Azithromycin, a macrolide antibiotic with potent activity against Toxoplasma gondii

Disturbance of fetal growth by azithromycin through induction of ER stress in the placenta

AIM

Azithromycin (AZM) is widely used to treat mycoplasma infection in pregnancy. However, there is no adequate evaluation of its side effect on the placenta. Here, by using human placental syncytiotrophoblasts and a mouse model, we investigated whether AZM use in pregnancy might adversely affect placental function and pregnancy outcome.

RESULTS

Transcriptomic analysis of AZM-treated human placental syncytiotrophoblasts showed increased expression of ER stress-related genes and decreased expression of genes for hormone production and growth factor processing. Verification studies showed that AZM increased the abundance of ER stress mediators (phosphorylated eIF2α, ATF4 and CHOP), and decreased the abundance of enzymes involved in progesterone and estradiol synthesis (STS, CYP11A1 and CYP19A1) and IGFBP cleavage (PAPPA and ADAM12) in human placental syncytiotrophoblasts. Inhibition of ER stress blocked AZM-induced decreases in the expression of CYP19A1, CYP11A1, PAPPA and ADAM12, suggesting that the inhibition of AZM on those genes' expression was secondary to AZM-induced ER stress. Further mechanism study showed that increased ATF4 in ER stress might repressively interact with C/EBPα to suppresstheexpression ofthose genes including CEBPAitself. Mouse studies showed that AZM administration decreased fetal weights along with increased ER stress mediators and decreased levels of insulin-like growth factor, estrogen and progesterone in the maternal blood, which could be alleviated by inhibition of ER stress.

INNOVATION AND CONCLUSION

These findings firstly support AZM, often used during pregnancy, may affect fetal growth by inhibiting crucial enzymes for estrogen and progesterone synthesis and disrupting crucial proteases for IGFBP cleavage via inducing ER stress in placental syncytiotrophoblasts.

Azithromycin concentration in rabbits' plasma and posterior segment of the eyes following oral drug administration: a dose-finding study for the application in ocular toxoplasmosis

INTRODUCTION

Azithromycin has been used as an ocular toxoplasmosis alternative treatment due to its pharmacokinetic profiles. However, sufficient concentrations to promote toxoplasmosis eradication is still unknown. This study was aimed to evaluate azithromycin levels in rabbits after three regimens equivalent to human doses for ocular toxoplasmosis.

METHODS

Three groups of New Zealand albino rabbits were given one of the following: azithromycin at 26 mg/kg BW daily (Group 1), 26 mg/kg BW every two days (Group 2), and 50 mg/kg BW once weekly (Group 3) for 14 days. Plasma and ocular azithromycin concentrations were examined.

RESULTS

Following 14 days, median ratio of plasma maximum azithromycin concentration to the minimum inhibitory concentration for Toxoplasma gondii (C-max/MIC) for Group 1, and 2 were 51.29, 5.33, while Group 3 was undetected. The median azithromycin concentration in the retina-choroid was higher than the MIC in Group 1 (1356.0 ng/ml) and Group 2 (189.0 ng/ml), but not in Group 3.

CONCLUSION

Azithromycin administered orally at the dose of 26 mg/kg BW daily or 26 mg/kg BW every two days resulted a sufficient criteria of C-max/MIC as well as retina-choroid concentration needed for its parasiticidal activity. However, well-conducted clinical trial is warranted to support its therapeutic potential in ocular toxoplasmosis.

Use of Azithromycin in Pregnancy: More Doubts than Certainties

Macrolides such as azithromycin are commonly prescribed antibiotics during pregnancy. The good oral bioavailability and transplacental transfer of azithromycin make this drug suitable for the treatment of sexually transmitted diseases, toxoplasmosis, and malaria. Moreover, azithromycin is useful both in the management of preterm pre-labor rupture of membranes and in the adjunctive prophylaxis for cesarean delivery. The aim of this comprehensive narrative review is to critically analyze and summarize the available literature on the main aspects of azithromycin use in pregnant women, with a special focus on adverse offspring outcomes associated with prenatal exposure to the drug. References for this review were identified through searches of MEDLINE, PubMed, and EMBASE. Fetal and neonatal outcomes following prenatal azithromycin exposure have been investigated in several studies, yielding conflicting results. Increased risks of spontaneous miscarriage, major congenital malformations, cardiovascular malformations, digestive system malformations, preterm birth, and low birth weight have been reported in some studies but not in others. Currently, there is no conclusive evidence to support that azithromycin use by pregnant women causes adverse outcomes in their offspring. Therefore, this agent should only be used during pregnancy when clinically indicated, if the benefits of treatment are expected to outweigh the potential risks.

