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36 Cards in this Set
- Front
- Back
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What is the definition of pharmacokinetics? |
The mathematical description of the plasma concentration-time course |
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What are the 4 factors of dose regimen? |
Dosage Route of Administration Frequency Duration of Administration Ex: Give 4.5 mL PO BID for 21 days |
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What makes up the optimum dose regimen? |
Effective Nontoxic Without prolonged drug residues in tissues of food animals |
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How is the rate of absorption measured? |
measured by time and is the time to peak plasma concentration |
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How is the extent of absorption measured? |
by systemic bioavailability (F%) def: the fraction of the dose which reaches systemic circulation intact *higher number the more bioavailable |
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What is the one compartment model? |
All tissues and organs which the drug penetrates behave as if they were in ready equilibrium with the blood |
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What is the two compartment model? |
A central and a peripheral comparment The log curve is a biphasic with an alpha (distribution) phase and a beta (elimination) phase. **more common than one compartment |
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What is the apparent Volume of Distribution (Vd)? |
The volume of fluid which would be required to contain the amount of the drug in the body if it were uniformly distributed and the concentration in that fluid was equal to the concentration in the plasma |
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When do you add the F% in the volume of distribution equation? |
When drug was given extravascularly instead of IV |
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What happens when a drug has a low Vd (Vd<1L/kg)? |
The drug has a limited distribution (tends to stay in the plasma) Ex: heparin- prevents blood from clotting |
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What happens when a drug has a high Vd (Vd>1l/kg)? |
The drug has a very wide distribution Ex: Morphine |
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How is elimination measured? |
by half life (T1/2) or total body clearance (CLB) |
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What is half life? |
The time required for the body to eliminate one half of the drug it contains |
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What does first order kinetics mean? |
The rate of removal of drug from the plasma is proportional to the concentration present at a given time (a constant PERCENT of drug eliminated) *Elimination of most drugs follows first order kinetics |
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What does zero order kinetics mean? |
The rate of elimination remains constant regardless of the amount of drug in the body (constant AMOUNT of drug eliminated) *Few drugs (aspirin in cats, phenylbutazone in dogs/horses) follow zero order kinetics |
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What is steady-state plasma concentration? |
The plasma concentration of drug when the amount of drug going in (infusion/dose) equals the amount of drug going out (elimination). CRI (maint.) = Rate of Elimination |
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Does a faster rate achieve Cpss faster, or does and increase in dose achieve Cpss faster? |
An increase in dose achieves Cpss faster. |
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After how many half lives will the drug be almost completely eliminated?
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after 5-6 half lives 5: 96.87% eliminated (3.13% left) 6: 98.44% eliminated (1.56% left) |
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What is total body clearance (CLB)? |
The rate of drug elimination from the body, by all routes, relative to the concentration of drug in plasma CLB=CLR + CLNR |
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What is the rate of elimination split up into? |
urine flow (mL/min) x urine drug conc. (mg/mL) |
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What causes decreased clearance? |
Increased Vd Increased half life |
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What can increase the half life of a drug? |
plasma protein binding |
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What is the extraction ratio? |
The fraction of the drug removed from the perfusing blood by an organ. E=(CA-CV)/CA Cl(organ)=Q(blood flow to organ)x E(extraction ratio) |
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What are some examples of drugs that have a high extraction ratio? |
Lidocaine Propranolol Diazepam Nitroglycerin *If given orally these drugs have a high first pass metabolism *High first pass effect = high extraction ratio |
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If NO drug is taken out (CV-concentration of drug in venous blood leaving the organ) then what will the ratio be? |
1 |
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If ALL drug is taken out (CV=CA) then what will the ratio be? |
0---The more drug taken out, the closer the ratio will be to 0 |
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What is the loading dose? |
The initial dose given to reach desired plasma concentration LD (mg) = Vd (L) x Cp (mg/L) |
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What is involved in calculating dose regimen? |
Maintenance dose Loading dose |
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What is the maintenance dose? |
Dosing rate = Clearance x desired steady-state concentration Daily dose = dose/min x 60 min/hour x 24 hours Dose x F/dosing interval = CLB x Cpss |
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For drugs that depend on renal clearance what do you have to adjust? |
The dose (concentration dependent) OR the dose interval (time dependent) |
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What is renal clearance usually estimated by? |
Creatinine clearance |
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What type of clearance do most drugs depend on? |
Renal clearance |
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What will cause a decrease in excretion? |
Renal disease (insufficiency) |
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What is Creatinine? |
By product of protein metabolism True waste products **No other tissue has any use for it |
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How does the creatinine get excreted? |
Freely filtered by glomerulus (small enough and not charged) No reabsorption, nor secretion by tubules Very easily excreted |
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Can patient serum creatinine be normal even if there is a renal sufficiency present? |
Yes. The creatinine level often do not increase until more than 60% of renal function is lost. (Need to lose 2/3 kidney function for creatinine buildup to show on blood diagnostics) |
