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Chapter 1A: Drug Action
Terms in this set (138)
The phase that, when taking medications orally, the drug becomes a solution so that it can cross the biologic membrane. This is the FIRST phase of drug action.
What % of drugs are taken by mouth?
When the drug is adminstered parenterally by subQ, IM, or IV
When doesn't the Pharmaceutic Phase exist?
Disentegration and Dissolution
What are the 2 phases in the Pharmaceutic Phase?
The breakdown of a tablet into smaller particles
The dissolving of the smaller particles in the GI fluid before absorption
Are fillers and inert substances, that are used in drug preparation to allow the drug to take on a particular size and shape and to enhance drug dissolution
The ions Potassium and Sodium (K and Na)
EX: Penicillin is poorly absorbed, so these additives help
Which additives can increase the absorbability of the drug?
Rate of Dissolution
The time it takes the drug to disentegrate and dissolve to become available for the body to absorb it
-Drugs in liquid form
-Drugs with a pH of 1 or 2 (acidic rather than alkaline b/c alkaline drugs have difficulty crossing cell membrane barriers)
What conditions allow for a faster absorption time?
The very young and the old
Who has less gastric acidity?
A tablet for oral use coated with materials that do not dissolve in stomach; coating dissolves in the intestine where absorption takes place---their effect may be delayed in onset
The study of what happens to the drug; how the drug is absorbed or excreted by the body
***Absorption, distribution, metabolism, excretion.
Process in which nutrients from digested food are taken into the body
Into the surface area of the small intestine through the action of the extensive mucosal villi
Where are most oral drugs absorbed?
If the villi are decreased in number because of the disease, drug effect, or the removal of the small intestine
When can absorption be reduced?
Protein-based drugs (insulin, growth hormones)
What type of drugs are destroyed in the small intestine by digestive enzymes?
Occurs mostly by diffusion (movement from higher concentration to lower concentration). With the process of diffusion, the drug does not require energy to move across the membrane.
Requires a carrier such as an enzyme or protein to move the drug against a concentration gradient. Energy is required for active absorption.
Cellular "drinking"; a type of endocytosis in which the cell takes fluid and dissolved solutes into small membranous vesicles.
Lipid (fat) and Protein, meaning lipid soluble drugs pass rapidly through the GI membrane
What is the GI membrane mostly composed of?
A carrier, either an enzyme or protein
What do water-soluble drugs need to pass through the membrane?
If they are nonionized (have no positive or negative charge)
When do large particles pass through the cell membrane?
Weak acid drugs (aspirin)
What kinds of drugs are less ionized in the stomach, therefore passing through the stomach lining easily and rapidly?
Their gastric secretions have a higher pH (alkaline)
What is special about an infant's gastric secretions?
An acidic environment
What do drugs such as calcium carbonate and many antifungals need to achieve greater drug absorption?
What is something that stimulates the production of gastric acid?
A large oral dose of penicillin is needed to offset the partial dose loss
If an acid, such as hydrochloric acid, can destroy some drugs (such as penicillin G), what must be done?
Parenteral drugs, eyedrops, eardrops, nasal sprays, respiratory inhalants, transdermal drugs, sublingual drugs
What drugs do not pass through the GI tract or liver?
Drugs that are lipid soluble and nonionized are absorbed faster than water-soluble and ionized drugs
Which drugs are absorbed the fastest?
Blood flow, pain, stress, hunger, fasting, food, and pH
What factors can afffect drug absorption?
In muscles that have more blood vessels (deltoids) than those that have fewer (gluteals) and subcutaneous tissue
Where (given IM) are drugs absorbed faster?
They pass from the intestinal lumen to the liver via the portal vein, which metabolizes some drugs to an inactive form that may then be excreted, thus reducing the amount of the active drug
What happens to the drugs that do not go directly into the systemic circulation following oral absorption?
A phenomenon in which drugs given orally are carried directly to the liver after absorption, where they may be largely inactivated by liver enzymes before they can enter the general circulation; oral drugs frequently are given in higher doses than drugs given by other routes because of this early breakdown
Lidocaine and some nitroglycerins because they have extensive first-pass metabolism and therefore most of the dose would be destroyed.
Which drugs are not given orally because of the First-pass Effect?
What is the term for the proportion of a drug that reaches systemic circulation?
After absorption and the first-pass metabolism---always less than 100%---but iv route is 100%
When does bioavailability occur for the oral route of drug administration?
20% to 40%--to obtain desired effect the oral dose could be higher than the drug dose for IV use
What is the bioavailability for for oral drugs that have a first-pass hepatic metabolism?
Factors that alter bioavailability
1. The drug form. 2. Route of administration. 3. GI mucosa and motility. 4. Food and other drugs. 5. Changes in liver metabolism caused by liver dysfunction or inadequate hepatic blood flow.
When does drug toxicity occur?
After a prolonged intake of medication or when a medication accumulates in the blood---because rapid absorption increases the bioavailability
The process by which drugs become available to body fluids and body tissues---is influenced by blood flow, the drug's affinity to tissue, and the protein binding effect
When drugs bound to protein (mostly albumin). The portion of the drug that is unbound is free active drug. The portion that is bound is inactive because it is not available to receptors. When free drug in circulation decreases, then more bound drug is released from the protein to maintain the balance of free drug.
