Pharm Basics Flashcards
Km
The concentration at which the reaction is half of maximum. Lower the Km, the higher the affinity.
Michaelis-Menten Equation
Vmax*S/Km+S
Michaelis-Menten Equation
Vmax*S/Km+S
Lineweaver Burk Plot
Plots against 1/V and 1/s
X intercept on lineweaver burk?
-1/Km. The further to the right (closer to zero), the lower the affinity
Y intercept on lineweaver burk
1/Vmax.
Slope on lineweaver burk
Km/Vmax
Slope on lineweaver burk
Km/Vmax
Characteristics of a reversible competitive inhibitor
Resemble substate, overcome by increasing S, bind active site, DO NOT CHANGE VMAX, increase Km.
Decrease potency of an enzyme
Characteristics of an irreversible competitive inhibitor
Resemble substate, not overcome by increasing S, bind active site, decrease Vmax, don’t change Km.
Decrease efficacy of an enzyme
Characteristics of an irreversible competitive inhibitor
Resemble substate, not overcome by increasing S, bind active site, decrease Vmax, don’t change Km.
Decrease efficacy of an enzyme
Noncompetitive inhibitor characteristics
Don’t resemble substrate, not overcome by increasing S, don’t bind active site,
Bioavailability
Fraction of administered drug that reaches systemic circulation unchanged. IV dose, F=100. For oral dose, F
Volume of distribution equation
Amount of drug in the body/plasma drug concentration
Drugs with low Vd
Remain mostly in blood, these include large/charged molecules
Drugs with medium Vd
Mostly in EFC. Include small hydrophilic molecules
Drugs with large Vd
Mostly in tissues including fat. Small lipophilic molecules especially if bound to tissue protein
Half-life equation
(0.693 x Vd)/CL
How many half-lives does it take to reach steady state?
3.3 to reach 90%. 4 or 5 to reach full steady state.
Clearance equation
Rate of elimination of the drug/plasma drug concentration.
VdXke (elimination constant)
Loading dose
(Cp X Vd)/ F
Cp is target plasma concentration
Maintenance dose
(CpXCLxt)/F
Zero order elimination
Rate of elimination is constant and not based on the amount of drug in the body. Includes Phenytoin, ethanol, aspirin (at high doses)
First order elimination
Rate of elimination is directly proportional to the drug concentration. There is a constant fraction of drug eliminated per unit time.
This is flow-dependent elimination
Weak acids
Treat overdose with bicarbonate, because are ionized in basic environment.
Phenobarbital, methotrexate, aspirin
Weak bases
Trapped in acidic environments, treat overdose with ammonium chloride.
Weak bases
Trapped in acidic environments, treat overdose with ammonium chloride.
Phase 1 metabolism
Oxidation/reduction/hydrolysis (usually cyp450)
Phase 2 metabolism
Glucuronidation, acetylation, sulftation. Yields very polar, inactive metabolites that are renally excreted.
Phase 2 metabolism
Glucuronidation, acetylation, sulftation. Yields very polar, inactive metabolites that are renally excreted.
Efficacy of a drug
The maximal effect a drug can produce.
High efficacy drugs include analgesics, antibiotics, antihistamines, and decongestants.
Potency of a drug
The amount of drug needed for a given effect. Increased affinity for receptors.
Include chemotherapeutics, antihypertensives, and cholesterol drugs
Competitive antagonist effect on curve
Shifts to the right, decreases the potency. Flumazenil (on gaba)
Noncompetitive antagonist/irreversible competitive antagonist effect on curve
Shifts it down. Prevents maximal effect. (ketamine is noncompetitive, phenoxybenzamine is irreversible competitive on alpha receptors
Therapeutic index
A measurement of drug safety.
TD50/ED50 = median toxic dose/ median effective dose.
Safe drugs have high TIs.
Low TI drugs include theophylline, digoxin, lithium
Receptor and g protein class A1 A2 B1 B2 M1 M2 M3 D1 D2 H1 H2 V1 V2
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