Does elagolix interact with lamotrigine?

Does Elagolix Interact with Lamotrigine?

No clinically significant pharmacokinetic interaction between elagolix and lamotrigine has been documented in the available evidence. The FDA drug label for elagolix does not list lamotrigine among drugs with known interactions, and no formal drug interaction studies between these two agents have been reported 1.

Key Evidence Analysis

Elagolix Metabolism and Drug Interaction Profile

Elagolix is primarily metabolized by CYP3A4 (major pathway), with minor contributions from CYP2D6, CYP2C8, and UGT enzymes 1. The drug also involves hepatic uptake via the OATP1B1 transporter 1.

From the FDA drug interaction studies, elagolix demonstrates:

• Moderate CYP3A4 induction: Elagolix 300 mg twice daily reduced midazolam (a CYP3A4 substrate) exposure by 54% for Cmax and 54% for AUC 1
• P-glycoprotein inhibition: Increased digoxin exposure by 71% (Cmax) and 26% (AUC) 1
• No effect on UGT substrates: No clinically significant changes in bupropion exposure were observed 1

Lamotrigine Metabolism

Lamotrigine is primarily metabolized by UGT glucuronidation (not CYP enzymes), making it less susceptible to CYP3A4-mediated interactions 2, 3, 4. The guidelines consistently note that lamotrigine interacts with drugs that affect glucuronidation pathways, particularly:

• Combined oral contraceptives (COCs): Significantly decrease lamotrigine levels by inducing glucuronidation 2
• Enzyme-inducing anticonvulsants: May affect lamotrigine metabolism
• Valproate: Inhibits lamotrigine metabolism, increasing levels

Why No Interaction is Expected

1. Different metabolic pathways: Elagolix (primarily CYP3A4) and lamotrigine (primarily UGT) utilize distinct elimination routes
2. Elagolix does not induce UGT significantly: The FDA label shows no clinically significant effect on bupropion (a UGT substrate) 1
3. No documented cases: Despite elagolix being on the market since 2018 for endometriosis and uterine fibroids 5, 6, no interaction reports with lamotrigine exist

Clinical Recommendations

• No dose adjustment of either drug is required when co-administering elagolix and lamotrigine
• Routine therapeutic drug monitoring of lamotrigine is not necessary solely based on elagolix co-administration
• Monitor for seizure control as standard practice in patients taking lamotrigine, regardless of elagolix use

Important Caveats

Watch for hormonal add-back therapy interactions: If elagolix is prescribed with estradiol/norethindrone acetate (E2/NETA) for add-back therapy 7, 8, be aware that:

• The ethinyl estradiol component in combined hormonal contraceptives significantly reduces lamotrigine levels by 25-40% through UGT induction 2
• However, the E2/NETA formulation used with elagolix contains estradiol (not ethinyl estradiol), which has less pronounced effects on UGT enzymes
• Still, monitor for potential changes in seizure control when initiating or discontinuing hormonal add-back therapy

Patients with SLCO1B1 polymorphisms: Those with reduced OATP1B1 function (SLCO1B1 521 C/C genotype, <5% of population) have 78% higher elagolix concentrations 1, but this does not alter the interaction profile with lamotrigine.