In a patient with hyponatremia (serum sodium 134 mEq/L) and a lithium serum level of 0.2 mEq/L, can the lithium dose be increased from 150 mg nightly to 300 mg nightly?

Yes, lithium can be increased from 150 mg to 300 mg nightly in this patient

The sodium level of 134 mEq/L represents only mild hyponatremia and does not constitute an absolute contraindication to lithium dose escalation, especially given the subtherapeutic lithium level of 0.2 mEq/L. However, this requires careful monitoring and attention to the underlying cause of hyponatremia.

Clinical Reasoning

Current Clinical Status

• Lithium level of 0.2 mEq/L is far below the therapeutic range of 0.6-1.2 mEq/L needed for maintenance therapy 1
• The sodium of 134 mEq/L is technically hyponatremia (defined as <135 mEq/L) but represents mild, likely asymptomatic hyponatremia
• At 150 mg nightly, the patient is receiving an extremely low dose that is unlikely to achieve therapeutic benefit

Why Dose Increase is Reasonable

Lithium and hyponatremia have a paradoxical relationship. The FDA label states lithium should "generally not be given" to patients with sodium depletion 1, but this warning primarily applies to severe hyponatremia or conditions causing ongoing sodium loss. Recent evidence actually shows that ongoing lithium therapy is associated with reduced risk of severe hyponatremia (adjusted OR 0.52) 2, likely due to lithium's tendency to cause nephrogenic diabetes insipidus, which opposes water retention.

The current lithium level of 0.2 mEq/L indicates the patient is receiving inadequate treatment for their psychiatric condition. Doubling to 300 mg nightly is a conservative dose escalation that will still keep the patient well below typical maintenance doses of 900-1200 mg daily 1.

Critical Monitoring Requirements

Before Increasing Dose

• Determine the cause of hyponatremia: Is this SIADH, volume depletion, or medication-related?
• Check volume status clinically (orthostatic vitals, mucous membranes, skin turgor)
• Review all medications for drugs that can cause hyponatremia (SSRIs, carbamazepine, diuretics)
• Obtain baseline creatinine to assess renal function

After Dose Increase

• Check serum sodium and lithium levels in 5-7 days after the dose increase
• Monitor for symptoms of either lithium toxicity (tremor, confusion, ataxia) or worsening hyponatremia (nausea, confusion, headache)
• Once stable, continue lithium level monitoring every 1-2 weeks until therapeutic range achieved 1
• Sodium should be rechecked if any clinical changes occur

Important Caveats

The sodium level of 134 mEq/L requires investigation regardless of lithium dosing. If the patient has:

• SIADH: Lithium may actually be beneficial as it has been used to treat SIADH 3, 4, though this is not first-line
• Volume depletion: This would be more concerning and requires correction with fluids and sodium replacement before aggressive lithium escalation
• Diuretic use: This significantly increases lithium toxicity risk and represents a relative contraindication 1

Do not continue escalating lithium if sodium drops below 130 mEq/L without first correcting the hyponatremia and identifying its cause. At that threshold, the hyponatremia itself becomes the priority 3.

Target Approach

1. Increase lithium to 300 mg nightly now
2. Address underlying cause of mild hyponatremia (adequate salt/protein intake, review medications)
3. Recheck sodium and lithium in 5-7 days
4. Continue gradual lithium titration toward therapeutic range (0.6-0.8 mEq/L) with parallel sodium monitoring
5. If sodium trends downward, pause lithium escalation and treat hyponatremia first

The key is that mild hyponatremia (134 mEq/L) with a grossly subtherapeutic lithium level favors cautious dose escalation with close monitoring, rather than withholding effective psychiatric treatment.