The pharmacodynamics of a drug is the relationship between drug concentration at the site of action and pharmacological response. The dose–effect curve is an example of how drug concentration changes with respect to response.
The study of pharmacokinetics and pharmacodynamics is fundamental to medicine, as it helps explain why certain treatments work, how much to use, and how often to use them.
Pharmacokinetics provides a quantitative framework for understanding the process of drug absorption, distribution, localization in tissues, biotransformation (metabolism) and elimination from the body. Pharmacokinetic properties of a drug can be used to predict its disposition profile in different parts of the body over time: where it will go, how fast it will get there, and in what quantities. Pharmacokinetic principles are applied to drug design strategies in order to maximize bioavailability and minimize side-effects. Pharmacokinetic studies also provide information about the dynamic nature of body processes that may affect drug distribution over time (e.g., gastric emptying rate influencing oral absorption; cardiac output affecting tissue perfusion).
Pharmacodynamics is the study of how a drug affects an organism and its components, in contrast to pharmacokinetics, the study of how the organism affects the drug. These two disciplines often overlap, but some examples of questions in pharmacodynamics.
Pharmacokinetics describes what your body does to a drug whereas pharmacodynamics describes what a drug does to your body. Pharmacodynamics aims to predict therapeutic outcome from knowledge of drug concentration history and pharmacological properties.
Here are some phases of Drug discovery & development:
- Pre-Clinical Phase:
The pre-clinical phase includes research on the chemical composition of the drug and lab testing on animals. This phase can take up to 2 years to complete, depending on the complexity of the product.
- Investigational New Drug (IND) Application:
Once pre-clinical data is collected and analyzed, an Investigational New Drug (IND) application is submitted to the FDA for review and approval. The FDA can approve or deny an IND application within 30 days, however, if additional questions arise during that time frame, a clinical hold may be placed on the IND application. Once the questions are answered by the sponsor, usually within 60 days, the FDA will then decide whether or not to approve it. If approved, a clinical trial can begin.
- Clinical Trial Phases:
After an IND application is approved by the FDA, clinical trials begin in order to test the drug on humans in a controlled environment. Drugs must pass three phases of trials before they are submitted for approval to be sold to the public: Phase I trials involve 20-80 healthy volunteers who receive increasing doses of a drug until major side effects are observed; Phase II trials involve hundreds of patients with a specific disease
Drug discovery and development has a long history. The first drug, aspirin, was discovered in 1853 by Charles Frédéric Gerhardt. Aspirin is an anti-inflammatory drug that has been used in the treatment of fevers and pain for more than 100 years. Over the past 40 years, the complexity of drug development has increased manifolds, requiring preclinical testing, investigational new drug (IND) applications, and completed clinical testing before marketing approval from the FDA. Generally, new drug applications (NDAs) or biologics license applications (BLA) are reviewed comprehensively before approval, and then drug performance is resubmitted to regulatory agencies for post-marketing studies. The overarching goal is to bring more efficient and safer treatments to the patients as quickly as possible after a thorough medical evaluation.
