3 Medical Mathematics: Absorption of Drugs Flashcards
What are the factors that affect drug absorption?
Factors related to the drug
Factors related to the animal
What is Absorption of drugs?
Is the transfer of the drug from the site of administration to the circulation
What are the factors that are related to the drug?
molecular size lipid solubility degree of ionization dissolution drug in water concentration of drug at absorptive site route of administration
Molecular size
The smaller the molecular size, the faster is penetration through the pores
Lipid solubility
The greater the lipid solubility, the greater is diffusion
Degree of ionization
The higher the ratio between N/I, the faster is diffusion
Dissolution of drug in water
Oral absorption of liquid drugs is faster than solid drugs.
Oral absorption of solid drugs depends on their rate of dissolution
Concentration of drug at absorptive site
Depends on the dose and concentration.
The higher the concentration the faster is absorption
List the Routes of administration of drugs
Sublingual and inhalation have a very rapid absorption.
Intramuscular is slower than sulingual and inhalation.
Subcutaneous is slower than intramuscular.
Oral is usually slower than injection
What are the factors related to the animal?
Blood flow Absorbing surface area Connective tissue Species Individual
Blood flow
Absorption of a drug from a particular site is related to blood flow to that site.
Increased blood flow increases drug absorption.
Drugs, physiological factors and disease can modify blood flow.
Heat or massage of intramuscular injection site increases blood flow and absorption.
Sympathetic stimulation increases blood flow to skeletal muscles.
Sympathetic stimulation decreases blood flow to the GI tract and subcutaneous sites
and skin.
Shock and edema decrease blood flow
Absorption from the GI tract
The upper part of the small intestine is the main site of absorption for all drugs given orally because of the extensive surface area and rich blood supply.
Therefore, the rate of absorption depends on the rate of gastric emptying.
Drugs and disease can modify the rate of gastric emptying.
What factors affect drug absorption from the GI tract?
The rate of absorption of solid drugs depends on their rate of dissolution. Activity of the gut. Presence of other substances. Blood flow. Species. Individual.
