💊 Lithium

Lithium is a mood stabiliser, primarily used in the treatment of bipolar disorder. It is a monovalent cation, and its therapeutic effects are thought to be mediated through various intracellular mechanisms.

The precise mechanism of action of lithium is not fully understood, but it is thought to modulate several neurotransmitter systems, including dopamine, serotonin, and noradrenaline. It also affects intracellular signalling pathways, such as the inositol phosphate pathway and glycogen synthase kinase-3 (GSK-3) inhibition, contributing to its mood-stabilising effects.

Lithium is primarily indicated for the prophylaxis of bipolar affective disorder, reducing the frequency and severity of both manic and depressive episodes. It is also used for the treatment of acute mania and hypomania. In some cases, it can be used as an augmentation strategy for treatment-resistant depression.

Absolute contraindications include severe renal impairment, Addison's disease, and untreated hypothyroidism. It should be used with extreme caution in patients with cardiovascular disease, severe dehydration, and concurrent use of drugs that affect renal function or electrolyte balance, such as NSAIDs and thiazide diuretics.

Common adverse effects include fine tremor, polyuria and polydipsia (due to nephrogenic diabetes insipidus), nausea, diarrhoea, and weight gain. More serious side effects include hypothyroidism, renal impairment, and cardiac arrhythmias. Lithium toxicity, which can be life-threatening, presents with coarse tremor, ataxia, confusion, and seizures.

Close monitoring of serum lithium levels is essential due to its narrow therapeutic index, typically 12 hours post-dose. Renal function (urea, creatinine, eGFR) and thyroid function (TSH) should be monitored regularly. Electrolytes, particularly sodium, should also be checked. ECG is recommended before initiation and periodically.

When prescribing, always check for allergies and ensure the patient is not pregnant or breastfeeding. Carefully review the patient's medication list for interacting drugs, especially NSAIDs, ACE inhibitors, ARBs, and thiazide diuretics. Counselling must cover the importance of regular blood tests, maintaining adequate hydration, and recognising symptoms of toxicity.

High-yield topics include the narrow therapeutic index of lithium and the critical importance of therapeutic drug monitoring. Recognition and management of lithium toxicity are essential. Understanding the long-term side effects, particularly renal and thyroid dysfunction, is frequently tested. The interaction with NSAIDs is a classic trap.

SBAs frequently test the signs and symptoms of lithium toxicity and the factors that can precipitate it (e.g., dehydration, NSAIDs). Questions may also focus on the essential monitoring requirements for lithium, including the timing of blood tests. Understanding its role in bipolar disorder prophylaxis is also a common theme.