In vitro effects of four macrolides (roxithromycin, spiramycin, azithromycin [CP-62,993], and A-56268) on Toxoplasma gondii

An updated review of chemical compounds with anti-Toxoplasma gondii activity

The opportunistic apicomplexan parasite Toxoplasma gondii is the etiologic agent for toxoplasmosis, which can infect a widespread range of hosts, particularly humans and warm-blooded animals. The present chemotherapy to treat or prevent toxoplasmosis is deficient and is based on diverse drugs such as atovaquone, trimethoprim, spiramycine, which are effective in acute toxoplasmosis. Therefore, a safe chemotherapy is required for toxoplasmosis considering that its responsible agent, T. gondii, provokes severe illness and death in pregnant women and immunodeficient patients. A certain disadvantage of the available treatments is the lack of effectiveness against the tissue cyst of the parasite. A safe chemotherapy to combat toxoplasmosis should be based on the metabolic differences between the parasite and the mammalian host. This article covers different relevant molecular targets to combat this disease including the isoprenoid pathway (farnesyl diphosphate synthase, squalene synthase), dihydrofolate reductase, calcium-dependent protein kinases, histone deacetylase, mitochondrial electron transport chain, etc.

Research on the effect and mechanism of antimicrobial peptides HPRP-A1/A2 work against Toxoplasma gondii infection

With increasing antibiotic resistance and drug safety concerns, novel therapeutics are urgently needed. Antimicrobial peptides are promising candidates that could address the spread of multidrug-resistant pathogens. HPRP-A1/A2 are known to display antimicrobial activity against gram-negative bacteria, gram-positive bacteria and some pathogenic fungi, but whether HPRP-A1/A2 work on Toxoplasma gondii (T gondii) is unknown. In this study, we found that the viability of tachyzoites that received HPRP-A1/A2 treatment was significantly decreased, and there was a reduction in the adhesion to and invasion of macrophages by tachyzoites after HPRP-A1/A2 treatment. HPRP-A1/A2 damaged the integrity of tachyzoite membranes, as characterized by membrane disorganization in and cytoplasm outflow from tachyzoites. In addition, in vivo injection with HPRP-A1/A2 resulted in a significantly decreased number of tachyzoites and an accelerated Th1/Tc1 response, and elicited pro-inflammatory cytokines in T gondii-infected mice. Furthermore, HPRP-A1/A2-treated splenocytes exhibited a significantly increased Tc1/Th1 response, and HPRP-A1/A2-stimulated macrophages inhibited the growth of carboxyfluorescein succinimidyl amino ester (CFSE)-labelled tachyzoites, which had higher TNF-α/IL-12 mRNA levels. Altogether, these results imply that HPRP-A1/A2 are effective against T gondii through damaging the structure of tachyzoites and inducing a protective immune response, which could offer an alternative approach against T gondii infection.

Treatment of Toxoplasmosis and Neosporosis in Farm Ruminants: State of Knowledge and Future Trends

Toxoplasmosis and neosporosis are closely related protozoan diseases that lead to important economic impacts in farm ruminants. Toxoplasma gondii infection mainly causes reproductive failure in small ruminants and is a widespread zoonosis, whereas Neospora caninum infection is one of the most important causes of abortion in cattle worldwide. Vaccination has been considered the most economic measure for controlling these diseases. However, despite vaccine development efforts, only a live-attenuated T. gondii vaccine has been licensed for veterinary use, and no promising vaccines against ne-osporosis have been developed; therefore, vaccine development remains a key goal. Additionally, drug therapy could be a valuable strategy for disease control in farm ruminants, as several drugs that limit T. gondii and N. caninum proliferation and dissemination have been evaluated. This approach may also be relevant to performing an initial drug screening for potential human therapy for zoonotic parasites. Treat-ments can be applied against infections in adult ruminants to minimize the outcomes of a primo-infection or the reactivation of a chronic infection during gestation or in newborn ruminants to avoid infection chronification. In this review, the current status of drug development against toxoplasmosis and neosporo-sis in farm ruminants is presented, and in an effort to promote additional treatment options, prospective drugs that have shown efficacy in vitro and in laboratory animal models of toxoplasmosis and neosporosis are examined

New antibacterials for the treatment of toxoplasmosis; a patent review

INTRODUCTION

Toxoplasma gondii is an opportunistic protozoan parasite responsible for toxoplasmosis. T. gondii is able to infect a wide range of hosts, particularly humans and warm-blooded animals. Toxoplasmosis can be considered as one of the most prevalent parasitic diseases affecting close to one billion people worldwide, but its current chemotherapy is still deficient and is only effective in the acute phase of the disease.

AREAS COVERED

This review covers different approaches to toxoplasmosis chemotherapy focused on the metabolic differences between the host and the parasite. Selective action on different targets such as the isoprenoid pathway, dihydrofolate reductase, T. gondii adenosine kinase, different antibacterials, T. gondii histone deacetylase and calcium-dependent protein kinases is discussed.

EXPERT OPINION

A new and safe chemotherapy is needed, as T. gondii causes serious morbidity and mortality in pregnant women and immunodeficient patients undergoing chemotherapy. A particular drawback of the available treatments is the lack of efficacy against the tissue cyst of the parasite. During this review a broad scope of several attractive targets for drug design have been presented. In this context, the isoprenoid pathway, dihydrofolate reductase, T. gondii histone deacetylase are promising molecular targets.

