New FDA Orphan Drugs: Cethromycin, Maribavir, rhPDGF-BB

Yael Waknine

March 23, 2007

March 23, 2007 -- The US Food and Drug Administration (FDA) has granted orphan drug designation for cethromycin in the prophylactic treatment of patients exposed to inhalation anthrax, maribavir in the prevention of cytomegalovirus viremia and disease in at-risk populations, and recombinant human platelet-derived growth factor in the treatment of osteonecrosis of the jaw.

Orphan Drug Cethromycin for Prophylaxis Against Inhaled Anthrax

On March 14, the FDA granted orphan drug designation for cethromycin (Advanced Life Sciences Holdings, Inc) in the prophylactic treatment of patients exposed to inhalation anthrax.

Cethromycin is a second-generation ketolide antibiotic that has shown in vitro activity against upper and lower respiratory tract pathogens, including penicillin- and macrolide-resistant gram-positive bacteria. It has been tested in 6 phase 3 clinical trials (N = ~3,800) to determine its safety and efficacy for the treatment of mild to moderate community-acquired pneumonia, bronchitis, pharyngitis, and sinusitis.

It has also shown significant in vitro activity against more than 30 Bacillus anthracis strains and is currently being tested in primates to determine its therapeutic efficacy for postexposure anthrax prophylaxis.
The company said it is collaborating with the US Army Medical Research Institute of Infectious Diseases (USAMRIID) and the National Institute of Health National Institute of Allergy and Infectious Diseases for the research and development of cethromycin against anthrax and other biowarfare agents.

Orphan Drug Maribavir to Prevent CMV Viremia and Disease in High-Risk Patients

On February 1, the FDA granted orphan drug designation for maribavir (ViroPharma, Inc) in the prevention of cytomegalovirus (CMV) viremia and disease in at-risk populations.

As with other herpes viruses, CMV can remain dormant for long periods of time. Although 50% to 85% of US adults are infected by age 40 years, those who are healthy experience little or no apparent illness.

In contrast, CMV infection can cause serious disease or death in those who are immunocompromised, such as HIV patients, transplant patients, and children born with primary CMV infection. Moreover, immunosuppressed patients (eg, bone marrow or organ transplant recipients) are at increased risk for severe pneumonitis, hepatitis, and complications leading to acute or chronic rejection. Currently available therapies are limited by toxicities, particularly bone marrow suppression and renal impairment.

Maribavir is an orally bioavailable product that represents a new class of drugs called benzimidazole ribosides. Unlike currently approved agents that inhibit CMV DNA polymerase, maribavir selectively inhibits viral DNA assembly and shedding of viral capsids from infected nuclei. It also has shown potent in vitro activity against CMV strains resistant to commonly used products.

"[T]he drug appears to be well tolerated with impressive anti-CMV activity in stem cell transplant patients, which has allowed us to initiate our international phase 3 development program," Colin Broom, MD, ViroPharma's chief scientific officer, says in a news release regarding phase 2 clinical trial results.

Platelet-Derived Growth Factor (rhPDGF-BB) Granted Orphan Drug Status for ONJ

On February 21, the FDA granted orphan drug designation forrecombinant human platelet-derived growth factor (rhPDGF-BB; BioMimetic Therapeutics, Inc) in the treatment of osteonecrosis of the jaw (ONJ).

ONJ most commonly occurs at the site of previous trauma (eg, tooth extraction) and typically presents with pain or swelling in the jaw, an irregular sore with exposed bone in the mandible or maxilla, infection (possibly with pus), and altered sensation (eg, numbness or heavy sensation).

The product's ability to stimulate bone and tissue healing via chemotaxis and mitogenesis may be helpful to patients who develop ONJ as an adverse effect of high-dose bisphosphonate therapy, according to a company news release. In vivo and in vitro studies have shown that rhPDGF-BB may also enhance processes important in angiogenesis at the wound site, a process critical for wound healing.


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