What is the recommended dose of lamotrigine for a patient taking birth control (hormonal contraception)?

Lamotrigine Dosing for Patients on Hormonal Contraception

When a patient is taking hormonal contraception, lamotrigine dosage should be increased by 50-100% compared to standard dosing due to significant reduction in lamotrigine plasma levels caused by combined hormonal contraceptives. 1

Key Interactions

• Combined hormonal contraceptives (CHCs) reduce lamotrigine plasma levels by >50%, potentially compromising seizure control or mood stabilization 1, 2
• This interaction occurs through increased glucuronidation of lamotrigine, as evidenced by higher lamotrigine-2-N-glucuronide/lamotrigine ratios in women taking CHCs 3
• The U.S. Medical Eligibility Criteria for Contraceptive Use classifies this interaction as clinically significant 4, 1
• Monitoring lamotrigine plasma levels is strongly advised when initiating or discontinuing CHCs 2

Specific Dosing Recommendations

For Patients Using Combined Hormonal Contraceptives:

• Increase lamotrigine dose by 50-100% from baseline when starting CHCs 1
• Monitor lamotrigine levels closely during the first few weeks of co-administration 2
• Be aware that the dose/concentration ratio is approximately 56% higher in women taking CHCs compared to those not on hormonal contraception 3
• Adjust dosing based on clinical response and serum levels 1

For Patients Using Progestin-Only Methods:

• No dosage adjustment is needed for lamotrigine when using:
  • Progestin-only pills (POPs) 4
  • Depot medroxyprogesterone acetate (DMPA) 4
  • Contraceptive implants 4
  • Levonorgestrel IUDs 1

Contraceptive Options for Patients on Lamotrigine

• Preferred options (Category 1 - no restrictions):

  • Progestin-only pills 4
  • DMPA injections 4
  • Contraceptive implants 4
  • Copper or hormonal IUDs 1

• Less ideal options (Category 3 - risks generally outweigh benefits):

  • Combined hormonal contraceptives (pills, patches, rings) due to complex dosing requirements and risk of breakthrough seizures 1

Important Monitoring Considerations

• When starting or stopping CHCs in a patient on lamotrigine:

  • Monitor lamotrigine plasma levels before and after the change 2
  • Watch for signs of toxicity when stopping CHCs (as lamotrigine levels may rise) 1
  • Monitor for breakthrough seizures or mood destabilization when starting CHCs (as lamotrigine levels may fall) 1

• Intermenstrual bleeding may occur in approximately 32% of women during co-administration of lamotrigine and CHCs 5

Clinical Pearls

• This interaction is specific to lamotrigine monotherapy; combinations with valproate may have different interaction profiles 1, 6
• Lamotrigine does not significantly affect the contraceptive efficacy of CHCs, though a modest decrease in levonorgestrel concentrations has been observed 5
• Contraceptive intrauterine devices containing levonorgestrel do not appear to interact with lamotrigine 3
• Consider non-hormonal or progestin-only contraceptive methods to avoid complex dosing adjustments 1