Vancomycin serum concentration monitoring: a continued debate

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

Does oral vancomycin use necessitate therapeutic drug monitoring?

PURPOSE

Oral vancomycin use has generally increased as a consequence of the need to treat and/or prevent Clostridium (Clostridiodes) difficile-associated disease (CDAD). This review examines the cumulative scientific evidence that guides therapeutic monitoring of oral vancomycin therapy.

METHODS

The existing publications were reviewed from the time of the drug's inception to July 2019. This review utilized access as available in PubMed, EMBASE, CINAHL Plus, and the Cochrane Library.

RESULTS

Case reports and small patient series have documented anecdotal-associated elevations in serum levels. Correlation of absorbed vancomycin with subsequent toxicity is difficult to determine, but serum levels approaching those obtained after parenteral administration have raised concern. Prolonged usage and total dosing over 500 mg/day among adult age ranges have been associated with accumulation. In addition, risk factors for vancomycin accumulation systemically after oral dosing include renal compromise, combined oral and other enteral therapy, severe CDAD, other intercurrent bowel inflammation, polypharmacy, and increased patient complexity/morbidity.

CONCLUSION

Until systemic toxicity from oral vancomycin absorption is better understood, individual considerations should be made for therapeutic serum monitoring during oral vancomycin treatment. Therapeutic drug monitoring is suggested for several high-risk situations in which high blood levels may be anticipated.

Benefits of therapeutic drug monitoring of vancomycin: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

The necessity of therapeutic drug monitoring (TDM) for vancomycin is controversial. The objective of the current review was to evaluate the available evidence for the necessity of TDM in patients given vancomycin to treat Gram-positive infections.

METHODS

Medline, Embase, Web of Sciences, the Cochrane Library and two Chinese literature databases (CNKI, CBM) were searched. Randomized controlled studies and observational studies that compared the clinical outcomes of TDM groups vs. non-TDM groups were included. Two reviewers independently extracted the data. The primary outcome was clinical efficacy of therapy. Secondary outcomes included vancomycin associated nephrotoxicity, duration of vancomycin therapy, length of hospital stay, and mortality. Meta-analysis was performed using the Mantel-Haenszel fixed effect method (FEM). Odds ratios (ORs) or weighted mean differences (WMD) with 95% confidence intervals (95%CIs) were calculated for categorical and continuous outcomes, respectively.

RESULTS

One randomized controlled trial (RCT) and five cohort studies were included in the meta-analysis. Compared with non-TDM groups, TDM groups had significantly higher rates of clinical efficacy (OR = 2.62, 95%CI 1.34-5.11 P = 0.005) and decreased rates of nephrotoxicity (OR = 0.25, 95%CI 0.13-0.48 P<0.0001). Subgroup analyses showed that TDM group had significantly higher rates of clinical efficacy in both cohort studies subgroup (OR = 3.04, 95%CI 1.34-6.90) and in Asian population subgroup (OR = 3.04, 95%CI 1.34-6.90). TDM group had significantly decreased rates of nephrotoxicity in all subgroup. There was no significant difference in duration of vancomycin therapy (WMD = -0.40, 95%CI -2.83-2.02 P = 0.74) or length of stay (WMD = -1.01, 95%CI -7.51-5.49 P = 0.76) between TDM and non-TDM groups. Subgroup analyses showed there were no differences in duration of vancomycin therapy. Only one study reported mortality rates.

CONCLUSIONS

Studies to date show that TDM significantly increases the rate of clinical efficacy and decreases the rate of nephrotoxicity in patients treated with vancomycin.

Population pharmacokinetic analysis of vancomycin in neonates. A new proposal of initial dosage guideline

AIM

To determine the population pharmacokinetic parameters of vancomycin in neonatal patients with a wide range of gestational age and birth weight, and subsequently to design an initial dosing schedule for vancomycin in neonates.

METHODS

Using nonlinear mixed-effects modelling (NONMEM VI), the pharmacokinetics of vancomycin were investigated in 70 neonates with postmenstrual age and body weight ranging 25.1-48.1 weeks and 0.7-3.7kg, respectively. A one-compartment linear disposition model with zero order input and first-order elimination was used to describe the data. Nine demographic characteristics and 21 co-administered drugs were evaluated as covariates of clearance (CL) and distribution volume (V(d) ) of vancomycin.

