ABSORPTION Flashcards
Absorption definition
Transfer of drug from site of administration to systemic circulation
Types of factors that can affect absorption
- Factors related to drug
- Factors related to patient
Examples of factors related to drug absorption
- Size of the drug
- Water and lipid solubility
- Ionization
- Nature of drug and its molecular weight
- Valency
- Preperation and dosage form
- Rate of disintegration
- Excipients
Drugs must be water/lipid soluble?
DRUGS MUST ME WATER AND LIPID SOLUBLE
Increasing lipid solubility, increases …..
Absorption
If the drug is insoluble in water it is …….
NOT absorbed
Lipid soluble drugs are ionized/non-ionized?
NON-IONIZED
Inorganic drugs have …….. molecular weight
SMALL
Organic drugs have …….. molecular weight
LARGE
Which iron ion is absorbed more?
Ferrous iron (Fe2+)»_space;»» Feric iron (Fe3+)
Dosage form:
Solution»_space; Suspension»_space; Tablets
………. has a rapid rate of disintegration
Paracetamol
……… has a slow rate of disintegration
Digoxin
Calcium carbonate decreases the absorption of ……..
tetracycline
Factors related to patient that affect drug absorption:
- Route of administration
- Absorbing surface
- Systemic circulation
- Specific factors
- Other drugs
Route of adminstration with decreasing absorption rate:
IV > IM > SC > Oral > skin
Surface area with descending absorption rate
Alveoli > Intestine >Stomach
Absorbing surface with decreasing vascularity:
Alveoli > Muscle > SC
When does systemic circulation have low absorption rate?
In shock or heart failures as blood flow to skin and muscles decreases
How to increase absorption of Vitamin B12
Increase secretions of intrinsic factors from the stomach
Effect of adrenaline on local anesthetics
Causes vasoconstriction so decreases absorption
Drugs that increase gastric emptying
Metoclopramide
Drugs that decrease gastric emptying
Atropine
Effect of metoclopramide on absorption rate
Metoclopramide increase gastric emptying so increase rate of absorption of drugs with rapid disintegration rate (paracetamol) and decrease rate of absorption of drugs with slow disintegration rate (digoxin)
Effect of Atropine on absorption rate
Atropine decrease gastric emptying so decreases rate of absorption of drugs with rapid disintegration rate (paracetamol) and increases rate of absorption of drugs with slow disintegration rate (digoxin)
Events that decrease oral absorption
- Diarrhea
- Malabsorption
- Decreased gut motility by morphine
RULE: The drug is absorbed in the …. media and excreted in the …. media
SAME……OPPOSITE
How pH can increase absorption rate
Acidic media in the stomach increases absorption of acidic drugs like asprin and barbiturates
Alkaline media in the intestines increases absorption of alkaline drugs like atropine, morphine, ephedrine and amphetamine
Where is tannic acid found
In TEA
How can the absorption of iron be lowered
By the presence of tannic acid
What interferes with the absorption of tetracycline?
Calcium in milk
What chemicals decreaes rate of absorption of most drugs
Cholestyramine and charcoal
Amino acids compete with …… and ……… its absorption
Levodopa …….. decreases
Irritant drugs may be given after food like
Asprin and iron
Synonyms of first pass metabolism
First pass effect
Pre-systemic metabolism
First pass metabolism definition
Drug metabolism before it reaches systemic circulation whereby the concentration of the drug is greatly reduced. It takes place after absorption from the GIT in the portal circulation
Barriers where drug concentration decreases in first pass metabolism
- Gut first pass
- Gut wall
- Hepatic first pass
Drugs that are destroyed during gut first pass
Penicillin is destroyed by gastric acidity
Hormones and proteins (insulin) are destroyed by gastric enzymes
Drugs that can’t pass through the lumen
L-DOPA, methyldopa, tyramine
L-DOPA is used to treat ….
Parkinson’s disease
Drugs that pass through the liver and are destructed by its enzymes in the hepatic first pass:
Nitroglycerine, Morphine, Propranolol, Natural sex hormones and lidocaine
Nitroglycerine is used to treat
Angina
To overcome hepatic first pass:
- Increase oral dose
- Use other route
Bioavailability definition:
The fraction of administered drug that reaches the systemic circulation in an unchanged form
Factors affecting the bioavailability of the drug:
Absorption rate and first pass metabolism
Bioavailability is …..% after IV route
100
Bioavailabilty formula for other routes that IV
Bioavailability of a route (F) =
(Area under curve (AUC)of the route / Area under curve (AUC)of IV) x 100
