High-performance liquid chromatographic determination of amphotericin B in human serum

Validated HPLC-UV method for amphotericin B quantification in a critical patient receiving AmBisome and treated with extracorporeal replacement therapies

Amphotericin B (AMB) is a polyene macrolide antifungal agent used for treating invasive fungal infections. Liposomal AMB is a lipid dosage form, available as AmBisome, which reduces the toxicity of the drug. A simple HPLC-UV method was developed for the determination of AMB in plasma to study its pharmacokinetic profile in a critical patient receiving AmBisome and treated with extracorporeal replacement therapies. Sample preparation was performed using plasma deproteinization and drug release from liposome by the addition of acetonitrile (ACN)/zinc sulfate and ultrasonication. Chromatographic separation was performed using a C18 column and a mobile phase consisting of phosphate buffer (pH 3.0)/ACN (65/35, v/v). The UV detector was set at 407 nm. The total run time analysis was 23 min. The method was validated according to the standard guidelines and applied to study the pharmacokinetics of AMB in a critical patient. The total run time analysis obtained was shorter than that of the previously reported methods, being useful for therapeutic drug monitoring or pharmacokinetic profile research.

Current role of LC-MS in therapeutic drug monitoring

The role of liquid chromatography coupled with mass spectrometry (LC-MS) techniques in routine therapeutic drug monitoring activity is becoming increasingly important. This paper reviews LC-MS methods published in the last few years for certain classes of drugs subject to therapeutic drug monitoring: immunosuppressants, antifungal drugs, antiretroviral drugs, antidepressants and antipsychotics. For each class of compounds, we focussed on the most interesting methods and evaluated the current role of LC-MS in therapeutic drug monitoring.

Measurement of Amphotericin B concentration by Resonant Raman Spectroscopy – a novel technique that may be useful for non-invasive monitoring

We wished to determine whether Resonant Raman Spectroscopy (RRS) could be used to measure Amphotericin B (AmB) at therapeutic and subtherapeutic concentrations in a model system mimicking the anterior chamber of the eye. The goal was to develop a technique for non-invasive measurement of AmB levels in the aqueous humor (AH) of the eye. A krypton-ion laser source (406.7 nm) was used for excitation and Resonant Raman Spectra were captured with a confocal system in an anterior chamber (AC) model. These spectra were used to develop a correlation curve for prediction of AmB levels. Subsequently, one rabbit was evaluated with this system after 5 days of intravenous AmB administration (1 mg/kg/day) and AmB concentrations measured by RRS were compared to those measured by high-performance liquid chromatography (HPLC). AmB exhibited a unique spectral peak at 1557 cm(-1). Integrated area of this peak linearly correlated with AmB concentration in our model AC. When integrated peak area from multiple in vivo measurements in one animal at steady-state was plotted on this correlation curve, we were able to predict AmB levels. These closely approximated those measured by HPLC. These measurements were not significantly affected by photobleaching or depth profile at acquisition. RRS at 406.7 nm is a method that may be useful for non-invasive monitoring of intraocular AmB levels. This instrument can help physicians decide when repeat, invasive delivery of this drug is warranted based on measurement of actual drug levels in the AH. Also, there is the potential to measure the ocular concentrations of other pharmaceutical agents with similar instruments.

Efficacy of PLD-118, a novel inhibitor of candida isoleucyl-tRNA synthetase, against experimental oropharyngeal and esophageal candidiasis caused by fluconazole-resistant C. albicans

PLD-118, formerly BAY 10-8888, is a synthetic antifungal derivative of the naturally occurring beta-amino acid cispentacin. We studied the activity of PLD-118 in escalating dosages against experimental oropharyngeal and esophageal candidiasis (OPEC) caused by fluconazole (FLC)-resistant Candida albicans in immunocompromised rabbits. Infection was established by fluconazole-resistant (MIC > 64 microg/ml) clinical isolates from patients with refractory esophageal candidiasis. Antifungal therapy was administered for 7 days. Study groups consisted of untreated controls; animals receiving PLD-118 at 4, 10, 25, or 50 mg/kg of body weight/day via intravenous (i.v.) twice daily (BID) injections; animals receiving FLC at 2 mg/kg/day via i.v. BID injections; and animals receiving desoxycholate amphotericin B (DAMB) i.v. at 0.5 mg/kg/day. PLD-118- and DAMB-treated animals showed a significant dosage-dependent clearance of C. albicans from the tongue, oropharynx, and esophagus in comparison to untreated controls (P Collapse

