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Pharm - Basics
Pharmacokinetics & Pharmacodynamics from First Aid 2013
| Question | Answer |
|---|---|
| Zero-order elimination: definition and examples | Constant amount eliminated per unit time. "PEA": Phenytoin, Ethanol, Aspirin |
| First-order elimination: definition | Rate of elimination is proportional to the drug concentration; i.e., a constant fraction is eliminated per unit time; i.e., half-life. |
| How does urine pH affect drug elimination? | Ionized species are trapped in urine and cleared quickly. Neutral forms precipitate out or may be reabsorbed. |
| Give some examples of weak acids in urine. What should be given to trap and clear them? | Aspirin, MTX, phenobarbital. Trapped in basic environment. Give bicarb. |
| Give some examples of weak bases in urine. What should be given to trap and clear them? | Amphetamines Trapped in acidic environment. Give ammonium chloride. |
| What happens in Phase I metabolism? | Reduction, oxidation, hydrolysis with CYP450. Usually yields active, water-solb metabolites. |
| What happens in Phase II metabolism? | Conjugation ("GAS"): glucouronidation, acetylation, sulfonation. Products are polar but inactive and are renally-excreted. |
| Which phase of metabolism do the elderly tend to lose first? | Phase I. They keep phase II (old people have GAS). |
| Efficacy vs. potency | Efficacy - max effect a drug can produce Potency - amount needed for given effect often prop to receptor affinity |
| Bioavailability (F) | Fraction of drug that reaches circulation unchanged (100% for IV). Oral is often <100 due to first-pass metabolism. |
| Volume of distribution equation | Vd = amount / concentration |
| Low Vd: compartment and drug types | Blood (4-8L); large/charged molecules, plasma protein-bound molecules |
| Medium Vd: compartment and drug types | ECF; small, hydrophilic molecules |
| High Vd: compartment and drug types | All tissues; small, lipophilic molecules, especially when bound to tissue proteins |
| Half-life equation | T = (0.7 * Vd) / CL |
| Clearance equation | CL = (Cu * Ufr) / Cp |
| Filtration fraction equation | FF = GFR/RPF = CL_Cr / CL_PAH |
| Maintenance dose equation | MD = Cp(ss) * CL (/bioavailability) |
| A drug infused at a constant rate takes ___ half-lives to reach steady state. | 4 to 5 |
| Competitive antagonism on efficacy/potency | Efficacy unchanged; potency decreased. Shifts curve to the right. |
| Noncompetitive antagonism on efficacy/potency | Efficacy decreased, cannot be overcome. |
| Partial agonism on efficacy/potency | Efficacy. Potency may be increased or decreased, depending on the drug. |
| Therapeutic index equation | LD50/ED50, high value is safer |
| Nicotinic receptor | ligand-gated Na+ (some K+) channels; found in autonomic ganglia or at muscles. |
| Muscarinic receptor | GPCR with second messengers |
Created by:
wmwebb89
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