Mood Stabilizers — Lithium and Anticonvulsants

• Lithium's Dual Mechanism: Lithium exerts its mood-stabilizing effects through two complementary pathways. First, it inhibits inositol monophosphatase in the phosphatidylinositol (PI) cycle, reducing intracellular inositol availability and dampening signaling through phospholipase C (PLC)-coupled G-protein receptors. This mechanism underlies regulation of norepinephrine and serotonin neurotransmission, critical dysregulated systems in bipolar disorder. Second, lithium inhibits glycogen synthase kinase-3β (GSK-3β), a serine/threonine kinase involved in protein degradation cascades, circadian rhythm regulation, and neurotrophin signaling. GSK-3β inhibition increases β-catenin stability and enhances Wnt signaling, promoting neuronal survival and synaptic plasticity. These effects are particularly relevant given evidence that bipolar disorder involves disrupted circadian rhythm regulation and impaired neuroplasticity.

• Anticonvulsant Mechanisms of Mood Stabilization: While anticonvulsants stabilize mood through partially distinct mechanisms from lithium, they converge on modulation of neuronal excitability and GABAergic inhibition. Valproate increases γ-aminobutyric acid (GABA) synthesis by inhibiting GABA transaminase and enhances GABA release; it also inhibits histone deacetylases (HDACs), influencing gene expression relevant to neuroinflammation and neuroprotection. Lamotrigine primarily works through voltage-gated sodium channel blockade and glutamate/aspartate release inhibition, reducing excitatory amino acid neurotransmission, which is thought to be excessive in bipolar depression. Carbamazepine similarly blocks sodium channels and also inhibits adenosine reuptake, enhancing adenosinergic inhibitory tone. Topiramate combines sodium channel blockade, enhancement of GABA-A receptor function, and carbonic anhydrase inhibition.

• Circadian Rhythm Dysregulation and Neuroprotection: Both lithium and anticonvulsants appear to address fundamental circadian rhythm abnormalities in bipolar disorder. Lithium lengthens the circadian period and enhances melatonin signaling, helping normalize the period lengthening observed in bipolar patients. Additionally, both drug classes demonstrate neuroprotective effects through multiple pathways: lithium and valproate activate anti-apoptotic proteins (Bcl-2, Bcl-xL) and promote neurotrophic factor signaling (brain-derived neurotrophic factor, BDNF), counteracting neuroinflammation and cellular stress implicated in bipolar pathology.

• Inflammatory and Immune System Modulation: Emerging evidence demonstrates that both lithium and anticonvulsants suppress pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) and microglia activation. This anti-inflammatory action is increasingly recognized as central to mood stabilization, as elevated inflammatory markers (CRP, IL-6) are found in bipolar disorder and correlate with mood severity and treatment response.

• Protein Kinase C (PKC) Inhibition and Signal Transduction: Lithium and valproate both inhibit protein kinase C, a critical integrator of neurotrophic signaling. Aberrant PKC signaling has been implicated in bipolar disorder's pathophysiology, and PKC inhibition normalizes cellular responses to growth factors and neurotransmitters.

• Bipolar I Disorder (Primary Indication for All Mood Stabilizers): Characterized by episodes of full mania (duration ≥1 week) with reduced need for sleep, grandiose ideation, pressured speech, and goal-directed hyperactivity. Genetic heritability is 70-90%, with polygenic inheritance patterns and environmental triggers (sleep disruption, stress, substance use) precipitating episodes. All mood stabilizers are indicated for acute mania and maintenance treatment. Bipolar I affects 0.5-1.5% of the population with equal gender distribution but higher female rates of mixed and depressive episodes.

• Bipolar II Disorder (Primarily Lamotrigine and Lithium): Defined by hypomanic episodes (duration 4-7 days, less severe than mania, no psychotic features) and depressive episodes. Unlike Bipolar I, Bipolar II lacks full manic episodes. Prevalence is 1-2%, often underdiagnosed due to milder presentation. Lamotrigine demonstrates particular efficacy for bipolar depression prevention, while lithium is effective across the mood spectrum.

• Cyclothymic Disorder and Mood Dysregulation: Lower-threshold chronic mood cycling with shorter episodes and intermediate severity. These conditions show similar genetic loading to bipolar disorder and may progress to full bipolar episodes, warranting preventive mood stabilization in selected cases.

• Acute Manic Episodes (Medication-Induced or Bipolar I/II): Antidepressant-induced mania or "switch" represents a critical indication for mood stabilizer initiation or optimization, particularly relevant when SSRIs or other antidepressants are employed. Bipolar patients on antidepressants monotherapy have high rates of mood destabilization; combination with mood stabilizers is standard of care.

