Rapid method for the analysis of itraconazole and hydroxyitraconazole in serum by high-performance liquid chromatography

An assay for the determination of itraconazole and its active metabolite hydroxyitraconazole in serum has been developed, using ketoconazole as internal standard. The procedure involved a one-step liquid-liquid extraction of the drug, its metabolite and the internal standard, followed by their separation by reversed-phase HPLC. In this paper the validation of this method is described.

Population pharmacokinetics of ceftazidime in cystic fibrosis patients analyzed by using a nonparametric algorithm and optimal sampling strategy

Postinfusion data obtained from 17 patients with cystic fibrosis participating in two clinical trials were used to develop population models for ceftazidime pharmacokinetics during continuous infusion. Determinant (D)-optimal sampling strategy (OSS) was used to evaluate the benefits of merging four maximally informative sampling times with population modeling. Full and sparse D-optimal sampling data sets were analyzed with the nonparametric expectation maximization (NPEM) algorithm and compared with the model obtained by the traditional standard two-stage approach. Individual pharmacokinetic parameter estimates were calculated by weighted nonlinear least-squares regression and by maximum a posteriori probability Bayesian estimator. Individual parameter estimates obtained with four D-optimally timed serum samples (OSS4) showed excellent correlation with parameter estimates obtained by using full data sets. The parameters of interest, clearance and volume of distribution, showed excellent agreement (R2 = 0.89 and R2 = 0.86). The ceftazidime population models were described as two-compartment kslope models, relating elimination constants to renal function. The NPEM-OSS4 model was described by the equations kel = 0.06516+ (0.00708.CLCR) and V1 = 0.1773 +/- 0.0406 liter/kg where CLCR is creatinine clearance in milliliters per minute per 1.73 m2, V1 is the volume of distribution of the central compartment, and kel is the elimination rate constant. Predictive performance evaluation for 31 patients with data which were not part of the model data sets showed that the NPEM-ALL model performed best, with significantly better precision than that of the standard two-stage model (P < 0.001). Predictions with the NPEM-OSS4 model were as precise as those with the NPEM-ALL model but slightly biased (-2.2 mg/liter; P < 0.01). D-optimal monitoring strategies coupled with population modeling results in useful and cost-effective population models and will be of advantage in clinical practice, as it allows pharmacokinetic-pharmacodynamic modeling with sparse data, thus describing the relationship between ceftazidime exposure and response in the treatment of acute exacerbations in patients with cystic fibrosis.

Stability of aztreonam in a portable pump reservoir used for home intravenous antibiotic treatment (HIVAT)

The stability of the monocyclic beta-lactam antibiotic aztreonam in portable pump reservoirs was studied during storage at temperatures of -20 degrees C and +5 degrees C and during drug delivery at 37 degrees C. Three 100-ml drug reservoirs and three glass containers containing 60 mg/ml aztreonam were stored at -20 degrees C and 2-ml samples were analysed in the freshly prepared solution and after thawing at days 7, 21, 28, 70 and after 6 months of storage. A separate triplicate batch of 100-ml prefilled drug reservoirs and glass containers containing a similar aztreonam concentration (60 mg/ml) were refrigerated and tested immediately after preparation and daily for 8 days and after 70 days. Solutions of aztreonam in duplicate freshly prepared reservoirs were tested for stability when the solution was pumped at 37 degrees C over a 24-h period. All solutions were inspected for visual changes and tested for pH. Drug concentration was analysed by high-performance liquid chromatography. No colour changes or pH differences were observed in any of the solutions in the reservoirs of containers. No statistically significant decrease in aztreonam concentration could be detected after 6 months of storage at -20 degrees C. Aztreonam was stable at 5 degrees C for at least 8 days. A 24-h pumping period at 37 degrees C showed a 3.6% decrease in aztreonam concentration. Aztreonam at a concentration of 60 mg/ml in a pump reservoir is sufficiently stable to be used in home intravenous antibiotic treatment programmes.

Prospective evaluation of a dose prediction algorithm for intravenous tobramycin in adolescent and adult patients with cystic fibrosis

The predictive performance of a new algorithm to calculate the initial daily dose of tobramycin in patients with cystic fibrosis (CF) was prospectively evaluated. Twenty-six patients with CF (15 men, 11 women, 18-45 years of age) with an acute exacerbation of their chronic pulmonary infection were treated with intravenous tobramycin. The initial dose was calculated with a previously presented algorithm. This algorithm was derived from correlation analysis performed on the adjusted daily dose guided by the determination of serum concentrations: dose (mg three times daily) = 90 + 2.13 x LBM (kg), where LBM (male) = (1.1 x body weight [BW]) - (128 x BW2/height2) and LBM (female) = (1.07 x BW) - (148 x BW2/height2). The predictive performance of this algorithm was evaluated comparing the calculated initial daily dose with the adjusted daily dose for peak and trough levels of 9-11 mg/L and 1.0 mg/L, respectively. Mean squared error and mean error were determined as reflections of precision and bias. The predictive performance of the algorithm was compared with historical data on the predictive performance of the standard equation to dose of 3.3 mg/kg body weight three times daily. The dose calculated with the algorithm proved to give peak serum concentrations in a narrower range and to have a greater precision, but bias was equal. Applying the algorithm, more patients had initial peak serum concentrations in the pre-determined range of 9-11 mg/L than when using the standard equation, so fewer dose adjustments had to be made.