Azithromycin reduces ocular infection during congenital transmission of toxoplasmosis in the Calomys callosus model

Toxoplasma gondii is a widely distributed obligatory intracellular parasite that causes severe disease to the fetus when transmitted during pregnancy. Drugs used to avoid congenital transmission have shown side effects, and their efficacy is controversial. The most widely used treatment for acute toxoplasmosis during pregnancy is pyrimethamine plus sulfadiazine, which has several side effects. In this work, we tested the efficacy of azithromycin in reducing congenital transmission of T. gondii in the large vesper mouse, Calomys callosus, a rodent. Females of C callosus were inoculated perorally with 20 cysts of ME49 strain of T. gondii on the day of fertilization, and fetuses were collected from the 15th to the 19th day of gestation. Azithromycin (300 mg/kg), in association with pyrimethamine (100 or 50 mg/kg) plus sulfadiazine (100 or 75 mg/kg) and folinic acid (15 mg/kg) (SPAf), or vehicle, were administered orally on different days after infection. Brain and ocular tissues were removed and processed for immunohistochemistry using a polyclonal antibody against T. gondii, or were processed for parasite DNA quantification. Toxoplasma gondii was detected in the brains of all females and in fetuses' eyes of C. callosus treated with SPAf. On the other hand, in females treated with azithromycin, there was a reduction of T. gondii in the brains of mothers, and no parasites were detected in eyes of fetuses, indicating that azithromycin may represent an alternative treatment for toxoplasmosis during pregnancy.

Efficacy of azithromycin in the treatment of cutaneous leishmaniasis

The present open pilot study was conducted to assess the efficacy of azithromycin for the treatment of patients with cutaneous leishmaniasis in Ara ua and Varzelândia, MG. Twenty-four patients with less of six months of disease evolution were treated after clinical examination, Montenegro test and a biopsy. The treatment schemes consisted of oral doses of 500 mg per day for 3, 5 and 10 days and of 1000 mg for two days. A clinical control was performed monthly and treatment cycles were repeated when necessary until full reepithelialization of the lesions. On the occasion of the final evaluation, 20 patients had completed the study and 17 of them (85%) were cured. The time to obtain a cure was 60 days ifor 6 (30%) patients, 90 days for 7 (35%), and 120 for 4 (20%). The three patients with treatment failure received a pentavalent antimonial for 20 days. No adverse reactions to the medication were observed and a 14 month follow-up did not show recurrence in any patient. These results suggest that azithromycin can be a good therapeutic option for the treatment of cutaneous leishmaniasis caused by Leishmania Viannia brasiliensis.

A prospective, randomized trial of pyrimethamine and azithromycin vs pyrimethamine and sulfadiazine for the treatment of ocular toxoplasmosis

OBJECTIVE

To compare the effects of two treatment regimens, one of which included azithromycin, for the treatment of sight-threatening (near optic disk or fovea) ocular toxoplasmosis.

DESIGN

Prospective, randomized open-labeled multicenter study, masked in part with regard to evaluation.

METHODS

PARTICIPANTS TOTAL ENROLLMENT: 46 patients with sight-threatening ocular toxoplasmosis; pyrimethamine and azithromycin group: 24 patients; pyrimethamine and sulfadiazine group: 22 patients.

INTERVENTION

Patients were randomized into two treatment regimens. Group 1 was treated with pyrimethamine and azithromycin complemented with folinic acid and the addition of prednisone from day 3. Group 2 was treated with pyrimethamine and sulfadiazine complemented with folinic acid and the addition of prednisone from day 3. Patients used study medications daily for 4 weeks. Ocular and laboratory examinations were performed at least weekly during the observation period. The study was masked in part with regard to evaluation.

MAIN OUTCOME MEASURES

An assessment was made of the time to resolution of the intraocular inflammatory activity, the size of the retinochoroidal lesion, and visual acuity before and after the treatment as well as all adverse effects of treatments.

RESULTS

Adverse effects were more frequent in the pyrimethamine/sulfadiazine group (P <.04), and three patients in this group had to discontinue treatment. The time to resolution of inflammatory activity, decrease in size of retinochoroidal lesions, and optimal visual acuity did not differ between the two treatment groups. The number of patients who developed recurrences during the first year after treatment was similar for both groups.

CONCLUSIONS

The efficacy of the multidrug regimen with pyrimethamine and azithromycin was similar to the standard treatment with pyrimethamine and sulfadiazine. However, the frequency and severity of adverse effects was significantly lower with a regimen containing pyrimethamine and azithromycin. Multidrug therapy with the combination of pyrimethamine and azithromycin appears to be an acceptable alternative for treatment of sight-threatening ocular toxoplasmosis.

The ketolide antibiotics HMR 3647 and HMR 3004 are active against Toxoplasma gondii in vitro and in murine models of infection

Ketolides are a new class of macrolide antibiotics that have been shown to be active against a variety of bacteria including macrolide-resistant bacteria and mycobacteria. We examined two ketolides, HMR 3647 and HMR 3004, for their in vitro and in vivo activities against the protozoan parasite Toxoplasma gondii. In vitro, both ketolides at concentrations as low as 0.05 microg/ml markedly inhibited replication of tachyzoites of the RH strain within human foreskin fibroblasts. HMR 3004 demonstrated some toxicity for host cells after they were exposed to 5 microg of the drug per ml for 72 h. In contrast, HMR 3647 did not show any significant toxicity even at concentrations as high as 25 microg/ml. In vivo, both ketolides provided remarkable protection against death in mice lethally infected intraperitoneally with tachyzoites of the RH strain or orally with tissue cysts of the C56 strain of T. gondii. A dosage of 100 mg of HMR 3647 per kg of body weight per day administered for 10 days protected 50% of mice infected with tachyzoites. The same dosage of HMR 3004 protected 100% of the mice. In mice infected with cysts, a dosage of 30 mg of HMR 3647 per kg per day protected 100% of the mice, whereas a dosage of 40 mg of HMR 3004 per kg per day protected 75% of the mice. These results demonstrate that HMR 3647 and HMR 3004 possess excellent activities against two different strains of T. gondii and may be useful for the treatment of toxoplasmosis in humans.

