Category: Formulation and Quality
Purpose: Pemetrexed, therapeutics for non-small cell lung cancer and pleural mesothelioma, is commonly provided as lyophilized injections, due to its extremely unstable property in solution. In general, pemetrexed is rapidly oxidized and this reaction is accelerated in aqueous solution. Although there are many studies for stability improvement of pemetrexed in solution, no critical factors for it were found. So, the purpose of this study is to investigate the factors that affect stability of pemetrexed in solution.
Methods: Pemetrexed disodium salt, D-mannitol, and each antioxidant (sodium sulfide, sodium sulfite, sodium metabisulfie, acetylcysteine, L-cysteine HCl, vitamin E TPGS, and monothioglycerol) were dissolved in water, and pH were adjusted to around 7.5. After 0.2 μm membrane filtration, it was loaded in a glass vial. The dissolved oxygen was removed and headspace air were replaced with nitrogen gas. The pemetrexed formulation was placed at various storage condition with box packaging to avoid light. During the proportion of antioxidants in the formulation kept maintaining, the effect of API concentration (12.5, 25, and 50 mg/mL), pH (6.0 ~ 8.5), dissolved oxygen (1 to 7 ppm), and headspace oxygen (1 to 11%) in vial on the stability of pemetrexed formulation were evaluated. Degradation products were measured by HPLC, and solution color was observed by spectrophotometer and visual inspection. The headspace oxygen concentration was measured using a non-destructive headspace oxygen analyzer. Additionally, the role of antioxidant was confirmed by quantifying the amount of antioxidant using HPLC and ICP-MS analysis.
Results: Many kinds of degradation products could be generated in pemetrexed solution through various degradation pathways. In this study, ketopemetrexed and oxidative dimer were mainly observed. These are generated when the pemetrexed reacts with oxygen. As control group, pemetrexed solution without antioxidant was stored at 60ºC for 3 weeks. In this group, oxidative dimers were increased significantly and color of the solution turned yellow. On the other hand, in pemetrexed formulation with antioxidant under same condition, the degradation products were reduced compared to the control group and there was no color change. To identify the critical factors of degradation products generation, serial comparative stability tests were performed. In this test, as the concentration of pemetrexed increased, degradation products decreased. And a narrow range of pH didn’t significantly affect formation of degradation products. But in the extreme acidic or alkali stressed condition, pemetrexed was easily degraded. To investigate the degree of oxidation of pemetrexed according to the oxygen concentration, samples containing dissolved oxygen of 1 to 7 ppm in the solution were prepared wherein amount of oxygen in the headspace of the vial was 1% to 11%. As a results, degradation products significantly increased and color of the solution turned to yellow in the group containing high oxygen concentration. On the contrary there was no color change in the low oxygen containing group and degradation products slightly increased. On the one hand, as a result of measuring the oxygen concentration in the headspace, the oxygen concentration was reduced from 11% to 3% because presumably pemetrexed or antioxidant consumed oxygen during oxidative reaction. It is also observed that amount of antioxidant decreasing during long-term stability test of pemetrexed formulation. This indicates that the antioxidant has reacted with oxygen in the formulation instead of pemetrexed.
Conclusion: In this study, various factors (pH, API concentration, and oxygen contents) affecting the stability of aqueous solution containing pemetrexed were evaluated. We found that antioxidants could reduce the oxidation of pemetrexed. And also, it seems that API concentration and pH were affected pemetrexed stability in solution. In particular, it has been confirmed that the amount of oxygen in the formulation has a significant effect on the stability of pemetrexed in aqueous solution. With all of this in consideration, final optimal formulation conditions (contain antioxidant, pH 7.5, and headspace oxygen below 0.5%) were established to overcome instability of pemetrexed in the solution. All the result showed that pemetrexed formulation considering formulation factors could be a promising way to develop stability enhanced pemetrexed injection.
Dong Han Won– Yongin-si, Kyonggi-do, Republic of Korea
Hwan Ho Kim– Yongin-si, Kyonggi-do, Republic of Korea
Hyung don Hwang– Yongin-si, Kyonggi-do, Republic of Korea
Jeong Woong Seo– Yongin-si, Kyonggi-do, Republic of Korea
Yu young Kim– Yongin-si, Kangwon-do, Republic of Korea
Yong Hwan Park– Yongin-si, Kyonggi-do, Republic of Korea
Sun-woo Jang– Yongin-si, Kyonggi-do, Republic of Korea