Can I initiate lithium 400 mg at bedtime without prior assessment and baseline investigations?

No—Lithium 400 mg at Bedtime Cannot Be Started Without Mandatory Baseline Investigations

You must obtain baseline laboratory studies before initiating lithium therapy, as lithium toxicity is closely related to serum levels and can occur at doses close to therapeutic levels, and facilities for prompt and accurate serum lithium determinations must be available before starting treatment. 1

Absolute Contraindications That Must Be Ruled Out First

Before prescribing any dose of lithium, you must exclude the following contraindications 1:

• Significant renal disease – Lithium is almost exclusively excreted via the kidney, and renal insufficiency causes considerable reduction in lithium clearance 2
• Significant cardiovascular disease
• Severe debilitation or dehydration
• Sodium depletion
• Current diuretic use – The risk of lithium toxicity is very high in patients receiving diuretics 1

If any of these conditions are present, lithium should generally not be given unless the psychiatric indication is life-threatening and the patient has failed other measures—in which case hospitalization with daily serum lithium determinations is mandatory 1.

Mandatory Baseline Laboratory Assessment

The American Academy of Child and Adolescent Psychiatry requires the following baseline studies before initiating lithium 3, 4:

• Complete blood count (CBC)
• Thyroid function tests (TSH, free T4)
• Urinalysis
• Blood urea nitrogen (BUN)
• Serum creatinine with estimated glomerular filtration rate (eGFR)
• Serum calcium
• Pregnancy test in females of childbearing potential

Additional baseline metabolic monitoring should include body mass index, waist circumference, blood pressure, fasting glucose, and fasting lipid panel 3.

Why 400 mg Nocte Is Likely Subtherapeutic

A dose of 400 mg once daily at bedtime is on the lower end of typical starting doses and may produce subtherapeutic levels 4:

• Standard initial dosing is typically 12-24 mmol (450-900 mg) per day, depending on age and body weight 2
• For acute mania, target serum lithium levels of 0.8-1.2 mEq/L (some sources cite 1.0-1.5 mEq/L) are typically required 3, 4, 5
• For maintenance therapy, concentrations of 0.6-1.0 mEq/L are generally recommended 4, 5
• A dose of 400 mg once daily may only produce levels of 0.4-0.6 mEq/L, which is below the therapeutic range for acute treatment 4

Timing of Serum Lithium Level Monitoring

Once lithium is initiated (after baseline labs are obtained), serum lithium levels must be monitored appropriately 3, 6:

• For once-daily dosing, serum lithium should be drawn 24 hours after the last dose (not 12 hours), as the 12-hour level will be artificially elevated by approximately 1.3 times compared to the true trough level 6
• During acute treatment, lithium levels should be checked twice per week until both the serum level and clinical condition stabilize 4
• Lithium requires 7-8 days to reach steady-state serum concentrations regardless of dosing schedule 4

Correct Initiation Protocol

The proper algorithm for starting lithium is 3, 4:

1. Obtain all baseline laboratory studies (CBC, thyroid function, renal function, urinalysis, calcium, pregnancy test)
2. Verify absence of contraindications (significant renal/cardiovascular disease, dehydration, diuretic use)
3. Start lithium at appropriate dose based on age, weight, and renal function—typically 450-900 mg/day in divided doses or once daily
4. Check serum lithium level after 5-7 days at steady state (24 hours post-dose for once-daily regimen)
5. Adjust dose to achieve target therapeutic range (0.8-1.2 mEq/L for acute mania, 0.6-1.0 mEq/L for maintenance)
6. Monitor levels twice weekly during acute phase until stable
7. Transition to maintenance monitoring every 3-6 months once stable 3, 4

Common Pitfalls to Avoid

• Never start lithium without baseline renal function tests—renal insufficiency is a contraindication and dramatically increases toxicity risk 1, 2
• Never assume 400 mg will be therapeutic—this dose is likely subtherapeutic for acute treatment and requires level-guided titration 4, 5
• Never draw lithium levels at 12 hours for once-daily dosing—this will overestimate the true trough level by 30% and lead to underdosing 6
• Never delay baseline labs "to get started quickly"—lithium toxicity can occur at doses close to therapeutic levels, and you must have monitoring capabilities in place before the first dose 1