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PK
Nagelhout
| Question | Answer |
|---|---|
| what allows a drug to move easier across a membrane? | low molecular weight and size non-polar lipophilic |
| Name two types of drug transporters | efflux and uptake |
| drugs are either a.. | weak acid or weak base |
| Drugs that are typically weak acids | Benzos, barbiturates and induction drugs |
| drugs that are typically weak bases | narcotics and local anesthetics |
| pKa is | the value at which H+ is donated or accepted |
| the degree of ionization is determined by | its pKa constant and the pH of solution |
| how can protein binding influence drugs | can bind with drug, its with low albumin (kidney and liver disease) could not respond properly |
| the bioavailability of. drug is | the amount of drug in systemic circulation and available to be used/distributed |
| define pharmacokinetics | what the body does to the drug how to deliver a drug so that plasma concentration is sufficient to elicit a response with minimal side effects |
| how do drugs get administered to tissues (regardless of route of administration) | the vascular system |
| factors influencing drug transfer | blood volume and rate molecular weight and size, charge or no charge of drug protein binding |
| an IV drug is delivered in its full amount, it has how much bioavailability | 100% |
| routes of adminstration | parenteral, enteral, pulmonary, topical |
| IV administration bioavailability and comments | bioavailability- 100 most rapid onset, can be given in large volumes, easily titrated |
| Oral administration bioavailability and comments | 5 to 100 bioavailability most convenient and least expensive can have significant first pas effect patient needs to cooperate |
| intranasal administration bioavailability and comments | highly vascular, best for lipid soluble products no first pass effect, rapid brain and SC concentrations |
| bioavailability | the extent to which a drug reaches its effective site after its introduction to the body |
| what determines the drugs duration of action and intensity | the rate at which systemic absorption occurs |
| factors influencing bioavailability (excluding route) | patients age, sex, race, pathology, co moribities, pH (septic??) |
| what happens when a local anesthetic is injected into an acidic environment (aka an infected wound)? | local=gets ionized (basic drug and is injected into acidic enviro, sucks up the H+ ions). drug is now ionized and carries a charge, more water-soluble and less lipid soluble, and unable to cross the lipid barrier and reach nerve |
| other names for first pass effect | presystemic metabolism, first pass hepatic metabolism |
| First pass effect | metabolism of drug in GI wall, liver before entering systemic circulation |
| First pass effect pathway | oral- GIT- gut drainage- portal circulation- to the liver- through heart/lungs-into body via veins |
| a high first pass effect can mean | less drug bioavailability and higher dosing |
| four enzyme systems associated with first pass effect | GI lumen, gut wall, intestinal bacteria, liver |
| Pro-drug definition | a drug that needs to be metabolized before becoming its active version and available to the body why? keep selective molecule from degrading before it has the ability to elicit response |
| compartment models are and do... | depict the body in sections/theoretical spaces with calculated volumes used to describe the PK of agents |
| these are helpful in determining serum and drug changes | compartment models |
| a single compartment represents | the entire body (doesn't account for lipid soluble anesthetics) |
| Central compartment | Vessel rich IV fluid and highly perfused tissues (heart, lungs, brain, live, kidneys) 10% body mass but 75% of cardiac output |
| Why is a two model compartment model used? | simplifies and explains the PK concepts that are more complicated shows size of compartments and rate drug is distributed to them |
| Peripheral compartment | vessel poor group muscle, fat, bone 90% body mass, 25% cardiac output |
| how do drugs leave the central compartment? | distribution into tissues or metabolism and excretion |
| "Flow" of drug through compartments is | central-vessel rich which conc- out to peripheral tissues-slowly-central conc drops-redistribution-excretion-elimination |
| Volume of Distribution | proportional expression the relates the amount of drug in the body to the drug serum concentration, apparent volume in which the drug is "in" after distribution |
| How to calculate the Vd | divide the IV dose by the plasma concentration (before elimination) |
| Vd of 100mg drug IV and plasma concentration of 20mcg/mL | 5L |
