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Author: Admin | 2025-04-28
Drugs affect only the rate at which existing biologic functions proceed. (See also Definition of Drug Dynamics.) Drugs do not change the basic nature of these functions or create new functions. For example, drugs can speed up or slow down the biochemical reactions that cause muscles to contract, kidney cells to regulate the volume of water and salts retained or eliminated by the body, glands to secrete substances (such as mucus, stomach acid, or insulin), and nerves to transmit messages.Drugs cannot restore structures or functions already damaged beyond repair by the body. This fundamental limitation of drug action underlies much of the current frustration in trying to treat tissue-destroying or degenerative diseases such as heart failure, arthritis, muscular dystrophy, multiple sclerosis, Parkinson disease, and Alzheimer disease. Nonetheless, some drugs can help the body repair itself. For example, by stopping an infection, antibiotics can allow the body to repair damage caused by the infection.Some drugs are hormones, such as insulin, thyroid hormones, estrogens, or cortisol. They can be used to replace natural hormones that are missing from the body.Reversibility of Drug ActionMost interactions between a drug and a receptor or between a drug and an enzymeare reversible: After a while, the drug disengages, and the receptor or enzyme resumes normal function. Sometimes an interaction is largely irreversible, and the drug’s effect persists until the body manufactures more enzyme. For example, omeprazole, a drug used in the management of gastroesophageal reflux and ulcers, irreversibly inhibits an enzyme involved in the secretion of stomach acid.Affinity and Intrinsic Activity of DrugsA drug’s action is affected by the quantity of drug that reaches the receptor and the degree of attraction (affinity) between it and its receptor on the cell’s surface. Once bound to their receptor, drugs vary in their ability to produce an effect (intrinsic
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