Search Results (360)

Background: Everolimus, an mTOR inhibitor used in oncology and organ transplantation, requires therapeutic drug monitoring due to the narrow therapeutic range of everolimus and substantial pharmacokinetic variation. Patient-derived data can function as a supplementary quality indicator for laboratory methods by providing real-world information on analytical performance. Methods: All routine whole-blood everolimus measurements performed at Akademiska University Hospital, Uppsala, Sweden, 2012 to 2025 were retrospectively evaluated. In total, 9,089 results were included. Annual and monthly concentration distributions were assessed using the 10th, 25th, 50th, 75th, and 90th percentiles. Long-term trends, sex differences, seasonal variation, and the impact of a method change from Architect (Abbott/Microgenics) to Cobas Pro e 801 (Roche) in 2021 were investigated. Results: Of 9089 results, 3335 were from females and 5754 from males. Concentration distributions were similar between sexes, with median concentrations of 4.47 and 4.33 µg/L, respectively; the overall median was 4.37 µg/L. Annual testing volumes remained stable. Median concentrations gradually declined from 5.22 µg/L in 2012 to approximately 4.0 µg/L in 2019–2020. Following introduction of the Cobas assay, patient concentration distributions shifted upward; compared with 2020, the 10th percentile increased by 45%, the median by 21%, and the 90th percentile by 11%. External quality assessment and method-comparison studies supported an analytical explanation. Conclusions: Everolimus concentration distributions were stable over time and showed no meaningful sex-related or seasonal variation. Patient percentile monitoring detected a clear analytical shift after method implementation and may serve as a practical supplementary quality indicator for TDM assays. Full article

Background: Therapeutic drug monitoring (TDM) has emerged as an important strategy for optimizing anti-tumor necrosis factor (anti-TNF) therapy in patients with inflammatory bowel disease (IBD). However, data regarding anti-TNF pharmacokinetics and immunogenicity from Middle Eastern populations remain limited. This study evaluated the associations between serum anti-TNF trough concentrations, anti-drug antibody (ADAb) levels, and therapeutic response among Iraqi patients with IBD receiving infliximab or adalimumab therapy. Methods: This cross-sectional observational study included 80 patients with Crohn’s disease or ulcerative colitis receiving maintenance infliximab or adalimumab therapy at a tertiary Gastroenterology Center in Iraq. Patients were categorized as responders or non-responders according to clinical disease activity indices and biochemical assessment. Serum trough levels of infliximab and adalimumab, as well as ADAb concentrations, were measured using an enzyme-linked immunosorbent assay (ELISA). Results: Responders had significantly higher serum trough concentrations than non-responders for both infliximab [3.75 µg/mL (IQR: 3.40–4.15) vs. 1.05 µg/mL (IQR: 0.92–1.12), p < 0.001] and adalimumab [6.32 µg/mL (IQR: 5.67–7.15) vs. 3.30 µg/mL (IQR: 2.70–4.26), p < 0.001]. Adalimumab-treated non-responders had significantly higher ADAb levels compared with responders (p = 0.047). Conclusions: Favorable therapeutic outcomes in Iraqi IBD patients treated with anti-TNF agents were associated with adequate serum trough levels and low ADAb levels. Reactive therapeutic drug monitoring may provide clinically valuable pharmacokinetic information capable of guiding individualized treatment optimization and identifying mechanisms of treatment failure in patients receiving infliximab or adalimumab therapy. Full article

