Interaction between posaconazole and amphotericin B in concomitant treatment against Candida albicans in vivo

In Vitro–In Vivo Correlation of Posaconazole–Amphotericin B Combination against Candida albicans: In Vitro Interacting Concentrations Are Associated with In Vivo Free Drug Levels

The in vitro/in vivo correlation of antifungal combination testing is necessary in order to assess the efficacy of combination regimens. We, therefore, attempted to correlate in vitro chequerboard testing of posaconazole (POS) and amphotericin B (AMB) with the in vivo outcome of combination therapy against experimental candidiasis in a neutropenic murine model. The AMB + POS combination was tested against a Candida albicans isolate. In vitro, a broth microdilution 8 × 12 chequerboard method with serial two-fold drug dilutions was used. In vivo, CD1 female neutropenic mice with experimental disseminated candidiasis were treated with i.p. AMB and p.o. POS alone and in combination at three effective doses (ED20, ED50 and ED80 corresponding to 20%, 50% and 80% of maximal effect, respectively). CFU/kidneys after 2 days were determined. The pharmacodynamic interactions were assessed based on Bliss independence interaction analysis. In vitro, a Bliss antagonism of −23% (−23% to −22%) was observed at 0.03–0.125 mg/L of AMB with 0.004–0.015 mg/L of POS, while a Bliss synergy of 27% (14%–58%) was observed at 0.008–0.03 mg/L of AMB with 0.000015–0.001 mg/L of POS. In vivo, Bliss synergy (13 ± 4%) was found when an AMB ED20 of 1 mg/kg was combined with all POS ED 0.2–0.9 mg/kg, while Bliss antagonism (35–83%) was found for the combinations of AMB ED50 2 mg/kg and ED80 3.2 mg/kg with POS ED80 of 0.9 mg/kg. Free drug serum levels of POS and AMB in in vivo synergistic and antagonistic combinations were correlated with the in vitro synergistic and antagonistic concentrations, respectively. Both synergistic and antagonistic interactions were found for the AMB + POS combination. POS compromised the efficacy of high effective AMB doses and enhanced low ineffective AMB doses. In vitro concentration-dependent interactions were correlated with in vivo dose-dependent interactions of the AMB + POS combination. In vivo interactions occurred at free drug serum levels close to in vitro interacting concentrations.

The Role of New Posaconazole Formulations in the Treatment of Candida albicans Infections: Data from an In Vitro Pharmacokinetic-Pharmacodynamic Model

Posaconazole is more active than fluconazole against Candida albicans in vitro and is approved for the treatment of oropharyngeal candidiasis but not for that of invasive candidiasis (IC). Here, we explored the efficacy of posaconazole against C. albicans in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model of IC and determined the probability of pharmacodynamic target attainment for the oral solution and intravenous (i.v.)/tablet formulations. Three clinical C. albicans isolates (posaconazole MICs, 0.008 to 0.25 mg/liter) were studied in the in vitro PK/PD dilution model simulating steady-state posaconazole PK. The in vitro exposure-effect relationship, area under the 24-h free drug concentration curve (fAUC_0-24)/MIC, was described and compared with in vivo outcome in animals with IC. PK/PD susceptibility breakpoints and trough levels required for optimal treatment were determined for EUCAST and CLSI 24-h/48-h (CLSI24h/CLSI48h) methods using the fAUC_0-24/MIC associated with half-maximal activity (EI₅₀) and Monte Carlo simulation analysis for oral solution (400 mg every 12 hours [q12h]) and i.v./tablet formulations (300 mg q24h). The in vitro mean (95% confidence interval [CI]) EI₅₀ was 330 (183 to 597) fAUC_0-24/MIC for CLSI24h and 169 (92 to 310) for EUCAST/CLSI48h methods, which are close to the near-stasis in vivo effect. The probability of target attainment for EI₅₀ was estimated; for the wild-type isolates (MIC ≤ 0.06 mg/liter), it was low for the oral solution and higher than 95% for the i.v./tablet formulations for the EUCAST/CLSI48h methods but not for the CLSI 24-h method. Non-wild-type isolates with EUCAST/CLSI48h MICs of 0.125 and 0.25 mg/liter would require trough levels of >1.2 and >2.4 mg/liter, respectively. Posaconazole i.v./tablet formulations may have a role in the therapy of invasive infections by wild-type C. albicans isolates, provided that a steady state is reached quickly. A PK/PD susceptibility breakpoint at the epidemiological cutoff (ECV/ECOFF) of 0.06 mg/liter was determined.

