Pharmacokinetics Continued Flashcards Preview

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Flashcards in Pharmacokinetics Continued Deck (21):
1

Factors affecting distribution

  • Amount of free drug
  • Specialized barriers
  • Blood flow (higher = better distribution)

2

Volume of Distribution (Apparent volume)

  • A proportionality factor that relates the amount of drug in the body to the concentration of drug measured in a biological fluid; does not indicate which tissues/fluids drug distributes to
  • Small Vd = limited distribution
  • Large Vd = extensive distribution into tissues
  • Vd (liters) = A (dose - amt of drug in body)/ C (plasma concentration)

3

Redistribution

  • A concentration equilibria is achieved with drugs redistributed to less well perfused organs; plays part in termination of a drug's pharmacological effect
  • Brain, heart, liver, kidneys --> sk mm, skin --> adipose, bone, CT

4

Metabolism is sometimes referred to as ________

Biotransformation

5

Most metabolically active tissue per unit weight is ________

The liver

6

Phase I of Metabolism

  • Making molecules lipophillic
  • Oxidation --> (electrophiles)
  • hydrolysis and/or reduction --> nucleophiles

7

Phase II of Metabolism

  • Making molecules hydrophilic to be excreted into urine
  • Glutathione conjugation, sulfation, acetylation, and glucuronidation

8

Cytochrome P450

Monooxygenase enzyme found in the ER and liver that functions to oxidize drugs in Phase I to make them readily available for Phase II

9

Felines lack what key element needed for Phase II?

critical enzymes necessary to perform glucuronidation; can compensate with acetylation and sulfonation

10

Causes of enzyme induction

increased enzyme transcription/translation or decreased enzyme degradation

11

Causes of enzyme inhibition

increased enzyme degradation, inhibition of enzyme synthesis, or enzyme inactivation by proteins/metals

12

Factors affecting metabolism

  • enzyme inhibition/induction
  • age (decreased in young and elderly)
  • reduced hepatic blood flow (heart failure)
  • gender (hormone influences)
  • mutations: Beagles & Irish wolfhounds w/ inability to metabolize caffeine

13

Prodrug activation

conversion of an inactive parent drug into an active metabolite

14

Excretion

the elimination of unchanged drug and metabolized drug products from the body

15

The main route of drug excretion is ________-

the kidney

16

What happens to drugs in the liver?

they are metabolized to become more water soluble to be excreted in the urine

17

Functions of the kidney in drug elimination

removing hydrophilic drugs that haven't been metabolized and by-products of cellular metabolism (creatinine)

18

Mechanisms of Renal Excretion

  1. Glomerular filtratrion - non-protein bound drugs (passive), dependent on CO
  2. Active tubular secretion - movement of unwanted materials from capillaries (needs energy)
  3. Tubular reabsorption - into blood, depends on lipid solubility of drug and urine pH

 

Net Renal Excretion = GF + AS - TR

19

Weakly acidic drugs would be better eliminated by a carnivore or an herbivore?

Herbivore, because have basic urine so drugs would be in ionized form and thus excreted in urine

20

What happens to metabolites in bile?

they are dumped into the intestine, then excreted into feces or reabsorbed into circulation to be filtered by the kidney

 

NOT the major route of elimination for most drugs

21

Clearance

volume of fluid cleared of drug from the body per unti of time (mL/min or L/hr); describes ability of the body to eliminate a drug

ClB = Cl(renal) + Cl(hepatic) + Cl(other)