Treatment of toxoplasmic encephalitis with the combination of clindamycin plus azithromycin in an HIV-infected patient: A case report

The existence of alternative oral therapies could help clinicians to treat toxoplasmic encephalitis (TE) in the HIV patients. The combination of azithromycin and clindamycin may serve as an effective treatment for TE in HIV-infected patients.

Biogenesis and maintenance of the apicoplast in model apicomplexan parasites

The apicoplast is a non-photosynthetic relict plastid of Apicomplexa that evolved from a secondary symbiotic system. During its evolution, most of the genes derived from its alga ancestor were lost. Only genes involved in several valuable metabolic pathways, such as the synthesis of isoprenoid precursors, heme, and fatty acids, have been transferred to the host genome and retained to help these parasites adapt to a complex life cycle and various living environments. The biological function of an apicoplast is essential for most apicomplexan parasites. Considering their potential as drug targets, the metabolic functions of this symbiotic organelle have been intensively investigated through computational and biological means. Moreover, we know that not only organellar metabolic functions are linked with other organelles, but also their biogenesis processes have developed and evolved to tailor their biological functions and proper inheritance. Several distinct features have been found in the biogenesis process of apicoplasts. For example, the apicoplast borrows a dynamin-related protein (DrpA) from its host to implement organelle division. The autophagy system has also been repurposed for linking the apicoplast and centrosome during replication and the division process. However, many vital questions remain to be answered about how these parasites maintain and properly inherit this symbiotic organelle. Here we review our current knowledge about its biogenesis process and discuss several critical questions remaining to be answered in this field.

Drugs in development for toxoplasmosis: advances, challenges, and current status

Toxoplasma gondii causes fatal and debilitating brain and eye diseases. Medicines that are currently used to treat toxoplasmosis commonly have toxic side effects and require prolonged courses that range from weeks to more than a year. The need for long treatment durations and the risk of relapsing disease are in part due to the lack of efficacy against T. gondii tissue cysts. The challenges for developing a more effective treatment for toxoplasmosis include decreasing toxicity, achieving therapeutic concentrations in the brain and eye, shortening duration, eliminating tissue cysts from the host, safety in pregnancy, and creating a formulation that is inexpensive and practical for use in resource-poor areas of the world. Over the last decade, significant progress has been made in identifying and developing new compounds for the treatment of toxoplasmosis. Unlike clinically used medicines that were repurposed for toxoplasmosis, these compounds have been optimized for efficacy against toxoplasmosis during preclinical development. Medicines with enhanced efficacy as well as features that address the unique aspects of toxoplasmosis have the potential to greatly improve toxoplasmosis therapy. This review discusses the facets of toxoplasmosis that are pertinent to drug design and the advances, challenges, and current status of preclinical drug research for toxoplasmosis.

Azithromycin versus Sulfadiazine and Pyrimethamine for non-vision-threatening toxoplasmic retinochoroiditis: a pilot study

Background

The purpose of this pilot study is to compare the efficacy and tolerance of azithromycin alone as opposed to standard treatment with sulfadiazine and pyrimethamine for active, non-vision-threatening toxoplasmic retinochoroiditis.

Material/Methods

We conducted a prospective, randomized, institutional clinical study comparing azithromycin to sulfadiazine and pyrimethamine for active, non-vision-threatening toxoplasmic retinochoroiditis. Nineteen out of 75 patients fulfilled inclusion criteria and were randomized into 2 treatment regimens. Nine patients were treated with sulfadiazine and pyrimethamine and 10 patients with azithromycin at a dose of 500 mg qd. Main outcome measures assessed were time to sharpening of lesion borders, time to lesion scarring, time to disease inactivity, and treatment tolerance.

Results

Azithromycin monotherapy achieved lesion scarring and disease inactivity in all but 1 patient. Although no statistically significant difference was found between the 2 patient groups as regards main outcome measures for treatment efficacy, all median times to endpoints (days) were longer for the azithromycin group – time to sharpening of lesion borders on clinical evaluation (25.5 vs. 24) and masked evaluation of photographs (30.5 vs. 24), time to lesion scarring on clinical evaluation (73 vs. 47) and masked evaluation of photographs (71.5 vs. 36) and time to disease inactivity (73 vs. 49). Treatment tolerance was significantly better for the azithromycin group (p=0.0005).

Conclusions

Azithromycin monotherapy at a dose of 500 mg per day was shown to be effective and well-tolerated for the treatment of active, non-vision-threatening toxoplasmic retinochoroiditis. Duration of treatment was clinically longer for the azithromycin group.

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.