Combination of Posaconazole and Amphotericin B in the Treatment of Candida glabrata Biofilms

Candidemia cases have been increasing, especially among immunosuppressed patients. Candida glabrata is one of the most resistant Candida species, especially to the azole drugs, resulting in a high demand for therapeutic alternatives. The minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), and minimum biofilm eradication concentration (MBEC) were determined for posaconazole (Pcz) and amphotericin B (AmB). The drug combinations of both drugs were evaluated on pre-formed biofilms of C. glabrata ATCC 2001, through XTT (2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay, colony forming units (CFU), crystal violet, and the fractional inhibitory concentration index (FICI). C. glabrata revealed higher susceptibility and biofilm reduction in the presence of AmB alone, but both drugs revealed a good capacity in the biomass elimination. In the majority of the tested combinations, the interactions were defined as indifferent (FICI ≤ 4). The combination of the two drugs does not seem to bring a clear advantage in the treatment of biofilms of C. glabrata.

Posaconazole: A new agent for the prevention and management of severe, refractory or invasive fungal infections

Posaconazole is the newest antifungal agent to be approved for use in Canada. With excellent in vitro activity against a broad spectrum of yeasts and filamentous fungi, as well as having a well-tolerated oral formulation, posaconazole offers many potential advantages. Of particular interest are its seemingly lower potential for cross-resistance with other azoles and its activity (unique among oral antifungal agents) against the zygomycetes. As the incidence of both common and uncommon fungal infections increases commensurate with the growing population of immunocompromised individuals, posaconazole may ultimately become an important therapeutic option. The present article reviews the in vitro and in vivo data describing its activity, and focuses on both the proven and the potential clinical applications of this new triazole agent.

Posaconazole: when and how? The clinician's view

Posaconazole is the newest triazole antifungal agent available as an oral suspension with an extended spectrum of activity against Candida species, Aspergillus species, Cryptococcus neoformans, Zygomycetes and endemic fungi. Among posaconazole advantages are the relatively low potential of cross-resistance with other azoles, few drug interactions compared with other azoles and its activity against Zygomycetes. Randomised, double-blind trials have shown that posaconazole is effective for prophylaxis against invasive fungal infections (IFI), especially aspergillosis, in high-risk patients. Results of Phase III clinical trials and case/series reports indicate that posaconazole is effective in treating oesophageal candidiasis, including azole-refractory disease, and other IFI refractory to standard antifungal therapies. To date, posaconazole has appeared to be well tolerated even in long-term courses; it has an excellent safety profile with gastrointestinal disturbances being the most common adverse events reported. The dose of posaconazole is 200 mg three times daily for prophylaxis, 800 mg daily in two or four divided doses for the treatment of IFI and 100 mg daily (200 mg loading dose) for the treatment of oropharyngeal candidiasis. On the basis of early clinical experience, it appears that posaconazole will be a valuable aid in the management of life-threatening fungal infections.

Helicobacter pylori: prevalence and antibiotic susceptibility among Kenyans

BACKGROUND

Helicobacter pylori infection in Kenya is staggeringly high. Evidence links infection of the gastric mucosa by H. pylori with subsequent development of gastric pathologies.

AIM

We investigated the prevalence of H. pylori in dyspeptic patients, its relationship with gastric pathologies, and associated antibiotic susceptibility profiles, and compared two media to find the appropriate medium that enhances growth and expedites culture and isolation.

METHODS

Rapid urease and histological tests were used to screen for H. pylori. Culture was performed to test sensitivity and evaluate media. Selective and nutritional supplements were added to culture media (Colombia blood agar and brain-heart infusion agar) for growth enhancement. E-test strips for metronidazole, amoxicillin and clarithromycin were used for susceptibility testing.

