What price success? The continuing saga of the toxic:therapeutic ratio in the use of aminoglycoside antibiotics

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.

Once-daily dosing regimen for aminoglycoside plus betalactam combination therapy of serious lower respiratory tract infections

Aminoglycosides are important antibacterial agents for treatment of serious gram-negative bacillary infections including lower respiratory tract infection. Once-daily aminoglycosides result in higher peak and lower trough plasma concentrations than conventional multiple daily dosing regimens; once-daily aminoglycoside therapy is equally effective, generally less toxic and much less expensive and therefore this regimen is more and more frequently used for treatment of suspected or confirmed gram-negative bacillary infections and of febrile episodes in neutropenic patients, in particular in combination with an appropriate betalactam antibiotic. Despite the lack of studies on this topic, once-daily aminoglycosides in combination with a betalactam agent can be used in subjects with lower respiratory tract infection, including patients with cystic fibrosis, in which tobramycin appears to be the aminoglycoside antibiotic of choice.

Once-daily administration of aminoglycosides

OBJECTIVE

To provide an overview of the efficacy and adverse effects associated with once-daily administration of aminoglycosides.

DATA SOURCES

An extensive MEDLINE search and review of journals was conducted to identify information for this review.

DATA SYNTHESIS

Aminoglycosides alone or in combination with beta-lactams are commonly used for their activity against gram-negative microorganisms. Numerous studies have been performed comparing efficacy and toxicity of once-daily administration of aminoglycosides with multiple-daily dosing. Two studies have found a significant difference in clinical efficacy between once-daily and multiple-daily dosing of aminoglycosides. Several studies have observed a lower incidence of toxicity with once-daily than multiple-daily dosing, but others have found no difference.

CONCLUSIONS

Review of the literature suggests that once-daily administration of aminoglycosides may be as safe and effective as multiple-daily dosing regimens for the treatment of certain infections caused by gram-negative bacteria.

Cost considerations in therapeutic drug monitoring of aminoglycosides

Aminoglycoside antibiotics are very important in the treatment of Gram-negative infections and as synergistic agents for the treatment of staphylococcal and streptococcal (group B streptococci and enterococci) infections. However, these agents have a narrow therapeutic index. Thus, a number of new antibiotics have been introduced in an attempt to reduce the number of patients treated with aminoglycosides. Unfortunately, these new antibiotics tend to be costly, and are often associated with development of resistance and treatment failure. Data suggest that a pharmacokinetic/pharmacodynamic relationship exists for some aspects of efficacy and toxicity of aminoglycosides. Serum drug concentrations and/or tissue accumulation are related to the development of nephrotoxicity, and individualised pharmacokinetic monitoring may decrease rates of nephrotoxicity. Peak serum drug concentrations and the ratio of peak serum drug concentration to minimum inhibitory concentration appear to correlate with clinical efficacy in the treatment of patients with bacteraemia or pneumonia. Therapeutic drug monitoring (TDM) has been used to optimise aminoglycoside therapy and reduce toxicity. Cost-effective approaches to drug selection and TDM are important considerations in the proper use of aminoglycosides.

Effect of dietary nitrogen intake on gentamicin disposition in sheep

The effect on gentamicin pharmacokinetics of a diet high (HP) (120 g/day) or low (LP) (25 g/day) in digestible proteins was studied in sheep. Gentamicin sulphate (4 mg/kg) and inulin (40 mg/kg) were administered by the intravenous route to six ewes of local Moroccan breed. The serum gentamicin concentrations were consistently higher in ewes that received a LP diet. Clearance was 0.93 +/- 0.13 ml/mm/kg in the LP group and 1.64 +/- 0.40 ml/mm/kg in the HP group. The volume of distribution at steady state (Vss) was lower in the LP group (11% of body weight) than in the HP group (21.8% of body weight). These diet-linked variations in pharmacokinetic parameters were also obtained in the disposition of inulin following the intravenous administration of a single dose. This suggests that the protein content of the diet modifies the distribution of body water and kidney function. The therapeutic, toxicological and hygienic implications of these modifications are discussed.

