Biopharmaceutics Lecture 1 Flashcards
Why is injection (as a route of administration) used?
Rapid response Can use drugs that would be destroyed in the GIT if taken orally Can use on patient groups such as: -unconscious patients -those who can't swallow -those nil by mouth
Describe the physiological surface barriers of the skin that drug from a transdermal dosage form/patch would have to cross
Stratum corneum (complex structure of dead cells) Epidermis (avascular, tightly-packed living cells)
Explain the difference between “drug” and “medicine”
Drug describes the pharmacological agent/therapeutic molecule/API by itself
Medicine describes the drug itself and excipients together
What are the disadvantages for using injections to deliver drugs?
- less convenient compared to oral route
- cost
- stability issues e.g. Microbial contamination, short shelf life
- patient pain
- can achieve suitable rate of absorption using oral route
Define bioavailability
Defined by FDA as the rate and extent to which the active ingredient is absorbed from a drug product and becomes available at the site of action.
Out of ADME, which letters are about bioavailability?
Bioavailability is about absorption only
Rate and extent at which drugs reach the systemic circulation
What is the absolute bioavailability of an IV injection?
100%
Define absolute bioavailability
The fraction of drug that arrives in the systemic circulation
What factors to bioavailability studies view?
- rate of absorption
- variables that affect rate and extent
- mechanisms involved
In ADME, what does M refer to?
Metabolism i.e. All changes to the drug in the body (gut wall, liver etc)
In the early stages of drug development, what does one focus upon?
Studying drug molecules in solution, interacting with isolated target cells
In the later stages of drug development, what does one focus upon?
Success depends on development of a suitable dosage form
Why don’t we just administer pure drug in solution and forget about formulation?
Usually too expensive to administer drug in solution
In transdermal drug delivery systems, what is added/removed to increase subcutaneous permeability?
Chemical enhancers are added
Describe the ideal properties of an API to be delivered via a TDDS
Low permeability
Low Mr
Lipophilic
How does the drug get absorbed in the GIT?
GI absorption - High surface area due to villi and microvilli
- Transcellular transport (through cells lipid bilayer)if lipophilic molecules
- Paracellular transport (gaps between cells) if hydrophilic drugs
Name some broad potential influences on drug availability for absorption
- Physiological
- Drug itself
- Dosage form
Describe some physiological effects that can influence drug availability for absorption
- rate of transit
- properties of lumen fluid (pH, etc)
- tissue properties at the site of absorption and the site of action
Describe some drug factors that can influence drug availability for absorption
LogP
Solubility
pKa
Pharmacological effects of the drug or other agents
Describe some dosage form factors that can influence drug availability for absorption
Particle size Size of dosage form itself Route of administration Disintegration rate Dissolution rate
Why in biopharmaceutics, does “available at the site of action” equal the same as “arrives at the systemic circulation”
- Practical reasons, blood is sampled easily, but tissues are not
- Pharmacokinetics- blood is the central compartment from which drug is distributed
- Absorption=process of drug going to central comportant (systemic circulation) by a route of administration
- Once drug is in the central compartment, formulation is then irrelevant as drug is dissolved in blood plasma. Formulation is only relevant when it comes to drug absorption
Give 6 examples of drugs used in transdermal drug delivery systems
GTN Nicotine Fentanyl Estradiol Testosterone Anti-nausea agents
