Pharmacology: Drug dose and delivery Flashcards
Why do most drugs not have PK’s?
it is very expensive to establish
What are PBPK’s? What are they used for?
Mathematical model to predict drug concentration in all tissues with time
Extremely useful for predicting PK across species
Vd can be predicted from a knowledge of drug plasma protein and tissue binding
What his Kleibers law?
The mass specific (per gram) metabolic rate needed to sustain an organism decreases with body weight(BW) to the ¼ power
Mass specific metabolic rate = Constant x BW to the power -0.25
How does cardiac output vary with size?
Cardiac output per BW decreases with size
CO = 180BW to the power -0.19
How does drug clearance vary with BW?
Plasma clearance is dependent upon blood flow to eliminating organ
Therefore the clearance of a drug is expected to be greater for a smaller species compared to a larger one based upon blood flow alone
Where does allometric scaling work best?
Allometry works well for clearance processes predominantly driven by blood flow (e.g. water. soluble renal clearance) but is less reliable when applied to drug metabolism clearance
Why might drug plasma protein binding vary?
Elderly and neonates have a lower concentration of plasma proteins compared to healthy adults
Disease states can affect concentration of plasma proteins
Drugs may be displaced from plasma proteins by other drugs that have a higher affinity (high PPB) leading to a change in their PPB
How does protect blogs for GI roundworms in cattle act as a controlled release drug?
Delivers morantel tartrate for up to 90 days for gastrointestinal roundworms in cattle
Controlled release through porous end discs (Depot effect as the bolus slowly dissolves
How do spot on’s act as a controlled release drug?
Oil-based spot-on administered to skin behind the neck distributes over the skin gradually for 30 days
Drugs are sequestered by sebaceous glands, which release drugs together with sebum onto skin over the therapeutic period at a level above that required to kill parasites
Drugs act noncompetitively and with high potency to inhibit flea glutamate-gated chloride channels and with lower potency to inhibit GABA-gated ones
How do PRID’s act as a controlled release drug?
Management of ovarian dysfunction in postpartum dairy cows
High-temperature injection mould process is used to cure a drug-impregnated silicone matrix over a nylon spine
Can help get cycling and non- cycling cows and heifers pregnant faster
What is an Osmotic Ruminal Therapeutic System?
eg. (IVOMEC-SR® bolus)
Delivers ivermectin for up to 135 days for parasite treatment
Contact with water swells capsule via osmosis which pushes flow moderator and releases agent