Detection of genital human papillomavirus (HPV) DNA by PCR and other conventional hybridisation techniques in male partners of women with abnormal Papanicolaou smears

OBJECTIVE

To study the prevalence of human papillomavirus (HPV) infection, using several different hybridisation techniques, in men whose female sexual partners had cervical HPV and/or cervical intraepithelial neoplasia (CIN).

METHODS

The male genital area was examined colposcopically and areas suspicious of HPV changes were biopsied. Each biopsy was subjected to histological examination and HPV DNA analysis by conventional DNA analysis such as Southern, reverse and dot blot as well as with polymerase chain reaction (PCR).

RESULTS

Colposcopic examination of men showed 133 to be normal whilst 82 (38%) had clinical or subclinical lesions. Of 55 colposcopically directed biopsies from the male lesions taken, detection of HPV DNA by hybridisation with conventional techniques and by PCR showed HPV DNA in 29 (53%) and 47 (85%) of biopsies respectively. Overall HPV types 6/11 were the predominant types. In 18 (33%) biopsies positive by PCR, multiple types were found.

CONCLUSION

HPV DNA was present in the majority of biopsy specimens taken, with HPV 6/11 being the predominant type. Among methods for HPV DNA detection, PCR was the most sensitive and useful technique.

Single-dose antibiotic therapy: what has the past taught us?

The proper dosage schedule of antibiotics has generally been determined empirically, due to the difficulty of clinical trials. Initially, the dosage was chosen to allow high sustained levels greater than MIC in the blood. Antibiotics (beta lactams, tetracyclins, macrolides) were given at high doses three to six times daily, whatever their kinetic properties. The data obtained by Eagle3 with beta lactams in animal models of streptococcal and treponemal infections outlined the importance of interval between doses on the in vivo efficacy. They also showed that increasing the dose of penicillin had a positive effect on the bactericidal activity only through the persistence of effective levels (greater than MIC) at the site of infection. Further illustrations were given through experimental and clinical studies with beta lactams or other compounds on different types of infections: LRTIs, UTIs, meningitis, and endocarditis. The importance of both dynamic (i.e., pattern of bactericidal effect) and kinetic (elimination half-life) parameters was thus further identified. Information on toxicity with some compounds with a narrow therapeutic index, such as aminoglycosides, indicated that increasing the dose to enhance efficacy had some limitations. This led to numerous studies on the relations between concentration and toxicity, stating that nephro- or ototoxicity were not directly related to peak level in serum. Experimental studies showed that OD administration of aminoglycosides was both more efficient and less toxic than the multiple-dose regimen of the same daily amount. Economic considerations progressively justified attempts to both reduce the dose and the work load related to multiple administrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzymuria in neonates receiving continuous intravenous infusion of gentamicin

Urinary excretion of the tubular enzymes NAG and AAP was investigated during gentamicin treatment of 105 newborn infants. The values found for NAG and AAP show a significant positive correlation. The urinary excretion of NAG was on the average 92% higher during gentamicin treatment as compared with non-treatment periods in the same newborn infant (33 infants). The same tendency applied to AAP. Newborn infants receiving continuous intravenous infusion of gentamicin were not found to be at greater risk of nephrotoxicity than those receiving intermittent gentamicin treatment, using NAG and AAP as an index of nephrotoxicity. The changes in NAg and AAP within treatment periods were studied. During gentamicin treatment an insignificant average increase in the urinary excretion of NAG occurred, whereas a significant decrease was found during non-treatment periods. A significant negative correlation was found between urinary excretion of NAG and birth weight/gestational age. The long-term effect of the higher excretion of NAG and AAP in newborn and adult patients during aminoglycoside treatment is unknown.