Evaluation of a fluorescence polarographic immunoassay with increased sensitivity for measurement of low concentrations of tobramycin in serum

The limits of quantitation of the assay of tobramycin in serum by the fluorescence polarization immunoassay system marketed by Abbott Laboratories (TDxFLx system) are 0.1 and 10.0 mg/L. For some pharmacokinetic studies, however, a more sensitive analysis is needed. The sensitivity of the TDxFLx system can theoretically be increased 10-fold by pipetting buffer solution into the sample well and 450 microliters serum into the predilution well. The assay modified in this way can be run with the usual calibration of the apparatus for normal analysis. The analytical performance of this modification of the TDxFLx assay was assessed. Tobramycin concentrations ranged from 0.01 to 1.0 mg/L. Analytical recovery ranged from 85 to 95%. The coefficients of variation for within-run and between-run precision ranged from 0.5% to 5% and from 2% to 6%, respectively, for control concentrations ranging from 0.05 to 0.75 mg/L. Based on recovery and precision results, the lower limit of quantitation was established as 0.025 mg/L. There was no significant detectable cross-reactivity from ceftazidime, aztreonam, flucloxacillin, cilastatin, or imipenem. There was a small, but significant cross-reactivity from gentamicin and netilmicin. Hyperbilirubinemia did not affect the assay, but hyperlipidemia gave falsely elevated results of the tobramycin assay. It was concluded that modification of the assay resulted in an acceptable method to quantify low concentrations of tobramycin in serum.

[Agranulocytosis caused by clozapine: the importance of leukocyte monitoring and efficacy of hematopoietic growth factors]

In four patients, a woman aged 85 and three men aged 33, 42 and 70 years, clozapine-induced agranulocytosis was diagnosed. In three patients the white cell counts were not performed as they should have been. Two patients were treated for their agranulocytosis with granulocyte colony-stimulating factor (G-CSF; filgrastim). Two patients were not treated. The literature concerning clozapine-induced agranulocytosis and its treatment with growth factors consists of only a few case reports. Therefore a definite conclusion about the efficacy of the treatment for this particular indication is not yet possible.

Inhalation of antibiotics in cystic fibrosis

Aerosol administration of antipseudomonal antibiotics is commonly used in cystic fibrosis. However, its contribution to the improvement of lung function, infection and quality of life is not well-established. All articles published from 1965 until the present time concerning the inhalation of antibiotics in cystic fibrosis were collected by computerized literature search and analysed. Effective aerosol delivery is compromised by nebulizers with limited capacity to produce particles in the respirable range. Twelve studies concerning maintenance treatment were published. Four uncontrolled studies evaluating antibiotic aerosol maintenance treatment in stable patients indicated a beneficial effect in terms of reducing the number of hospital admissions. Eight placebo-controlled studies were found; six of these showed a significant improvement of lung function in the treatment group. Four studies showed a reduction of the number of hospital admissions. In some studies, there was a considerable negative effect of the nebulized placebo solution on the outcome, probably due to the improper choice of its osmolarity. Studies with antibiotic aerosols as adjunct to intravenous therapy in cystic fibrosis patients with an acute exacerbation showed no enhancement of the clinical effects of the intravenous antibiotic by the aerosol; sputum colony counts, however, were lower. Toxicity studies carried out so far have shown no renal or ototoxicity; however, long-term toxicity studies still have to be performed using higher dosages. Introduction or selection of resistant bacteria is relatively rare, but remains a matter of concern. Aerosol maintenance treatment with an appropriate antibiotic in high enough dosage can be recommended for patients with cystic fibrosis chronically infected with P. aeruginosa, and may improve lung function and reduce the number of hospital admissions due to an acute exacerbation.

Inhalation of antibiotics in cystic fibrosis

Aerosol administration of antipseudomonal antibiotics is commonly used in cystic fibrosis. However, its contribution to the improvement of lung function, infection and quality of life is not well-established. All articles published from 1965 until the present time concerning the inhalation of antibiotics in cystic fibrosis were collected by computerized literature search and analysed. Effective aerosol delivery is compromised by nebulizers with limited capacity to produce particles in the respirable range. Twelve studies concerning maintenance treatment were published. Four uncontrolled studies evaluating antibiotic aerosol maintenance treatment in stable patients indicated a beneficial effect in terms of reducing the number of hospital admissions. Eight placebo-controlled studies were found; six of these showed a significant improvement of lung function in the treatment group. Four studies showed a reduction of the number of hospital admissions. In some studies, there was a considerable negative effect of the nebulized placebo solution on the outcome, probably due to the improper choice of its osmolarity. Studies with antibiotic aerosols as adjunct to intravenous therapy in cystic fibrosis patients with an acute exacerbation showed no enhancement of the clinical effects of the intravenous antibiotic by the aerosol; sputum colony counts, however, were lower. Toxicity studies carried out so far have shown no renal or ototoxicity; however, long-term toxicity studies still have to be performed using higher dosages. Introduction or selection of resistant bacteria is relatively rare, but remains a matter of concern. Aerosol maintenance treatment with an appropriate antibiotic in high enough dosage can be recommended for patients with cystic fibrosis chronically infected with P. aeruginosa, and may improve lung function and reduce the number of hospital admissions due to an acute exacerbation.

