Population pharmacokinetics of fluconazole given for secondary prevention of oropharyngeal candidiasis in HIV-positive patients

OBJECTIVES

To determine fluconazole population pharmacokinetics and explore the relationships between fluconazole average concentration and treatment effectiveness or microbiological resistance induction during a study aimed at evaluating the efficacy, tolerability and resistance induction after secondary prevention with fluconazole (150 mg weekly) versus placebo in human immunodeficiency virus-positive (HIV+) patients with oropharyngeal candidiasis.

METHODS

Population pharmacokinetic parameters of fluconazole determined from 458 serum drug concentration measurements obtained over 37 months in 132 HIV + patients not receiving highly active antiretroviral therapy. Mean estimates and variabilities were generated using non-linear regression analysis. Logistic and linear regression analyses were used to explore the relationships between the estimated average concentration of fluconazole and candidiasis relapse or fungal resistance towards fluconazole.

RESULTS

Fluconazole kinetics were best described by a one-compartment model with first-order oral absorp tion from the gastrointestinal tract. The pharmacokinetics were influenced only by body weight. No effect was observed for gender, age, height or lymphocyte CD4 counts. The mean apparent population clearance was 0.79 l/h, the volume of distribution 571 and the absorption constant (ka) 0.93 h(-1). Inter-occasion variability in clearance (45%) was large relative to intersubject variability (21%). Taking into account the average fluconazole concentration or the time above the minimal inhibitory concentrations did not clinically improve the prediction of the occurrence of oropharyngeal relapse or microbiological resistance.

CONCLUSION

The relationship between fluconazole concentrations and preventive effectiveness was poor. Together with the rather large inter-occasion variability in fluconazole clearance, this suggests no role of therapeutic drug monitoring in optimising fluconazole treatment for secondary prevention.

Extractionless method for the simultaneous high-performance liquid chromatographic determination of urinary caffeine metabolites for N-acetyltransferase 2, cytochrome P450 1A2 and xanthine oxidase activity assessment

Urinary metabolic ratios of caffeine are used in humans to assess the enzymatic activities of cytochrome P450 isoenzyme 1A2 (CYP1A2), xanthine oxidase (XO) and for phenotyping individuals for the bimodal N-acetyltransferase 2 (NAT2), all of them involved in the activation or detoxification of various xenobiotic compounds. Most reported analytical procedures for the measurement of the urinary metabolites of caffeine include a liquid-liquid extraction of urine samples prior to their analysis by reversed-phase HPLC. At neutral to basic pH however, 5-acetylamino-6-formylamino-3-methyluracil (AFMU), a metabolite of caffeine, spontaneously decomposes to 5-acetylamino-6-amino-3-methyluracil (AAMU). Since AAMU is not extracted in most organic solvents, the extent of AFMU decomposition cannot be precisely assessed. Although the decomposition reaction can be minimized by immediate acidification of the urine, accurate results can only be obtained when both AAMU and AFMU are monitored, or alternatively, if AAMU is measured after complete transformation of AFMU into AAMU in basic conditions. We report a liquid chromatographic method for the simultaneous quantitative analysis of the five urinary metabolites of caffeine used for the CYP1A2, XO and NAT2 phenotyping studies: AAMU, AFMU, 1-methylxanthine, 1-methyluric acid and 1,7-dimethyluric acid. These metabolites are satisfactory separated from all other known caffeine metabolites as well as endogenous urinary constituents. Sample treatment does not require any liquid-liquid extraction procedure. Urine samples are diluted and centrifuged before being injected (10 microl) onto a YMC-Pack Polyamine II (250x4.6 mm) column. A step-wise gradient elution program is applied using acetonitrile-0.75% (v/v) formic acid: (91:9) at 0 min-->(75:25) at 25 min-->(65:35) at 35 min-->(65:35) at 45 min, followed by a re-equilibration step to the initial solvent composition. The flow-rate is 1.0 ml/min and the separations are monitored by UV absorbance at 260 and 280 nm. The procedure described here represents a substantial improvement over previous methods: a single analysis and a minimal urine sample treatment enables the simultaneous quantitation of five caffeine metabolites, notably AFMU and AAMU, used for the determination of CYP450 1A2, XO and NAT2 enzyme activity. Importantly enough, phenotyping individuals for the bimodal NAT2 is made possible without the uncertainty associated with the deformylation of AFMU, which is likely to happen at all steps prior to the analysis, during sample storage and even in the bladder of the subjects.

