Absorption & Distribution Pharm Flashcards
*Routes of Administration of Medications
Enteral- oral/rectal
Parenteral- intravascular, intrathecal, intramuscular, subcutaneous
Mucous Membranes- inhalation, sublingual, nasal, vaginal, ocular, urinary
Topical/Transdermal- skin
*Routes of Drug Administration are absorbed and distributed by…
Oral- drug placed in GI tract, first pass metab, blood
Rectal: drug placed in lower GI tract, avoid 1st pass metab, blood
Intravascular- place drug into blood streatm, absorption phase bypassed, 100% Bioavail.
Intrathecal- place drug into CSF, bypass BBB
Intramuscular- drug injected into skeletal muscle
Subcutaneous- drug injected into tissue just below skin
Mucous Membrane- avoids 1st pass metab, direct delivery to affected tissue
Transdermal- lipophilic drugs can passively diffuse across skin, 100% Bioavail.
*Factors affecting Drug Absorption
Administration route Rate of dissolution Drug formulation Physical factors: -blood flow -surface area -contact time -GI motility -Gastric emptying time -food Diffusion -concentration gradient of drug -lipid solubility -pH levels on each side of membrane Transport: -active -passive
*DIffusion (drugs) Across Lipid Bilayer
Simple diffusion Channel Protein Carrier Protein Active Transport Concentration Gradient
*Drug Permeability/ Rate of Transport across Membranes depends on:
molecular size lipophilicity charge degree of ionization blood flow protein binding
- Small, hydrophobic/lipophillic, non-polar, non-ionized molecules passively diffuse the most rapidly.
Drug molecules tend to be ionized when….
in a pH opposite fluid
ex. basic drug in acidic fluid
Non-ionized or ionized drugs tend to move across membrane via passive diffusion.
non-ionized
*Ionized require active transport mechanisms, facilitated diffusion, or endo/exocytosis
Drugs are usually _____ acids or _______ bases and where/how would they diffuse across the plasma membrane?
weak, weak
Basic drugs are able to absorbed into intestines (not a lot of H+; do not become ionized, basic environment)
Acidic drugs are better able to be absorbed into stomach (lots of H+, do not become ionized d/t already acidic environment) A basic drug would pick up a H+ thereby gaining a charge and becoming ionized and not diffusing across the membrane.
*Factors affecting Distribution of Medications in body
- blood flow to tissue
- size of organ
- solubility of drug
- capillary permeability
- binding (plasma protein)
- volume of distribution
Blood flow affects on distribution of drug
tissues with high blood flow receive significant amount of drug in a short time
Size of organ affects on distribution of drug
very large organ take up large quantities of drug if allowed to reach steady state
pH trapping
review slide 43
Volume of Drug Distribution (Vd)is..
the amount of drug in the body/plasma concentration
Vd is affected by
drug pKa lipid solubility gender age disease body comp (muscle mass, body fat, etc)
4 Compartment Model of Drug Distribution
Blood- initially high, but falls rapidly
Vessel-rich group- first to accumulate drug
Muscle- less perfused than VRG but LARGER c
Fat- much of drug has been metabolized and excreted by the time it reaches here.