Volume of Drug Distribution (Vd)---drugs with a larger volume of drug distribution have a longer half-life and stay in the body longer
What is dependent on drug dose and its concentration in the body?
Highly Protein-Bound Drugs
Drugs greater than 89% bound to protein
Moderately Highly Protein-Bound Drugs
61% to 89%
Moderately Protein-Bound Drugs
30% to 60%
Low Protein-Bound Drugs
Less than 30%
Drugs not bound to protein; are active and can cause pharmacologic response
More bound drug is released from the protein to maintain balance of the free drug. Drugs bound to proteins cannot leave the systemic circulation to get to the site of action, which is why only free drug is active.
As the free drug in circulation decreases...
They compete for protein-binding sites, thus causing mor efree drug to be released into the circulation---causing drug accumulation and possible drug toxicity. Also, a low serum protein level decreases the number of protein-binding sites and can cause an increase in the amount of free drug in the plasma, possibly causing drug toxicity.
What happens when 2 highly protein-bound drugs are given concurrently?
According to the % in which the drug binds to protein
How is drug dose prescribed?
Patients with Liver or Kidney disease who are malnourished---leads to fewer protein-binding sites, leading to excess free drug and drug toxicity
Who may have an abnormally low serum albumin level?
Who is more likely to have hypoalbuminemia?
Excessive loss or reduced synthesis of albumin
Excess free or unbound drugs go to nonspecific tissue binding sites until needed and excess free drug in the circulation does not occur---a decreased drug dose is needed as there is not as much protein circulated for the drug to bind to
What happens when some health conditions result in a low serum protein level?
Most anticonvulsants bind to?
Most antidysrhythmics (lidocaine, quinidine) bind to?
Check the protein-binding percentage of all drugs administered---also check the patient's plasma protein and albumin levels, because a decrease in plasma protein (albumin) decreases protein-binding sites, permitting more free drug in circulation
What can a nurse do to prevent drug toxicity?
Abscesses, exudates, body glands, and tumors---antibiotics do not distribute well at these sites
***Also some drugs can accumulate in fat, bone, liver, muscle, and eye tissues
What can hinder drug distribution?
Blood-Brain Barrier (BBB)
Protective speration between blood and brain cells. This makes it difficult for substance (such as anticancer drugs) to penetrate capillary walls and enter the brain. Highly lipid soluble drugs can cross this. Drugs not bound to proteins and are not lipid soluble cannot cross this, which makes it difficult to distribute the drug.
The process by which the body inactivates or biotransforms drugs---liver is primary site
Inactivated by liver enzymes and are then converted or transformed by hepatic enzymes to inactive metabolites or water-soluble substances for excretion
How are most drugs broken down in the liver?
The liver metabolizes the lipid-soluble drug substance to a water-soluble substance for renal excretion. However, some drugs are transformed into active metabolites, causing an increased pharmacological response.
Because a large % of drugs are lipid soluble, what does the liver do?
By inhibiting metabolizing enzymes in the liver
How can liver diseases cause drug toxicity?
Half-Life of a Drug
The time it takes for half of the drug concentration to be eliminated (metabolized). For example a drug is 500mg, and the half life is 3hrs to eliminate 250mg, and another 3hrs. to eliminate 125mg, and so on.
Routes through which drugs can leave the body include (1) kidneys (2) lungs (3) bile (4) skin. In most cases, drug metabolized prior to elimination by the liver.
Filter free unbound drugs, water-soluble drugs, and drugs that are unchanged
What do the kidneys do?
Eliminate volatile drug substances and products metabolized to CO2 and H20
What do the lungs do?
Urine pH---varies from 4.5 to 8
Influences drug excretion
Promotes elimination of weak base drugs
Promotes elimination of weak acid drugs (aspirin)---of overdose on aspirin, patient takes sodium bicarbonate to change urine pH to alkaline to promote excretion, cranberry juice can also inhibi eliminaition of aspirin
If results in decreased glomerular filtration rate (GFR) or decreased renal tubular secretion, drug excretion is slowed or impaired, causing drug accumulation, also a decrease in blood flow to kidneys can alter drug excretion
Excretions in patient with Kidney Disease
Measurement of the rate at which creatinine is cleared from the blood by the kidney
Waste product of muscle metabolism, filtered out of the blood by the kidneys and excreted in urine
Blood Urea Nitrogen (BUN)
Which blood test is commonly used to evaluate kidney function?
lower values b/c of decreased muscle mass
CLcr values in older adult and female patients
In an increase in serum creatinine levels and a decrease in urine creatinine clearance
A decrease in GFR results?
Drug dosage likewise may need to be decreased (possibly in older adults or as a result of kidney disorders)
When creatinine clearance is decreased?
The process by which a medication works on the body.
Primary/Secondary effects or both
What can drug response cause?