Background/Objectives: Saliva may provide a non-invasive alternative to blood sampling for therapeutic drug monitoring (TDM) of mycophenolic acid (MPA) in children. This study assessed MPA and, secondarily, mycophenolic acid glucuronide (MPAG) in non-centrifuged Salivette^® devices to determine an acceptable interval between saliva collection and laboratory processing. Methods: Phosphate-buffered saline (PBS), artificial saliva, and saliva from five healthy adult volunteers were externally spiked with MPA and MPAG at 5 and 500 ng/mL and applied to Salivette^® cotton swabs. Samples were stored for 12, 24, and 48 h at 22 °C and 6 °C and analyzed by liquid chromatography-tandem mass spectrometry. Percentage deviations from nominal concentration within ±15% were considered acceptable. Results: In PBS, both analytes met the acceptance criterion for up to 24 h under both conditions. In artificial saliva, both met the criterion for at least 24 h and, under some conditions, for 48 h. In human saliva, all volunteer-level MPA results met the criterion after 12 h at both temperatures, whereas MPAG did not consistently meet it. Mean MPA deviations across volunteers ranged from −10.8 to 1.9% at 22 °C and from −12.3 to 2.4% at 6 °C. Conclusions: MPA met the acceptance criterion after 12-h in non-centrifuged Salivette^® devices, supporting the feasibility of a 12-h pre-centrifugation interval under comparable conditions. Prompt centrifugation and processing are advisable when MPAG determination is required. Confirmation using incurred post-dose saliva from pediatric patients receiving mycophenolate mofetil is required. Full article

Feline infectious peritonitis (FIP) is responsive to treatment with the adenosine analogue GS-441524 (GS-44) and its prodrug, remdesivir (REM); both are now available on veterinary prescription in many countries. Therapeutic drug monitoring (TDM) of GS-44 has the potential to support dose selection for individual cats; however, TDM assays are currently only offered by one UK-based laboratory. This study describes a simple, cost-effective, and environmentally conscious high-performance liquid chromatography (HPLC) method for the quantification of GS-44 in feline plasma or serum. The method was validated in accordance with the International Council for Harmonisation M10 guidelines for bioanalytical methods. Calibration standards demonstrated linearity across a range of 2.59 to 5048.28 ng/mL, R² = 0.9880, with a lower limit of quantification of 2.59 ng/mL and upper limit of quantification of 5048 ng/mL; this is equivalent to an assay range of 0.06 to 208 µM. Precision, accuracy and spike recovery were within ±15% for 14 of 17 standard concentrations (±20% at the lowest three). Carry-over, dilution integrity, and analyte stability under common storage conditions all met the method’s requirements. This is a simple, robust and accurate eco-friendly method suitable for adoption by diagnostic laboratories, enabling routine TDM for cats undergoing treatment for FIP with GS-44 and/or REM. Full article

Background and Objectives: Antibody–drug conjugates (ADCs) have become a major therapeutic platform in breast cancer and other solid tumors. Trastuzumab deruxtecan (T-DXd), trastuzumab emtansine (T-DM1), and sacituzumab govitecan (SG) differ substantially in antibody target, linker, payload, drug-to-antibody ratio, and bystander effect, resulting in heterogeneous pulmonary and cardiac toxicity profiles. This narrative review critically compares interstitial lung disease (ILD)/pneumonitis and cardiotoxicity associated with these three agents, aiming to prevent inappropriate extrapolation of toxicity algorithms and to provide a practical, agent-specific framework for multidisciplinary care. Materials and Methods: A targeted narrative search of PubMed/MEDLINE, Google Scholar, ClinicalTrials.gov, regulatory product information, and oncology/cardio-oncology guidance was performed and updated on 24 August 2026. Priority was given to regulatory documents, pivotal trials, pooled safety analyses, real-world cohorts, systematic reviews, and multidisciplinary recommendations. Pharmacovigilance data and case reports were included only to characterize rare events. Results: T-DXd is associated with a clinically important ILD/pneumonitis risk (approximately 12–15% in pooled analyses), predominantly grade 1–2 but occasionally fatal, requiring proactive surveillance, immediate interruption for suspected disease, and grade-directed corticosteroid therapy. T-DM1 shows a low but established pneumonitis incidence of approximately 1%, with permanent discontinuation recommended upon diagnosis. SG-related pneumonitis is rare and incompletely defined, without a T-DXd-like surveillance mandate. Both T-DM1 and T-DXd retain trastuzumab-derived cardiac monitoring requirements; symptomatic heart failure remains uncommon, although protocol-defined LVEF declines appear more frequent with T-DXd. SG lacks an established cardiomyopathy signal. Conclusions: Cardiopulmonary toxicity of ADCs is agent-specific rather than a class effect. Monitoring intensity, diagnostic thresholds, and management pathways must be tailored to the individual drug, regimen, indication, dose, patient comorbidity, and prior therapy. Close collaboration among oncology, radiology, pulmonology, and cardio-oncology is essential to preserve both treatment efficacy and patient safety. Full article

