TDM DRUGS

Question 1

What is the difference between pharmacokinetics and pharmacodynamics?

Answer 1

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)

Question 2

What is the volume of distribution?

Answer 2

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.

Question 3

List the 3 processes of drug clearance by the kidneys?

Answer 3

Glomerular filtration
active tubular secretion
passive tubular reabsorption

Question 4

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?

Answer 4

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

Question 5

What is the usual target range for Vancomycin?

Answer 5

10 - 15 mg/L

Question 6

When is the higher target range of 15 - 20 mg/L used for Vancomycin?

Answer 6

For conditions such as:
 MRSA pneumonia
Osteomyelitis 
CNS infections
Endocarditis
bactereamia (bacteria in the blood)

Question 7

When should we take the first vancomycin level?

Answer 7

Before the third dose- (so after two doses)

Take a TROUGH level (1 hour before third dose is due!)

Question 8

What is the target trough level for amikacin?

Answer 8

< 5 mg/L

Question 9

What is the target concentration range for phenytoin? When should we take a trough level?

Answer 9

target: 10 - 20 mg/L

Take a TROUGH level 2- 4 weeks after starting the drug

Question 10

What are some of the signs of Phenytoin toxicity?

Answer 10

Nystagmus (rapid blinking)
Ataxia (loss of voluntary movement control- muscle rigidity and spasms)
Coma

Question 11

What is purple glove syndrome?

Answer 11

It can happen with intravenous use of phenytoin

The extremities become swollen, discoloured and painful

Question 12

What is the target range for sodium valproate? When should a level be taken?

Answer 12

50-100mg/L

TROUGH level taken after 2 days

Question 13

What is the target range for Digoxin?

Answer 13

1.5 - 2 mcg/L

Question 14

When should digoxin levels be taken?

Answer 14

6 HOURS POST DOSE

Question 15

What are some of the signs of digoxin toxicity?

Answer 15

Vision changes- blind spots, blurred vision, changes in how colors look, seeing spots

irregular pulse

confusion

nausea and vomitting

Question 16

Digoxin, Lithium and phenytoin toxicity both involve symptoms of the eyes. What do each drug display?

Answer 16

Digoxin- visual changes e.g. blind spots, seeing yellow spots, blurred vision

Phenytoin- nystagmus (uncontrollable blinking)

Lithium- blurred vision

Question 17

What is the target range for lithium levels?

Answer 17

0.5- 1 mmol/L

Question 18

When should lithium levels be checked?

Answer 18

12-24 hours POST DOSE

after 5-7 days of initiation

Question 19

What are the signs of Lithium Toxicity?

Answer 19

Blurred vision
Muscle weakness
Slurred speech
Confusion
Seizures
Renal damage
Increased risk of Hypothyroidism

Question 20

How does sodium effect lithium levels?

Answer 20

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

Question 21

Does dehydration lead to increased or decreased lithium levels?

Answer 21

Increased! -important to avoid dehydration

Question 22

What should we regularly check the function of in patients receiving lithium (2 organs)?

Answer 22

Renal function

Thyroid function

Question 23

Target Theophylline concentrations? When should a level be taken?

Answer 23

10 - 20mg/L

Take level 4-6 hours after a modified release dose.

Question 24

What can theophylline toxicity result in?

Answer 24

QT interval prolongation

Increased risk of convulsions

Question 25

When should INR be checked after a dose adjustment/ initiation of warfarin? What is the half life of warfarin

Answer 25

48 hours post 1st dose

Half life is around 40 hours

Question 26

What is the target level for carbamazepine? When should a trough level be taken?

Answer 26

4-10 mg/L

Trough at least 2 weeks after starting or dose change

Question 27

In patients on warfarin, when should phytomenadione (vitamin K) be given IV?

Answer 27

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

Question 28

How does vitamin K (phytomenadione) work in warfarin overdose?

Answer 28

Phytomenadione promotes hepatic synthesis of clotting factors therefore reverses anticoagulation of warfarin

Question 29

In patients on warfarin, when should phytomenadione (vitamin K) be given ORALLY?

Answer 29

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

Question 30

What is the difference between Phenindione and Phytomenadione?

Answer 30

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