Therapeutic drug monitoring

Question 1

Carbamazepine therapeutic range

Answer 1

4 to 10mg/L

Question 2

Carbamazepine toxic effects

Answer 2

Incoordination, blurred vision, diplopia, drowsiness, nystagmus, ataxia, arrhythmias, nausea and vomiting, diarrhoea, hyponatremia

Question 3

When should carbamazepine levels be taken?

Answer 3

Trough level - immediately before next dose

Question 4

Factors that might increase carbamazepine levels

Answer 4

Hepatic disease, erythromycin, cimetidine, diltiazem, verapamil, isoniazid

Question 5

Factors that might decrease carbamazepine levels

Answer 5

Phenytoin or phenobarbitol

Question 6

What is special about carbamazepine metabolism?

Answer 6

Carbamazepine induces its own metabolism. Consequently, although steady state is achieved 2 to 3 weeks after initiating therapy, any change in dosage during chronic therapy will take approximately 1 week to produce a new steady state concentration

Question 7

Rough conversion from oral to rectal carbamazepine

Answer 7

In general, the recommended rectal dose is 25% higher than the oral dose

Question 8

Digoxin therapeutic range

Answer 8

1 to 2 mcg/L

Question 9

Digoxin toxic effects

Answer 9

Nausea, vomiting, arrhythmias, visual disturbances, weakness and lethargy

Question 10

When should digoxin levels be taken?

Answer 10

Take at least 6 hours after an oral dose

Question 11

Factors increasing digoxin concentrations

Answer 11

Renal failure, hepatic disease and concurrent use with amiodarone, diltiazem, verapamil, quinine, atorvastatin.

Question 12

Conversion between digoxin tablets and digoxin oral solution

Answer 12

One 62.5mcg tablet = approx 50mcg of liquid

Question 13

What electrolyte imbalances can potentiate digoxin toxicity?

Answer 13

Low k+, mg or Ca

Question 14

At what time period does NICE recommend lithium levels are taken?

Answer 14

Check one week after starting lithium one week after every dose change

Question 15

Target lithium level for acute episodes of mania or patients who have previously relapsed

Answer 15

0.8-1mmol/L

Question 16

Target lithium levels in elderly/maintenance therapy

Answer 16

0.4-1-mmol/L

Question 17

When should serum lithium levels be taken?

Answer 17

12 hours post dose

Question 18

How should lithium be stopped?

Answer 18

NICE recommends that when stopping lithium the dose should be reduced gradually over at least 4 weeks and preferably up to 3 months

Question 19

Signs of lithium toxicity

Answer 19

GI disturbances, visual disturbances, polyuria, muscle weakness, fine tremor, seizures, arrhythmias,

Question 20

Phenytoin therapeutic serum levels

Answer 20

10-20mg/L

Question 21

Conversion from phenytoin sodium (capsules) and phenytoin base (suspension)

Answer 21

100mg of sodium = 92mg of base

Question 22

Symptoms of phenytoin toxicity

Answer 22

Nystagmus, diplopia, slurred speech, ataxia, confusion and hyperglycemia

Question 23

Phenytoin monitoring with IV use

Answer 23

Monitor ECG and blood pressure

Question 24

When should theophylline plasma levels be taken after initiating treatment?

Answer 24

5 days after starting oral treatment or 3 days after any dose adjustments

Question 25

What time should plasma theophylline levels be taken?

Answer 25

Levels should be taken 4-6 hours after MR dose

Question 26

Factors that increase plasma-theophylline levels

Answer 26

Heart failure, hepatic impairment, in viral infections

Question 27

Factors that decrease plasma-theophylline concentrations

Answer 27

Smokers, by alcohol consumption

Question 28

Signs of theophylline overddose

Answer 28

Vomiting, agitation, restlessness, tachycardia, hyperglycemia Haematesis, convulsions. Severe hypokalaemia may develop rapidly

Question 29

Target plasma theophylline levels

Answer 29

Plasma-theophylline concentration 10-20mg/L (55-110micromol/L) although a lower plasma concentration of 5-15mg/L may be effective