The potential role of azithromycin in the treatment of prophylaxis of toxoplasmosis

Infection with Toxoplasma gondii is the most common parasitic infection worldwide with an estimated prevalence of 1-2 billion people. The risk of developing severe toxoplasmosis is higher for immunocompromised individuals and fetuses of mothers who have acquired a primo-infection. The current therapy of choice for toxoplasmosis is the synergistic combination of pyrimethamine and sulphadiazine. This therapy is highly effective but its use is complicated in immuno-compromised individuals due to adverse secondary effects. In addition, since pyrimethamine is potentially teratogenic, its use is not recommended during early pregnancy. Clindamycin, a lincosaminide, in combination with pyrimethamine has been shown to be an acceptable therapeutic alternative in patients who are unable to tolerate pyrimethamine plus sulphadiazine. In the search for new, effective compounds with less adverse or toxic effects, recent efforts have focused on the new macrolides and the azalides. Here, the results of the investigations and, in particular, the theoretical considerations for the potential use of azithromycin in the therapy of toxoplasmosis in immunocompromised individuals are reviewed.

[Clarithromycin combined with pyrimethamine in cerebral toxoplasmosis--a report of 2 cases]

The authors report the use and the outcome of claritromycin associated with pyrimethamine in the treatment of toxoplasma encephalites in two patients with AIDS. Both patients had the diagnosis stablished on clinical grounds, positive sorology (IgG) for toxoplasmosis and computed-tomographic (CT) scan of the brain showing lesions consistent with T. gondii encephalitis. The two patients were initially treated with pyrimethamine and sulfadiazine, which was changed to clindamycin due to allergic reactions. These reactions (skin rash) occurred with clindamycin as well and the patients were treated with claritromycin and pyrimethamine. The scheduled regimens were 1.5 to 2 g of clarithromycin plus 25 mg of pyrimethamine. The clinical response was very good in both cases with regression of neurologic signs and encephalitic abnormalities observed on CT scan. The authors suggest that clarithromycin associated with pyrimethamine may be an alternative treatment for toxoplasmosis in AIDS patients, who cannot receive or tolerate sulfa treatment.

In vitro assays elucidate peculiar kinetics of clindamycin action against Toxoplasma gondii

In order to characterize the delayed effect of clindamycin and macrolide antibiotics against Toxoplasma gondii tachyzoites (E. R. Pfefferkorn and S. E. Borotz, Antimicrob. Agents Chemother. 38:31-37, 1994), we have carefully examined the replication of parasites as a function of time after drug addition. Intracellular tachyzoites treated with up to 20 microM clindamycin (> 1,000 times the 50% inhibitory concentration) exhibit doubling times indistinguishable from those of controls (approximately 7 h). Drug-treated parasites emerge from infected cells and establish parasitophorous vacuoles inside new host cells as efficiently as untreated controls, but replication within the second vacuole is dramatically slowed. Growth inhibition in the second vacuole does not require continued presence of drug, but it is dependent solely on the concentration and duration of drug treatment in the first (previous) vacuole. The susceptibility of intracellular parasites to nanomolar concentrations of clindamycin contrasts with that of extracellular tachyzoites, which are completely resistant to treatment, even through several cycles of subsequent intracellular replication. This peculiar phenotype, in which drug effects are observed only in the second infectious cycle, also characterizes azithromycin and chloramphenicol treatment, but not treatment with cycloheximide, tetracycline, or anisomycin. These findings provide new insights into the mode of clindamycin and macrolide action against T. gondii, although the relevant target for their action remains unknown.

Calibration of an in vitro assay system using a non-adherent cell line to evaluate the effect of a drug on Toxoplasma gondii

A TG 180 non-adherent cell culture with Toxoplasma gondii and spiramycin was performed in order to calibrate TG 180 cells used in a therapeutic assay system. TG 180 cells were infected with the RH strain of T. gondii, and spiramycin was added at final concentrations of 1, 2, 4, 8, 12, 16, 20 and 25 micrograms/ml. A least-squares linear regression with confidence interval was calculated from the experimental curve and allowed the determination of the 50% inhibitory concentration of spiramycin. The IC50 of 13.7 micrograms/ml obtained is comparable with the results of the literature. The system including TG 180 cells (recently cultured in vitro) provides a rapid, accurate and economical determination of the effects of a drug on Toxoplasma gondii.