Treat-to-target management in inflammatory bowel disease (IBD) combines symptoms, fecal and serum biomarkers, endoscopy, histology, and cross-sectional imaging, but these measures frequently diverge. Discordance may reflect analytical variation, timing, disease location, phenotype, comorbidity, or partially non-overlapping biological processes. We performed a critical narrative review using a structured PubMed/MEDLINE search, supplemented by citation chaining and publisher searches. Guidelines, systematic reviews, diagnostic studies, cohorts, randomized trials, and selected mechanistic studies were prioritized. Fecal calprotectin (FC) and lactoferrin primarily reflect intestinal neutrophilic inflammation, whereas C-reactive protein (CRP) and related serum indices reflect a nonlocalizing systemic response. The fecal immunochemical test (FIT) detects gastrointestinal bleeding, and leucine-rich alpha-2 glycoprotein (LRG) remains promising but insufficiently standardized. We distinguish five biological biomarker domains—namely, fecal–neutrophil; serum–systemic; epithelial/barrier; restitution/resolution; and fibrosis/extracellular matrix (ECM) remodeling—from symptoms and clinical indices, pharmacologic measurements, and phenotype-directed reference assessments. Circulating barrier, repair, and matrix-turnover markers remain investigational. Reactive therapeutic drug monitoring (TDM) for anti-tumor necrosis factor (anti-TNF) agents has the most mature evidence. Vedolizumab and ustekinumab show exposure–response associations, but actionable thresholds are unvalidated, and clinical TDM is not established for newer biologics or oral small molecules. After objective confirmation of disease activity, the framework may support phenotype-directed therapeutic decisions but is not a validated algorithm. Clinically important disagreement should prompt assessment of sampling, assay, timing, infection, medication-related confounding, and pretest probability before phenotype-directed endoscopy, histology, imaging, or reactive TDM is selected. A single discordant result should neither trigger treatment escalation nor exclude active or structural disease. Full article

Background: Isavuconazole, a broad-spectrum triazole antifungal, exhibits high lipophilicity and extensive plasma protein binding, properties that may predispose it to sequestration within extracorporeal membrane oxygenation (ECMO) circuits. This study aimed to characterize the pharmacokinetics (PK) of isavuconazole and to evaluate drug sequestration within the ECMO circuit in critically ill patients receiving ECMO support. Methods: We conducted a prospective, exploratory, single-center observational study including critically ill patients receiving ECMO (veno-venous (VV) or veno-arterial (VA)) and treated with intravenous isavuconazole. Serial blood samples were collected simultaneously from the patient’s arterial line and from pre- and post-membrane oxygenator sampling sites. Non-compartmental analysis was performed on arterial line samples to estimate PK measures, and concentration differences across sampling sites were analyzed to estimate circuit-related drug loss. PK/pharmacodynamic (PD) target attainment was assessed using established efficacy thresholds (AUC_0–24/MIC ≥ 25 and Cmin > 2 mg/L). Results: A total of 41 plasma samples from 3 critically ill patients (2 VV-ECMO, 1 VA-ECMO) were included in the analysis. Limited, component-specific isavuconazole loss was observed in tubing and connectors (6.62% ± 20.8%, p = 0.294) and across the entire ECMO circuit (7.74% ± 20.2%, p = 0.211). Likewise, no relevant concentration difference was detected across the membrane oxygenator (0.849% ± 6.15%, p = 0.642). Interindividual variability was observed across PK parameters, particularly in measures of elimination and distribution. All patients achieved predefined PK/PD efficacy targets, with mean Cmin and AUC_0–24/MIC of 3.07 ± 0.261 mg/L and 85.3 ± 4.03, respectively, and none exceeded the established toxicity threshold. Conclusions: Preliminary results showed variable concentration differences across ECMO sampling sites, with no consistent pattern of isavuconazole loss across the ECMO circuit under the conditions evaluated. All patients achieved predefined PK/PD efficacy targets using currently recommended dosing regimens; however, interindividual PK variability was observed, supporting the potential value of therapeutic drug monitoring (TDM) to guide individualized dosing decisions in this population. Larger population PK studies are warranted to further characterize determinants of isavuconazole exposure during ECMO support and refine evidence-based dosing strategies. Full article

