pharmacokinetics

Question 1

intravenous drug distribution

Answer 1

intravenous = enter through bloodstream

Question 2

percutaneous drug distribution

Answer 2

under skin

Question 3

intrathecal drug distribution

Answer 3

cerebral spinal fluid

Question 4

describe factors affecting absorption

Answer 4

• diffusion through lipids
  
  • lipid solubility partition coefficient
  • lipophilicity
  • diffusivity
  • polar/non polar
  • renal elimination
  • BBB
• pH and ionisation
  
  • charge of molecules
  • dissociation constant

Question 5

describe factors affecting distribution

Answer 5

• volume of distribution
  
  • Vd = Dose/cp(desired plasma conc of drug)
• blood brain barrier
  
  • when inflamed = leaky
• binding to plasma proteins
  
  • high binding = increase in conc of drug required as protein binding sites become saturated
• body fat
  
  • partition into specific tissues ie more fat = less drug in plasma membranes as get trapped in fat

Question 6

describe factors affecting metabolism

Answer 6

• genetics
• disorders
• drug interactions

Question 7

describe factors affecting elimination/excretion

Answer 7

• renal excretion
  
  • glomerular filtration
    
    • > 20KD
  • active tubular secretion
    
    • used for weak acids and bases
  • passive diffusion
  • traps weak acids in urine
• GI excretion
• lung excretion

Question 8

Understand and be able to use the Henderson-Hasselbalch Equation

Answer 8

(dissociation)
relationship between the pH of a buffer-containing fluid with the relative ratio of the Weak Acid (H-B) andWeak Base(B-) forms of that buffer

Question 9

Describe how drugs are metabolized and eliminated from the body

Answer 9

• phase 1: anabolic = produce reactive compound
• phase 2: catabolic = conjugation to produce inactive product
  - catalysed by intracellular microsomal enzymes
• metabolites (polar) → renal elimination
• stable adducts (non-polar) → billiary elimination

Question 10

Describe what a prodrug is and their use in pharmacology

Answer 10

• drugs that are inactive upon delivery and undergo metabolism to become active
• decreases toxicity/targets specific tissues

e.g aspirin, heroin, L-dopa, codeine