gapcom 4/4 Drug Absorption (X)
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- define pharmacodynamics
- mechanisms of drug action are the processes of pharmacodynamics. site of action. quantitative study of drug action and its effects on body tissues and organs.
- define pharmacokinetics
- examines movement of a drug over time through the body
- 4 fundamental pathways of drug movement
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processes of pharmacokinetics
1. absorption (input - drug at site of administration)
2. distribution (drug in plasma)
3. metabolism
4. elimination (output) - define absorption
- absorption is the transfer of a drug from its site of administration to the bloodstream
- what are the dif types of transport that help with absorption?
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1. passive transfer (aq diffusion [filtration&bulk flow], lipid diffusion [simple diffusion], carrier-facilitated diffusion.
2. active transport. can be reduced by compounds or conditions that inhibit energy production; non-competitive inhibition; competitive inhibition.
3. ion pair transport
4. endocytosis - explain the influence of pH on drug absorption
- most drugs either weak acids or weak bases. drug's pKa value represents the pH at which 50% of the molecules in solution are ionized. drugs exist in ionized form when exposed to their pH-opposite environment. acids are increasingly ionized in a basic environment. bases are increasingly ionized in an acid environment. diffusion of weak acid will go across lipid membrane with an (HA); whereas weak base will cross lipid membrane deprotonated (B). acids ionized when pH is increased; distribution of drug depends on ambient pH and pKa of the drug. When pH is less than PkA, the protonated forms HA and BH+ predominate. When pH is greater than pKa, the deprotonated forms A- and B predominate. differences in the pH of the body fluids can lead to drug trapping in certain compartments.
- what are the physical factors influencing absorption
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1. blood flow to the absorption site (ex more bloodflow to intestine over stomach means more absorption)
2. total SA available for absorption (intestine microvilli to stomach SA)
3. contact time at the absorption surface (moves through system less time to absorb. drug with meal means absorbed more slowly) - define bioavailability
- fraction of administered drug that reaches the sytemic circulation. bioavailability is expressed as the fraction of administered drug that gains access to the systemic circulation in a chemically unchanged form. BIOAVAILABILITY FRACTION = percent of drug absorbed unchanged. In chart, determination is area under curve in AUC oral/AUC injected x 100. plasma conc of drug vs time graph.
- what are factors that influence bioavailability
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1. first pass hepatic metabolism
2. solubility of the drug
3. chemical instability in dif areas of body
4. nature of the drug formulation (e.g. particle size, salt form, crystal polymorphism) - what are the variety of forms for drug delivery
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1. tablets
2. capsules
3. solutions
4. suspensions
5. modified release products
6. injectable solutions
7. ointments
8. creams
9. suppositories
10. form of pro-drug (precursor of active drug) - besides enteral and parenteral, what are 'other' routes of drug administration
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1. inhalation - rapid delivery across large surface area of lungs
2. intranasal (cocaine)
3. drug into CSF -intrathecal/intraventricular
4. topical - local effect of drug desired. solutions, ointments, creams, suppositories, aerosols. site applied eye, ear, skin, mouth, throat, lung, rectum vagina
5. transdermal - achieves systemic effects by transdermal patch for sustained delivery of drugs. through skin produce systemic affects by high potency (convenient szie delivery system), relative brief persistence in the body (prompt removal drug), ex. nicotine patch - what are dif forms of drug formulation
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1. deliver to GI in convenient form: tablets, capsules, solutions, and suspensions.
2. liquid formulations - good for adjusting oral dose on an individual basis and for people having difficulty in swalling tablets or capsules
3. controlled - release formulation - relaese drug over prolonged time through GI tract - types of enteral drug administration
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-oral - consider state of consciouness, NV, stomach contents and acid environment, first pass effect
-sublingual - avoids first pass metabolism. precents destruction of drug by intestinal enzymes or by low pH in stomach.
-rectal - 50% of the drainage of the rectal region bypasses the portal circulation.prevents destruction of drug by intestinal enzymes or by low pH in stomach. - types of parenteral drug administration
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used for drugs poorly absorbed from GI tract and for agents unstable in GI tract (ex. penicillin, insulin).
1. IV. avoids GI tract, rapid effect. downside cannot be recalled by emesis, may introduce bacteria at injection site
2. intramuscular - can be aq solns or specialized depot preparations
3. subcutaneous - requires absorption and is slower than IV route. minimizes risk assoc with IV. ex. epi and lidocaine - define bioequivalence
- two related drugs are bioequivalent if they show comparable bioavailability and similar times to achieve peak blood flow concentrations.
- define therapeutic equivalence
- two similar drugs are therapeutically equivalent if they have comparable efficacy and safety. two drugs that are bioequivalent may not be therapeutically equivalent