Activities of Azithromycin and Amphotericin B against Naegleria fowleri In Vitro and in a Mouse Model of Primary Amebic Meningoencephalitis

Abstract

Inhalation of fresh water containing the free-living ameba Naegleria fowleri may lead to a potentially fatal infection known as primary amebic meningoencephalitis. Amphotericin B is the only agent with established clinical efficacy in the treatment of primary amebic meningoencephalitis in humans, but therapy with this drug is often associated with adverse effects on the kidneys and other organs, and not all persons treated with amphotericin B have survived. We investigated the in vitro activity and in vivo efficacy of newer therapeutic agents in an attempt to identify other useful agents for treating primary amebic meningoencephalitis. Azithromycin has shown in vitro activity against Acanthamoeba spp. and in vivo activity against experimental toxoplasmosis. In our study, the MIC of azithromycin against N. fowleri was 13.4 M (10 g/ml), which was 123 times greater than the MIC of amphotericin B, which was 0.108 M (0.1 g/ml). Azithromycin protected 100% of mice infected with N. fowleri at a dose of 75 mg/kg/day for 5 days, whereas amphotericin B protected only 50% of mice at a dose of 7.5 mg/kg/day for 5 days, and all control mice died during the 28-day observation period. We conclude that azithromycin has both in vitro and in vivo activity versus N. fowleri and may be a useful addition to therapy for primary amebic meningoencephalitis.Primary amebic meningoencephalitis is a rapidly fatal infection caused by the free-living ameba Naegleria fowleri. Victims are usually healthy, young individuals with a recent history of swimming or other water-related activities. N. fowleri gains entry to the nasal cavity during inhalation or aspiration of contaminated water. The ameba then migrates along the olfactory nerves, crosses the cribriform plate, and gains access to the central nervous system. Within the brain, N. fowleri causes extensive inflammation, hemorrhage, and necrosis, leading to death in 3 to 7 days (12).Mortality among patients with primary amebic meningoencephalitis is greater than 95% (4). This grave prognosis is due to the rapid progression of the disease, the often delayed diagnosis, and the lack of effective therapeutic agents. Since primary amebic meningoencephalitis was identified, a wide range of therapeutic agents against N. fowleri have been evaluated, including many antifungal, antiprotozoal, antibacterial, and antipsychotic agents. Most of these drugs were determined to have little or no efficacy against N. fowleri, either in vitro or in vivo (5)(6)(7)(8)22).Of the drugs that have been evaluated against N. fowleri, amphotericin B, an antifungal drug, is the only agent with established clinical efficacy. Studies have demonstrated the in vitro and in vivo activity of amphotericin B against various strains of N. fowleri (5-8, 13, 17, 19, 20, 21), and at least seven patients with primary amebic meningoencephalitis have been successfully treated with amphotericin B alone or in combination with other drugs (1,2,14,16,19,25).Although amphotericin B remains the first choice for treatment of primary amebic me...

Therapeutic effect of rokitamycin in vitro and on experimental meningoencephalitis due to Naegleria fowleri

“…or Acanthamoeba spp. [7,9,26,27]. Although amphotericin B is the only agent used consistently as treatment for patients with PAME, amphotericin B is a very toxic antibiotic and may cause renal toxicity, electrolyte disturbances, haematopoietic effects and other organ damage, as well as chills, fever, nausea, vomiting and headache [11][12][13].…”

“…This result suggests that rokitamycin may be an effective drug against N. fowleri in in vitro and in vivo studies. In a mouse model, experiments were performed by treatment of mice with drugs three times, on Days 3, 7 and 11 post infection, which might more closely resemble the clinical setting because patients do not present symptoms until several days after infection [9]. The in vivo activity and low toxicity of rokitamycin make it a potentially attractive drug in the treatment of PAME.…”

“…Other antimicrobials that have been tested, mostly in vitro, are clotrimazole, itraconazole, fluconazole, ketoconazole and chlorpromazine, with varying degrees of efficacy [7,8]. Azithromycin has been described for the effective treatment of experimental PAME in mice [9]. In recent years, miltefosine, which was used as an anticancer drug, and voriconazole, which was used in systemic fungal infections, were found to be effective in in vitro studies [10].…”

Improvement of Antiamoebic Activity of Rokitamycin Loaded in Chitosan Microspheres

“…An amount of free drug or microspheres corresponding to 2 mg of RK were used. At predetermined times (5,10,15,20,25,30,45, 60, 90, 120 and 180 min), 1 mL samples were withdrawn and the sample volume was replaced with fresh phosphate buffer. The samples withdrawn were centrifuged for 10 min at 13,000 rpm and the supernatant analysed.…”

“…They have been extensively used for the treatment of bacterial infections, as they are able to interfere selectively with protein biosynthesis by binding to the 50S component of the prokaryotic ribosome. Macrolides have broad-spectrum activities against gram-positive and gram-negative bacteria, including actinomycetes and mycobacteria, as well as treponemes, mycoplasmas, chlamydiae, rickettsiae, and some protozoa [1][2][3][4][5]. Rokitamycin is a semisynthetic 16-membered-ring macrolide of the leucomycin group [6].…”