RADIOISOTOPES

In recent years, new method called “microdose study” has been developed to directly investigate pharmacokinetics in the human body using a limited amount of ¹⁴C labeled candidate compounds which is less than 100 µg or 1％ of the dose that yields pharmacological effects. Drug development costs are expected to be dramatically decreased by this new method. Since the required abundance sensitivity of ¹⁴C analysis in the microdose studies is 10⁻¹⁰–10⁻¹², Accelerator Mass Spectrometry (AMS) is presently used for this purpose. However, the high cost and limited throughput in ¹⁴C analysis by AMS may prevent from wide expansion of the microdose studies to drug development. As an alternative method, we are developing ¹⁴C detection system based on Cavity Ring-Down Spectroscopy (CRDS) for microdose studies.