Routes of drug administration

Routes of Drug Administration www.freelivedoctor.com

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

Drug Absorption
The rate at which a drug reaches it site of action depends on:
Absorption - involves the passage of the drug from its site of administration into the blood
Distribution - involves the delivery of the drug to the tissues

Drug Absorption
Mechanisms of solute transport across membranes
passive diffusion
filtration and bulk flow
endocytosis
ion-pairing
active transport
Drug Absorption animation

Ion Trapping cont: Body fluids where a pH difference from blood pH will favor trapping or reabsorption: stomach contents small intestine breast milk aqueous humor (eye) vaginal secretions prostatic secretions www.freelivedoctor.com

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)

Lipid-Water Partition Coefficient
The ratio of the concentration of the drug in two immiscible phases: a nonpolar liquid or organic solvent (representing the membrane); and an aqueous buffer, pH 7.4 (representing the plasma)

Lipid-Water Partition Coefficient
The higher the lipid/water p.c. the greater the rate of transfer across the membrane
polarity of a drug, by increasing ionization will the lipid/ water p.c.
polarity of a drug, suppression of ionization will the lipid/ water p.c.

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

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

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

Sublingual/Buccal
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

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

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

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

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

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

First-pass Effect cont. Magnitude of first pass hepatic effect: Extraction ratio (ER) ER = CL liver / Q ; where Q is hepatic blood flow (usually about 90 L per hour. Systemic drug bioavailability (F) may be determined from the extent of absorption (f) and the extraction ratio (ER): F = f x (1 -ER) www.freelivedoctor.com

First-pass Effect www.freelivedoctor.com

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 www.freelivedoctor.com

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

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 !@#$% www.freelivedoctor.com

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

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 www.freelivedoctor.com

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. www.freelivedoctor.com

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.

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

intravenous 30-60 seconds
intraosseous 30-60 seconds
endotracheal 2-3 minutes
inhalation 2-3 minutes
sublingual 3-5 minutes
intramuscular 10-20 minutes
subcutaneous 15-30 minutes
rectal 5-30 minutes
ingestion 30-90 minutes
transdermal (topical) variable (minutes to hours)
Route for administration -Time until effect- www.freelivedoctor.com

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

Time-release preparations
Depot or reservoir preparations - parental administration (except IV), may be prolonged by using insoluble salts or suspensions in non-aqueous vehicles.

The ROA is determined by the physical characteristics of the drug, the speed which the drug is absorbed and/ or released, as well as the need to bypass hepatic metabolism and achieve high conc. at particular sites www.freelivedoctor.com Important Info

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

Routes of drug administration

by raj kumar on Apr 20, 2010

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