Routes Routes of of Drug Drug Administration Administration

Routes Routes of of Drug Drug Administration Administration 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

Drug Absorption Factors which influence the rate of absorption the physicochemical properties of the drug routes of administration dosage forms circulation at the site of absorption concentration of the drug

Drug Absorption Mechanisms passive of absorption diffusion filtration endocytosis active transport

Lipid-Water Partition Coefficient The higher the lipid/water p.c. the greater the rate of absorption decrease the lipid/ water p.c will increase polarity of a drug, by increasing ionization. increase the lipid/ water p.c. Will decrease polarity of a drug, suppression of ionization

Routes of Drug Administration 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.) 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 avoid first-pass effect

Sublingual/Buccal Disadvantages small doses unpleasant taste of some drugs

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 intestine and delivered to the liver via the portal circulation.

First-pass Effect

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 non-efficient - only part of the drug may be absorbed Expose to 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. effect too slow for emergencies unpleasant taste of some drugs Not suitable to use in unconscious patient

Rectal Uses 1. unconscious patients and children 2. if patient is nauseous or vomiting 3. good for drugs affecting the bowel such as laxatives 4. irritating drugs contraindicated

Parenteral Routes Intravascular (IV)- placing a drug directly into the blood stream Intramuscular (IM) - drug injected into skeletal muscle Subcutaneous - Absorption of drugs from the subcutaneous tissues

Intravenous Absorption phase is zero (100% bioavailability) 1.Precise and accurate onset of action, 2. large amounts can be given 3. High risk of adverse effects e.g. risk of embolism

Intramuscular .Pain at injection sites for certain drugs Used for oily or suspension drugs

Subcutaneous 1. slow absorption 2. absorption is limited by blood flow,

Inhalation 1.gaseous and volatile agents and aerosols 2.rapid onset of action due to rapid reach circulation a.large surface area b.high blood flow

Topical Mucosal membranes (eye drops, antiseptic, sunscreen,.) Skin a. Dermal - ointment (local action) b. Transdermal - absorption of drug through skin (systemic action) i. no first pass metabolism e. g patches

Route for administration -Time until effect intravenous 30-60 seconds inhalation 2-3 minutes sublingual 3-5 minutes intramuscular 10-20 minutes subcutaneous 15-30 minutes rectal 5-30 minutes Oral 30-90 minutes transdermal (topical) variable (minutes to hours)

Experiment :1 30 md/kg of phenobarbital sodium to rats by Oral IP IM Action: loss of righting reflex, ataxia, anasethia. Record onset time and recovery time Experiment: 2 Effect of route of drug administration on drug action: Magnesium sulphate I.P 1.0 gm/kg sedation Oral 6.0 gm/kg laxation