Pharmacokinetics Flashcards
(22 cards)
What is the definition of pharmacokinetics?
The study of movement of drug molecules in the patient/animal
- Describes ADME processes
What is the definition of pharmacodynamics?
The study of action of drug, including time-course of actions
How is the dosage of drug determined?
- The desired effect has been shown to occur after administration of the dose - due to the pharmacodynamic properties of the drug
- If the drug is presented at the target site at a connection that is therapeutically effective, this is dependent on the pharmacokinetic properties of the drug
What is ADME?
Administration
Distribution
Metabolism
Excretion
Why is water solubility essential?
- For the site of administration to achieve absorption
- For a drug to be distributed
- At the site of action to reach the biochemical target (receptor, enzyme, etc)
- For excretion
What is plasma’s role in drug solubility?
Plasma carried the drugs to site of action (except for locally acting drugs)
Routes of administration?
- Intravenous injection (i.v.)
- Intramuscular injection (i.m.)
- Subcutaneous injection (s.c.)
- Epidural injection
- Intra-articular injection
- Intra-peritoneal injection
- Oral
Types of oral administration?
- Tablets
- Capsules
- Powders
- Solutions
- Suspensions
IV route…
- Fastest route to blood
- 100% bioavailability
Intramuscular route…
- Slower than IV route
- Suitable for slow release drugs
Subcutaneous route…
- Slower than IV
- Suitable for slow release drugs
Oral delivery or drugs…
- Tablets and capsules swallowed
- Solutions and suspension by oral syringe
- Solutions and suspensions by nasogastric tube or orogastric tube
Oral tablets include excipients including…
- Binders
- Glidants/lubricants
- Disintegrants
- Preservatives
- Colours
- Coatings
Absorption factors include…
- Age
- Species
- Gender
- Genetic factors
- Metabolism
- State of health/disease
Benefits of oral disintegration…
- Larger surface area to volume ratio after disintegration
- Faster dissolution
Lipinskis guidelines developed in 1997
Rule of 5
- No more than 5 H-bond donors
- No more than 10 H-bond receptors
- Molecular weight less than 500
- logP < 5 (P is octanol/water partition coefficient)
AUC (area under the curve) results
The area under the curve shows how much the target tissue has been exposed to the drug
What is volume of distribution?
Volume of distribution is the theoretical volume that would be necessary to contain the total amount of administered drug at the same concentration as is observed in the blood plasma
- Vd = total amount of drug in the body/concentration of drug in blood plasma
How does the drug leave the blood?
Small-molecule drugs can pass through the endothelial cells or diffuse through them to get into the interstitial fluid space in the tissue
What is tissue perfusion?
- Affects how rapidly drugs are distributed to different tissues
- Varies between animal species
- Distribution of drugs is rapid to well vascularised tissues
- Distribution of drugs is slow to poorly vascularised tissues
Example of tissue perfusion…
Pentothal
- Anaesthetic in veterinary
- Acts in brain within a few minutes
- Redistributed slowly to fat from the brain
- Obese animals recover quickly from anaesthesia
- Lean breeds of dogs have prolonged recoveries
What is protein binding in plasma?
Drugs bind to proteins e.g. albumin
- Slow dynamic equilibrium between drug free and complexed drugs
- Drugs can only pass through the capillary wall and move into target tissue if not bound to protein
- Drugs complexed to albumin cannot pass through
