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2. 1. Evaluate the NADIR saturation of CD49d in patients receiving NTZ_EID of 300mg/6weeks.
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4. 2. Study its effectiveness and calculate the cost cutting related to EID.
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With a standard dose(SD) of 300mg/4weeks of Natalizumab(NTZ), almost complete saturation(>80%) of alpha4 integrin(CD49d) receptor in the CD4+T lymphocytes is obtained. It is known that NTZ in extended interval dose(EID) is effective and is considered a strategy that can decrease the incidence of Progressive Multifocal Leukoencephalopathy(PML).

The appropriate interval dose is not known, it is important to find markers to individualize the treatment.

EID reduce the costs of the treatment, decreases side effects and improves the quality of life of the patient.

Descriptive and prospective study of patients who after at least 13 administrations of NTZ_SD moved to EID/6weeks. Clinical and radiological parameters: annual rate of relapse(ARR), Disability Scale(EDSS), gadolinium enhancing T1Gd(+) and new T2 lesions in brain MRI. The NADIR_saturation of CD49d was measured by multiparametric quantitative flow cytometry in peripheral blood lymphocytes. Cost cutting was calculated by reduction of drug dose. The protocol was approved by the pharmaco-therapeutic Committee of the Hospital. All patients signed the informed consent.

21 patients; 61.9% women; mean age 43.48±9.92 years; duration of MS 14.67±8.5 years. Under treatment with NTZ_DS: EDSS 4.15±1.39; ARR previous year 1.76±0.83; brain MRI T1Gd(+)(47.6%) and >9 T2_lesions(90.5%). Duration of NTZ_SD 41.33±29.05 and NTZ_ EID 34.24±20.33 months.

During the treatment periods NTZ_SD and NTZ_ EID respectively: 20/21(95%) of the patients remained free of relapse(p=0.82); ARR 0.0095±0,044 and 0,024±0.11(p=0.65); EDSS 3.45±1.72 and 3.57±1.84(p=0.95); 95% and 100% of the patients did not have T1Gd(+) or new T2_lesions.  

NADIR_saturation of CD49d during EID period was 62.03±11.44%(14 patients analyzed).

NTZ_EID/6weeks reduce 4.3 NTZ administration/year.

A lower level of CD49d_saturation is obtained with NTZ_EID/6weeks and does not compromise its effectiveness. NTZ_EID/6weeks reduce significantly the cost related to treatment.