Ch 1 Drug action: Pharmaceutic, pharmacokinetic, and pharmacodynamic phases

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Pharmaceutic - Disintegration - Dissolution Pharmacokinetic - Absorption - Distribution - Metabolism (Biotransformation) - Excretion (Elimination) Pharmacodynamic - Dose Response and Maximal Efficacy - Onset, Peak, Duration of Action - Receptor Theory - Therapeutic Index/Therapeutic Range (Window) - Peak/Trough Levels - Loading Dose - Side Effects, Adverse, Toxic Effects - Pharmacogenetics - Tolerance/Tachyphylaxis

nursing responsibilities

a challenging aspect of nursing care; safely administer medications; promote medication therapeutic effects

80

Approximately ____% of drugs are taken by mouth.

pharmaceutic

1 of 3 phases for a drug taken by mouth; aka the dissolution phase (drug action); the drug becomes a solution so that it can cross the biologic membrane;
*when administered subQ/IM/IV, this phase is not present

uses disintegration and dissolution

disintegration

one of two parts of the pharmaceutic phase;
occurs when a tablet breaks down into smaller particles

dissolution

one of two parts of the pharmaceutic phase;
occurs after disintegration; dissolves the smaller particles of a tablet in the GI fluid before absorption

Tablet → Disintegration → Dissolution

pharmacokinetic

1 of 3 phases for a drug taken by mouth; aka 'what the body does to drugs'; composed of 4 processes: absorption, distribution, metabolism, excretion

pharmacodynamic

1 of 3 phases for a drug taken by mouth; aka 'what a drug does to the body'; the study of drug concentration and its effects on the body; where a biologic or physiologic response results
can produce primary or secondary physiologic effect or both

uses onset, peak, and duration to determine dosing

absorption

one of four processes within pharmacokinetics; is the movements of drug particles from the GI tract to body fluids by passive means, active means, or pinocytosis

GI membrane is composed mostly of lipids and protein, so:
water-solube drugs need a carrier
lipid-solube pass rapidly

first-pass effect

aka hepatic first pass; the process in which the drug passes to the liver first (via portal vein); examples include warfarin (coumadin) and morphine
Lidocaine is not given po because of first-pass effect, most of dose would be destroyed

bioavailability

a subcategory of absorption; is the percentage of the administered drug dose that reaches the systemic circulation

oral drugs: 20-40% of dose reach the systemic circulation; to obtain the desired drug effect, the oral dose could be 3-5x larger than the IV drug dose
IV: usually 100% reach systemic circulation

factors that alterbioavailability: drug form, route of administration, GI mucosa/motility, foods/other drugs, changes in liver metabolism (dysfunction or inadequate blood flow) → can increase bioavailability (only if drug is metab by liver)

distribution

second of four processes within pharmacokinetics; is the process by which the drug becomes available to body fluids/tissues; is influenced by blood flow, drug's affinity to the tissues, and the protein binding effect

protein-binding effect

part of distribution within pharmacokinetics; drugs are bound by varying degrees (percentages) to proteins as they are distributed in the plasma
<30% are low protein-bound
30-69% moderately protein-bound
61-89% moderately highly protein-bound
89+% are highly protein-bound drugs

*the portion of the drug that is bound is INACTIVE because it is not available to receptors
portion that remains unbound is free, active drug

free drugs

aka drugs not bound to protein; part of distribution within pharmacokinetics are active and can cause a pharmacologic response; as the amount in the circulation decreases, more bound drug is released from the protein to maintain the balance of free drug

when two highly protein-bound drugs are given concurrently, they compete for protein-binding sites → causes more free drug to be released into circulation → drug accumulation/ possible toxicity

pt with a low protein level (liver or kidney disease, or malnourished...lab = hypoalbuminemia) → decreases the protein binding sites → causes an increase in the amount of free drug in the plasma → possible drug overdose

avoid possible toxicity

nurse role: check the protein-binding percentage of all drugs administered to a client; check client's plasma protein and albumin levels

depending on the drug, the result could be life-threatening

volume of drug distribution

aka Vd; part of distribution within pharmacokinetics; is dependent on drug dose and its concentration in the body; the larger the Vd, the longer its half-life and its stay in the body

metabolism

aka biotransformation; third of four processes of pharmacokinetics; liver is the primary site, drugs metabolized in GI tract also

half-life

aka t½ of a drug; is the time it takes for one half of the drug concentration to be eliminated; metabolism and elimination affect t½ of a drug

example: liver or kidney dysfunction → half-life of the drug is prolonged/less drug is metabolized and eliminated

a drug goes through several half-lives before more than 90% of drug is eliminated
example: 650 mg of aspirin with a half-life of 3 hours. 3 hours for the first half-life ti eliminate 325 mg, 6 hours to eliminate 162 mg, etc to sixth half-life (18 hours) for 10 mg aspirin left in body