Diet acids and alkalis influence calcium retention in bone

The urine-acidifying properties of food constituents depend on their content of non-oxidizable acids or precursors. Acidifying constituents such as animal proteins may negatively affect calcium metabolism and accelerate bone resorption, thus representing an aggravating factor for osteoporosis. This four-period, double-crossover study investigated whether a diet intervention specifically focused on acid load could modify calcium metabolism in humans. Eight healthy volunteers underwent a four-day metabolic preparation with two types of diets, one rich in acid ash-forming nutrients, and one providing base-forming nutrients (including bicarbonate-rich mineral water), both having similar contents of calcium, phosphate, sodium, proteins and calories. On the fourth day, a single oral dose of 1 g calcium was given, either as carbonate or as gluconolactate. Serial blood and urine samples revealed that the diet affected blood pH (average difference 0.014, p=0.002) and urine pH (average difference 1.02, p<0.0001) in the expected direction, but had no influence on the absorption of the calcium supplement. The acid-forming diet increased urinary calcium excretion by 74% when compared with the base-forming diet (p<0.0001), both at baseline and after the oral calcium load, and C-telopeptide excretion by 19% (p=0.01), suggesting a skeletal origin for the excess calcium output. This observation confirms that renally excreted acids derived from food influence calcium metabolism, and that alkalizing nutrients inhibit bone resorption. Further studies are needed to determine the clinical impact of dietary counseling for avoiding diet acids as a preventive measure against osteoporosis.

Trace lithium in mood disorders

BACKGROUND

Variations in trace (endogenous) lithium exchanges have been postulated to play a role in the pathophysiology of affective diseases. This prospective study aimed to check whether plasma, erythrocytes and urine trace lithium levels were altered in mood disorders.

METHODS

Trace lithium was determined by atomic absorption spectrophotometry in patients without mood stabilizing drugs or somatic diseases, hospitalized for bipolar affective disorders, major depressive episodes, and other psychiatric disorders with depressive features. Patients admitted for psychotic disorders without mood alterations and healthy volunteers served as controls.

RESULTS

There were no differences in trace lithium status between the groups. Erythrocytes/plasma ratios appeared higher than described on therapeutic lithium (1.6+/-0.7, N = 199).

LIMITATIONS

The study had sufficient power to detect clinically significant differences in whole body lithium handling between the groups. However, it did not address alterations of lithium exchanges across neuronal membranes or the blood-brain barrier.

CONCLUSIONS

Alterations of membrane exchanges hypothetically associated with mood disorders are not reflected in plasma or erythrocytes trace lithium levels. The occurrence of mood disorders seems not to be related to abnormalities in endogenous lithium.

Effects of a dual inhibitor of angiotensin converting enzyme and neutral endopeptidase, MDL 100,240, on endocrine and renal functions in healthy volunteers

OBJECTIVE

To investigate the endocrine and renal effects of the dual inhibitor of angiotensin converting enzyme and neutral endopeptidase, MDL 100,240.

DESIGN

A randomized, placebo-controlled, crossover study was performed in 12 healthy volunteers.

METHODS

MDL 100,240 was administered intravenously over 20 min at single doses of 6.25 and 25 mg in subjects with a sodium intake of 280 (n = 6) or 80 (n = 6) mmol/day. Measurements were taken of supine and standing blood pressure, plasma angiotensin converting enzyme activity, angiotensin II, atrial natriuretic peptide, urinary atrial natriuretic peptide and cyclic GMP excretion, effective renal plasma flow and the glomerular filtration rate as p-aminohippurate and inulin clearances, electrolytes and segmental tubular function by endogenous lithium clearance.

