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Pharm - Basics

Pharmacokinetics & Pharmacodynamics from First Aid 2013

QuestionAnswer
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