Use of restricted antibiotics in primary care

The objective of this study was to detect and evaluate the use of restricted antibiotics (RAs) in our ambulatory care site. We retrospectively analyzed 1084 treatments of a selected group of intramuscularly administered antibiotics that are usually considered restricted for use in hospitals. Five cephalosporins, four aminoglycosides, and one acylureidopenicillin were analyzed. The study was conducted in 47 primary health centers over six months. We reported the information on a special order form for parenteral prescriptions and evaluated the selection and the dosing interval of each antibiotic. Of the 1084 treatments, cefonicid was the antibiotic most frequently prescribed (61.3 percent), followed by tobramycin (15.3 percent), cefotaxime sodium (6.7 percent), amikacin (3.8 percent), cefuroxime (3.8 percent), mezlocillin (3.7 percent), netilmicin sulfate (3.7 percent), ceftizoxime sodium (0.8 percent), cefoxitin (0.5 percent), and streptomycin sulfate (0.4 percent). Based on our survey criteria, 59 percent of the 710 orders that indicated diagnosis had a correct or possibly correct indication; the remaining percentage was considered unnecessary therapy or poor drug choice. Of the 1050 orders that indicated a dosing interval, 75.4 percent showed an appropriate dosing interval. We assume that most of the infections treated in our ambulatory care site could be resolved with or without common antibiotics. In this study we obtained objective data of the use of ten RAs in order to determine if their use in ambulatory patients was justified. We observed that a small number of prescriptions agreed with the recommended criteria stated in this survey for use of these antibiotics in outpatient infections.

Detection of Chlamydia trachomatis by the polymerase chain reaction in swabs and urine from men with non-gonococcal urethritis

A polymerase chain reaction (PCR) was developed for Chlamydia trachomatis in which a 380 base pair DNA fragment was amplified. Amplification occurred with the DNA from the 15 serovars but not with that from other Chlamydia spp or with DNA from a variety of other organisms. Chlamydial DNA (10(-16) g) could be detected and the PCR seemed to be able to detect single organisms. Urethral swabs were obtained from 37 men with acute non-gonococcal urethritis (NGU), 18 (49%) of whom were positive for C trachomatis by MicroTrak. As a result of clinical re-examinations 65 urethral swabs were available for analysis by the PCR. In comparison with MicroTrak, PCR had a sensitivity of 95%, a specificity of 94%, a positive predictive value of 86% and a negative predictive value of 98%. The PCR was apparently less sensitive (82%) in tests on urine samples. Overall, however, values of sensitivity and specificity of the PCR compared favourably with those of MicroTrak. The PCR for C trachomatis is likely to be a valuable technique for research, but problems of DNA contamination suggest that it should not be recommended for routine diagnosis.

Once-daily aminoglycoside therapy

The once-daily administration of aminoglycosides is an attractive concept. In animal experiments and clinical trials, there is either a reduction in or no influence on the risk of toxicity. Less frequent dosing reduces the contact time between host tissue binding sites and drug. Thanks to the PAE and perhaps other as-yet-unrecognized factors, the fall in the level in serum below the MIC does not appear to impair antibacterial efficacy; in fact, the higher peak level in serum may enhance drug efficacy early in a dosage interval. In neutropenic patients, the in vivo PAE may be lost or small-colony variants with a shorter PAE may be selected unless a concomitant beta-lactam is administered. Because it will be some time before data from clinical trials in the United States are available, because the results from the international trials are encouraging, and because there is potential benefit to patients, it seems reasonable for infectious diseases consultants to cautiously initiate the educational process necessary to implement once-daily aminoglycoside therapy in their institutions.