Background/Objectives: Vancomycin remains a cornerstone antibiotic for Gram-positive infections, but its narrow therapeutic window and marked pharmacokinetic variability in critical patients complicate dosing. This study aimed to analyze survival and identify factors associated with mortality in intensive care unit (ICU) patients receiving vancomycin under therapeutic drug monitoring (TDM). Methods: A single-center, retrospective cohort study was conducted at City Clinical Hospital named after I.V. Davydovsky (Moscow, Russia) between December 2021 and January 2026 (IRB protocol VANCO-2021). A total of 190 adult patients from surgical, therapeutic, and cardiac ICUs receiving vancomycin for at least 3–5 days were analyzed; trough concentrations were determined by HPLC-MS/MS. Cox proportional hazards, spline Cox, and segmented (piecewise) Cox models were applied to identify mortality predictors, with bootstrap subsampling assessing threshold robustness. Results: Three independent predictors of mortality were identified: ln(minimum vancomycin concentration) (HR = 1.644, p = 0.028), age (HR = 1.019, p = 0.037), and serum creatinine (HR = 1.004, p < 0.001). A data-driven threshold trough concentration (Ctrough) of 25.5 µg/mL was identified, above which mortality increased substantially (63.0% vs. 26.4%; p < 0.05). The adjusted hazard ratio for Ctrough ≥ 25.5 µg/mL was approximately 1.88 (p = 0.054); bootstrap subsampling yielded an uncertainty interval of 23.2–33.6 µg/mL. Conclusions: Elevated minimum vancomycin concentrations exceeding 25.5 µg/mL are independently and statistically associated with increased mortality in ICU patients, likely reflecting altered drug exposure and illness severity rather than a direct causal effect. Systematic TDM is essential for maintaining vancomycin within the therapeutic range. Full article

Background: Therapeutic drug monitoring (TDM) for piperacillin/tazobactam has become established in intensive care. TDM should be used in a structured approach to optimize dosing. We evaluated a newly designed TDM- and algorithm-based clinical-pharmacy-service to determine whether it is appropriate for optimization. Methods: We developed a clinical pharmacy service providing algorithmic recommendations for optimizing piperacillin/tazobactam dosing based on piperacillin TDM. After implementing the clinical pharmacy service, we evaluated the treatment of intensive-care patients with piperacillin/tazobactam in terms of achieving the minimum-inhibitory-concentration-(MIC)-related target concentration at the following four time points: t1, t2, t3, and t4 (1–4 working days after piperacillin/tazobactam therapy was started). Results: A total of 132 patients (including 36% women), median age 78 years, received piperacillin/tazobactam therapy. Sepsis or septic shock was the most common indication (43%), while a pulmonary focus was most frequent (40%). From 132 patients (t1), 19% had “too low piperacillin concentrations”, 20% “appropriate concentrations”, and 61% “too high concentrations”. After recommendations were given (acceptance rate 100%) the corresponding numbers from 93 remaining patients (t2) were 16%, 35%, and 48%, from 49 patients (t3) 8%, 53%, and 39% and from 29 patients (t4) 38%, 45%, and 17%. In (t1), dose reduction was the main recommendation (49%). The number of patients with “appropriate concentrations” increased in one comparison (t1–t2: n.s.; t1–t3: p = 0.0013; t1–t4: n.s.; Bonferroni-corrected McNemar test), while “too high concentrations” decreased (t1–t2: p = 0.0080; t1–t3: p = 0.0056; t1–t4: p = 0.0095). “too low concentrations” were not influenced (t1–t2: n.s.; t1–t3: n.s.; t1–t4: n.s.). Conclusions: Inappropriate piperacillin plasma concentrations were common. A TDM- and algorithm-based clinical-pharmacy-service especially decreased the number of overdosed patients in routine practice. Full article