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MESH Headings

• Animals
• Antifungal Agents/pharmacology
• Area Under Curve
• Candida albicans/drug effects
• Candida albicans/enzymology
• Candidiasis/microbiology
• Candidiasis, Oral/microbiology
• Cycloleucine/adverse effects
• Cycloleucine/analogs & derivatives
• Cycloleucine/pharmacokinetics
• Cycloleucine/therapeutic use
• Drug Resistance, Fungal
• Enzyme Inhibitors/adverse effects
• Enzyme Inhibitors/pharmacokinetics
• Enzyme Inhibitors/pharmacology
• Esophageal Diseases/microbiology
• Female
• Fluconazole/pharmacology
• Half-Life
• Immunosuppression Therapy
• Isoleucine-tRNA Ligase/antagonists & inhibitors
• Rabbits

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Affiliation(s)

Vidmantas Petraitis Immunocompromised Host Section, Pediatric Oncology Branch, National Cancer Institute, National Institutes of Health, Building 10, Rm. 13N240, Center Dr., Bethesda, MD 20892, USA.
Ruta Petraitiene
Amy M Kelaher
Alia A Sarafandi
Tin Sein
Diana Mickiene
John Bacher
Andreas H Groll
Thomas J Walsh

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Amphotericin B in oil-water lecithin-based microemulsions: formulation and toxicity evaluation

A novel lecithin-based microemulsion containing AmB was developed to reduce the toxic effects of the drug, comparing it with the commercial formulation Fungizone. Phase diagrams containing the microemulsion region were constructed for pseudoternary systems composed of isopropil myristate (IPM)/Brij((R)) 96V/lecithin/water. The incorporation of AmB to the microemulsions was done following the Phase Inversion Temperature (PIT) method or by diluting the drug in the aqueous phase of the disperse system before forming the microemulsion. The percentage of drug entrapped in the microemulsion was analyzed by an HPLC method obtaining recoveries > 98%. Mean droplet size of the microemulsions chosen for the acute toxicity evaluation was of 45 nm, and the rheological studies showed that those microemulsions mentioned followed a Newtonian behavior. Different studies are described in this work to prove the stability of these new dosage forms. Acute toxicity results, determined by a graphic method, the probit binary model and the Reed and Muench method showed that lethal dose 50 (LD(50)) for AmB microemulsions was of 2.9 mgkg(-1) compared to 1.4 mgkg(-1) for the commercial deoxycholate suspension, Fungizone. The overall results indicate that treatment with AmB microemulsions was less toxic than Fungizone, suggesting a potential therapeutic application.

Quantitation of Free and Total Amphotericin B in Human Biologic Matrices by a Liquid Chromatography Tandem Mass Spectrometric Method

Amphotericin B remains the standard of care for the treatment of invasive and disseminated fungal infections. Various lipid-based formulations of amphotericin B have been developed to improve its therapeutic index by decreasing toxicity. Previous bioanalytic methods using microbial inhibition or high-pressure liquid chromatography quantified total amphotericin B (free, plasma protein-bound, and lipid-complexed). Sensitivity of this method with a low limit of quantitation of 0.05 microg/mL was inadequate to determine free (unbound) amphotericin B. A sensitive LC/MS/MS method was developed to determine the total amphotericin B value in human plasma and other biologic matrices and the free amphotericin B concentration in plasma. For determination of total plasma amphotericin B concentrations, the sample was diluted and injected onto the LC/MS/MS. For total amphotericin B in other matrices and free amphotericin B in plasma, solid-phase extraction was used. Natamycin served as an internal standard. A PE Sciex API 3000 (Sciex; Concord, Ontario, Canada) was used to assess free amphotericin B in plasma ultrafiltrate determination and an API 3+ for the other matrices, with electrospray interfaced to a C18 analytic column. The low limit of quantitation was 1 ng/mL for ultrafiltrate. For total amphotericin B, the low limits were 2 microg/mL for plasma, 0.05 microg/mL for urine, and 0.4 microg/mL for fecal homogenate. The methods were validated to show the standard range linearity, sensitivity, selectivity, accuracy, precision, and stability of amphotericin B in the matrices tested.

