What is the interaction between hormonal birth control and lamotrigine?

Interaction Between Hormonal Birth Control and Lamotrigine

Hormonal contraceptives containing estrogen significantly reduce lamotrigine serum concentrations by approximately 40-60%, which may lead to breakthrough seizures, while progestin-only contraceptives do not affect lamotrigine levels. 1

Key Interactions by Contraceptive Type

Combined Hormonal Contraceptives (containing ethinyl estradiol)

• Ethinyl estradiol induces glucuronidation enzymes that metabolize lamotrigine 2
• Results in 40-60% decrease in lamotrigine serum concentration 3
• Classified as Category 3 (risks generally outweigh benefits) for women taking lamotrigine 1
• Clinical consequences:
  • Breakthrough seizures or increased seizure frequency when starting combined hormonal contraceptives 3
  • Risk of lamotrigine toxicity (adverse effects) when stopping combined hormonal contraceptives 3

Progestin-Only Contraceptives

• No significant drug interactions reported between progestin-only contraceptives and lamotrigine 1, 2
• Classified as Category 1 (no restrictions) for all progestin-only methods: 1
  • Progestin-only pills (POPs)
  • Depot medroxyprogesterone acetate (DMPA) injections
  • Implants

Management Algorithm

1. For women starting lamotrigine who need contraception:

   • Recommend progestin-only methods (DMPA injection, implant, or progestin-only pill) 1
   • Avoid combined hormonal contraceptives containing ethinyl estradiol 1

2. For women already on lamotrigine who want to start hormonal contraception:

   • First choice: Progestin-only methods (DMPA, implant, or progestin-only pill) 1
   • If combined hormonal contraceptives must be used:
     • Monitor lamotrigine levels before and after starting contraception
     • Anticipate need to increase lamotrigine dose by approximately 50-100% 3
     • Schedule more frequent follow-up to assess seizure control

3. For women already on combined hormonal contraceptives who need to start lamotrigine:

   • Consider switching to progestin-only method before starting lamotrigine 4
   • If continuing combined hormonal contraceptive:
     • Initial lamotrigine dose may need to be higher than standard
     • Monitor levels closely during hormone-free week (pill-free interval) when lamotrigine levels may rise

4. For women using both lamotrigine and combined hormonal contraceptives:

   • Monitor for:
     • Breakthrough seizures during active hormone weeks
     • Signs of lamotrigine toxicity (dizziness, diplopia, ataxia, rash) during hormone-free weeks
   • Consider maintaining continuous hormonal contraception (skipping hormone-free weeks) to avoid fluctuations in lamotrigine levels

Important Caveats and Pitfalls

1. Hormone-free week concerns:

   • Lamotrigine levels may rise during the hormone-free week of combined hormonal contraceptives
   • This fluctuation can lead to toxicity symptoms during the hormone-free week
   • Consider continuous hormonal contraception to avoid these fluctuations

2. Contraceptive failure risk:

   • Lamotrigine does NOT reduce contraceptive efficacy 1, 5
   • Unlike enzyme-inducing antiepileptic drugs (carbamazepine, phenytoin, phenobarbital), lamotrigine does not compromise contraceptive effectiveness

3. Hormone replacement therapy (HRT):

   • Similar to combined hormonal contraceptives, estrogen-containing HRT may reduce lamotrigine concentrations 6
   • Monitor lamotrigine levels when starting or stopping HRT

4. Monitoring recommendations:

   • Measure lamotrigine serum concentrations:
     • Before starting hormonal contraception
     • 2-3 weeks after starting hormonal contraception
     • After any change in hormonal contraception regimen
   • Adjust lamotrigine dose based on serum concentrations and clinical response

By understanding these interactions and following appropriate management strategies, clinicians can help women maintain both seizure control and effective contraception.