Can you start Lamictal (lamotrigine) if the Blood Urea Nitrogen (BUN) level is elevated?

Lamotrigine Initiation with BUN of 20 mg/dL

Yes, you can start Lamictal (lamotrigine) with a BUN level of 20 mg/dL as this value is only at the upper limit of normal range and does not represent a contraindication to lamotrigine therapy.

Understanding BUN in Clinical Context

• A Blood Urea Nitrogen (BUN) level of 20 mg/dL is at the upper limit of the normal range (typically 7-20 mg/dL) and is not considered a significant elevation that would preclude lamotrigine initiation 1
• BUN can be affected by multiple factors including protein intake, hydration status, and medication use, making it a less specific marker for renal function than creatinine or estimated glomerular filtration rate (eGFR) 1
• Mild elevations in BUN are common in many clinical scenarios and do not necessarily indicate significant renal impairment 1

Lamotrigine Pharmacokinetics and Renal Function

• Lamotrigine is primarily metabolized by glucuronidation in the liver, with 43-87% of the dose recovered in urine as glucuronide metabolites 2
• The drug exhibits first-order linear kinetics during long-term administration, with a mean half-life ranging from 22.8 to 37.4 hours in patients on lamotrigine monotherapy 2
• Unlike some medications that require significant dose adjustments for mild renal impairment, lamotrigine does not require dose modification for mild elevations in BUN 2

Dosing and Titration Recommendations

• Lamotrigine should be initiated at a low dose and gradually titrated over a 6-week period to minimize the risk of serious rash 3
• The standard titration schedule for adults with bipolar disorder typically starts at 25 mg daily for 2 weeks, then 50 mg daily for 2 weeks, then 100 mg daily for 1 week, before reaching the target dose of 200 mg daily 3
• Dose adjustments are primarily required when lamotrigine is co-administered with enzyme-inducing drugs (like carbamazepine) or enzyme-inhibiting drugs (like valproate), rather than for mild renal function changes 3, 2

Monitoring Recommendations

• Regular monitoring of renal function is advisable when starting any new medication, especially in patients with borderline renal function 1
• If BUN continues to rise significantly after starting lamotrigine, or if other markers of renal function worsen, reassessment may be warranted 1
• While therapeutic drug monitoring is not routinely required for lamotrigine, a proposed therapeutic range of 1-4 mg/L has been suggested in some studies 2

Safety Considerations

• The most significant safety concern with lamotrigine initiation is the risk of serious rash (including Stevens-Johnson syndrome), which occurs in approximately 0.1% of patients with bipolar disorder 3
• This risk is minimized through appropriate dose titration rather than being related to renal function 3
• Lamotrigine is generally well-tolerated with common side effects including headache, nausea, infection, and insomnia 3
• Unlike many psychotropic medications, lamotrigine does not appear to cause significant weight gain 3, 4

Clinical Efficacy

• Lamotrigine has demonstrated efficacy in delaying mood episodes in bipolar I disorder, with particular benefit in preventing depressive episodes 3, 4
• It has shown some efficacy in the treatment of acute bipolar depression, though findings have been inconsistent 4
• Lamotrigine has not demonstrated efficacy in the treatment of acute mania 3, 4

In conclusion, a BUN level of 20 mg/dL should not prevent the initiation of lamotrigine therapy. The standard titration schedule can be followed with appropriate clinical monitoring.