RESULTS

Weight-normalized clearance of vancomycin was influenced by postmenstrual age (PMA) and co-administration of amoxicillin-clavulanic acid. Weight-normalized volume of distribution was influenced by co-administration of spironolactone. CL and V(d) of the typical individual in this study population (PMA = 34.6 weeks, weight = 1.7kg) were estimated to be 0.066lh(-1) kg(-1) (95% CI 0.059, 0.073lh(-1) kg(-1) ) and 0.572lkg(-1) (95% CI 0.505, 0.639lkg(-1) ), respectively. This model was used to predict a priori serum vancomycin concentrations in a validation group (n= 41), which were compared with observed concentrations to determine the predictive performance of the model. The 95% confidence interval of mean prediction error included zero for both peak and trough vancomycin concentrations.

CONCLUSIONS

Postmenstrual age, co-administration of amoxicillin-clavulanic acid and spironolactone have a significant effect on the weight-normalized CL and V(d) . An initial dosage guideline for vancomycin is proposed for preterm and full-term neonates, whereas the population pharmacokinetic model can be used for dosage individualization of vancomycin.

Observations on vancomycin use in U.S. hospitals

PURPOSE

Current knowledge and policies regarding vancomycin use and the clinical performance of vancomycin in U.S. hospitals were assessed.

METHODS

A questionnaire was sent to interested hospital pharmacists. An observational study of hospitalized adults who received at least 72 hours of i.v. vancomycin for a culture-confirmed gram-positive infection followed. Hospital antibiograms were obtained for gram-positive susceptibility data.

RESULTS

A total of 59 respondents completed the survey. Survey results revealed that vancomycin is rarely restricted. Investigators from 24 hospitals, 16 (67%) of which were teaching facilities, collected retrospective data from the records of 200 patients. Infection sites included blood, lower respiratory tract, and skin and soft tissue. Staphylococcus aureus was isolated from 52% of positive cultures; 75% of these were methicillin-resistant S. aureus (MRSA). Serum vancomycin concentrations were monitored in 95% of patients; results from 22 hospitals were evaluable. Trough serum vancomycin concentrations were higher in teaching versus nonteaching hospitals (p < 0.001). Peak serum vancomycin concentrations were also higher in teaching versus nonteaching hospitals (p < 0.05). Clinical responses from 22 hospitals were evaluable; the mean success rate of 82% did not significantly differ between teaching and nonteaching hospitals. Vancomycin- associated adverse events occurred in 13 patients (6.5%) and were reported more frequently for patients in teaching versus nonteaching hospitals (p = 0.02).

CONCLUSION

Observational data suggest that vancomycin remains an effective antibiotic with infrequent discontinuations due to adverse events, and trough serum vancomycin concentrations are monitored routinely. Antibiogram data revealed that the prevalence of MRSA continues to increase.

Clinical efficacy of therapeutic drug monitoring in patients receiving vancomycin

Efficacy of therapeutic drug monitoring (TDM) of vancomycin (VCM) was retrospectively investigated in 184 patients with methicillin-resistant Staphylococcus aureus (MRSA) infection. The incidence of nephrotoxicity was compared between the patients who received TDM practice (TDM group, n=73) and did not (non-TDM group, n=111). Creatinine clearance (CLcr) values decreased significantly after the VCM therapy in the non-TDM group (p<0.05). The patients with MRSA bacteremia or pneumonia were classified into two groups according to peak concentrations of VCM: above 25 microg/ml (Group A: n=29) and below (Group B: n=24). Mean duration of VCM therapy (14.1 d) in Group A was significantly shorter than that (27.0 d) in Group B. Mean cumulative total VCM doses (13.3 g) in Group A was significantly less than that (25.0 g) in Group B. These results indicate that monitoring peak concentration is essential to obtain better clinical effects for VCM therapy, and that the peak concentration above 25 microg/ml is more effective.

