Pharm Test 1 Flashcards
Elimination is dependent on
which organ is eliminating the drug
The organ that is eliminating a drug is dependent on
- Whether or not the drug is a high-extraction drug
- what the blood flow is through that organ
If the blood flow through an elimination organ is normal, we call it
high
If the blood flow through an elimination organ is limited, we call it
low
Oral morphine doesn’t provide the full effect because
After the GI tract morphine goes into the liver and the liver removes a lot of it. It is a high extraction drug
What is the range for a high extraction drug?
> 0.7
What is the range for an intermediate extraction drug?
0.3-0.7
What is the range for a low extraction drug?
<0.3
What is Q in the extraction ratio?
The blood flow through an elimination organ.
What is the Clorgan formula?
Clorgan=QE
What is E in the extraction ratio?
the percentage of drug that comes out of an elimination organ
If you have a high E and a low Q, what is your Clorgan?
Low
If you have a low E and a high Q, what is your Clorgan?
Low
If you have a high E and a high Q, what is your Clorgan?
high
If you have a low E and a low Q, what is your Clorgan?
low
Why is the half life important?
It helps us determine how we should dose a patient and how much we should dose them
Define half life
the time it takes the body to get rid of half of the concentration of a drug in the blood
What is the half life formula?
T1/2=0.7XVd/CL
What is giving a drug in “steady state” mean?
Giving the drug at the same rate that the body is eliminating it.
What do we do to reach target concentration quickly?
Give a bolus of a drug
For a drug that has a 4 hour half life, how many half lives would it take for the drug given at steady state to reach target concentration in the blood?
16 hours
For a drug that has a 4 hour half life, how many half lives would it take for the drug to be completely eliminated from the blood after the infusion is stopped?
16 hours
What effects half life?
Many things, including disease state
A true half life will be _____ than the calculated half life
greater
If you don’t wait 4 half lives before taking another dose of the drug, what will happen?
The drug will accumulate in the plasma and can become toxic very quickly
How is bioavailability denoted?
F
What does bioavailability tell us?
How much of the drug reaches systemic circulation
What is the bioavailability of an IV drug?
100%
What factors effect bioavailability?
- Physical properties of the drug (hydrophylicity, PKA, solubility)
- Fomulation/route
- GI- diet, gastric emptying, transporters, health
- interactions with other drugs
- disease state
- circadian rhythm
What is first pass elimination?
The first system that the drug goes through that changes the concentration of the drug.
What are routes that bypass first pass elimination?
- IV
- IM
- SC
- Inhalation
*has it’s own first past effect - sublingual
- transdermal
- rectal
*suppositories might move upward, therefore only 50% bypass hepatic circulation
What is target concentration based on?
What we are trying to accomplish in the patient (pain relief, controlling afib)
What is the most important factor of the dosing ratess?
Clearance
How do you solve for dosing ratess?
CL X Target concentration
For bioavailability that is less than 100%, how is the formula changed?
Dosing rateoral=dosing rate (calc.)/Foral
The CL X Target concentration is divided by the bioavailability.
If your bioavailability is less, your are going to have to give _____ of the drug
more
What is an intermittent dose for oral drugs?
Giving a pill every few hours instead of constantly.
Dosing rate X dosing interval (in hours)
If you are given the target concentration, the clearance, and the time interval how do you solve for the intermittent dose?
- Dosing ratess=CL X Target Concentration
- Dosing rateoral=dosing cate (calc.)/ForalX dosing interval
Describe what is happening in this graph.
The black line is the drug being given in steady state. It is showing that after 4 half lives, the drug reaches 10mg/L and the patient is receiving the targeted effect of the drug.
The red line shows the drug being given every 8 hours. The patient has peaks and troughs that’s staying right around the target concentration.
The blue line is the drug being given every 24 hours. You can see that at the peaks the patient is receiving a much higher effect than the target concentration, but the troughs are also much lower. In the case of this siezure drug, you can see how the troughs would leave this patient open to having seizures.
How to calculate the loading dose?
LD=Vd X TC
The loading dose is assumed that it is given over
5 minutes
Why is rate of administrations critical for potentially toxic drugs?
Giving a bolus too fast doesn’t allow time for the drug to distribute into compartments and therefore reaches toxic levels in the plasma very quickly
How do we monitor for therapeutic dosing?
Peak and trough tests
When is the peak test taken?
5-10 minutes after drug administration
When is the trough test taken?
30 minutes before the next dose
What do the peak and trough tests tell us?
Assessment of individual response to standard population pharmacokinetic variables.
To be able to dose the drug to each individual patient based on their disease state, other drugs they’re on etc.
If you have a drug that preferentially stays in the fat, which weight do you use?
their actual weight