Pharmacology
Terms
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- Multiple Compartments
- Each compartment has its own volume of distribution. Each pair of compartments also has rate constants that describe the rates at which drugs move between the compartments.
- CYP3A4
- Enhanced oxidative metabolism of its substrates (Drug S). This causes a reduction in the plasma drug concentration and subsequently decreased drug effects.
- Half-Life of drug
- t1/2 = 0.693/k
- Will a drug with a high affinity for plasma proteins tend to have a large or small volume of distribution?
- Small Volume of Distribution
- Half-life
- Increased volume of dist and Decreased Clearance will increase the half-life.
- Loading dose
- Css * Vd
- Exponential decrease
- C = Coe^-kt
- Dose
- = Vd * Cp
- Fraction removed / min
- Amt. removed /min / amt in body
- Amt. Removed per min
- Cp * Cl
- Pharmacokinetics
- The quantitative analysis of the relationship between the dose of a drug and the ensuing changes in drug concentration in the blood and other tissues
- Bioavailability
- (F) = AUC_oral / AUC_iv (Efficiency at which a drug is absorbed)
- Concentration
- = amount / Volume
- Volume of Distribution(Vd)
- = amount / concentration
- Oral vs. IV
- Oral takes longer to act than IV
- Continuous intravenous infusion
- •Time to steady state depends on half-life •At steady state, rate of administration = rate of elimination
- Effect of ionization of Drug
- •Charged drugs do not cross membrane. •pH affects movement of drug.
- Zero-Order Elimination
- •Rate of elimination is constant regardless of drug concentration• Constant amount of drug eliminated per unit time
- Concentration at steady state (Css)
- Css = Rate of administration / Cl
- Will a very lipophilic drug tend to have a large or a small volume of distribution?
- Large Volume of Distribution
- *Grapefruit Juice
- Inhibits enzymes(CYP3A4) in GI Wall and Sinusoids in the liver.
- Mechanism of Drug Movement
- • Passive Diffusion •Facilitated Diffusion •Active Transport
- First-Order Elimination
- •Rate of elimination is proportional to drug concentration •Constant fraction of drug eliminated per unit time
- Pharmacokinetic Phases
- •Absorption •Distribution •Metabolism •Elimination
- Kinetic Rate Constant
- k = Cl/Vd
- Clearance Calculation
- •Amount removed per unit volume / plasma concentration (Cp) •Determines elimination halflife
- Clearance (Cl)
- The volume of plasma that would have to lose all of the drug that it contains within a unit of time (usually 1 min) to account for an observed rate of drug elimination
- Biotransformation
- The chemical modification (or modifications) made by an organism on a chemical compound
- Renal Clearance(Qkidney)
- The volume of plasma that is totally cleared of a drug in 1 min during passage through the kidneys.
- Main route Oral Absorption
- GI Lumen -> GI Wall -> Portal Vein -> Liver -> Hepatic Vein -> Systemic Circulation
- Aspirin Absorption
- More readily absorbed in the stomach due to the higher pH. Aspirin gets protonated via HCL and crosses the membrane.
- Tetracycline on empty stomach
- Ca+ can bind Tetracycline preventing its transport and absorption.
- What happens when metabolism is inhibited?
- Higher bio-availability. Inhibition occurs in GI Wall and Liver.
- Pharmacodynamics
- Study of the biochemical and physiological effects of drugs and their mechanism of action.
- Apparent volume of distribution (Vd)
- The volume of fluid which the drug would occupy if it were evenly distributed through that volume at the concentration measured in the plasma (central compartment).
- Drug dissolution
- Solid Dose(Release) -> Oral Release(Dissolution) -> Oral Solution(absorption) -> Plasma
- Routes of administration
- •Oral •Intravenous •Intramuscular •Subcutaneous •Transmucosal •Transdermal
- *Movement of drugs between Compartments
- Site of Action <-> Systemic Circulation <-> Tissues
- Complex Formation
- Drugs that bind to other molecules cannot cross cell membrane.
- Distribution
- Movement of drugs between compartments.
- Rate of administration
- Css * Cl
- Drug elimination
- Site of Action <-> Systemic Circulation(Biotransformation in the Liver) <-> Tissues
- St. John's Wort
- Results in the increased metabolism of drugs, resulting in decreased concentration and clinical effect.