- Done on laboratory animals
- Good clinical practices (set of guidelines to be followed while conducting a clinical trial) is not applicable in this phase.
- Microdosing study
- Subtherapeutic dose applied on small group of healthy human volunteers
- Determines pharmacokinetics (especially bioavailability).
Investigational new drug (IND):
- Application to conduct a human study for a new drug
- IND is submitted between preclinical studies and phase 1.
- Small group of healthy human volunteers
- Pharmacokinetics & pharmacodynamics > Safety
- Dosing route
- Maximum tolerable dose
- Toxicity is best assessed in phase 1 (but overall assessed in all phases).
- Done on small group of patients
- Dosing range
- Maximum risk of drug failure
- Drug efficacy is first determined in phase 2.
- Large group of patients
- Best phase for determining drug efficacy & safety
- Confirm the actual dose.
New drug application (NDA):
- Application for marketing a new drug
- NDA is submitted between phase 3 & 4.
- Postmarketing surveillance
- Done on general population
- Detection of rare and chronic adverse effects
- Minimum duration: 2 years.