Clindamycin for toxoplasma encephalitis in AIDS

Treatment of Toxoplasmosis: Historical Perspective, Animal Models, and Current Clinical Practice

Primary Toxoplasma gondii infection is usually subclinical, but cervical lymphadenopathy or ocular disease can be present in some patients. Active infection is characterized by tachyzoites, while tissue cysts characterize latent disease. Infection in the fetus and in immunocompromised patients can cause devastating disease. The combination of pyrimethamine and sulfadiazine (pyr-sulf), targeting the active stage of the infection, is the current gold standard for treating toxoplasmosis, but failure rates remain significant. Although other regimens are available, including pyrimethamine in combination with clindamycin, atovaquone, clarithromycin, or azithromycin or monotherapy with trimethoprim-sulfamethoxazole (TMP-SMX) or atovaquone, none have been found to be superior to pyr-sulf, and no regimen is active against the latent stage of the infection. Furthermore, the efficacy of these regimens against ocular disease remains uncertain. In multiple studies, systematic screening for Toxoplasma infection during gestation, followed by treatment with spiramycin for acute maternal infections and with pyr-sulf for those with established fetal infection, has been shown to be effective at preventing vertical transmission and minimizing the severity of congenital toxoplasmosis (CT). Despite significant progress in treating human disease, there is a strong impetus to develop novel therapeutics for both the acute and latent forms of the infection. Here we present an overview of toxoplasmosis treatment in humans and in animal models. Additional research is needed to identify novel drugs by use of innovative high-throughput screening technologies and to improve experimental models to reflect human disease. Such advances will pave the way for lead candidates to be tested in thoroughly designed clinical trials in defined patient populations.

Current management of infectious complications in the injecting drug user

The diagnosis and management of infectious complications associated with injection drug use (IDU) are among some of the more challenging aspects of working with substance abusing populations. As the population of injection drug users age, we expect the number and severity of these complications to increase. Commonly seen infections, such as bacterial endocarditis and bacterial infections of bones, joints, and soft tissue, are now frequently complicated by concurrent immunodeficiency. Parenterally and sexually transmitted viral hepatitis is responsible for significant IDU morbidity and mortality. The human leukemia/lymphoma virus types I and II are increasing in prevalence in the IDU with uncertain long-term clinical effects. Immune dysfunction has been described in the IDU for decades, but the impact of host immune compromise on the transmission and the course of HIV-1 has yet to be fully appreciated. The integration of the treatment of substance abuse and its concurrent psychiatric disorders with the management of infectious complications, including immunodeficiency, promises to improve patient compliance with possible savings of overall medical costs.

Plasma pyrimethamine concentrations during long-term treatment for cerebral toxoplasmosis in patients with AIDS

Steady-state plasma pyrimethamine levels were measured by gas chromatography. The specimens were taken from 74 adults with advanced human immunodeficiency virus infection receiving pyrimethamine-containing drugs for prophylaxis or curative therapy of reactivated cerebral toxoplasmosis. During an overall treatment period of 1,049 months, 1,012 plasma samples were investigated. Pyrimethamine concentrations could be evaluated in 904 plasma samples. The weekly dosage of pyrimethamine ranged from 25 to 1,400 mg; one patient with severe diarrhea received 2,100 mg/week. Steady-state plasma pyrimethamine concentrations were achieved after 12 to 20 days. Pyrimethamine concentrations evidently increased with the weekly dosage given. Mean concentrations were 253 +/- 151 ng/ml with 50 mg of pyrimethamine per week, 471 +/- 214 ng/ml with 100 mg of pyrimethamine per week, 1,893 +/- 1,182 ng/ml with 350 mg of pyrimethamine per week and 3,369 +/- 1,726 ng/ml with 1,050 mg of pyrimethamine per week. A widespread interpatient range was found for every dosage. With the simultaneous use of enzyme-inducing comedication, the plasma pyrimethamine levels decreased in several patients. Mild chronic liver disease did not influence plasma pyrimethamine concentrations. To avoid ineffective therapy or severe side effects, monitoring of pyrimethamine could be useful in patients receiving enzyme-inducing comedications and in patients with severe diarrhea or poor compliance.

Paradoxical effect of clindamycin in experimental, acute toxoplasmosis in cats

Cats were experimentally inoculated parenterally with the ME49 strain of Toxoplasma gondii to characterize the efficacies of two different dosages of orally administered clindamycin hydrochloride in the treatment of ocular toxoplasmosis. Concentrations of clindamycin hydrochloride at levels previously suggested to be inhibitory to T. gondii replication in vitro were achieved in the serum and aqueous humor but not in the cerebrospinal fluid. Antibiotic therapy, initiated 7 days after inoculation, resulted in no significant difference in the morphometric severity of ocular posterior segment lesions compared with that in the control groups. Treatment appeared to blunt T. gondii-specific immunoglobulin M production but had no significant effect on immunoglobulin G titers. Paradoxically, clindamycin administration was associated with increased morbidity and mortality from hepatitis and interstitial pneumonia, which are characteristic of generalized toxoplasmosis. Serum tumor necrosis factor alpha activity was detected at moderate levels in all groups of cats and correlated with the severity of clinical disease. The results of the study suggest that clindamycin, when administered at this specific time interval following inoculation, does not ameliorate ocular lesions and has a detrimental effect on the clinical course of acute, experimental toxoplasmosis in cats. The factors responsible for and the relevance of this detrimental effect to naturally occurring toxoplasmosis in humans and pet cats were not clear from the study but may relate to an antibiotic-associated decrease in the antitoxoplasmic activity of phagocytic cells responsible for the control of T. gondii.