Toxoplasmosis during pregnancy: a case report and review of the literature

Although toxoplasmosis is considered harmless for a non-pregnant woman, it is potentially harmful during pregnancy, especially at first trimester. The aim of this study is to increase our alertness and monitoring in case of toxoplasmosis during pregnancy, given that when diagnosed it can be effectively treated.We present a case of a healthy 26 years old adult woman, found with toxoplasmosis during the 13th week of pregnancy. The role of frequent maternal and fetus immunological tests, PCR-tests of the amniotic fluid and ultrasound screening of the fetus throughout pregnancy was of great value. The patient was treated with spiramycin (1 grx3) from the 16th week of pregnancy. The patient was subjected to cesarean delivery at the 36th week of pregnancy due to preterm contractions and history of previous cesarean delivery. The newborn was a healthy girl with a birth weight of 2880 gr. A two-year follow up of the baby revealed no medical condition. Maternal infections are a serious medical condition during pregnancy. Toxoplasmosis when diagnosed on time and treated properly can lead to healthy offspring.

Engineering the rRNA decoding site of eukaryotic cytosolic ribosomes in bacteria

Structural and genetic studies on prokaryotic ribosomes have provided important insights into fundamental aspects of protein synthesis and translational control and its interaction with ribosomal drugs. Comparable mechanistic studies in eukaryotes are mainly hampered by the absence of both high-resolution crystal structures and efficient genetic models. To study the interaction of aminoglycoside antibiotics with selected eukaryotic ribosomes, we replaced the bacterial drug binding site in 16S rRNA with its eukaryotic counterpart, resulting in bacterial hybrid ribosomes with a fully functional eukaryotic rRNA decoding site. Cell-free translation assays demonstrated that hybrid ribosomes carrying the rRNA decoding site of higher eukaryotes show pronounced resistance to aminoglycoside antibiotics, equivalent to that of rabbit reticulocyte ribosomes, while the decoding sites of parasitic protozoa show distinctive drug susceptibility. Our findings suggest that phylogenetically variable components of the ribosome, other than the rRNA-binding site, do not affect aminoglycoside susceptibility of the protein-synthesis machinery. The activities of the hybrid ribosomes indicate that helix 44 of the rRNA decoding site behaves as an autonomous domain, which can be exchanged between ribosomes of different phylogenetic domains for study of function.

Mitochondrial ribosome as the target for the macrolide antibiotic clarithromycin in the helminth Echinococcus multilocularis

The mitochondrial rRNA of the tapeworm species Echinococcus multilocularis carries an adenine at sequence position 2058 (numbering according to that for Escherichia coli) of the large-subunit rRNA (lsrRNA), while the nucleus-encoded rRNA, as determined in this study, is characterized by 2058G. This indicates a dichotomy in the drug susceptibilities of ribosomes: cytoplasmic ribosomes are predicted to be resistant to macrolide antibiotics, while mitochondrial ribosomes lack the most common chromosomal resistance determinant, lsrRNA 2058G. Upon incubation with the macrolide clarithromycin, the formation of vesicles from metacestode tissue was reduced in a dose-dependent manner. Electron microscopy revealed distinct morphological alterations both of the mitochondria and of the vesicle wall (e.g., loss of microtriches) in drug-treated vesicles. Adult worms lost their motility and displayed morphological changes (shortening and constriction of proglottids and the presence of vacuoles) upon incubation with clarithromycin. Our findings demonstrate that macrolides have distinct in vitro effects on E. multilocularis, endorsing the use of sequence-based in silico approaches for exploitation of available ribosomal drugs as anthelmintic agents.

Avaliação da eficácia da azitromicina e pirimetamina em camundongos infectados por cepa cistogênica de Toxoplasma gondii

Foi avaliada a eficácia da administração prolongada de azitromicina e pirimetamina em camundongos infectados com cepa cistogênica de Toxoplasma gondii. Os animais foram inoculados intraperitonealmente com um cisto de T. gondii e, após 20 dias, divididos em quatro grupos: GI infectados não tratados, GII infectados e tratados concomitantemente com pirimetamina (12,5mg/kg/dia) e azitromicina (100mg/kg/dia), GIII infectados e tratados com a mesma dose de pirimetamina e GIV infectados e tratados da mesma forma com azitromicina. O tratamento, via oral, estendeu-se por 120 dias; após este período os animais foram sacrificados e foi feita a contagem dos cistos no cérebro. A associação de ambos os medicamentos proporcionou melhores resultados, diminuindo a contagem de cistos no cérebro dos animais tratados de forma concomitante.

