Can a common antihistamine boost multiple sclerosis treatment?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Male or female participants aged 18 to 65 years, inclusive. 2. Diagnosis of multiple sclerosis (MS) according to the 2024 revised McDonald diagnostic criteria. 3. Women of childbearing potential must have a negative pregnancy test and agree to use effective contraception during the study. 4. Participants must be able to understand the study requirements and provide written informed consent. If applicable, informed consent may be provided by the participant's legally authorized representative. Exclusion Criteria: 1. Use of drugs that may interact with terfenadine through CYP3A4 inhibition, including certain azole antifungal agents or macrolide antibiotics. 2. Congenital long QT syndrome, atrioventricular block, abnormal baseline QTc interval (\>450 ms in males or \>470 ms in females), hypokalemia or hypomagnesemia, or concomitant use of drugs known to prolong the QT interval. 3. Significant hepatic dysfunction. 4. Active or clinically significant infection. 5. Secondary demyelinating diseases of the central nervous system. 6. Vascular, genetic, metabolic, neoplastic, toxic, or other diseases that may cause central nervous system demyelination or neurological symptoms that could interfere with study assessments. 7. Myocardial infarction, unstable ischemic heart disease, stroke, or New York Heart Association (NYHA) class IV heart failure within 12 weeks before screening. 8. Pregnancy, breastfeeding, or plans to become pregnant during the study period. 9. Inability or unwillingness to comply with the study follow-up schedule or study procedures. 10. Contraindication to lumbar puncture. 11. Inability or unwillingness to undergo the required magnetic resonance imaging (MRI) examinations. 12. Participation in another clinical trial within 3 months before screening.