The effect that is DESIRABLE
The effect that can be DESIRABLE or UNDESIRABLE
The principle that that the effect of a certain chemical on an individual depends on the dose or concentration of that chemical
The largest effect that a drug can produce
Onset of Action
The time MEC is reached and the response occurs
Occurs when the drug reaches its highest blood or plasma concentration.
Duration of Action
The length of time the concentration of a drug in the blood or tissues is sufficient to elicit a response.
Evaluates three parameters of drug action: the onset of drug action, peak action, and duration of action.
Theory that drugs act through receptors by binding to the receptor to produce or prevent a response
Meds have to bind with...which are proteins found in nature, found in cell membranes
Drug-Binding Sites! Found primarily on Proteins, Glycoproteins, Proteolipids, and Enzymes
Before a drug enters a bacterial cell it must first bind to proteins on the surface of the cell; these proteins are called
Four families including (1) kinase-linked receptors (2) ligand-gated ion channels, (3) G protein-coupled receptor systems, and (4) nuclear receptors
Site at which drugs bind
Drugs bind to the cell surface, this activates the enzyme (inside the cell), and a response is initiated
Ligand-gated ion channels
A protein pore in the plasma membrane that opens or closes in response to a chemical signal, allowing or blocking the flow of specific ions.
G protein-coupled receptor systems
A large family of integral membrane proteins involved in signal transduction. They have 7 membrane-spanning alpha-helices. A signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein.
Found in the cell nucleus (not on the surface) of the cell membrane. Activation of receptors through the transcription factors is prolonged. With the first three receptor groups, activation of the receptors is rapid
The drugs that mimic neurotransmitters; produce a response
Drugs that block neurotransmitters; block a response
By the inhibitory action of the drug concentration on the receptor site
How can the effects of an antagonist be determined?
Is the antagonist drug concentration required to inhibit 50% of the maximum biological response
Located in the bladder, heart, blood vessels, stomach, bronchi, and eyes
Drugs that affect various sites and have properties of non-specificity---such as Bethanechol
A patient is brought to the Emergency Department after a motor vehicle accident. The patient is diagnosed with multiple injuries including a bladder injury. The patient is taken to surgery and develops a nonobstructive postoperative urinary retention. What drug would the nurse expect to be ordered for this patient?
Drugs that affect various receptors or have properties of non-selectivity---such as Chlorpromazine
By stimulating or inhibiting enzyme activity or hormone production
How might drugs that produce a response but do not act on a receptor act?
Categories of Drug Action
Stimulation, depression, replacement, inhibition or killing of organisms, and irritation.
Category of drug action in which the rate of cell activity or secretion from a gland increase or decrease
Cell activity and function of an organism are reduced
(Insulin) Replace essential body compounds
Interfere with bacterial cell growth (penicillin)
Laxatives do this to the wall of the colon, thus increasing peristalsis and defecation
Window between therapeutic effect and toxic effect
Therapeutic Dose (ED50)
Drug level required for clinical treatment of a particular infection
The point at which 50 percent of the test organisms show a negative effect from a toxin.
The amount of a drug necessary to produce death.
***The closer the ratio is to 1, the greater the danger of toxicity
Have a narrow margin of safety; drug dose might need adjustment and plasma (serum) levels must be monitored
If the ED is 25% or 75%...
A wide margin of safety and less danger of producing toxic effects---no need to monitor serum levels if this is the case
Drugs with a high TI have?
The dosages range or serum concentration that achieves the desired drug effects.
The Plasma Drug level should be monitored periodically, to avoid toxicity
If Therapeutic range is narrow...
Peak Drug Levels
Indicate the rate of absorption of the drug
Trough Drug Levels
Indicate the rate of elimination of the drug
Toxicity can occur
If the peak or trough level is too high...
No therapeutic effect is achieved
If the peak is too low...
Peak Drug Level
The highest plasma concentration of drug at a specific time---indicate the rate of absorption
Trough Drug Level
Is the lowest plasma concentration of a drug, and it measures the rate at which the drug is eliminated. Trough levels are drawn immediately before the next dose of drug is given, regardless of route administration.
The first dose of a drug that is larger than all subsequent doses of the same drug; used when it takes more drug to reach steady state than it does to maintain it.
The process of establishing the correct therapeutic dose for maintaining optimal function without toxic effects
Any effects of a medication other than the desired ones.
Reactions that are unexpected; however, potentially life threatening---DIFFERENT FROM SIDE EFFECTS
The effects due to excessive dosage or drug accumulation
Area of pharmacology that examines the role of genetics in drug response.
Alter the metabolism of the drug in converting its chemical form to an inert metabolite, thus enhancing or diminishing drug action
What can genetic factors do?
A progressive decrease in a person's responsiveness to a drug.
Rapid decrease in responsiveness to a drug, possible causes are narcotics barbiturates, laxatives, and psychotropic agents ADDICTION
A nonspecific improvement that occurs as a result of a person's expectations of change rather than as a direct result of any specific therapeutic treatment.
2. Protein-binding Percentage
3. Normal Side Effects
4. Therapeutic Ranges of the Drug
What must a nurse know to avoid TOXIC EFFECTS?
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