Bioavailability tutorial Flashcards
What are excipiants?
Other materials used in medicines that aren’t the drug itself
What do excipiants do?
Improve its chemical or biological stability or to increase its acceptability to the patient by improving its flavour, fragrance or appearnace
What is the process of making a medicine containing a drug called?
The formulation
What are advantages of an oral route of administration of a medicine?
It permits self medication
It does not require rigorously sterile preparations
The incidence of anaphylactic shock is lower than IV
There is a capacity to prevent complete absorption eg vomiting or lavage
What are disadvantages of an oral route of administration of a medicine?
They are inappropriate for drugs that:
- are liable in acid pH of stomach or otherwise degraded
- undergo extensive ‘first pass’ metabolism
It requires patient compliance
What are the advantages of intravenously administrating a drug
Rapid onset of action
Avoids poor absorption from and the destruction within the GI tract
What are the disadvantages of intravenously administrating a drug
Slow injection necessary to avoid toxic bolus
Higher incidence of anaphylactic shock
Trained personnel required
Complications possible eg embolism, phlebitis, pain
What are the advantages of administrating a drug via inhalation
Ideal for small molecules, particles, gases, volatile liquids, aerosols
Enormous surface area presented by alveolar membranes
Simple diffusion, also phagocytic cells clear particles
What are the disadvantages of administrating a drug via inhalation
Possible localised effect within the lung (unless this is desired)
What are the advantages of intramuscularly administrating a drug
Relatively high blood flow, increased during exercise and enables depot therapy (prolonged absorption from pellet, microcrystalline suspension or solution in oily vehicle)
What are the disadvantages of intramuscularly administrating a drug
Possible infection and nerve damage, especially in gluteal region
What are the advantages of subcutaneously administrating a drug
Local administration, dissemination can be minimised for local effect
Enables depot therapy
What are the disadvantages of subcutanously administrating a drug
Pain
Abscess
Tissue necrosis
What are the advantages of percutaneously administrating a drug
Local application and action
Lipid soluble compounds diffuse rapidly (may be assisted by vehicles)
What are the disadvantages of percutaneously administrating a drug
Local irritation and skin reactions
Alterations of skin structure eg steroids lead to subcutaneous adipose tissue
Why are excipients added to a drug formulation?
Flavourings, colourings, things to make it a solid or liquid, stabilizer?, in order to make the drug big enough to hold - to provide bulk, improve absorption (performance), capsule is to protect drug from low ph in stomach so can affect lower down
What are examples of agents that can be used as excipients
Inorganic materials eg chalk, talc, glucose, lactose, a counter ion for the drug which can make it taste better by making salt
solvents like water, alcohol or oil
What is bioavailability?
amount of a drug contained in a medicine that enters the systemic circulation in an unchanged form after administration of the product
Why is it important for a drug to be bioavailable
So it can react in the desired way to treat the patient. If the conc that reaches the desired place isn’t high enough then the drug won’t be effective
Does the measurement of bioavailability always reflect the effectiveness of a drug?
No, as some medicines like creams don’t need to travel systemically. These already reach the target organ before entering the body - similarly respiratory conditions can be treated like this. Also pro drugs have low bioavailability as activated within the body
What factors influence bioavailabiity
- the physicochemical characteristics of the drug (ionisation in gut)
- gastrointestinal pH
- whether or not the drug is passively or actively transported
- gastrointestinal motility
- particle size of the drug
- physicochemical interaction between drug and gut contents (e.g. chemical interaction between calcium and tetracycline antibiotics)
What are the different ways aspirin can be administrated?
aspirin tablets B.P. – ordinary aspirin tablets sold in chemists
soluble aspirin – these are dissolved in water and the solution swallowed
enteric-coated aspirin – these have a sugar and wax coating which remains intact in dilute acid but quickly dissolves in alkali
What is the bioequivalence of a drug?
Evidence that the new ‘generic’ product behaves sufficiently similar to the existing one
How can drugs be metabolised to inactive products?
the microbes within the gut lumen
enzymes present in the gut wall
enzymes in the liver
