Natalizumab (brand name: TYSABRI®) is a recombinant humanized IgG4κ monoclonal antibody. It blocks the migration of immune cells by inhibiting α4-integrin and is used in the treatment of relapsing multiple sclerosis (MS). Based on information from the FDA package insert, this article summarizes key details regarding side effect management and medication use in special populations, providing references for clinical application.

1. Side Effects and Countermeasures

(1) Common Adverse Reactions

Clinical trials show that approximately 35% of patients experience headaches, 24% experience fatigue, and 15% experience joint pain. The incidence of infections is 1 case per patient-year, mainly consisting of upper respiratory tract infections (18%) and urinary tract infections (15%). Mild side effects usually do not require treatment interruption; symptomatic management (such as the use of painkillers and rest) is recommended.

(2) Management of Severe Side Effects

① Hypersensitivity Reactions: The incidence is less than 1%, presenting symptoms such as urticaria, hypotension, and dyspnea, mostly occurring within 2 hours of infusion. Infusion should be stopped immediately, and emergency treatment with antihistamines and glucocorticoids should be administered.

② Immunosuppression Risk: Concurrent use with other immunosuppressants is prohibited, as it may increase the risk of infection. If severe infections such as pneumonia (0.6%) or cholecystitis (0.8%) occur, permanent discontinuation of the drug is necessary.

③ Infusion Reactions: These occur in 22% of patients and can be alleviated by slowing down the infusion rate and administering pre-treatment anti-allergic medications (5).

(3) Laboratory Monitoring

After medication administration, lymphocyte and monocyte counts may increase (reversible within 16 weeks), so regular blood routine tests are required. The incidence of abnormal liver function is 5%, and it is recommended to recheck liver enzymes every 3 months (6).

2. Key Points for Medication Use in Special Populations

(1) Pregnant Women

Animal experiments indicate that high doses of the drug may cause fetal thrombocytopenia (at 7 times the clinical dose), while data in humans is limited. The risks and benefits must be weighed during pregnancy, and drug discontinuation is recommended.

(2) Children and Elderly Patients

The drug is not approved for use in patients under 18 years old due to insufficient safety and efficacy data. There is a lack of adequate research in patients over 65 years old, so individualized evaluation is required.

(3) Patients with Hepatic or Renal Impairment

Pharmacokinetic studies on patients with hepatic or renal impairment have not been conducted, so the drug should be used with caution in this population.

3. Other Precautions

(1) Vaccination

There is no data available on the effect of TYSABRI® on vaccine efficacy or the safety of live vaccines. It is recommended to complete routine immunization before starting treatment with this drug.

(2) Antibody Production

Six percent of patients produce persistent antibodies, which leads to drug ineffectiveness (plasma drug concentration < 1 mcg/mL) and an increased risk of infusion reactions. Such cases need to be identified through serum testing.