Efficacy of azithromycin in a murine toxoplasmosis model, employing a Toxoplasma gondii strain from Turkey

A murine toxoplasmosis model with Balb/C mice was used to investigate the therapeutic and prophylactic efficacy of azithromycin in a native strain of Toxoplasma gondii. Initially, seven groups--four studies and three controls--were established and 10(3) tachyzoites of this native strain of T. gondii were injected intraperitoneally to the mice in groups 1, 2, 3, 4 and 7. Azithromycin was given to groups 1-4 at different times of infection orally between 100 and 300 mg/kg/day for 10 days. Azithromycin was found to be effective at 200 mg/kg/day and above in the prophylaxis, at 250 mg/kg/day and above in the treatment of toxoplasmosis. These results suggest that azithromycin is effective in the prophylaxis and early infection of a highly virulent strain of T. gondii, and it doubled the survival time in the late infection. Azithromycin could be an alternative treatment regimen for human toxoplasmosis, if supported by further clinical investigations.

Maternal and transplacental pharmacokinetics of azithromycin

OBJECTIVE

The purpose of this study was to characterize the pharmacokinetics of orally administered azithromycin in the term gravid woman.

STUDY DESIGN

Twenty women who were scheduled for elective cesarean delivery were enrolled prospectively and received 1 g of oral azithromycin at either 6, 12, 24, 72, or 168 hours before the operation. All women received spinal anesthesia, at which time a sample of cerebrospinal fluid was obtained for analysis. Maternal serum and urine were obtained immediately before the operation. Intraoperatively, samples of myometrium, maternal adipose tissue, placenta, amniotic fluid, and umbilical arterial and venous cord blood were obtained. Azithromycin levels were determined quantitatively with high-pressure liquid chromatography with electrochemical detection.

RESULTS

All participants tolerated the preoperative azithromycin without significant adverse reactions. Peak maternal serum azithromycin levels occurred within 6 hours of drug administration. Although high serum levels of azithromycin were reached early, a rapid decline in drug concentration was noted over the initial 24 hours after the drug administration (6-hour: 311 ng/mL; 24-hour: 63 ng/mL). In contrast, azithromycin levels in myometrial, adipose, and placental tissue were higher (>500 ng/mL) and sustained for up to 72 hours after administration. High urine levels of azithromycin (>5000 ng/mL) were noted similarly during the initial 72 hours after drug administration. Umbilical arterial and venous serum azithromycin levels were low (19-38 ng/mL) during the first 72 hours. Amniotic fluid levels were highest at 6 hours (151 ng/mL) and declined rapidly. Maternal cerebrospinal azithromycin concentrations were undetectable for all time points.

CONCLUSION

Azithromycin has a rapid serum half-life in the term gravid woman with a prolonged half-life and high-sustained antibiotic levels noted within myometrium, adipose, and placental tissue. Given the broad antimicrobial spectrum and placental penetration, azithromycin may have potential use for the treatment of perinatal infections.

Dose-escalation, phase I/II study of azithromycin and pyrimethamine for the treatment of toxoplasmic encephalitis in AIDS

OBJECTIVE

To assess the safety, tolerance and activity of increasing doses of azithromycin in combination with pyrimethamine for the treatment of toxoplasmic encephalitis (TE) in patients with AIDS.

DESIGN

A phase I/II dose-escalation study of oral azithromycin in combination with pyrimethamine.

SETTING

Eight clinical sites in the United States.

PATIENTS

Forty-two adult HIV-infected patients with confirmed or presumed acute TE.

METHODS

Patients were enrolled into three successive cohorts receiving azithromycin 900, 1200 and 1500 mg a day with pyrimethamine as induction therapy. The induction period was 6 weeks followed by 24 weeks of maintenance therapy.

MAIN OUTCOME MEASURES

Patient response was evaluated clinically and radiologically.

RESULTS

Of the 30 evaluable patients, 20 (67%) responded to therapy during the induction period. Ten experienced disease progression. Of the 15 patients who received maintenance therapy, seven (47%) relapsed. Six patients discontinued treatment during the induction period as a result of reversible toxicities. Treatment-terminating adverse events occurred most frequently among the patients receiving the 1500 mg dose.

CONCLUSION

The combination of azithromycin (900-1200 mg a day) and pyrimethamine may be useful as an alternative therapy for TE among patients intolerant of sulfonamides and clindamycin, but maintenance therapy with this combination was associated with a high relapse rate. The combination was safe, but low-grade adverse events were common.

The transplacental transfer of the macrolide antibiotics erythromycin, roxithromycin and azithromycin

OBJECTIVE

To investigate the transplacental transfer of the macrolide antibiotics erythromycin, roxithromycin and azithromycin.