RESULTS

The prevalence of H. pylori infection in children was 73.3%, and 54.8% in adults. All the H. pylori investigated in this study were largely sensitive to clarithromycin (100%, minimum inhibiting concentration (MIC) <2 microg/ml), amoxicillin (100%, MIC <2 microg/ml) and metronidazole (95.4%, MIC <8 microg/ml). There was, however, occasional resistance to metronidazole (4.6%, MIC >8 microg/ml). Both Colombia blood and brain-heart infusion agar, with the supplements, effectively supported H. pylori growth. Growth was achieved in an average of 36 hours for primary isolations and 24 hours for subcultures.

CONCLUSION

The media described here reduce the time required to culture and isolate bacteria and perform susceptibility testing. Despite the high prevalence of H. pylori infection, the associated pathology is low and does not parallel H. pylori prevalence in the population.

Combination antifungal therapy: the new frontier

The past decade has seen a significant increase in the incidence of invasive fungal infections. The antifungal armamentarium for the treatment of serious fungal infections remains limited. A possible approach to overcoming antifungal drug resistance and high mortality rates seen in severe fungal infections is to combine two or three classes of antifungals, especially if the drugs have different mechanisms of action. Combinations of new agents along with more traditional antifungals have now been shown to possess some synergistic or at least additive activity against many fungi in in vitro and animal studies. On the other hand, caution is still needed since some antifungal combinations have also demonstrated antagonistic activity. Well-controlled clinical trials are still required to define the most efficacious antifungal regimen. Furthermore, these trials should also evaluate the side-effect potential of combination regimens and the pharmacoeconomic impact these regimens may have.

Antifungal efficacy and pharmacodynamics of posaconazole in experimental models of invasive fungal infections

Posaconazole is a novel lipophilic antifungal triazole with potent and broad-spectrum activity against opportunistic, endemic and dermatophytic fungi. This activity extends to organisms that are often refractory to existing triazoles, amphotericin B or echinocandins such as Candida glabrata, Candida krusei, Aspergillus terreus, Fusarium spp. and the Zygomycetes. A large number of experimental animal models of invasive fungal infections has demonstrated the potent and broad-spectrum efficacy of posaconazole in vivo, both in normal and in immunocompromised animals. Consistent with these preclinical data, posaconazole showed strong a antifungal efficacy in phase II and phase III clinical trials in immunocompromised patients with oropharyngeal and oesophageal candidiasis and as salvage therapy in patients with invasive fungal infections, and was effective as antifungal prophylaxis in high-risk patients. This paper reviews the preclinical disposition, antifungal efficacy and pharmacodynamics of posaconazole in and its implications for treatment and prevention of invasive fungal infections.

Successful treatment of disseminated mucormycosis with a combination of liposomal amphotericin B and posaconazole in a patient with acute myeloid leukaemia

The combination of resection of infected tissue and antifungal therapy is the treatment of choice in mucormycosis. In disseminated mucormycosis, where surgery is impossible, the mortality is almost 90%. We report the first case of disseminated mucormycosis that was cured with a combination therapy of liposomal amphotericin B and posaconazole without surgical intervention.

Posaconazole: clinical pharmacology and potential for management of fungal infections