Mississippi mud no more: cost-effectiveness of pharmacokinetic dosage adjustment of vancomycin to prevent nephrotoxicity

OBJECTIVE

To determine the cost-effectiveness of pharmacokinetic dosage adjustment of vancomycin to prevent nephrotoxicity. An analysis was performed for subpopulations of patients receiving nephrotoxic agents (aminoglycosides, amphotericin, and acyclovir), those in the intensive care unit, and those on the oncology service.

METHODS

Decision analysis was used to model the cost-effectiveness of pharmacokinetic dosage adjustment of vancomycin. The reference case was determined, in part, by a retrospective review of 200 patients randomly selected from our clinical pharmacology consultation service. Patients were aged 18 years or older and had received intravenous vancomycin for at least 48 hours, with at least two--one peak and one trough--vancomycin serum concentrations obtained during therapy. Results of published clinical trials were used to determine the probability of vancomycin-induced nephrotoxicity.

RESULTS

The mean cost of treating nephrotoxicity was 11,233 dollars at our institution. The mean cost for all patients was 25,166 dollars (sensitivity analysis 15,000-27,500 dollars)/nephrotoxic episode prevented. The subgroup analysis revealed a cost of 8,363 dollars (sensitivity analysis 4,368-10,500 dollars)/nephrotoxic episode prevented in intensive care patients, 5,000 dollars (sensitivity analysis 1,687-13,250 dollars ) in oncology patients, and a dominant strategy showing a cost savings of 5,564 dollars (sensitivity analysis 2,724-12,428 dollars) in those receiving concomitant nephrotoxins.

CONCLUSION

Although pharmacokinetic monitoring and dosage adjustment are effective methods for reducing the toxicity of many drugs, controversy exists regarding the necessity of such monitoring with vancomycin. Evaluation by decision analysis over a range of assumptions, varying probabilities, and costs reveals that pharmacokinetic monitoring and vancomycin dosage adjustment to prevent nephrotoxicity are not cost-effective for all patients. However, such dosage adjustment demonstrates cost-effectiveness for patients receiving concomitant nephrotoxins, intensive care patients, and probably oncology patients.

Impact of Monitoring Vancomycin Peak and Trough Concentrations versus Trough Concentrations Alone on Dose Adjustments: An Outcomes Analysis

Objective:

To determine whether monitoring both steady-state peak and trough serum vancomycin concentrations or steady-state trough serum vancomycin concentrations alone resulted in differences between two groups of patients in terms of dose adjustment, clinical outcome, and toxicity.

Design:

The study was a retrospective chart review of patients treated with vancomycin during two time periods. Group 1 represented patients hospitalized between July 1, 1996, and January 31, 1997. These patients routinely had vancomycin peak and trough concentrations measured. Group 2 represented patients hospitalized from July 1, 1997, to January 31, 1998, who were monitored with trough vancomycin concentrations only.

Setting:

A university teaching hospital.

Patients:

Adults at least 18 years of age who received a constant dose of intravenous vancomycin for at least three consecutive days were eligible for inclusion in the study. Patients were selected from lists generated by the Microbiology Department. The lists contained vancomycin serum concentrations measured during those time frames.

Main Outcome Measures:

The main outcome measure was to assess whether dose adjustments by prescribers were influenced by both vancomycin peak and trough concentrations or by the trough concentration alone.

Results:

Forty-nine and 37 patients met the criteria for inclusion into group 1 and group 2, respectively. The mean duration of therapy in group 1 (15 ± 10 d) was not statistically different from that of group 2 (14 ± 12 d). Patients in both groups received a mean daily vancomycin dose of approximately 1,500 mg. In analyzing treatment decisions, trough concentration was the only significant factor influencing a change in total daily dose of vancomycin (p = 0.038). Furthermore, although the method of vancomycin serum concentration monitoring varied between the two groups, the mean clinical outcome parameters were comparable.

Conclusions:

Prescribers tended to adjust vancomycin regimens based only on trough serum concentrations; monitoring peak serum vancomycin concentrations did not enhance patient care. Mean outcome parameters in the two groups were comparable.

