Study of BP-SCIG 20% in Patients With Primary Immunodeficiency (PID)

Inclusion Criteria: * a signed informed written consent of the patient/patient's parents or legally authorised representative to take part in the study; * children from 0 to 18 years of age, of both sexes; or adult patients: males and females older than 18 years; * a diagnosis of primary immunodeficiency with impaired antibody production document-supported according to the ESID criteria, requiring replacement therapy with immunoglobulins; * patients with a body weight of no less than 9.1 kg; * patients who received replacement therapy with intravenous immunoglobulin (IVIG) products at intervals from 21 to 28 days at the dose of 0.4-0.8 g/kg, for at least 4 months prior to the start of the study and have total serum IgG levels ≥5 g/L\*, which is confirmed by the results of no less than 2 measurements performed immediately before the scheduled IVIG administration after signing the ICF, or patients who received replacement therapy with subcutaneous immunoglobulin (SCIG) products at the dose of 0.4-0.8 g/kg per month, for at least 4 months prior to the start of the study, and have total serum IgG levels ≥5 g/L\*, based on the results of no less than 2 measurements performed immediately before the scheduled SCIG administration after signing the ICF; or patients with a newly established diagnosis of PID who have not yet received replacement therapy with IgG products (treatment-naïve patients) and have a serum IgG level ≤ 4 g/L; * absence of episodes of serious bacterial infections (bacteraemia or sepsis, bacterial meningitis, osteomyelitis/septic arthritis, bacterial pneumonia, visceral abscess) while taking the previous medicinal product and absence of episodes of hospitalisation for at least 3 months prior to inclusion in the study and during the screening period (prior to the first administration of the IMP BP-SCIG 20%); * a negative pregnancy test (in female patients with childbearing potential); readiness to use reliable methods of contraception throughout the study period; * patient's ability, in the Investigator's judgement, to comply with all the requirements of the study protocol. Exclusion Criteria: * at the request of the patient/patient's parents/patient's legally authorised representative at any time and for any reason; * patient developing serious and/or unexpected AEs/ARs during the study, which require discontinuation of the product; * blood transfusions or transfusions of blood components and products, with the exception of the IMP; * the need to use medicinal products disallowed as part of this study; * systematic lack of patient compliance with the treatment regimen prescribed by the Investigator; * systematic lack of patient compliance with the procedures specified in this protocol; * exclusion based on screening results, including emergence of episodes of serious bacterial infections while receiving a previous IV immunoglobulin product and episodes of hospitalisation during the screening period (before the first administration of the IMP BP-SCIG 20%). * Receiving the IMP BP-SCIG 20% for less than 4 months; * Presence of episodes of serious bacterial infections (bacteraemia or sepsis, bacterial meningitis, osteomyelitis/septic arthritis, bacterial pneumonia, visceral abscess) at the time of investigation of PK parameters.