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EMT Prep

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Efficacy vs. Potency - Pharmacology - EMTprep.com

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Merck Manual, 2019

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NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version

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.

Most interactions between a drug and a receptor or between a drug and an enzyme are 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.

A 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 activity). A drug's affinity and intrinsic activity are determined by its chemical structure.

Drugs that activate receptors (agonists) must have both great affinity and intrinsic activity: They must bind effectively to their receptors, and the drug bound to its receptor (drug-receptor complex) must be capable of producing an effect in the targeted area. In contrast, drugs that block receptors (antagonists) must bind effectively but have little or no intrinsic activity because their function is to prevent an agonist from interacting with its receptors.

A drug's effects can be evaluated in terms of potency, efficacy, or effectiveness.

Potency (strength) refers to the amount of drug (usually expressed in milligrams) needed to produce an effect, such as relief of pain or reduction of blood pressure. For instance, if 5 milligrams of drug A relieves pain as effectively as 10 milligrams of drug B, drug A is twice as potent as drug B.

Efficacy is a drug's capacity to produce an effect (such as lowering blood pressure). For example, the diuretic furosemide eliminates much more salt and water through urine than does the diuretic hydrochlorothiazide. Thus, furosemide has greater efficacy than hydrochlorothiazide.

Effectiveness differs from efficacy in that it takes into account how well a drug works in real-world use. Often, a drug that is efficacious in clinical trials is not very effective in actual use. For example, a drug may have high efficacy in lowering blood pressure but may have low effectiveness because it causes so many side effects that people take it less often than they should or stop taking it entirely. Thus, effectiveness tends to be lower than efficacy.

Greater potency, efficacy, or effectiveness does not necessarily mean that one drug is preferable to another. When judging the relative merits of drugs for a person, doctors consider many factors, such as side effects, potential toxicity, duration of effect (which determines the number of doses needed each day), and cost.

Last full review/revision March 2017 by Abimbola Farinde, PhD, PharmD

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version

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Drug Action - Drugs - Merck Manuals Consumer Version

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NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version 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.

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Areo Saffarzadeh, 2012

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Pharmacokinetics for Students: Absorption, Distribution, Metabolism, and Elimination -Lect 1

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Khan Academy, 2019

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Circulatory system physiology | NCLEX-RN | Test prep | Khan Academy

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Your heart sits in the middle of your chest and pumps blood from about 4 weeks after conception until the day that you die. This little pump is the size of your clenched fist and it never stops. Watch these videos to learn more about how the heart works, blood flow in arteries and veins, blood pressure, and lymphatics.

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Khan Academy, 2019

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Circulatory system diseases | NCLEX-RN | Test prep | Khan Academy

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With the heart pumping 24/7, it's crucial that things flow smoothly (pun intended!). Unfortunately, this isn't always the case. The underlying reasons for circulatory system problems vary from your genes to your lifestyle. To combat this growing problem in the world, we need a better understanding of these diseases.

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Khan Academy, 2019

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Respiratory system physiology | NCLEX-RN | Test prep | Khan Academy

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With every inhale, air rushes through your windpipe to your lungs. After 20 to 30 branch points, oxygen diffuses into the liquid around the alveoli and slips into your blood. Carbon dioxide travels from the blood to the air and leaves the body when you exhale.

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Khan Academy, 2019

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Respiratory system diseases | NCLEX-RN | Test prep | Khan Academy

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Our lungs are composed of a bronchial tree (think of an upside down tree with millions of leaves), blood vessels bringing blood in and out, and a protein-rich fluid that forms a matrix holding everything together! If any part of this well-balanced organ isn't working properly, a person can be left feeling short of breath.

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Simple Nursing, 2013

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Respiratory Drugs: Memorization Tips for Nursing Students

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Khan Academy, 2019

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Renal system physiology | NCLEX-RN | Test prep | Khan Academy

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If you want to learn more about the renal system, then urine the right place (pun intended)! Every thirty minutes, your kidneys filter you entire blood supply and remove toxic wastes. These paired organs are key to maintaining electrolyte and water homeostasis in your body.

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Simple Nursing, 2013

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Diuretics *Part 3* PRECAUTIONS!!! (loop, thiazides, K+ sparin

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Khan Academy, 2019

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NCLEX-RN questions on pulmonary conditions 1

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A quiz for NCLEX-RN style questions related to the pulmonary conditions tutorial

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Khan Academy, 2019

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NCLEX-RN practice questions | Test prep | Khan Academy

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Learn for free about math, art, computer programming, economics, physics, chemistry, biology, medicine, finance, history, and more. Khan Academy is a nonprofit with the mission of providing a free, world-class education for anyone, anywhere.

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Learning Nurse, 2019

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Learning Nurse, 2019