Assessment of bioelectrical impedance for individualizing gentamicin therapy in neonates

The use of bioelectrical impedance (BI) analysis as a non-invasive approach for individualizing gentamicin therapy in newborn infants has been investigated in a two phase study. In Phase I, 1/impedance and length were identified as statistically significant predictors of the distribution volume of gentamicin (Adj R2 = 0.78, CV = 12.42%), and length/impedance and post-conceptual age were predictors of total systemic clearance (Adj R2 = 0.83, CV = 14.5%), following the administration of 2.5 mg.kg-1 gentamicin to 17 neonates (gestational age (GA) 27 to 36 weeks). In a prospective validation of these relationships in an independent (Phase II) group of 27 infants (GA 26 to 41 weeks), predicted serum gentamicin concentrations were close to those achieved. Several instances of high prediction errors (predicted minus achieved levels) were observed in infants with known or suspected renal impairment and they caused significant (P < 0.05) perturbation in the bias and accuracy of the models. Daily BI measures over a four to five day period were able to detect individual changes in the fat-free body compartments, which were translated into alterations in gentamicin regimens. This simple, non-invasive and relatively inexpensive bedside technique provides a potentially valuable means to individualize gentamicin therapy without relying on the measurement of serum gentamicin concentration.

Simple microscale high-performance liquid chromatographic method for determination of furosemide in neonatal plasma

A simple microscale high-performance liquid chromatographic method using fluorescence detection for the quantitation of furosemide in neonatal plasma is described. Sample pre-treatment involved protein precipitation of 25 microliters of plasma with 100 microliters of acetonitrile. The mobile phase consisted of acetonitrile (460 ml) and 0.08 M orthophosphoric acid (540 ml) and was delivered at 1.1 ml/min. Calibration curves were linear from 0.1 to 25 micrograms/ml. Within-day and between-day imprecision (coefficient of variation) was 3.9-6.1, and 6.1-12.2%, respectively. Furosemide was eluted after 6.5 min and naproxen (internal standard) after 11.5 min. The assay was validated for application in neonatal plasma containing a wide range of albumin concentrations.

Measurement of dothiepin and its major metabolites in plasma by high-performance liquid chromatography

This paper describes a reversed-phase high-performance liquid chromatographic method which will simultaneously measure dothiepin and its three major metabolites (northiaden, northiaden-S-oxide and dothiepin-S-oxide) in plasma using trimipramine as internal standard. Sample preparation involved a basic extraction using diethyl ether followed by an acid back-extraction. The method we report is linear over the range 50-1000 ng/ml (r = 0.999), for all analytes. Total imprecision is less than 11% (coefficient of variation) and accuracy is greater than 94% (n = 20). Recovery of analytes varied considerably from 51.7% for northiaden-S-oxide to 90.2% for dothiepin-S-oxide.

The ketoconazole-cyclosporin interaction in an elderly renal transplant patient

Administration of ketoconazole to an elderly renal transplant patient who was taking cyclosporin resulted in markedly increased whole blood cyclosporin concentrations and evidence of both renal and hepatic dysfunction.

Temelastine does not affect theophylline pharmacokinetics in normal subjects

The pharmacokinetics of theophylline (i.v. aminophylline 250 mg) were studied in a balanced, double-blind crossover following the administration of oral temelastine (100 mg) or placebo, twice daily for 7 days, to 10 normal volunteers. Comparison of volumes of distribution, elimination rate constants, elimination half-lives and areas under the plasma concentration-time curve indicated that temelastine had no significant effect on theophylline pharmacokinetics.

Measurement of gliclazide in plasma by radial compression reversed-phase liquid chromatography

We describe a rapid, specific, and precise analysis for gliclazide in plasma by radial compression, reversed-phase, "high-performance" liquid chromatography. Gliclazide and the internal standard, 3-chlorogliclazide, are eluted after 4.4 and 6.8 min, respectively. Only 100 microL of plasma and minimal sample workup are required. The limit of detection for gliclazide in plasma is 0.5 mg/L (1.55 mumol/L) at 229 nm. Precision (CV) of the assay for 10 and 1 mg of gliclazide per litre is 2.1% and 6.4%, respectively.

Measurement of gliclazide in plasma by radial compression reversed-phase liquid chromatography

We describe a rapid, specific, and precise analysis for gliclazide in plasma by radial compression, reversed-phase, "high-performance" liquid chromatography. Gliclazide and the internal standard, 3-chlorogliclazide, are eluted after 4.4 and 6.8 min, respectively. Only 100 microL of plasma and minimal sample workup are required. The limit of detection for gliclazide in plasma is 0.5 mg/L (1.55 mumol/L) at 229 nm. Precision (CV) of the assay for 10 and 1 mg of gliclazide per litre is 2.1% and 6.4%, respectively.

