The role of pharmacological profiling in safety assessment

The profiling of new drug candidates for general pharmacological properties requires a systematic examination of the functional effects of agents in a variety of in vitro and in vivo assays. Both the behavioral and physiological consequences of drug treatment are monitored in models of central nervous system, cardiovascular, autonomic, gastrointestinal, and renal functions. Broad functional profiling provides valuable information to the preclinical pharmacologist with respect to the selectivity of new agents and may serve to identify new and useful therapeutic indications of investigational drugs. At the same time, knowledge of the effects on these physiological systems can also play an important role in safety assessment. Pharmacological activity of a new agent that is both unintended and undesirable can be referred to as "pharmacological toxicity." In general, the spectrum of toxicities disclosed in pharmacological profiling includes a variety of acute functional or physiological effects which are not life-threatening and are readily reversible. On rare occasions, unanticipated and life-threatening pharmacological effects (e.g., convulsions, arrhythmias) are detected which can seriously detract from the usefulness of a new agent and may therefore deter the drug development process. It should also be noted that repeated exposure to acute pharmacological effects may lead to less obvious chronic findings, such as target organ effects or tumor formation in animals. The interpretation of pharmacological toxicity with respect to the safety profile of a new drug candidate is dependent not only upon the types of reactions observed and the doses at which they occur but also upon the nature of the effects elicited as to whether they represent expected extensions of the primary mechanism of action of a compound or constitute reactions unrelated to the primary pharmacological activity. The ultimate impact of pharmacological toxicity, as with all adverse findings in preclinical assessment, is dependent upon the projected therapeutic margin of safety as well as the risk-to-benefit ratio for new drug entities. In addition to supplementing the existing armamentarium of preclinical safety studies, pharmacological profiling can also play an important role in (1) the selection of new drug candidates with reduced toxic potential, (2) the design and conduct of preclinical toxicology studies, (3) the investigation of preclinical and clinical safety issues, and (4) the identification of potential functional effects to be monitored most closely in clinical trials of new drug entities.