Therapeutic Drug Monitoring Targets Research Articles

Evaluation of Real-World Vancomycin Dosing and Attainment of Therapeutic Drug Monitoring Targets.

In 2020, the Infectious Diseases Society of America (IDSA) recommended a change in vancomycin therapeutic drug monitoring from trough-based to AUC/MIC-based to optimize vancomycin's efficacy and reduce nephrotoxicity. Many hospitals have not implemented this change due to barriers such as the cost of AUC/MIC software and lack of provider familiarity. The purpose of this study was to determine the rate of AUC/MIC ratio target attainment using current trough-based vancomycin dosing practices at a city hospital. The rates of acute kidney injury (AKI) were also evaluated. Vancomycin orders were reviewed retrospectively to determine the expected AUC/MIC ratios using first-order pharmacokinetic equations over a 7-month period. Orders were excluded if they were written for a one-time dose, for individuals less than 18 years of age, or for those on hemodialysis. A total of 305 vancomycin orders were included in this review. Overall, 27.9% (85/305) of vancomycin orders attained the AUC/MIC ratio target of 400-600 mg·h/L as recommended by the guidelines. Nearly 35% (106/305) achieved AUC/MIC ratios below 400 mg·h/L and 37.4% (114/305) achieved AUC/MIC ratios above 600 mg·h/L. Orders for obese patients were significantly more likely to have below the target AUC/MIC ratios (68% vs. 23.9%, X2 48.48, p < 0.00001) and non-obese patients were significantly more likely to have above the target AUC/MIC ratios (45.7% vs. 12%, X2 27.36, p < 0.00001). The overall rate of acute kidney injury observed was 2.6%. Most vancomycin orders did not attain therapeutic drug monitoring targets, reflecting the ongoing clinical challenge of optimizing vancomycin doses and implementing new guideline recommendations.

Therapeutic Drug Monitoring of Infliximab in Acute Severe Ulcerative Colitis.

Therapeutic drug monitoring (TDM) is a useful strategy in ulcerative colitis (UC). Nearly a quarter of UC patients will experience acute severe UC (ASUC) in their lifetime, including 30% who will fail first-line corticosteroid therapy. Steroid-refractory ASUC patients require salvage therapy with infliximab, cyclosporine, or colectomy. Fewer data are available for the use of TDM of infliximab in ASUC. The pharmacokinetics of ASUC make TDM in this population more complex. High inflammatory burden is associated with increased infliximab clearance, which is associated with lower infliximab drug concentrations. Observational data support the association between increased serum infliximab concentrations, lower clearance, and favorable clinical and endoscopic outcomes, as well as decreased rates of colectomy. Data regarding the benefit of accelerated or intensified dosing strategies of infliximab-as well as target drug concentration thresholds-in ASUC patients remain more equivocal, though limited by their observational nature. Studies are underway to further evaluate optimal dosing and TDM targets in this population. This review examines the evidence for TDM in patients with ASUC, with a focus on infliximab.

Does metabolite matter? Defining target itraconazole and hydroxy-itraconazole serum concentrations for blastomycosis.

Itraconazole is the recommended first-line treatment for mild-to-moderate blastomycosis and consolidation treatment of moderate-to-severe disease. Itraconazole is metabolised into three metabolites, including an active metabolite hydroxy-itraconazole. Literature provides little evidence indicating whether therapeutic drug monitoring targets should be based on itraconazole parent compound alone or a sum of itraconazole and hydroxy-itraconazole serum concentrations. This study aims to compare clinical outcomes and adverse drug events (ADEs) of combined itraconazole and hydroxy-itraconazole concentrations versus itraconazole parent compound alone in patients with blastomycosis. This study was a retrospective cohort review of patients ≥18 years with probable or proven Blastomyces infection who received itraconazole with at least one documented serum itraconazole concentration. The primary outcome was rate of partial or complete treatment response across three patient groups: (1) Itraconazole parent compound >1.0mcg/ml (parent), (2) parent compound <1.0mcg/ml, but a combined itraconazole and hydroxy-itraconazole >1.0mcg/ml (combined) and (3) failure to achieve a combined or parent concentration >1.0mcg/ml (subtherapeutic) for >75% of the duration of itraconazole therapy. A total of 80 patients were included (parent=32, combined=36, subtherapeutic=12). No statistically significant difference was observed for rate of partial or complete treatment response (97% parent vs 94% combined, p= .99). Significantly higher mortality due to blastomycosis was observed in patients in the subtherapeutic group (0% parent vs 3% combined vs 25% subtherapeutic, p= .01). This study supports an itraconazole therapeutic target combining itraconazole and hydroxy-itraconazole >1.0mcg/ml for blastomycosis treatment.

