Dear Editor,

We agree with the principles described by Younger et al in "Subcutaneous Immunoglobulin Replacement Therapy: Ensuring Success."1 In particular, it is important to have a "patient-specific regimen that will meet each patient's needs" and that the way to do this is to go through the questions they describe regarding length and frequency of infusion, number of needles, and pump usage. We do feel, however, that the article missed an opportunity to fully describe the range of immunoglobulin (Ig) options available for treating adult patients with primary immunodeficiency (PI). Unfortunately, omitted in the discussion was the mention of HyQvia (immune globulin 10% with recombinant human hyaluronidase [rHuPH20]), a novel facilitated subcutaneous immunoglobulin (IgSC) recently approved in both the United States and Europe for the treatment of PI in adults.2-5

While IgSC is an excellent alternative to intravenous immunoglobulin (IgIV), the major limitations and treatment burden of conventional IgSC are the need to use several infusion sites (1-8) to administer a single dose and the need to dose frequently (daily to biweekly). HyQvia overcomes these barriers by enabling the delivery of up to a full monthly therapeutic dose (up to 600 mL/infusion site) of Ig via 1 to 2 SC infusion site(s). This is possible because rHuPH20 (the enzyme administered as part of the treatment) mimics the naturally occurring enzyme hyaluronidase, depolymerizing the gel-like hyaluronanan and increasing the dispersion of fluid in the SC tissue. rHuPH20 acts locally and transiently as a spreading factor to reversibly modify the SC tissue and makes it possible to increase the volume and flow rates of Ig into the local SC space.6 Thus, HyQvia enables patients to receive Ig treatment at an infusion frequency and rate similar to IgIV but with better systemic tolerability compared with IgIV.

HyQvia was approved on the basis of a pivotal Phase 3 study and a subsequent extension study, which together provide up to 3.5 years of safety data.5,7,8 The efficacy data indicate that the rate of serious bacterial infections in PI patients was well below the regulatory requirement of less than 1 per patient year. Safety data indicate that HyQvia was well tolerated with no serious adverse reactions reported after up to 3.5 years of treatment. Local adverse reactions were comparable to those observed in conventional IgSC studies despite 20- to 30-fold greater volumes per site and 10- to 15-fold greater infusion rates than those administered with conventional IgSC. While 18% of patients developed antibodies to rHuPH20 (with no clinical consequences and with declining titer levels over time), no patients developed neutralizing antibodies to rHuPH20. In summary, the data indicate that HyQvia provides IgG replacement therapy that meets the standards for IgG replacement therapies.

As indicated in the FDA-approved US prescribing information, patients are converted from IgIV to HyQvia at the same dose (100%) as their previous IgIV treatment (ie, 1-to-1 conversion). A direct conversion is possible because of the increased bioavailability of Ig when delivered using HyQvia. In contrast, a dose increase of 137% is required with conventional IgSC.

The recent approval of HyQvia increases the treatment options available to patients with PI, allowing for greater possibilities to plan a patient-specific regimen that meets each patient's needs. All the characteristics of HyQvia mentioned above make it possible to combine the best features of IgSC and IgIV to decrease the lifelong treatment burden and optimize the treatment experience for adult patients with PI.

Leon Rozen, MBBS, FRCPA, AFRACMA

Kim Duff, BSN, RN

Catherine Taggart, MBA, RN, CRNI(R)

Jeanette Scott, BSN, RN

References