Principles Flashcards
What is bioavailability
The rate at which an active drug reaches the site of action and the extent to which it is available to the target tissue.
Area under cruve of log plasma concentration against time
What is a biologic agent
A product made from living organisms or containing components of living organisms and used in the prevention, diagnosis, or treatment of disease.
What is an emulsion
A mixture of 2 immiscible components.
What is pharmacodynamics
biochemical and physiological effects of drugs/
agents on a biological system
What is phamacokinetics
absorption, distribution, metabolism, and excre- tion of drugs/agents in a biological system
What is a suspension
A mixture of a substance with poor solubility and a dispersion medium in which the substance is evenly distributed.
Why can topically administered agents in the eye give rise to systemic effects?
Absorbed by nasal and nasopharyngeal mucosae directly into systemic circulation - escape first pass metabolism
What are first order kinetics?
Linear
Rate of drug transfer is proportional to the amount of drug present (i.e. half-life is constant) and can be defined by linear differential equations
(Most drugs)
What is zero order kinetics
Non linear
Transfer related to functional capacity of body rather than drug concetration.
Drug dynamics show saturation at high drug concentrations.
saturation may occur when capacity of drug metabilising liver ensymes is suppassed leading to unmetabolised drugs in circulation
What is tissue binding?
Prolongs retention of a drug in a compartment by rendering unavailable for tissue kinetics
Efficacy of the drug is reduced but duration is increased
E.g. melanin binds atropine and pilocarpine
Importance of lipid solubility? How can drugs pass through cell membranes?
Ophthalmic drug penetration increases with lipid solubility
Lipid soluble drugs will penetrate the eye more readily
Diffusion directly through lipid
Diffusion through aqueous pores that traverse the lipid
Using carrier molecules
Pinocytosis by cells
What does absorption of a drug depend on?
Lipid solubility
Inversely on polarity and degree of ionisation.
More unionized drug - more likely to be lipid soluble and transferred by passive diffusion through the membrane
Active transport vs facilitated diffusion
Active transport requires energy as against concentration gradient
Protein binding important for facilitated diffusion as keeps free concentration low and maintains gradient
What do drugs bind to in blood/tissue? Why?
Bind to plasma or tissue proteins
Bound drug is inactive
Albumin binds many drugs
Bound fraction represents a store
Dissociation as free drug is eliminated minimises the fall in concentration
CYP450 inducers
Carbemazepine
Rifampicin
bArbiturates
Phenytoin
Nicotine
