Drug specific data

Question 1

What common drugs have a narrow therapeutic window and need monitoring?

Answer 1

• Digoxin
• Theophylline
• Lithium
• Phenytoin
• Gentamicin
• Vancomycin

Question 2

How is drug monitoring performed?

Answer 2

• Clinical state i.e therapeutic effects and signs of toxicity
• Serum drug level

Small incremental drug dose increases are important especially in zero order kinetics where small increments can result in big changes.

Question 3

What are the common toxic side effects of digoxin?

Answer 3

• Confusion, nausea, visual halos and arrhythmias

Question 4

What are the common toxic side effects of lithium?

Answer 4

Early: Tremors
Intermediate: Tiredness
Late: Arrhythmias, seizures, coma, renal failure, diabetes insipidus

Question 5

What are the common toxic side effects of phenytoin?

Answer 5

Teratogenicity, peripheral neuropathy, nystagmus, ataxia, gum hypertrophy

Question 6

What are the common toxic side effects of gentamicin and vancomycin?

Answer 6

Ototoxicity and nephrotoxicity

Question 7

What are the three treatments for if you suspect toxicity?

Answer 7

1) Stop drug +/- alternative
2) Supportive measures (usually IVF)
3) Give antidote if available

Question 8

How do you prescribe gentamicin?

Answer 8

Doses calculated on patients weight and renal function

• i.e high dose 5-7mg/kg OD
• Severe renal failure (<20mL/min creatinine clearence) or ENDOCARDITIS may get divided dose i.e 1mg/kg 12hrly (Renal failure) or 8 hourly (endocarditis) - Depends on hospital policy

Question 9

How do you monitor gentimicin?

Answer 9

Peak and trough monitoring:

Peak (1hr post dose): 3-5mg/L (endocarditis), 5-10mg/L everything else. (if out of range adjust dose)

Trough (just before next dose) <1mg/L (endocarditis), <2mg/L everything else. if out of range then adjust dosing interval

Question 10

What is the target INR for most patients on warfarin?

Answer 10

2.5 when on warfarin unless there is recurrent thromboembolism whilst on warfarin then it becomes 3.5.

Question 11

If there is a major bleed whilst on warfarin i.e hypotension, bleeding in brain or eye (confined spaces) what do you do?

Answer 11

• Stop warfarin
• 5-10mg IV vit K
• Prothrombin complex

Question 12

Whats the management for elevated INR on warfarin?

Answer 12

No bleeding:
INR 5-8 = Omit warfarin for 2 days and then reduce dose.
>8 = Omit and give 1-5mg PO Vit K

Minor bleeding:
INR 5+, Omit warfarin and give 1-5mg IV vit K

Question 13

What drugs commonly cause constipation?

Answer 13

• Opioids
• Anticholinergics
• SE of many others