ORLANDO (FRONTLINE MEDICAL NEWS) –A recombinant form of factor XIII was effective at preventing serious bleeding episodes in young children with factor XIII-A subunit deficiency, a rare and serious bleeding disorder.

In a small international phase III trial, there were no major bleeding episodes among six young children treated for at least 1 year with recombinant factor XIII (rFXIII; trade name Tretten), reported Susan L. Kearney, MD, of Children’s Hospitals and Clinics of Minnesota in Minneapolis.

“Prophylaxis was effective. The annualized bleeding rate was zero and the mean trough [FXIII activity] was greater than 10%,” she said at a moderated poster session at the World Federation of Hemophilia World Congress. “We feel that recombinant factor XIII is safe and effective in pediatric subjects less than 6 years of age with congenital factor XIII-A subunit deficiency, similar to the older age cohort.”

Factor XIII-A subunit deficiency is a rare and serious heritable bleeding disorder associated with spontaneous intracranial hemorrhage and other unpredictable types of serious bleeding.

In a previous phase III trial , 77 patients, ranging in age from 7 to 60 years, received rFXIII for bleeding prophylaxis. When given monthly, the recombinant factor was effective at preventing serious bleeding in 90% of patients. The most commonly reported adverse events were headache, pain in the extremities, and injection site pain.

Based on these results, the Food and Drug Administration granted rFXIII orphan-drug designation for treatment of patients 6 and older with factor XIII-A subunit deficiency.

In the trial reported here, investigators from the United States, United Kingdom, Israel, and Denmark enrolled three boys and three girls under age 6 who had previously completed a single dose efficacy and safety study of rFXIII. The patients received intravenous rFXIII at a dose of 35 IU/kg every 28 days for a minimum of 52 weeks.

The total treatment duration ranged from 1.8 to 3.5 years, for a total of 16.6 patient years.

There were no thromboembolic events or systemic allergic reactions, the primary safety endpoint of the study. One patient experienced three incidences of atopic dermatitis, however; two serious adverse events related to head injuries from falls during play occurred in one patient, who did not experience intracranial hemorrhage.

Two adverse events were deemed to be probably or possibly related to rFXIII: a case of viral gastroenteritis affected one patient who recovered without a change in dose, and mild fluctuating lymphocytopenia seen at baseline persisted in another patient throughout the trial.

There were no inhibitory or noninhibitory antibodies to rFXIII detected in any patient during the trial, and there were no bleeding episodes requiring additional treatment. The 14 minor bleeding episodes seen in five patients did not require treatment with an FXIII-containing product, the authors noted.

“It’s a very rare disorder, but … the phenotype is quite severe and patients are severely affected. So this product is very useful,” said Lakshmi Srivaths, MD, a pediatric hematologist at Texas Children’s Hospital in Houston. She was not involved in the study. Unlike patients with hemophilia A or B, who require frequent factor infusions, the long half-life of this product means patients need just once-a-month infusions “that change the phenotype very significantly.”

Dr. Kearney disclosed grant/research support from Novo Nordisk, which funded the study. Some coauthors reported consulting or employment with the company.