Posaconazole is a novel lipophilic antifungal triazole that inhibits cytochrome P450-dependent 14-alpha demethylase in the biosynthetic pathway of ergosterol. Inhibition of this enzyme leads to an accumulation of toxic 14-alpha methylsterols and a depletion of ergosterol, resulting in a perturbation of the function of the fungal cell membrane and blockage of cell growth and division. In vitro, posaconazole has potent and broad-spectrum activity against opportunistic, endemic and dermatophytic fungi. This activity extends to organisms that are often refractory to existing triazoles, amphotericin B or echinocandins, such as Candida glabrata, Candida krusei, Aspergillus terreus, Fusarium spp. and the Zygomycetes. A large variety of animal models of invasive fungal infections have provided consistent evidence of efficacy against these organisms in vivo, both in normal and immunocompromised animals. Posaconazole is available as an oral suspension and optimal exposure is achieved when the drug is administered in two to four divided doses along with food or a nutritional supplement. The compound has a large volume of distribution, in the order of 5 l/kg, and a half-life of approximately 20 h. Posaconazole is not metabolized to a significant extent through the cytochrome P450 enzyme system and is primarily excreted in an unchanged form in the feces. Although it is inhibitory, cytochrome P3A4 has no effect on 1A2, 2C8, 2C9, 2D6 and 2E1 isoenzymes, and therefore, a limited spectrum of drug-drug interactions can be expected. Pharmacokinetic studies in special populations revealed no necessity for dosage adjustment based on differences in age, gender, race, renal or hepatic function. Posaconazole has demonstrated strong antifungal efficacy in Phase II and III clinical trials in immunocompromised patients with oropharyngeal and esophageal candidiasis. Posaconazole also showed promising efficacy as salvage therapy in a large Phase II study including 330 patients with invasive fungal infections intolerant to or refractory to standard therapies. Posaconazole appears to be well tolerated in a manner comparable with that of fluconazole and it is currently under regulatory review in the USA and Europe for the treatment of refractory invasive fungal infections. This drug profile reviews the preclinical and clinical pharmacology of posaconazole and its potential role for prevention and treatment of invasive fungal infections.

Posaconazole Oral Suspension

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Posaconazole enhances the activity of amphotericin B against Aspergillus hyphae in vitro

The MICs and fractional inhibitory concentrations of posaconazole (POS) and voriconazole (VRZ), alone and in combination with amphotericin B (AMB), for the conidia and hyphae of 100 Aspergillus isolates were evaluated. POS-AMB had more synergistic activity against hyphae (75% of isolates) than VRZ-AMB (37%) and significantly more synergistic activity against hyphae than against conidia (12%).

Posaconazole: a broad-spectrum triazole antifungal

Posaconazale is a new triazole drug being investigated in phase III clinical trials for the treatment and prevention of invasive fungal infections. In-vitro and in-vivo studies showed that posaconazole has broad-spectrum activity against most Candida species, Cryptococcus neoformans, Aspergillus species, Fusarium species, zygomycetes, and endemic fungi. Posaconazole is given orally two to four times daily. This triazole is widely distributed in the body, metabolised mainly by the liver, and is well tolerated, even in long-term courses. Adverse events are generally mild and include headache and gastrointestinal complaints. Posaconazole has shown promising clinical efficacy against life-threatening fungal infections that are often refractory to the currently available antifungal therapies-eg, invasive aspergillosis, fusariosis, and the emerging zygomycosis.

Posaconazole

Posaconazole is a triazole antifungal agent, administered as an oral suspension, with an extended spectrum of in vitro activity. Posaconazole 800 mg/day demonstrated clinically relevant activity against a range of fungi in patients with invasive fungal infections who were refractory to, or intolerant of, other antifungal therapy in an open-label, multicentre, phase III study (330 patients received posaconazole and 279 patients served as external controls). In aspergillosis, the global response success rate at the end-of-therapy visit (primary endpoint) was significantly higher in posaconazole recipients than in external controls (42% vs 26%). Posaconazole was also associated with overall success rates of 54% in zygomycosis, 46% in fusariosis, 43% in Pseudallescheria infection, 80% in phaeohyphomycosis and 100% in histoplasmosis. Success rates were 48% in refractory candidiasis, 69% in refractory coccidioidomycosis, 48% in refractory cryptococcal infection and 82% in refractory chromoblastomycosis or mycetoma. Posaconazole also demonstrated potential in febrile neutropenia in an open-label phase II study (success rate of 81% 7 days after the end of treatment). In a noncomparative, multicentre, phase III study in patients with advanced HIV infection who had azole-refractory oropharyngeal and/or oesophageal candidiasis, posaconazole 400 or 800 mg/day resulted in a clinical response in 132 of 176 patients (75%). Oral posaconazole suspension was generally well tolerated in patients with invasive fungal infections, including patients who received treatment for >or=1 year.