Pharmacokinetics Flashcards
Direct penetration of membrane
most common, large, lack a transport system, must be lipid soluble
Channels and Pore
very few use, small compounds (potassium and sodium), select channels
Transport systems
move drugs through the cell membrane, require energy, selective for a particular drug, p-glycoprotein
Molecules that can’t penetrate cellular membranes
polarized molecules: no net - unevenly distributed, ions: positive and negative, cell membrane not polar
Acids tend to ionize (give up a proton)
in an alkaline environment (less transportable)
Bases tend to ionize (accept a proton)
in an acid environment (less transportable_
Acidic drugs accumulate
on the alkaline side
Basic drugs will accumulate
on the acidic side
Absorption
the movement of a drug from its site of administration into the blood
Factors affecting absorption
rate of absorption, surface area, blood flow, lipid solubility, pH
External routes of administrations
via the GI tract
Parenteral routes of administration
Outside the GI tract (by injection)
IV, SQ, IM
Oral administration
tablets, time-released, sustained-release
Oral advantages
safe, convenient, inexpensive
Oral disadvantages
variable absorption, stomach acid, liver, Pt adherence, GI irritation
Parental administration advantages
more rapid onset (IV), control of plasma level, patient’s cant and wont take orals
Parental administration disadvantages
high cost, inconvenient, irreversibility, fluid overload, infection, embolism
Distribution
movement of drugs throughout the body, blood transport drugs to tissues and organs, leave at capillary beds
Protein binding
drugs can form reversible bonds with proteins, plasma albumin, hypoalbuminemia, hyperalbuminemia
Albumin does what
stays in the bloodstream because its a large molecule
Restricts drug distribution if
drug is bound
Biotransformation
chemical alteration of drug structure
Most metabolism takes place in the
liver
Therapeutic consequences of metabolism
accelerates renal excretion, drug inactivation, increase therapeutic action, activation of prodrugs, toxicity
Special considerations
age, induction/inhibition of drug-metabolizing enzyme, first-pass effect, nutritional status
Excretion
removal of drugs from body - kidneys
Glomerular filtration
moves drugs from blood to tubular urine; protein-bound drugs remain in blood
Passive tubular reabsorption
lipid-soluble drugs undergo; ions and polar compounds stay in urine
Active tubular secretion
active pumps for organic acids and based from blood to urine
Breast milk drug excretion
lipid soluble readily; polar, ionized, or protein-bound don’t cross
Bile drug excretion
secreted into small intestines and excreted via feces
Lungs drug excretion
volatile anesthetic
Minimum Effective Concentration (MEC)
the plasma drug level below which therapeutic effects will not occur
Toxic concentration
plasma levels where toxic effects begin
Therapeutic range
range between MEC and toxic concentration
Drug half life
time required for the amount of drug in the body to decrease by 50%
