Drug monitoring

Question 1

What are the features of digoxin toxicity?

Answer 1

• Confusion
• Nausea
• Visual halos
• Arrhythmias

Question 2

What are the features of lithium toxicity?

Answer 2

• Early: tremor
• Intermediate: tiredness
• Late: arrhythmias, seizures, coma, renal failure and diabetes insipidus

Question 3

What are the features of phenytoin toxicity?

Answer 3

• Gum hypertrophy
• Ataxia
• Nystagmus
• Peripheral neuropathy
• Teratogenicity

Question 4

What are the features of gentamicin toxicity?

Answer 4

• Ototoxicity
• Nephrotoxicity

Question 5

What are the features of vancomycin toxicity?

Answer 5

• Ototoxicity
• Nephrotoxicity

Question 6

What is the normal dose of gentamicin?

Answer 6

• Doses calculated according to weight and renal function
• High dose regimen of 5-7mg/kg OD
• Pt’s with severe renal failure (creatinine clearance <20ml/min) or endocarditis may receive a divided daily dosing (1mg/kg) 12hrly (in renal failure) or 8hrly (in endocarditis)

Question 7

How does the gentamicin monitoring nomogram work?

Answer 7

• Measure gentamicin levels at particular times e.g. 6-14hr after gentamicin infusion started
• In q36h area - 36hr dosing etc
• Above 48hr area, repeat level and only redose when concentration <1mg/l

Question 8

What are the gentamicin levels?

Answer 8

Peak:
- Normal in IE: 3-5mg/l
- Normal in everything else: 5-10mg/l
Trough (just before next doses):
- In IE: <1
- In everything else: <2

Question 9

What is the management of a paracetamol overdose?

Answer 9

N-acetyl cysteine (NAC) and supportive management with IV fluids

Question 10

How do you interpret a paracetamol level nomogram?

Answer 10

• Record at least 4 hours after ingestion
• If plasma paracetamol level is below line then patient doesn’t need NAC
• If plasma level above they need NAC
• If patient took staggered overdose or time of ingestion is unknown then NAC is advised

Question 11

What is the target INR?

Answer 11

• Usually 2.5
• Metal replacement heart valves may be >2.5 - depends on type and location of valve
• Recurrent VTE >2.5

Question 12

How often is INR monitored?

Answer 12

At first every week, then monthly when stable. Alcohol affects the metabolism of warfarin.

Question 13

What needs to be monitored with olanzapine?

Answer 13

Fasting blood glucose at baseline and regular intervals - hyperglycaemia and diabetes can occur.

Question 14

What needs to be monitored with digoxin?

Answer 14

U&Es
- Plasma digoxin concentration is not measured unless toxicity, non-compliance or inadequate effect are suspected
- Hypokalaemia increases risk of digoxin toxicity

Question 15

What needs to be monitored on clozapine?

Answer 15

• FBC must be checked weekly for the first 18 weeks, then fortnightly for up to a year, then monthly
• Blood lipids and weight every 3 months for the first year, then yearly
• Fasting blood glucose should be measured at baseline, after 1 month then every 4-6 months
• Close medical supervision during initiation - risk of collapse because of hypotension and convulsions.

Question 16

What are important interactions with methotrexate?

Answer 16

• NSAIDs - low platelet count
• Trimethoprim - bone marrow suppression symptoms
• PPIs - increase level of methotrexate