Interconnection between organellar functions, development and drug resistance in the protozoan parasite, Toxoplasma gondii

The protozoan parasite Toxoplasma gondii causes severe disease in animals and humans. In AIDS patients, for example, the encephalitis it produces is a major cause of death. Part of the very successful strategy adopted by the parasite centers on its ability to differentiate from the actively growing tachyzoite form to a chronic, almost latent state called the bradyzoite. The molecular signals and precise triggers involved in this differentiation process are not known. Drugs for treating toxoplasmosis are not capable of clearing the infection apparently because of their inability to eradicate the bradyzoites. Recently, as part of our efforts to understand the mode of action of a promising new drug, atovaquone, we have generated and analysed a mutant that is resistant to this drug. Surprisingly, we found that this mutant is predisposed to spontaneously differentiate from the tachyzoite to bradyzoite form in vitro (Tomavo & Boothroyd, submitted). Given that atovaquone is believed to act on the parasite mitochondria, we were interested to explore the relationship between mitochondrial function and differentiation. We find that atovaquone and a number of other drugs targeted to mitochondria will cause wild type parasites to differentiate from tachyzoites to bradyzoites suggesting some sort of adaptive response to a decrease in mitochondrial activities. The fact that atovaquone-resistant mutants are hypersensitive to clindamycin, a drug believed to work on the putative plastid of these parasites, suggests a model for how the mitochondrion and plastid interact and how they may be tied into the process and state of differentiation. This model is presented and discussed.

Human antiprotozoal therapy: past, present, and future

Human protozoal infections are ubiquitous and occur worldwide. In many cases, antiprotozoal agents currently in use predate the modern antibiotic era. Despite the relative lag in development of new antiprotozoal agents, the 1990s have witnessed an increasing level of interest in these infections, inspired by international travel and immigration, a growing awareness of antiprotozoal drug resistance, and the significance of acute and recrudescent protozoal infections in immunosuppressed hosts. This review summarizes for nonclinician readers the past, present, and future therapies for common human protozoal infections, as well as pharmacologic mechanisms of action and resistance and common toxicities associated with these agents.

Therapeutic approaches for AIDS-related toxoplasmosis

OBJECTIVE

To summarize current knowledge of prophylaxis and treatment of AIDS-related toxoplasmosis.

DATA SOURCES

A MEDLINE search (1985-1994) was used to identify pertinent literature, including reviews.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Pertinent information, as judged by the authors, was selected for discussion.

DATA SYNTHESIS

Trimethoprim/sulfamethoxazole (TMP/SMX) appears to be useful for prophylaxis against toxoplasmosis in patients with AIDS. The most effective TMP/SMX dose for prevention of toxoplasmosis needs to be determined. Dapsone in combination with pyrimethamine therapy may be an effective alternative for toxoplasmosis prophylaxis. The most effective regimen for the treatment of AIDS-related toxoplasmosis is the combination therapy of pyrimethamine/sulfadiazine. In patients who cannot tolerate sulfadiazine therapy because of adverse effects or allergy, pyrimethamine with clindamycin therapy may be considered as a second-line alternative. Lifelong suppressive therapy is required after either treatment regimen to prevent relapse. Other newer agents such as azithromycin, clarithromycin, atovaquone, or timetrexate-leucovorin need further studies to confirm their true effectiveness in the treatment of toxoplasmosis.

CONCLUSIONS

TMP/SMX remains a useful agent in prophylaxis against toxoplasmosis. Pyrimethamine/sulfadiazine is the most effective combination in the treatment of acute toxoplasmosis.

Parasitic infections of the central nervous system in children. Part II: Disseminated infections

In the second segment of this three-part review of parasitic infections of the central nervous system in children, we consider parasitic infections which typically involve various tissues and organs in addition to the brain and spinal cord. Parasites capable of dissemination in immunocompetent hosts are discussed first, and, as in Part I, organisms are grouped according to their predominant geographic location. This is followed by a discussion of the unique aspects of toxoplasmosis, strongyloidiasis and infection with microsporidia in immunocompromised patients, with an emphasis on the central nervous system.

Pyrimethamine plus azithromycin for treatment of acute toxoplasmic encephalitis in patients with AIDS

A prospective study was conducted to evaluate azithromycin in combination with pyrimethamine for treatment of acute Toxoplasma encephalitis in patients with AIDS. Of the 14 patients given 75 mg pyrimethamine and 500 mg azithromycin daily for four weeks, eight were evaluable for clinical response. Five responded favorably, one had an intermediate response and two an unfavorable response. Of the nine patients evaluable for radiological response, six responded favorably, and three had an intermediate response. Eleven adverse events occurred in nine patients: rash (n = 5), abnormal liver function (n = 2), vomiting (n = 3) and hypoacousia (n = 1). This pilot study suggests that the combination of pyrimethamine and azithromycin may be further investigated and that the optimal dosage of azithromycin has yet to be determined.

Comparison of two medications in central nervous system toxoplasmosis in patients with AIDS

We retrospectively examined 39 patients with AIDS and central nervous system toxoplasmosis in order to determine the efficacy and safety of two combinations: pyrimethamine-sulfadiazine and pyrimethamine-clindamycin. The results showed a response rate of 79% for the sulfadiazine association and a high failure rate in the clindamycin group. Side effects with sulfadiazine were slightly more frequent, but with desensitization protocols discontinuation was kept down. The combination of pyrimethamine and sulfadiazine, associated, when necessary, with desensitization schedules, was confirmed to be first choice therapy for cerebral toxoplasmosis in AIDS patients. The role of alternative regimens needs further evaluation.