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22 Cards in this Set
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Identify the characteristics of firstorder kinetics and compare and contrast those of zeroorder kinetics




1st order kinetics

most drugs follow 1st order kinetics
exponential a constant fraction of drug present is eliminated per unit of time rate of process is proportional to drug concentration Halftime (t1/2) is independent of drug concentration 

0 order kinetics

Encountered only occasionally
constant amount of the drug is eliminated per unit time, i.e., rate is independent of drug concentration Halftime (t1/2) increases with dose and is dependent on drug concentration 

Describe the cartesian and plot for firstorder kinetics

inversely parabolic


Describe the semilog plot for firstorder kinetics.

linear sloped down


Describe the cartesian and semilog plots for zeroorder kinetics

linear sloped down and parabolic


Describe the cartesian and semilog plots for masslaw kinetics.

This is a mixedorder system. e.g. Renal tubular secretion of drugs for which there is a maximum tubular transport capacity. If plasma level is too high (i.e., exceeds Tm), you get zeroorder until level falls, and then you get firstorder kinetics.
Rate of process is a function of drug concentration, the concentration of the enzymes and their affinity 

The halftime, t 1/2, can be estimated as follows

t 1/2 = 0.693/Ke
• Where Ke is the elimination rate constant 

Describe the time course of plasma drug levels following IV bolus

Two phases:
1)Distribution phase 2) Elimination or equilibrium phase b. The exponential (firstorder) processes of absorption or elimination are essentially complete after 45 halftimes. 

Describe the time course of plasma drug levels following oral administration

sharp increase then inversely parabolic decent (1st order)  semilog plot shows flat slope


Describe the time course of plasma drug levels following IV infusion

During IV infusion, the drug concentration continues to rise until the rate of elimination equals to the constant (zero order) rate of infusion, then a plateau level of drug concentration is maintained.


Describe the factors that affect the time course of plasma levels following IV infusion.

1) Plateau state:
• Attained after 45 halftimes. • Time to plateau is independant of dose. 2) Plateau concentration: • Proportional to dose. • Proportional to halftime. • Inversely proportional to dosage interval (time in b/n dosing) 

Define bioavailability

Defined as the fraction of unchanged drug reaching the systemic circulation following administration by any route. For an IV dose of a drug, the bioavailability is 100%.
Measured by comparing plasma levels (AUC) of a drug after a particular route of administration (e.g., oral) with the achieved by IV injection. AUC reflects the extent of drug absorption. 

What are the factors that influence drug bioavailability.

1)Firstpass hepatic metabolism, e.g., propranolol
2)Solubility of drug: Drugs that are too hydrophilic or too lipophilic are poorly absorbed. For a drug to be readily absorbed, it must be largely lipophilic yet have some solubility in aqueous solution. 3)Chemical instability in gastric pH. 4)Nature of drug formulation, e.g., particle size, salt form, crystal polymorphism and the presence of inactive ingredients can influence the ease of dissolution and alter the rate of absorption. 

• Distinguish between maintenance and loading dose regimen.

Comparison of maintenance versus loading dose regimen:
1) Loading dose: • Immediate therapy. • May cause initial drug toxicity. 2) Maintenance dose: • Eliminates risk of toxic effects. • Permits accurate adjustment of dosage during drug accumulation. 

t 1/2 ( half life)=

For firstorder kinetics:
*t 1/2 = 0.693/Ke Ke =rate constant of elimination 

Ke =

For firstorder kinetics:
*Ke =0.693/t1/2 

Vd (volume of distribution =

* Vd = amount of drug in body/plasma concentration
Vd is large when the drug is highly concentrated in tissues; Vd is small when the drug is extensively bound to plasma protein. 

Cl (clearance) =

Clearance (Cl): Total body clearance of the drug is defined as the volume of blood or plasma effectively cleared of drug by elimination(metabolism and excretion) per unit time.
It is the sum of clearance from all organs of elimination. As elimination of most drugs is carried out largely by the kidney and the liver, then * Cl = Cl renal + Cl hepatic 

IV infusion rate=

IV Infusion: The infusion rate equals elimination rate at STEADY STATE.
* Infusion rate= CP X Cl(amt/time)(amt/vol)(vol/time) 

intermittent injection dose =

*Dose = C pav X Cl X dosage interval
where C pav = average plasma concentration at the plateau 

oral maintenance and loading doses during a dosage regimen.

?
