Poisons and Prescribing

Question 1

Appreciate the range of poisons that can be taken

Answer 1

• Paracetamol
• Hypnotics (diazepam, zoplicone)
• Salicylates (aspirin)
• Ecstasy
• Amitriptyline (tricyclic)
• Opiates
• Other anti-depressants
• Cocaine

Question 2

Describe how unwell poisoned patients may present

Answer 2

• UMN signs (anticholinergics)
  
  • Hypertonia
  • Hyperreflexia
  • Extensor plantars
• Coma
• Dystonic movements
• Dilated/constricted pupils
• Hypo/hyperventilation
• acidosis/alkalosis
• Hypokalaemia/ hyponatraemia/ hypoglycaemia
• Tachycardia, hypertension, fever

Question 3

Describe the general management for patients with poisoning

Answer 3

• ABCDE approach
• History - including collateral history
• Examination findings
  
  • Blood, urine, ECG
• Usually supportive care
• Appropriate antidotes when indicated

Question 4

Describe how paracetamol can cause hepatotoxicity

Answer 4

• Paracetamol metabolised in the liver into NAPQI through phase I oxidation, which is very reactive and toxic
• NAPQI at normal doses is detoxified by phase II conjugation with glutathione
  
  • If glutathione levels drop (increased free radical or excessive paracetamol level), NAPQI builds up
• At high doses, paracetamol becomes zero order and leads to saturation
  
  • Also causes saturation of NAPQI
• NAPQI build up leads to necrotic hepatic cell death and possible renal failure
• Treated by replacing glutathione through giving N-acetylcysteine

Question 5

What does drug therapy and dose depend on

Answer 5

• Genetics
• Age
• Organ function
• Drug interactions
• Nature of disease
• Dose-response curve

Question 6

Describe the causes of medication error

Answer 6

• Clarity of handwriting/spelling
• Abbreviations
• Inappropriate dosing for route of administration
• Unclear drug units
• Loading dose regimes

Question 7

Describe why elderly patients are more at risk of polypharmacy

Answer 7

• Pharmacokinetic
  
  • Impaired first pass metabolism - increased bioavailability
  • Reduced renal clearance
  • Impaired hepatic clearance
• Pharmacodynamics
  
  • Age-related reduction in receptor sites
    
    • Reduced homeostatic reserve - increased sensitivity to drugs affecting postural control, cognitive function and visceral muscle function

Question 8

Know the rules of prescribing

Answer 8

• Check sources
• Clarity of handwriting
• Black ink
• Legible signature and sign name
• PRN medications - indication, frequency and maximum dose
• Changes to Rx - rewrite in full, sign and date changes, document in notes