Pharmacokinetics Flashcards
Determines the rate of absorption
Time - plasma drug concentration relationship
What is “First order kinetics”
Example; half - life
- Constant percentage, each time, is absorbed/disappeared from the site of administration
- The rate of change of drug concentration is directly proportional to the concentration of the drug at the time. (merck)
What is “zero order kinetics”
Example; drugs do not have true half - life
- Fixed rate of drug absorption and elimination
- Constant amount of drug absorbed per unit of time
Drugs do not have true half - life
Ex. Ethanol is eliminated at 10 ml/hr regardless of how much you drink
P - phenytoin
P - phenylbutazone
E - ethanol
A - aspirin
D - dicumarol
Measures the drug concentration from the 1st absorption to the last. It determines bioavailability
Area under the curve (AUC)
(True or False). Drugs with high Vd have much higher concentrations in extravascular tissue?
True
The time it takes for a drug concentration to be reduced to half of its initial concentration?
Half - time (t 1/2)
Half - time includes the process of?
B - biotransformation
E - elimination
D - distribution
In order (D. B. E.)
The rate of drug elimination is directly proportional to concentration. Follows the 1st order kinetic process.
It is also the single most important factor determining drug concentrations
Total Body Clearance
The fraction of unchanged drug reaching the systemic circulation following administration by any route
Bioavailability
Drugs are exposed to low pH ranges, digestive enzymes, enteric microflora and ingesta that vary greatly between species
Oral route ( by mouth; per os; per orem, p.o.)
Aqueous solution is preferable, which leads immediately high blood levels with rapid onset of action
Intravenous route
In the subcutaneous route, absorption can be enhanced by increasing the blood supply to the area thoroughly?
Warmth or vigorous massage or
Inclusion of the enzyme “hyaluronidase” in the formulation
Enumerate sites of absorption
G - gastro - intestinal
R - respiratory tract
I - intraperitoneal
P - parenteral
S- skin
Factors affecting gastro - intestinal absorption
- Lipid solubility of drugs
- Degree of ionization (Drugs must be less ionized)
- Nonionized
Factors affecting parenteral route absorption
V - vascularity of the site
V - volume of injection
O - osmolality of the solution
C - concentration and lipid solubility of the drug
How to increase the rate of absorption in the parenteral route?
- heating, massage, or exercise
- add hyaluronidase in large volume in SC
How to decrease the rate of absorption in the parenteral route?
- immobilization of the site, local cooling, a tourniquet
- incorporation of vasoconstrictor, an oil base, implant pellets, insoluble “depot” preparation
How to reduce the chances of inducing drug reactions in the intravenous route
Allow at least one circulation time (1-2 minutes) to complete an intravenous injection
Absorption from this route is usually complete but drugs may undergo first pass effect, as they are also absorbed into the hepatic portal circulation from the peritoneal cavity
Intraperitoneal absorption
Most important in xenobiotics
Passive diffusion
P - glycoprotein
Facilitate transport
Intestinal epithelial cells and renal tubular cells
Pinocytosis
The anesthetic effect of thiopental is terminated by:
A. Biotransformation
B. Redistribution
C. Excretion
D. Distribution
B. Redistribution
Drugs exhibiting the redistribution phenomenon are
Highly lipid - soluble
