How do I dose lamotrigine (anticonvulsant medication) in patients using birth control (hormonal contraception)?

Dosing Lamotrigine with Birth Control

When lamotrigine is used with combined hormonal contraceptives (CHCs), the lamotrigine dose will likely need to be increased by approximately 50-100% due to significant reduction in lamotrigine plasma levels caused by CHCs. 1, 2

Key Interactions Between Lamotrigine and Contraceptives

Combined Hormonal Contraceptives (CHCs)

• CHCs significantly reduce lamotrigine plasma levels by >50%, requiring dose adjustments 2
• The U.S. Medical Eligibility Criteria for Contraceptive Use classifies this interaction as Category 3 (risks generally outweigh benefits) 1
• Pharmacokinetic studies show lamotrigine levels decrease significantly during CHC use, potentially leading to increased seizure activity 1
• This interaction occurs only with lamotrigine monotherapy; combinations with non-enzyme-inducing antiepileptics (like sodium valproate) may not have the same interaction 1

Progestin-Only Contraceptives

• Progestin-only pills (POPs), depot medroxyprogesterone acetate (DMPA), and implants do not significantly interact with lamotrigine 1
• These methods are classified as Category 1 (no restrictions) for use with lamotrigine 1
• No drug interactions have been reported between lamotrigine and progestin-only contraceptives 1

Intrauterine Devices (IUDs)

• Both copper IUDs and levonorgestrel IUDs are classified as Category 1 (no restrictions) for use with lamotrigine 1
• These methods do not interact with lamotrigine and can be used without dose adjustments 1

Practical Dosing Algorithm

1. For patients starting lamotrigine while already on CHCs:

   • Begin with standard lamotrigine titration schedule
   • Monitor lamotrigine levels after reaching maintenance dose
   • Expect to require higher maintenance doses (50-100% higher) than standard 2
   • Consider therapeutic drug monitoring to guide dose adjustments

2. For patients adding CHCs to existing lamotrigine therapy:

   • Measure baseline lamotrigine level before starting CHC
   • Monitor for breakthrough seizures or mood symptoms after starting CHC
   • Increase lamotrigine dose by approximately 50-100% based on clinical response and levels 2
   • Re-check lamotrigine levels 2-4 weeks after starting CHC

3. For patients discontinuing CHCs while on lamotrigine:

   • Reduce lamotrigine dose by approximately 50% when stopping CHC 2
   • Monitor closely for signs of lamotrigine toxicity (dizziness, diplopia, ataxia, rash)
   • Check lamotrigine levels 2-4 weeks after stopping CHC
   • Be particularly vigilant during the first 1-2 weeks after CHC discontinuation, as this is when the most dramatic increases in lamotrigine levels occur 3

Important Monitoring and Safety Considerations

• Therapeutic drug monitoring is advisable when initiating or withdrawing CHCs in women on lamotrigine therapy 2
• The most dramatic increase in lamotrigine levels occurs within the first 1-2 weeks after stopping CHCs 3
• Watch for signs of lamotrigine toxicity when stopping CHCs: headache, dizziness, diplopia, ataxia, nausea, and rash 4
• Serious rash, including Stevens-Johnson syndrome, is a rare but serious concern with lamotrigine, especially with rapid dose escalation 4

Alternative Contraceptive Options

• For women requiring lamotrigine, consider these contraceptive alternatives:
  • Copper IUD (Category 1) - no interactions with lamotrigine 1
  • Levonorgestrel IUD (Category 1) - no interactions with lamotrigine 1
  • Progestin-only pills (Category 1) - no significant interactions 1
  • DMPA injections (Category 1) - no significant interactions 1
  • Implants (Category 1) - no significant interactions 1

These non-CHC methods avoid the complex dosing adjustments and potential seizure breakthrough or mood destabilization that can occur with CHC-lamotrigine interactions 1.