Therapeutic Drug Monitoring of Antibiotics: Defining the Therapeutic Range.

In the present narrative review, the authors aimed to discuss the relationship between the pharmacokinetic/pharmacodynamic (PK/PD) of antibiotics and clinical response (including efficacy and toxicity). In addition, this review describes how this relationship can be applied to define the therapeutic range of a particular antibiotic (or antibiotic class) for therapeutic drug monitoring (TDM). Relevant clinical studies that examined the relationship between PK/PD of antibiotics and clinical response (efficacy and response) were reviewed. The review (performed for studies published in English up to September 2021) assessed only commonly used antibiotics (or antibiotic classes), including aminoglycosides, beta-lactam antibiotics, daptomycin, fluoroquinolones, glycopeptides (teicoplanin and vancomycin), and linezolid. The best currently available evidence was used to define the therapeutic range for these antibiotics. The therapeutic range associated with maximal clinical efficacy and minimal toxicity is available for commonly used antibiotics, and these values can be implemented when TDM for antibiotics is performed. Additional data are needed to clarify the relationship between PK/PD indices and the development of antibiotic resistance. TDM should only be regarded as a means to achieve the main goal of providing safe and effective antibiotic therapy for all patients. The next critical step is to define exposures that can prevent the development of antibiotic resistance and include these exposures as therapeutic drug monitoring targets.

Evaluation of amikacin use and comparison of the models implemented in two Bayesian forecasting software packages to guide dosing

Bayesian forecasting software can assist in guiding therapeutic drug monitoring (TDM)-based dose adjustments for amikacin to achieve therapeutic targets. This study aimed to evaluate amikacin prescribing and TDM practices, and to determine the suitability of the amikacin model incorporated into the DoseMeRx® software as a replacement for the previously available software (Abbottbase®). Patient demographics, pathology, amikacin dosing history, amikacin concentrations and Abbottbase® predicted TDM targets (area under the curve up to 24 hours, maximum concentration and trough concentration) were collected for adults receiving intravenous amikacin (2012-2017). Concordance with the Australian Therapeutic Guidelines was assessed. Observed and predicted amikacin concentrations were compared to determine the predictive performance (bias and precision) of DoseMeRx®. Amikacin TDM targets were predicted by DoseMeRx® and compared to those predicted by Abbottbase®. Overall, guideline compliance for 63 courses of amikacin in 47 patients was suboptimal. Doses were often lower than recommended. For therapy >48h, TDM sample collection timing was commonly discordant with recommendations, therapeutic target attainment low and 34% of dose adjustments inappropriate. DoseMeRx® under-predicted amikacin concentrations by 0.9mg/L (95% confidence interval [CI] -1.4 to -0.5) compared with observed concentrations. However, maximum concentration values (n=19) were unbiased (-1.7mg/L 95%CI -5.8 to 0.8) and precise (8.6% 95%CI 5.4-18.1). Predicted trough concentration values (n=7) were, at most, 1mg/L higher than observed. Amikacin area under the curve values estimated using Abbottbase® (181mgh/L 95%CI 161-202) and DoseMeRx® (176mgh/L 95%CI 152-199) were similar (P=.59). Amikacin dosing and TDM practice was suboptimal compared with guidelines. The model implemented by DoseMeRx® is satisfactory to guide amikacin dosing.

Intrapulmonary Pharmacokinetics of First-line Anti-tuberculosis Drugs in Malawian Patients With Tuberculosis.

