High performance liquid chromatographic (HPLC) and other non-biological methods for quantitation of antifungal drugs

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.

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.

Improved high-performance liquid chromatographic determination of amphotericin B in human serum and plasma

An improved reversed-phase high-performance liquid chromatographic procedure is described for the determination of Amphotericin B (AMB) in human serum and plasma. The procedure involves the addition of the internal standard, p-nitroaniline, to the sample (0.1 ml) followed by protein precipitation with acetonitrile. The supernatant is injected directly onto a C8 chromatographic column and eluted with an acetonitrile-aqueous 0.01 M sodium acetate buffer, pH 7.4, mobile phase. A spectrophotometric detector operated at 405 nm is used. Retention times for internal standard and AMB are 5.2 and 6.6 min, respectively. The assay standard curve is linear between 0.05-2.0 micrograms cm-3. Within- and between-run relative standard deviations (RSD) for high and low concentrations of the drug are less than 5.30%. Analytical recovery of added AMB in serum is 98.4-101.4%. Data obtained by microbiological assay correlated well (r = 0.936) with LC results. Some commonly co-administered drugs and high concentrations of bilirubin are shown not to interfere.

Treatment of systemic fungal infections: recent progress and current problems

Systemic mycoses continue to emerge as life-threatening infections. Considerable progress in treating these infections is being achieved through better application of established available antifungal agents (amphotericin B, flucytosine, miconazole and ketoconazole), and through development of promising investigational agents (fluconazole, itraconazole). Systemic fungal infections, however, continue to present major problems, including clinical resistance, microbiological resistance, emergence of new pathogens, and involvement of more immunocompromised patients. The purpose of this paper, therefore, is to review the recent progress and current problems in treatment of systemic fungal infections.

Rapid determination of amphotericin B levels in serum by high-performance liquid chromatography without interference by bilirubin

A high-performance liquid chromatographic method for the determination of amphotericin B concentrations in human serum without bilirubin interference was developed and compared with a microbiological assay. The high-performance liquid chromatographic assay utilized a reversed-phase trimethyl silica column, simple sample preparation, and visible detection. Reproducibility studies yielded coefficient-of-variation ranges from 1.02 to 2.11% for within-day precision and 2.88 to 4.32% for between-day precision. The correlation coefficient with the microbiological assay was 0.984 for amphotericin B.

Sensitive high-pressure liquid chromatographic assay for amphotericin B which incorporates an internal standard

We developed a rapid, sensitive, high-pressure liquid chromatographic (HPLC) procedure which incorporates a commercially available internal standard, 1-amino-4-nitronaphthalene, to measure amphotericin B in serum. Recovery was quantitative (greater than or equal to 90%), and the standard curve was linear from 0.04 to at least 10.0 micrograms/ml. The reproducibility of the assay was good, with intrarun coefficients of variation from 2.0 to 6.8% and interrun coefficients of variation from 4.9 to 10.0%. Comparison by linear regression analysis of the HPLC assay with an agar well diffusion bioassay gave a correlation coefficient of 0.942, with the HPLC assay exhibiting greater precision and sensitivity. No interference was encountered from over 20 drugs and three amphotericin B analogs. However, serum specimens that contained high concentrations of conjugated bilirubin (greater than 3 mg/dl) produced interfering peaks in both this assay and other previously reported HPLC assays for amphotericin B. We also describe a solid-phase extraction procedure which effectively removes this interference and uses an alternative internal standard (N-acetyl amphotericin B).

Rapid determination of 5-fluorocytosine levels in blood

Levels of 5-fluorocytosine in blood were rapidly calculated by determining the amount of competition in the creatinine iminohydrolase (creatinine deiminase; EC 3.5.4.21) assay for creatinine with the Kodak Ektachem system (Eastman Kodak Co., Rochester, N.Y.). The correlation with bioassay values was extremely high (r = 0.982). Standards and samples were highly stable over time.

Improved procedure for determination of flucytosine in human blood plasma by high-pressure liquid chromatography

Several high-pressure liquid chromatography procedures for the determination of flucytosine in serum or plasma have appeared. Some of these suffer from significant disadvantages, and none was applicable in our routine clinical therapeutic-drug-monitoring laboratory. A new high-pressure liquid chromatography assay for flucytosine was therefore developed. A 100-microliter sample of plasma was treated with an aqueous 5-iodocytosine internal-standard solution, and the mixture was deproteinized with trichloroacetic acid. A portion of the protein-free supernatant was diluted with 0.1 M ammonium phosphate, and an aliquot of the resulting solution was injected into the high-pressure liquid chromatography system. Chromatography was performed on a strong-cation-exchange column with a mobile phase containing aqueous ammonium phosphate, phosphoric acid, methanol, and acetonitrile. Detection was at 254 nm. The assay was shown to be linear in the 10 to 200-micrograms/ml drug-concentration range. Forty other drugs were tested for potential interference with the assay, and none was found. For routine use, a single-point working standard containing 75 micrograms of flucytosine per ml was used, giving intraassay coefficients of variation at 50 and 150 micrograms/ml of 1.8 and 2.3% respectively, whereas the day-to-day coefficient of variation at 50 micrograms/ml was 10.0%. Advantages of the procedure include the small sample size, the use of a convenient and reliable internal standard, speed, and simplicity. The assay is highly suitable for routine clinical drug-analysis laboratories.