Determination of amphotericin B in human plasma using solid-phase extraction and high-performance liquid chromatography

A rapid and selective HPLC method is described and validated for measuring amphotericin B (AB) in plasma. The procedure involves the solid phase extraction of AB from plasma by incorporating 1-amino-4-nitronaphthalene as an internal standard during the last elution step in extraction followed by HPLC analysis with UV detection at 407 nm. The chromatographic separation is achieved in less than 10 min on a reversed-phase C-18 column using acetonitrile-disodium edetate (20 mM) (45:55, v/v) at pH 5.0 as eluent. A linear response over the concentration range of 0.0100--2.00 microg ml(-1) is obtained having a detection limit of 0.00500 microg ml(-1) for AB. The mean extraction recovery is found to be 98.1+/-1.1% (n=15). The within-day and day-to-day R.S.D. were less than 2% (n=15) and 6.54% (n=45) respectively. This method is applied for quantifying AB trough levels in the plasma of cancer patients who have been on antifungal therapy with AmBisome. It can further be applied either for AB therapeutic monitoring or single/multiple pharmacokinetic analysis of AB in plasma.

Dosage-dependent antifungal efficacy of V-echinocandin (LY303366) against experimental fluconazole-resistant oropharyngeal and esophageal candidiasis

V-echinocandin (VER-002; LY303366) is a semisynthetic derivative of echinocandin B and a potent inhibitor of fungal (1, 3)-beta-D-glucan synthase. We studied the antifungal efficacy, the concentrations in saliva and tissue, and the safety of VER-002 at escalating dosages against experimental oropharyngeal and esophageal candidiasis caused by fluconazole-resistant Candida albicans in immunocompromised rabbits. Study groups consisted of untreated controls, animals treated with VER-002 at 1, 2.5, and 5 mg/kg of body weight/day intravenously (i.v.), animals treated with fluconazole at 2 mg/kg/day i.v., or animals treated with amphotericin B at 0.3 mg/kg/day. VER-002-treated animals showed a significant dosage-dependent clearance of C. albicans from the tongue, oropharynx, esophagus, stomach, and duodenum in comparison to that for untreated controls. VER-002 also was superior to amphotericin B and fluconazole in clearing the organism from all sites studied. These in vivo findings are consistent with the results of in vitro time-kill assays, which demonstrated that VER-002 has concentration-dependent fungicidal activity. Esophageal tissue VER-002 concentrations were dosage proportional and exceeded the MIC at all dosages. Echinocandin concentrations in saliva were greater than or equal to the MICs at all dosages. There was no elevation of serum hepatic transaminase, alkaline phosphatase, bilirubin, potassium, or creatinine levels in VER-002-treated rabbits. In summary, the echinocandin VER-002 was well tolerated, penetrated the esophagus and salivary glands, and demonstrated dosage-dependent antifungal activity against fluconazole-resistant esophageal candidiasis in immunocompromised rabbits.

Distribution of lipid formulations of amphotericin B into bone marrow and fat tissue in rabbits

The distribution of the three currently available lipid formulations of amphotericin B (AmB) into bone marrow and fat tissue was evaluated in noninfected rabbits. Groups of four animals each received either 1 mg of AmB deoxycholate (D-AmB) per kg of body weight per day or 5 mg of AmB colloidal dispersion, AmB lipid complex, or liposomal AmB per kg per day for seven doses. Plasma, bone marrow, fat, and liver were collected at autopsy, and AmB concentrations were determined by high-performance liquid chromatography. At the investigated dosages of 5 mg/kg/day, all AmB lipid formulations achieved at least fourfold-higher concentrations in bone marrow than did standard D-AmB at a dosage of 1 mg/kg/day. Concentrations in bone marrow were 62 to 76% of concurrent AmB concentrations in the liver. In contrast, all AmB formulations accumulated comparatively poorly in fat tissue. The results of this study show that high concentrations of AmB can be achieved in the bone marrow after administration of lipid formulations, suggesting their particular usefulness against disseminated fungal infections involving the bone marrow and against visceral leishmaniasis.

