CH 2 - Basics of Pharmacology (Watkins)

Absorption

is the process by which a substance moves into the bloodstream from the site where it was administered. A drug can be administered in one of two ways: (1) enterally, which means the drug is given directly into the gastrointestinal (GI) system orally, rectally, or through a tube entering this system; or (2) parenterally, by all other routes that do not touch the GI system.

• medication is absorption depends on how it is administered and whether it is topical (act locally) or systemic (act on one or more body systems)

Adverse reaction

is a severe side effect that can cause severe harm or death, such as hallucinations, hypotension, or anaphylactic shock. An example is airway swelling.

Agonist

when it is taken with another drug so the two can work together

Antagonist

drugs do the opposite by rendering another drug less effective.

Bioavailability

how much of the drug is absorbed for use

Biotransformation or Metabolism

means that the medication is chemically transformed to a less active or inactive form, called a metabolite.

• The liver (does most of the work), kidneys, and intestines metabolize drugs

distribution

The second phase in the drug cycle is ____________, which is the delivery of a drug to the appropriate site after the drug has been absorbed into the bloodstream.

• well-perfused organs such as the brain, heart, kidneys, and lungs receive the majority of the medication.

excretion

occurs when the extra medication and waste products are eliminated from the body. This process occurs mainly through the kidneys. ensures that drugs and their transformed products are removed and do not build up in the body (called cumulation). If buildup occurs, the patient may become very ill.

half-life

A medication’s ______________ is the length of time required for its concentration to decrease by one-half in the blood plasma and therefore affects its duration of potency.

idiosyncratic

a unique reaction to any drug

• may not have occurred in clinical trials because it is so rare

pharmacokinetics

study of how the body absorbs, distributes, and excretes drugs (the drug cycle)

receptors

All cells have numerous receptors that are activated or blocked by messengers to produce an effect. Think of a receptor as a lock and the messenger—in this case the medication—a key.

side effects

are usually mild, such as nausea, constipation, or sensitivity to light.

synergism

occurs when a drug combination provides a more potent effect than when each drug is taken separately

teratogenic

interferes with normal fetal development

toxic

too much can be _______ , or poisonous, to the patient.

The Drug Cycle

This cycle has four main phases:

• absorption (how the medication enters our bloodstream)

• distribution (how the medication travels to the appropriate site)

• metabolism or biotransformation (how our body breaks the medication down into usable components and waste products)

• excretion (how our body eliminates the extra medication and waste products)

Factors that may vary the absorption rate

• fat or lipid solubility

• pH

• Concentration of the medication

• length of contact

• age

• food

• depth of breathing

factors influencing the time it takes to complete the drug cycle

• therapeutic level

• potency

• interactions w/ other medicine

• route of administration

• health of the patients organs

specialized physiological “barriers”

densely packed cells that allow nutrients and certain chemicals, but not other substances, including medications, to pass from the blood through the tissue.

• Examples of these densely packed cells include the blood-brain barrier, the blood-testicular barrier, and the blood-placental barrier.

ototoxicity

result of hearing loss or balance

USP/NF

official source of medication information for drugs approved by the U.S.

• has two volumes; the first is written primarily for the prescriber, and the second is written in lay terms to make it easy for patients to understand.

Food and Drug Administration (FDA)

It is updated every 5 years, with frequent supplements. This publication provides standards for identification, quality, strength, and purity of substances

Physicians’ Desk Reference (PDR)

This text contains information about thousands of drugs and is indexed by trade name, generic name, classification, and manufacturer. Color photographs of most common drugs are included to help identify medications when patients are unsure about what they are taking.

Therapeutic level

refers to the point at which the drug has the optimum desired effect. Too little of the drug can be less than effective; too much can be toxic, or poisonous. Drugs are usually administered at the lowest dose possible to obtain therapeutic levels.