Application of Bayes theorem to aminoglycoside-associated nephrotoxicity: comparison of extended-interval dosing, individualized pharmacokinetic monitoring, and multiple-daily dosing

Impact of Therapeutic Drug Monitoring on Once-Daily Regimen of Amikacin in Patients With Urinary Tract Infection: A Prospective Observational Study

BACKGROUND

Amikacin is a semisynthetic antibiotic used in the treatment of gram-negative bacterial infections and has a narrow therapeutic index. Although therapeutic drug monitoring is recommended for amikacin, it is not routinely performed because of the use of a less toxic once-daily regimen. Only few studies have evaluated the role of therapeutic drug monitoring in patients treated with amikacin. The objective of our study was to find an association between the pharmacokinetic parameters of amikacin and the time required for a clinical cure, creatinine clearance, and frequency of ototoxicity in patients with urinary tract infection treated for 7 or more days.

METHODS

A prospective study was conducted on patients with urinary tract infections who were administered amikacin for 7 or more days. Blood samples were obtained from the patients to measure the maximum drug concentration (Cmax) and trough concentration (Ctrough). Minimum inhibitory concentration (MIC) values were determined for patients with positive urine cultures. Serum creatinine levels were estimated every 3 days. The auditory assessment was performed using pure tone audiometry at baseline and weekly until the patients were discharged. Levels of amikacin were analyzed using a validated liquid chromatography-tandem mass spectrometry method.

RESULTS

Of 125 patients analyzed, the median time required for a clinical cure was less in the group of patients who achieved a Cmax/MIC ratio ≥8 than it was in those who did not achieve this level [7 versus 8 days (P = 0.02)]. The Ctrough of amikacin was associated with the change in serum creatinine level (P = 0.01) and the incidence of nephrotoxicity (P = 0.004).

CONCLUSIONS

In patients receiving short-term amikacin therapy, Cmax/MIC value can be used to predict the time required for a clinical cure. Ctrough can be used to predict the occurrence of nephrotoxicity in patients receiving amikacin therapy.

Interest of therapeutic drug monitoring of aminoglycosides administered by a monodose regimen

BACKGROUND

Although the once-daily regimen of aminoglycosides (AG) is considered as predominantly used by many centers, the level of evidence of Therapeutic Drug Monitoring (TDM) of AG in cases of once-daily has not been clearly defined. The objective of this study is to evaluate the impact of TDM in achievement or maintaining target serum concentrations in patients receiving once-daily administration of AG.

METHODS

We performed a retrospective analysis of data from patients having received a once daily amikacin or gentamicin and underwent routine TDM. A longitudinal follow up was performed. Data were analyzed according to the adhesion or not to recommendations. A logistic regression was performed in order to evaluate the effect of covariates (age, gender, weight, creatinine clearance [CLcr], TDM-based dose adjustment, weighted dose of AG) on the achievement of non-toxic Cmin.

RESULTS

A total 437 blood samples issued from 324 patients were analyzed. The cut-off value of Clcr associated with a risk of toxic Cmin was≤41.66mL/min (OR: 11.29; 95%CI: 7.21-17.61; P<0.0001). Eighty-eight patients (27.1%) have at least two sampling points. The univariate analysis showed that the age, weight, CLcr and TDM-based dose adjustment were found to be significant factors in the achievement of non-toxic Cmin. In multivariate analysis, only TDM-based dose adjustment remains a significant factor in the achievement of non-toxic Cmin (OR: 6.66; 95%CI: 2.26-19.63; P=0.0006).

CONCLUSION

Our study demonstrates the usefulness of TDM-based dosing adjustment of AG antibiotics in achieving nontoxic trough concentrations, particularly in critically ill patients, as they are prone to a renal impairment.

Once-daily gentamicin dosing in pediatric patients without cystic fibrosis

STUDY OBJECTIVE

To estimate an appropriate once-daily gentamicin dose and dosing interval for non-critical care pediatric patients older than 3 months of age without cystic fibrosis.

DESIGN

Pharmacokinetic analysis of data from a retrospective medical record review.

SETTING

Large academic children's hospital.

PATIENTS

One hundred fourteen non-critical care pediatric patients older than 3 months of age without cystic fibrosis who received multiple-daily dosing regimens of gentamicin between September 2007 and April 2008.