High-performance liquid chromatographic determination of amphotericin B in plasma and tissue. Application to pharmacokinetic and tissue distribution studies in rats

A sensitive HPLC method with piroxicam as internal standard was developed for assaying amphotericin B in plasma and tissue. An Ultrabase-C18 column and a simple mobile phase consisting of an acetonitrile-acetic acid (10%)-water (41:43:16) mixture were used. The flow-rate was 1 ml/min and the effluent was monitored at 405 nm. The linearity of the assay method was up to 1000 ng/ml and 100 micrograms/g for plasma and tissue, respectively. Intra-day and inter-day RSDs were below 10% for all the sample types. This HPLC assay has been applied to determine amphotericin B in plasma and tissue samples taken during pharmacokinetic and tissue distribution studies in rats.

A high-performance liquid-chromatographic assay for amphotericin B in a hydrophilic colloidal paste base

A stability-indicating high-performance liquid-chromatographic (HPLC) assay has been developed for amphotericin B (AmB) in a paste, containing AmB, tobramycin (or gentamicin) sulphate, colistin sulphate, liquid paraffin and Orabase. Extraction of AmB was performed by partitioning the antibiotic between N,N-dimethylformamide (DMF) and cyclohexane, which led to precipitation of the polymeric materials and extraction of the liquid paraffin into the cyclohexane and AmB into the DMF. Analysis by HPLC of the latter layer gave a linear relationship between concentration and peak area response for the AmB over the range 5.0 x 10(-4) to 7.5 x 10(-3)% (w/v) (r = 0.9995) with a relative standard deviation of +/- 1.46% (n = 8). The efficiency of extraction was 1006 +/- 2.4% (n = 5).

Quantitation of amphotericin B in plasma by second-derivative spectrophotometry

A method is described for determining amphotericin B in plasma using second-derivative spectrophotometry after deproteinization. The assay was based on the absorbance at 407.5 nm. The second-derivative spectrum recorded between 350 and 450 nm allowed identification of the analyte and showed absence of drug interference. Only bilirubin interfered at high concentration (> or = 50 mumol l-1. The linear concentration ranges were 0.05 -5.0 mg l-1 (r = 0.999, slope = 2.731, intercept = 0.008). Between-day CV < or = 9.7%, within-day CV < or = 5.5%, analytical recovery close to 100% were suitable for clinical investigations. This method provides better specificity than direct absorbance, is simpler and faster than a high performance liquid chromatography assay and can be used routinely by any laboratory possessing a spectrophotometer with a derivative accessory.

Mechanism of amphotericin B resistance in Leishmania donovani promastigotes

Amphotericin B (AmB)-resistant Leishmania donovani promastigotes were selected by increasing drug pressure, and their biological features were compared with those of the wild-type parent strain. The 50% inhibitory concentration for resistant cells was 20 times higher than that for the wild-type. Resistance was stable after more than 40 passages in drug-free medium, and resistant promastigotes were infective to macrophages in vitro but lost their virulence in vivo. They had 2.5 times longer generation time, decreased AmB uptake, and increased AmB efflux in comparison to the wild type. Fluorescence measurement with a specific plasma membrane probe, 1-[4-(trimethylammonio)-1,6-diphenylhexa]-1,3,5-triene, showed increased membrane fluidity in drug-resistant promastigotes. Analysis of lipid composition showed that in resistant cells saturated fatty acids were prevalent, with stearic acid as the major fatty acid, and the major sterol was an ergosterol precursor, the cholesta-5, 7, 24-trien-3beta-ol and not ergosterol as in the AmB-sensitive strain.

New high-performance liquid chromatographic method for amphotericin B analysis using an internal standard

A simple and reproducible HPLC method for the analysis of amphotericin B (AmB) in serum, lung and liver using natamycin as the internal standard was developed. AmB and natamycin were extracted from serum, lung and liver and were separated using an isocratic elution from C18 reversed-phase column. The mobile phase consisted of acetonitrile-10 mM acetate buffer pH 4.0 (37:63, v/v). The HPLC system had two detectors in series. One was set at 303 nm and the other at 383 nm for the detection of natamycin and AmB, respectively. The retention times of AmB and natamycin were 15 and 6 min, respectively. The recovery efficiency was 96%-70%. The limit of quantification was 0.1 microgram/ml. The assay was reproducible, the within-day coefficient of variation (n = 6) was < 8% for serum, lungs and liver. The between-day variability (n = 6) was < 7.7% for serum, liver and lungs at 1 microgram/ml or 1 microgram/g tissue concentration. The assay was linear within the range 1-40 micrograms/ml (r2 = 0.99).

