Brian Wiens

Andexanet Alfa for the Reversal of Factor Xa Inhibitor Activity

BACKGROUND Bleeding is a complication of treatment with factor Xa inhibitors, but there are no specific agents for the reversal of the effects of these drugs. Andexanet is designed to reverse the anticoagulant effects of factor Xa inhibitors. METHODS Healthy older volunteers were given 5 mg of apixaban twice daily or 20 mg of rivaroxaban daily. For each factor Xa inhibitor, a two-part randomized placebo-controlled study was conducted to evaluate andexanet administered as a bolus or as a bolus plus a 2-hour infusion. The primary outcome was the mean percent change in anti-factor Xa activity, which is a measure of factor Xa inhibition by the anticoagulant. RESULTS Among the apixaban-treated participants, anti-factor Xa activity was reduced by 94% among those who received an andexanet bolus (24 participants), as compared with 21% among those who received placebo (9 participants) (P<0.001), and unbound apixaban concentration was reduced by 9.3 ng per milliliter versus 1.9 ng per milliliter (P<0.001); thrombin generation was fully restored in 100% versus 11% of the participants (P<0.001) within 2 to 5 minutes. Among the rivaroxaban-treated participants, anti-factor Xa activity was reduced by 92% among those who received an andexanet bolus (27 participants), as compared with 18% among those who received placebo (14 participants) (P<0.001), and unbound rivaroxaban concentration was reduced by 23.4 ng per milliliter versus 4.2 ng per milliliter (P<0.001); thrombin generation was fully restored in 96% versus 7% of the participants (P<0.001). These effects were sustained when andexanet was administered as a bolus plus an infusion. In a subgroup of participants, transient increases in levels of d-dimer and prothrombin fragments 1 and 2 were observed, which resolved within 24 to 72 hours. No serious adverse or thrombotic events were reported. CONCLUSIONS Andexanet reversed the anticoagulant activity of apixaban and rivaroxaban in older healthy participants within minutes after administration and for the duration of infusion, without evidence of clinical toxic effects. (Funded by Portola Pharmaceuticals and others; ANNEXA-A and ANNEXA-R ClinicalTrials.gov numbers, NCT02207725 and NCT02220725.).

A Controlled Trial of a Formalin-Inactivated Hepatitis A Vaccine in Healthy Children

BACKGROUND Although inactivated hepatitis A vaccine is known to be well tolerated and immunogenic in healthy children and adults, its efficacy has yet to be established. METHODS To evaluate the efficacy of the hepatitis A vaccine in protecting against clinically apparent disease, we conducted a double-blind, placebo-controlled trial in an Hasidic Jewish community in upstate New York that has had recurrent outbreaks of hepatitis A. At the beginning of a summer outbreak, 1037 healthy seronegative children 2 to 16 years of age were randomly assigned to receive one intramuscular injection of a highly purified, formalin-inactivated hepatitis A vaccine or placebo. A case was defined by the presence of typical signs and symptoms, a diagnostic increase in IgM antibody to hepatitis A, and a serum concentration of alanine aminotransferase at least twice the upper limit of normal. Cases occurring greater than or equal to 50 days after the injection were included in the evaluation of efficacy. The children were followed for a mean of 103 days. RESULTS A total of 519 children received vaccine, and 518 received placebo. The vaccine was well tolerated, with no serious adverse reactions. From day 50 after the injection, 25 cases of clinically apparent hepatitis A occurred in the placebo group and none in the vaccine group (P less than 0.001), confirming that the vaccine had 100 percent protective efficacy. Before day 21, seven cases occurred in the vaccine group and three cases in the placebo group. After that time, there were no cases among vaccine recipients and 34 cases among placebo recipients. CONCLUSIONS The inactivated purified hepatitis A vaccine that we tested is well tolerated, and a single dose is highly protective against clinically apparent hepatitis A.

Andexanet Alfa for Acute Major Bleeding Associated with Factor Xa Inhibitors

BACKGROUND Andexanet alfa (andexanet) is a recombinant modified human factor Xa decoy protein that has been shown to reverse the inhibition of factor Xa in healthy volunteers. METHODS In this multicenter, prospective, open-label, single-group study, we evaluated 67 patients who had acute major bleeding within 18 hours after the administration of a factor Xa inhibitor. The patients all received a bolus of andexanet followed by a 2-hour infusion of the drug. Patients were evaluated for changes in measures of anti-factor Xa activity and were assessed for clinical hemostatic efficacy during a 12-hour period. All the patients were subsequently followed for 30 days. The efficacy population of 47 patients had a baseline value for anti-factor Xa activity of at least 75 ng per milliliter (or ≥0.5 IU per milliliter for those receiving enoxaparin) and had confirmed bleeding severity at adjudication. RESULTS The mean age of the patients was 77 years; most of the patients had substantial cardiovascular disease. Bleeding was predominantly gastrointestinal or intracranial. The mean (±SD) time from emergency department presentation to the administration of the andexanet bolus was 4.8±1.8 hours. After the bolus administration, the median anti-factor Xa activity decreased by 89% (95% confidence interval [CI], 58 to 94) from baseline among patients receiving rivaroxaban and by 93% (95% CI, 87 to 94) among patients receiving apixaban. These levels remained similar during the 2-hour infusion. Four hours after the end of the infusion, there was a relative decrease from baseline of 39% in the measure of anti-factor Xa activity among patients receiving rivaroxaban and of 30% among those receiving apixaban. Twelve hours after the andexanet infusion, clinical hemostasis was adjudicated as excellent or good in 37 of 47 patients in the efficacy analysis (79%; 95% CI, 64 to 89). Thrombotic events occurred in 12 of 67 patients (18%) during the 30-day follow-up. CONCLUSIONS On the basis of a descriptive preliminary analysis, an initial bolus and subsequent 2-hour infusion of andexanet substantially reduced anti-factor Xa activity in patients with acute major bleeding associated with factor Xa inhibitors, with effective hemostasis occurring in 79%. (Funded by Portola Pharmaceuticals; ANNEXA-4 ClinicalTrials.gov number, NCT02329327 .).

