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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Pharmacokinetics

A

What the body does to the drug

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2
Q

Movement of drug molecules across cell barriers, can be either …. or …..

A

Lipophilic –> diffusion through lipid

Hydrophilic –> diffusion through aqueous channel

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3
Q

Transport across a concentration gradient, can be either …. or …..

A

Passive –> from high to low concentration, without energy (facilitate diffusion, passive diffusion)

Active –> from low to high, with energy (primary active transport –> ATP or secondary active transport –> symport or antiport

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4
Q

P-glycoprotein (P-gp) (7)

A
  • one of the key transporter systems in the body
  • ABC transporters family, multi-drug resistance protein 1 (MDR-1)
  • ATP dependent transport molecule (GI tract, blood-brain barrier, placenta…)
  • “pumps” drugs from intra-cellular intro extracellular space
  • imp modulator of intestinal drug transport, expel drugs from intestinal mucosa into lumen (contributes to first pass elimination)
  • drugs that inhibit it (ex: varapil) –> increase bio availability of other drugs –> increase the concentration of toxic drugs in plasma
  • drugs that induce it (rifampin) –> decrease bio availability of other drugs –> decrease plasma concentration
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5
Q

pH and ionization (3)

A
  • pKa: pH at which 50% of the drug is in its non- ionized form and 50% is in its ionized form
  • Ionized is polar, it does not cross barriers very well; so, it would be eliminated quickly via the kidney
  • Example: aspirin. It is absorbed by ion trapping. When it is in the stomach its in the non-ionized form so its absorbed. But when it enters the blood, it becomes ionized again so it cannot go back to the stomach, that’s why it is called ion trapping.
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6
Q

Binding of drugs to plasma proteins (6)

A
  • Albumin binds acidic drugs
  • B- globulin and acidic glycoprotein binds basic drugs
  • Saturable binding –> ?
  • Extensive binding –> ?
  • Competition
  • Drugs bind to proteins in order to be transported
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7
Q
  1. Absorption

2. Main routes

A
  1. drug goes from site of administration into plasma

2. oral, sublingual, rectal, application to epithelial surface, inhalation.

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8
Q

Factors affecting GI absorption (5)

A
  1. GI motility
  2. GI pH
  3. Particle size and formulation
  4. Physiochemical factors - weak acids and bases are well absorbed, strong acids and bases are poorly absorbed
  5. Splanchnic blood flow - if you increase it, absorption of the drug could increase and vice-versa
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9
Q

Bio-availability (5)

A
  • part of the drug which reaches systemic circulation
  • oral dose –> portal circulation –> liver –> systemic circulation
  • intravenous dose –> systemic circulation –> liver
  • Rectal administration –> majority of drug goes directly to systemic circulation, but if it not inserted deep enough it will go through portal circulation and to liver etc
  • calculated from (area under the plasma concentration curve) AUC(route)/ AUC(IV)
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10
Q

Bio-equivalence (2)

A
  • biological equivalence of 2 proprietary preparations of drug
  • if 2 products are bio-equivalent, it means that they would be expected to be clinically the same
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11
Q

First-pass (pre-systemic) metabolism (3)

A
  • take into account how much of the drug will be metabolized in the liver and in the gut wall
  • the concentration of the drug is greatly reduced before it reaches systemic circulation
  • oral, sublingual, rectal, inhalation, injection
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12
Q

Where in the body can drugs be metabolized? (2)

A
  • Mainly in the liver, but everywhere

- Liver and kidney are the most imp organs responsible for elimination of the drugs

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13
Q

Bio-transformation

A

-chemical modification made by organism on chemical compound (drug, toxin, nutrient)

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14
Q

Drug metabolism

-Phases (5)

A
  1. Phase I
  2. Phase II
  3. Genetic factors
  4. Induction of drug metabolism
  5. Inhibition of drug metabolism
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15
Q

Drug metabolism

-Phase I (5)

A
  • catabolic
  • more polar (water-soluble) or more reactive product by unmasking or inserting polar functional groups such as OH, SH, NH2
  • Oxidation - cytochrome p450, monoamine oxidase, alcohol dehydrogenase
  • Reduction - warfarin, clonazepam, naloxone
  • Hydrolysis - aspirin
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16
Q

Drug metabolism

-Phase II (5)

A
  • anabolic
  • increase water solubility by conjugation (adding groups)
  • groups that can be added are: glucuronate, acetate, glutathione, glycine, sulfate, methyl groups
  • enterohepatic circulation
  • inactive and polar products that are readily excreted
17
Q

Drug metabolism

-Induction of drug metabolism (2)

A
  • usually in the liver

- by increase synthesis of smooth endoplasmic reticulum (which contains high concentrations of phase I enzymes)

18
Q

In which phase (I or II) is the drug metabolized? (2)

A
  • it could be matabolized in either of them

- for example, in phase II is when paracetamol is first metabolized

19
Q

Pharmacogenetics

A

Genetic factors that affect a drug response

20
Q

Volume of distribution (5)

A
  • the ratio of the amount of drug in the body to the drug concentration in the plasma (blood)
  • Very small: drug binds extensively to plasma proteins (WARFARIN)
  • Small: not bind to plasma protein, highly ionized (do not cross cell membrane), not bind to tissues (GENTAMYCIN)
  • Medium: not bind to plasma protein or tissue, not polar (THEOPHYLLINE)
  • Large: drug binds extensively to tissues (DIGOXIN)
21
Q

Clearance of drug (3)

A
  • volume of plasma containing the drug that is “cleaned” from the drug in unit time
  • for many drugs –> clearance is the same at different doses
  • Clearance= rate of elimination/ plasma concentration
22
Q

Relationship between:

elimination half-life and clearance (2)

A
  • 1/2 life is proportional to volume of distribution

- 1/2 life is inversely proportional to clearance

23
Q

Half- life (2)

A
  • 3-4 half lives of dosing at a constant rate are considered adequate to produce the effect expected at steady state
  • 95% of the drug is always eliminated after 4-5 half-lives
24
Q

Steady state (2)

A
  • condition in which the rate of drug elimination equals the rate of administration
  • the average total amount of drug in the body does not change over multiple dosing cycles
25
Q

First- order kinetic (3)

A
  • most drugs in clinical use obey the first- order kinetics
  • increase the plasma drug concentration = increase in the rate of drug elimination
  • constant half-life and proportion of plasma “cleaned”
26
Q

Zero-order kinetic (3)

A
  • increase plasma drug concentration, the rate of drug elimination will not increase
  • rate of drug elimination is the only constant (it is independent of drug concentration)
  • proportion of plasma “cleaned” will not be constant

Pharmacology (29 decks)

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