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Pharm Exam 1 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

pharmacokinetics

A
  • time course of drug action as it relates to the concentration of drug in the plasma
  • ADME = Absorption, Distribution, Metabolism, and Excretion
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2
Q

rational therapeutic regimens

A
  • dose
  • absorption
  • first pass metabolism
  • area under the curve
  • elimination clearance
  • patient compliance
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3
Q

measurement of drug concentration in plasma

A

-for most drugs, the concentration of drug at its site of action will be related to the concentration of the drug in the systemic circulation. Therefore it can be used to predict therapeutic and/or toxic effects of drugs

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4
Q

Area under the curve clinical significance

A
  • used to compare the amount of drug that reaches the systemic circulation by different routs of administration: bioavailability (F)
  • used to compare clearance (CL) of a drug in different individuals after administration of the same dose
  • AUC= dose iv/CL or AUC= dose p.o./ (CL/F)
  • CLx/CLy = AUCy/AUCx
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5
Q

drug absorption

A

-the processes by which drugs move from their site of administration to the plasma

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6
Q

processes following oral drug administration

A
  • disintegration of solids and dissolution of drug in fluids of GI tract
  • passage of drug across or between cells to reach the systemic circulation
  • stomach and small intestine have large surface area for absorption and the drug leaves that area via passive diffusion and drug transporters to the systemic circulation
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7
Q

factors affecting drug absorption

A
  • chemical composition of drug and delivery formulation
  • regional differences in blood flow
  • transport mechanisms
  • permeability characteristics (lipid solubility)
  • ion trapping
  • non-specific binding
  • surface area
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8
Q

types of passive transport

A
  • paracellular transport
  • diffusion
  • facilitated diffusion
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9
Q

aqueous diffusion

A
  • small molecules
  • passive movement driven by concentration gradient
  • route may be paracellular or via aqueous pores
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10
Q

lipid diffusion

A
  • passive process
  • driven by concentration gradient
  • the rate of absorption increases with increasing drug concentration
  • the more lipid-soluble, the faster the rate of transport
  • lipid soluble drugs cross mbs readily, but they may be poorly soluble in aqueous gut fluids which may limit their absorption
  • lipid solubility is affected by the degree of ionization- henderson hasselbach equation
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11
Q

Henderson Hasselbach equation

A

pKa = pH + log ([AH]/[A-]) or ([BH+]/[B])

-the ionized form is less lipid soluble– A- or BH+

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12
Q

Where in the body are acids/bases best absorbed?

A
  • weak acids- bet in stomach (lower pH)
  • weak bases - best at higher pH
  • both are well absorbed in the small intestine
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13
Q

Degree of ionization depends on difference between pH and pKa how?

A

-pH- pKa = -3, Acids = .1, Bases = 99.9
-pH-pKa= -2, acids =1, bases = 99
-pH-pKa = -1, acids = 10, bases =90
-pH-pKa =0, acids =50, bases =50
etc.

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14
Q

ion trapping

A
  • non-ionized forms can diffuse across lipid membranes, so it equilibrates between blood and urine. Then more of the substance can be trapped on one side or the other based on the pH of the compartment
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15
Q

First pass metabolism

A

some drugs are highly metabolized when they pass through the liver- only a fraction (F) of the absorbed drug reaches the systemic circulation
-intestinal and hepatic

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16
Q

enterohepatic circulation

A

Drug may be secreted into the bile and reabsorbed via the intestine. This can delay delivery to the systemic circulation and may reduce bioavailability

17
Q

Stomach contents and absorption

A

stomach contents and gastric emptying can affect the rates of drug absorption
ex. Ca2+ from food in the stomach tends to bind drugs and decrease absorption

18
Q

bioavailability

A

-fraction of the administered dose that reaches the systemic circulation in its active form
-a drug can have less than 100% bioavailability if it is incompletely absorbed or if it undergoes metabolism
Foral= AUCp.o/AUCi.v.

