How are new drugs disseminated in Japan? Analysis using the National Database of Health Insurance Claims of Japan.

Drug lag refers to the difference in the time of a new drug's approval in different countries; the dissemination of the new drug after approval within the countries is another problem. We examined the nationwide dissemination of 11 cancer drugs approved in Japan between 2011 and 2015 using the National Database of Health Insurance Claims data. We extracted data on the number of cancer drug prescriptions from 47 prefectures and associated demographic information, such as age and sex. Eight diabetes drugs were also examined for comparison. We observed a lag between the marketing approval date of the drugs and their first use. To further explore the rise and pattern of each drug's dissemination, we analyzed the trend of the cumulative number and total of new prescriptions for each prefecture. The results showed that the first month of new cancer drug prescriptions varied across prefectures. On average, they lagged by up to 2 months in the slowest prefectures, whereas the variation was almost nonexistent for diabetes drugs. The patterns of dissemination varied more among cancer drugs across the seven Japanese geographical regions. After the initial prescription, the number of prescriptions showed a steep rise for most cancer drugs, whereas the increase was gradual for diabetes drugs. In conclusion, the dissemination of cancer drugs had a greater lag time than that of diabetes drugs. Further research is needed to explore the causative factors to ensure that all effective drugs are equally accessible for those who need them.