For patients with PIDDs, parenteral immunoglobulin (IG) administration is lifesaving. PIDDs are grouped into 10 categories: immunodeficiencies affecting cellular and humoral immunity; combined immunodeficiencies with associated or syndromic features; predominantly antibody deficiencies; diseases of immune dysregulation; congenital defects of phagocyte number or function or both; defects in intrinsic and innate immunity; autoinflammatory disorders; complement deficiencies; bone marrow failure; and phenocopies of PIDD. These conditions are managed with either IV immunoglobulin (IVIG), conventional SC immunoglobulin (cSCIG), or “facilitated” SC immunoglobulin (fSCIG) replacement therapy. However, there are subtle differences between these IGRT formulations that clinicians need to be aware of.

Recently, a clinician’s guide was published to educate healthcare providers about the differences between these formulations, their advantages and disadvantages, and to assist with initiating, optimizing, and monitor SCIG.

Advantages of SCIG over IVIG include that venous access is not required, administration is less time consuming (although it is more frequent), patients can be trained to self-administer or SCIG can be administered as part of home care services, and SCIG is associated with fewer systemic adverse infusion reactions since smaller doses are administered. SCIG is available as a 16.5% and 20% solution, 20% liquid (cSCIG preparations), and 10% liquid IGRT combined with human recombinant hyaluronidase. The latter is termed fSCIG since the hyaluronidase increases the dispersion and absorption of IGRT by locally heightening the permeability of SC tissue. It does this by the temporary depolymerization of hyaluronan, which is a polysaccharide found in the extracellular matrix of connective tissue, thereby allowing for less frequent treatment intervals compared with cSCIGs with the frequency of administration being similar to IVIG.

A benefit of higher concentration cSCIG formulations is that they are associated with reduced infusion time and smaller volume administration. Larger infusion volumes and higher infusion rates can be administered with fSCIG compared with cSCIG.

The FDA requires an increase of IG dose of about 40% when switching from IVIG to cSCIG for most cSCIG formulations.

Factors to consider when choosing an IGRT formulation include route and site of administration, frequency, dose, administration setting (i.e., infusion center or at home), treatment tolerability, ability to self-inject, and patient preferences and lifestyle.

It is important to counsel patients with agammaglobulinemia who are immunoglobin-naïve (i.e., have previously not been treated with IVIG) that it may take longer and/or they may need more frequent dosing of cSCIG compared with those who switched from IVIG.

Dosing for cSCIG is usually 100 mg/kg to 200 mg/kg weekly, with dosages adjusted based on trough serum IgG levels and clinical response, which can be assessed by the frequency of infections. For patients who are converting from IVIG to SCIG, a strategy to achieve the same IgG tissue level with SCIG is for the total monthly dosage of IVIG to be multiplied by 1.37 for the 16% IgG formulation or by 1.53 for the 20% IgG formulation. Others have suggested a dosage adjustment of 137% when going from IVIG to cSCIG. If area-under-the-curve dosing is used for conversion of SCIG from IVIG, there is a 17% increase in trough IgG levels, which may improve infection-related outcomes. No conversion is needed for patients transitioning from IVIG to fSCIG. Due to the discrepancies in IGRT dosing methods and variations in pharmacokinetics, individualized treatment plans based on patients’ clinical response are needed.

For patients transitioning from IVIG to SCIG, initial doses should be administered in a supervised setting and patients need to demonstrate tolerability and ability to self-inject if they are providing their own care as opposed to care rendered by home care nurses. fSCIG can be administered monthly and may enhance compliance. When administered monthly, the dose of fSCIG that has been studied is 600 mL per injection site. The number and time between infusions can be adjusted.

Patient preference is essential in providing care as some patients may prefer the 16.5% or 20% cSCIG formulations over fSCIG since lower infusion volumes are needed and it may be more comfortable despite the more frequent administration needed. Others may prefer the once monthly dosing of fSCIG both for convenience and because they need larger IgG dosages.

Pharmacists can assist in optimizing IGRT treatment plans and in educating patients about the advantages and disadvantages of the various formulations.

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.