BackgroundFurther work is required to understand the intrapulmonary pharmacokinetics of first-line anti-tuberculosis drugs. This study aimed to describe the plasma and intrapulmonary pharmacokinetics of rifampicin, isoniazid, pyrazinamide, and ethambutol, and explore relationships with clinical treatment outcomes in patients with pulmonary tuberculosis.MethodsMalawian adults with a first presentation of microbiologically confirmed pulmonary tuberculosis received standard 6-month first-line therapy. Plasma and intrapulmonary samples were collected 8 and 16 weeks into treatment and drug concentrations measured in plasma, lung/airway epithelial lining fluid (ELF), and alveolar cells. Population pharmacokinetic modeling generated estimates of drug exposure (Cmax and AUC) from individual-level post hoc Bayesian estimates of plasma and intrapulmonary pharmacokinetics.ResultsOne-hundred fifty-seven patients (58% HIV coinfected) participated. Despite standard weight-based dosing, peak plasma concentrations of first-line drugs were below therapeutic drug-monitoring targets. Rifampicin concentrations were low in all 3 compartments. Isoniazid, pyrazinamide, and ethambutol achieved higher concentrations in ELF and alveolar cells than plasma. Isoniazid and pyrazinamide concentrations were 14.6-fold (95% CI, 11.2–18.0-fold) and 49.8-fold (95% CI, 34.2–65.3-fold) higher in ELF than plasma, respectively. Ethambutol concentrations were highest in alveolar cells (alveolar cell–plasma ratio, 15.0; 95% CI, 11.4–18.6). Plasma or intrapulmonary pharmacokinetics did not predict clinical treatment response.ConclusionsWe report differential drug concentrations between plasma and the lung. While plasma concentrations were below therapeutic monitoring targets, accumulation of drugs at the site of disease may explain the success of the first-line regimen. The low rifampicin concentrations observed in all compartments lend strong support for ongoing clinical trials of high-dose rifampicin regimens.

Review article: determination of the therapeutic range for therapeutic drug monitoring of adalimumab and infliximab in patients with inflammatory bowel disease.

Clinical application of therapeutic drug monitoring (TDM) to optimise anti-TNF therapies in patients with IBD depends upon target ranges. To review methodology used to determine therapeutic ranges and critically compare and contrast its application to infliximab and adalimumab. A systematic review was performed, and relevant literature was summarised and critically examined. Upper limits of the therapeutic range are determined by toxicity, a plateau response and cost. Lower limits are determined by optimal concentration on the target of action in vitro and/or in vivo, or by correlation of drug levels with clinical efficacy using area-under-receiver-operator-curve (AUROC) analysis. In 43 studies, there were huge variations in time at which infliximab and adalimumab levels were measured, the end-points used (clinical remission to mucosal healing), the clinical setting (active disease vs maintenance phase) and the reason for TDM (proactive vs reactive). In the maintenance phase for infliximab, lower trough limits 2.8-5.7µg/mL are reported depending upon end-points used, with consistent AUROC 0.68-0.77. Adalimumab TDM targets are even less consistent with a lower limit 5.9-11.8µg/mL (AUROC 0.66-0.83) in some studies, but no cut-off can be identified that is significantly associated with outcome in others, related to inherent pharmacokinetic and pharmacodynamic differences, and heterogeneity of study design. Evidence for exposure-response relationship is stronger for infliximab than adalimumab. Due to heterogeneity in settings for drug level measurements, therapeutic ranges vary. These factors need to be taken into account when interpreting the evidence and extending this to therapeutic strategies for IBD patients.

