| Question | Answer |
| Km | [S] at Vmax, low Km => high affinity |
| Noncompetitive inhibitor | -Does not resemble substrate
-Does not bind to active site
-Cannot be overcome by increased [S]
-Decreases Vmax, no effect on Km
-Decreases efficacy of substrate |
| Competitive inhibitor | -Resembles substrate
-Binds to active site
-Can be overcome by increased [S]
-Decreases Km, no effect on Vmax
-Decreases potency of substrate |
| Volume of Distribution (Vd) | = (Amount of drug in body)/(Concentration of drug in plasma)
Low Vd => distributes in blood
Med Vd => distributes in extracellular space/body water
High Vd => distributes in tissues |
| Clearance | = (rate of elimination)/(plasma concentration) = Vd x Ke |
| Loading dose | = Cp x Vd/F
Not affected by renal/hepatic dysfunction |
| Maintenance dose | = Cp x Cl/F
Decreased by renal/hepatic dysfunction |
| Zero-order elimination | Constant amount of drug eliminated over time, regardless of concentration
Phenytoin, Ethanol, Aspirin |
| First-order elimination | Elimination rate proportional to concentration, constant fraction of drug eliminated per unit time (exponential decay) |
| Weak acids | Trapped in basic environments, treat overdose w/ bicarb
Phenobarbitol, MTX, TCAs, aspirin
HB + OH- --> B- + H2O |
| Weak bases | Trapped in acidic environment, treat overdose w/ ammonium chloride
Amphetamines
BOH + H+ --> B+ + H2O |
| Phase I metabolism | Reduction, oxidation, hydrolysis
Yields slightly polar, water-soluble metabolites, often still active
CyP450
Lost first by elderly patients |
| Phase II metabolism | Acetylation, glucuronidation, sulfation
Yields very polar, inactive metabolites for renal excretion
Conjugation, separate from P450 |
| Therapeutic index | = median LD50/median ED50 |
