Lithium

Lithium is a naturally occurring element (the lightest alkali metal) that has been used in psychiatry since 1949, making it one of the oldest medications still in frontline use. Despite decades of research, its precise mechanism of action remains incompletely understood, but several key pathways have been identified ^{[1, 2, 3]}:

1. Inositol depletion: Lithium inhibits the enzyme inositol monophosphatase (IMPase), reducing the recycling of inositol and dampening overactive phosphatidylinositol (PI) signaling in neurons. This is believed to selectively affect hyperactive neural circuits (as seen in mania) while having less effect on normally functioning circuits ^{[1, 2]}.

2. GSK-3 inhibition: Lithium directly inhibits glycogen synthase kinase-3 (GSK-3), a key enzyme involved in cell signaling, gene expression, and neuroplasticity. GSK-3 inhibition promotes neuroprotective and neurotrophic effects, including increased BDNF (brain-derived neurotrophic factor) and gray matter volume ^{[2, 3]}.

3. Neuroprotection: Lithium has demonstrated neuroprotective effects in multiple studies — it increases gray matter volume, promotes neurogenesis, and reduces markers of neurodegeneration. This may explain its unique ability to reduce suicide risk beyond its mood-stabilizing effects ^{[2, 3, 5]}.

4. Neurotransmitter modulation: Lithium modulates serotonin and dopamine neurotransmission, though these effects are complex and not fully characterized ^{[1, 2]}.

Lithium is uniquely effective at preventing both manic and depressive episodes in bipolar disorder and is the only psychiatric medication with robust evidence for reducing suicide risk — a property not shared by anticonvulsant mood stabilizers like valproic acid or lamotrigine ^{[3, 5]}.

Starting lithium requires a structured approach with baseline lab work and regular monitoring ^{[1, 6]}:

Before starting: Your doctor will order baseline labs including kidney function (BUN, creatinine, eGFR), thyroid function (TSH, free T4), electrolytes, calcium, CBC, ECG (if over 40 or cardiac risk), and a pregnancy test for females ^[1].

Week 1-2: Treatment typically starts at 300 mg two or three times daily (or 600 mg at bedtime for some formulations). Common early side effects include nausea, mild tremor, increased thirst, and frequent urination — these often improve over the first few weeks. Taking lithium with food reduces GI side effects ^{[1, 6]}.

Week 2-4: A blood level is drawn approximately 5-7 days after starting (at steady state), measured 12 hours post-dose (trough level). The target range is 0.6-1.2 mEq/L for acute treatment. Dose adjustments are made based on blood levels and clinical response ^[1].

Months 1-3: TSH and kidney function are rechecked. Your doctor will establish a stable dose. Once stabilized, blood levels are typically checked every 3-6 months, along with kidney function and thyroid function every 6-12 months ^{[1, 6]}.

Long-term: Lithium is typically a long-term (often lifelong) medication for bipolar disorder. Abrupt discontinuation significantly increases relapse risk, especially for manic episodes. If discontinuation is needed, it should be tapered very gradually over weeks to months ^{[1, 3]}.

Lithium should be taken with food or milk to reduce GI side effects (nausea, stomach upset) ^[1].

Hydration is critical: Lithium is excreted by the kidneys and competes with sodium for reabsorption. Dehydration is the most common cause of lithium toxicity. Maintain consistent, adequate fluid intake (at least 8-10 glasses of water daily). Be especially careful in hot weather, during exercise, and during illness with vomiting or diarrhea ^{[1, 6]}.

Salt (sodium) intake: Maintain a consistent sodium intake. Both sudden sodium restriction (e.g., starting a low-salt diet) and sudden sodium loading can affect lithium levels. Do not make major changes to salt intake without consulting your doctor ^{[1, 6]}.

Caffeine: Caffeine increases lithium excretion. Consistent moderate caffeine intake is fine, but sudden large changes (starting or stopping heavy coffee consumption) can alter lithium levels. Keep caffeine intake relatively constant ^[1].

Alcohol: Alcohol causes dehydration, which can increase lithium levels. It also impairs judgment and worsens mood instability. Moderate to heavy drinking should be avoided. If drinking occasionally, ensure extra hydration ^[1].