2107. Azole Therapeutic Drug Monitoring (TDM) in a Multiracial Cohort with Varied Pharmacogenetics

BackgroundVoriconazole (VOR) and posaconazole (POS) exhibit wide pharmacokinetic variability. Various factors including race and genetic polymorphisms are at play and this may affect treatment response. We aim to evaluate the utility of VOR/POS TDM among Southeast Asians that are predominantly intermediate/poor VOR metabolizers.MethodsAll adults with VOR/POS TDM performed at our institution from 2015 to 2018 were included. We determined proportion of patients and doses required to achieve TDM targets [(2 – 5.5 mg/L (VOR) or ≥ 0.7 and ≥ 1.0 mg/L (POS prophylaxis and treatment respectively)], and correlate levels with treatment efficacy and safety.ResultsVOR/POS TDM was performed mostly among patients with hematological malignancy or solid-organ transplant (146/174, 83.9%). Less than half (32/70, 45.7%) of patients on VOR achieved target—18 (25.7%) were < 2 mg/L while 20 (28.5%) had levels > 5.5 mg/L. Doses required to achieve TDM target ranged from 1.9–11.4 mg/kg/day. Drug interactions, critically ill state and change in drug formulation were major causes of intra-patient variability. One-fifth (n = 14) experienced transaminitis; corresponding VOR trough levels were 0.5–> 7.5 mg/L. Neurotoxicity was also seen in 3 (4.3%) patients—all 3 had VOR trough ≥ 6.7 mg/L and saw symptom resolution upon dose reduction. There appears to be no association between the achievement of TDM targets and response rates. Majority (81/104, 77.9%) of patients on POS achieved TDM targets. Patients prescribed POS tablet were significantly more likely to attain targets compared with suspension 600 mg/day [19/26 (73.0%) vs. 27/62 (43.5%), P < 0.05] and 800 mg/day [17/26 (65.3%) vs. 4/16 (25.0%), P < 0.05)]. Of 23 with sub-therapeutic levels, 19 (82.6%) responded to dose increase and/or change in acid-reducing agents. Breakthrough infection occurred despite troughs ≥ 0.7 mg/L [5/42 (11.9%) vs. 2/40 (5.0%) when < 0.7 mg/L (P = 0.3)]. Treatment failure was observed in 2 patients (troughs > 1.0 mg/L).ConclusionVOR/POS TDM should be implemented in Southeast Asians due to significant unpredictability in dose exposure and potential to avoid need for switch to alternative anti-fungals due to intolerability. Higher POS trough cutoff may be required for effective anti-fungal prophylaxis.Disclosures All authors: No reported disclosures.

Therapeutic Drug Monitoring of Oral Anti-Hormonal Drugs in Oncology.

Oral anti-hormonal drugs are essential in the treatment of breast and prostate cancer. It is well known that the interpatient variability in pharmacokinetic exposure is high for these agents and exposure-response relationships exist for many oral anti-hormonal drugs. Yet, they are still administered at fixed doses. This could lead to underdosing and thus suboptimal efficacy in some patients, while other patients could be overdosed resulting in unnecessary side effects. Therapeutic drug monitoring(TDM), individualized dosing based on measured blood concentrations of the drug, could therefore be a valid option to further optimize treatment. In this review, we provide an overview of relevant clinical pharmacokinetic and pharmacodynamic characteristics of oral anti-hormonal drugs in oncology and translate these into practical guidelines for TDM. For some agents, TDM targets are not well established yet and as areference the median pharmacokineticexposure could be targeted (exemestane: minimum plasma concentration(Cmin) 4.1ng/mL and enzalutamide: Cmin 11.4mg/L). However, for most drugs, exposure-efficacy analyses could be translated into specific targets (abiraterone: Cmin 8.4ng/mL, anastrozole: Cmin 34.2ng/mL, and letrozole: Cmin 85.6ng/mL). Moreover, prospective clinical trials have shown TDM to be feasible for tamoxifen, for which the exposure-efficacy threshold of its active metabolite endoxifen is 5.97ng/mL. Based on the available data, we therefore conclude that individualized dosing based on drug concentrations is feasible and promising for oral anti-hormonal drugs and should be developed further and implemented into clinical practice.

Valganciclovir Pharmacokinetics in Patients Receiving Oral Prophylaxis Following Kidney Transplantation and Model-Based Predictions of Optimal Dosing Regimens.

