Acute Poisoning - TCAs, Lithium & Digoxin

Tricyclic Antidepressants

2.5-3.5g of amitriptyline

Anticholinergic effects = Neuro & Cardio problems
Usually w/i 6 hrs = severe effects:
- Ventricular arrhythmias
- Seizures
- Hypotension
- Respiratory depression

Lithium

Different forms:

- liquid peaks at 30mins
- tablets peaks at 4-5hrs
1/2 life = 8 - 45hrs

Higher toxicity - in HT, DM, CCF


Digoxin

Plasma = >10ng/mL

Toxicity

Fatigue, blurred vision, disturbed colour perception (Van Gogh's halos)

Anorexia, nausea, vomiting, diarrhoea, abdominal pain

Headache, dizziness, confusion, delirium, and occasionally hallucinations

Cardiac arrhythmias - most common cause of mortality & most common pattern =  SVT + AV Block

Hypokalaemia predisposes
Hyperkalaemia a consequence

Ix
Upper normal limit = 2ng/mL (without predisposing factors)
Measure plasma levels 6hrs after last dose

Tx
Activated charcoal (within 6-8hrs) or cholestyramine
Correct electrolyte abnormalities - careful replacement of potassium (too rapid can increase AV block)
Hyperkalaemic = glucose, insuline and sodium bicarbonate
Digoxin-specific antibody Fab fragments - binds to circulating digoxin
if >10mg ingested in adults
if >4mg ingested in children
or plasma concentration >10ng/mL
or >5mmol/L with life-threatening arrhythmia - VT, VF, progressive bradycardia/high-degree AV nodal block

Partial response/resistance
Underlying heart disease/late administration/ too small a dose

NB dramatic hypokalaemia can occur after digibind threapy at 1-4hrs therefore MONITOR!!

Extracorporeal techniques

Haemodialysis/haemoperfusion
- helps with hyperkalaemia/volume overload with renal failure
h/e less helpful due to digoxin's large distribution and binding to tissue