kg and 74.0 mg.1(-1).h, respectively. The method appeared to be more precise than empirical dosing at achieving the target AUC even though the final recommended dose had more variability than the starting dose. Although the study was uncontrolled, observed nephrotoxicity (2%) and ototoxicity (up to 6.9%) were no greater than expected from the results of other studies. There were no deaths related to antibiotic failure.

CONCLUSIONS

The AUC method was practical, and more appropriate for once-daily dosing than the conventional method of aiming for target peak and trough concentrations. Dose adjustment can be made before the next dose.

Prevention of drug-induced nephrotoxicity in the intensive care unit

Acute renal failure (ARF) occurs in 5% to 25% of all admissions to an intensive care unit (ICU). The development of ICU-associated ARF increases the average mortality from about 15% to more than 60%. ARF is also associated with significant prolongation of hospital stay as well as substantial expense. Recent studies suggest that a significant percent of hospital-acquired ARF is caused by nephrotoxins. This brief review will discuss the frequency of occurrence, pathophysiology, risk factors, clinical course, and prevention of nephrotoxicity that may occur after exposure to aminoglycosides, nonsteroidal anti-inflammatory drugs, and radiographic contrast agents.

Parenteral aminoglycoside therapy. Selection, administration and monitoring

Aminoglycosides are potent water-soluble antibiotics, with peak concentration-dependent bactericidal activity against many pathogenic aerobic Gram-negative bacilli and Staphylococcus aureus. For systemic therapy, they must be given parenterally (intravenously or intramuscularly). In the body they remain largely extracellular, but penetration into cerebrospinal fluid and other secretions is meagre. They display trough concentration-dependent reversible nephrotoxicity and The commonly irreversible ototoxicity, which may present after treatment ceases. Gentamicin is the usual all-purpose agent of choice, tobramycin is slightly more effective against Pseudomonas aeruginosa infections, amikacin is the least susceptible to degradation by bacterial enzymes and netilmicin is probably the least toxic. Clinical and drug concentration monitoring have a role in therapy. Aminoglycosides exhibit enduring antibacterial activity (especially against Gram-negative bacilli) many hours after tissue concentrations become negligible. Appreciation of this postantibiotic effect is leading to replacement of conventional multiple daily doses by large single daily doses. The latter regimens confer at least equivalent efficacy and less risk of toxicity (particularly renal). However, single daily dosage may be unsuitable for immunocompromised patients and in those with infective endocarditis, where there is insufficient experience. Cotreatment with beta-lactams is commonly used in order to exploit the synergism between these agents, particularly in enterococcal endocarditis and severe Gram-negative sepsis. Liposomal aminoglycosides are promising parenteral formulations. After being taken up by phagocytes they reach the liver, spleen and sites of inflammation; subsequently they are gradually released. To substantiate the applicability of these hitherto experimental formulations, findings from clinical studies are keenly awaited.

Aminoglycoside dosing considerations in intensive care unit patients

OBJECTIVE

Factors affecting aminoglycoside dosing requirements in critically ill adult patients were reviewed.

DATA SOURCES

A literature search was performed from 1979 to 1992 and articles pertaining to aminoglycoside dosing were obtained.

STUDY SELECTION

Only studies appearing in peer-reviewed journals were selected. Topics selected included: bactericidal kill kinetics, once-daily dosing regimens, critical illness, toxicity, aminoglycosides, intensive care unit, and lung penetration.

CONCLUSIONS

Studies suggest that larger initial aminoglycoside doses are necessary in critically ill patients (tobramycin/gentamicin 3 mg/kg or amikacin 9 mg/kg) to achieve adequate peak serum concentrations. Current studies have not shown an increase in the incidence of aminoglycoside toxicity when using these larger initial doses. Follow-up monitoring is dependent upon the patient's physiology and risk factors for aminoglycoside-induced toxicity.