The postantibiotic effect: a review of in vitro and in vivo data

The term postantibiotic effect (PAE) refers to a period of time after complete removal of an antibiotic during which there is no growth of the target organism. The PAE appears to be a feature of most antimicrobial agents and has been documented with a variety of common bacterial pathogens. Several factors influence the presence or duration of the PAE including the type of organism, type of antimicrobial, concentration of antimicrobial, duration of antimicrobial exposure, and antimicrobial combinations. In vitro, beta-lactam antimicrobials demonstrate a PAE against gram-positive cocci but fail to produce a PAE with gram-negative bacilli. Antimicrobials that inhibit RNA or protein synthesis produce an in vitro PAE against gram positive cocci and also produce a PAE against gram-negative bacilli. In vitro methods used to determine the PAE include colony counts, optical density, and measurement of adenosine triphosphate in bacteria. The exact mechanisms by which antimicrobials induce the PAE have not been clearly delineated. Animal studies reveal in vivo PAEs in accordance with PAEs obtained in vitro for most organism/antimicrobial combinations. The clinical relevance of the PAE is probably most important when designing dosage regimens. The presence of a long PAE allows aminoglycosides to be dosed infrequently; the lack of an in vivo PAE suggests that beta-lactam antimicrobials require frequent or continuous dosing. Important questions remain to be answered concerning the PAE.

Simplified procedures for applying the polymerase chain reaction to routinely fixed paraffin wax sections

The polymerase chain reaction was applied to the analysis of DNA contained in archival paraffin wax embedded material. DNA suitable for the reaction was obtained from these tissues by simple extraction methods, without previous dewaxing of tissue sections. When compared with unfixed material, the reaction efficiency was compromised, so that an increased number of amplification cycles were required to produce equivalent amounts of amplified product. This in turn led to an increase in amplification artefacts, which can be minimised by a simple modification of the standard reaction. Amplification of relatively large DNA fragments was not always successful, and it seems prudent to bear this in mind when designing oligonucleotide primers which are to be used for the amplification of archival material. The efficiency of the procedure can be improved by dividing the amplification cycles into two parts: this reduces the amount of reagent needed, is relatively simple and inexpensive, and can be performed in one working day.

Empiric treatment of infection during granulocytopenia

Results from clinical trials conducted over the past 15 years suggest the following: a) Early empiric therapy with broad-spectrum antibiotics directed against Gram-negative bacillary bacteremia is necessary in febrile granulocytopenic cancer patients; b) The level and dynamics of the granulocyte count are extremely important in determining the outcome of bacteremia; c) Most empiric antimicrobial regimens will require therapeutic modifications; these alterations are necessary and contribute to a high overall success rate; d) Only microbiologically documented infections and especially bacteremias are useful for comparison of initial response to antimicrobial regimens; e) The response rate of Gram-negative bacillary bacteremia is clearly influenced by the susceptibility of the causative pathogen to the beta-lactam component of the empiric regimen; emergence of resistance to some beta-lactam antibiotics is quite common and necessitates successive modifications of empiric regimens with time; f) The combination of an anti-pseudomonal beta-lactam with an aminoglycoside is recommended as the standard for empiric therapy in febrile granulocytopenic cancer patients, especially in those with severe and persistent granulocytopenia who are suspected of having Gram-negative bacillary bacteremia; less neutropenic and/or asymptomatic patients may do well with monotherapy; g) Gram-positive pathogens have become a common cause of bacteremia in granulocytopenic cancer patients; the response rate to empiric regimens may be suboptimal but the associated mortality is low; h) Patients with severe granulocytopenia and protracted fever whose blood cultures remain negative are at high risk for contracting fungal infections; in these patients, empiric antifungal agents are probably indicated.