19
Q

salt factor

A

in rare cases, a drug may be prepared in a formulation that provides a fraction of the total weight of drug as active drug and the remainder as an inactive salt
-the fraction of total drug that will be delivered as active drug to the systemic circulation is called the salt factor (S)

20
Q

sublingual/buccal dose administration

A
  • bypasses portal circulation and therefore avoids first pass metabolism
  • higher pH may be beneficial for absorption of more basic drugs
  • can have a bad taste or be uncomfortable
21
Q

rectal dose administration

A
  • about 50-60% of the absorbed drug by-passes the portal circulation and therefore avoids the first pass metabolism
  • useful in cases of nausea and vomiting
  • inconvenient and uncomfortable
22
Q

inhalation of drugs

A
  • absorption is via passive diffusion and is facilitated by a large surface area
  • can be volatile gases or aerosol preps
  • drug absorption varies with depth and duration of inspiration so in the hospital would titrate to desired effect or us a metered inhaler
23
Q

topical drug administration

A
  • usually for local therapy

- highly lipid-soluble forms may reach the systemic circulaion

24
Q

transdermal drug administration

A
  • passive diffusion of drugs across the skin driven by a concentration gradient
  • controlled release of drug into the patient enables a steady blood level profile
  • user friendly= improved patient compliance
  • avoids GI system so no GI irritation and no first pass metabolism
  • skin barrier limits the number of drugs that can be delivered by passive diffusion from an adhesive patch
25
Q

injection of drugs

A
  • blood flow to the area maintains that conc gradient
  • drug absorption is faster in highly vascularized tissues
  • greater degree of reliability and precision of administered dose
  • fewer problems with absorption (no metabolism or GI)
  • disadvantages- needles, pain, tissue irritation, limited volume, drugs must be in solution
26
Q

subcuatneous administration

A
  • slow,even absorption
  • rate of absorption may be modified by altering blood flow (heat/cold)
  • may be used as a depot
  • not effective when peripheral circulation is impaired
  • limited volume
27
Q

intramuscular absorption

A
  • more rapid absorption than subQ because it is more vascularized
  • can modify rate of absorption by modifying blood flow (heat)
  • potential for infection/nerve damage
  • risk of inadvertent IV administration
28
Q

IV administration

A
  • fastest and most reliable means of achieving a defined blood level
  • risk of overdose by bolus effect, so give drug slowly
29
Q

factors influencing distribution

A
  • regional differences in blood flow
  • tissue mass
  • transport mechanisms
  • permeability characteristics (ex BBB)
  • ion trapping
  • protein binding
30
Q

proetin binding to drugs

A
  • many drugs bind to plasma proteins– albumin binds acidic drugs, and alpha-1 acid glycoprotein binds basic drugs
  • protein bound drugs are retained in the plasma
31
Q

one compartment distribution

A
  • a rapid equilibrium is achieved between plasma and tissue distribution following drug administration
  • plasma concentration-time profile declines mono-exponentially
32
Q

two-compartment distribution

A
  • rapid distribution to a central compartment (plasma) is followed by slow distribution ot other tissues/binding sites (second compartment)
  • this results in a bi-exponential plasma concentratio-time profile (distribution phase and then elimination phase)
33
Q

Volume of distribution

A
  • measure of how evenly distributed a drug is in the body
  • theoretical volume of fluid into which the total drug administered would have to be diluted to produce the concentration in plasma
  • relates dose to plasma concentration of drug (dose/Co)=Vd
  • an increase in unbound fraction of total drug (like in hypoalbuminemia) will result in an increase in the apparent volume of distribution
34
Q

fluid compartments in the body

A
  • plasma = 5%
  • interstitial fluid = 16%
  • intracellular fluid 35%
  • transcellular fluid 2%
  • fat 20%
  • extracellular fluid = plasma+interstitial fluid+lymph (1%)
  • transcellular fluid = cerebrospinal, intraocular, perioneal, pleural, and synovial fluids and digestive secretions
35
Q

drug distribution to compartments based on lipid solubility

A
  • lipid insoluble drugs = confined to plasma and interstitial fluids and most don’t enter the brain
  • lipid soluble drugs reach all compartments, and they may accumulate in fat which can cause Vd to exceed total body volume (because the drug accumulates outside of the plasma)
36
Q

drug reservoirs

A
  • fat and muscle especially can act as drug reservoirs
  • gradual release of drug from these sites can prolong the therapeutic effect or result in toxicity
  • plasma proteins can also serve as a drug reservoir (ex. sulfonamides may compete for protein binding and increase the unbound fraction of other drugs)

Pharm Exam 1 (10 decks)

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