By Anne Harding
NEW YORK (Reuters Health) Jan 27 - Extended treatment with trimethoprim-sulfamethoxazole may reduce the risk of recurrence in patients with Toxoplasma gondii retinochoroiditis (TGR), according to a new study of 95 patients.
After an initial 45-day treatment with the drug combination, none of the patients who were randomly assigned to continue the therapy for a year developed recurrent disease, compared to about 13% of patients given placebo.
Toxoplasmosis is a parasitic infection usually kept in check by the immune system, although it can harm immunocompromised individuals and babies born to women who contract the infection for the first time during pregnancy, according to the Centers for Disease Control and Prevention.
TGR is treatable but not curable, noted Dr. Abdhish Bhavsar, a surgeon at the Retina Center of Minnesota in Minneapolis. Dr. Bhavsar, who reviewed the new study for Reuters Health, is also a spokesman for the American Academy of Ophthalmology.
There is no standard treatment for TGR, Dr. Joao Paulo Fernandes Felix and colleagues from the Universidade Estadual de Campinas in Sao Paolo, Brazil, who conducted the new study, wrote in a report online January 6th in the American Journal of Ophthalmology. An open-label trial published in the same journal in 2002 suggested trimethoprim-sulfamethoxazole reduced recurrence risk, they add, but the control group did not receive a placebo and examiners were not masked to treatment group.
"These factors may affect the ability to interpret drug side effects, they may also affect follow-up, and may introduce bias during the examinations," the researchers write.
To address these issues, Dr. Felix and his team enrolled 100 patients with active recurrent TGR, all of whom were treated with 800 mg trimethoprim and 160 mg sulfamethoxazole in a single tablet twice daily for 45 days. Five patients dropped out after this period, and the remaining 95 were randomized to continue treatment or to receive placebo. Ninety-three patients completed the one-year follow-up. None of the 46 patients in the active treatment group had a recurrence during follow-up, versus six of the 47 (12.8%) given placebo (p=0.03).
There was no difference between the groups in changes in best-corrected visual acuity, and no cases of treatment-limiting toxicity.
"As suggested by other authors, trimethoprim-sulfamethoxazole therapy may be appropriate for specific individuals who have demonstrated histories of frequent and/or severe recurrences," Dr. Felix and his colleagues write. "It should also be considered for people who are at greatest risk for vision loss, such as those with retinochoroidal scars adjacent to the fovea, where any reactivation can result in profound vision loss."
Dr. Justus Garweg of the Swiss Eye Institute in Luzerne also reviewed the study for Reuters Health. He said in an email, "This therapy is much better tolerated and safer than the most established and broadest used combination of pyrimethamine and sulfadiazine and thus may evolve (into) the treatment standard for ocular toxoplasmosis in the absence of allergy to sulfonamides."
"For me personally, there is enough and sufficiently strong circumstantial evidence justifying the use of the well tolerated combination with trimethoprim and sulfamethoxazole for the treatment of recurrent ocular toxoplasmosis," he added.
One major advantage of trimethoprim-sulfamethoxazole is its accessibility and low cost, Dr. Bhavsar said. He currently uses quadruple therapy (clindamycin, sulfadiazine, pyrimethamine, and prednisone) in his own patients who have no intolerances to the medications, he added. "My main concern is that the organism is difficult to treat in the first place, so using a multi-drug approach may be better," he said.
Also, Dr. Bhavsar noted, few patients in his practice develop recurrences within a year of treatment. "The one-year results are a little bit tricky to interpret, because what I would like to see are five to 10 year results or longer."
Dr. Felix did not respond to a request for comments.
Am J Ophthalmol 2014.
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