Once versus thrice daily gentamicin in patients with serious infections

Aminoglycosides are usually given in two or three divided doses. A once-daily regimen might be more effective and less toxic. We have conducted a randomised trial in consecutive patients with serious infections for whom an aminoglycoside seemed warranted. Exclusion criteria were neutropenia or severely impaired renal function. 123 patients were enrolled. For efficacy analysis only those patients were considered in whom treatment with the aminoglycoside was not stopped within 72 h (n = 67); toxicity was analysed on patients receiving aminoglycosides for more than 48 h and not using other nephrotoxic medication (n = 85). Gentamicin 4 mg/kg every day (OD) or gentamicin 1.33 mg/kg three times daily (MD) (with dose-reduction in case of renal dysfunction) were given intravenously. In almost all patients intravenous amoxycillin 1 g every 6 h was also started. Baseline characteristics were comparable in both arms. A good clinical response was observed in 32/35 (91%) of the OD and in 25/32 (78%) in the MD group (difference 13%, 95% confidence interval -6.4% to +26.9%). 2 patients in each group died with uncontrolled infection. An insufficient bacteriological response (persistent positive cultures, resistance, or superinfection) was observed in 2 patients with OD and 3 patients with MD. In patients treated for more than 48 h duration of therapy and mean doses were 7.0 days (1590 mg) and 7.4 days (1672 mg) in OD and MD respectively. Mean first serum trough/peak levels were 0.6/10.2 mg/L and 1.4/5.2 mg/L. Nephrotoxicity (a rise in serum creatinine of 45 mumol/L or more) developed in 2/40 (5%) in OD and 11/45 (24%) in MD (p = 0.016). Risk factors for nephrotoxicity were duration of therapy and baseline creatinine clearance rate. High-tone audiometry was performed when possible; no significant differences were found in hearing loss (3/12 and 3/11) or prodromal signs of ototoxicity (5/12 and 4/11). A once-daily dosing regimen of gentamicin is at least as effective as and is less nephrotoxic than more frequent dosing.

Pharmacodynamic effects of antibiotics. Studies on bacterial morphology, initial killing, postantibiotic effect and effective regrowth time

Pharmacodynamics of antibiotics deals with time course of drug activity and mechanisms of action of drugs on bacteria. In this thesis pharmacodynamic parameters have been studied after brief exposure of gram-positive bacteria to daptomycin, imipenem or vancomycin and after short exposure of gram-negative bacteria to amikacin, ampicillin, aztreonam, cefepime, cefotaxime, ceftazidime, ceftriaxone, cefuroxime, imipenem, mecillinam, or piperacillin. The studies have been focused on morphological alterations, initial killing, postantibiotic effect (PAE) and effective regrowth time (ERT) and a method, based on bioluminescence assay of intracellular ATP has been used. The basic principle behind this technique is that ATP in living cells is present in a relatively constant amount, and hence affords a measure of the number of microbial cells. The PAE describes the delayed regrowth of bacteria after brief exposure to antibiotics. The number of cells measured after this antibiotic exposure describes the initial killing and is also the start value for calculating the PAE. PAEs of 2-3 h were obtained by bioluminescence for gram-positive bacteria exposed to imipenem or vancomycin. This is in agreement with results obtained by viable count and is probably due to similar weak initial decrease in cell density when assayed by both methods. Long (greater than 3 h) concentration dependent PAEs and moderate (less than or equal to 1 log10) initial decrease in intracellular ATP were in general seen for gram-positive bacteria exposed to daptomycin and for gram-negative bacteria exposed to imipenem or amikacin when assayed by bioluminescence. These very long PAEs and rather weak initial killing have to be compared with the shorter PAEs and stronger initial killing reported by us and others using viable count. Furthermore, this study showed that there was a relatively good concordance between microscopy and bioluminescence, which are direct methods, in determining the initial killing and PAE of imipenem on Escherichia coli. The ERT, defined as the time for bacterial density to increase 1 log10 from the pre-exposure inoculum, was independent of the method used for measuring regrowth of E. coli after brief exposure to imipenem. The combination of mecillinam with ampicillin, aztreonam, ceftazidime or piperacillin and the combination of amikacin with ceftazidime, ceftriaxone or piperacillin induced longer PAEs on gram-negative bacteria than the sum of PAEs of the individual antibiotics. A strong initial killing in combination with a long PAE cause a long ERT and may allow the antibiotic concentration to stay below MIC during long periods of time without any regrowth. This may, in clinical practice, have implications for long dosing intervals.