Mood stabilisers: comparing lithium, valproate, carbamazepine and lamotrigine

One goal, four different safety profiles

All four drugs aim to reduce manic or depressive episodes, but they are not interchangeable from a monitoring standpoint. Lithium and the antiseizure agents valproate and carbamazepine are titrated using blood levels, tolerance and response, while lamotrigine is titrated slowly on a fixed schedule because a rapid increase raises the risk of serious rash. Lithium's full effect on mania can take a week or more, so early agitation does not mean it has failed.

Exam questions often hide the drug name in a symptom. Coarse tremor and vomiting point to lithium; abdominal pain with vomiting on valproate raises pancreatitis; sore throat and bruising on carbamazepine suggest a blood disorder; a new rash on lamotrigine calls for urgent review. Build the habit of naming the drug first, then the specific risk.

Lithium: levels, sodium and toxicity cues

Common early effects include fine tremor, nausea, diarrhoea, thirst and passing more urine. Acute toxicity begins with coarse tremor, brisk reflexes, persistent headache, vomiting and confusion, and can progress to stupor, seizures and arrhythmias. Toxicity is more likely in older adults, reduced kidney function and sodium loss from fever, vomiting, diarrhoea or diuretics.

Thiazide diuretics, ACE inhibitors and NSAIDs other than aspirin can raise lithium levels, so review new prescriptions and over-the-counter painkillers. Longer term, lithium can cause hypothyroidism, raised calcium and kidney changes, so thyroid, kidney and calcium checks form part of follow-up. Teach steady fluid and salt intake and to seek advice during illness with vomiting or diarrhoea.

When a level is ordered, confirm the timing relative to the last dose as local protocol specifies, because a sample drawn at the wrong time can mislead. Always interpret the number together with the patient's symptoms: a result within the usual range does not cancel concern about clear clinical signs of toxicity.

Valproate, carbamazepine and lamotrigine

Valproate commonly causes nausea, sedation and weight gain; rare serious effects include liver injury and pancreatitis, so report jaundice, dark urine, abdominal pain or persistent vomiting. Carbamazepine can cause dizziness and unsteadiness, and very rarely aplastic anaemia or agranulocytosis. Its risk of severe skin reactions is highest in people of Asian ancestry with an inherited risk factor.

Lamotrigine can cause rash and, rarely, Stevens-Johnson syndrome, particularly when the dose rises faster than recommended. The label advises stopping at the first sign of rash unless clearly unrelated, so the nurse reports any rash promptly rather than waiting. Valproate more than doubles lamotrigine levels, while carbamazepine lowers them, which is why combination changes need prescriber oversight.

Pregnancy planning and patient teaching

Among mood stabilisers, valproate is the most likely to cause birth defects and is generally avoided in pregnancy; carbamazepine is also typically avoided. Lithium has been associated with cardiac malformations, though the absolute risk is low and it is sometimes continued with specialist input. Lamotrigine appears to carry lower risk. Raise contraception and pregnancy plans early, since harm can occur before pregnancy is recognised.

Teach patients not to stop suddenly or double doses, to attend blood tests as scheduled, and to bring every new medicine to the pharmacist. Ask for teach-back of the specific warning signs for their own drug. A patient taking lithium should describe what to do during gastroenteritis; one taking lamotrigine should explain that a new rash means calling straight away.

Worked exam-style scenario

Imagine a hypothetical patient stable on lithium who started regular ibuprofen for back pain a week ago and now has vomiting, coarse hand tremor and slurred, slowed thinking. Options include giving an antiemetic and observing, encouraging more ibuprofen for comfort, giving the next lithium dose with food, or holding lithium and escalating for an urgent level and assessment.

Holding and escalating is the strongest answer because the picture fits early toxicity, and NSAIDs can raise lithium levels. An antiemetic hides the problem. Giving lithium with food adds to the load. If the same patient instead took lamotrigine and reported a new rash, the priority would be urgent reporting rather than waiting to see if it spreads.

Sources and further reading

MSD Manual Professional: Medications for treatment of bipolar disorders. Lithium adverse effects, toxicity signs and interacting drugs; valproate, carbamazepine and lamotrigine risks; pregnancy considerations.

DailyMed: LAMICTAL (lamotrigine) prescribing information. Boxed warning on serious rash, stopping at first sign of rash, and valproate and carbamazepine interactions.

MedlinePlus: Carbamazepine. Severe skin reactions with highest risk in people of Asian ancestry with an inherited risk factor.