Lithium
⚠️ Toxicity: Lithium has a narrow therapeutic index.
- Therapeutic: 0.4–1.0 mmol/L (target 0.6–0.8).
- Toxic: >2 mmol/L.
Management: Hydration + haemodialysis if severe.
📖 About
- Check the BNF or local guidance before prescribing.
- Mood stabiliser with well-established role in bipolar disorder and related conditions.
- Low therapeutic index → requires careful monitoring.
⚙️ Mode of Action
- Alters intracellular signalling pathways.
- Acts on secondary messengers (e.g., adenylate cyclase, G-protein signalling, phosphoinositol turnover).
- Exact mechanism remains incompletely understood.
💊 Indications
- Bipolar disorder — prophylaxis and acute mania/hypomania.
- Adjunct in treatment-resistant depression.
- Cluster headache (off-label).
💉 Dose
- Typical range: 400 mg – 1.2 g daily (single or divided doses).
- Baseline tests: U&E, creatinine, TFTs, calcium before starting.
🧪 Monitoring
- Check level 4–7 days after initiation/dose change, at 12 h post-dose (“trough level”).
- Maintain serum concentration 0.6–0.8 mmol/L (sometimes lower in elderly).
- Ongoing: monitor renal and thyroid function regularly.
🚫 Contraindications / Cautions
- Avoid in significant renal impairment or severe cardiovascular disease.
- Caution in elderly, dehydration, or patients on interacting drugs (see below).
- Contraindicated with active untreated hypothyroidism.
⚠️ Interactions (Increase Toxicity Risk)
- Thiazide diuretics, ACE inhibitors, ARBs, NSAIDs.
- Loop diuretics (milder risk, still relevant).
- Verapamil + lithium → neurotoxicity.
- Risk ↑ in dehydration, advanced age, renal disease.
❌ Side Effects
- GI upset (nausea, vomiting, diarrhoea).
- Neurological: tremor, ataxia, confusion, seizures (if toxic).
- Weight gain, oedema.
- Nephrogenic diabetes insipidus (blocks vasopressin-induced adenylate cyclase).
- Hypothyroidism, hyperparathyroidism (chronic use).
- Long-term: chronic kidney disease (rare but serious).
📚 References