• Major Depressive Disorder with Bipolar Spectrum Features: Patients with unipolar depression who have family history of bipolar disorder, multiple depressive episodes, early age of onset, or mixed features may benefit from mood stabilization to prevent treatment-emergent mania.

• Genetic and Environmental Vulnerability Factors: Family history (first-degree relative with bipolar disorder increases risk 10-fold), prenatal/perinatal complications, childhood trauma, substance use disorders, and circadian rhythm disruption all increase bipolar disorder penetrance and severity, necessitating mood stabilization.

• Acute Manic Episode (Presenting Problem for Lithium/All Mood Stabilizers): Patients present with markedly elevated, expansive, or irritable mood persisting ≥1 week. Associated features include dramatically decreased need for sleep (feeling rested after 2-3 hours), racing thoughts, pressured speech that is difficult to interrupt, grandiose delusions or inflated self-esteem, increased goal-directed activity (excessive spending, hypersexuality, promiscuity), and significant functional impairment. Flight of ideas (rapid topic switching) and distractibility are characteristic. Psychotic features (mood-congruent hallucinations or delusions of grandeur) may be present, and severe agitation, aggression, or risky behavior may necessitate psychiatric hospitalization. The pathophysiologic basis involves excess catecholaminergic and glutamatergic activity, insufficient GABAergic inhibition, and disrupted prefrontal-limbic connectivity.

• Hypomanic Episode (Bipolar II Presentation): Similar to mania but with reduced severity and duration (4-7 consecutive days). Decreased need for sleep is nearly universal. Goal-directed activity increases but without the severe functional impairment or psychotic features of mania. Irritability rather than elevation of mood may predominate. Patients often feel subjectively well and may lack insight into illness severity, making treatment engagement challenging.

• Depressive Episode in Bipolar Disorder (Indication for Lamotrigine, Lithium; Relative Contraindication for Valproate): Presents with sustained depressed mood, anhedonia, guilt, hopelessness, suicidality, hypersomnia or insomnia, psychomotor retardation, and concentration difficulties. Bipolar depression differs from major depressive disorder in several ways: onset is often more acute, hypersomnia and hyperphagia are more common, psychomotor retardation is prominent, and suicide risk is paradoxically higher than in unipolar depression despite similar symptom severity. Mixed features (simultaneous manic and depressive symptoms) are increasingly recognized as common and particularly high-risk for suicide.

• Mixed Episode (High-Risk Presentation): Simultaneous presence of manic and depressive symptoms (e.g., racing thoughts with suicidal ideation, increased goal-directed activity with profound hopelessness). Mixed episodes carry substantially elevated suicide risk and typically require combination mood stabilizer therapy. All mood stabilizers are appropriate, though lithium and valproate show particular efficacy for mixed mania.

• Rapid Cycling (Challenging Presentation Requiring Optimization): Four or more mood episodes annually, often with shorter intervals between episodes. Thyroid dysfunction must be excluded (particularly relevant with lithium), and lamotrigine, valproate, or combination therapy is often required; antidepressant monotherapy frequently worsens rapid cycling.

• Maintenance Euthymia with Residual Symptoms: Even when mood episodes resolve, patients may experience subsyndromal depression or hypomania, impaired concentration, and social/occupational dysfunction. Mood stabilizers prevent episode recurrence but may not fully normalize cognition or functioning, necessitating adjunctive psychotherapy and psychosocial interventions.

• Physical Examination Findings: During acute mania, patients may exhibit psychomotor agitation, rapid speech pace, decreased attention (unable to maintain focus), poor hygiene (in acute states), and signs of behavioral excess (evidence of spending sprees, risky sexual behavior disclosure). Vital signs may show tachycardia and elevated blood pressure reflecting sympathetic hyperactivity. During depression, psychomotor retardation, flattened affect, poor eye contact, and self-neglect are observed. Importantly, physical examination does not directly diagnose bipolar disorder but documents severity and medical complications (thyroid assessment for lithium effects, tremor monitoring, skin examination for carbamazepine/lamotrigine rash).

• Diagnostic Criterion for Bipolar I Disorder (DSM-5): One or more manic episodes meeting full criteria (distinct period of abnormally and persistently elevated, expansive, or irritable mood lasting ≥1 week, plus ≥3 manic symptoms—decreased need for sleep, racing thoughts, increased talkativeness, distractibility, increased goal-directed activity, excessive risk-taking, or risky behavior—with significant functional impairment). One or more depressive episodes may occur but are not required for diagnosis. Bipolar II requires ≥1 hypomanic episode (4-7 days, same symptom criteria but with less functional impairment and no psychosis) and ≥1 major depressive episode.

