Oral
Intradermal, topical
Inhalation
Sublingual, buccal
intravenous
Subcutaneous, intramuscular
Meds must pass through the layer of cells that line the GI tract.
Swallowing before dissolution allows gastric pH to inactivate the medication.
capillary walls have large spaces between cells, no significant barrier.
close proximity of epidermal cells
NO barriers
inspiratory effort