Interindividual variability in drug response remains a major challenge in clinical pharmacology despite substantial advances in therapeutic drug monitoring (TDM), pharmacogenomics, pharmacokinetics/pharmacodynamics (PK/PD), and model-informed precision dosing (MIPD). Although these approaches have improved individualized therapy, clinically important variability in efficacy and toxicity persists because drug response is determined not only by systemic exposure but also by target engagement, disease biology, compensatory pathways, organ function, immune status, and dynamic patient-specific molecular states. Recent advances in multiomics, systems pharmacology, and artificial intelligence (AI) provide an opportunity to integrate these complementary biological and clinical dimensions within more comprehensive precision pharmacotherapy frameworks. This narrative review examines the evolving integration of PK, PD, TDM, pharmacometrics, multiomic technologies, mechanistic AI, and systems pharmacology across drug development and clinical care. Particular emphasis is placed on the limitations of exposure-based dosing alone, the biological determinants of interindividual variability, the transition from conventional TDM toward adaptive model-informed monitoring, and emerging approaches for integrating molecular and clinical data to support individualized therapeutic decision-making. Operon™ is discussed as an illustrative example of an internally operated mechanistic systems biology platform to demonstrate how biologically informed computational frameworks may integrate pharmacological and multiomic information within drug development workflows. The review further examines applications in polypharmacy, drug–drug interaction assessment, clinical trial enrichment, regulatory science, and adaptive dosing, while emphasizing that analytical validity, clinical validity, clinical utility, prospective validation, transparency, and clearly defined contexts of use remain essential prerequisites for clinical implementation. Collectively, these developments support a transition from concentration-guided dosing toward mechanism-informed precision pharmacotherapy that integrates drug exposure with biological response and clinical outcomes while maintaining rigorous standards for validation and regulatory acceptance. Full article

Background: Substantial inter-individual variability in imatinib systemic exposure may influence both efficacy and toxicity. Based on recommendations of the International Association for Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT), the IRCCS-CRO of Aviano started in 2018 offering physicians the opportunity to monitor plasma concentrations of imatinib and its active metabolite, norimatinib, as part of a diagnostic service for patients with Gastrointestinal Stromal Tumor (GIST). This study aims to evaluate the potential clinical utility of imatinib Therapeutic Drug Monitoring (TDM) in predicting response and toxicity in a real-world cohort of 63 patients with GIST. Methods: Imatinib and its active metabolite norimatinib trough concentrations (C_min) were quantified using a validated LC–MS/MS method. Associations between drug exposure and clinical–demographic characteristics, treatment-related toxicity, and progression-free survival (PFS) were evaluated. Results: A total of 437 plasma samples from 63 patients were collected. Marked inter- and intra-patient variability in imatinib exposure was observed (43% and 31% respectively); 67% of patients receiving 400 mg/day had a C_min below the recommended target concentration (1100 ng/mL). Female sex was significantly associated with higher imatinib exposure (median C_min 1114 vs. 786 ng/mL in males; p = 0.0018). Combined age–sex analysis showed a significant difference between women and men < 60 years (1041 vs. 668 ng/mL; p = 0.0068, Bonferroni-adjusted). A strong exposure–toxicity relationship emerged, with higher imatinib levels in samples collected at toxicity occurrence vs. the others (1728 vs. 927 ng/mL; p < 0.0001), without a direct association between sex and toxicity. No significant association between C_min and PFS was observed; however, disease progression was more frequent in patients with C_min < 500 ng/mL and absent in those with C_min >1500 ng/mL (60% vs. 0%, respectively). Conclusions: TDM was found to be a potentially useful tool for predicting clinically relevant toxicity and outcome. Sex and age significantly influence exposure, supporting tailored dosing strategies. Full article

