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Week 3: Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Pharmacokinetics

A

How a drug molecule moves through your body from administration to elimination.

  • Absorption
  • Distribution
  • Metabolism
  • Clearance
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2
Q

Pharmacodynamics

A

How a drug molecule affects its target to produce the desired physiological effect.

  • Therapeutic Effect
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3
Q

Passive Diffusion/Simple Diffusion

A

Molecules diffuse from a site of high concentration to a site of lower concentration.

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4
Q

Facilitated Diffusion

A

Molecules diffuse from a site of high concentration to a site of lower concentration but requires a transmembrane integral protein.

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5
Q

Active Transport

A

Movement of molecules from a site of low concentration to a site of higher concentration and MUST use ATP.

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6
Q

Non-Saturable Diffusion

A

Diffusion that doesn’t have proteins that get saturated.

Ex. Passive/Simple Diffusion

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7
Q

Saturable Diffusion

A

The rates of diffusion are limited by the amount of transport protein present.

Ex. Facilitated Diffusion & Active Transport

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8
Q

pKa

A

The pH at which half of the molecules are charged and half are neutral.

  • pKa is when there is 1:1 ratio of hydrophilic form to hydrophobic form.
  • pKa ≠ pH
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9
Q

pH < pKa

A

A Drug exists more in its acidic form.

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10
Q

pH > pKa

A

A Drug exists more in its basic form.

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11
Q

Henderson-Hasselbalch Equations

A

Weak Acids: [A-] / [HA] = 10^pH-pKa

Weak Bases: [B] / [BH+] = 10^pH-pKa

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12
Q

Bioavailability

A

the fraction of a drug dose that reaches the systemic circulation.

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13
Q

Bioavailability of Oral Drugs

A

Measured in the liver AFTER the first-pass effect.

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14
Q

Vd (Volume of Distribution)

A

The volume of TBW in which a drug will divide.

Vd=Q/Cp

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15
Q

Plasma Protein

A

Helps hydrophobic drugs more soluble in plasma and stay in the plasma membrane.

  • The protein-bound percentage of a drug doesn’t change by the dosage of the drug.
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16
Q

Cytochrome p450 (CYP450)

A

Liver enzymes (in SER) responsible for the chemical degradation/modification of drugs via phase I and phase II reactions.

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17
Q

Phase I

A

Functionalization Phase: Inactivates majority of drug.

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18
Q

Phase II

A

Conjugation Phase: Inactivates drug and facilitate renal and hepatic clearance.

*Phase II makes the drug more POLAR and LARGER to increase clearance.

19
Q

Acetaminophen

A

A type of drug that goes through both phases I and II.

* It goes through oxidation during phase I and glutathionation during phase II.

20
Q

Phase I Reaction Examples

A
  • Oxidation (most common)
  • Reduction
  • Hydrolysis
21
Q

Phase II Reaction Examples

A
  • Glucuronidation (most common)
  • Glutathione-conj.
  • Glycine-conj.
  • sulfation
  • acetylation
  • methylation
  • don’t memorize other than glucuronidation: but be able to distinguish them vs. phase I reactions.
22
Q

Phase I Enzymes

A

Catalyzed by:

  1. Oxidation/Reduction: Cytochrome p450 (CYP families 1-3)
  2. Hydrolysis: Epoxide hydrolase
23
Q

Phase II Enzymes

A

Catalyzed by: “transferases”

  1. Glucuronidation: UDP-glucouronosyntransferase
  2. Glutathione-conj.: Glutathione-S-transferase
  3. sulfation: sulfotransferase
  4. acetylation: N-acetyltransferse
  5. Methylation: methyltransferase
24
Q

Clopidogrel (plavix)

A

A type of drug that gets activated from its pro-drug through Phase I.

  • Clopidogrel (pro-drug) –> active anti-coagulant
25
Q

Rate of Drug Metabolism vs. Enzyme

A

The rate of drug metabolism depends on how much drug there is relative to the metabolizing enzyme.