METHODS

Twenty-one term placentas were obtained with maternal consent immediately after delivery and a two-hour nonrecirculating perfusion of a single placental cotyledon was performed. Erythromycin (2 microg/mL), roxithromycin (2 microg/mL) and azithromycin (0.3 microg/mL) were infused to the maternal inflow at a constant rate, with antipyrine as a reference compound, and their appearance in the fetal circulation was followed. Drug concentrations were measured by high performance liquid chromatography for 120 min.

RESULTS

The mean transplacental transfers (TPT(SS)) for erythromycin, roxithromycin and azithromycin were 3.0%, 4.3% and 2.6%, respectively, calculated as the ratio between the steady state concentrations in fetal venous and maternal arterial sides. Similar results were obtained when the TPT was calculated as the absolute amount of drug transferred across the placenta during 2-hour perfusion (TPT(A)). No significant differences were found among the three macrolides in TPT(SS) (P = 0.39) or TPT(A) (P = 0.35). The TPT(SS) of erythromycin, roxithromycin and azithromycin were 41%, 35% and 32% of the freely diffusable reference compound antipyrine, respectively. Steady state was reached in 60 minutes in each perfusion indicating sufficient perfusion time.

CONCLUSION

The limited transplacental transfer of erythromycin, roxithromycin and azithromycin suggests compromised efficacy in the treatment of fetal infections. On the other hand, the placenta seems to produce an effective barrier reducing the fetal exposure when these three macrolides are used to treat maternal infections.

Evaluation of the efficacy of atovaquone alone or in combination with azithromycin against acute murine toxoplasmosis

Mice were infected intraperitoneally with 10,000 tachyzoites of Toxoplasma gondii (RH) strain and, 24 h later, were treated orally for 10 days with atovaquone and azithromycin, either alone or in combination. Evaluation of the efficacy of the drugs was performed by microscopic examination of smears prepared from the organs of the mice, and by subinoculation of visceral and brain suspensions from surviving mice into healthy mice at the end of the experiments. It was found that 58%, 83% and 100% of the mice survived after administration of 75, 150 or 200 mg/kg per day of azithromycin, respectively. Moreover, 8%, 17% and 25% of the mice survived after treatment with atovaquone at 20, 50 or 100 mg/kg per day, respectively. No synergistic or additive effects of combinations of atovaquone and azithromycin were observed. However, azithromycin did not eradicate the parasite from the brain and viscera of the infected mice, whereas atovaquone at 20, 50 and 100 mg/kg per day removed the parasite from viscera and at 100 mg/kg per day eradicated the parasite from the brain of infected mice. The combinations of atovaquone and azithromycin failed to completely eradicate the parasite from the brain and viscera of infected mice.

Azithromycin: antimalarial profile against blood- and sporozoite-induced infections in mice and monkeys

The spectrum of antimalarial activity of the new macrolide antibiotic azithromycin was evaluated against blood- and sporozoite-induced infections with a chloroquine-resistant strain of Plasmodium yoelii nigeriensis (N-67) in Swiss mice and with simian parasite Plasmodium cynomolgi B in rhesus monkeys. Against experimental rodent malaria, a 70 mg/kg/day dose showed curative blood-schizontocidal activity in a four-dose regimen administered orally from day 0 to day 3 or from day 2 to day 5 to mice harboring established infection. The curative response was also obtained with a 40 mg/kg/day dose administered in an extended seven-dose (days 0-6) regimen. Azithromycin was also effective in the causal prophylactic test, since a 50 mg/kg dose from day -1 to day +2 protected mice against P. y. nigeriensis (N-67) sporozoite challenge. In comparison, erythromycin did not show either of the above activities up to a 405 mg/kg/day dose in identical regimens. Comparison of the ED(90) values showed that azithromycin was 31-fold more effective than erythromycin as a blood schizontocide. In the simian model, trophozoite-induced infections of P. cynomolgi B were cured with 25 mg/kg/day azithromycin administered for 7 days. In the causal prophylactic test, the prepatent period was significantly extended in monkeys challenged with P. cynomolgi B sporozoites, presumably because of the growth inhibition of preerythrocytic schizonts in hepatocytes. Azithromycin did not exhibit any hypnozoitocidal (dormant exoerythrocytic stages) activity at 25 mg/kg/day in a seven-dose regimen.

