Identification of an unknown radionuclide by measuring the decrease in radioactivity.

See also Decay.

The dilution analysis is used to calculate the quantity of an unknown substance by addition of a radioactively marked substance with a well-known quantity and a well-known specific activity.

Different stages of the drug development and approval process in the USA, lead from preclinical trials (testing in animals), first application in humans through limited and broad clinical tests, to postmarketing studies.

	Years	Test Population	Purpose	Success Rate
Preclinical Testing	3.5	Laboratory and animal studies	Assess safety and biological activity	5,000 compounds evaluated
File IND at FDA
Phase I	1	20 to 80 healthy volunteers	Determine safety and dosage	5 enter trials
Phase II	2	100 to 300 patient volunteers	Evaluate effectiveness, look for side effects
Phase III	3	1000 to 3000 patient volunteers	Verify effectiveness, monitor adverse reactions from long-term use
File NDA at FDA
FDA	2.5	Review process / Approval		1 approved
	12 Total
Phase IV	Additional Post marketing testing required by FDA

By Dale E. Wierenga, Ph.D. and C. Robert Eaton
Office of Research and Development
Pharmaceutical Manufacturers Association

'In reviewing this report, it is important to keep in mind the realities of the drug discovery and development process. The U.S. system of new drug approvals is perhaps the most rigorous in the world. On average, it costs a company $359 million to get one new medicine from the laboratory to the pharmacist's shelf, according to a February 1993 report by the Congressional Office of Technology Assessment.'

See also Phase 1 2 3 4 Drug Trials, Clinical Trial, Food and Drug Administration, and European Medicines Agency.

(ECG) An electrocardiogram is a test that records a graph of electrical activity in the heart over time. An electrocardiogram is used in the diagnostic of heart abnormalities, abnormal cardiac rhythms (arrhythmias or dysrhythmias) and heart muscle damage.

The flare phenomenon is an increased activity uptake, seen in scintigraphic procedures in the early phases of therapy or due to healing processes.