Lithium Dosing Calculator

The Lithium Dosing Calculator provides individualized lithium carbonate dosing estimates based on patient parameters including body weight, age, renal function, and target serum level. Lithium remains the gold standard mood stabilizer for bipolar disorder, with over 70 years of clinical use and the strongest evidence base for preventing both manic and depressive episodes, reducing suicide risk, and providing long-term neuroprotection.

Lithium is a monovalent cation that is handled by the kidneys similarly to sodium. Approximately 95% of lithium is eliminated renally, with clearance approximately 20-25% of creatinine clearance. This strong relationship between renal function and lithium elimination makes creatinine clearance the most important pharmacokinetic determinant of lithium dosing. Age-related decline in renal function is the primary reason elderly patients require substantially lower doses.

The therapeutic range for lithium varies by clinical context. For acute mania, target trough levels of 0.8-1.2 mEq/L are recommended to achieve antimanic efficacy. For maintenance therapy, lower levels of 0.6-0.8 mEq/L provide adequate prophylaxis with reduced side effect burden. Some experts recommend even lower maintenance targets (0.4-0.6 mEq/L) in elderly patients or those with renal concerns, though efficacy at these lower levels is less well established.

Lithium has a narrow therapeutic index, with toxicity occurring at levels only modestly above the therapeutic range. Mild toxicity (tremor, nausea, diarrhea) may occur at 1.5-2.0 mEq/L. Moderate toxicity (confusion, ataxia, coarse tremor) at 2.0-2.5 mEq/L. Severe toxicity (seizures, coma, cardiac arrhythmias, renal failure) at >2.5 mEq/L. Chronic lithium toxicity can occur at lower levels than acute toxicity due to tissue accumulation.

Dosing typically begins at 600-900 mg/day for adults, divided into BID or TID doses for immediate-release formulations. Extended-release formulations (Lithobid) can often be given once daily at bedtime, which may improve adherence and reduce peak-related side effects while maintaining therapeutic trough levels. Initial levels are checked 5-7 days after starting (steady state), drawn 12 hours after the last dose.

Several factors affect lithium levels beyond dose and renal function. Dehydration, sodium depletion, NSAIDs, ACE inhibitors, and thiazide diuretics can significantly increase lithium levels. Theophylline, caffeine, and sodium loading decrease levels. Patients must maintain adequate hydration and consistent sodium intake. Any medication changes, dietary shifts, or illness affecting fluid status should prompt level rechecking.

Long-term lithium use requires monitoring of renal function (creatinine and eGFR every 6-12 months), thyroid function (TSH every 6-12 months, as lithium causes hypothyroidism in 20-30% of patients), parathyroid function (calcium annually, as lithium can cause hyperparathyroidism), and serum lithium levels (every 3-6 months when stable).

This calculator provides pharmacokinetically informed dosing estimates to guide initial lithium prescribing and dose adjustments.