Table 1.

Microdose study elements that inform radiopharmaceutical phase 1 or phase 0 trials.

Microdose Study Element	Phase 1 trial design impact	Phase 0 trial design impact
Primary biodistribution endpoint	Sets dosage recommended for phase 1 study	Sets dosage providing target modulation
Biomarker assay	Adds exploratory pharmacodynamic assay	Adds integral pharmacodynamic endpoint
Bioimaging or dosimetry	Adds exploratory pharmacodynamic assay	Adds integrated pharmacodynamic endpoint
Dose dilution sub-study	Identifies CTCAE toxicity of special interest	Sets dosage for desired target modulation
Dose administration	Rationalizes multiple cycle administration	Justifies single cycle administration
Single species safety evaluation	Rationalizes 15–18 patient study	Justifies 8–10 subject study
Pharmacokinetics	Provides batched blood sampling frequency	Provides real-time blood sampling frequency

CTCAE, Common Terminology Criteria for Adverse Events (current version).