New antimicrobial agents

In any discussion of new antimicrobial agents in the 1990s, a warning and a plea are necessary. The spreading emergence of resistance among bacteria raises concerns for the effectiveness of antimicrobial therapy. Penicillin-resistant pneumococci are probably of most significance in pediatrics and are increasing in frequency, in part related to the use of antimicrobial therapy in young children to treat such infections as otitis media. New practice guidelines have suggested the more limited use of antimicrobial agents in treating serious otitis media. When pediatricians do treat, they should select effective agents. Limiting therapy to brief courses with effective and narrow-spectrum agents may be helpful also. Treating long enough to ensure eradication in serious infections is equally important. Methicillin-resistant S aureus are also increasing and are increasingly a concern in community-acquired infections and nosocomial infections. Using topical agents, such as mupirocin, to treat impetigo and other superficial skin infections can limit exposure to systemic agents and may delay the spread of resistance. Vancomycin-resistant enterococcal infections, an infrequent pediatric problem, are most frightening because no alternative therapies are available. Their occurrence is directly related to use of vancomycin in the communities that are affected. Containing the spread of drug-resistant bacteria will likely require a concerted effort by both physicians and the public. The indiscriminate use of antimicrobial agents to treat non-bacterial infections should be contained. The public must be educated to understand that antimicrobial agents are ineffective against viral infections. In the setting of managed care, educating administrators who make practice decisions that cheaper is not always better will be crucial. The issues of day-care infections and spread of potential pathogens must take on increasing attention and methods to decrease infection sought. Curbing inappropriate use of antimicrobial agents will be as important as learning the nuances between new agents.

Prevention of Pneumocystis carinii pneumonia and of cerebral toxoplasmosis by roxithromycin in HIV-infected patients

The prevention of cerebral toxoplasmosis and of Pneumocystis carinii pneumonia is an essential objective in the management of patients infected with HIV. Given that roxithromycin is active in vitro against Toxoplasma gondii and that in 1989 Dolermann reported the effective treatment of P. carinii respiratory infections with erythromycin, a randomized pilot study was undertaken in 52 patients infected with HIV. Patients were treated with either: a monthly dose of pentamidine aerosol (300 mg); roxithromycin once a week (300 mg t.i.d.); or a combination of pentamidine aerosol and roxithromycin. Intention to treat analysis was applied to these 52 patients, all of whom received at least one treatment dose. Five out of 18 patients treated with pentamidine aerosol, 1/17 patients treated with pentamidine aerosol + roxithromycin and none of the 17 patients treated with roxithromycin developed cerebral toxoplasmosis (p = 0.038). P. carinii pneumonia was diagnosed in one patient in the pentamidine aerosol-treated group, in one patient treated with roxithromycin and in none of the patients treated with pentamidine aerosol + roxithromycin (non-significant difference). Four cases of Mycobacterium tuberculosis and Mycobacterium avium-intracellulare infection were seen in the pentamidine aerosol-treated group (p = 0.028) and none in the roxithromycin groups. Adverse events leading to the discontinuation of treatment occurred in 5/34 (14.7%) patients treated with roxithromycin. Nausea, abdominal pain and raised transaminases occurred in four patients and a skin allergy in the final patient. Roxithromycin appears to be effective in the prevention of pulmonary pneumocystis infection and of cerebral toxoplasmosis in HIV-infected patients. However, these results require confirmation in a larger study.

Effectiveness of spiramycin for treatment of congenital Toxoplasma gondii infection in rhesus monkeys

The effectiveness of spiramycin for the treatment of rhesus monkey fetuses congenitally infected with Toxoplasma gondii was studied. Eight monkeys were infected at day 90 of pregnancy. This is comparable to the second trimester of organogenetic development in humans. Transmission of infection was found prenatally in five of the eight monkeys by detection of the parasite in the amniotic fluid. Treatment with spiramycin (20 mg/kg/day in two intermittent doses given intravenously) was started as soon as fetal infection was proven and was continued until birth. Nine to 14 days after initiation of treatment, the parasite was still detectable in amniotic fluid samples from four of these five cases. However, the parasite was detected only by PCR and not by mouse inoculation. T. gondii was also detected only by PCR in the placenta of one monkey that delivered prematurely. This monkey received spiramycin treatment for only 2 weeks. In the four monkeys that received treatment for about 7 weeks, the parasite was not present at birth in the placenta nor in amniotic fluid or neonatal organs. Spiramycin accumulates mainly in maternal tissues. Although concentrations in neonatal tissue were found to be 5 to 28 times higher than the corresponding concentrations in neonatal serum, the concentrations in neonatal tissue were still 11 to 16 times lower than those found in the mothers. However, no spiramycin was found in the fetal brains. Early treatment with spiramycin may prevent transmission of infection to the fetus but most probably cannot interrupt an existing brain infection, which is the most severe outcome of congenital toxoplasmosis in humans.

Pharmacokinetics of spiramycin in the rhesus monkey: transplacental passage and distribution in tissue in the fetus

Transplacental transfer of spiramycin was investigated in a rhesus monkey model to study whether the antibiotic reaches therapeutic levels in the fetus. Spiramycin concentrations were measured by bioassay and high-performance liquid chromatography. Pharmacokinetic parameters were determined for bioactive spiramycin as measured by the bioassay. Pharmacokinetic pilot studies showed that spiramycin distribution follows a two-compartment model in rhesus monkeys. Following a single intravenous dose of 50 or 250 mg, dose-dependent kinetics were observed. At a dose of 50 mg, 10% of the dose was excreted unchanged in the urine. At the higher dose of 250 mg, an oliguric effect was observed. Spiramycin concentrations in fetal serum were measured over time while the maternal concentration was maintained at a constant level. During a 5-h experiment, a maximum fetal-maternal serum ratio of 0.27 was found. In three fetuses, concentrations in serum and tissue were measured following intravenous administration of 50 mg of spiramycin twice daily to the mother for at least 7 days. The fetal-maternal serum ratios were found to be 0.4 to 0.58 after intravenous administration of the final dose of 50 mg to the mother. It appeared that spiramycin accumulated in the soft tissues, especially in the liver and spleen, of both the mother and the fetus. The concentration in placental tissue appeared to be 10 to 20 times that of the concentration in fetal serum. The concentration of spiramycin in amniotic fluid was about five times higher than the concentration in fetal serum. Another important observation was that absolutely no spiramycin was found in the brain.

