Pharmacology Flashcards
First order
Rate of elimination is proportional to the plasma drug concentration (processes involved in elimination do not become saturated)
A constant % of the plasma drug is eliminated over a unit of time
Zero order
Rate of elimination is NOT proportional to the plasma drug concentration (metabolism processes become saturated)
A constant amount of the plasma drug is eliminated over a unit of time
Cmax
maximum plasma concentration
tmax
time taken to reach Cmax
Clearance (CL)
removal of drug by all eliminating organs
Bioavailability of IV
100% bioavailability, absorption and tmax are not relevant
Half life (t1/2)
Dependent on clearance (CL) of drug from body by all eliminating organs (hepatic, renal, faeces, breath)
Dependent of volume of distribution (Vd) - A drug with large Vd will be cleared more slowly than a drug with a small Vd
When a drug considered cleared in clinical practice
A drug will be 97% cleared from the body after 5 x half lives
Relevance of t1/2 in clinical practice- drug dosing
short t1/2 will need more frequent dosing
Relevance of t1/2 in clinical practice- Organ dysfunction
t1/2 may be increased, Reduced CL increases t1/2, Time to Css increases (5 x t1/2), Css increases, Therefore dose reduction required
Relevance of t1/2 in clinical practice- Adverse drug reactions or management of toxicity
how long will drug take to be removed and symptoms to resolve
Relevance of t1/2 in clinical practice- Short t1/2 increases risk of discontinuation/withdrawal symptoms
drugs may need dose weaning on cessation
Repeat IV dosing
Most drugs require repeated dosing
Peaks and troughs in plasma concentration causing oscillation around the mean
Does repeat iv change time to Css compared to single dose of the same amount
Time to Css does not change (roughly 5 half lives)
Why is steady state important?
Aim for Css which lies between the Maximum safe concentration (MSC) and minimum effective concentration (MEC)
Method for Reducing time to steady state
A loading dose will speed up time to steady state
Zero order kinetics
Drugs are metabolised by an amount (e.g in mg) in a unit of time. Metabolism is dependent on mechanisms that become saturated. Elimination is irrespective of plasma concentration.
Zero order kinetics- is plasma concentration proportional to dose?
Plasma concentration is not proportional to dose. Small increases in dose may cause large increases in plasma concentration. There caution needed when adjusting doses
Pharmacogenomics
The use of genetic and genomic information to tailor pharmaceutical treatment to an individual
Genomics
The study of the genomes of individuals and organisms that examines both the coding and non-coding regions. The study of genomics in humans focuses on areas of the genome associated with health and disease
Pharmacogenetic approach
- Patient is diagnosed with condition x
- Patient’s genome used to identify most appropriate treatment and dose
- Patient receives optimal treatment
Genomic variation in Pharmacodynamics
variations in drug receptor
-variations in efficacy (‘on’ targets)
-increased incidence of adverse drug reactions (ADRs) (‘on’ and ‘off’ targets)
Pharmacology definition
The study of how medicines work and how they affect our bodies
Pharmacokinetics
The fate of chemical substance administered to a living organism- what the body does to the drug