Dose Individualization of Pemetrexed - IMPROVE-II

Rationale: Pemetrexed is a multi-targeted folate antagonist, which is primarily indicated for the treatment of advanced non-small cell lung cancer (NSCLC) and mesothelioma. Dosing of cytotoxic agents like pemetrexed requires balancing the dual risk of sub-therapy and toxicity. Administration of pemetrexed to patients with a creatinine clearance \<45 ml/min is currently not advised. Pemetrexed is dosed based on body surface area (BSA), while renal function and dose are the sole determinants for systemic exposure. This causes 3 major issues: 1. In patients with renal dysfunction, BSA-based dosing may lead to haematological toxicity 2. Patients have to discontinue treatment due to declining renal function, and are withheld effective treatment 3. Even in patients with adequate renal function (GFR \>45 ml/min) treatment may be improved by individualized dosing based on renal function, resulting in less toxicity. Also, BSA-based dosing may lead to ineffective therapy in patients with above average renal function. The investigators aim to address these problems. Objective: The overall main objective is to develop a safe and effective individualized dosing regimen for pemetrexed. Study design: IMPROVE-II is an open label, double arm, randomized study to compare renal function-based dosing of pemetrexed versus BSA-based dosing on attainment of therapeutic exposure. Study population: IMPROVE-II includes 94 patients with NSCLC or mesothelioma that are eligible for pemetrexed treatment. Intervention: patients will be randomized in a 1:1 ratio to Arm A (BSA-based dosing according drug label) or to Arm B (renal function based dosing). The renal function-based dose will be calculated to reach the target AUC. Pharmacokinetic assessment after administration will be performed after the first pemetrexed dose in both arms. Main study endpoints: The fraction (percentage) of patients with attainment of therapeutic exposure with BSA-based dosing versus renal function-based dosing. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The investigators consider the extra burden from participating in the planned studies limited. The extra interventions compared to routine care, consist of sampling extra blood. The pharmacokinetic assessments require placement of one additional intravenous catheter. To ensure minimal impact of study participation on daily life, a limited sampling strategy will be used. Patients may benefit from participating in IMPROVE I and -II, as they will be treated with a potentially safe and effective drug that is dosed individually, which prevents toxic exposure.