The instability of ibrutinib in plasma at room temperature necessitates temperature-controlled sample transport, complicating therapeutic drug monitoring (TDM) and multicenter studies. Dried plasma spots (DPSs) offer a potential advantage by enabling sample storage and transport under ambient conditions. The aim of this study was to develop and validate an LC-MS/MS method for the simultaneous quantification of ibrutinib and ritonavir in plasma and DPSs. Following validation of an extended plasma calibration range, DPS method development included card selection and subsequent validation in accordance with ICH M10 and EMA guidelines. The analytical method demonstrated robust performance in plasma for both analytes. For DPS sampling, ritonavir fulfilled all validation criteria. In contrast, ibrutinib showed significant instability in DPS samples at room temperature after 48 h and did not meet the predefined acceptance criteria under these conditions. Refrigerated storage improved stability within the acceptance criteria for at least one week. The developed method is suitable for simultaneous quantification of ibrutinib and ritonavir in plasma and for ritonavir in DPSs. While DPS sampling may offer logistical advantages, its successful application is dependent on analyte stability. For ibrutinib, the requirement for refrigerated storage limits the anticipated benefits, and further research is needed to optimize dried sampling strategies. Full article

Background/Objectives: Antimicrobial stewardship programmes (ASPs) are essential for improving antimicrobial use and limiting the emergence of antimicrobial resistance. Although national ASP key performance indicators (KPIs) have been implemented across Saudi Ministry of Health (MOH) hospitals, large-scale evaluations of programme performance remain limited. This study evaluated national ASP performance across MOH hospitals from 2021 to 2024 using formal KPIs and complementary stewardship measures. Methods: This retrospective multicentre surveillance analysis included 124,452 antimicrobial prescription reviews from 96 Saudi MOH hospitals actively reporting stewardship activities. Hospitals were classified according to ASP capacity as category A, B, or C. The evaluated KPIs included protocol adherence, restricted-antibiotic dispensing compliance, active intervention rate, annual trends in optimization interventions, and physician acceptance of ASP recommendations. Secondary assessments included appropriateness of therapy management, therapeutic drug monitoring (TDM) for vancomycin and aminoglycosides, and hospital-level antimicrobial use expressed as defined daily doses per 100 available bed-days. Multivariable logistic regression was used to identify factors associated with guideline non-adherence and physician non-acceptance. Results: Overall protocol adherence was 87.1%, exceeding the national target of 80%, while the active intervention rate was 64.6%, exceeding the 60% benchmark. Restricted-antibiotic dispensing compliance reached 87.6% but remained below the 100% target. Physician acceptance of ASP recommendations was high at 93.0%, although it did not achieve the national target of 98%. The optimization-intervention KPI was not met because de-escalation, antibiotic discontinuation, and intravenous-to-oral conversion did not demonstrate a sustained annual increase. Appropriate ongoing therapy management was documented in 68.3% of cases with available data, whereas TDM was requested in 44.5% of eligible vancomycin or aminoglycoside cases. Antimicrobial use varied across years and hospital categories, with higher monitored broad-spectrum and reserve-agent use in higher-capacity hospitals. Lower ASP capacity, non-critical care settings, and combination therapy were consistently associated with less favourable stewardship outcomes. Conclusions: Saudi MOH hospitals actively reporting stewardship activities demonstrated favourable performance in protocol adherence, intervention activity, and physician acceptance. However, persistent gaps in restricted-antibiotic dispensing, optimization interventions, TDM, and inter-hospital variation indicate the need for continued strengthening of ASP infrastructure, monitoring, and feedback systems. Future research should link stewardship indicators with clinical outcomes, antimicrobial resistance trends, and patient safety. Full article

