New treatments target infectious diseases

"For a while, to a degree, people had an idea that bacterial infections, to a large extent, were conquered," says Robert S. Kirsner, M.D., Ph.D., associate professor in the University of Miami's department of dermatology and cutaneous surgery. Accordingly, he says researchers focused on other infectious processes such as those due to viruses, which were considered the biggest public health scourge through the 1980s and 1990s.

"In fact," he says, "advances in treatments for common bacterial and skin infections have lagged behind. There were really very few new antibiotics developed in the 1990s for skin infections, especially drug-resistant infections, while the resistance has increased dramatically. There's been a significant rise in methicillin-resistant Staphylococcus aureus (MRSA), and more recently a different subtype of MRSA," namely, community-acquired MRSA (CA-MRSA).

Other resistant organisms causing concern include both S. aureus and enterococcus that are resistant to vancomycin, Dr. Kirsner adds.

"At our hospital and in many others," he says, "three-fourths of the patients who have S. aureus grown from their skin or wounds have MRSA. But an emerging number of patients in the community have CA-MRSA. CA-MRSA differs because of different antibiotic sensitivities and mechanisms of action." Furthermore, he says that because CA-MRSA can produce certain toxins that mimic symptoms of other conditions such as pyoderma gangrenosum, appropriate diagnosis is key.

"Fortunately," he adds, "the pharmaceutical companies have responded to some extent in recent years, developing a host of new antibiotics treatments."

New antibiotics

New antibiotic treatments include Zyvox (linezolid, Pfizer) and, during the past year, drugs such as tigecycline, an intravenous minocycline derivative that Dr. Kirsner says has proven comparable to vancomycin and aztreonam.

Other new IV antibiotics include ertapenem and dalbavancin, the latter of which he says offers "amazingly convenient dosing." Two different weekly doses - the first week 1 g, then 500 mg in the second - performed as well as two weeks of twice-daily linezolid for MRSA skin infections (Jauregui LE et al. Clin Infect Dis. 2005 Nov 15;41(10):1407-1415. Epub. 2005 Oct 6.), Dr. Kirsner says.

Bacterial infections rank among the most common infections dermatologists see, as well as the most potentially dangerous, he adds.

Global society

In addition to the increasing prevalence and virulence of infectious disease, he says the global nature of modern society is delivering a greater number of unusual infections to U.S. dermatologists' doorsteps.

"One of them is leishmaniasis among returning soldiers," Dr. Kirsner says. "It's important that clinicians add this to their differential diagnosis because we are seeing and may continue to see these conditions more frequently."

Onychomycosis

Regarding onychomycosis, he says prevalence figures continue to rise because the U.S. population continues to change. "As we have an older population - patients with increasing incidence of diabetes and vascular disease - there's an increasing incidence of onychomycosis," he says.