Ofatumumab is a fully human monoclonal anti-CD20 antibody increasingly used in Nephrotic Syndrome patients with failure or intolerance to Rituximab. Similarly to other antiCD20 antibodies, infusion-related reactions are reported and prevented by systematic premedication. We describe our infusion protocole based on a higher concentration of ofatumumab than previously reported (in 500ml versus 1000ml of saline serum) and its tolerance.

Material and methods:

We retrospectively analysed 63 ofatumumab infusions in 21 patients. Median age at diagnosis was 3,2 years and at treatment 9 years. All patients had previously received rituximab, with failure to obtain B cell depletion in 13 patients. Patients with Steroid and multidrug Dependant NS (n=16) received a 750mg/1.73m² infusion, that could be repeated after B cell recovery. Patients with Multi-Drug Resistant NS (n=5) received a first infusion of 300mg/1.73m² followed by 5 weekly infusions of 2000mg/1.73m². Ofatumumab was diluted in 500 ml of normal saline and infused, after systematic premedication by paracetamol, methylprednisolone and dexchlorphéniramine,at constant rates from 3 to 200ml/h at first dose and 12 to 200 ml/h at others. 

Results:

 B cell depletion was obtained in all patients after first ofatumumab infusion. Mean dilution concentration was 1.0g/l (min-max 0.7-1,8g/l) for 750 mg/1.73m²infusions and 3g/l (1.8-4)for 2000mg/1.73m²infusions. No serious infusion reaction was recorded. Minor reactions were recorded in 13 of the 63 infusions (21%), respectively 9/31 “750 mg/1.73m²”infusions, 3/5 “300 mg/1.73m²”infusions, none of the weekly 2000mg/1.73m²and 1 reinfusion of 2000mg/1.73m² after B cell repletion. Symptoms were itchy throat (n=7), skin rash or pruritis n=4), abdominal pain and nausea (n=3), thoracic oppression (n=1).

Conclusions:

 Ofatumumab can be safely diluted in 500ml of normal saline, which is an interesting condition in small children or patients with multiresistant nephrotic syndrome and salt restriction.