National guidelines for the judicious use of glycopeptides in Belgium

OBJECTIVE

The 'HICPAC guidelines', published in the USA in 1995 stressed the crucial role of restrictive usage of glycopeptides in the strategy to limit the emergence and spread of resistant enterococci. Because controversy still remains in Belgium on the necessity and feasability of restricting glycopeptide usage, the infectious diseases advisory board (IDAB) developed a consensus statement on the judicious use of glycopeptides in Belgium.

METHODS

The literature on the indications for glycopeptide treatment was reviewed, categorized and discussed by a working party of the IDAB.Consequently, the IDAB reached consensus on the warranted indications for glycopeptide use in Belgium.

RESULTS

The opinion of the IDAB-members is reported in a consensus statement specifying the indications for treatment and for prophylaxis with glycopeptide antimicrobials, as well as the situations where glycopeptides should not be used, taking into account the specific epidemiology of bacterial resistance, the availability of antibiotics and the common prescribing practices in Belgium.

CONCLUSIONS

The IDAB concludes that restrictive usage of glycopeptides must also be a priority in Belgium. Guidelines on the judicious use of these antibiotics adapted to the national situations must contribute to this objective.

Accuracy of measured vancomycin serum concentrations in patients with end-stage renal disease

OBJECTIVE

To review information related to the accuracy of vancomycin serum drug concentrations in patients with end-stage renal disease, focusing on available assays and mechanisms of cross-reactivity.

DATA SOURCES

Primary and review articles identified from a MEDLINE search (January 1980-June 1999) and through secondary sources.

STUDY SELECTION AND DATA EXTRACTION

All articles identified were evaluated, and all relevant information was included in this review.

DATA SYNTHESIS

Falsely elevated vancomycin serum concentrations may occur in patients with renal dysfunction. The underlying mechanism is due to the formation and accumulation of a pseudo-metabolite, the vancomycin crystalline degradation product (CDP). Vancomycin is converted to CDP when exposed to heat, including normal body temperature. Because the molecular structures of CDP and vancomycin are similar, both molecules are detected by polyclonal immunoassay systems used in clinical laboratories. This cross-reactivity leads to falsely elevated serum vancomycin concentrations in excess of 50-70%. Such large assay inaccuracies may result in improper dosage adjustments and therapeutic failures. A monoclonal immunoassay system has been developed that does not significantly cross-react with CDP.

CONCLUSIONS

To appropriately interpret laboratory results, it is essential for clinicians to be aware of the vancomycin-CDP cross-reactivity problem and to be familiar with the specific assay used to measure vancomycin concentrations in patients with renal dysfunction.

Laboratory guidelines for monitoring of antimicrobial drugs

Few antimicrobial drugs meet the requirements for therapeutic drug monitoring. Those that are monitored include the aminoglycosides (gentamicin, tobramycin, and amikacin), chloramphenicol, and in some cases, vancomycin. For these drugs, there is evidence of a relationship between serum concentration, efficacy, and/or the incidence of adverse or toxic events. Monitoring begins with the appropriate timing of collection and continues through the analytical process to the integration of all data used to guide the clinician’s next decision.

New modified fluorescence polarization immunoassay does not falsely elevate vancomycin concentrations in patients with end-stage renal disease

Recent literature has urged caution in the interpretation of vancomycin serum concentrations in patients with end-stage renal disease (ESRD), because falsely elevated levels in excess of 70% have been reported with the most commonly used fluorescence polarization immunoassay (FPIA). The purpose of this study was to evaluate the performance of a recently modified FPIA assay for use in patients with ESRD, in comparison to high-performance liquid chromatography (HPLC) and an enzyme-mediated immunoassay technique (EMIT). Serum vancomycin samples were prospectively collected from adults with ESRD undergoing chronic hemodialysis. Each sample was stored at -70 degrees C until analyzed in duplicate by FPIA, EMIT, and HPLC. In an in vitro experiment, blank serum samples with 15 microg/ml vancomycin were spiked with increasing amounts of CDP and analyzed in duplicate with the modified FPIA assay. When compared to HPLC, no statistically significant difference was found in patients with ESRD with the use of the modified FPIA assay (mean concentrations, HPLC 14.92 microg/ml, FPIA 15.96 microg/ml), with FPIA exhibiting a positive bias of 0.64 microg/ml and a precision of +/-3.49 microg/ml (n = 18, p = 0.44). The mean EMIT concentration was 18.34 microg/ml, with a positive bias of 3.43 microg/ml and a precision of +/-5.17 microg/ml (p < 0.01). The addition of increasing amounts of CDP to vancomycin in vitro resulted in concentrations similar to those expected in the absence of significant cross-reactivity with the modified FPIA assay. The modified FPIA assay is a satisfactory tool for monitoring vancomycin serum concentrations in patients with ESRD undergoing hemodialysis. Results obtained with EMIT were not as precise as with FPIA.

