Etrasimod is a sphingosine-1-phosphate (S1P) receptor modulator indicated for the treatment of moderately to severely active ulcerative colitis (UC) in adults. The drug exerts its therapeutic effect by reversibly blocking the migration of lymphocytes from lymphoid tissues to the periphery, thereby reducing the number of lymphocytes in peripheral blood.

What Are the Side Effects of Etrasimod?

Common Side Effects

Headache (9%-27%).

Increased liver enzymes (5%-6%).

Dizziness (5%).

Nausea (3%-4%).

Arthralgia (4%).

Hypertension (3%).

Urinary tract infection (3%).

Serious Side Effects of Etrasimod That Require Vigilance

Infection Risk

It can cause lymphopenia (lymphocyte count decreases to an average of 45% of the baseline level), increasing the risk of bacterial, viral (e.g., herpes virus, varicella-zoster virus), and fungal (e.g., Cryptococcus) infections.

Warning symptoms: Fever, painful urination, neurological symptoms (headache accompanied by neck stiffness).

Management measures: Lymphocyte count should be tested before medication administration; treatment should be delayed in patients with active infections; and therapy should be discontinued in cases of severe infections.

Cardiovascular Events

Bradycardia: A decrease in heart rate (average reduction of 7.2 beats per minute) may occur after the first dose, which may be accompanied by atrioventricular (AV) conduction delay.

Contraindicated populations: Patients who have had a myocardial infarction, stroke, or New York Heart Association (NYHA) Class III/IV heart failure within 6 months, or those with Mobitz type II/third-degree atrioventricular block.

Hepatic Toxicity

4.5% of patients experience alanine transaminase (ALT) levels ≥ 3 times the upper limit of normal (ULN).

Monitoring requirements: Liver enzymes should be tested before medication use and when symptoms such as nausea or jaundice occur.

Macular Edema

This is a class effect of S1P receptor modulators; fundus examinations should be performed regularly before and during treatment.

Symptoms: Blurred central vision, abnormal color perception.

Other Serious Risks

Progressive multifocal leukoencephalopathy (PML): Rare but potentially fatal.

Posterior reversible encephalopathy syndrome (PRES): Manifested by sudden headache, confusion, and seizures.

Cutaneous malignancies: Regular skin examinations are required before and during medication use.

Precautions for Taking Etrasimod

Contraindicated Populations

Patients with severe hepatic impairment (Child-Pugh Class C).

Pregnant women (may cause fetal malformations).

Poor metabolizers of CYP2C9 who are concurrently using strong CYP2C8/CYP3A4 inhibitors.

Management of Special Populations

Pregnant women: Effective contraception should be used during medication administration and for 1 week after drug discontinuation; treatment should be stopped immediately if pregnancy is detected.

Lactating women: Breastfeeding should be avoided.

Elderly patients: No dosage adjustment is required, but enhanced monitoring is necessary.

Drug Interactions

Contraindicated combinations: Rifampicin (a strong inducer), fluconazole (a dual inhibitor).

Combinations requiring caution: Beta-blockers, antiarrhythmic drugs (increase the risk of bradycardia).

Vaccination

Live vaccines should be administered 4 weeks before starting Etrasimod treatment.

Live vaccines should be avoided during treatment and for 5 weeks after discontinuing Etrasimod.