Quinupristin-dalfopristin is active against Toxoplasma gondii

Synercid and each of its components (quinupristin and dalfopristin) were examined for their activities against Toxoplasma gondii. In vitro, intracellular replication of tachyzoites was inhibited by synercid and each of its two components. The 50% inhibitory concentrations of synercid, quinupristin, and dalfopristin were 1.6, 2.7, and 6.3 microg/ml, respectively. Thus, synercid was markedly more active than its components. Treatment of acutely infected mice with 100 or 200 mg of synercid per kg of body weight per day administered intraperitoneally for 10 days resulted in survival of 50% (P = 0.0002) and 100% (P < 0.0001) of infected mice, respectively, whereas all control mice died by day 18. In contrast, treatment with 200 mg of either quinupristin and dalfopristin per kg per day alone resulted in only 20% survival; treatment with 50 mg of either drug per kg per day resulted only in the prolongation of time to death. These results suggest that synercid may be useful for treatment of toxoplasmosis in humans.

[The evaluation of the efficacy of azithromycin and pyrimethamine used alone or in combination in the treatment of an experimental infection in mice by Toxoplasma gondii]

The efficacy of azithromycin and pyrimethamine in experimental infection of mice with Toxoplasma gondii was tested. Daily dosages of 200 mg/kg and 12.5 mg/kg, respectively, were given orally over a period of ten days. The medications were administered in combination or separately. The combined use of the drugs yielded better results, and a similar investigation using a cystogenic strain of the parasite will be conducted in a future study.

The macrolides: erythromycin, clarithromycin, and azithromycin

In addition to erythromycin, macrolides now available in the United States include azithromycin and clarithromycin. These two new macrolides are more chemically stable and better tolerated than erythromycin, and they have a broader antimicrobial spectrum than erythromycin against Mycobacterium avium complex (MAC), Haemophilus influenzae, nontuberculous mycobacteria, and Chlamydia trachomatis. All three macrolides have excellent activity against the atypical respiratory pathogens (C. pneumoniae and Mycoplasma species) and the Legionella species. Azithromycin and clarithromycin have pharmacokinetics that allow shorter dosing schedules because of prolonged tissue levels. Both azithromycin and clarithromycin are active agents for MAC prophylaxis in patients with late-stage acquired immunodeficiency syndrome (AIDS), although azithromycin may be the preferable agent because of fewer drug-drug interactions. Clarithromycin is the most active MAC antimicrobial agent and should be part of any drug regimen for treating active MAC disease in patients with or without AIDS. Although both azithromycin and clarithromycin are well tolerated by children, azithromycin has the advantage of shorter treatment regimens and improved tolerance, potentially improving compliance in the treatment of respiratory tract and skin or soft tissue infections. Intravenously administered azithromycin has been approved for treatment of adults with mild to moderate community-acquired pneumonia or pelvic inflammatory diseases. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens, particularly Streptococcus pneumoniae, group A streptococci, and H. influenzae. The emergence of macrolide resistance with these common pathogens may limit the clinical usefulness of this class of antimicrobial agents in the future.

Effect of clarithromycin and azithromycin on production of cytokines by human monocytes

We examined the in vitro effect of clarithromycin and azithromycin on cytokine production by LPS and Pansorbin stimulated human monocytes. At concentrations that are physiologically achievable, both antibiotics affected in vitro production of IL-1alpha, IL-1beta, IL-6, IL-10, GM-CSF and TNF-alpha to varying degrees. Of those individuals in whom a significant increase or decrease in cytokine production was noted, clarithromycin treatment resulted in a significant suppression of production of each cytokine in 71% and a significant increase in 29% of the individuals. Similar results were noted with azithromycin. The results with IL-6 and TNF-alpha in the clarithromycin studies were most striking. A significant decrease was noted in 60% of individuals for IL-6 and 86% for TNF-alpha. For azithromycin, the most interesting results were for IL-1alpha (decrease in 100% of individuals) and for TNF-alpha (decrease in 100% of individuals). These results show that both clarithromycin and azithromycin alter cytokine production in human monocytes and thus possess immunomodulatory activity.

Simultaneous high-performance liquid chromatography analysis of azithromycin and two of its metabolites in human tears and plasma

This article describes a high-performance liquid chromatographic (HPLC) method for the measurement of azithromycin (AZI) and two of its metabolites, 9a-N-desmethylazithromycin (ADES) and N-desmethylazithromycin (NDES), in human tears and plasma. The drug, metabolites, and internal standard (n-propylazithromycin [IS]) were detected electrochemically after injection of the extracted sample into the HPLC system. The peak height ratio (AZI, ADES, or NDES to IS) varied linearly, with concentrations in the ranges of 0.1 mg/L to 2.0 mg/L (tears) and 0.01 mg/L to 2.0 mg/L (plasma) of AZI, ADES, and NDES; the correlation coefficient (r) was more than 0.994 mg/L for all of the compounds (n=6). The analysis of tear samples collected at different intervals within 12 hours to 144 hours after a dose of 20 mg/kg of AZI from a trachoma patient yielded concentrations ranging from 1.52 mg/L to 0.34 mg/L for AZI, 0.79 mg/L to 0.27 mg/L for ADES, and 1.99 mg/L to less than 0.20 mg/L for NDES. The concentration of AZI in plasma ranged from 0.15 mg/L to 0.01 mg/L, whereas ADES and NDES were undetectable.