Roxithromycin. An update of its antimicrobial activity, pharmacokinetic properties and therapeutic use

Roxithromycin is a derivative of the macrolide antibacterial erythromycin with in vitro antibacterial activity resembling that of the parent compound. The drug has activity against some Staphylococcus spp., many Streptococcus spp., Moraxella (Branhamella) catarrhalis, Mycoplasma pneumoniae, Legionella pneumophila and Chlamydia trachomatis as well as many less common organisms. Measured using recently proposed guidelines, roxithromycin has in vitro activity against Haemophilus influenzae. In comparison with that of its parent compound, the pharmacokinetic profile of roxithromycin is characterised by high plasma, tissue and body fluid concentrations and a long half-life permitting an extended dosage interval. Roxithromycin has proven clinical efficacy in upper and lower respiratory infections, skin and soft tissue infections, urogenital infections and orodental infections, and appears to be as effective as more established treatments including erythromycin, amoxicillin/clavulanic acid and cefaclor. The drug has also shown promise in a variety of more specialised indications including opportunistic infections in human immunodeficiency virus (HIV)-positive patients and as part of a Helicobacter pylori eradication regimen. Roxithromycin is very well tolerated with an overall incidence of adverse events of approximately 4%. Thus, roxithromycin is an attractive therapeutic alternative in its established indications, especially when the option of once-daily administration is considered.

Ocular pharmacokinetics of orally administered azithromycin in rabbits

Azithromycin was orally administered to Dutch-belted rabbits following extracapsular lens extraction in one eye. At various times the animals were sacrificed, and serum and ocular tissues were obtained for drug level determination by HPLC-EC. Following a single dose, peak levels of drug in ocular tissues were measured within 8 hours (cornea > 0.5 micrograms/g [15mg/kg]; > 1.5 micrograms/g [3Omg/kg]). Highest levels were obtained in iris and ciliary body ( > 15 micrograms). Measurable tissue levels persisted for at least 120 hours. Trough levels increased proportionately during drug multiple dose administration. Five days following five daily 15mg/kg doses, corneal levels exceeded 0.5 micrograms/g, and iris and ciliary levels were higher than 15 micrograms/g. Aqueous humor and serum levels were equivalent. Vitreous humor levels, though higher than aqueous humor, were consistently < 1 microgram/ml. Extracapsular cataract extraction did not significantly affect drug uptake.

The new macrolides. Azithromycin and clarithromycin

Clarithromycin and azithromycin are among the new generation of macrolides that have recently been approved for use. Compared with currently available antibiotics, these agents may be given less frequently and, in the case of azithromycin, for a shorter duration. In vitro data suggest an antimicrobial advantage of both clarithromycin and azithromycin against atypical mycobacterial and toxoplasmal species and possibly Haemophilus influenzae. The cost of both these agents is substantially higher than that of erythromycin and doxycycline, although the convenience of single-dose azithromycin is appealing compared with a 7-day course of doxycycline for chlamydial urethritis and cervicitis. These agents appear to offer advantages over erythromycin in the treatment of Mycobacterium avium-intracellulare. Additional data are needed to establish their role in other bacterial infections.

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.

Toxoplasma gondii: susceptibility and development of resistance to anticoccidial drugs in vitro

Anticoccidial drugs were evaluated for activity and for the development of resistance in a model of Toxoplasma gondii growing in human fibroblast cultures. Of 13 anticoccidial drugs tested, 9 had selective antitoxoplasma activity (50% inhibitory concentration, in micrograms per milliliter): decoquinate (0.005), arprinocid-N-oxide (0.015), robenidine (0.03), the aryl triazine CP-25,415 (0.2), toltrazuril (0.4), clopidol (1), dinitolmide (Zoalene; Dow) (10), and the carboxylic acid ionophores monensin (0.001) and salinomycin (0.04). Glycarbylamide, amprolium, nicarbazin, and the 6-(p-bromophenoxy)-7-chloro analog of halofuginone (Stenorol; Roussel-UCLAF) (CP-63,567) were toxic for the fibroblasts. Since Eimeria tenella has a similar drug susceptibility profile, anticoccidial drugs can be viewed as a potential source of new antitoxoplasma therapies. The development of resistance has limited the usefulness of most of these drugs as anticoccidial agents; in coccidia, resistance to all except the ionophores occurs readily in vivo. We explored the development of resistance in T. gondii by attempting to select mutants in vitro from parasites mutagenized with ethylnitrosourea. Mutants that had 20- to 50-fold-reduced susceptibility to decoquinate, arprinocid-N-oxide, and CP-25,415 were obtained. Ionophore-resistant T. gondii mutants were also selected in vitro; however, there was only a twofold difference in susceptibility between these mutants and the wild type. For three drugs (clopidol, robenidine, and toltrazuril), we were unable to select resistant mutants. For experimental anticoccidial drugs, there is currently no in vitro method for assessing the risk of development of resistance in Eimeria species. Our results suggest that T. gondii may offer a useful surrogate for this assessment.

In vitro evaluation of the activities of azithromycin alone and combined with pyrimethamine against Toxoplasma gondii

By using an in vitro microassay to assess drug interaction, azithromycin combined to pyrimethamine was found more active than pyrimethamine alone against Toxoplasma gondii, and additivity between those drugs was demonstrated. Our results show that the combination of azithromycin and pyrimethamine may lead to a more rapid control of T. gondii.