A high-performance liquid chromatographic assay for the determination of amphotericin B serum concentrations after the administration of AmBisome, a liposomal amphotericin B formulation

A sensitive and selective high-performance liquid chromatographic (HPLC) method has been developed for the determination of amphotericin B in human serum. After methanol deproteinization, amphotericin B and 3-nitrophenol (internal standard) are separated by reversed-phase chromatography and detected by ultraviolet absorbance. The analysis of human serum after the standard addition of amphotericin B (0.05-200.0 micrograms/mL) demonstrated excellent precision and accuracy over a five-day period. The HPLC assay uses two standard curve ranges. The high sensitivity curve range for low AmBisome dosage (1.0 mg/kg) is 0.05-20.0 micrograms/mL (curve 1), and the second curve range for the higher AmBisome dose regimens (2.5-5.0 mg/kg) is 0.5-200 micrograms/mL (curve 2). The intraday and interday coefficients of variations for standard curve 1 were 0.5-4.6% and 3.0-11.5%, respectively. The limit of quantitation was 0.05 microgram/mL. The intraday and interday coefficients of variation for standard curve 2 were 2.0-3.6 and 6.9-10.1, respectively. No interfering peak at the retention time for Amphotericin B and the internal standard were present in blank serums or serum samples spiked with fifteen potential co-administrated drugs with Amphotericin B treatment. The method was used to quantitate serum concentrations of amphotericin B in patients after the administration of AmBisome, a liposomal formulation of amphotericin B.

Rapid determination of amphotericin B in serum and urine by third-order derivative spectrophotometry

A derivative spectrophotometric method for rapid monitoring of amphotericin B in serum and urine down to 30 ng/mliters is described. Samples are treated with acetonitrile, and amphotericin B is directly quantified in the crude extracts on the basis of the intensity of the peak that appears at 402 nm when the normal absorption spectrum is submitted to third-order derivative processing. Accuracy data suggested recoveries in the range of 84.3-94.9% for serum and 85.6-93.4% for urine. The precision of the method was better than 11.3% for serum and 9.2% for urine when samples contained as low as 29.6 ng/mliters of amphotericin B. Ease of applicability, short analysis time, low cost, and reliability are the main advantages of the method.

Determination of amphotericin B in human serum by liquid chromatography

A rapid reversed-phase high-performance liquid chromatographic method with a 30-mm long column is described for assaying amphotericin B in serum. After deproteinization of serum samples with methanol, the supernatant was injected onto a reversed-phase C18 column, using 2.5 mM Na2EDTA-acetonitrile (70:30, v/v) as the mobile phase. Amphotericin B was eluted at 1.5 min. Calibration plot of the peak area against concentration was linear from 0.05 to 25 micrograms/ml (C.V. of 3%). Within-day and day-to-day imprecision (C.V.) ranged between 1.33% and 3.61%. The application was evaluated in 55 serum samples from patients treated with amphotericin B.

Determination of amphotericin B in cerebrospinal fluid by solid-phase extraction and liquid chromatography

A highly sensitive and reproducible liquid chromatography (LC) method for the determination of Amphotericin B in cerebrospinal fluid has been developed and validated. This LC-based method involves using nystatin as an internal standard and solid-phase extraction for sample preparation, followed by reversed-phase separation monitored by absorbance at 410 nm. The method has a limit of quantification of less than 1 ng ml-1 and excellent precision and accuracy, with both percentage relative standard deviation and percentage relative error less than 10%. The established linearity range was 1-10 ng ml-1 (r2 > 0.99). The extraction recovery of Amphotericin B from the cerebrospinal fluid is higher than 90% over the entire linear range. The method has been successfully employed for studying the penetration of Amphotericin B into the central nervous system in dogs and human.

