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3 phases of drug action
- 1. pharmaceutic
- 2. pharmakinetic
- 3. pharmacodynamic
- Drug becomes a solution so that it can cross the biologic membrane. No pharmaceutic phase when drug is administered:
- *parenterally by subQ
- *intramuscular (IM)
- *intravenous (IV)
- Two phases: Disintegration: breakdown of tablet into smaller particles
- Dissolution: Dissolve in the GI fluid before absorbtion
- time it takes drug to disintegrate and dissolve to be come available for the body to absorb it.
- **Faster in acidic fluids (stomach)--slower for young and elderly b/c of decreased gastric acidity.
Resist disinteration in stomach until reach alkaline E of small intestine...delayed onset of effect. Don't crush!
Pharmacokinetic Phase=4 processes involved
- Metabolism (biotransformation)
First pass Effect (hepatic first pass)
Compare oral vs. IV routes
Factors that affect:
- % of drug dose that reaches systemic circulation
- Oral routes: bioavailability occurs after absorption and hepatic drug metabolism--so always less than 100%--sometimes only 20-30%, so oral drug dose is much higher than for IV route.
- IV Route=usually 100% bioavaillability
- 1. drug form, 2. route, 3. GI mcosa and motility 4. Food and other drugs 5. changes in liver metabolism caused by liver disfunction
Process by which drug becomes available to body fliuds and body tissues.
- % of drug that binds to proteins. Only drugs not bound can have pharmacologic effect (free drugs).
- Two drugs that are highly-bound to proteins compete for proteins and can thus have greater pharm effect. Low protein levels can also increase pharm effet of drugs (fewer protein binding sites, more free drugs).
- Also, some drugs bind with specific parts fo protein (albumin or globulin). When pt with liver or kidney disease or malnourished, have abn low serum albumin, so fewer protein-binding sites, more free drug-->drug toxicity.
Always check protein-binding %
Always check pt plasma protein adn albumin levels!
Where is most drug metabolism occuring?
- Occurs in GI tract and liver, mostly liver.
- Liver inactivates most drugs for excretion.
- Cirrhosis and hepatitis alter drug metabolism and can increase drug accumulation-->toxicity.
Time it takes for half o the drug dose to be eliminated.
Steady-state serum concentration
Reached by caculating how many half-lives it takes to fully saturate body.
- Main route through kidneys
- Affected by pH of urine (can change pH of urine to increase excretion).
very important to check!!
- most accurate test to determine renal function.
- Creatinine is metabolic byproduct of muscle that is excreted by kidneys. varies with age and gender (lower in old and female d/t lower muscle mass).
- How drugs effect body
- Drugs usually have both primary adn secondary effects.
Relationship b/t the minimal vs the maximal amt of drug dose needed to produce the desired drug response.
Time it takes to reach minimum effective concentration (ME) after drug administered.
Occurs when drug reaches its highest blodo or plasma concentration.
Duration of action
Length of time the drug has a pharmacologic effect.
Most receptors found on cell membranes: ON proteins, glycoproteins, proteolipids, and at enzymes.
Receptor Families (4):
- *Kinase-linked receptors
- *Ligand-gated ion channels
- *G protein-coupled receptor systems
- *nuclear receptors: in nucleus
Drugs that produce an effect
Drugs that block an effect.
Categories of Drug Action (4)
- 1. Stimulation
- 2. Replacement
- 3. Inhibition or killing organisms
- 4. Irritation
Estimates teh margin of safety of a drug that measures the effective dose (ED) in 50% of animals or people and the lethal dose (LD) in 50% of animal/people. The lower the TI, the close you need to watch for adverse affects. The closer to 1, the higher hte risk of toxicity.
Peak Drug Level
Highest plasma concentration--should take blood sample. Indicates rate of absorption.
Trough drug level
- Lowest plasma concentration. Measures rate at which drug is eliminated. Draw blood immediately before next dose is given.
- Used for drugs with narrow therapeutic index.
Large initial dose is given to achieve a rapid minimum effective concentration of a drug.
Side effects vs adverse effects
Adverse is always undesirable. must always be reported adn documented.
Effect of drug action that varies from predicted response b/c of genetic factors.
Decreased responsiveness of drug over time.
Rapid decrease in response to drug.
What drugs forms are absorbed fastest?
Liquids form vs. solid.
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