Azithromycin. A review of its antimicrobial activity, pharmacokinetic properties and clinical efficacy

Azithromycin is an acid stable orally administered macrolide antimicrobial drug, structurally related to erythromycin, with a similar spectrum of antimicrobial activity. Azithromycin is marginally less active than erythromycin in vitro against Gram-positive organisms, although this is of doubtful clinical significance as susceptibility concentrations fall within the range of achievable tissue azithromycin concentrations. In contrast, azithromycin appears to be more active than erythromycin against many Gram-negative pathogens and several other pathogens, notably Haemophilus influenzae, H. parainfluenzae, Moraxella catarrhalis, Neisseria gonorrhoeae, Urea-plasma urealyticum and Borrelia burgdorferi. Like erythromycin and other macrolides, the activity of azithromycin is unaffected by the production of beta-lactamase. However, erythromycin-resistant organisms are also resistant to azithromycin. Following oral administration, serum concentrations of azithromycin are lower than those of erythromycin, but this reflects the rapid and extensive movement of the drug from the circulation into intracellular compartments resulting in tissue concentrations exceeding those commonly seen with erythromycin. Azithromycin is subsequently slowly released, reflecting its long terminal phase elimination half-life relative to that of erythromycin. These factors allow for a single dose or single daily dose regimen in most infections, with the potential for increased compliance among outpatients where a more frequent antimicrobial regimen might traditionally be indicated. The potential disadvantage of low azithromycin serum concentrations, however, is that breakthrough bacteraemia may occur in patients who are severely ill; nevertheless, animal studies suggest that tissue concentrations of azithromycin are more important than those in serum when treating respiratory and other infections. The clinical efficacy of azithromycin has been confirmed in the treatment of infections of the lower and upper respiratory tracts (the latter including paediatric patients), skin and soft tissues (again including paediatric patients), in uncomplicated urethritis/cervicitis associated with N. gonorrhoeae, Chlamydia trachomatis or U. urealyticum and in the treatment of early Lyme disease. Azithromycin was as effective as erythromycin and other commonly used drugs including clarithromycin, beta-lactams (penicillins and cephalosporins), and quinolone and tetracycline antibiotics in some of the above infections. Some patients with acute exacerbations of chronic bronchitis due to H. influenzae may be refractory to therapy with azithromycin (as is the case with erythromycin) indicating the need for physician vigilance, although it should be noted that azithromycin is of equivalent efficacy to amoxicillin in the treatment of such patients. In the therapy of urethritis/cervicitis associated with C. trachomatis, N. gonorrhoea or U. urealyticum, a single dose azithromycin regimen offers a distinct advantage over currently available pharmacological options, while providing effective therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity of clarithromycin alone or in combination with other drugs for treatment of murine toxoplasmosis

The activity of the macrolide antibiotic clarithromycin was examined alone or in combination with other drugs for the treatment of acute or chronic infections with Toxoplasma gondii in mice. A dose of 300 mg of clarithromycin per kg per day administered alone for 10 days, beginning 24 hours after infection, protected 10 to 30% of mice infected with lethal inocula of tachyzoites or tissue cysts of different strains of T. gondii, including some strains isolated from patients with both AIDS and toxoplasmosis. Although clarithromycin was protective, a wide variation in its activity against different strains was observed. Survival of infected mice was increased significantly by treatment with clarithromycin in combination with pyrimethamine or with sulfadiazine. Treatment of chronically infected mice with clarithromycin at 300 mg/kg/day administered alone for 8 weeks resulted in significant reduction in the numbers of T. gondii cysts in their brains. The combination of clarithromycin and minocycline resulted in an activity against T. gondii cysts that was significantly greater than the activity of clarithromycin or minocycline administered alone. These results indicate a role for clarithromycin in the treatment of human toxoplasmosis, particularly when this antibiotic is used in combination with other drugs with activity against T. gondii.

Azithromycin: the first azalide antibiotic

OBJECTIVE

To discuss the chemistry, mechanism of action, spectrum of activity, pharmacokinetics, clinical trials, adverse-effect profile, drug interactions, and dosage guidelines of azithromycin, the first azalide antibiotic.

DATA SOURCES

Pertinent literature published between 1988 and the present was identified via a MEDLINE search. Of 77 articles retrieved, 37 have been referenced.

STUDY SELECTION

Azithromycin is a new agent, and as such, limited data regarding this drug are available in the literature. We evaluated all pharmacokinetic, microbiologic, and basic science articles pertaining to azithromycin, and reviewed the clinical efficacy trials that we believed were of good quality for each indication for which azithromycin has received approval to date. Comparative clinical trials involving large numbers of patients, clinical outcome assessments, and recommendations for azithromycin use are included.

DATA SYNTHESIS

Azithromycin is a macrolide derivative and the first of the 15-membered ring azalide class of antimicrobials. Although its mechanism of action and susceptibility to resistance are similar to those of the macrolide antibiotics, azithromycin's extended spectrum of activity includes gram-positive and gram-negative organisms, as well as atypical pathogens. Azithromycin is stable at gastric pH and has an absolute bioavailability of approximately 37 percent following oral administration. Although its serum concentrations are typically low, the drug concentrates to a high degree in tissue. Azithromycin is cleared primarily by the biliary and fecal routes; its serum half-life is in excess of 60 hours. Several clinical trials have proven that a 5-day course of azithromycin administered once a day is equally efficacious to a 7- to 14-day course of other commonly used oral antimicrobials, administered two to four times a day, for the treatment of upper and lower respiratory tract and skin and skin-structure infections. Urethritis and cervicitis caused by chlamydia are treated with a single 1-g dose. Trials have shown azithromycin's adverse-effect profile to be equal or even superior to that of other agents, with only 0.7 percent of patients discontinuing therapy versus 2.6 percent for comparable drugs.