RESULTS

Supine systolic blood pressure was consistently decreased by MDL 100,240, particularly after the high dose and during the low-salt intake. Diastolic blood pressure and heart rate did not change. Plasma angiotensin converting enzyme activity decreased rapidly and dose-dependently. In both the high- and the low-salt treatment groups, plasma angiotensin II levels fell and renin activity rose accordingly, while plasma atrial natriuretic peptide levels remained unchanged. In contrast, urinary atrial natriuretic peptide excretion increased dose-dependently under both diets, as did urinary cyclic GMP excretion. Effective renal plasma flow and the glomerular filtration rate did not change. The urinary flow rate increased markedly during the first 2 h following administration of either dose of MDL 100,240 (P < 0.001) and, similarly, sodium excretion tended to increase from 0 to 4 h after the dose (P = 0.07). Potassium excretion remained stable. Proximal and distal fractional sodium reabsorption were not significantly altered by the treatment. Uric acid excretion was increased. The safety and clinical tolerance of MDL 100,240 were good.

CONCLUSIONS

The increased fall in blood pressure in normal volunteers together with the preservation of renal hemodynamics and the increased urinary volume, atrial natriuretic peptide and cyclic GMP excretion distinguish MDL 100,240 as a double-enzyme inhibitor from inhibitors of the angiotensin converting enzyme alone. The differences appear to be due, at least in part, to increased renal exposure to atrial natriuretic peptide following neutral endopeptidase blockade.

Sinistrin clearance for determination of glomerular filtration rate: a reappraisal of various approaches using a new analytical method

Several approaches are available to estimate the glomerular filtration rate (GFR) from the sinistrin clearance. To compare such approaches, GFR was estimated in six healthy volunteers, both after a bolus injection and a bolus dose followed by a 6-hour infusion. A recently developed high-performance liquid chromatography method was used for the determination of sinistrin levels, enabling precise measurements in plasma and urine samples with high sensitivity. Blood and urine were sampled up to 6 hours. Four calculation methods for estimating GFR were applied: 1) classical ratio of urinary excretion rate over plasma concentration (UV/P); 2) two-point (log-linear regression slope times monocompartmental volume of distribution) after bolus; 3) ratio of dose over area under the curve (D/AUC) after bolus; and 4) ratio of infusion rate over steady-state concentration during infusion (Rinf/P). The results obtained by fitting a pharmacokinetic model to all the plasma and urine data served as the standard against which the performance of the respective calculation methods were examined. The UV/P method performed poorly on bolus data, mainly by underestimating GFR at late times; on both bolus and infusion data, it suffered from important imprecisions on the urinary volume. The two-point method appeared applicable only between 2 and 4 hours after the bolus dose. The D/AUC method with extrapolation to infinity was highly reliable when integrating the concentrations up to 3 hours or more after the bolus dose. The Rinf/P method was satisfactory if applied later than 2 to 3 hours after the loading dose. The advantages and drawbacks of each method have to be evaluated in relation to the particular clinical setting in which GFR is to be estimated.

Determination of the polyfructosan sinistrin in biological fluids by HPLC with electrochemical detection

A sensitive HPLC method with electrochemical detection was developed for the determination of the polyfructosan sinistrin in human plasma and urine. Proteins and interfering components such as glucose were removed from plasma and urine samples by solid phase extraction on C18 cartridges. Chromatographic separations were achieved at 85 degrees C on a 300 mm x 7.8 mm i.d. column, using ion moderated partition chromatography with distilled water at a flow rate of 0.6 ml min-1. After post-column addition of NaOH 0.3 M (0.6 ml min-1), the electrochemical detection of the eluate was performed with a sequence of three potentials (0.05 V, -0.8 V, 0.6 V) of specific pulse duration 300, 100 and 100 ms respectively. Xylose was used as internal standard for the quantitative determinations. The calibration curves were linear (r2 > 0.992) over the working range 5-300 micrograms ml-1. This method has been characterized, validated and applied successfully in a study comparing two modes of glomerular filtration rate determination in healthy volunteers (bolus vs. constant rate infusion of sinistrin).

Application of semi-preparative high-performance liquid chromatography to difficult natural product separations

Semi-preparative high-performance liquid chromatography on RP-18 with methanol-water as the mobile phase was used for the separation of homologous antifungal chromenes and related homologous dichromenes from Hypericum revolutum Vahl (Guttiferae). In the course of the structural elucidation of new saponins from Phylolacca dodecandra L'Hérit. (Phytolaccaceae), two isomeric oleanane saponins were separated on RP-8 with acetonitrile-water as the mobile phase.