Duration of protection from clinical hepatitis A disease after vaccination with VAQTA

Recent papers examining the expected persistence of anti‐hepatitis A virus antibody following vaccination with inactivated hepatitis A vaccine have estimated that geometric mean antibody levels will remain above cut‐off levels for 10–30 years. However, the methodology used in these papers did not take into account any estimates of variability between subjects. In this paper data from the persistence of antibody after the administration of another vaccine, VAQTA® (hepatitis A vaccine, inactivated; MSD), were used to develop further models of antibody decay. Using individual subject estimates instead of group means allowed the estimation of time to negativity for various percentiles of the population (including the median), and the construction of confidence intervals on estimates of time to negativity. Data from studies of subjects who seroreverted to negativity, and subsequently received a booster dose, were also considered to show that subjects who lose detectable antibody are likely to remain protected from hepatitis A disease by persistent immune memory and rapid anamnestic response soon after exposure to hepatitis A virus. The estimates of duration of protection suggest that VAQTA® will provide protection for many years, first through presence of antibody and further through an anamnestic response based on persistent immune memory.

Worldwide experience with the CR326F-derived inactivated hepatitis A virus vaccine in pediatric and adult populations: an overview.

The worldwide experience to date with VAQTA, a highly purified formalin-inactivated hepatitis A vaccine containing alum-adjuvant, is reviewed. No serious adverse experience related to vaccination has been reported. The vaccine has proven highly immunogenic, with seroconversion detectable after a single dose in 90-99% of children 2-16 years old, and of adults under 77 kg (170 lb) body weight. There is a trend toward lower one-dose seroconversion rates with increasing age and with weight > 77 kg. Early seroconversion in the latter groups may require two 25-unit doses given 2, 4 or 8 weeks apart, or a higher priming dose. Seroconversion induced by this vaccine has been shown to signify protection from clinical hepatitis A disease. The few vaccines whose titers have waned to borderline levels responded anamnestically to a booster, suggesting that the vaccine induces an immune memory response and should provide long-term protection.

Concurrent administration of inactivated hepatitis A vaccine with immune globulin in healthy adults

301 healthy adult volunteers were randomized to one of three treatment groups: inactivated hepatitis A vaccine alone; inactivated hepatitis A vaccine with immune globulin (Ig) concurrently; or Ig alone. The first two treatment groups received a second dose of hepatitis A vaccine at week 24. Anti-HAV was measured 4, 8, 12, 24 and 28 weeks after the primary immunization. When comparing subjects receiving inactivated hepatitis A vaccine alone to those receiving vaccine and Ig, the seropositivity rates were not significantly different at 4, 8, 12 and 28 weeks, but at week 24 the seropositivity rate was lower in the group receiving both vaccine and Ig compared to the group receiving vaccine alone (92.0% compared to 97.0%). At weeks 8, 12 and 24 the geometric mean titers (GMTs) were significantly lower for subjects receiving both vaccine and Ig. The GMTs were not significantly different after the second dose of vaccine. At all time points, the lower serum antibody concentrations observed in subjects receiving both inactivated hepatitis A vaccine and Ig were nevertheless substantially higher than the cutoff for assay seropositivity and much higher than after Ig alone; these differences are therefore clinically insignificant.

Antibody responses of healthy infants to a recombinant hepatitis B vaccine administered at two, four, and twelve or fifteen months of age

Hepatitis B vaccine was administered to healthy infants on two investigational schedules that fall within ranges recommended by the U.S. Public Health Service Advisory Committee on Immunization Practices and by the American Academy of Pediatrics Committee on Infectious Diseases. A month after receiving vaccine at 2, 4, and 12 or 15 months of age, 98% and 100% of the children had > 10 mIU antibodies to hepatitis B surface antigen per milliliter, with gemometric mean titers of 1358 mIU/ml and 3424 mIU/mL, respectively.

Anatomy of a trial: a historical view of the Monroe inactivated hepatitis A protective efficacy trial

The performance of vaccine protective efficacy trials is often more complex than reports of final results suggest. The current article reviews the background, planning and preparations for the Monroe, NY, protective efficacy trial of a formalin-inactivated, alum-adjuvanted hepatitis A vaccine (VAQTA, manufactured by Merck Research Laboratories). The vaccine trial was carried out at Kiryas Joel, a Hasidic Jewish community which had experienced numerous annual outbreaks in a local environment with similarities to day-care centers. Careful communication, and cooperation of community leadership, a flexible technical resource team, and knowledge of an epidemic already ongoing in a sister community whose members were due to arrive for summer holidays, permitted rapid and efficient completion of the trial with a striking demonstration of protection after a single vaccine dose.