Medications (drugs) encompass a broad range of substances utilized to treat, mitigate, or prevent ailments, alleviate symptoms, or diagnose illnesses. Whether it's to manage pain, fight an infection, or regulate bodily functions; drugs play a vital role in healthcare. They can be administered in various ways, including ingestion, injection, inhalation, or absorption through the skin. Once inside the body, drugs interact with specific targets, altering normal physiological functions, understanding how drugs work is crucial for healthcare professionals and patients alike.
Pharmacokinetics: Absorption, Distribution, Metabolism, and Excretion (ADME)
1. Absorption: When a drug is ingested, it is absorbed into the bloodstream. Different routes of administration affect the rate and efficiency of absorption. For example:
Oral administration: Medicines taken orally are absorbed through the gastrointestinal tract. Factors such as the drug's solubility, formulation, and the presence of food can influence absorption.
Injection: Injected drugs enter the bloodstream more rapidly than those taken orally, as they bypass the digestive system.
Topical application: Drugs applied to the skin or mucous membranes are absorbed through those surfaces.
2. Distribution: After absorption, the drug is distributed throughout the body. This is influenced by factors such as blood flow, the drug's ability to pass through cell membranes, and tissue affinity. Drugs bind to plasma proteins, which affects their distribution. For example, fat-soluble drugs can be stored in fatty tissues.
3. Metabolism: Metabolism, or biotransformation, is the process by which the body chemically changes a drug into a form that can be more easily excreted. The liver primarily performs this function. The primary goal of drug metabolism is to make the drug more polar so that it can be excreted by the kidneys.
4. Excretion: Excretion is the removal of drugs from the body. The kidneys are the primary organs responsible for drug excretion, although drugs can also be excreted via bile, sweat, saliva, and breath.
Pharmacodynamics: How Drugs Interact with the Body
1. Drug Receptors: Most drugs exert their effects by binding to specific receptors. Receptors are proteins located on the surface of cells or within cells. When a drug binds to a receptor, it triggers a series of biochemical events that result in a physiological response. There are several types of drug receptors:
Agonists: Drugs that bind to a receptor and activate it, producing a biological response.
Antagonists: Drugs that bind to a receptor but do not activate it. Instead, they block the receptor, preventing other molecules from binding to it.
Partial agonists: Drugs that bind to a receptor and produce a partial response.
2. Enzyme Inhibition: Some drugs work by inhibiting enzymes, which are proteins that catalyze biochemical reactions in the body. By inhibiting specific enzymes, drugs can alter or block physiological processes. For example, angiotensin-converting enzyme (ACE) inhibitors are commonly used to treat high blood pressure by inhibiting the enzyme responsible for producing angiotensin II.
3. Ion Channels: Drugs can also interact with ion channels, which are pore-forming proteins located in the cell membrane. By opening or closing these channels, drugs can affect the flow of ions into or out of the cell, thereby altering cell function.
4. Transporter Proteins: Transporter proteins are responsible for moving molecules across cell membranes. Some drugs work by inhibiting or activating these transporter proteins, thereby affecting the movement of specific substances in and out of cells.
Factors Affecting Drug Response:
1. Age: The very young and the elderly may metabolize drugs differently than healthy adults.
2. Genetics: Genetic variations can affect how individuals respond to drugs.
3. Diet: Food can affect the absorption and metabolism of certain drugs.
4. Disease: Certain diseases can alter the way drugs are absorbed, distributed, metabolized, and excreted.
5. Drug Interactions: Some drugs can interact with each other, either enhancing or inhibiting their effects.
Examples of Drug Action in the Body
1. Analgesics (Pain Relievers): Analgesics work by blocking pain signals in the nervous system or by reducing inflammation. For example:
Acetaminophen: Reduces pain and fever by inhibiting the production of prostaglandins.
Nonsteroidal anti-inflammatory drugs (NSAIDs): Reduce pain and inflammation by inhibiting the enzyme cyclooxygenase (COX), which is involved in the production of prostaglandins.
2. Antibiotics: Antibiotics work by targeting bacterial cells while leaving human cells unharmed. They can interfere with bacterial cell walls, protein synthesis, or DNA replication, ultimately killing or inhibiting the growth of bacteria.
3. Antidepressants: Antidepressants work by increasing the levels of certain neurotransmitters in the brain, such as serotonin, norepinephrine, or dopamine.
4. Antihypertensives: Antihypertensive drugs work by relaxing blood vessels, reducing blood volume, or decreasing the force of the heart's contractions, all of which result in lower blood pressure.
Drugs exert their effects through pharmacokinetic and pharmacodynamic processes, involving absorption, distribution, metabolism, and excretion (ADME) as well as interactions with specific targets such as receptors, enzymes, ion channels, and transporter proteins. By comprehending these mechanisms, healthcare providers can optimize treatment outcomes while minimizing adverse effects in patients.
References:
What happens to medicine in your body? – biomedical beat blog (no date) National Institute of General Medical Sciences. Available at: https://biobeat.nigms.nih.gov/2023/09/what-happens-to-medicine-in-your-body/ (Accessed: 24 April 2024).
-Written by Sohni Tagore
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