• Mood Episode Screening Tools: The Mood Disorder Questionnaire (MDQ) is a 13-item self-report screening tool with 73% sensitivity and 90% specificity for bipolar disorder screening in primary care settings. The Young Mania Rating Scale (YMRS) quantifies manic symptom severity (0-60 scale; >15 suggests significant mania) and is used to monitor acute treatment response. The Hamilton Depression Rating Scale (HAM-D) or Patient Health Questionnaire-9 (PHQ-9) assesses depressive severity. The Altman Self-Rating Mania Scale (ASRM) is a brief 5-item screening tool (cutoff ≥5 suggests hypomania/mania).

• Baseline Laboratory Assessment Before Initiating Mood Stabilizers:
• Lithium-Specific: Baseline serum creatinine and BUN (assess renal function; lithium is renally eliminated and can cause chronic kidney disease), 24-hour urine creatinine clearance or estimated GFR (CKD-EPI), baseline thyroid-stimulating hormone (TSH) and free T4 (lithium inhibits thyroid peroxidase and causes hypothyroidism in 20-30% of patients), baseline weight and fasting glucose, urinalysis (assess for nephrogenic diabetes insipidus), and pregnancy status/contraception assessment (lithium increases Ebstein's anomaly risk if exposed first trimester).
• Valproate-Specific: Baseline liver function tests (LFTs: AST, ALT, bilirubin, albumin; valproate is hepatotoxic), complete blood count (CBC; thrombocytopenia risk), ammonia level (assess for underlying hyperammonemia), pregnancy status (valproate is highly teratogenic; FDA pregnancy category X with >30% congenital malformation rate), and pancreatitis risk stratification.
• Lamotrigine-Specific: Baseline skin examination documentation (photographic if possible to establish baseline for rash comparison), HLA-B*1502 testing in Asian populations (strong association with Stevens-Johnson syndrome), and pregnancy status (lamotrigine has more favorable teratogenic profile than valproate but still carries risk).
• Carbamazepine-Specific: Baseline LFTs, CBC, baseline skin examination, HLA-A*3101 testing (associated with carbamazepine-induced serious skin reactions), and pregnancy status.
• Universal: Complete metabolic panel (electrolytes, glucose, kidney/liver function), lipid panel, weight, blood pressure, and fasting glucose or hemoglobin A1c baseline.

• Therapeutic Lithium Monitoring:
• Serum lithium level drawn 12 hours post-dose at steady state (5 days of dosing). Target therapeutic range is 0.6-1.2 mEq/L for maintenance therapy and 1.0-1.5 mEq/L for acute mania (though higher levels increase toxicity risk without proportional efficacy gain). Levels >1.5 mEq/L carry significant toxicity risk; >2.0 mEq/L is toxicity threshold.
• Steady-state kinetics: Lithium has narrow therapeutic window, long half-life (24 hours), and renal elimination with potential for bioaccumulation. Trough levels (12 hours post-dose) most accurately reflect body lithium burden.
• Periodic monitoring: Once stable, lithium levels checked every 3-6 months; more frequent monitoring with renal impairment, dehydration, or concurrent nephrotoxic drugs (NSAIDs, ACE inhibitors).

• Anticonvulsant Drug Level Monitoring:
• Valproate: Therapeutic range typically 50-125 μg/mL for mood stabilization (lower than antiepileptic range of 50-100 μg/mL in some guidelines). Steady state reached at 3-5 days. Levels not always predictive of mood response; clinical response guides dosing.
• Lamotrigine: No validated therapeutic window; dose titration is gradual (to minimize Stevens-Johnson syndrome risk) and guided by clinical response rather than levels. Levels may be checked if toxicity suspected or in special populations (pregnancy, hepatic impairment).
• Carbamazepine: Therapeutic range 4-12 μg/mL. Carbamazepine is a potent CYP3A4 inducer causing autoinduction; levels decline 25-50% over initial 3-4 weeks of therapy requiring dose adjustment. Steady state typically reached at 3-4 weeks.

• Liver Function Monitoring: Baseline and periodic LFTs essential for valproate and carbamazepine. Valproate-associated hepatotoxicity is rare (1-2 per 100,000, more common <2 years age) but potentially fatal; LFTs checked at baseline and 1, 3, and 6 months, then every 6-12 months. Elevated transaminases (even 3x upper limit of normal) may warrant monitoring intensification or medication change; frank jaundice or encephalopathy mandates immediate discontinuation.