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.

Effects of dual combinations of antifolates with atovaquone or dapsone on nucleotide levels in Plasmodium falciparum

The triazine antifolates, cycloguanil and 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-[(2,4,5-trichlorophenoxy)propy loxy]-1,3,5-triazine hydrobromide (WR99210), and their parent biguanide compounds, proguanil and N-[3-(2,4,5-trichlorophenoxy)propyloxy]-n-(1-methylethyl)-imido dicarbonimidic-diamine hydrochloride (PS-15), were tested in combination with a series of antimalarial drugs for synergism against Plasmodium falciparum growing in erythrocytic culture. Four synergistic combinations were found: cycloguanil dapsone, WR99210-dapsone, proguanil-atovaquone, and PS-15-atovaquone. Cycloguanil-dapsone or WR99210-dapsone had a profound suppressive effect on the concentration of dTTP in parasites while that of dATP increased. Depletion of dTTP is consistent with cycloguanil or WR99210 inhibiting dihydrofolate reductase and dapsone inhibiting dihydropteroate synthase. For the combinations proguanil-atovaquone and PS-15-atovaquone, the levels of nucleoside triphosphates (NTPs) and dNTPs were generally suppressed, suggesting that inhibition is not through nucleotide pathways but probably through another metabolic mechanism(s). Combinations of two synergistic pairs of antimalarial drugs, (proguanil-atovaquone)-(cycloguanil-dapsone) and (PS-15-atovaquone)-(WR99210-dapsone), were tested, and it was found that NTPs and dNTPs decreased much more than for a single synergistic combination. Dual synergistic combinations could play an important role in the therapy of multidrug-resistant malaria, just as combination chemotherapy is used to treat cancer.

Toxoplasmosis and parvovirus B19

Pregnant women might well improve their chances for a successful pregnancy outcome by following the advice of W. C. Fields: avoid contact with small children and animals whenever possible. Failing widespread acceptance of this philosophy, management of T. gondii and parvovirus B19 infections continues to be a challenge for the foreseeable future.

Treatment regimens for patients with toxoplasmic encephalitis

Toxoplasma gondii is an obligate intracellular parasitic protozoan that infects a variety of warm-blooded animals, including humans. Infection is usually asymptomatic in immunocompetent individuals but may be devastating in immunocompromised individuals such as those with acquired immunodeficiency syndrome (AIDS). Clinical manifestations of infection in immunocompromised patients include the development of encephalitis. It has been estimated that approximately 30% of patients with AIDS who are latently infected will eventually develop toxoplasmic encephalitis. The most common regimen used to treat toxoplasmic encephalitis is a combination of pyrimethamine 50 to 100 mg/d and sulfadiazine 4 to 8 g/d, with or without folinic acid 10 mg/d. This regimen, however, commonly leads to adverse effects or relapses. Other pharmacologic approaches include the use of clindamycin rather than sulfadiazine, the macrolide antibiotics, atovaquone, 5-fluorouracil, trimethoprim/sulfamethoxazole, minocycline or doxycycline, trimetrexate with folinic acid, dapsone, rifabutin, pentamidine, and diclazuril. None of these alternative regimens has been proven to be more effective than the standard pharmacologic therapy. An evolving approach is the use of immunotherapy, such as interleukin-2, -6, and -12; interferon-gamma; and alpha-tumor necrosis factor. Restoring a competent immune system may be the only cure for toxoplasmosis and other opportunistic infections.

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.

Diagnosis and Treatment of Toxoplasmosis of the CNS in Patients with AIDS

Toxoplasmic encephalitis is a very common opportunistic infection in patients with AIDS (occurring in 5 to 15% of cases). It is the most frequent CNS manifestation in patients with previous Toxoplasma infection, as determined by the presence of specific antibodies.A diagnosis of toxoplasmic encephalitis should be suspected in patients who present with clinical symptoms such as fever, headaches or any neurological abnormalities associated with the presence of intracerebral abscess on computerised tomography scans and/or magnetic resonance imaging. Early diagnosis leading to early treatment is the best prognostic factor for this treatable, but severe, disease.The diagnosis is assessed by the response to therapy with a combination of pyrimethamine (50 mg/day) and sulfadiazine (4 g/day), which should lead to improvement within 5 to 10 days. The duration of acute therapy should be 3 to 6 weeks. A combination of pyrimethamine plus clindamycin is second-line therapy in patients who are intolerant of pyrimethamine and sulfadiazine (30 to 50% of cases). Maintenance therapy should be life-long to avoid relapses.The widespread use of primary prophylaxis with cotrimoxazole (trimethoprim-sulfamethoxazole) or a combination of dapsone plus pyrimethamine in patients who are positive for antitoxoplasmic antibodies and have a CD4+ lymphocyte count of less than 200 cells/μl (200 × 10(6) cells/L) tends to decrease the incidence of toxoplasmic encephalitis. Physicians need to provide information to patients on the usefulness of primary prophylaxis to optimise compliance with treatments.

