[Improvement of package insert CYP information for prescription drugs marketed in Japan].

In clinical practice, one drug is frequently used in combination with one or more other drugs, rather than as a sole regimen, and therefore healthcare providers need to carefully consider drug interactions. As mechanisms of drug interactions, metabolic enzymes of drugs are seen as one of the most likely interactive sites, where a majority of drugs are metabolized by cytochrome P450 (CYP). For this reason, providing appropriate information on CYP in package inserts is of grave importance. In fact, the package insert is the primary tool for supplying information on drugs to healthcare providers. The present study was designed to determine how many package inserts of prescription drugs marketed in Japan were providing CYP information. We searched the April 2003 version of "Drugs in Japan DB," which listed 2,022 prescription drugs, and found that only 239 package inserts (11.8%) mentioned CYP information and that only 194 (9.6%) specified CYP isozymes. To assess the improvement of package inserts, we searched "Drugs in Japan DB" from the January 2000 version to the April 2003 version. We found that CYP information had increased year by year (eg, 7.8-11.8% annually). For newly approved drugs, an analysis of the relationship between approval year and CYP information in package inserts (April 2003 version) revealed that recently approved drugs had more CYP information (eg, 45.5-51.3% of drugs in 1999-2002, compared to 6.8-26.1% in 1991-1996). A search for regulatory review documents for new drugs approved from 1999 to 2002 suggested that this recent improvement could be related to the increased number of studies identifying CYP isozymes involved in the metabolism or interaction with other drugs. Another reason for the recent improvement may be the fact that the guideline for package inserts for prescription drugs was revised in 1997, and the guidelines for drug interaction and pharmacokinetic studies were published between 1997 and 1999.