Spectrophotometric methods for simultaneous determination of betamethasone valerate and fusidic acid in their binary mixture

Five spectrophotometric methods were successfully developed and validated for the determination of betamethasone valerate and fusidic acid in their binary mixture. Those methods are isoabsorptive point method combined with the first derivative (ISO Point--D1) and the recently developed and well established methods namely ratio difference (RD) and constant center coupled with spectrum subtraction (CC) methods, in addition to derivative ratio (1DD) and mean centering of ratio spectra (MCR). New enrichment technique called spectrum addition technique was used instead of traditional spiking technique. The proposed spectrophotometric procedures do not require any separation steps. Accuracy, precision and linearity ranges of the proposed methods were determined and the specificity was assessed by analyzing synthetic mixtures of both drugs. They were applied to their pharmaceutical formulation and the results obtained were statistically compared to that of official methods. The statistical comparison showed that there is no significant difference between the proposed methods and the official ones regarding both accuracy and precision.

Detection of Aspergillus fumigatus mycotoxins: immunogen synthesis and immunoassay development

Immunological detection of secreted low molecular weight toxins represents a potentially novel means of diagnosing infection by the fungus Aspergillus fumigatus. Two such metabolites, gliotoxin and helvolic acid, were selected and conjugated to thyroglobulin for antisera generation in rabbits. Gliotoxin was initially activated using N-[p-maleimidophenyl] isocyanate (PMPI) and subsequently conjugated to S-acetyl thioglycolic acid N-hydroxysuccinimide-activated thyroglobulin, whereas helvolic acid was activated with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) in the presence of thyroglobulin prior to immunisation. To facilitate subsequent antisera evaluation, both toxins were similarly conjugated to bovine serum albumin (BSA). Matrix-Assisted Laser Desorption Ionisation-Time Of Flight (MALDI-TOF) mass spectrometry and SDS-PAGE analysis confirmed covalent attachment of toxins to BSA in the ratios of 15 and 2.4 mol per mol BSA for gliotoxin and helvolic acid, respectively. Resultant high titer antisera were capable of detecting both BSA-conjugated toxins (inhibitory concentration (IC)(50): 4-5 microg/ml). Free toxins were also detectable by competitive immunoassay, whereby 10 microg/ml free gliotoxin (30 microM) and helvolic acid (17 microM), respectively, inhibited antibody binding to cognate toxin-BSA previously immobilised on microwells. This work confirms that sensitive and specific antisera can be raised against fungal toxins and may have an application in diagnosing fungal infection.

Detection and quantification of phytotoxic metabolites of Sarocladium oryzae in sheath rot-infected grains of rice

AIMS

The present study describes the detection and quantification of the Sarocladium oryzae metabolites, helvolic acid and cerulenin in extracts of rice grains collected from plants infected with sheath rot. It also describes the phytotoxicity of these metabolites on rice seedlings.

METHODS AND RESULTS

Helvolic acid and cerulenin in sheath rot-infected rice grains were detected using thin layer chromatography (TLC) and nuclear magnetic resonance (NMR) analyses. On the TLC plates helvolic acid and cerulenin moved as brownish yellow spots and showed R(F) values of 0.61 and 0.49, respectively. A standard assay curve was developed on the basis of selective toxicity of helvolic acid towards Calvibacter michiganensis ATCC 2140 and cerulenin towards Candida albicans 1150. The amounts of helvolic acid and cerulenin on the basis of standard assay curve were 2.2 and 1.75 microg g(-1) of infected seeds. Treatment of IR 36 rice seedlings with metabolites induced chlorosis and reduced shoot length by 20%, root length by 30% and root number by 7% relative to control.

CONCLUSIONS

Helvolic acid and cerulenin were detected in infected rice grains and these metabolites induced chlorosis and reduced the seed viability and seedling health of rice.