Distribution of azithromycin into brain tissue, cerebrospinal fluid, and aqueous humor of the eye

To measure the concentrations of azithromycin in the central nervous system, 20 patients with brain tumors (group I) received a single 500-mg oral dose of azithromycin either 24, 48, 72, or 96 h prior to the tumor removal operation and 10 patients with cataracts undergoing surgery (group II) and 7 patients scheduled to undergo lumbar puncture (group III) received the same dose of azithromycin 24 h prior to the operation or procedure. Serum from all patients, brain tissue from group I, aqueous humor from group II, and cerebrospinal fluid from group III were assayed for azithromycin concentration. The mean concentrations of azithromycin in brain tissue 24, 48, 72, and 96 h after administration were 2.63 +/- 2.58, 3.64 +/- 3.81, 0.74 +/- 0.37, and 0.41 micrograms/g, respectively. In contrast, the concentrations of azithromycin in cerebrospinal fluid and aqueous humor of the eye were very low or undetectable. Therefore, these data show that azithromycin appears to be widely distributed into brain tissue but not into cerebrospinal fluid or aqueous humor of the eye.

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.

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.

Activity of epiroprim (Ro 11-8958), a dihydrofolate reductase inhibitor, alone and in combination with dapsone against Toxoplasma gondii

We examined the effect of epiroprim (Ro 11-8958), a dihydrofolate reductase inhibitor, alone and in combination with dapsone, against Toxoplasma gondii. In vitro, the anti-T. gondii effects of epiroprim and dapsone were observed at nanogram-per-milliliter levels when a 72-h uracil assay and an infection rate of one parasite per 120 macrophages were used. In combination, these drugs exerted a synergistic effect that, however, was only parasitostatic. In a model of acute infection, mice were infected intraperitoneally with 10(4) parasites of the RH strain of T. gondii and were treated for 14 days by gavage (therapy divided into two daily dosages), starting 24 h after infection. Used alone, dapsone and epiroprim, each at a dose of 50 mg/kg of body weight per day, protected 10 and 0% of the mice, respectively. When these drugs were administered simultaneously, a 100% survival rate was observed. Pyrimethamine-sulfadiazine (4 and 250 mg/kg/day, respectively) protected 100% of the mice. A 3-week therapy of chronically infected mice with either epiroprim (50 mg/kg/day), dapsone (50 mg/kg/day), or pyrimethamine (15 mg/kg/day) reduced the numbers of T. gondii cysts and the inflammation in their brains. A combination of epiroprim and dapsone, both at 50 mg/kg/day, further reduced the number of brain cysts in comparison with the number after the corresponding monotherapies. Epiroprim may have a role in the prophylaxis or therapy of human toxoplasmosis, especially when combined with other drugs active against T. gondii, such as dapsone.

Localization of azithromycin in Toxoplasma gondii-infected cells

Agents effective against intracellular pathogens must enter infected cells, crossing vacuolar membranes surrounding the organisms and then penetrating into the microbe and localizing to the microbial target site. We have characterized these parameters for azithromycin entry into Toxoplasma gondii-infected Chinese hamster ovary cells and murine macrophage-like J774 cells. Azithromycin uptake into infected host cells was concentrative and was dependent upon proton gradients. Subcellular fractionation of azithromycin-loaded infected CHO cells demonstrated > 95% intracellular drug in host cell lysosomes and cytosol, with < 5% associated with the parasite. Uptake of azithromycin into the T. gondii vacuole increased if parasites were coated with antibody prior to internalization by murine J774 cells, conditions which result in the formation of acidified phagolysosomes. No redistribution or retention of azithromycin in the parasite was observed when drug efflux from antibiotic-loaded infected CHO cells was monitored. Azithromycin entry into extracellular T. gondii was concentrative, was temperature and pH dependent, and was not different when azithromycin-sensitive and -resistant parasites were compared. These results demonstrate that azithromycin concentrates primarily in acidified compartments in parasites and host cells. The high concentration of azithromycin within these compartments may not be biologically relevant to inhibition of intracellular parasite growth by this agent.

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.

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.