Drug Absorption/Biotransformation? Flashcards Preview

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Flashcards in Drug Absorption/Biotransformation? Deck (35):
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Pharmacodynamics

mechanisms of drug action are the processes of Pharmacodynamics

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Pharmacokinetics

examines the movement of a drug over time through the body

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Bioavailability

% of dose that gets into body

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Bioequivalence

similarity between two formulations of same drug

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Speed of drug onset

how long it takes the drug to begin working

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Dosing interval

how often the drug should be given

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site of action

whether the drug stays local or acts systemically

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what is drug absorption?

the movement of drug molecules across biological barriers (mostly layers of cells) from the site of administration to the blood stream

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What affects drug absorption?

rate of release of drug from pharmaceutical preparation
membrane permeability of drug
surface area in contact with drug
blood flow to site of absorption
destruction of drug at or near site of absorption

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what determines rate of release of drug from pharmaceutical preparation?

Dosage form
additives (excipients)
manufacturing parameters
delayed release preparations
sustained release preparations

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Dosage form

solutions - no delay, immediate response
capsules & tablets - delay (dissolution) followed by rapid release
creams, ointments & suppositories - no delay, but slow release

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Additives (excipients)

decrease rate of dissolution - binders, lubricants, coating agents
increase rate of dissolution - disintegrants
Variable effects on rate of dissolution - diluents, coloring agents, flavoring agents

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Manufacturing parameters

tablet compression - hard tablets dissolve more slowly
tablet shape - round tablets dissolve more slowly
tablet size - large tablets dissolve more slowly

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Delayed release preparations

enteric coating - dissolve in intestines, not stomach

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sustained release preparations

Reservoir diffusion products - drug diffuses from pill core through membrane shell
Matrix diffusion products - diffuses through matrix in which it is embedded
Matrix dissolution products - released as matrix dissolves
osmotic tablets - pumped out of tablet by osmotic forces
Ion-exchange products - bound to resin exchanges with endogenous ions

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Lipophilicity

increases membrane permeability
presence of aliphatic and aromatic structures
absence of polar groups

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Ionization

decreases membrane permeability
weak acids in intestines are mostly ionized (intestinal pH ranges from 6.6 to 7.5)
weak bases in stomach are mostly ionized (stomach pH ranges from 1 to 2)

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Henderson-Hasselbach equation

pH = pKa + [nonprotonated species/protonated species]
For acids: pH = pKa + log [A-]/[HA]
For bases: pH = pKa + log [B]/[BH+]

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when pH is less than pKa,

the protonated forms HA and BH+ predominate

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when pH is greater than pKa, the

deprotonated forms A- and B predominate

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when pH = pKa then

HA = A-
BH+ = B

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What parts of the anatomy have a low surface area?

eyes, nasal, buccal cavity, rectum, stomach large intestines

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High surface area anatomy

small intestines and lungs

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Low blood flow areas of the body

eyes, stomach, large intestines, rectum, subcutaneous tissue

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High blood flow areas of the body

small intestines, lungs, muscle, buccal cavity, nasal cavity

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what determines whether a drug is destroyed at or near site of administration?

Liver - hepatic enzymes (first pass effect)
colon - intestinal microflora
stomach - digestive enzymes and acids

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Considering types of administration what is most safe to least safe?

highest safety is Oral -> SC -> IM -> IV

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Routes of administration that would be highly bioavailable to least?

IV is the highest, IM = SC > oral

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Onset of action of routes of administration

fastest is IV > IM > SC > oral

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Most interaction with food to least?

Oral > IV = IM = SC

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Highest volume of drug required to least

Oral = IV > IM > SC

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Availability of sustained release dosage forms

Highest with IM > oral > SC > IV

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Tolerance to "funky" vehicles

Highest with Oral = IM = SC > IV

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Sublingual administration

rapid absorption that bypasses liver

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Rectal

great for patient that is vomiting or cannot (will not) swallow medication