SIGNIFICANCE AND IMPACT OF THE STUDY

Antimicrobial and phytotoxic metabolites, helvolic acid and cerulenin are present in infected grains and reduce the seed viability and seedling health. These metabolites may increase the pathogenic potential and survival of S. oryzae in rice seed by competing with other seed-borne fungi.

[Comparative diffusion of fusidic acid, oxacillin, and pristinamycin in dermal interstitial fluid after repeated oral administration]

OBJECTIVE

The aim of this study was to use the suction bullae technique to compare skin diffusion of 3 antibiotics commonly used for skin infections (fusidic acid, oxacillin, pristinamycin) and to estimate their potential activity at the site of skin infections.

SUBJECTS AND METHODS

This comparative open study was conducted in 12 healthy volunteers using a repeated latin square experimental scheme. Antibiotic concentrations in serum and suction bullae fluid were measured by high performance liquid chromatography after 5.5 days of repeated oral administration of fusidic acid (1 g/d), oxacillin (2 g/d), and pristinamycin (2 g/d).

RESULTS

Mean antibiotic concentrations in serum and interstitial fluid (suction bullae fluid) were highest for fusidic acid with a Cmax at 91.3 +/- 23.0 mg/l and 45.5 +/- 18.0 mg/l respectively (interstitial fluid/serum ratio=49 +/- 10 p. 100). For oxacillin, Cmax was 8.3 +/- 3.6 mg/l and 0.98 +/- 0.49 mg/l (ratio 13 +/- 5 p. 100). Pristinamycin concentrations were low with a Cmax at 0.51 +/- 0.40 and 0.26 +/- 0.15 mg/l (ratio 73 +/- 57 p. 100). Comparing the area under the interstitial fluid and the serum concentration-time curves showed that the best diffusion was obtained with pristinamycin (114 +/- 61 p. 100), followed by fusidic acid (57 +/- 13 p. 100) and oxacillin (48 +/- 25 p. 100).

DISCUSSION

These data were used to calculate indicators of potential efficacy in the interstitial dermal fluid: inhibitor quotient (Cmax/MIC) and AUIC (ASC/MIC), indicator of the time antibiotic concentrations are maintained above the minimal inhibitor concentration (MIC). This showed that fusidic acid was potentially more active against all staphylococci. For streptococci, the observed interstitial concentrations of pristinamycin and of fusidic acid should theoretically inhibit streptococci A growth, but oxacillin was the most adapted antibiotic.

Concentration and bactericidal activity of fusidic acid and cloxacillin in serum and synovial fluid

Fusidic acid and cloxacillin were studied in patients who underwent joint aspiration for noninfectious disorders. Nine patients were given oral 500 mg fusidic acid tid for 72 h, the last dose being given 4, 8 or 12 h before the joint aspiration. Cloxacillin was administered in a single 2 g iv dose to 9 patients, 0.5, 4 or 8 h before the aspiration. Bactericidal activity was determined against five isolates each of methicillin-susceptible and methicillin-resistant Staphylococcus aureus. Satisfactory activity (> or = 1:3) was detected in the serum in patients who received fusidic acid, while in the synovial fluids titres reflected borderline effectiveness (c. 1:2). Despite drug concentrations and excellent MICs, fusidic acid demonstrated markedly lower inhibitory and bactericidal activity against S. aureus than did cloxacillin.

Feasibility of measuring lipophilic or protein-bound drugs in the dermis by in vivo microdialysis after topical or systemic drug administration

