Pharm Exams 1 Flashcards
Properties that determine the onset, intensity, and duration of drug action
Absorption, distribution, metabolism, elimination
Absorption
Transfer from site of administration to blood
Distribution
Transfer from blood to tissue and target sites
Mechanisms of drug absorption
Passive diffusion, facilitated diffusion, active transport, endocytosis
Oral administration advantages
*Safest
*Most common
*Convenient and economical
Oral administration disadvantages
*limited absorption for some drugs
* food may affect absorption
*patient compliance necessary
*drugs may be metabolized before systemic absorption
IV administration advantages
*can have immediate effects
*ideal if dosed large volumes
* suitable for irritating substances
* valuable emergency situations
*dosage titration permissible
*ideal high molecular weight proteins and peptide drugs
IV Administration disadvantages
*Unsuitable for oily substances
*bolus injection may result in adverse effects
* most substances must be slowly injected
*strict aseptic techniques required
SQ administration advantages
*suitable for slow release drugs
*ideal for some poorly soluble suspensions
SQ administration disadvantages
*pain or necrosis if drug irrritating
*unsuitable for drugs administered in large volumes
IM administration advantages
*suitable if drug volume moderate
*suitable oily vehicles and certain irritating substances
*preferable to IV if patient must self administer
IM Administration disadvantages
*affects certain lab tests (creatinine kinase)
*can be painful
*can cause intramuscular hemorrhage
Transdermal (patch) administration advantages
*bypasses first effect
*convenient and painless
*ideal for lipophilic drugs and drugs with poor oral bioavailability
*ideal for drugs that are quickly eliminated from the body
Transdermal administration disadvantages
*allergies
*drug must be highly lipophilic
*may cause delayed delivery of drug to pharmacological site of action
*limited to drugs that can be taken in small daily doses
Rectal administration advantages
*partially bypasses first pass effect
*bypasses destruction by stomach acid
*ideal in patients who are vomiting or comatose
Rectal administration disadvantages
*drugs may irritate rectal mucosa
*not a well accepted route
Inhalation administration advantage
*rapid absorption, can have immediate effects
*ideal for gases
*effective for patients with respiratory problems
*dose can be titrated
* localized effect to target lungs: lower doses than oral or parenteral administration
Inhalation administration disadvantage
*most addictive route
*patient may have difficulty regulating dose
*some patients may have difficulty using inhalers
Sublingual administration advantages
*bypasses first effect
* bypasses destruction by stomach acid
* drug stability maintained because the pH of saliva is relatively neutral
*may cause immediate pharmacological effects
Sublingual administration disadvantages
*limited to certain types of drugs
*limited to drugs that can be taken in small doses
*may lose part of the drug dose if swallowed
Passive Diffusion
Molecules diffuse from an area of higher concentration to an area of lower concentration
***
Think passing a ball you would throw to someone holding less
Facilitated diffusion
Use of transport proteins that move molecules or ions
***
Think of transport proteins as a facility they move through
Facilitated diffusion
Use of transport proteins that move molecules or ions
Active transport
Molecules diffuse from area of lower concentration to area of higher concentration, require ATP
***
Active=energy, more energy to push through a busy area than into a quiet area
Endocytosis
Cells take substances from surrounding environment by engulfing within plasma membrane vesicles
***
ENdo ENgulf
Factors that influence drug absorption
*pH
*blood flow
*total surface area
*contact time
*expression p. Glycoprotein
How does pH influence drug absorption?
Influences charge of a drug. Charged drugs do not cross membranes easily and are therefor not well absorbed
Weak acids are better absorbed in ___ environment
Acidic
Weak bases are better absorbed in ____ environment.
Basic
How does blood flow influence drug absorption?
Reduced blood flow= reduced exposure to drug. The concentration gradient is lowered and absorption is reduced by passive diffusion.
In the kidney, glomeruli have what type of capillaries?
Fenestrated capillary, the largest filtration slits which allow drugs to pass.
What type of capillaries are found in the liver?
Sinusoidal capillary, sinusoids are also discontinuous endothelial cells.
The blood brain barrier is a tight barrier that only allows ___ soluble compounds to get past.
Lipid
The capillaries of the blood brain barrier are what type?
Continuous capillary
How does total surface area influence drug absorption?
Larger surface area allows for better absorption (more space for absorption to take place) and also typically has a larger blood supply for a drug to move down the concentration gradient.
Contact time
Longer contact time = increased absorption, shorter contact time=decreased absorption
How does the expression of P Glycoprotein influence drug absorption?
Significantly decreased drug absorption by actively pumping drugs back into the intestinal lumen. This limits the amount of drug that can enter the bloodstream from the gut. Essentially a barrier to drug absorption
Bioavailability
The rate and extent to which a drug is absorbed after administration.
Formula for bioavailability
Area under the curve (non IV)/ Area under the curve by IV
Four factors that influence bioavailability
*1st pass hepatic metabolism
*Drug solubility
*drug stability
*drug formulation
First pass hepatic metabolism affect bioavailability?
Oral administration requires drugs to go through the liver where they can be metabolized
How does Drug solubility influence bioavailability?
A readily absorbed drug must be lipophilic to cross membranes easily
How does Drug stability influence bioavailability?
Drugs taken orally must pass the acidic stomach, chemical structure will determine bioavailability
How does drug formulation influence bioavailability?
Drug formulation alters chemistry: particle size, coatings, binders
tablet, capsule, cream, gel, etc