Valganciclovir is used as oral prophylaxis for cytomegalovirus (CMV) infection in kidney transplant recipients. However, limited pharmacokinetic data exist to guide dosing in this patient group. This study aimed to describe the population pharmacokinetics of valganciclovir in a large sample of kidney transplant recipients and predict optimal dosing based on Monte Carlo simulations. Therapeutic drug monitoring (TDM) data from adult kidney transplant recipients who received valganciclovir prophylaxis during a 10-year study period were collected retrospectively. A non-parametric pharmacokinetic analysis and Monte Carlo simulations to determine the probabilities of reaching an area under the drug concentration-time curve (AUC) target of 40-50mg·h/L with various dosing regimens at different levels of renal function were conducted using the Pmetrics™ package for R. This study included 792 ganciclovir concentration measurements derived from 97 patients. A one-compartment oral absorption model best described the data. The final covariate model was as follows: CL(ganciclovir)=TVCL×(CLCR/51)0.75, where CL is the clearance, TVCL is the typical value of ganciclovir clearance, creatinine clearance (CLCR) according to the Cockcroft-Gaultt equation and 51 is the mean CLCR determined in the study. In the simulations, the probability of reaching the targeted AUC was insufficient when using the recommended dosing regimens for prophylaxis, especially in patients with impaired renal function at CLCR<50mL/min. Higher doses of valganciclovir corrected to renal function are suggested for use as oral prophylaxis for CMV infection in kidney transplant recipients. Further study is required to establish TDM targets to ensure adequate drug concentrations while avoiding potentially toxic drug exposures.

Therapeutic drug monitoring in the past 40 years of the Journal of Antimicrobial Chemotherapy.

Since the Journal of Antimicrobial Chemotherapy was first published in 1975, papers addressing therapeutic drug monitoring (TDM) have been a regular feature. Initially they focused on laboratory aspects of drug concentration measurement then they changed more to the application of TDM in a clinical setting. Over its history, the Journal has provided its readership with the latest technological and scientific advances in TDM and has helped to drive changes in TDM that have directly impacted on patient care. These have varied from improvement in the quality of antimicrobial measurements through better identification of dosage regimens and TDM targets that help predict outcome and adverse events. Despite these advances in our understanding of the science and practice of TDM, there remain many areas of uncertainty. As we move into the next 40 years, it is clear that the Journal will continue to provide the readership with the latest science and opinion in this important area.

Amikacin use and therapeutic drug monitoring in adults: do dose regimens and drug exposures affect either outcome or adverse events? A systematic review.

The objectives of this study were to identify the amikacin dosage regimens and drug concentrations consistent with good outcomes and to determine the drug exposures related to nephrotoxicity and ototoxicity. A literature review was conducted in Medline, EMBASE and the Cochrane Central Register of Controlled Trials. Full journal articles reporting randomized controlled trials, controlled clinical trials, interrupted time series trials, and controlled before and after studies involving amikacin therapeutic drug monitoring (TDM) and dose adjustment were considered for inclusion. Seventeen studies for inclusion were identified, comprising 1677 participants. Amikacin doses ranged from 11 to 15 mg/kg/day with 13 studies using 15 mg/kg/day. Studies were generally designed to compare different aminoglycosides rather than to assess concentration-effect relationships. Only 11 papers presented data on target concentrations, rate of clinical cure and toxicity. Target peak concentrations ranged from 15 to 40 mg/L and target troughs were typically <10 or <5 mg/L. It was not clear whether these targets were achieved. Measured peaks averaged 28 mg/L for twice-daily dosing and 40-45 mg/L for once-daily dosing; troughs averaged 5 and 1-2 mg/L, respectively. Fifteen of the included studies reported rates of nephrotoxicity; auditory and vestibular toxicities were reported in 12 and 8 studies. This systematic review found little published evidence to support an optimal dosage regimen or TDM targets for amikacin therapy. The use of alternative approaches, such as consensus opinion and a review of current practice, will be required to develop guidelines to maximize therapeutic outcomes and minimize toxicity with amikacin.

