PCL201H1 Lecture Notes - Lecture 6: Lipophobicity, Circulatory System, Bioavailability

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PCL201
Winter 2014
Lecture 6 Drug Administration
1. Overview and important considerations in drug administration
2. Examination of various routes and techniques of drug administration
a) Topical
b) Percutaneous/transdermal
c) GI tract (sublingual, oral, rectal)
d) Pulmonary
e) Injection (SC, IM, IV, IA, IP)
3. Selection of route
1. Overview and important considerations in drug administration
Route of administration: the method by which the drug is introduced into the body
o Any drug (except those that act topically) must be absorbed into circulation
Must consider:
o Physiochemical properties of the drug
o Target site
o Systemic vs. local
Systemic: drug enters systemic circulation
Local: drug stays at site of administration (topical)
o Speed and duration
o Bioavailability
The proportion absorbed from the site of administration that reaches
the circulation unchanged, depends heavily on route of administration
100% for drugs given IV and less for other methods (e.g. oral)
Reduced if incompletely absorbed from site of administration or first-
pass metabolism
First-pass metabolism: metabolism of the drug in the liver before
reaching general circulation
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PCL201
Winter 2014
Orally administered drugs are absorbed from GI tract and
delivered to the liver via the portal vein before general
circulation
o Bioactivation (prodrug)
o Toxicity
o Practicality and convenience
o Other factors
Enteral vs. parenteral
o Enteral: through GI (oral, sublingual, and rectal routes)
o Parenteral: not through GI (injection routes)
2. Examination of various routes and techniques of drug administration
a) Topical
Works locally
Direct application to site of action
E.g. ointments, eye drops, sprays, intrathecal injections
b) Percutaneous/transdermal
Absorption into circulation through skin
o Best with lipid soluble drugs
Few substances are completely impermeable
E.g. birth control patch
c) GI tract (sublingual, rectal, oral)
Sublingual
Absorbed through oral mucosa into circulation
o Drugs intended for local action in the mouth that don’t require systemic
absorption are classified are topically administered
E.g. nitroglycerine tablets
Rectal
Absorbed in the terminal segment of large intestine
Used when oral is unsuitable (e.g. nausea, unconsciousness, drug unstable in
gastric pH)
o May be used topically (e.g. laxatives)
E.g. suppositories, enemas
Oral (PO or per os)
Often swallowed
Absorption through GI epithelial and mucosa
Effectiveness depends on:
o pH of GI and stability of drug in that pH
o Breakdown by enzymes
o Gastric emptying rate (whether or not you’re taking it with food)
Bioavailability can increase or decrease
o Physical activity (less blood flow to GI when exercising)
o Concentration of drug
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