Pharmacokinetics and safety of a unilamellar liposomal formulation of amphotericin B (AmBisome) in rabbits

A unilamellar liposomal formulation of amphotericin B (LAmB) known as AmBisome was safely administered intravenously to 20 rabbits at 0.5, 1.0, 2.5, 5, or 10 mg/kg of body weight, whereas of 12 rabbits given desoxycholate amphotericin B (DAmB) intravenously at 0.5, 1.0, or 1.5 mg/kg, 2 died of acute cardiac toxicity when DAmB was administered at the highest dose. Single-dose LAmB (1 mg/kg) achieved a maximum concentration in serum (Cmax) of 26 +/- 2.4 micrograms/ml and an area under the curve to infinity (AUC0-infinity) of 60 +/- 16 micrograms.h/ml, while single-dose DAmB (1.0 mg/kg), by comparison, achieved a lower Cmax (4.7 +/- 0.2 micrograms/ml; P = 0.001) and a lower AUC0-infinity (30.6 +/- 2.2 micrograms.h/ml; P = 0.07). Following administration of a single dose of LAmB (10 mg/kg), a disproportionately higher Cmax (287 +/- 14 micrograms/ml) and AUC0-infinity (2,223 +/- 246 micrograms.h/ml) occurred, indicating saturable elimination. After chronic dosing (n = 4) with LAmB at 5.0 mg/kg/day for 28 days or DAmB at 1.0 mg/kg/day for 28 days, LAmB achieved daily peak levels of 122.8 +/- 5.8 micrograms/ml and trough levels of 34.9 +/- 1.8 micrograms/ml, while DAmB reached a peak of only 1.76 +/- 0.11 microgram/ml and a trough of 0.46 +/- 0.04 microgram/ml (P < or = 0.001). Significant accumulations of amphotericin B into reticuloendothelial organs were observed, with 239 +/- 39 micrograms/g found in the liver after chronic LAmB dosing (5 mg/kg/day), which was seven times higher than the 33 +/- 6 micrograms/g after DAmB dosing (1 mg/kg/day) (P = 0.002). Accumulation in kidneys, however, remained 14-fold lower (P =0.04) following LAmB dosing (0.87 +/- 0.61 microgram/g) than after DAmB dosing (12.7 +/- 4.6 microgram/g). Nephrotoxicity occurred in only one of four LAmB treated animals, while it occurred in all four chronically DAmB-treated animals: mild hepatozicity with transaminase elevations was seen in one LAmB-treated rabbit. We conclude that LAmB safely achieved higher Cmax(s) and AUC0-infinity(s) and demonstrated saturable, nonlinear elimination from plasma via reticuloendothelial organ uptake. Take reduced nephrotoxicity of LAmB correlated with diminished levels of amphotericin B in the kidneys.

Comparison of high-performance liquid chromatography and bioassay of amphotericin B in serum

For the determination of amphotericin B in serum a high-performance liquid chromatography (HPLC) method using simple protein precipitation and an isocratic mobile phase as well as a plate diffusion bioassay are described. Using 5-fluorocytosine-resistant strain of Candida albicans and peptone in medium as an antagonist of 5-fluorocytosine allows simple measurement of amphotericin B both in the absence and in the presence of 5-fluorocytosine. The correlation coefficient (r) between bioassay and HPLC runs is 0.88. Generally, the biological determination gives slightly higher values of amphotericin B than the HPLC method. Both methods are useful for amphotericin B drug monitoring.

High-performance liquid chromatographic analysis of amphotericin B in plasma, blood, urine and tissues for pharmacokinetic and tissue distribution studies