Lithium dosing is guided entirely by serum blood levels, not by a fixed dose ^{[1, 6]}:

Acute Mania [1, 6]: - Starting dose: 300 mg two or three times daily (or 600-900 mg/day in divided doses) - Target serum level: 0.8-1.2 mEq/L - Trough levels drawn 12 hours post-dose, at steady state (5-7 days after initiation or dose change) - Titrate based on levels and clinical response; typical dose range 900-1800 mg/day

Maintenance (Bipolar Disorder) [1, 3]: - Target serum level: 0.6-0.8 mEq/L (some patients benefit from 0.8-1.0 mEq/L) - Lower maintenance levels (0.6-0.8 mEq/L) balance efficacy with tolerability - Typical dose: 600-1200 mg/day

Monitoring schedule [1, 6]: - Lithium levels: weekly during titration; every 3-6 months once stable - Renal function (BUN, creatinine, eGFR): every 6-12 months - Thyroid function (TSH): every 6-12 months - Calcium and PTH: annually - Weight, BMI: every visit

Special populations [1]: - Elderly: Start lower (150-300 mg/day); reduced renal clearance requires lower doses; target levels 0.4-0.8 mEq/L - Renal impairment: Dose must be reduced proportionally; contraindicated in severe renal failure - Children/adolescents: Weight-based dosing; lower doses than adults

Formulations [1]: - Lithium carbonate IR: 150, 300, 600 mg capsules/tablets (dosed 2-3 times daily) - Lithium carbonate ER (Lithobid): 300, 450 mg tablets (dosed 1-2 times daily; less GI upset, smoother levels) - Lithium citrate solution: 300 mg/5 mL (8 mEq/5 mL)

Lithium is one of the most affordable psychiatric medications available ^[1].

Generic lithium carbonate: Approximately $10-$30 per month for a 30-day supply. Available on many $4 generic lists.

Lithobid (extended-release brand): Generic extended-release lithium is also inexpensive — approximately $15-$40/month.

Lithium citrate solution: Slightly more expensive than capsules/tablets; approximately $20-$50/month.

Insurance: Lithium is Tier 1 on essentially all formularies. Copays are minimal.

Monitoring costs: The main ongoing cost with lithium is the required regular blood work (lithium levels, kidney function, thyroid function). These are typically covered by insurance but should be factored into the total cost of lithium therapy — approximately 4-6 blood draws per year once stable.

Cost comparison: Lithium is significantly less expensive than newer mood stabilizers — lamotrigine ($30-$80/month generic), valproic acid ($20-$50/month generic), and especially second-generation antipsychotics used as mood stabilizers (aripiprazole, quetiapine — $200-$800/month brand).

Pregnancy [1, 7]:

Lithium crosses the placenta and is classified as a known human teratogen, though the absolute risk is much lower than historically believed ^[7].

First trimester — Ebstein anomaly risk: Early reports suggested a very high risk of the cardiac malformation Ebstein anomaly. Modern epidemiological data show the absolute risk is approximately 1 in 1,000 exposed pregnancies — a 20-fold increase over the background rate (1 in 20,000) but still a low absolute risk of 0.1% ^[7]. A fetal echocardiogram at 16-20 weeks gestation is recommended for exposed pregnancies ^[7].

Second/third trimester risks: Neonatal complications include floppy infant syndrome, nephrogenic diabetes insipidus, hypothyroidism, cardiac arrhythmias, and rarely, Ebstein anomaly with later exposure. Lithium levels should be monitored frequently during pregnancy (physiological changes in renal clearance alter lithium levels) and the dose may need reduction before delivery to prevent neonatal toxicity ^{[1, 7]}.

Clinical decision: For women with severe bipolar I disorder at high risk of relapse, continuing lithium during pregnancy may be appropriate given the low absolute teratogenic risk, particularly if the alternative is a destabilizing manic or depressive episode. This is an individualized risk-benefit discussion ^{[3, 7]}.

Breastfeeding: Lithium is excreted in breast milk at approximately 50% of maternal serum levels, and infant serum levels can reach 10-50% of maternal levels ^[1]. Breastfeeding on lithium is generally not recommended by most guidelines due to the risk of infant lithium toxicity, dehydration sensitivity, and the need for infant blood monitoring if attempted ^{[1, 7]}.

Lithium has been available as a generic for decades. The original brand names (Eskalith, Lithobid) are no longer marketed as brands in the US ^[1].

Available formulations: - Lithium carbonate immediate-release: 150 mg, 300 mg, 600 mg capsules and tablets (multiple manufacturers) - Lithium carbonate extended-release: 300 mg, 450 mg tablets (generic Lithobid — fewer GI side effects, can be dosed once or twice daily) - Lithium citrate oral solution: 8 mEq/5 mL (equivalent to 300 mg lithium carbonate per 5 mL)

ER vs IR: Extended-release formulations produce lower peak levels and may cause less nausea and tremor. Some clinicians prefer ER for maintenance. However, IR may be preferred when more precise dose adjustments are needed ^[1].

All generic lithium products are therapeutically equivalent. The choice between formulations is based on tolerability, dosing convenience, and clinical preference.