TDM DRUGS Flashcards
What is the difference between pharmacokinetics and pharmacodynamics?
Pharmacokinetics:
study of the time course of ADME (what happens to the drug in the body/ what the body does to the drug)
Pharmacodynamics:
the study of the biochemical and physiological effects of drugs and the mechanisms of their actions (what the drug does to the body)
What is the volume of distribution?
A hypothetical volume of body fluid that would be required to dissolve the total amount of drug needed to achieve the same concentration as that found in the blood.
List the 3 processes of drug clearance by the kidneys?
Glomerular filtration
active tubular secretion
passive tubular reabsorption
Why is it that if a patient has a low protein (albumin) level, we may need to dose adjust drugs with a narrow therapeutic window?
Protein binding describes a drug which is highly bound to proteins in the blood ie albumin.
If a drug is highly protein bound and the patient has a low albumin level then there will be an increase in the amount of free drug causing toxicity.
Doses and levels have to be corrected for protein levels in the body
What is the usual target range for Vancomycin?
10 - 15 mg/L
When is the higher target range of 15 - 20 mg/L used for Vancomycin?
For conditions such as: MRSA pneumonia Osteomyelitis CNS infections Endocarditis bactereamia (bacteria in the blood)
When should we take the first vancomycin level?
Before the third dose- (so after two doses)
Take a TROUGH level (1 hour before third dose is due!)
What is the target trough level for amikacin?
< 5 mg/L
What is the target concentration range for phenytoin? When should we take a trough level?
target: 10 - 20 mg/L
Take a TROUGH level 2- 4 weeks after starting the drug
What are some of the signs of Phenytoin toxicity?
Nystagmus (rapid blinking)
Ataxia (loss of voluntary movement control- muscle rigidity and spasms)
Coma
What is purple glove syndrome?
It can happen with intravenous use of phenytoin
The extremities become swollen, discoloured and painful
What is the target range for sodium valproate? When should a level be taken?
50-100mg/L
TROUGH level taken after 2 days
What is the target range for Digoxin?
1.5 - 2 mcg/L
When should digoxin levels be taken?
6 HOURS POST DOSE
What are some of the signs of digoxin toxicity?
Vision changes- blind spots, blurred vision, changes in how colors look, seeing spots
irregular pulse
confusion
nausea and vomitting
Digoxin, Lithium and phenytoin toxicity both involve symptoms of the eyes. What do each drug display?
Digoxin- visual changes e.g. blind spots, seeing yellow spots, blurred vision
Phenytoin- nystagmus (uncontrollable blinking)
Lithium- blurred vision
What is the target range for lithium levels?
0.5- 1 mmol/L
When should lithium levels be checked?
12-24 hours POST DOSE
after 5-7 days of initiation
What are the signs of Lithium Toxicity?
Blurred vision Muscle weakness Slurred speech Confusion Seizures Renal damage Increased risk of Hypothyroidism
How does sodium effect lithium levels?
Sodium restriction (low sodium) enhances the renal tubular reabsorption of lithium thus leading to potentially toxic high levels of lithium
Sodium decreased= lithium level increased
Does dehydration lead to increased or decreased lithium levels?
Increased! -important to avoid dehydration
What should we regularly check the function of in patients receiving lithium (2 organs)?
Renal function
Thyroid function
Target Theophylline concentrations? When should a level be taken?
10 - 20mg/L
Take level 4-6 hours after a modified release dose.
What can theophylline toxicity result in?
QT interval prolongation
Increased risk of convulsions
When should INR be checked after a dose adjustment/ initiation of warfarin? What is the half life of warfarin
48 hours post 1st dose
Half life is around 40 hours
What is the target level for carbamazepine? When should a trough level be taken?
4-10 mg/L
Trough at least 2 weeks after starting or dose change
In patients on warfarin, when should phytomenadione (vitamin K) be given IV?
Major bleeding in patients on warfarin (in combination with dried prothrombin complex or fresh frozen plasma)
INR > 8.0 with minor bleeding in patients on warfarin
INR 5.0–8.0 with minor bleeding in patients on warfarin
How does vitamin K (phytomenadione) work in warfarin overdose?
Phytomenadione promotes hepatic synthesis of clotting factors therefore reverses anticoagulation of warfarin
In patients on warfarin, when should phytomenadione (vitamin K) be given ORALLY?
INR > 8.0 with no bleeding in patients on warfarin
Reversal of anticoagulation prior to elective surgery (after warfarin stopped)- Use IV prior to emergency surgery
What is the difference between Phenindione and Phytomenadione?
Phytomenadione = Vitamin K
promotes hepatic synthesis of clotting factors therefore reverses anticoagulation of warfarin
Phenindione Inhibits clotting factor synthesis and therefore acts as an anticoagulant
