Disposition of Drugs Flashcards
Stages of drug Disposition
- absorption
- distribution
- biotransformation
- excretion
Factors Affecting Simple Diffusion
- Concentration Gradient
- Lipid solubility
- Degree of ionization
pka
pH at which a weak electrolyte is 50% ionized and 50% nonionized
Ionization of a drug depends on?
- pH of the drug
- aka of the drug
- pH of the medium (environment)
The rate of diffusion depends on what?
Drugs cross biological membranes in the non-ionized form. (lipid soluble & do not carry electric charges) The rate of diffusion depends on the ratio between the non ionized form of the drug & the ionized form (N/I)
Acidic drugs ionize in what kind of medium?
Alkaline medium
Basic drugs ionize in what kind of medium?
Acidic medium
Facilitated diffusion
carrier mediated transport that doesn’t need energy. (downhill movement)
Example of facilitated diffusion
Movement of glucose across a muscle cell membrane by insulin sensitive glucose transporter is an example of facilitated diffusion
Example of pinocytosis
Sequestration of amino glycoside antibiotics by renal tubular cells
Drugs cross cell membranes mainly by what type of diffusion?
Simple diffusion
Can charged drugs cross biological membranes?
No
This type of drug can cross biological membranes
weak acidic or weak basic drugs cross biological membranes in the uncharged (non-ionized) form.
T/F uncharged molecules more readily cross cell membranes than charged molecules
TRUE
T/F
acidification of the urine accelerates the secretion of a weak base, pKa=8
Does plasma protein binding prolong the half-life of the drug
YES
poorly perfused tissues
bone & adipose tissue
Moderately perfused tissues
muscle & skin
highly perfused tissues
brain, liver, kidney & endocrine glands
Tetracycline has an affinity to what type of tissues
Calcium in skeletal muscles (don’t give this medicine w/ cheese)
Amino glycosides have an affinity to what type of tissue?
Kidney tissue
Iodine has an affinity to what tissue?
Thyroid gland traps iodine
what is the most common cognation reaction?
Conjugation to glucuronic acid
Cats are deficient in
gmucuronly transferases (also in hydroxylation & dealkylation)
Dogs lack what enzymes
acetylating enzymes
Drug examples that have extensive first-pass effect
Lidocaine, propranolol & morphine
Ruminants & horses have high levels of what enzymes
oxidative enzymes (birds lack these enzymes)
Drug inhibitors
Ketoconazole (used w/ cyclosporin for dermatitis & it has a low safety margin & ketoconazole can inhibit some of the enzymes in cyclosporin), Chloramphenicol, cimetidine
Drug enzyme inducers
Phenobarbital, phenylbutazone, griseofulvin, & rifampin