Mood Stabilizers: Monitoring & Long-Term Adverse Effects

Why mood stabilizers need monitoring

Narrow margins. Lithium, valproate, carbamazepine, and lamotrigine prevent relapse in bipolar disorder, but each has a narrow safety margin, a signature organ toxicity, and important interactions. Vignettes ask which baseline test was missed, which new prescription caused toxicity, or how to manage a predictable long-term effect without abandoning an effective drug.

Lithium: levels, interactions, and toxicity

Baseline work-up. Lithium is excreted almost entirely by the kidneys, so renal function governs dosing. Before the first dose obtain creatinine and eGFR (± urinalysis), TSH, serum calcium, weight, and a pregnancy test in anyone who could conceive, plus an ECG if the patient is older than 40 or has cardiac disease.

Serum levels. Levels are 12-hour troughs drawn in the morning before the next dose; a sample taken a few hours after a dose catches the peak and looks falsely toxic. The maintenance target is 0.6–1.0 mEq/L, with up to about 1.2 mEq/L for acute mania. The half-life is roughly 24 hours, so steady state takes about 5 days: recheck about 5 days after starting, after any dose change, or after an interacting drug is added. Once stable, check levels every 3–6 months and creatinine, TSH, and calcium every 6–12 months. Older adults need lower doses and are more vulnerable to toxicity.

Interactions. After filtration, lithium is reabsorbed with sodium in the proximal tubule, so anything that depletes sodium or lowers GFR raises the level on an unchanged dose: thiazides, ACE inhibitors and ARBs, NSAIDs, dehydration, vomiting or diarrhea, low-salt diets, and worsening kidney function. Loop diuretics have a smaller effect but still warrant a repeat level; acetaminophen is the preferred analgesic.

Toxicity. Levels above about 1.5 mEq/L usually cause symptoms: vomiting and diarrhea first, then coarse tremor, ataxia, slurred speech, confusion, hyperreflexia or myoclonus, seizures, and coma. Chronic toxicity, typically an older patient who adds an interacting drug or becomes dehydrated, can be severe at levels only modestly above range. Hold lithium, give IV normal saline, and follow levels and renal function; dialyze (EXTRIP) for decreased consciousness, seizures, or dysrhythmias at any level, a level >4.0 mEq/L with impaired kidney function, or a level >5.0 mEq/L regardless. Activated charcoal does not bind lithium; whole-bowel irrigation is reserved for large sustained-release overdoses.

A fine postural tremor at a therapeutic level is a side effect; a coarse tremor with ataxia or confusion is toxicity until a level proves otherwise.

Long-term effects of lithium

Other effects. Weight gain, acne and psoriasis flares, benign leukocytosis, T-wave flattening or sinus node dysfunction, and mental dulling are common. Lithium is teratogenic, with a link to Ebstein anomaly. Lithium-induced hypothyroidism can mimic or worsen depression, so check TSH when mood dips.

Worth protecting. Lithium lowers suicide risk in mood disorders, a strong reason to manage its side effects rather than stop it.

Valproate and carbamazepine

Valproate monitoring. Obtain LFTs and a CBC with platelets at baseline and periodically, with weight and pregnancy status; the therapeutic level for mania is roughly 50–125 μg/mL. Boxed warnings cover hepatotoxicity (greatest in children younger than 2 years, patients on several anticonvulsants, and mitochondrial POLG disease), pancreatitis (check lipase for abdominal pain with vomiting, even at therapeutic levels), and teratogenicity.

Other valproate effects. Dose-related thrombocytopenia, tremor, weight gain, and hair loss are common. Valproate impairs the urea cycle and can cause hyperammonemic encephalopathy with normal LFTs, so check ammonia in a lethargic or confused patient. Women may develop hyperandrogenism, menstrual irregularity, and polycystic ovary features. Valproate inhibits glucuronidation and roughly doubles lamotrigine levels.

Valproate is the most teratogenic mood stabilizer: neural tube defects (spina bifida in about 1–2%), other major malformations, and lower IQ and higher autism risk after in-utero exposure. Avoid it in women of childbearing potential; if truly unavoidable, require reliable contraception plus folic acid.

Carbamazepine screening. In patients of Asian ancestry (for example, Han Chinese or Thai), test for HLA-B*15:02 first; carriers have a markedly higher risk of SJS/TEN and need a different drug, avoiding oxcarbazepine and phenytoin, which share the risk. Serious rash is most likely in the first few months. HLA-A*31:01 (European and Japanese ancestry) predicts other hypersensitivity reactions such as DRESS.

Blood and sodium. A boxed warning covers agranulocytosis and aplastic anemia: CBC at baseline and periodically. Mild benign leukopenia is common, but marked neutropenia or infection means stopping. Carbamazepine also causes SIADH with euvolemic hyponatremia (oxcarbazepine even more), hepatotoxicity, diplopia and ataxia at high levels, and neural tube defects.

Enzyme induction. Carbamazepine induces CYP3A4, including its own metabolism (autoinduction), so levels fall over the first 2–4 weeks and the dose must be raised and the level rechecked. It lowers levels of oral contraceptives, warfarin, lamotrigine, and many antipsychotics; hormonal pills, patches, and rings become unreliable, so an IUD or depot medroxyprogesterone is preferred. CYP3A4 inhibitors such as macrolides, azole antifungals, and grapefruit juice push carbamazepine into toxicity.

Lamotrigine and bipolar depression

Rash risk. Lamotrigine SJS/TEN risk is concentrated in the first 8 weeks and rises with rapid titration, exceeding the starting dose, and coadministered valproate, which calls for half the usual dose and titration. Carbamazepine requires larger doses, and estrogen-containing contraceptives lower lamotrigine levels. Stop at the first sign of a drug rash; after more than 5 half-lives off the drug, restart the titration from the lowest dose.

Maintenance role. Lamotrigine is preferred for maintenance when depressive episodes dominate: weight-neutral, no routine blood monitoring, and lower teratogenic risk than valproate or carbamazepine. It has no antimanic effect, and the six-week titration makes it useless for an acute episode.

Acute bipolar depression. Quetiapine or lurasidone is first line, with cariprazine, lumateperone, and olanzapine-fluoxetine as alternatives. Both need metabolic monitoring (weight, glucose, lipids); quetiapine sedates and adds weight, while lurasidone causes akathisia and must be taken with food. Antidepressant monotherapy is avoided because it risks a switch into mania.