The development of a new drug involves different stages, during which a variety of data are produced.
The "discovery" stage involves the synthesis or isolation of new chemicals. Initial screening tests determine whether the new chemicals possess sufficient biological activity to be worthy of further investigation. The nature of pharmaceutical research has changed dramatically in the last twenty years with the application of the "rational drug design" method and the use of combinatorial chemistry. With discovery by design, scientists use knowledge about the causes of human disorders, the properties of drug compounds, and their action in the human organism to conceptualize the structure of an "ideal" molecule that is expected to restore the altered equilibrium. Laboratory chemists then search for substances whose molecular structures match as closely as possible the theoretical model (Gambardella, 1995, p. 23). This methodology reduces the cost of the "discovery" stage, but does not eliminate the need for bioassay, animal and other tests of the new drugs.
Once a promising new chemical is identified, its non-toxicity and efficacy must be confirmed. The testing procedures involve different stages and phases (see Box 1).
On the basis of the results of these tests, national authorities can assess whether to grant marketing authorization for a new chemical entity. All the safety and efficacy tests must normally be completed before the authority approves the product. The authority may also require additional clinical tests. In 1980, the duration of these studies varied from about 1 to 7 years and averaged slightly less than 3 years. This period has been significantly reduced since then (Raggett, 1996, p. 26).
Testing new drugs
In the preclinical stage, the new chemical entity (NCE) is tested in animals to assess its pharmacodynamic, phamacokinetic and toxicological profile. Results of these tests are studied carefully before tests in human beings are carried out.
Safety and Efficacy Testing
The types of tests, the procedures to be used, and the standards to be met to demonstrate safety and efficacy may vary among therapeutic classes and even among drugs for use within a therapeutic class. This stage includes different phases.
In Phase I chemical testing, a small group of healthy volunteers receive dosages of the investigational drug for a short period of time. The primary purpose is to look for evidence of toxicity or unexpected undesirable reactions, and to study the bioavailability and pharmacokinetics of the NCE/drug applied to patients.
Phase II of clinical testing has a similar purpose to phase I, but considering the therapeutic context. Its primary objective is to ascertain the effectiveness of the investigational drug.
Phase III clinical trials are conducted on a large member of patients; they often involve several hundred human subjects and are conducted for substantial periods. These tests are designed to determine the efficacy of the investigational drug and to uncover any unanticipated side effects that the drug may have, considering age and gender influence, drug interactions and specific dosage for different indications.
While the phase III trials are under way, long-term animal toxicity studies are undertaken to determine the effects of prolonged exposure and the effects on subsequent generations. The duration of the studies vary widely among therapeutic classes. For drugs that affect the reproductive system or that will be used over long periods of time, animal toxicity studies are typically expensive and lengthy.
In addition to test data, national authorities require information on the quantitative and qualitative composition and other attributes of the product, as well as on manufacturing methods.
Marketing approval is generally granted for a specific drug used for a specific therapy. Changing the composition of the drug, combining it with other drugs in a single product or selling the drug for a different therapeutic purpose requires new approval.