Do vancomycin serum levels predict failures of vancomycin therapy or nephrotoxicity in cancer patients?

The purpose of this study was to determine if patients with high vancomycin (VAN) serum levels experience more toxicity than underdosed patients with lower (VAN) levels, and whether low VAN serum levels cause therapeutic failures in patients with gram-positive bacteremia. In 198 cancer patients trough and peak serum levels of VAN were measured. Acute toxicity (Red Man syndrome) appeared in 3 patients (1.5%). Patients previously or currently treated with other nephrotoxic compounds (134 patients) presented the same incidence of nephrotoxicity as those receiving VAN for the first time in monotherapy (64 patients). VAN did not increase the toxicity when patients were dosed simultaneously or previously with aminoglycosides or amphotericin B. Our second observation, when studying serum levels in our 198 patients was that high VAN trough serum levels (trough > 15 microg/mL) were associated with significantly more nephrotoxicity (33.3% vs. 11.1%, P < 0.03) than low levels in the subgroups of either pretreated patients or unpretreated with other nephrotoxic drugs. None of 198 patients who had trough levels below 15 microg/mL had peak levels exceeding 40 microg/mL. This suggests that only serum monitoring of trough levels may predict nephrotoxicity. A case control study was conducted to compare a group of 22 VAN failures with 22 successfully treated patients matched in underlying disease and neutropenia who were treated in the same period, under the same antibiotic policy, at the same cancer center, for gram-positive bacteremia. Persisting, enterococcal, or mixed enterococcal plus staphylococcal bacteremia were the only statistically significant risk factors which predicted therapy failure in cancer patients. Neither peak nor trough VAN serum levels predicted failure or cure of gram-positive bacteremia in cancer patients.

Comparison of conventional dosing versus continuous-infusion vancomycin therapy for patients with suspected or documented gram-positive infections

