PK4 Flashcards
(14 cards)
What are the 2 factors affecting drug pharmacokinetics and what has to happen to fix it?
Therapeutic efficacy (increased or decreased)
Toxicity (increased or decreased)
Adjustment of dosing interval or dose is required
What are the drug product factors potentially altering drug PK?
Lipid solubility
Stability
Dose (firs and zero order)
Acidic or basic nature and renal excretion
Chirality
Plasma protein binding
Effect on hepatic enzymes
Product formulation
Why is it important to administer alkalising or acidifying agent to alter the urine pH?
This will alter the elimination of drugs, for example if suddenly the patient is not reacting to the drug or has severe side affects you want to wash out the drug as fast as you can
What is Chirality?
Chemistry of the drug gives some of them mirror images
Why is Chirality important?
The PK properties of one enantiomer may differ from the other.
One enantiomer may be converted to the other in the body
The mirror one can be toxic or have side effects such as Ketamine isomer potency R form causes hallucinations
What can repeated treatment lead to?
Repeated treatment causes a change in the rate of metabolism of these drugs—> increasing the dose at certain periods as it can be metabolised faster than usual or even has to change the drug
What are the consequences of liver enzyme inhibition or induction?
Plasma drug conc will be decreased (induction) ot increased (inhibition)
Therapeutic efficacy may be lost (induction) or toxic effects may develop (inhibition)
Dosing intervals may need to be adjusted- you need to keep monitoring the levels in the plasma so you can adapt the dosage of the drug to prevent toxicity or decrease in action
Give examples of why formulation is important?
Formulation:pill/solution content in other words how its made up for administration.
Solution for intramuscular injection can be altered so that the aqueous solubility is reduced, this prolongs the action of the drug.
Drugs that are broken down in acidic conditions can be protected by an enteric coating
The particle size or structure of tablets can be altered so there is slow or sustained release
What is the effect of administering drug with food? empty stomach cmax is higher then that with food peak.
Decrease Cmax, does not affect Tmax.
With food: can be because it may irritate the stomach
Or the action might be better with or without food (absorption)
Some of the drug might bound onto food and excreted by faeces so never enters the body tissues.
Bioavaiilability increased before food then after food.
What happens when a horse is given phenylbutazone before and after feed?
Phenylbutazone will react with the hay, and will be released in the caecum, if no hay it will be absorbed very quickly compared with food
What is the effect of administering drug with food? Increased Cmax Decreased Tmax with food
What is the effect of administering drug with food? empty stomach cmax is higher then that with food peak.
Give some factors that influence absorption from the GIT?
Gastric or intestinal motility, increased motility decreases the time of drug absorption
Spanchic Blood flow, decreaed absorption
Stability of Drug
Damge to or loss of the epithelial barrier reduces drug absorption
Why is taking the drug at the same time of day importnant?
Doseat the same time of day to avoid variation factors such as metabolic rate or blood flow to the GIT which may affect drug Pharmacokinetics.
Improve the efficacy of the drug, hormone levels change which can regulate how the drug are moved around the body and how they are absorbed
What do neonates have different to adults in terms of PK?
Reduced rate of renal excretion
Reduced rate of hepatic metabolism
Lower amount of plasma protein binding
Greater asorption from the GIT (bioavailability)
Possible increased permeability of blood-brain barrier
Increased volume of distribution
