TC > 0.05 as a Pharmacokinetic Parameter of Paclitaxel for Therapeutic Efficacy and Toxicity in Cancer Patients

Paclitaxel therapeutic drug monitoring - International association of therapeutic drug monitoring and clinical toxicology recommendations

Paclitaxel, one of the most frequently used anticancer drugs, is dosed by body surface area, which leads to substantial inter-individual variability in systemic drug exposure. We evaluated clinical evidence regarding the scientific rationale and clinical benefit of individualized paclitaxel dosing based on measured systemic concentrations, known as therapeutic drug monitoring (TDM). In retrospective studies, higher systemic exposure is associated with greater toxicity and efficacy of paclitaxel treatment across several disease types and dosing regimens. In prospective trials, TDM reduces variability in systemic exposure, and has been demonstrated to reduce toxicity while retaining treatment efficacy for 3-weekly dosing in patients with advanced non-small cell lung cancer. Despite the demonstrated benefits of paclitaxel TDM, clinical adoption has been limited due to the challenges with sample collection and analysis. Based on our review, we strongly recommend TDM for patients receiving every 3-week paclitaxel in combination with a platinum agent for advanced NSCLC, due to the prospectively demonstrated clinical benefits, and find moderate evidence to recommend TDM for paclitaxel 3-hour infusions for other tumor types and preliminary evidence suggesting potential usefulness for paclitaxel administered by 1-hour infusions.

The correlation between paclitaxel chemotoxicity and the plasma albumin level in cancer patients

WHAT IS KNOWN AND OBJECTIVE

The aim of this study was to evaluate the pharmacokinetics of paclitaxel in cancer patients with hypoalbuminemia following paclitaxel-containing chemotherapy and to provide a reference for the prevention of adverse events (AEs) after paclitaxel administration.

METHODS

Peripheral blood was collected from cancer patients treated with paclitaxel. The plasma concentration of paclitaxel was determined by ultra-high performance liquid chromatography after 24 ± 8 h of chemotherapy, and individual paclitaxel time above a threshold concentration of 0.05 μmol/L (T_c>0.05 ) was calculated using the population pharmacokinetic model. Haematological and non-haematological toxicities were monitored after chemotherapy, and the correlation between different chemotherapy toxicities and T_c>0.05 was evaluated using the Prism software.

RESULTS AND DISCUSSION

The enrolled patients were divided into the hypoalbuminemia group and normal albumin level group. The mean T_c>0.05 values in the normal albumin level and hypoalbuminemia groups were 36.89 and 24.93 h, respectively (P < 0.001). The risk of myelosuppression was positively correlated with T_c>0.05 . Due to the lower T_c>0.05 , the incidences of immediate AEs such as gastrointestinal reactions and rashes were higher in the hypoalbuminemia group than in the normal albumin level group, and the incidences of delayed AEs such as myelosuppression and neurotoxicity were lower in the hypoalbuminemia group.

WHAT IS NEW AND CONCLUSIONS

Plasma albumin level has a conclusive effect on T_c>0.05 , which can predict the potential clinical toxicity of paclitaxel. The study provides a theoretical basis for administration of paclitaxel.

Paclitaxel exposure-toxicity analysis reveals a pharmacokinetic determinant for dose-limiting neutropenia in East-Asian solid tumor patients: results from two prospective, phase II studies

PURPOSE

The time of a paclitaxel (PTX) concentration remains above 0.05 μM (Tc > 0.05) has been associated with PTX-induced adverse effects in Caucasians, while limited studies were reported in Asians. This study was aimed to explore the characteristics of Tc > 0.05 and the relationship between PTX exposure and toxicity in East-Asian patients.

METHODS

This study was based on two prospective phase II clinical trials and patients with advanced nasopharyngeal cancer (NPC) and non-small cell lung cancer (NSCLC) who were naïve to PTX were included independently. Eligible patients receive PTX (175 mg/m²) and carboplatin (AUC = 5) treatment every 3 weeks. PTX pharmacokinetic analysis was accessed. The relationship between PTX exposure and toxicities after first cycle as well as clinical efficacy was evaluated.

RESULTS

A total of 93 NPC and 40 NSCLC patients were enrolled. PTX exposure was consistent in two trials with average Tc > 0.05 duration of 38.8 h and 38.4 h, respectively. Average Tc > 0.05 in patients with grade 3/4 neutropenia was significantly higher than those without severe neutropenia in NPC patients (P = 0.003) and NSCLC patients (P = 0.007). Cut-off value of Tc > 0.05 were identified from the NPC cohort and then verified in the NSCLC cohort, dividing patients into high exposure Tc > 0.05 group (> 39 h) and low exposure group (≤ 39 h). Incidence of grade 3/4 neutropenia were significantly higher in the high exposure group in NPC cohort (43.3% vs 10.0%, P < 0.001) and NSCLC cohort (42.1% vs 9.5%, P = 0.028). No significant relationship between Tc > 0.05 and efficacy were observed.

CONCLUSION

Patients with PTX Tc > 0.05 duration above 39 h experience more severe neutropenia than those under 39 h. Prospective studies are needed to verify this threshold.

