The compatibility of irinotecan hydrochloride injection (Topotecin® injection) was studied regarding changes in pH following the addition of 0.1N NaOH or 0.1N HC1 solution along with changes in external appearance, pH and contents of both irinotecan and admixed drugs following mixing with 20 kinds of other injections. Study on stability of the drug with a change in pH showed that irinotecan hydrochloride was stable under the acidic condition. Admixtures of irinotecan hydrochloride injection with each of the 20 kinds of the injections showed neither a change in external appearance nor a change in pH over a 24-h period under the study conditions.
With the admixture with Solu-Medrol® or Ipsilon S® pH was raised to more than 6.5, and the contents of irinotecan fell to 90% until 3-h after mixing. Accordingly, mixing with these injections should be avoided. However, there was no change in the content of irinotecan hydrochloride in the other admixtures except the two injections. This study suggests that the compatibility of irinotecan hydrochloride injection depends on the delactonization reaction of the drug. Mixing irinotecan hydrochloride with alkaline injections should be avoided. Notably, compatibility of irinotecan hydrochloride injection with other injections is predictable by observating the pH immediately after mixing.