A sensitive and reproducible high-performance liquid chromatographic method was developed to assay ampherotericin B in plasma, blood, urine and various tissue samples. Amphotericin B was isolated from each sample matrix by solid-phase extraction (Bond-Elut). The eluate from Bond-Elut containing amphotericin B was injected onto a reversed-phase C18 column (Waters, mu Bondpak, 10 microns, 300 mm x 3.9 mm I.D.) with a mobile phase of 45% acetonitrile in 2.5 mM Na2EDTA at 1 ml/min. Detection of amphotericin B was by ultraviolet absorption at 382 nm. Blood and tissues were homogenized and extracted with methanol prior to Bond-Elut extraction. The extraction efficiencies of amphotericin B from plasma, blood and tissues were approximately 90, 70 and 75%, respectively. The sensitivity of the assay was less than or equal to 5 ng/ml for plasma, less than or equal to 25 ng/ml for blood, 2.5 ng/ml for urine and 50 ng/g for tissues. The linearity of the assay method was up to 2.5 micrograms/ml for plasma, 5 micrograms/ml for blood, 500 ng/ml for urine and 500 micrograms/g for tissues. The assay was reproducible with an intra-day coefficient of variation (C.V., n = 3) of less than 5% in general for plasma, blood and tissues. The inter-day C.V. of the assay was less than 5% for plasma (n = 5), less than 10% for blood (n = 4) and less than 5% for tissues (n = 3). The overall variability in the urine assay was generally less than 10%. This method has demonstrated significant improvement in the sensitivity and reproducibility in assaying amphotericin B in plasma and especially in blood, urine and tissues. We have employed this assay to compare the pharmacokinetic and tissue distribution profiles of amphotericin B in rats and dogs following administration of Fungizone and ABCD (amphotericin B-cholesteryl sulfate colloidal dispersion), a lipid-based dosage form. In addition, the assay method for plasma and urine samples can also be applied to pharmacokinetics studies of amphotericin B in man.

Comparison of nephrotoxicities of different polyoxyethyleneglycol formulations of amphotericin B in rats

The aim of the present study was to assess whether amphotericin B (AmB)-Myrj 59, AmB-polyoxyethyleneglycol 24 cholesterol (PC), and AmB-Synperonic A50 (SA50) were less nephrotoxic than AmB-deoxycholate (DC). Rats were treated with the different AmB formulations (10 mg/kg of body weight) intraperitoneally or with the surfactants alone. A group of control rats receiving the vehicle was also examined. After 6 days of daily intraperitoneal injections of AmB-DC, decreased body weight and glomerular filtration rate as well as increased degree of diuresis, uremia, microalbuminuria, and N-acetyl-beta-D-glucosaminidase excretion in urine were noted. Urinary excretion of potassium and sodium was also decreased in AmB-DC-treated rats. Most of these effects were more pronounced with AmB-PC and AmB-SA50. In contrast, AmB-Myrj 59 was less nephrotoxic than AmB-DC. Indeed, after 6 days of treatment with AmB-Myrj 59, the natriuria, kaliuria, albuminuria, and glomerular filtration rates were unchanged compared with those of controls. Moreover, the body weight loss and uremia increase of the rats treated by AmB-Myrj 59 were less than those of the rats treated with the commercial preparation. Among the surfactants, only PC was toxic for the rats. The intrinsic toxicity of PC and the higher systemic exposure to AmB could contribute to increased toxicities of AmB-PC and AmB-SA50, respectively. AmB-Myrj 59 was less nephrotoxic than AmB-DC at equivalent areas under the plasma concentration-time curves. These preliminary results suggest that this formulation could be a good alternative to the commercial product.

Flow cytometric assay for estimating fungicidal activity of amphotericin B in human serum

We describe a simple and rapid bioassay for estimating fungicidal activity of Amphotericin B in human serum using flow cytometry. The method exploits the fact that Candida albicans damaged by Amphotericin B show a decrease in size and take up propidium iodide to exhibit a red fluorescence after deoxycholate treatment. These phenomena display characteristic dose dependencies, and their assessment permits serum fungicidal activity to be broadly grouped into three categories: (1) subfungicidal; (2) fungicidal; and (3) strongly fungicidal. In normal human serum, these three categories correspond to Amphotericin B concentrations of 0 less than or equal to 0.5 micrograms/ml, 0.75-1.5 micrograms/ml, and greater than 2 micrograms/ml, respectively. Pilot analysis of serum samples obtained from four patients undergoing Amphotericin B therapy confirmed the feasibility of using the flow cytometric assay for estimating drug fungicidal activity ex vivo. The method is very simple, generates results within 5 h, and could prove useful for monitoring therapy with this effective but toxic drug.

