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A few useful drugs have been known since humans first began ingesting or injecting substances and recording the results (see The History of Pharmacology in Chapter 1), but the majority of agents in current use have been developed during the last 100 years using a variety of pharmacologic and toxicologic techniques. These new chemicals and the efforts to market them have in turn led to a variety of methods of legal regulation. This chapter describes the methods of new drug development and some aspects of drug regulation in the United States.

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The most common first steps in the development of a new drug are the discovery or synthesis of a potential new drug compound or the elucidation of a new drug target. When a new drug molecule is synthesized or discovered, subsequent steps seek an understanding of the drug's interactions with its biologic targets. Repeated application of this approach leads to compounds with increased efficacy, potency, and selectivity (Figure 5–1). In the United States, the safety and efficacy of drugs must be defined before marketing can be legally carried out. In addition to in vitro studies, relevant biologic effects, drug metabolism, pharmacokinetic profiles, and particularly an assessment of the relative safety of the drug must be characterized in vivo in animals before human drug trials can be started. With regulatory approval, human testing may then go forward (usually in three phases) before the drug is considered for approval for general use. A fourth phase of data gathering and safety monitoring is becoming increasingly important and follows after approval for marketing. Once approved, the great majority of drugs become available for use by any appropriately licensed practitioner. Highly toxic drugs that are nevertheless considered valuable in lethal diseases may be approved for restricted use by practitioners who have undergone special training in their use and who maintain detailed records.

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Figure 5–1
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The development and testing process required to bring a drug to market in the USA. Some of the requirements may be different for drugs used in life-threatening diseases (see text).

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Careful analysis indicates that a majority of new drugs originate in research carried out in public sector institutions (universities, research institutes). However, because of the economic investment required and the need to efficiently access and integrate multiple technologies, most new drugs are then developed in pharmaceutical companies. Enormous and increasing costs, with estimates from $150 million to several billion, are involved in the development of a single new drug that reaches the marketplace. Only 2 of 10 marketed drugs return their research and development (R&D) investments, thus providing considerable motivation to develop "blockbuster drugs." Thousands of compounds may be synthesized and hundreds of thousands tested from libraries of compounds for each successful new drug lead, which then frequently needs to be further optimized for reasons of potency, selectivity, drug metabolism, and dosing ...

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