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DRUG ACTIONS—PHARMACODYNAMICS

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  358

2026-08-11

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DRUG ACTIONS—PHARMACODYNAMICS

The study of how drugs act in the body is called Pharmacodynamics. Certain organs in the body, such as the brain contain cells that have active sites called receptors. Drugs are designed to bind to a particular type of receptor. When the drug finds and binds to its receptor, the receptor causes the cell to fulfil a particular function or process. For example, when a drug binds to a certain receptor on the pancreas, insulin is secreted into the bloodstream. A drug that binds to a receptor and causes it to exert its function on the cell is called an agonist. Some drugs may bind to a receptor but not cause it to exert the action of the cell to which the receptor is attached. These substances are called antagonists. Antagonists can serve to block or reverse the actions of agonists. An example of this agonist/antagonist relationship can be found in heroin or other narcotics. Heroin is a powerful central nervous system (CNS) depressant. An overdose of heroin can cause death by depressing the CNS so much that respiration ceases and the person dies. A person who has such an overdose can be given Nalaxone, a heroin antagonist. Nalaxone will compete with heroin for the same receptor sites in the brain, but as an antagonist will not cause CNS depression. Determining the effective dose of a therapeutic drug can be a very complex process. It depends upon the person and his/ her physical condition and the severity of the illness being treated. The whole process is based upon knowledge of pharmacodynamics and the characteristics of the receptors for the drug being tried. A great deal of research continues today in the search for better antagonists for a wider variety of drugs, including alcohol. There are also drugs that cause a violent reaction in a person who has imbibed alcohol. These drugs are not antagonists; they are designed to prevent a person from drinking alcohol.