Transcript Drug absorption

Drug absorption
Drugs need to …
• Be effectively absorbed
• Be properly distributed
• Remain to produce an effect
Developments towards efficacy…
• Capsules – against degradation by gastric acid
• Modified –release tablets- extend action duration
• Prodrugs- precursor (forerunner) of a drug. It must undergo
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chemical conversion by metabolic processes before becoming an
active pharmacological agent using body processes to convert agents
into active compounds
patches for trans-dermal delivery
Dermal implants
Inhalers
Intrauterines – long term drug delivery in women
Dosage- adjustable self- injection devices
Examples - prodrugs
• E.g. Sulfasalazine is a prodrug. It is not active
in its ingested form. It has to be broken down by
bacteria in the colon into two products -- 5aminosalicylic acid (5ASA) and sulfapyridine -before becoming active as a drug.
MR Tablets
• Gliclazide 30mg
• used in diabetes mellitus
• increases the amount of insulin released by the
pancreas and helps the body use insulin more
efficiently.
Dosage- adjustable self- injection
Nutropin AQ Pen®
• delivers liquid GH (growth hormone) from a
prefilled cartridge
• For children/ teenagers with growth failure
How drugs are absorbed…
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Passive diffusion down a concentration gradient
Cell membrane and fat-solubility of drugs
Active transport
Disintegration and dissolution of tablets
Presystemic metabolism
Passive diffusion
• Drugs are absorbed from intestine, skin, mucous
membranes by diffusion across cell membranes
through the concentration gradient ( the
movement of a substance from a higher to lower
place concentration)
Cell membrane and fat-solubility of drugs
• Oral drugs must cross the cell membranes of the
intestinal villi
• Fat soluble molecules can pass directly through
the cell membrane.
• E.g. instantaneous absorption of anti-anginal
drug GTN ( glyceryl trinitrate )across the buccal
mucosa - lining of the cheeks and the back of the lips, inside the
mouth where they touch the teeth.
• The spray is absorbed almost as fast as an i.v.
injection
Active transport
• Cells have active transport mechanismscarriers transporting ions, sugars, amino acids
in and out of cells that can move drugs from low
to high concentration
• E.g. levodopa (to treat Parksinson’s disease)
• Fluorouracil ( anti-cancer drug) are actively
transported across the intestinal mucosa.
• N.B – important to know that some cardiac drugs act by
increasing or decreasing cellular transport mechanisms
Disintegration and dissolution of tablets
• Plain tablets disintegrate then dissolve in
stomach
• For maximal concentration in small intestine, a
drug should be taken before food
Presystemic metabolism
• Break down of drugs by enzymes- mainly in liver
and some in intestinal mucosa, lungs and
skeletal muscle
• Extensive metabolism results in decreased
plasma concentration of drug.
• Drug dosage already accounts for the calculation