Our aim was to assess the microdialysis technique for determining in vivo drug levels of a lipophilic and a protein-bound model drug in the dermis. Forearm skin of healthy volunteers received topical 2% fusidic acid or 0.1% betamethasone-17-valerate formulations twice daily as occluded treatment on irritative dermatitis. Microdialysis sampling in the dermis after 48 h was without measurable drug. Hairless rats received maximized treatment with occluded applications of 10% fusidic acid or 4% betamethasone-17-valerate in ethanol for 72 h followed by microdialysis. Mean levels of betamethasone-17-valerate were 11-45 ng/ml; fusidic acid was not measurable. Systemic administration in clinical doses to rats was without measurable drug levels; increasing doses to 312 mg/kg of fusidic acid and 158 mg/kg of betamethasone-17-valerate yielded betamethasone-17-valerate levels of 25-44 ng/ml and fusidic acid levels of 10-90 ng/ml. This study demonstrates the challenges arising when using microdialysis for measuring in vivo-drug levels. For the drugs chosen it was necessary to administer very high systemic doses or apply a high topical drug concentration to obtain measurable drug levels in the dialysates. Drug levels were in the nanomolar range and demonstrated reproducible and dynamic monitoring of in vivo drug levels in the skin. Using microdialysis for sampling highly protein-bound or lipophilic drugs in the skin requires very sensitive analytical methods, and the sensitivity of the analysis is likely to be the limiting factor.

A comparative evaluation of three detectors in the HPLC analysis of sodium fusidate

A reversed phase liquid chromatographic (HPLC) method is proposed for the determination of sodium fusidate, a steroid antibiotic, in a commercial ointment using three different detectors: a) fluorescence detector, after a preliminary derivatization with 2-bromoacetyl-6-methoxynaphthalene (Br-AMN), b) UV detection and c) evaporative light scattering detector (ELSD). Fluorescent derivatization was applied directly to the diluted sample, without any purification, whilst UV and ELSD detectors involved a preliminary liquid-liquid extraction procedure to obtain accurate analysis data.

Levels of fusidic acid in skin blister fluid and serum after repeated administration of two dosages (250 and 500 mg)

The fusidic acid steady-state concentrations in serum (S) and skin suction blister fluid (SBF) after oral doses of 250 and 500 mg administered twice daily for 6 days, as film-coated tablets of sodium fusidate, were studied in eight healthy subjects. The mean peak serum concentrations after the 250- and 500- mg regimens were 39 +/- 5 and 102 +/- 11 mg/l, respectively, obtained between 2 and 3 h after drug intake. The corresponding values for SBF, obtained later, between 2 and 12 h after drug intake, were 21 +/- 5 and 79 +/- 11 mg/l. As measured by the ratio of area under the concentration vs. time curve (SBF/S), fusidic acid penetration is 69-75%, whatever the dose. With either regime, the fusidic acid SBF and serum levels exceed the minimal inhibitory concentration of bacteria usually found in skin infections, especially Staphylococcus species. A dose of 250 mg twice a day appears sufficient to treat these infections and could be tested in clinical studies.

[A spectrophotometric method of analysis of fusidic acid]

A spectrophotometric method for assay of fusidic acid is described. The method is based on reaction with a reagent consisting of acetic anhydride and concentrated sulfuric acid. Mathematical processing of the results of the main substance determination in fusidic acid preparations showed that the error did not exceed 2 per cent. Procedures for spectrophotometric assay of fusidic acid in control of the processes of its biosynthesis, isolation and purification were developed. The procedures provided control of the technological process of fusidic acid production.

Static and dynamic properties of tissue cage fluid in rabbits

The properties of tissue cage fluid in a steel net tissue cage model in rabbits were compared to those of serum by determination of the protein profile, the cell contents, and the pharmacokinetics of 125I albumin, 3H sucrose and 3H fusidic acid. The dominating serum proteins demonstrated by crossed immunoelectrophoresis were also detected in tissue cage fluid but at lower levels and at various ratios. The cell pattern gradually changed from an initial dominance of polymorphonuclear cells to lymphocytes during the five weeks following the subcutaneous implantation of the cages. The distribution of the highly protein-bound fusidic acid was markedly slower and the maximal tissue cage fluid level significantly lower than that of sucrose. Equilibrium of 125I albumin between serum and tissue cage fluid was slowly achieved during the following two weeks. The advantages and disadvantages of tissue cage models for studies of drug pharmacokinetics are discussed. The properties of tissue cage fluid and the possibility of repeated sampling make the model suitable for studies of experimental local infections. The influence of therapeutic agents and the host's response to the infectious process may also be elucidated.