Ten patients were treated with conventional dosing (CD) and continuous-infusion (CI) vancomycin therapy in this prospective, randomized, crossover study. Patients were randomized to receive either CD or CI therapy for 2 consecutive days and then crossed over to receive the opposite regimen for 2 days. CD therapy consisted of 1 g of vancomycin every 12 h. CI therapy consisted of a 500-mg loading dose followed by 2 g infused over 24 h. Ten serum samples were obtained on the second day of each therapy for pharmacokinetic and pharmacodynamic analyses. Two clinical isolates of Staphylococcus aureus, one methicillin sensitive (MSSA 1199) and one methicillin resistant (MRSA 494), were chosen for pharmacodynamic evaluation of both regimens. The patient demographics (means +/- standard deviations [SD]) were as follows: sex, six males, four females; age, 36 +/- 11 years; and serum creatinine, 0.72 +/- 0.18 mg/dl. Mean pharmacokinetic parameters +/- SD for CD therapy were as follows: elimination rate constant, 0.16 +/- 0.07 h-1; half-life, 5.6 +/- 3.5 h; volume of distribution, 33.7 +/- 25 liters, 0.5 +/- 0.2 liters/kg; maximum concentration in serum, 53.4 +/- 19.3 micrograms/ml; and minimum concentration, 8.4 +/- 5.9 micrograms/ml. The steady-state concentration for CI was 20.2 +/- 11.1 micrograms/ml. Overall, both regimens resulted in the MIC being exceeded 100% of the time. The mean CD trough serum bactericidal titer (SBT) was 1:8, and the average CI SBTs were 1:16 for both isolates. Even though there was no statistically significant difference between CD trough and CI SBTs, the CI SBTs remained > 1:8 for 100% of the time versus 60% of the time for CD therapy. During CI therapy, 20 and 40% of the patients maintained SBTs of > 1:32 throughout the dosing interval for MSSA 1199 and MRSA 494, respectively. During CD therapy, however, only 10% of patients maintained SBTs of > 1:32 during the entire dosing interval for both isolates. The mean areas under the bactericidal titer-time curve (AUBC24s) +/- SD for MSSA 1199 were 528 +/- 263 for CD therapy and 547 +/- 390 for CI therapy. The mean AUBC24s +/- SD against MRSA 494 were 531 +/- 247 for CD and 548 +/- 293 for CI therapy. Similar to the AUBC24, the mean area under the concentration-time curve for a 24-h dosing interval divided by the MIC (AUC/MIC24) ratios +/- SD were 550.0 +/- 265.7 for CD and 552.6 +/- 373.4 for CI therapy, respectively. No statistically significant differences were found between any of the pharmacodynamic parameters for CD and CI therapy. In addition, no adverse effects with either CD or CI therapy were observed during the study. We conclude that CI and CD vancomycin therapy demonstrated equivalent pharmacodynamic activities. Although CI therapy was more likely to result in SBTs that remained above 1:8 for the entire regimen, the clinical impact of this result is unknown. Serum drug concentration variability was observed with both treatment regimens but to a lesser extent with CI administration. CI administration of vancomycin should be further evaluated to determine the clinical utility of this method of administration.

Falsely elevated serum vancomycin concentrations in hemodialysis patients

Fluorescence polarization immunoassay (FPIA) is the most widely used clinical vancomycin assay in the United States. Questions exist regarding the accuracy of this polyclonal assay in patients with end-stage renal disease (ESRD). While several studies have reported discrepancies in vancomycin serum concentrations determined by FPIA compared with other vancomycin assays, no study has investigated the accuracy of vancomycin serum concentrations determined by FPIA in patients with ESRD undergoing maintenance hemodialysis. Therefore, we compared the assay performance of FPIA and enzyme multiplied immunoassay technique (EMIT) in six subjects with ESRD receiving high-efficiency hemodialysis. Subjects underwent 6 consecutive weeks of hemodialysis treatment with a cellulose acetate dialyzer (CA210) and received 1 g vancomycin intravenously once weekly during the last hour of dialysis. Vancomycin serum concentrations were determined by both EMIT and FPIA methodologies. From the serum concentration results of both assays, vancomycin dosing recommendations were calculated to achieve a desired steady-state peak concentration of 35 mg/L and trough concentration of 10 mg/L. Overall, vancomycin serum concentrations reported by FPIA were significantly higher than those reported by EMIT. The mean difference between assays in the peak serum concentrations at weeks 1, 4, and 6 was 7.5, 11.5, and 11.2 mg/L, respectively. The mean difference in trough serum concentrations at weeks 1, 4, and 6 was 4.2, 6.2, and 5.2 mg/L, respectively. The FPIA overestimation of the EMIT values (calculated as FPIA-EMIT) varied widely among study subjects with a range of 0.0 mg/L to 27.0 mg/L for peak serum concentrations and 0.0 mg/L to 12.8 mg/L for trough serum concentrations. The mean doses calculated based on FPIA results were significantly lower than the EMIT-derived doses. No significant difference was observed in the calculated dosing intervals. These results demonstrate that FPIA significantly overestimates vancomycin serum concentrations compared with EMIT in patients with ESRD undergoing high-efficiency hemodialysis. The overestimation by FPIA may result in significantly different vancomycin dosing recommendations, leading to underdosing and the potential for therapeutic failures. Due to the unpredictability of the overestimation by FPIA, we were unable to formulate vancomycin dosing guidelines for institutions that use FPIA. Therefore, we recommend that the EMIT vancomycin assay be used in patients with ESRD to ensure appropriate dosing.