MEASUREMENTS AND MAIN RESULTS

Patient-specific pharmacokinetic parameters were calculated using drug concentrations obtained at steady state. Once-daily doses were extrapolated for each patient to achieve goal peak and trough concentrations. Using the average of these doses and the patient-specific pharmacokinetic parameters, theoretical once-daily peak and trough concentrations were calculated for each patient. Patient characteristics were analyzed to determine differences between patients who did and those who did not achieve adequate peak concentrations. Mean +/- SD pharmacokinetic parameters were as follows: elimination rate constant 0.32 +/- 0.06 hour(-1), half-life 2.28 +/- 0.54 hours, and volume of distribution 0.24 +/- 0.08 L/kg. The only patient demographic characteristic found to have a significant effect on the extrapolated peak concentration was age. The following age-specific once-daily doses were calculated: 3 months to less than 2 years, 9.5 mg/kg; 2 years to less than 8 years, 8.5 mg/kg; and 8-18 years, 7 mg/kg.

CONCLUSION

Age was the primary factor in determining the once-daily dose of gentamicin in our pediatric population. Further prospective research is necessary to determine the safety and efficacy of these age-based, once-daily doses for gentamicin.

Lost in publication: Half of all renal practice evidence is published in non-renal journals

Physicians often scan a select number of journals to keep up to date with practice evidence for patients with kidney conditions. This raises the question of where relevant studies are published. We performed a bibliometric analysis using 195 renal systematic reviews. Each review used a comprehensive method to identify all primary studies for a focused clinical question relevant to patient care. We compiled all the primary studies included in these reviews, and considered where each study was published. Of the 2779 studies, 1351 (49%) were published in the top 20 journals. Predictably, this list included Transplantation Proceedings (5.9% of studies), Kidney International (5.3%), American Journal of Kidney Diseases (4.7%), Nephrology Dialysis Transplantation (4.3%), Transplantation (4.2%), and Journal of the American Society of Nephrology (2.4%). Ten non-renal journals were also on this list, including New England Journal of Medicine (2.4%), Lancet (2.3%), and Diabetes Care (2.2%). The remaining 1428 (51%) studies were published across other 446 journals. When the disciplines of all journals were considered, 59 were classified as renal or transplant journals (42% of articles). Other specialties included general and internal medicine (16%), endocrinology (diabetes) and metabolism (6.5%), surgery (6.2%), cardiovascular diseases (6.1%), pediatrics (4.3%), and radiology (3.3%). About half of all renal practice evidence is published in non-renal journals. Browsing the top journals is important. However, relevant studies are also scattered across a large range of journals that may not be routinely scanned by busy physicians, and keeping up with this literature requires other continuing education strategies.

Drug-induced acute kidney injury

PURPOSE OF REVIEW

The purpose of this review is to describe the most prevalent mechanisms of drug-induced acute kidney injury, to define the risk factors for nephrotoxicity, and to analyze the available evidence for preventive measures.

RECENT FINDINGS

Drug toxicity remains an important cause of acute kidney injury that, in many circumstances, can be prevented or at least minimized by vigilance and early intervention. Recent studies have resulted in increased insight into the subcellular mechanisms of drug nephrotoxicity. Further improvement is to be expected from the identification of early markers of nephrotoxicity and an increasing involvement of a clinical pharmacist.

SUMMARY

The main mechanisms of nephrotoxicity are vasoconstriction, altered intraglomerular hemodynamics, tubular cell toxicity, interstitial nephritis, crystal deposition, thrombotic microangiopathy, and osmotic nephrosis. Before prescribing a potentially nephrotoxic drug, the risk-to-benefit ratio and the availability of alternative drugs should be considered. Modifiable risk factors should be corrected. The correct drug dosage should be prescribed. Patients should be pre-hydrated and the glomerular filtration rate should be frequently monitored during the administration of a potentially nephrotoxic drug. Studies are needed to further elucidate the mechanisms of nephrotoxicity to design more-rational prevention and treatment strategies. Computer-based prescriber-order entry and an appropriately trained intensive care unit pharmacist are particularly helpful to minimize medication errors and adverse drug events.