Background: Volumetric absorptive microsampling (VAMS) is an emerging tool for therapeutic drug monitoring (TDM) of several drugs including antiseizure medications (ASMs). Here, we compared the concentrations of carbamazepine (CBZ), levetiracetam (LEV), lacosamide (LCS), topiramate (TPR) and the benzodiazepine (BZ) clobazam (CLB) in plasma and VAMS samples. Methods: VAMS samples were collected by fingerprick in pediatric patients followed at our center. Patients were also subjected to conventional venous blood sampling. Plasma and VAMS samples were analyzed by using a UHPLC-MS/MS validated kit for AEs and BZs (ClinMass LC-MS/MS Complete Kit^®). A cross-validation analysis was performed by using Spearman correlation (rho), Deming regression and Bland–Altman plots. Results: Two analytical methods for measuring selected AEs and BZs in VAMS samples were developed and validated in accordance with the ICH M10 guidelines. Based on Bland–Altman results, a satisfactory agreement was observed between VAMS and plasma for CBZ, LCS, TPR, LEV and N-CLB. Considering the absence of interchangeability between capillary blood and plasma levels for CBZ-Diol, -Epoxi and CLB, a blood to plasma ratio was used to convert VAMS values into estimated plasma concentrations. Comparison of estimated vs. observed plasma results showed a successful predictive performance for this conversion approach. Conclusions: A positive agreement between plasma and VAMS was found for CBZ, LCS, TPR, LEV and N-CLB. Conversely, a conversion factor based on blood to plasma ratio should be adopted to convert CBZ-Diol, -Epoxi and CLB VAMS results into estimated plasma concentrations. This study confirmed the utility of VAMS for TDM of selected ASMs in pediatric patients during routine clinical practice. Full article

Background: Pazopanib, cabozantinib, sorafenib, axitinib, tivozanib, and sunitinib are widely used tyrosine kinase inhibitors (TKIs) targeting the vascular endothelial growth factor receptor signaling pathway. Considerable interindividual pharmacokinetic variability, together with established exposure–toxicity relationships, underlines the need for reliable analytical methods for therapeutic drug monitoring (TDM). The aim of this study was to develop and validate an LC–MS/MS method for the simultaneous determination of these six TKIs and the two metabolites, sorafenib N-oxide and desethyl-sunitinib, in human plasma and to investigate their stability under relevant preanalytical conditions. Methods: Plasma samples were prepared by protein precipitation and analyzed using LC–MS/MS with positive electrospray ionization and multiple reaction monitoring. Validation included assessments of linearity, accuracy, precision, lower limit of quantification, dilution integrity, carry-over, and stability under different storage conditions. As proof of concept, the method was applied to plasma samples from patients receiving TKI treatment. Results: All analytes demonstrated linear responses across the validated calibration ranges. Validation parameters met predefined acceptance criteria for all analytes, except for sorafenib N-oxide, which exhibited CV% values slightly above the acceptance limit (15%). All compounds remained stable during storage at −80 °C for at least five years. Furthermore, all analytes were stable at room temperature for 24 h, except sorafenib N-oxide, which showed instability under these conditions. Analysis of patient samples confirmed the suitability of the method for clinical application. Conclusions: We established and validated a fast, sensitive, and accurate LC–MS/MS method enabling simultaneous quantification of six TKIs and two metabolites in human plasma. The analytical method was successfully applied to plasma samples from patients in treatment with the six TKIs, demonstrating proof of concept for its application in TDM. Full article