Measurement of the concentration of amphotericin B in brain tissue of scrapie-infected hamsters with a simple and sensitive method

A simple, sensitive, and reproducible assay for the measurement of the amphotericin B concentration in tissue extracts was developed by using the fourth derivative of the absorption spectrum of amphotericin B between wavelengths of 330 and 430 nm. The amphotericin B concentration in spleen and brain was proportional to the total amount administered. The amphotericin B concentration in the brain was highly correlated with the increase in the mean incubation period of intracerebrally scrapie-infected hamsters.

Successful treatment with liposomal amphotericin B in two patients with persisting fungemia

Two granulocytopenic patients in whom fungemia persisted despite therapy with deoxycholate amphotericin B were subsequently successfully treated by daily intravenous administration of amphotericin B entrapped in sonicated liposomes made of egg yolk lecithin, cholesterol and stearylamine in a molar ratio of 4:3:1. High serum concentrations of amphotericin B could be maintained in both patients during therapy with liposomal amphotericin B and were associated with high in vitro antifungal activity. Liposomal amphotericin B was tolerated much better than the deoxycholate preparation. These findings suggest that the liposomal amphotericin B preparation is superior in the treatment of fungemia in granulocytopenic patients, and that randomized trials are warranted.

Tissue concentrations and bioactivity of amphotericin B in cancer patients treated with amphotericin B-deoxycholate

We have studied amphotericin B concentrations in tissues of 13 cancer patients who died after having received 75 to 1,110 mg (total dose) of amphotericin B-deoxycholate for suspected or proven disseminated fungal infection. Amphotericin B concentrations were measured by high-pressure liquid chromatography (HPLC) and by bioassay, the latter being done on tissue homogenates as well as on tissue methanolic extracts. The fungistatic and fungicidal titers of the tissue homogenates were also tested against three strains of Candida albicans and one strain of Aspergillus fumigatus. Tissue concentrations of amphotericin B measured by HPLC varied with the tested tissues as well as with the total dose of amphotericin B-deoxycholate administered and ranged from 0.4 to 147.1 micrograms/g. A mean of 38.3% (range, 23.0 to 51.3%) of the total dose was recovered by HPLC from all of the tested organs. Bioassay of tissue methanolic extracts reached 58 to 81% of the concentration measured by HPLC, whereas only 15 to 41% was recovered from the homogenates. Overall, 27.5% of the total dose was recovered from the liver, 5.2% was recovered from the spleen, 3.2% was recovered from the lungs, and 1.5% was recovered from the kidneys. The median concentration in bile was 7.3 micrograms/ml, suggesting that biliary excretion could contribute to amphotericin B elimination to an estimated range of 0.8 to 14.6% of the daily dose. Fungicidal titers were seldom measured in tissues, but fungistatic titers were observed and were linearly correlated with amphotericin B concentration measured by HPLC. In conclusion, only a small proportion of the amphotericin B administered as amphotericin B-deoxycholate to patients seems diffusible and bioactive.

Pilot study of amphotericin B entrapped in sonicated liposomes in cancer patients with fungal infections

A pilot study with amphotericin B incorporated in sonicated liposomes (ampholiposomes) made of egg phosphatidylcholine, cholesterol and stearylamine in a molar ratio 4:3:1 was performed in cancer patients with fungal infections. Fifteen patients received a total of 117 intravenous infusions of ampholiposomes. The total dose of amphotericin B administered per patient ranged from 20 to 1004 mg (mean 472 mg). The number of infusions per patient varied from 1 to 20 (mean 8) and the duration of treatment from 1 to 29 days (mean 10 days). Infusion of doses up to 1.8 mg/kg was well tolerated. None of the common side-effects of Fungizone, the colloidal suspension of amphotericin B, occurred; it was noteworthy that patients had no renal function impairment. Serum amphotericin B concentrations given as ampholiposomes were much higher than those obtained with Fungizone. With a daily treatment schedule, peak and trough serum amphotericin B concentrations, as measured by HPLC, were 10 to 20 micrograms/ml and 5 to 10 micrograms/ml respectively; while they did not exceed 2 micrograms/ml and 1 microgram/ml with Fungizone. Amphotericin B given as ampholiposomes had a prolonged serum beta half-life (25.3 +/- 16.0 h). Higher serum antifungal activity was observed with ampholiposomes as compared to Fungizone. We concluded that ampholiposomes have a better therapeutic index than Fungizone.