Pharmacokinetics of ceftazidime in adult cystic fibrosis patients during continuous infusion and ambulatory treatment at home

Acute exacerbations of Pseudomonas aeruginosa lung infections were treated with ceftazidime (CTZ) by continuous infusion (CI) in eight adult cystic fibrosis (CF) patients. CTZ pharmacokinetics were studied after a single dose and during CI (100 mg/kg/24 h) with a CADD-PLUS infusion pump at home for 3 weeks. Individual CTZ pharmacokinetic parameters after single-dose administration were a half-life (t1/2 beta) of 1.90 +/- 0.85 h (mean +/- SD), a volume of distribution (Vs) of 0.28 +/- 0.08 L/kg, and a total body clearance (CL) of 0.152 +/- 0.014 L/h/kg. CL during CI was 0.147 +/- 0.019 L/h/kg, equal to the CL after a single dose. CTZ clearance at the start and at the end of the treatment did not differ. The mean fraction of the dose recovered from the urine was 92.6% (range 85.6-98.5%). Renal clearance was 0.147 +/- 0.015 L/h/kg and was not influenced by the pulmonary exacerbation. The early-morning serum concentrations were significantly higher than the afternoon levels (p < 0.02). The mean CTZ serum concentration during CI was 28.7 +/- 5.0 mg/L. Clinical condition and quality of life improved significantly during and after treatment. With the pharmacokinetic population data from the single-dose study, the CTZ steady-state concentrations during CI could be predicted [precision (root mean squared prediction error) 3.1 mg/L; bias (mean prediction error) 0.4 mg/L]. This method may serve as a model in the development of CTZ continuous-infusion dosage regimens in CF home treatment.

Suggestions for the optimization of the initial tobramycin dose in adolescent and adult patients with cystic fibrosis

Clinical pharmacokinetic data of intravenously administered tobramycin in 34 patients with cystic fibrosis (CF) were correlated with patient parameters. Patients began tobramycin therapy with 10 mg/kg/day in three divided doses. Peak and trough serum concentrations were measured. Tobramycin dose was adjusted to a 30 min postdose peak of 10 mg/L and a predose trough of 1 mg/L. Pharmacokinetic data were calculated according to a one-compartment open model and were correlated with clinical data. Tobramycin half-life and total body clearance did not correlate with age, actual body weight, lean body mass, height, or body surface area. Tobramycin volume of distribution correlated with actual body weight (p < 0.02), lean body mass (p < 0.002), height (p < 0.05), and body surface area (p < 0.01), but not with age. The required daily dose after adjustment to a peak serum concentration of 10 mg/L and a trough level of 1 mg/L correlated with lean body mass (p < 0.02) and body surface area (p < 0.05). Based on our findings, the initial daily dose of tobramycin in patients with CF should be calculated by lean body mass rather than actual body weight or body surface area. A formula is presented to calculate the initial daily dose of tobramycin in CF patients who have normal renal function. Monitoring of tobramycin serum levels remains, however, necessary.

Validation of tobramycin monitoring in adolescent and adult patients with cystic fibrosis

The predictive performance of a dosage calculation method for the optimization of tobramycin therapy was studied retrospectively in 29 patients with cystic fibrosis. The dosage calculation method was based on a linear one-compartment open model. It used peak and trough serum concentrations of the aminoglycoside. Bias in the peak concentration was 0.20 mg/L and precision was 1.2 mg/L. Bias in the trough concentration was -0.06 mg/L and precision was 0.33 mg/L. The results were clinically satisfactory. Comparison with previously published results of the predictive performance of other dosage calculation methods showed that the method studied was at least as good.

[Neonatal withdrawal symptoms following the use of clomipramine during pregnancy]

The case is described of a neonate who suffered from withdrawal symptoms within 24 hours after birth as a result of the use of clomipramine by the mother during pregnancy. The symptoms consisted of increased irritability, alternating hyper- en hypotonia, hyperreflexia, cyanosis and hypothermia. He was treated with clonazepam with good result. Prescription of clomipramine during pregnancy should be restricted to specific cases and the doses should be kept as low as possible. Because the symptoms are withdrawal symptoms, phenobarbital should not be used as treatment, as it increases drug metabolism by the liver causing an even faster decrease of plasma concentrations of clomipramine. Clonazepam is the drug of choice.

[Parkinsonism following addition of fluoxetine to the treatment with neuroleptics or carbamazepine]

This article describes three patients who developed parkinsonism when fluoxetine was added to their existing medication (neuroleptics or carbamazepine). Based on published pharmacological and neuroanatomical research we postulate a serotonin-dopamine antagonism to be operative in the development of drug-induced parkinsonism. Alternatively, the possibility of a pharmacokinetic interaction remains.