<Tr> <Td> Phase II </Td> <Td> Testing of drug on patients to assess efficacy and side effects </Td> <Td> therapeutic dose </Td> <Td> clinical researcher </Td> <Td> 100--300 patients with specific diseases </Td> <Td> approximately 33% </Td> <Td> determines whether drug can have any efficacy; at this point, the drug is not presumed to have any therapeutic effect whatsoever </Td> </Tr> <Tr> <Td> Phase III </Td> <Td> Testing of drug on patients to assess efficacy, effectiveness and safety </Td> <Td> therapeutic dose </Td> <Td> clinical researcher and personal physician </Td> <Td> 300--3,000 patients with specific diseases </Td> <Td> 25--30% </Td> <Td> determines a drug's therapeutic effect; at this point, the drug is presumed to have some effect </Td> </Tr> <Tr> <Td> Phase IV </Td> <Td> Postmarketing surveillance--watching drug use in public </Td> <Td> therapeutic dose </Td> <Td> personal physician </Td> <Td> anyone seeking treatment from their physician </Td> <Td> N / A </Td> <Td> watch drug's long - term effects </Td> </Tr> <P> Before pharmaceutical companies start clinical trials on a drug, they conduct extensive pre-clinical studies . These involve in vitro (test tube or cell culture) and in vivo (animal) experiments using wide - ranging doses of the study drug to obtain preliminary efficacy, toxicity and pharmacokinetic information . Such tests assist pharmaceutical companies to decide whether a drug candidate has scientific merit for further development as an investigational new drug . </P>

Difference between phase ii and iii clinical trials