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Biomedical subjects

B G Charles

Publications and source records attributed to B G Charles.

71 records · Page 4Linked to original sources

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.

Analysis of Variance↗

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.

Administration, Oral↗

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.

Chromatography, High Pressure Liquid↗

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.

Absorption↗

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.

Caffeine↗

Plasma pharmacokinetics of intravenous and intramuscular furosemide in the camel (Camelus dromedarius).

Single bolus intravenous (i.v.) and intramuscular (i.m.) doses of furosemide (1.5 mg kg(-1)) were administered in a crossover design to three female and three male adult, dromedary camels. Plasma furosemide concentrations were assayed by HPLC and sodium, potassium and chloride concentrations were measured using ion-selective electrodes. Plasma furosemide concentration-time plots indicated multi-compartment disposition, and there was considerable intersubject variability in the pharmacokinetic parameters. The mean (SD) i.v. terminal elimination half-life was 118 (67) minutes. The systemic clearance was 5.4 (1.2) ml min(-1) kg(-1). and the steady-state volume of distribution was 0.43 (0.14) litre kg(-1). The mean absorption time after i.m. dosing was 33 (62) minutes, while the absolute bioavailability was 71 (20) per cent. The glucuronide metabolite of furosemide was not detected in plasma. Clearance was lower, volume of distribution was larger, and half-life was longer compared with published data for dogs, horses, rats and humans. Plasma potassium and sodium concentrations were significantly diminished (P<0.05) by an average of 35.6 per cent (two to six hours post-dose) and 11.3 per cent (eight hours post-dose), respectively. Plasma chloride concentrations were not significantly affected by furosemide administration.

Animals↗

Periextubation caffeine in preterm neonates: a randomized dose response trial.

OBJECTIVE: To compare the effectiveness of three dosing regimens of caffeine for preterm infants in the periextubation period. METHODS: A randomized double-blind clinical trial of three dosing regimens of caffeine citrate (3, 15 and 30 mg/kg) for periextubation management of ventilated preterm infants was undertaken. Infants born <32 weeks gestation who were ventilated for>48 h were eligible for the study. Caffeine citrate was given as a once daily dose for a period of 6 days commencing 24 h prior to a planned extubation, or within 6 h of an unplanned extubation. The primary outcome measure was extubation failure, defined as neonates who were unable to be extubated within 48 h of caffeine loading or who required reventilation or doxapram dose within 7 days of caffeine loading. Continuous recordings of oxygen saturation and heart rate were undertaken in a subgroup of enrolled infants. RESULTS: A total of 127 babies were enrolled into the study (42, 40, 45, in the 3, 15, and 30 mg/kg groups, respectively). No statistically significant difference was demonstrated in the incidence of extubation failure between dosing groups (19, 10, and 11 infants in the 3, 15, and 30 mg/kg groups, respectively), however, infants in the two higher dose groups had statistically significantly less documented apnoea than the lowest dose group. Of the 37 neonates with continuous pulse oximetry recordings, those on higher doses of caffeine recorded a statistically significantly higher mean heart rate, oxygen saturations and less time with oxygen saturations <85%. CONCLUSIONS: This trial indicated there were short-term benefits of decreased apnoea in the immediate periextubation period for ventilated infants born <32 weeks gestation receiving higher doses of caffeine. Further studies with larger numbers of infants assessing longer-term outcomes are necessary to determine the optimal dosing regimen of caffeine in preterm infants.

Apnea↗