Prospective randomized study of once-daily versus thrice-daily netilmicin regimens in patients with intraabdominal infections

One hundred and ninety-seven patients with intraabdominal infections were enrolled in a prospective randomized multicenter study of netilmicin administered once daily (n = 98) versus thrice daily (n = 99) in combination with tinidazole administered once daily. Randomization was achieved for the infection site, clinical severity score, daily and total netilmicin dose, and duration of treatment. The mean maximum peak and trough levels of netilmicin in serum were 21.1 and 1.3 mg/l respectively for once daily treated patients, and 10.0 and 2.3 mg/l for thrice daily treated patients (p less than 0.05 for both parameters). The clinical response did not differ between patients treated once daily and those treated thrice daily. Overall rates for clinical cure, improvement and failure of therapy were 77%, 17% and 6% respectively. No significant differences were found between once daily and thrice daily regimens in the occurrence of auditory, vestibular and renal toxicity, overall rates being 5%, 1% and 10% respectively. Impairment of renal function was significantly related to higher maximum netilmicin serum trough levels during therapy, a higher clinical severity score and advanced age. It is concluded that netilmicin given once daily is as effective and safe as the multiple dose regimen. However, monitoring of aminoglycoside serum through levels is still advisable, especially in the old and severely ill patient.

Treatment of sepsis in an intensive care unit

The management of severe bacterial sepsis is an integral part of intensive care medicine. Early and appropriate treatment with antimicrobials positively affects mortality and significantly reduces the time spent in both intensive care and the hospital. Drug choice is usually made on a "best guess" basis and instituted prior to receipt of appropriate blood, sputum, urine or drainage culture results. Bactericidal drugs should be given in combination, delivered by intravenous bolus and directed towards broad cover of all likely pathogens. Aminoglycoside/ureidopenicillin combinations are synergistic and widely used--often combined with metronidazole. Aminoglycoside toxicity can be reduced by giving the drug once daily (OD) rather than by traditional multiple daily dosing (MDD) and by measuring peak and trough serum levels. Efficacy is increased by attention to the peak serum level/MIC ratio which determines the response to treatment. Several newer agents have been more recently introduced. These drugs include ceftazidime, imipenem/cilastatin, the quinolones and clavulanic acid/semisynthetic penicillin combinations. Other newer drugs currently under evaluation include aztreonam, teicoplanin, the penems and carbapenems.

Susceptibility of enterococci and epidemiology of enterococcal infection in the 1980s

Enterococcisensu strictoform part of the normal gut flora (1) and may be found in the mouth, vagina and anterior urethra (2). They are opportunist pathogens which can cause serious infection including endocarditis. Nosocomial enterococcal infection appears to be increasing both in the UK (Public Health Laboratory Service [PHLS] Communicable Disease Surveillance Centre [CDSC], unpublished) and the USA (3) and to correspond to usage of broad spectrum β-lactam antimicrobial agents (4−7) and invasive surgical devices (8, 9). At the same time, the incidence of enterococci resistant or tolerant to previously commonly employed antimicrobial agents or their synergistic combinations is increasing and is compromising therapy of serious enterococcal infection. Strains of enterococci with high-level resistance to streptomycin and kanamycin (minimal inhibitory concentrations [MICs] > 2000 mg/L) were first reported in 1970 (10, 11) and rapidly became widespread (8, 12−14).

Alternative dosing strategy for aminoglycosides: impact on efficacy, nephrotoxicity, and ototoxicity

Accumulating evidence suggests that the therapeutic margin of aminoglycoside therapy may be improved by manipulation of dosing strategy. Recent understanding of concentration-dependent bactericidal activity and postantibiotic effect argues that the aminoglycosides may be administered in larger doses and at longer dosing intervals than currently recommended without compromising efficacy. Preliminary clinical experience suggests that once-daily regimens are as efficacious as conventional intermittent injections in the treatment of gram-negative infectious including urinary tract infections, cystic fibrosis, and bacteremia in nonneutropenic patients. The transient, high peak serum concentrations achieved in once-daily dosing have not been associated with excessive nephrotoxicity or ototoxicity thus far. Decreased accumulation in renal cortex as a result of saturable renal uptake after the single daily dose may even reduce the incidence or severity of renal damage. Further studies on more patients are required to substantiate these preliminary findings.