Determination of sodium fusidate and fusidic acid in dosage forms by high-performance liquid chromatography and a microbiological method

A new High-performance liquid chromatographic (HPLC) method for the assay of sodium fusidate (I) or fusidic acid in dosage forms was developed and compared to a microbiological assay. A linear relationship was obtained between absolute peak area and amount of I(r = 0.99+) in the 50-1000-microgram/ml range. In the microbiological assay, Staphylococcus aureus (NCTC 6571) was the test organism, using an agar diffusion technique. With five test levels of the standard, potencies were interpolated from standard curve using a log transformation straight-line method with least-squares fitting (r = 0.99+). Both methods were applied to assay I (or fusidic acid) in tablets, a suspension, and an ointment. Excellent agreement was observed between results of the two methods.

The sustained release of antimicrobial drugs from bone cement. An appraisal of laboratory investigations and their significance

The release of gentamicin sulphate, sodium fusidate and diethanolamine fusidate from Palacos and CMW cements was studied using elution and serial plate transfer tests. Further tests were made to assay the drug remaining in the cement after antibacterial activity could no longer be detected by the above methods, to detect the sustained slow release of the residual drug, and to ascertain the mechanism of release. The results confirmed that the release of gentamicin sulphate could be detected for longer from Palacos cement than from CMW cement, but the opposite was true for sodium fusidate. Little difference was found in the case of diethanolamine fusidate. Comparison of elution and serial plate transfer tests, and of results of elution in buffers of different pH, demonstrated that the test method employed had a significant effect on the results, and the omission of details of methodology from some publications made comparison and evaluation of results difficult. Varying quantities of residual drug were found in cement from which antibacterial activity could no longer be demonstrated; further tests for sustained, slow release showed that the antibiotic did not remain fixed in the cement but was released at a rate too slow to be detected in the elution and serial plate transfer tests. It is concluded that antibiotics are released from the cement by a process of diffusion, but tests to determine the mechanism of diffusion were unhelpful. The theory of diffusion of drugs through solid matrices, and the clinical implications of the experimental findings, are discussed.

[Process of sodium fusidate inactivation as affected by oxygen and humidity]

The effect of oxygen and moisture on stability of sodium fusidate was studied. It was shown that inactivation of the antibiotic in the atmosphere of oxygen was due to its oxidation in the preparations with low humidity levels. In the preparations with high humidity levels, the main cause of the antibiotic inactivation was hydrolysis with respect to C-16-O-acetyl group. When sodium fusidate was air stored, the salts of 24, 25-dioxy-and 24, 25-dioxy-11-monoketofusidic acids were identified among the products of its inactivation. The salts of 24,25-dioxy-11-monoketofusidic acid were also prepared by oxidation of fusidic acid with potassium permanganate in a weak alkaline medium. The possibility of using sodium sulfite and metabisulfite as stabilizers for th antibiotic storage was shown.

Antibiotic-loaded acrylic cement

Laboratory experiments and clinical investigations have confirmed the various claims made originally by Buchholz and Engelbrecht (1970) that antibiotic-loaded acrylic cement releases the antibiotic into the surroundings in useful concentrations. Palacos R cement released higher concentrations than CMW, Simplex and Sulfix brands of cement and over longer periods. Concentrations of gentamycin and fucidin were sufficient to penetrate dead cortical bone. These conclusions need to be assessed with animal studies, mechanical testing and clinical results before the ideal place of antibiotic-loaded acrylic cement is established.

[Utilization of automatic systems for determining the biological activity of antibiotics by the agar diffusion method]

The Automatic Zone Analyzer AR-140 of Millipor intertech., inc. is an apparatus used for measurement of inhibition growth zones of test-microbes and estimation of antibiotic activity. The analyzer provides automatic registration of the data with high levels of accuracy and at least 99% reproducibility. The analyzer gives an effect in saving time as compared to the manual method by 5-7 times for the single-dose procedure and by 10-12 times for the three-dose procedure.