Optimized Dosing: The Next Step in Precision Medicine in Non-Small-Cell Lung Cancer

In oncology, and especially in the treatment of non-small-cell lung cancer (NSCLC), dose optimization is often a neglected part of precision medicine. Many drugs are still being administered in "one dose fits all" regimens or based on parameters that are often only minor determinants for systemic exposure. These dosing approaches often introduce additional pharmacokinetic variability and do not add to treatment outcomes. Fortunately, pharmacological knowledge is increasing, providing valuable information regarding the potential of, for example, therapeutic drug monitoring. This article focuses on the evidence for the most promising and easily implemented optimized dosing approaches for the small-molecule inhibitors, chemotherapeutic agents, and monoclonal antibodies as treatment options currently approved for NSCLC. Despite limitations such as investigations having been conducted in oncological diseases other than NSCLC or the retrospective origin of many analyses, an alternative dosing regimen could be beneficial for treatment outcomes, prescriber convenience, or financial burden on healthcare systems. This review of the literature provides recommendations on the implementation of dose optimization and advice regarding promising strategies that deserve further research in NSCLC.

Feasibility of pharmacometabolomics to identify potential predictors of paclitaxel pharmacokinetic variability

PURPOSE

Paclitaxel is a commonly used chemotherapy drug with substantial variability in pharmacokinetics (PK) that affects treatment efficacy and toxicity. Pharmacometabolomic signatures that explain PK variability could be used to individualize dosing to improve therapeutic outcomes. The objective of this study was to identify pretreatment metabolites or metabolomic signatures that explain variability in paclitaxel PK.

METHODS

This analysis was conducted using data previously collected on a prospective observational study of 48 patients with breast cancer receiving weekly 80 mg/m² paclitaxel infusions. Paclitaxel plasma concentrations were measured during the first infusion to estimate paclitaxel time above threshold (T_c>0.05) and maximum concentration (C_max). Metabolites measured in pretreatment whole blood by nuclear magnetic resonance spectrometry were analyzed for an association with T_c>0.05 and C_max using Pearson correlation followed by stepwise linear regression.

RESULTS

Pretreatment creatinine, glucose, and lysine concentrations were positively correlated with T_c>0.05, while pretreatment betaine was negatively correlated and lactate was positively correlated with C_max (all uncorrected p < 0.05). After stepwise elimination, creatinine was associated with T_c>0.05, while betaine and lactate were associated with C_max (all p < 0.05).

CONCLUSION

This study identified pretreatment metabolites that may be associated with paclitaxel PK variability demonstrating feasibility of a pharmacometabolomics approach for understanding paclitaxel PK. However, identification of more robust pharmacometabolomic predictors will be required for broad and routine application for the clinical dosing of paclitaxel.

Exploring pharmacogenetics of paclitaxel- and docetaxel-induced peripheral neuropathy by evaluating the direct pharmacogenetic-pharmacokinetic and pharmacokinetic-neuropathy relationships

Introduction: Peripheral neuropathy (PN) is an adverse effect of several classes of chemotherapy including the taxanes. Predictive PN biomarkers could inform individualized taxane treatment to reduce PN and enhance therapeutic outcomes. Pharmacogenetics studies of taxane-induced PN have focused on genes involved in pharmacokinetics, including enzymes and transporters. Contradictory findings from these studies prevent translation of genetic biomarkers into clinical practice. Areas covered: This review discusses the progress toward identifying pharmacogenetic predictors of PN by assessing the evidence for two independent associations; the effect of pharmacogenetics on taxane pharmacokinetics and the evidence that taxane pharmacokinetics affects PN. Assessing these direct relationships allows the reader to understand the progress toward individualized taxane treatment and future research opportunities. Expert opinion: Paclitaxel pharmacokinetics is a major determinant of PN. Additional clinical trials are needed to confirm the clinical benefit of individualized dosing to achieve target paclitaxel exposure. Genetics does not meaningfully contribute to paclitaxel pharmacokinetics and may not be useful to inform dosing. However, genetics may contribute to PN sensitivity and could be useful for estimating patients' optimal paclitaxel exposure. For docetaxel, genetics has not been demonstrated to have a meaningful effect on pharmacokinetics and there is no evidence that pharmacokinetics determines PN.

Does Older Age Lead to Higher Risk for Neutropenia in Patients Treated with Paclitaxel?

PURPOSE

There is ongoing concern regarding increased toxicity from paclitaxel in elderly patients, particularly of severe neutropenia. Yet, data so far is controversial and this concern is not supported by a clinically relevant age-dependent difference in pharmacokinetics (PK) of paclitaxel. This study assessed whether age is associated with increased risk for paclitaxel-induced neutropenia.

METHODS

Paclitaxel plasma concentration-time data, pooled from multiple different studies, was combined with available respective neutrophil count data during the first treatment cycle. Paclitaxel pharmacokinetic-pharmacodynamic (PK-PD) data was modeled using a non-linear mixed effects approach and a semiphysiological neutropenia model, where systemic paclitaxel exposure was linked to reduced proliferation of neutrophils. The impact of age was evaluated on relevant variables in the model, using a significance threshold of p < 0.005.

RESULTS

Paclitaxel PK-PD data was evaluated from 300 patients, with a median age of 65 years (range 23-84 years), containing 116 patients ≥70 years (39%). First cycle neutrophil counts were adequately described by a threshold effect model of paclitaxel on the proliferation rate of neutrophils. Age as a continuous or dichotomous variable (≥70 versus <70 years) did not significantly impact sensitivity of the bone marrow to paclitaxel nor the average maturation time of neutrophils (both p > 0.005), causing a decline in the respective interindividual variability of <1%.

CONCLUSION

Results from this large retrospective patient cohort do not suggest elderly patients to be at an increased risk of developing paclitaxel-associated neutropenia during the first treatment cycle. Reflexive dose reductions of paclitaxel in elderly patients are unlikely to improve the risk of severe neutropenia and may be deleterious.