26
Q

Zero-Order kinetics

some drugs

A

When drug is in excess. Operates at Vmax.

  • Independent of drug concentration
  • Constant amount of drug administered
  • T1/2 not constant
27
Q

First-Order kinetics

most drugs

A

When enzyme (CYP) is in excess. Operates below Vmax.

  • Dependent on drug conc. (Direct relationship)
  • Constant proportion (%) of drug administered
  • T1/2 constant
28
Q

Enterohepatic circulation

A

The process which allows metabolized drugs to be reabsorbed by enterocytes (gut wall bacteria).

*This process increases the drug’s half-life (time required to reduce to half).

29
Q

Antibiotics Effect on Enterohepatic circulation

A

Some antibiotics may inhibit enterohepatic circulation and increase elimination.

30
Q

Drug-Drug Interaction Affecting Absorption 1

A

Omeprazole vs. Cefpodoxime

  • Cefpodoxime is a cephalosporin antibiotic that becomes hydrophobic in the stomach (low pH).
  • Omeprazole inhibits this process by increasing pH in the stomach.
  • Cefpodoxime becomes less absorbable.
31
Q

Drug-Drug Interaction Affecting Absorption 2

A

Digoxin vs. Antibiotics

  • Digoxin is used to treat heart failure and arrhythmia which gets degraded by gut bacteria.
  • Antibiotics inhibit this process and can lead to drug toxicity or overdose.
32
Q

Drug-Drug Interaction Affecting Distribution

A

NSAIDS & Warfarin

  • NSAIDS competes with Warfarin for the same binding site of Albumin plasma protein.
  • NSAIDS will inhibit warfarin from binding and increase free warfarin and increase bleeding risk.
33
Q

Drug-Drug Interaction Affecting Metabolism (Through CYP Enzymes)

A
  1. CYP Inhibiting Drug
    - Inhibit CYP enzyme that metabolizes (inactivates) a drug, thus leading to toxicity.
  2. CYP Inducing Drug
    - Induce CYP enzyme that metabolizes (inactivates) a drug, thus leading to decreased efficacy of the drug.
34
Q

CYP Inhibiting Example

A

Omeprazole vs. Clopidogrel

  • Clopidogrel pro-drug gets activated by a CYP during phase I.
  • Omeprazole inhibits that CYP which prevents clopidogrel from being activated and therefore reducing its anti-coagulating effect (increased clotting risk).
35
Q

CYP Inducing Example

A

Acetaminophen vs. ethanol

  • Acetaminophen gets deactivated by a CYP through phase I and/or phase II.
  • Ethanol induces the CYP towards phase I to constantly convert acetaminophen to toxic metabolites leading to hepatotoxicity.
36
Q

Drug-Drug Interaction Affecting Clearance

A

Verapamil vs. Digoxin

  • Digoxin binds to P-gp protein on kidney epithelial cell for elimination in urine.
  • Verapamil inhibits p-gp and prevents digoxin from being cleared, possibly leading to digoxin toxicity.
37
Q

Physiological Changes with Age

Absorption

A
  1. Reduced SI surface area

2. Increased gastric pH

38
Q

Physiological Changes with Age )

Distribution

A
  1. Reduced body water content

2. Reduced muscle and increased fat content

39
Q

Physiological Changes with Age )

Metabolism

A
  1. Reduced liver function
40
Q

Physiological Changes with Age )

Clearance

A
  1. Reduced renal function
41
Q

Beers Criteria

A

Recommended changes in the dosage of drugs for Older Patients

42
Q

Polymorphisms & Pharmacokinetics

A

Genetic Variations of proteins (receptors/enzymes/transporters) can cause individuals to have different levels of absorption/clearance of a drug.

43
Q

P-glycoprotein

A

aka. MDR1

  • It is a transmembrane protein that pumps drugs out of cells.
  • Has many polymorphisms are found in humans which can alter its activity.

Week 3: Pharmacology (2 decks)

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