CONCLUSIONS

Azithromycin represents a significant improvement in the treatment of selected community-acquired infections. Although this agent may revolutionize the treatment of sexually transmitted diseases caused by chlamydia, it also should impact the management of respiratory tract and skin and skin-structure infections. Because of its unique pharmacokinetics and excellent adverse-effect profile, patient compliance should be greatly enhanced compared with other commonly used oral antimicrobials. Azithromycin's primary role in the near future will be in the community setting. Although its use in the hospital may be limited, this drug will be a convenient therapeutic option to have on hand in the emergency room and outpatient clinic. Azithromycin may also be used in the future to treat opportunistic infections in immunocompromised patients.

Synergistic activity of azithromycin and pyrimethamine or sulfadiazine in acute experimental toxoplasmosis

The efficacy of azithromycin administered alone or combined with pyrimethamine or sulfadiazine was examined in a murine model of acute toxoplasmosis. Outbred Swiss mice acutely infected with tachyzoites of the virulent RH strain were treated for 10 days from day +1 postinfection. The efficacy of each regimen was assessed in terms of survival rates and sequential titration of parasites in blood, brain, and lungs by using a tissue culture method. Administration of azithromycin at 300, 150, or 75 mg/kg of body weight per day resulted in prolonged survival relative to that of untreated controls; sequential examination of parasite burden showed early eradiaction of Toxoplasma gondii from the lungs, whereas dissemination to the brain was not prevented. A remarkable synergistic effect was observed when azithromycin (150 mg/kg/day) was administered in combination with pyrimethamine or sulfadiazine at noncurative dosages, i.e., 12.5 and 200 mg/kg/day, respectively. In mice treated with azithromycin plus sulfadiazine and azithromycin plus pyrimethamine, parasite burdens in blood and organs, relapses after cessation of therapy, and mortality were all markedly reduced relative to mice treated with any of the agents alone. These results show that azithromycin, which is remarkably active on pulmonary Toxoplasma infection, significantly potentiates the curative effect of sulfadiazine or pyrimethamine.

Synergistic combination of azithromycin and sulfadiazine for treatment of toxoplasmosis in mice

Experiments were performed in vivo in a mouse model of acute toxoplasmosis to evaluate the effectiveness of the combination azithromycin/sulfadiazine. Azithromycin alone or sulfadiazine alone, at doses that did not provide any protection against death due to toxoplasmosis, were remarkably and significantly synergistic against murine toxoplasmosis when administered in combination.

Coccidian infections in AIDS. Toxoplasmosis, cryptosporidiosis, and isosporiasis

Cryptosporidium sp. and Isospora belli are coccidian protozoan parasites that were long recognized as pathogens for many animal species. The medical community became acquainted with these organisms with the advent of AIDS. Both parasites are associated with persistent, debilitating enteritis and, in the case of Cryptosporidium, biliary tract involvement in patients with AIDS. For the immunocompetent host, infection with these two pathogens usually results in self-limited diarrhea. Cryptosporidiosis appears to occur more often than isosporiasis, but the true prevalence of both infections for various populations of humans is unknown. Clinically, cryptosporidiosis is indistinguishable from isosporiasis. Diagnosis is based on finding the acid-fast (red staining oocyst in stained fecal specimens). There is no known effective therapy for cryptosporidiosis, whereas patients with isosporiasis respond promptly to treatment with trimethoprim-sulfamethoxazole. Patients with AIDS and isosporiasis have a high relapse rate after achieving complete remission and therefore need to be maintained on suppressive therapy. Much more needs to be learned about these two fascinating, "newly recognized" parasites.

Spectrum of activity of azithromycin

In recent years, a number of newer macrolides have been developed. One such antibiotic is azithromycin, which has a 15-membered ring structure and is classed as an azalide. The limitations of erythromycin and the discovery of pathogenic bacteria such as Campylobacter, Legionella and Chlamydia species provide incentives to study the usefulness of newer antibiotics of this class. Azithromycin has good activity against staphylococci, streptococci, Moraxella catarrhalis and other rapidly growing pyogenic bacteria. The good activity of azithromycin against Haemophilus influenzae (MIC90 0.5 mg/l) is particularly important as erythromycin has only marginal activity against this organism. Azithromycin has also been shown to be more potent than the macrolides against Enterobacteriaceae. In common with erythromycin and tetracycline, the agent has good activity against Legionella, Chlamydia and Campylobacter. Opportunistic infections involving Toxoplasma gondii and Pneumocystis carinii are an increasing problem and azithromycin is particularly interesting in view of its activity against these difficult-to-treat organisms.

Pyrimethamine-clarithromycin combination for therapy of acute Toxoplasma encephalitis in patients with AIDS

Clarithromycin, a new macrolide, is effective in treating experimental Toxoplasma gondii infection. A pyrimethamine-clarithromycin combination was evaluated for the treatment of acute Toxoplasma encephalitis in 13 AIDS patients. The scheduled regimen was 2 g of clarithromycin per day and 75 mg of pyrimethamine per day for 6 weeks. The protocol was completed in eight patients and stopped in five patients (because of voluntary withdrawal by two patients, deterioration of neurological condition and thrombocytopenia in two patients, and suspicion of liver toxicity in one patient). The clinical and computed tomography scan responses at week 6 of treatment were 80 and 50%, respectively. Two patients died, one of toxoplasmic encephalitis and the other of cerebral bleeding due to pyrimethamine-induced thrombocytopenia. Adverse events related to therapy were nausea and/or vomiting (38%), skin rash (38%), significant increase of liver tests (24%), hearing loss (15%), and severe hematological abnormalities (31%). In this pilot study, a pyrimethamine-clarithromycin combination was shown to be comparable to the conventional regimen for the treatment of acute Toxoplasma encephalitis in AIDS patients.

