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Basic Biopharmaceutics
Chapter 10
Biopharmaceutics
• The study of the factors associated with drug
products and physiological processes, and the
resulting systemic concentration of the drugs.
How Drugs Work
• Drugs produce either desired or undesired
effects on the body.
– Once the drug is in the blood, drugs are circulated
throughout the body.
– Both the drug and the body influence where the
drug will go.
– The place where the drug causes an effect to
occur is called the site of action.
How Drugs Work
• The objective of drug therapy is to deliver the
right drug, in the right concentration, to the
right site of action, and at the right time to
produce the desired effect.
How Drugs Work
• When a drug produces an effect, it is
interacting at a molecular level with cellular
material or structure.
• Cellular material directly involved in the
action of the drug is called a receptor.
• The receptor is described as a lock into which
the drug molecule fits as a key.
• Drugs are selective in their action, they only
act on specific targeted receptors and tissues.
How Drugs Work
• Pharmacological effects of these interactions
are agonists (agonism) or antagontists
(antagonism).
– Agonist – drugs that activate receptors to
accelerate or slow normal cellular function
– Antagonists – drugs that bind with receptors but
do not activate them. They block receptor action
by preventing other drugs or substances from
activating them
ADME Process
Blood concentration of a drug are the result of
four simultaneously occurring processes:
– Absorption
– Distribution
– Metabolism
– Excretion
– Besides the ADME process, an important factor of
drug concentration is how drugs move through
biological membranes by diffusion.
Absorption
• Once a drug is released from its dosage formulation,
the process that transfers it into the blood is called
absorption.
• One of the primary factors affecting oral drug
absorption is the gastric emptying time.
– This the time that the drug remains in the stomach before
it is emptied into the small intestine
– Most absorption occurs in the small intestine.
– Some factors increase the gastric emptying time, but most
slow it.
– If a drug remains in the stomach too long, it can be
degraded or destroyed, and its effect decreased.
Absorption
• Gastric emptying time can be affected by:
– Amount and type of food in the stomach
– The presence of other drugs
– The person’s body position
– The person’s emotional state
Distribution
• Blood carries the drug throughout the body
and to its sites of action.
• Drugs are rapidly distributed to organs having
high blood flow rates such as the heart, liver
and kidneys.
• Distribution to the muscle, fat, and skin is
slower because they have lower blood flow
rates.
Metabolism
• Drug metabolism refers to the body’s process of
transforming drugs.
• The transformed drug is called a metabolite.
• The primary site of drug metabolism is in the liver.
• When transformed in the liver a drug is broken down
into inactive or active molecules. Inactive are
excreted through the kidneys and active produce
effects and excreted later.
Excretion
• Most drugs are excreted in the urine by the
kidneys. The functional unit of the kidney is
the nephron.
• Some oral drugs that are difficult to break
down can be excreted in the feces (poop).
• The job of the kidney is to filter the blood and
remove waste products.