| L fluid in ECF (Plasma + ISF) | 14L= 10 (ISF) + 4 (plasma) |
| L fluid in ICF | 28L |
| total body water in L | 42L |
| what does the Vd represent? | how extensively a drug will distribute throughout the body |
| a drug that is widely distributed will have a Vd of _____ and what properties? | >0.6L/kg most likely lipid soluble |
| a drug that is not widely distributed will have a Vd of ____ and what properties? | <0.4L/kg and likely water soluble |
| Propofol Vd | quickly to brain because vessel rich- quickly redistributes b/c highly fat soluble- redistribution causes drop in initial effects- continued admin |
| Vd of bolus dose calculation | total dose/by area under plasma concentration curve |
| A drug with a greater area under the plasma concentration curve means | the longer a drug acts and the drug intensity increases steady state differs from bolus dose |
| AlphaPhase of plasma concentration curve | the distribution phase, into tissues from central compartment |
| What would a steep slope at the alpha phase indicate | that the drug moves quickly from central compartment into tissues, aka lipid soluble |
| the second phase of the plasma distribution curve | beta phase after equilibrium, rapid decrease because of elimination |
| what shape does the beta phase take on a plasma concentration curve | it is less steep, plateau shape, indicating a gradual decline in drugs plasma concentration |
| how is elimination half life determined | using the elimination phase on a plasma concentration curve |
| when does a steady state occur | the amount of elimination in a given times equals the amount of drug being added to the system |
| drug metabolism is synonymous with | biotransformation |
| metabolism definition and goal | an enzyme-catalyzed change in the chemical structure of agents change lipid soluble drugs into water soluble forms to be excreted by the kidneys metabolism can take places in GIT, heart, brain, skin, lungs, etc |
| consequences of drug metabolism | metabolites are toxic to the body, a new drug that is active within the body, |
| zero order kinetics | drugs, even at therapeutic levels, exceed the body ability to excrete/metabolize (ETOH) the available enzyme systems are saturated, regardless of the plasma concentration, a set amount is eliminated at a time |
| first order kinetics | drugs are eliminated from the body at a rate proportional to the plasma concentrations (more drug = more eliminated) a fraction of the total drug is eliminated per unit time |
| Phase I elimination | RedOx, hydrolysis, the process drugs undergo becoming polarized and water soluble, able to be excreted in the kidneys |
| Phase II elimination | the process of adding a polar molecule to a drug to aid in elimination |
| elimination half life | the time allotted for the plasma concentration to decrease by half after rapid bolus injection same time to go from 100 to 50 as 10 to 5 |
| the number of half lives elapsed when a drug is considered out of the body | 4-5 half lives |
| what is the reason that half life is constant? | drugs are eliminated by either zero or first order kinetics |
| Michaelis-Menten models | explains that some drugs are dosage dependent in determining their elimination, zero order at high doses and first order once drug levels fall phenytoin |
| context sensitive half time is | the clinically relevant measure of drug concentrations taking into account the method /duration of administration the time to halving of the blood concentrations after termination of drug admin by an infusion designed to maintain constant concentration |
| advantages to context sensitive half life | allows for rational drug selection based on anticipated infusion duration when my drug conc hits 50% and pt beings to "wake up" how long will that take and when should I turn off the drug? |
| Clearance | determined by the properties of the drug and the body's capacity to eliminate it the volume of plasma completely cleared of a drug by metabolism/excretion per unit of time |
| what does clearance influence? | the steady-state concentration of drug given at repeated intervals or infusion |
| how is the rate of clearance determined? | the blood flow rate and organ ability to eliminate |
| Clearance = | Q x E |
| high clearance drugs (hepatic clearance) | hepatic blood flow ought weighs enzymatic activity in clearing so a decrease in bad flow would drastically decrease the rate of elimination lipid soluble excretion/metabolism |
| renal clearence | requires drugs be h2o soluble or will be reabsorbed (propofol) pH of urine can influence elimination |
| Other factors that influence PK | age, gender, temperature, disease states, genetics |
Created by:
lokandrews
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