• Renal Function Monitoring (Lithium-Specific): GFR baseline and annually; cr

Lithium — narrow therapeutic index, renally cleared

• Nephrogenic diabetes insipidus: lithium enters principal cells via ENaC and impairs vasopressin-stimulated aquaporin-2 insertion, producing polyuria, polydipsia, and dilute urine with a rising serum sodium. Amiloride (blocks ENaC entry) is the preferred agent; thiazides also work but raise lithium levels.
• Hypothyroidism and goiter: lithium blocks thyroid hormone release; check TSH periodically and treat with levothyroxine rather than stopping lithium.
• Hyperparathyroidism with hypercalcemia: lithium raises the calcium set-point of the parathyroid calcium-sensing receptor.
• Neurologic: fine resting tremor at therapeutic levels (propranolol helps); coarse tremor, ataxia, dysarthria, myoclonus, confusion, seizures signal toxicity. Chronic use may cause tubulointerstitial nephropathy.
• Precipitants of toxicity: volume depletion, thiazides, NSAIDs, ACE inhibitors/ARBs, and declining GFR all reduce lithium clearance.
• No antidote exists: management is IV isotonic fluids and stopping the drug; the EXTRIP workgroup recommends hemodialysis for very high levels or impaired consciousness, seizures, or life-threatening dysrhythmias.

Valproate — FDA boxed warnings for hepatotoxicity, pancreatitis, and teratogenicity

• Hyperammonemic encephalopathy: inhibition of carbamoyl phosphate synthetase I plus carnitine depletion; ammonia can rise with normal LFTs. Levocarnitine is the reversal agent.
• Other: dose-related thrombocytopenia and platelet dysfunction, weight gain, alopecia, tremor, PCOS. Enzyme inhibition raises lamotrigine levels.
• Pregnancy: neural tube defects and reduced childhood IQ; ACOG and FDA labeling advise avoiding valproate in pregnancy and in persons who may become pregnant when alternatives exist.

Lamotrigine and carbamazepine

• Lamotrigine: Stevens-Johnson syndrome/TEN — risk driven by rapid titration; also DRESS and hemophagocytic lymphohistiocytosis. Any rash mandates immediate discontinuation.
• Carbamazepine: agranulocytosis/aplastic anemia, SIADH with hyponatremia, SJS/TEN (HLA-B*1502 in Asian ancestry), and potent CYP3A4 induction with autoinduction — failing oral contraceptives is the classic consequence.
• Topiramate: carbonic anhydrase inhibition → calcium phosphate stones, metabolic acidosis, oligohidrosis; also word-finding difficulty, weight loss, and acute angle-closure glaucoma.

• Lithium plus a new thiazide or NSAID: the stem shows tremor, vomiting, ataxia, and confusion days after adding hydrochlorothiazide, ibuprofen, or an ACE inhibitor. Reduced renal clearance is the mechanism; the single best next step is stopping lithium and giving isotonic saline, not giving an "antidote" — none exists.
• Polyuria on lithium is nephrogenic DI, not SIADH: expect dilute urine that fails to concentrate after desmopressin, with a normal-to-high serum sodium. Amiloride is the drug of choice. The classic distractor is carbamazepine, which does the opposite — SIADH with hyponatremia.
• Ebstein anomaly: first-trimester lithium exposure and atrialized right ventricle with apically displaced tricuspid leaflets. Absolute risk is low, so the exam answer is usually a fetal echocardiogram and shared decision-making, not automatic discontinuation.
• Lithium uniquely reduces suicide risk in bipolar disorder — the one association examiners repeatedly test when choosing among mood stabilizers for a patient with prior attempts.
• **Lamotrigine is the bipolar depression agent** and requires slow titration to limit Stevens-Johnson syndrome. Any spreading rash, mucosal involvement, or fever means stop the drug immediately and do not rechallenge.
• Valproate inhibits lamotrigine metabolism: when the two are combined, the lamotrigine starting dose and titration rate must be halved. This drug–drug pair is a favorite stem.
• Valproate's boxed triad: hepatotoxicity, pancreatitis, and teratogenicity (neural tube defects, lower childhood IQ). ACOG and FDA labeling favor avoiding it in pregnancy or in patients who may become pregnant. Lethargy plus asterixis with normal LFTs points to hyperammonemic encephalopathy — check ammonia and give levocarnitine.
• Check the level correctly: lithium is a 12-hour trough at steady state. A level drawn a few hours after a dose looks falsely "toxic" and is a common trap.
• Carbamazepine induces CYP3A4 — contraceptive failure and falling levels of coadministered drugs; obtain a CBC for agranulocytosis and screen HLA-B*1502 in patients of Asian ancestry per FDA labeling.