Pharmacokinetics Flashcards
• Administration regimens using Vensim: (3)
– STEP function
– PULSE function
– PULSE TRAIN function
What is pharmacokinetics? (3)
• Branch of pharmacology • Rates at which drugs are: – Absorbed – Distributed – Metabolised – Eliminated • How drugs move within the body
• So far we’ve considered rates that are
– Constant
– Exponential
– Always started at time zero
However, drug administration regimens… (2)
– Not always constant
– Don’t always start at time zero
• In Vensim we have a set of functions:
– STEP function
– PULSE function
– PULSE TRAIN function
NOTE: Dose = rate x duration
What does the graph for a constant rate for a ZOS look like?
What is a step function?
• Constant rate – ZOS • Step Function – Does not start at zero • Application – Intravenous drip
How do you work out the step?
What are the applications of a pulse function?
- Bolus injection
• Single large dose delivered over a short period
• Generally given when patient requires meds immediately in bloodstream - Ingesting a single dose of drugs
• A pill or multiple pills taken over a short period
• e.g. Analgesia (pain killers)
A pulse function is not ____.
repeated
What does the graph for a pulse function look like?
What is the area under the rate curve of the pulse function?
𝐴𝑟𝑒𝑎 𝑢𝑛𝑑𝑒𝑟 𝑅𝑎𝑡𝑒 𝑐𝑢𝑟𝑣𝑒 = h𝑒𝑖𝑔h𝑡 ∗ 𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛
The area under Rate curve of pulse function =
Change in Level (Dose)
What is the formula for the dose of a pulse function?
𝐷𝑜𝑠𝑒 = h𝑒𝑖𝑔h𝑡 ∗ 𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛
What is the formula for the height of a pulse function?
1 h𝑒𝑖𝑔h𝑡 = 𝐷𝑜𝑠𝑒 ∗ 1/𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛
What are the applications of a pulse train function?
- Series of bolus injections
• Repeated single large doses delivered over short periods - Ingesting a single dose of drugs at regular intervals
• A pill or multiple pills taken over a short period
• e.g. Antibiotics; hormone replacement drugs
Consistent time between ___ for a pulse train function.
doses
What is the pulse train function graph?
What is the pulse train function graph?
What is the function equation?
height * PULSE TRAIN ( start , dur , rt , end )
What is the importance of a time step? (2)
- Extremely important with pulses
* Too large and you can miss pulse completely
What is the importance of a time step? (2)
- Extremely important with pulses
* Too large and you can miss pulse completely
In Vensim, dose = ____.
Dose = rate x duration
What is the importance of modelling of a single compartment model? (3)
– Simplifying assumption
– Makes analysis easier
– Modelling the body as one single compartment
What are the units of the auxiliary variable?
What is clearance? (3)
• Important concept in system dynamics
• Dimensional consistency but there is a slightly
more subtle meaning
• Allows us to use:
– Concentration of drug instead of the absolute amount of drug
– FOS elimination
What type of value is clearance and what is the equation for clearance? (2)
• Clearance is a constant value
– Characteristics of a FOS
– Modified version of rate constant (k) SCALED by Volume of Distribution (V)
𝑐𝑙𝑒𝑎𝑟𝑎𝑛𝑐𝑒 = 𝑘 ∗ 𝑉
How would the clearance variable appear on an LRD?
What is the formula for the amount of the drug (level) ?
𝐴 = ∫ 𝐴𝑑𝑚𝑖𝑛𝑖𝑠𝑡𝑟𝑎𝑡𝑖𝑜𝑛 − 𝐸𝑙𝑖𝑚𝑖𝑛𝑎𝑡𝑖𝑜𝑛 𝑑𝑡
What is the formula for the concentration of the drug?
Level/Volume
What is the formula for clearance?
𝑐𝑙𝑒𝑎𝑟𝑎𝑛𝑐𝑒 = 𝑘 ∗ 𝑉
What is the formula for the elimination rate?
𝐸𝑙𝑖𝑚𝑖𝑛𝑎𝑡𝑖𝑜𝑛 = 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 ∗ 𝑐𝑙𝑒𝑎𝑟𝑎𝑛𝑐𝑒
What are the characteristics of administration? (2)
• Administration
– Repeats at regular intervals (PULSE TRAIN)
height * PULSE TRAIN ( start , dur , rt , end )
For administration:
– start = 10 hours = _____ {minutes}
– dur = 6 seconds = _____ {minutes}
– rt = 12 hours = _____ {minutes}
= 10 * 60
= 6 / 60
= 12 * 60
• Administration – end: • 3 days, twice daily is 6 doses total • Must account for the start time and duration to ensure all 6 doses are accounted for – end = \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
= (1060) first dose + (512*60) time for remaining doses + (6/60) duration {minutes}
• Administration
– height:
• Administration is a rate, and the dose is an amount!
• Assume the dose is evenly administered over the duration of each pulse
height = ______________.
h𝑒𝑖𝑔h𝑡 = 𝐷𝑜𝑠𝑒 ∗1/𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛
– height = 500 * (60/6) {mg/min}
What does the full graph for a pulse train function look like?
