What Makes a 'Good' Drug?
Effective molecules bind well to their target.
In addition to binding well, a ‘good’ drug has to fulfill additional parameters:
- Optimize its ability to target the intended site (selectivity)
- Remain attached to the site (affinity)
- Optimize its strength (potency, efficacy, effectiveness)
- Optimize safety (minimize side effects)
In other words, drugs cannot only be effective. They must be safe, relatively easy to manufacture, be easily absorbed in the blood, be stable in various conditions, among other things. These further categories are known as drug dynamics and drug kinetics.
Says Merck, one of the nation’s top tier drug development companies:
Other factors, such as whether the compound is absorbed through the intestinal wall and whether it is stable in body tissues and fluids, are also considered. These factors involve what the body does to the drug (drug kinetics) and what the drug does to the body (drug dynamics).
Ideally, a drug is
- Highly selective for its target site: It has little or no effect on other body systems—that is, it has minimal or no side effects (see Overview of Adverse Drug Reactions).
- Very potent and effective: Low doses can be used, even for disorders that are difficult to treat.
- Effective when taken by mouth (absorbed well from the digestive tract) for convenient use.
- Reasonably stable in body tissues and fluids: So ideally, one dose a day is adequate (shorter-acting drugs may be preferred for disorders that need only brief treatment).
Thus, the best drug candidates are those that are not only effective, but safe, easily absorbed in the skin, have metabolic and chemical stability, and are soluble in the bloodstream. This can explain why small molecule compounds that are effective in vitro in cells do not always prove to be the best tolerated by humans.