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What are the three phases of drug action?
- Pharmaceutic
- Pharmacokinetic
- Pharmacodynamic
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exipients
Inert substances added to a drug to enhance absorption or for other reasons
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Who has a more acidic GI tract, an infant or an adult?
Adult
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Rate Limiting
The time it takes a drug to disintegrate and dissolve or to be ready for absorption.
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Why is it important NOTto crush enteric coated or beaded capsules or tablets?
Crushing will alter PLACE and TIME of absorption.
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What are the two most common reasons to take meds with food?
- Increase absorption
- Protect GI tract
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Discribe the pharmaceutic phase of drug action.
- Breakdown of med into small enough particles to be dissolved in solution.
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Describe the pharmacokinetic phase of drug action.
- The process of drug movement to achieve drug action:
- absorption
- distribution
- metabolism
- excretion
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What are the three modes of absorption?
- Passive absorption - Diffusion
- Active absorption - needs carrier (usually H2O sol)
- Pinocytosis - cell engulfs drug and carries into cell
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What kind of drugs ar absorbed faster?
Lipid soluble/non-ionized
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What factors affect drug absorption?
- Route
- GI mucosa
- First Pass Affect
- Blood flow
- pain
- stress
- hunger
- fasting
- food
- pH
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What is it called when a drug passes through the liver first, after absorption. (via portal vein)
Hepatic first pass or First pass effect
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What are three things that can happen to a drug in the liver?
- totally metabolized
- metabolized into something more active
- no effect
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Bioavailability
The amount (%) of a drug that reaches systemic circulation.
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Of the three proteins in the blood which can bind with meds, which is the most important?
Albumin
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What factors affect biovailability?
- Drug form
- Route of administration
- GI mucosa
- Food
- Other drugs ie Laxatives affect gastric emptying
- Changes in liver function
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Drug Distribution
Process by which a drug becomes available to body fluids and tissues.
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What happens to drugs in the liver?
- First Pass Effect: Initial Metabolism
- Lipid to H20 for excretion
- Some drugs transformed into active metabolites
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What factors affect drug distribution?
- Blood flow
- Drug's affinity to tissue
- Protein binding affect
- Lipid solubility
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What are the degrees of protein binding?
- Highly Protein Bound - > 89%
- Moderately Protein Bound - 61-89%
- Low Protein Bound - < 30%
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What should the nurse check to help guard against drug toxicity?
- ALB
- protein binding percentage of med
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Drug Metabolism
Breaking down of drugs
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Where does drug metabolism occur in the body?
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What happens to most drugs in the liver?
Inactivation by liver enzymes
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What is drug half-life (t1/2)?
Time it takes for 1/2 of drug concentration to be eliminated.
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What are 2 main factors that affect drug half-life?
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What is a long t1/2?
> 24 hr
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What is a short t1/2?
4 - 8 hr
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How many half-lives does it take to reach a steady state of drug concentration?
3 - 5
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What is the main route of drug elimination?
- Through the kidneys.
- Others include bile, lungs, feces, saliva, sweat
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How does urine pH affect excretion of drugs?
- Low pH promotes elim of weak base drugs
- High pH promotes elim of weak acid drugs
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What effect does kidney disease have on drug elimination?
decr GFR will decr elim (and incr concentration)
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What is the most accurate test used to determine renal function?
Creatinine clearance (CRCL)
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What is creatinine?
- A metabolic byproduct of muscle that is excreted by the kidneys. Compares creatinine with levels in urine with that in blood.
- 85-135 N
- < 60 renal impairment
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What is Pharmacodynamics?
The study of drug concentration and its effects on the body.
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Onset, Peak, and Duration of Action
- Onset of action - time to reach min effective conc. (MEC)
- Peak action - time when drug reaches its max blood conc.
- Duration of action - Length of time a drug has pharmacologic effect
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Where are most drug receptors?
- Cell mebrane
- Most are protein, glycoproteins, proteolipids, enzymes
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What are the names of the 4 receptor families?
- Kinase-linked receptors
- Ligand-gated ion channels
- G protein-gated ion channels
- Nuclear receptors
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Agonist
A drug that produces a response
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Antagonist
A drug that blocks a response
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Where are cholenergic receptors located and what do they do?
- Bladder, heart, blood vessels, lungs, eyes
- A drug that stimulates or blocks the cholenergic receoptors affects ALL anatomic sites of receptor locations
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Non-specific drugs
Drugs that evoke a variety of responses throughout the body.
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Non-slective drugs
Drugs that may act at different receptors
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What happens to drugs in the liver?
- First-Pass Effect: Initial metabolism
- Lipid to H20 soluble for excretion
- Some drugs transformed into active metabolites
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What are the 4 categories of drug action?
- Stimulation or depression
- Replacement
- Inhibition or kill organisms
- Irratation
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What can incr T1/2 of drugs?
Liver or renal impairment
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Therapeutic Index (TI)
- Estimates the margin of safety of a drug
- Low TI - DANGER!
- Monitor serum levels if low TI.
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Therapeutic Range (window)
Between MEC (min effec. conc.)and MTC (minimum toxic conc.)
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What do drug peak levels indicate?
Rate of absorption
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What do trough levels indicate?
Rate of elimination
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When is monitoring peak and trough levels indicated?
When drugs are given with a narrow TI
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Loading Dose
A large initial dose of drug given to rapidly achieve a MEC in plasma.
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Tolerance
Decr in responsiveness to a drug over time.
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Tachyphylaxis
Rapid decr in reponse to a drug
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What % of drugs are taken by mouth?
80%
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What kind of person is most likely to have less gastric acidity?
Very young and elderly
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What are the 4 processes of pharmacokinetiks?
- Adsorption
- Distribution
- Metabolism
- Elimination
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What is enteral admistration?
via oral or gastric mucosa, small intestine, rectum
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Bioavailability
Amount of drug that reaches circulation
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What is the Hepatic First Pass Effect?
Meds being metabolized before they are able to be distributed. This may produce metabolites equal to, less than or more than original drug.
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What are methods of topical administration?
skin, eyes, ears, nose, lungs
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What is parenteral administration?
Administration of meds by route other that ailmentary canal, IM, IV, SQ
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What stomach acidity helps to disintegrate and absorb drugs more rapidly?
1-2 (low)
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What does a nurse need to know about a drug to avoid toxic effects?
- T1/2
- protein binding %
- normal SE
- Therapeutic Range
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