Variability in protein binding of teicoplanin and achievement of therapeutic drug monitoring targets in critically ill patients: Lessons from the DALI Study

The aims of this study were to describe the variability in protein binding of teicoplanin in critically ill patients as well as the number of patients achieving therapeutic target concentrations. This report is part of the multinational pharmacokinetic DALI Study. Patients were sampled on a single day, with blood samples taken both at the midpoint and the end of the dosing interval. Total and unbound teicoplanin concentrations were assayed using validated chromatographic methods. The lower therapeutic range of teicoplanin was defined as total trough concentrations from 10 to 20mg/L and the higher range as 10–30mg/L. Thirteen critically ill patients were available for analysis. The following are the median (interquartile range) total and free concentrations (mg/L): midpoint, total 13.6 (11.2–26.0) and free 1.5 (0.7–2.5); trough, total 11.9 (10.2–22.7) and free 1.8 (0.6–2.6). The percentage free teicoplanin for the mid-dose and trough time points was 6.9% (4.5–15.6%) and 8.2% (5.5–16.4%), respectively. The correlation between total and free antibiotic concentrations was moderate for both the midpoint (ρ=0.79, P=0.0021) and trough (ρ=0.63, P=0.027). Only 42% and 58% of patients were in the lower and higher therapeutic ranges, respectively. In conclusion, use of standard dosing for teicoplanin leads to inappropriate concentrations in a high proportion of critically ill patients. Variability in teicoplanin protein binding is very high, placing significant doubt on the validity of total concentrations for therapeutic drug monitoring in critically ill patients.

Population pharmacokinetics of mycophenolic acid in children and young people undergoing blood or marrow and solid organ transplantation

To characterize the population pharmacokinetics of mycophenolic acid (MPA) and evaluate dose regimens using a simulation approach and accepted therapeutic drug monitoring targets in children and young people undergoing blood or marrow, kidney and liver transplantation. MPA concentration-time data were collected using an age specific sampling protocol over 12h. Some patients provided randomly timed but accurately recorded blood samples. Total and unbound MPA were measured by HPLC. NONMEM was employed to analyze MPA pharmacokinetic data. Simulations (n= 1000) were conducted to assess the suitability of the MPA dose regimens to maintain total MPA AUC(0,12h) within the range 30 and 60mg l(-1) h associated with optimal outcome. A two-compartment pharmacokinetic model with first-order elimination best described MPA concentration-time data. Population mean estimates of MPA clearance, inter-compartmental clearance, volumes of distribution in the central and peripheral compartments, absorption rate constant and bioavailability were 6.42 l h(-1) , 3.74 l h(-1) , 7.24 l, 16.8l, 0.39h(-1) and 0.48, respectively. Inclusion of bodyweight and concomitant ciclosporin reduced the inter-individual variability in CL from 54.3% to 31.6%. Children with a bodyweight of 10kg receiving standard MPA dose regimens achieve an MPA AUC below the target range suggesting they may be at a greater risk of acute rejection. The population pharmacokinetic model for MPA can be used to explore dosing guidelines for safe and effective immunotherapy in children and young people undergoing transplantation.

A Randomized Controlled Trial of Therapeutic Drug Monitoring in Treatment-Naive and -Experienced HIV-1-Infected Patients

To improve the utility of therapeutic drug monitoring (TDM) by defining the proportion of patients with and predictors of above or below target protease inhibitor (PI) or nonnucleoside reverse transcriptase inhibitor (NNRTI) concentrations. This 48-week, multicenter, open-label clinical trial randomized patients to TDM versus standard of care (SOC). Serial pharmacokinetics, including a week-2 3-sample sparse collection, and expert committee TDM recommendations were given to TDM-arm patients' providers. Seventy-four (39%) of 190 patients had week-2 concentrations outside of targets and 122 (64%) of 190 had nontarget exposure at least once over 48 weeks. Providers accepted 75% of TDM recommendations. Among patients with below-target concentrations, more TDM-arm than SOC-arm patients achieved targets (65% vs. 45%; P = 0.09). Increased body weight and efavirenz or lopinavir/ritonavir use were significant predictors of nontarget concentrations. Patients at target and patients who achieved targets after TDM-directed dose modifications trended toward greater viral load reductions at week 48 than patients with below-target exposures (HIV RNA reductions: 2.4, 2.3, and 1.9 log10 copies/mL, respectively; P = 0.09). Most patients had nontarget PI and/or NNRTI concentrations over 48 weeks. TDM recommendations were well accepted and improved exposure. Patients below TDM targets trended toward worse virologic response.