4.3 Mood Stabilizers & Lithium
Key Takeaways
- Lithium's therapeutic range is 0.6-1.2 mEq/L; toxicity appears above 1.5 mEq/L and becomes severe/life-threatening above 2.0 mEq/L.
- Lithium levels are drawn as a trough, about 12 hours after the last dose; a coarse tremor signals toxicity, while a fine tremor is an expected therapeutic effect.
- Dehydration, a low-sodium diet, NSAIDs, thiazide diuretics, and ACE inhibitors all raise lithium levels by reducing renal clearance.
- Valproate (therapeutic range 50-125 mcg/mL) carries black-box risks of hepatotoxicity, pancreatitis, and teratogenicity (neural tube defects).
- Carbamazepine carries black-box risks of agranulocytosis/aplastic anemia and SJS/TEN (higher with the HLA-B*1502 allele); lamotrigine requires slow titration to reduce SJS/TEN risk, especially when combined with valproate.
Mood stabilizers treat bipolar disorder across its manic, depressive, and maintenance phases, but each agent in this class carries a distinct, serious toxicity that the nurse must monitor for by number, not by guess. The PMH-BC exam rewards precise recall of therapeutic ranges, toxicity thresholds, and required labs.
Lithium
Lithium remains a gold-standard mood stabilizer for bipolar disorder, particularly for reducing suicide risk, but it has a narrow therapeutic index.
| Level | Meaning |
|---|---|
| 0.6-1.2 mEq/L | Therapeutic range |
| Above 1.5 mEq/L | Toxicity: nausea, vomiting, diarrhea, coarse hand tremor, ataxia, muscle weakness, slurred speech |
| Above 2.0 mEq/L | Severe/life-threatening toxicity: confusion, seizures, cardiac arrhythmias, renal failure, coma — can be fatal |
Drawing the level correctly matters: lithium levels are drawn as a trough, roughly 12 hours after the last dose — typically a morning sample before the AM dose, with the prior evening dose given as usual. A level drawn too soon after dosing overstates the true level.
A fine hand tremor is an expected, benign side effect at therapeutic levels; a coarse tremor is a red-flag sign of toxicity and should prompt an immediate level check and provider notification.
Required monitoring: renal function (BUN/creatinine) and thyroid function (TSH — lithium can cause hypothyroidism and goiter) at baseline and periodically thereafter; baseline ECG in patients with cardiac risk factors; serum sodium.
Interactions that raise lithium levels (by reducing renal clearance): dehydration, a low-sodium diet, NSAIDs, thiazide diuretics, and ACE inhibitors. Patients need explicit teaching to maintain steady fluid and sodium intake, avoid NSAIDs, and notify their prescriber before starting a new diuretic or ACE inhibitor — illness with vomiting, diarrhea, or fever also raises toxicity risk by causing dehydration. Hot weather, heavy exercise, and sauna use can produce the same effect through sweating-related fluid and sodium loss, so patients need proactive teaching before these situations, not just after symptoms appear.
Lithium is available in immediate-release and extended-release formulations (for example, lithium carbonate versus Lithobid); switching between formulations or between brand and generic without provider awareness can meaningfully change absorption and blood levels given the drug's narrow therapeutic index, so consistency matters as much as the dose itself.
Valproate (Valproic Acid / Divalproex Sodium)
Valproate's therapeutic range is 50-125 mcg/mL. Key risks:
- Hepatotoxicity — a black-box warning; obtain baseline and periodic liver function tests, especially in the first six months.
- Pancreatitis — a black-box warning that can occur at any point in treatment; report abdominal pain, nausea, and vomiting immediately.
- Thrombocytopenia — monitor CBC/platelets.
- Teratogenicity — a black-box warning for neural tube defects; valproate should be avoided in pregnancy and used cautiously in women of childbearing potential, with contraception counseling.
- Hyperammonemia — can cause lethargy and altered mental status even with normal liver function tests.
Carbamazepine
Carbamazepine carries a black-box risk of agranulocytosis and aplastic anemia, requiring baseline and periodic CBC monitoring — instruct patients to report fever, sore throat, or other signs of infection immediately. It also carries a black-box risk of Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), with markedly higher risk in patients carrying the HLA-B*1502 allele (most common in patients of Asian ancestry); genetic testing is recommended before starting in at-risk populations. Additional concerns include hepatotoxicity, hyponatremia (via SIADH), and autoinduction — carbamazepine induces its own hepatic metabolism (and that of many other drugs via CYP450 induction), so doses often need adjustment a few weeks into treatment. This same enzyme induction reduces the effectiveness of many co-administered drugs, including hormonal contraceptives and warfarin, so patients need explicit counseling about backup contraception and closer anticoagulation monitoring.
Lamotrigine
Lamotrigine is effective for bipolar depression and maintenance (less effective for acute mania) but requires slow, deliberate dose titration over several weeks — rapid titration is the single biggest modifiable risk factor for SJS/TEN, a black-box warning. The risk is further increased when lamotrigine is combined with valproate, because valproate inhibits lamotrigine's metabolism and raises its blood level; the lamotrigine starting dose and titration schedule must be reduced when the two are co-prescribed. Any new rash while titrating lamotrigine warrants same-day provider contact and should not be dismissed as a minor reaction.
A frequently tested teaching point: if a patient misses several consecutive days of lamotrigine, the protective tolerance built during titration is lost, and the medication must be restarted at the original low titration dose rather than resumed at the prior maintenance dose — resuming at a higher dose after a gap re-creates the rapid-titration pattern that raises SJS/TEN risk.
Clinical Application
A bipolar patient on lithium who presents with vomiting, ataxia, and a coarse tremor after a week of a stomach virus needs an immediate lithium level — dehydration from the illness has likely pushed the level into the toxic range. A patient started on lamotrigine who develops a rash three weeks into titration needs the medication held and the provider notified the same day, not "watched for a few more days."
A patient on lithium therapy for bipolar disorder develops a stomach virus with several days of vomiting and diarrhea. Which finding would most concern the nurse for lithium toxicity?
A patient is started on lamotrigine for bipolar depression maintenance and is already taking valproate for the same condition. What is the priority nursing consideration?