Therapeutic drug monitoring

Question 1

Phenytoin

Signs of toxicity

When to measure?

Answer 1

Ataxia and nystagmus

Phenytoin levels do not need to be monitored routinely but trough levels, immediately before dose should be checked if:

• adjustment of phenytoin dose
• suspected toxicity
• detection of non-adherence to the prescribed medication

Question 2

Digoxin

Signs of toxicity

When to measure?

Answer 2

Arrhythmias, heart block, confusion, xanthopsia (seeing yellow)

Measured at least 6h post dose

Question 3

Lithium

Signs of toxicity

Range?

When to measure?

Answer 3

Tremor (early), lethargy, fits, arrhythmias, renal failure

range = 0.4 - 1.0 mmol/l

Levels should be taken 12 hours post dose.

Question 4

Gentamicin

Signs of toxicity

When to measure?

Answer 4

Ototoxic and nephrotoxic

both peak (1 hour after administration) and trough levels (just before the next dose) are measured

Question 5

Theophyline

Signs of toxicity

Answer 5

Arrythmias, anxiety, tremor, convulsions

Question 6

Ciclosporin

When to measure?

Answer 6

trough levels immediately before dose