Changes in prescription patterns and drug costs following the launch of generic pemetrexed products: a retrospective study in Japan.

Abstract

BACKGROUND: Pemetrexed (PEM) is an antimetabolite antineoplastic agent that has been available in generic form in Japan since June 2021. As a hazardous drug (HD), the use of a closed-system transfer device (CSTD) is recommended. Some generics, including 800-mg vials, are not available for the original product; however, changes in prescribing patterns following the introduction of generics remain unclear. This study examined the prescription volume and drug costs of PEM before and after the launch of generics. METHODS: Clinical data were analyzed using the MDV analyzer® (Medical Data Vision Co., Ltd.). Patients who received PEM between June 2020 and May 2023 were enrolled. Study outcomes included the number of prescriptions, dose per prescription, drug costs (yen), and vials used. Data were categorized into original PEM, generics without 800-mg vials, and generics with 800-mg vials. RESULTS: A total of 89,078 prescriptions were analyzed. In the last 3 months of the study, prescription counts (proportions) were 966 (14.8%) for original PEM, 404 (6.2%) for generics without 800-mg vials, and 5,155 (79.0%) for generics with 800-mg vials. The mean prescribed doses were 773.2 mg, 789.6 mg, and 777.8 mg, respectively. The mean drug costs were 193,683 yen, 84,583 yen, and 78,770 yen, respectively. The average numbers of vials per prescription, calculated from the total number of vials and prescriptions, were 3.4, 3.5, and 2.3, respectively, indicating that generics with 800-mg vials were associated with approximately one fewer vial per prescription compared to other groups. CONCLUSIONS: After the introduction of generics, a shift in prescription patterns was observed, with an increasing proportion of products with 800-mg vials. Although mean prescribed doses were similar across groups, generics with 800-mg vials appeared to be more cost-effective and utilized fewer vials per prescription within this study population. The reduction in the number of vials suggests a potential decrease in CSTD use, which could contribute to lowering material costs. These results provide important insight for future drug development and for strategies aimed at reducing healthcare expenditures, including material costs.