4-8 hours: short half-life
24+ hours: long half-life (digoxin at 36 hours), taking several days for the body to completely eliminate the drug

elimination

aka excretion; fourth of four processes of pharmacokinetics; main route is through the kidneys; other routes include bile, feces, lungs, saliva, sweat, and breast milk

lungs eliminate volatile drug substances and products metabolized to carbon dioxide and water

kidneys

main route of elimination; filter free unbound drugs, water-soluble drugs, and drugs that are unchanged; protein-bound drugs cannot be filtered through this route; once the drug is released from the protein, it is a free drug and is eventually excreted in the urine

dose response

part of the pharmacodynamic phase; is the relationship between the minimal versus the maximal amount of drug dose needed to produce the desired drug response; some clients respond to the lower dose, or need a high dose to elicit the desired response

maximal efficacy

part of the pharmacodynamic phase; the maximum drug effect;
example: morphine prescribed for pain relief; the maximum efficacy of morphine is greater than that of tylenol (regardless of how much tylenol is given)

onset

"______ of action"; part of the pharmacodynamic phase; is the time it takes to reach the minimum effective concentration after a drug is administered

peak

"______ action"; part of the pharmacodynamic phase; occurs when the drug reaches its highest blood or plasma concentration

duration

"_______ of action"; part of the pharmacodynamic phase; is the length of time the drug has a pharmacologic effect

receptor theory

part of the pharmacodynamic phase; most receptors (protein in nature) are found in cell membranes; drug-binding sites are primarily on proteins/glycoproteins/proteolipids/enzymes; drugs act through receptors by binding to the receptor to initiate a response or to prevent a response;

the activity of many drugs is determined by the ability of the drug to bind to a specific receptor; the better the drug fits at the receptor site, the more biologically active the drug is (key and lock)

agonist

drugs that produce a response

antagonist

drugs that block a response

nonspecific drug effect

effect where one receptors produces a variety of physiologic responses, depending on where in the body that receptor is located

example: cholinergic receptors are located in the bladder, heart, blood vessels, lungs, and eyes. a drug that stimulates/blocks these receptors affects all anatomic sites of location

nonspecific drugs

drugs that affect various sites; have properties of nonspecificity

example: Bethanechol (Urecholine) is prescribed for postop urinary retention (by increasing bladder contraction); it stimulates cholinergic receptors in bladder, but also in other sites as a result
→ HR decreases, BP decr, gastric acid incr., bronchioles constrict, pupils constrict

nonselective drugs

drugs that affect various receptors or have properties of nonselectivity

examples:
Chlorpromazine (Thorazine) acts on the norepinephrine, dopamine, acetylcholine, and histamine receptors → variety of responses

epinephrine acts on alpha1, alpha2, beta1, beta2 receptors

drug action

four categories of ______ _______ include
1) stimulation/depression - epinephrine to ↑HR
2) replacement - insulin
3) inhibition or killing of organisms - antibx
4) irritation - laxatives/GI system

therapeutic index

aka TI; estimates the margin of safety of a drug through the use of a ratio that measures the effective dose in 50% of persons or animals and the lethal dose in 50% of animals; the closer the ratio is to 1, the greater the danger of toxicity

TI = LD/ED

low therapeutic index: have a narrow margin of safety < monitor plasma (serum) drug levels
high therapeutic index: have a wide margin of safety

peak drug level

the highest plasma concentration of drug at a specific time; these levels indicate the rate of absorption; requested for drugs that have a narrow therapeutic index and are considered toxic

po: peak time could be 1-3 hours after administration
IV: peak could occurs 10 minutes after admin

a blood sample should be drawn at the proposed peak time, according to route of administration

trough drug level

the lowest plasma concentration of drug at a specific time; measures the rate at which the drug is eliminated; requested for drugs that have a narrow therapeutic index and are considered toxic

blood sample is drawn immediately before the next dose of drug is given, regardless of route of administration

loading dose

a large initial dose of drug; given to achieve an immediate drug response by rapid minimum effective concentration in the plasma

side effects

physiologic effects not related to desired drug effects

adverse reaction

more severe than side effects; they are a range of untoward effects (unintended/occurring at normal doses) of drugs that cause mild to severe side effects; always undesirable, must always be reported and documented (bc they represent variances from planned therapy)
includes anaphylaxis (cardiovasc collapse)

toxic effects

aka toxicity; can be identified by monitoring the plasma (serum) therapeutic range of the drug

pharmacogenetics

the scientific discipline studying how the effect of a drug action varies from a predicted drug response because of genetic factors/hereditary influence

tolerance

a decreased responsiveness over the course of therapy

tachyphylaxis

a rapid decrease in response to the drug

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