1. Routes of Drug Administration
Robert L. Copeland, Ph.D.
Department of Pharmacology

2. Drug Absorption
Absorption is the process by which a drug enters the bloodstream without being chemically altered
The movement of a drug from its site of application into the blood or lymphatic system

3. Drug Absorption Factors which influence the rate of absorption
types of transport
the physicochemical properties of the drug
protein binding
routes of administration
dosage forms
circulation at the site of absorption
concentration of the drug

4. Ion Trapping:
Kidney:
Nearly all drugs filtered at the glomerulus:
Most drugs in a lipid-soluble form will be absorbed by passive diffusion.
To increase excretion: change the urinary pH to favor the charged form of the drug:
Weak acids: excreted faster in alkaline pH (anion form favored)
Weak bases: excreted faster in acidic pH (cation form favored)

5. Routes of Drug Administration
Important
Info
The route of administration (ROA) that is chosen may have a profound effect upon the speed and efficiency with which the drug acts

6. The possible routes of drug entry into the body may be divided into two classes:
Enteral
Parenteral

7. Enteral Routes sublingual - placed under the tongue
Enteral - drug placed directly in the GI tract:
sublingual - placed under the tongue
oral - swallowing (p.o., per os)
rectum - Absorption through the rectum

8. Sublingual/Buccal Advantages
Some drugs are taken as smaller tablets which are held in the mouth or under the tongue.
Advantages
rapid absorption
drug stability
avoid first-pass effect

9. Sublingual/Buccal Disadvantages inconvenient small doses
unpleasant taste of some drugs

10. Oral
Advantages
Convenient - can be self- administered, pain free, easy to take
Absorption - takes place along the whole length of the GI tract
Cheap - compared to most other parenteral routes

11. Oral
Disadvantages
Sometimes inefficient - only part of the drug may be absorbed
First-pass effect - drugs absorbed orally are initially transported to the liver via the portal vein
irritation to gastric mucosa - nausea and vomiting

12. Oral Disadvantages cont.
destruction of drugs by gastric acid and digestive juices
effect too slow for emergencies
unpleasant taste of some drugs
unable to use in unconscious patient

13. First-pass Effect
The first-pass effect is the term used for the hepatic metabolism of a pharmacological agent when it is absorbed from the gut and delivered to the liver via the portal circulation. The greater the first-pass effect, the less the agent will reach the systemic circulation when the agent is administered orally

14. Rectal 1. unconscious patients and children
2. if patient is nauseous or vomiting
3. easy to terminate exposure
4. absorption may be variable
5. good for drugs affecting the bowel such as laxatives
6. irritating drugs contraindicated

15. Parenteral Routes
Intravascular (IV, IA)- placing a drug directly into the blood stream
Intramuscular (IM) - drug injected into skeletal muscle
Subcutaneous - Absorption of drugs from the subcutaneous tissues
Inhalation - Absorption through the lungs

18. Intravascular Absorption phase is bypassed (100% bioavailability)
1.precise, accurate and almost immediate onset of action,
2. large quantities can be given, fairly pain free
3. greater risk of adverse effects
a. high concentration attained rapidly
b. risk of embolism
c. OOPS factor or

19. Intramuscular 1. very rapid absorption of drugs in aqueous solution
2.repository and slow release preparations
3.pain at injection sites for certain drugs

20. Subcutaneous
1. slow and constant absorption
2. absorption is limited by blood flow, affected if circulatory problems exist
3. concurrent administration of vasoconstrictor will slow absorption

21. Inhalation 1.gaseous and volatile agents and aerosols
2.rapid onset of action due to rapid access to circulation
a.large surface area
b.thin membranes separates alveoli from circulation
c.high blood flow
Particles larger than 20 micron and the particles impact in the mouth and throat. Smaller than 0.5 micron and they aren't retained.

22. Inhalation cont. Respiratory system. Except for IN, risk hypoxia.
Intranasal (snorting) Snuff, cocaine may be partly oral via post-nasal dripping. Fairly fast to brain, local damage to septum. Some of the volatile gases also appear to cross nasal membranes.
Smoke (Solids in air suspension, vapors) absorbed across lung alveoli: Nicotine, opium, THC, freebase and crack cocaine, crystal meth.Particles or vapors dissolve in lung fluids, then diffuse. Longer action than volatile gases. Tissue damage from particles, tars, CO.
Volatile gases: Some anaesthetics (nitrous oxide, ether) [precise control], petroleum distillates. Diffusion and exhalation (alcohol).
Lung-based transfer may get drug to brain in as little as five seconds.

23. Topical
Mucosal membranes (eye drops, antiseptic, sunscreen, callous removal, nasal, etc.)
Skin
a. Dermal - rubbing in of oil or ointment (local action)
b. Transdermal - absorption of drug through skin (systemic action)
i. stable blood levels
ii. no first pass metabolism
iii. drug must be potent or patch becomes to large

24. Route for administration
-Time until effect-
intravenous seconds
intraosseous seconds
endotracheal 2-3 minutes
inhalation 2-3 minutes
sublingual 3-5 minutes
intramuscular minutes
subcutaneous minutes
rectal 5-30 minutes
ingestion minutes
transdermal (topical) variable (minutes to hours)

25. Time-release preparations
Oral - controlled-release, timed-release, sustained-release
designed to produce slow,uniform absorption for 8 hours or longer
better compliance, maintain effect over night, eliminate extreme peaks and troughs

26. Very Important
Info!
No single method of drug administration is ideal for all drugs in all circumstances