Rapid HPLC analysis of cefoxitin in plasma and urine

A rapid, specific and precise method is described for the analysis of cefoxitin in plasma and urine by reversed-phase, high performance liquid chromatography (HPLC). Cefoxitin and the internal standard, 3-isobutyl-l-methyl xanthine are eluted after 5.3 and 7.5 min, respectively. The assay sensitivity limit is 1 to 2 mg/l of cefoxitin sodium at 254 nm. Commonly prescribed antibiotics do not interfere. The assay is suitable for routine monitoring and pharmacokinetic studies of cefoxitin.

Oral bioavailability of theophylline from hydroalcoholic and alcohol-free preparations

We investigated the bioavailability of theophylline in eight healthy subjects following the oral administration of theophylline (128 mg) in hydroalcoholic (Brondecon elixir) and alcohol-free (Nuelin syrup preparations. The trial was open, randomised and cross-over. Theophylline was rapidly absorbed from both preparations. Bioavailability was assessed by measuring peak theophylline concentration, time to peak, absorption half-life and area under the curve. We concluded that the bioavailability of theophylline from each orally administered product was similar.

Rapid liquid-chromatographic determination of metformin in plasma and urine

We describe an analysis for metformin in plasma and urine by use of cation-exchange "high-performance" liquid chromatography. The assay requires only 0.5 mL of sample and involves pretreatment with trichloroacetic acid containing an internal standard (1-propylbiguanide), followed by centrifugation and injection into the chromatograph. The column eluent is monitored at 230 nm. Metformin and 1-propylbiguanide give retention times of 8 and 10 min, respectively. Within-day and between-day precision (CV) for the assay of plasma containing 2 mg (1.2 X 10(-5) mol) of metformin hydrochloride per liter was 3.6 and 3.9%, respectively. Similar precision was obtained for urine. The limit of detection is about 0.1 mg (6.0 X 10(-7) mol) of metformin hydrochloride per liter. Several commonly used drugs, including other oral hypoglycemic agents, do not interfere with this method.

Rapid liquid-chromatographic determination of metformin in plasma and urine

We describe an analysis for metformin in plasma and urine by use of cation-exchange "high-performance" liquid chromatography. The assay requires only 0.5 mL of sample and involves pretreatment with trichloroacetic acid containing an internal standard (1-propylbiguanide), followed by centrifugation and injection into the chromatograph. The column eluent is monitored at 230 nm. Metformin and 1-propylbiguanide give retention times of 8 and 10 min, respectively. Within-day and between-day precision (CV) for the assay of plasma containing 2 mg (1.2 X 10(-5) mol) of metformin hydrochloride per liter was 3.6 and 3.9%, respectively. Similar precision was obtained for urine. The limit of detection is about 0.1 mg (6.0 X 10(-7) mol) of metformin hydrochloride per liter. Several commonly used drugs, including other oral hypoglycemic agents, do not interfere with this method.

Comparative bioavailability study of theophylline tablets marketed in Australasia

Average peak concentrations of theophylline in plasma (range, 15 mumol/L) were not significantly different when Nuelin, Brondecon and Choledyl tablets were administered to healthy subjects. The fraction of the theophylline dose absorbed from these preparations was comparable (range, 0.82 to 0.90). In contrast, the absorption of theophylline was significantly different (P < 0.001) when the times to reach peak theophylline concentration were compared. Mean peak theophylline concentrations were achieved 1.5 hours after administration of either Nuelin or Brondecon tablets and nine hours after Choledyl administration. Nuelin and Brondecon are considered to be bioequivalent. Choledyl may be used when side effects caused by rapid theophylline absorption are to be avoided.

Action of caffeine and theophylline on staphylococcal penicillinase synthesis

Both caffeine and theophylline acting in subinhibitory concentrations inhibit the synthesis of penicillinase in Staphylococcus aureus. Neither of these compounds inactivate the enzyme. Inhibition of penicillinase synthesis is attributed to the lack of formation of penicillinase rather than the elimination of the extrachromosomal plasmid.

Cultivation of Staphylococcus aureus in a synthetic medium of low ultraviolet absorptivity

A new synthetic medium having negligible ultraviolet absorbance is described for growing staphylococci in experiments requiring ultraviolet spectrophotometry of cell-free portions of the culture.