Background Pemetrexed (PEM) is administered over a long term to patients with non-squamous cell lung cancer as a maintenance therapy after platinum combination induction chemotherapy. Although decreased renal function owing to long-term PEM exposure has been reported, changes in the renal function of individual patients have not been reported. This study aimed to evaluate serum creatinine (Scr) in individual patients over time and determine whether long-term PEM exposure contributed to increased Scr. Methods A retrospective study was performed using 90 non-squamous cell lung cancer patients, who had received maintenance therapy with PEM ± bevacizumab (BEV) after carboplatin + PEM ± BEV therapy at the Sapporo Minami-Sanjo Hospital from February 2012 to February 2019. Using Scr at the start of induction chemotherapy as the baseline, we calculated the correlation coefficient (r) of the rate of Scr change in an individual patient and the number of treatment courses to divide patients into two groups for comparison: patients with + 0.4 < r ≦ + 1.0 and an observed positive correlation (the r+0.4< group), and patients with − 1.0 ≦ r ≦ + 0.4 and no observed positive correlation (the r+0.4≧ group). Results Statistically significant differences between the r+0.4< group and the r+0.4≧ group were observed for the following parameters: the median cumulative dose of PEM (interquartile range) [9100 (6365, 12,260) mg/body vs. 5600 (4140, 7440) mg/body, P < 0.01]; the number of patients taking nonsteroidal anti-inflammatory drugs at the start of treatment [15 patients (31%) vs. 3 patients (7%), P < 0.01]; and the median number of treatment courses starting from induction chemotherapy [11 (8, 14) courses vs. 8 (6, 11) courses, P < 0.01]. Next, the results of univariate and multivariate analyses demonstrated that the cumulative dose of PEM (≧ 7000 mg/body vs < 7000 mg/body, OR 2.40; 95% CI, 1.22–4.75, P = 0.01) was an independent explanatory variable of the r+0.4< group. Conclusions Long-term PEM exposure may induce chronic renal dysfunction. Hence, maintaining kidney function during PEM treatment by reducing the use of combination drugs and the risk of other renal dysfunctions, such as dehydration, may help patients continue therapy and contribute to their long-term survival.

Currently, various hyperphosphatemia drugs are administered orally to hemodialysis patients in order to lower serum phosphorus levels. However, it is known that medication adherence is poor, possibly due to greater pill burden taken each time and their complicated schedules. Therefore, large amounts of unused hyperphosphatemia drugs are likely to be leftover. The increase in leftover prescribed drugs leads to the unnecessary elevation of medical care costs. To date, however, the available information on leftover hyperphosphatemia drugs in hemodialysis outpatients is limited. In this study, we performed an interview survey of medication adherence to hyperphosphatemia drugs among 60 hemodialysis outpatients and evaluated the cost of the leftover drugs. Thirty-four patients showed good adherence. On the other hand, 19 patients self-adjusted to take hyperphosphatemia drugs according to their daily diet. When assessing the serum phosphorus levels for these patients over the past year, the values often exceeded the targeted range (3.5 6.0 mg/mL). Furthermore, 35 patients kept hyperphosphatemia drugs at their home. When estimating the cost derived from leftover drugs using the bootstrap method, main distribution of drug cost was shown to be in the range of 2000 to 2500 yen. This drug cost seemed to in part re‰ect preparation for an emergency. A serious problem was that 14 patients had previous experience in discarding hyperphosphatemia drugs. This study suggested that more appropriate pharmaceutical care according to each patient's situation is essential in improving phosphorus control in hemodialysis outpatients and in reducing the waste of medical resources.