Drug Disposition: Absorption Flashcards
(1) Define “therapeutic window.”
therapeutic window is the plasma drug concentration above which there is a therapeutic response but below which there is a toxic response
(2) Contrast absorption and distribution of a
absorption is the process in which the drug moves into the blood stream, distribution is the the process where the drug moves from the blood stream to the tissue
(2) What variables affect drug absorption? (6)
dissolution time (solid forms) solubility concentration at site of admin perfusion rate v. diffusion rate area of absorbing surface membrane permeability
(2) Describe difference in perfusion rate effecting drug distribution.
organs receive different blood flow (perfusion) and that effects how much of the drug they can be delivered and how fast
(3) Describe how a drug can be diffusion limited.
a drug whose transport rate is limited by diffusion rate will not be changed by the perfusion rate
(3) Describe how a drug can be perfusion limited.
a drug whose transport is limited by perfusion will show a different rate of transport when perfusion is increased or decreased
(3) Drug molecules move through membranes by a process of ________, through various sized pores in the membranes.
diffusion
(2) What factors effect the rate of simple diffusion of a drug?
concentration gradient chemical nature of the compound (lipid,polar etc) area and permeability of the membrane thickness of the membrane (Described by Flux and Fick's Law)
also local pH
(4) Define weak acid and weak base.
weak acid = proton donator
weak base= proton acceptor
(5) When are weak bases/acids charged… when protonated or unprotonated?
weak acids when protonated are neutral
weak bases when protonated are charged (+)
(5) What is unique about the situation when the pH is equivalent to an acid’s pka?
the species will be 50/50 protonated/unprotonated
(5) What is ion trapping?
depending on whether a drug is charged or not (based on protonation and pH) it may stay within a give compartment because it is unable to cross the cell membrane due to its charge (body fluids/compartments vary in pH)
(6)State the Henderson-Hasslebalch equation.
pKa-pH= log( protonated/unprotonated)
(6) Would you consider both facilitated diffusion and active transport as specific and able to be saturated
yes, both facilitated diffusion and active transport are molecularly specific and can be saturated.
(7) What are the 3 enteric routes of drug administration?
oral (PO); sublingual (SL); and rectal (PR)
(7) Name important considerations when admin drug PO.
safe, easy and economical but slower and variable absorption which is subject to the 1st pass effect and pH partitioning
(7) What is important to remember when administering drugs SL or PR? (concerns are distinct for each)
sublingual provides quick absorption that avoids the first pass effect, great for lipophillic substances; rectal in the form of suppositories or enemas reduces the 1st pass effect and is useful if the patient is vomiting or unconscious
(7) Describe advantages and disadvantages of admin via parenteral routes.
rapid onset with predictable action and bypasses gut enzymes, gut flora and liver (more control); drugs must be sterile, more expensive and less self-admin, danger of thrombus or embolism
(7) Name 7 parenteral routes for drug administration.
subcutaneous (SC), intramuscular (IM), intravenous (IV) and topical, intraarterial, intrathecal, pulmonary
(7) What are the characteristics and limitations of SC admin?
slow absorption can provide sustained effect or depots (oil or pellet) for long duration of action; not suitable for large volumes or irritating substances
(7) What are the characteristics and limitations of IM admin?
rapid absorption of aqueous solution with high blood flow, can inject more irritating substances but soreness my result with injection (note- some anipsychotics given this way in long acting form to help with patient compliance
(7) Describe indications and benefits for IV drug admin.
highly accurate dosing, absorption dependent only on rate of infusion, suitable for large volumes and irritating substances; not suitable for oily solution or insoluble drugs
(7) Where and why are topical admins used?
where: skin, eyes, mucous membranes
why: to deliver drug at or immediately beneath the point of application
(7) Name one reason the following parenteral routes are used: intraarterial, intrathecal, pulmonary
intraarterial: chemotherapeutics or diagnostic agents
intrathecal: spinal anesthesia or to bypass BBB
pulmonary: admin gaseous, volatile or aerosols; rapid absorption (**important to consider the size of particles in pulmonary admin)