Clinical microbiology of azithromycin

Azithromycin contains an aza-methyl substitution in the 15-membered aglycone ring and as such it is the prototype antibiotic of the azalide class, similar in mechanism of activity to the macrolides. It demonstrates a broad spectrum of activity against many aerobic and anaerobic Gram-positive species, and also inhibits a number of important aerobic and anaerobic Gram-negative bacteria. Significantly, azithromycin shows good activity against Haemophilus influenzae, an organism against which older macrolide antibiotics have proved disappointing. It is highly effective in inhibiting clinically significant intracellular pathogens such as Chlamydia trachomatis and Legionella. Bactericidal activity is seen for certain streptococci and for H. influenzae. Closely linked with azithromycin's microbiologic activity are its novel pharmacokinetics. Azithromycin moves rapidly from blood to tissue compartments where it remains for prolonged periods. Although serum concentrations remain low, the levels attained in the tissues (often greater than 2 mg/kg) are higher than the minimum inhibitory concentration for many common pathogens, and delivery of drug to infection sites by phagocytic cells contributes to these concentrations. This penetration into eukaryotic and prokaryotic cells may be responsible for azithromycin's expanded spectrum of activity, particularly against intracellular organisms. The use of antibiotic blood levels as breakpoints for susceptibility would appear to be inappropriate in the case of azalides. Rather, levels of drug at the tissue site of infection should be considered as guides to predicting efficacy. The in vitro activity of azithromycin, together with its unique tissue pharmacodynamics, define an agent that should demonstrate utility in infections of the respiratory tract, skin and skin structures, and certain sexually transmitted diseases.

In vivo activity of the macrolide antibiotics azithromycin, roxithromycin and spiramycin against Toxoplasma gondii

The macrolide antibiotics azithromycin, roxithromycin and spiramycin were examined in parallel for in vivo activity against Toxoplasma gondii. Azithromycin was considerably more active in protecting mice against death due to acute toxoplasmosis even when the other two antibiotics were used at twice its dose. The higher activity of azithromycin prompted a further examination of its activity against five different strains of Toxoplasma gondii, including two isolated from patients with AIDS. Although variable degrees of protection against death were noted, treatment with 200 mg/kg/day for ten days was sufficient to promote survival of 100% of mice infected with inocula as high as 1 x 10(5) tachyzoites of Toxoplasma gondii. 90% of mice inoculated with 1 x 10(5) tachyzoites of strain MO, isolated from an AIDS patient, and treated orally with 200 mg/kg/day for ten days survived the infection whereas only 40% of mice infected with the same inoculum of the SOU strain, also isolated from an AIDS patient, survived. Tissue concentrations of azithromycin were examined in treated infected and non-infected mice. In both groups of mice azithromycin attained high concentrations in liver, spleen and heart, which exceeded concurrent serum levels by 25- to 200-fold. The concentrations in the brain were almost tenfold higher than the concentrations in serum after treatment with 200 mg/kg/day for ten days. Moreover, the concentrations in brains of infected mice were approximately two-fold higher than in brains of non-infected mice.

Comparative activity of macrolides against Toxoplasma gondii demonstrating utility of an in vitro microassay

The utility of spiramycin for preventing transplacental transmission of toxoplasmosis and the efficacy of conventional macrolides against Toxoplasma gondii are subjects of active debate. An in vitro microassay was developed to determine the relative inhibitory activity against T. gondii of 24 conventional macrolides derived from erythromycin and tylosin (14- and 16-membered macrolides, respectively). Macrolides and T. gondii RH tachyzoites were added to monolayers of BT cells grown in 96-well plates. Plates were incubated for 20 h at 37 degrees C, and the growth of T. gondii was then measured by the selective incorporation of [3H]uracil in trichloroacetic acid-precipitable material during an additional incubation of 20 h. Dose-response curves and 50 and 90% inhibitory concentrations (IC50 and IC90, respectively) were determined for each drug. Microscopic examination was performed on stained replicates of the infected monolayers, and the relative toxicities of the drugs for host cells were determined. Spiramycin and tylosin showed only limited activity against T. gondii (IC50 of 20.16 and 20.00 micrograms/ml, respectively). Erythromycin and azithromycin had a better anti-Toxoplasma activity with IC50 of 14.38 and 8.61 micrograms/ml, respectively, whereas drugs like desmycosin, dirithromycin, and roxithromycin had no detectable activity. Although many macrolides inhibited intracellular proliferation of T. gondii, azithromycin was the only macrolide demonstrating prolonged inhibitory activity on the replication of intracellular tachyzoites. We conclude that conventional 14- and 16-membered macrolides often interfere with the growth of, but may not kill, T. gondii RH tachyzoites in vitro.

Effect of clindamycin on pneumonia from reactivation of Toxoplasma gondii infection in mice

Clindamycin was used to treat the reactivation of a chronic Toxoplasma gondii infection in mice. Clindamycin reduced mortality by 44% when used prophylactically (P less than 0.001) but appeared to be less effective when used to treat clinically apparent reactivation. Further studies should be conducted to establish the efficacy of clindamycin for the treatment of toxoplasmosis in humans.