Pharmacokinetics of cisapride in the horse

The purpose of this study was to determine the pharmacokinetics and absolute bioavailability of cisapride after intravenous (i.v.) and intragastric (i.g.) administration in healthy, adult horses. Five animals received single doses of 0.1 mg/kg, 0.2 mg/kg and 0.4 mg/kg cisapride by the i.g. route in an open, randomized fashion on different occasions separated by a washout period of at least 48 h. Four of these horses were also given a single i.v. dose of 0.1 mg/kg cisapride. Jugular venous blood was collected periodically up to 24 h after dosing. Plasma cisapride concentrations were measured by high-performance liquid chromatography. There was considerable inter individual variability in pharmacokinetic parameters. The mean (SD) values for systemic clearance (CI) and steady-state volume of distribution (Vss) were 494 (43.6) mL/h/kg and 1471 (578) mL/kg, respectively. Although the rate of cisapride absorption was quite rapid, only about half the i.g. dose was absorbed systemically. The average terminal half-life (t1/2) calculated over three i.g. doses was 2.06 h and that for i.v. administration was 2.12 h. The pharmacokinetics of cisapride from 0.1 mg/kg to 0.4 mg/kg were independent of the i.g. dose.

NONMEM population pharmacokinetic modeling of orally administered cyclosporine from routine drug monitoring data after heart transplantation

The population pharmacokinetics of cyclosporine (CsA) in adult recipients of cardiac transplants were determined from sparse, retrospective drug monitoring data accumulated for at least 3 months after surgery. All were receiving oral CsA twice daily, and morning trough levels in whole-blood were measured by high-performance liquid chromatography. Additional data included height, weight, gender, age, ethnicity, hematocrit, total bilirubin, and concurrent drug use. Population modeling was performed using NONMEM on 36 randomly selected patients, assuming a one-compartment model with first-order absorption and elimination. Improved fits were obtained by incorporating the following expression in the model to adjust oral bioavailability as a function of postoperative day (POD): F = 0.2 + 10 x ABS (POD - 7)/([POD + 10] x 60). Interpatient variability (CV%) in clearance (CL) was 20.2%. There was a mean bias of 8.5% at the average CsA concentration of 250 ng/ml when the predictive performance was assessed statistically in a reserved subset of 33 patients who received cardiac transplants. For the entire population (n = 69 patients), the average CsA CL and terminal half-life (T1/2) were, respectively: CL (l/h) = 0.256 x weight (kg); T1/2 = 11.0 hours, or CL (l/h) = 0.184 x weight (kg); T1/2 = 14.7 hours, if there was concomitant diltiazem administration. These results compared favorably with those reported elsewhere for studies of postcardiac transplant kinetics using the traditional multiple blood sampling approach.

Effect of oral levodopa treatment on articulatory function in Parkinson's disease: preliminary results

To quantify lip function in 16 patients with Parkinson's disease, a computerized semiconductor lip pressure transducer system was used prior to subjects being administered oral levodopa and at approximately 0.5 hr, 1.5 hr, and 3.0 hr postmedication. Two blood samples were taken from each subject at varying times during the levodopa dosage interval, and the exact time and dosage of levodopa were noted. Lip function measurements were expressed as percentage changes from baseline and were plotted for each subject against time and levodopa concentrations to determine the effects of levodopa therapy on articulatory function. The results supported the effectiveness of levodopa therapy in improving lip function. In particular, lip pressures recorded during both speech and nonspeech tasks tended to improve after levodopa administration, the lip measures improving somewhat in parallel with the rise and fall of blood plasma levodopa concentrations. Evidence of a hysteresis effect was noted.

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.

Population pharmacokinetics of intravenous amoxicillin in very low birth weight infants

The population pharmacokinetics of amoxicillin were determined in 40 very premature infants (< or = 32 week gestational age, < 1500 g birth weight) who were receiving intravenous amoxicillin (50 mg/ kg, every 12 h) during the first days after birth. Serum amoxicillin concentrations were measured by HPLC. Clearance (CL) and volume of distribution (Vd) were modeled alone and under the influence of demographic and clinical covariates with a 1-compartment model with first-order elimination. The final population models with influential covariates were: CL(L/h) = 0.0000610 x body weight (g) and CL (L/h) = 0.0000805 x body weight (g), for infants also receiving gentamicin and not receiving gentamicin, respectively; Vd(L) = 0.678. The interpatient standard deviation (SD) for CL was 0.0351 L/h, and for Vd was 0.365 L. The intrapatient variability (SD) among observed and model-predicted serum concentrations was 13.7 mg/L. Evaluation of the predictive performance of this model in another group of infants (n = 16) indicated statistically insignificant bias (p > 0.05) of 3 mg/L among pairs of observed and Bayesian-predicted amoxicillin concentrations. The average population CL was smaller, but the average Vd and terminal half-life (t1/2) were larger than previously reported for healthy adults.

Haemodynamic responses and population pharmacokinetics of midazolam following administration to ventilated, preterm neonates

OBJECTIVE

To evaluate the effects of intravenous midazolam on haemodynamic variables and cerebral blood flow velocity (CBFV) and to determine the pharmacokinetics using a population approach in very low birthweight (VLBW) ventilated infants.

METHODOLOGY

Physiological variables were measured at predetermined times in 10 infants with birthweight < or = 1500 g following a bolus dose of intravenous midazolam (0.1 mg/kg). Heart rate, mean arterial blood pressure (MAP) and transcutaneous CO2 (TcPCO2) were recorded and CBFV was assessed by Doppler ultrasound. Midazolam concentrations were also measured and pharmacokinetic parameters determined using a population modelling package.

RESULTS

No change in heart rate occurred during the study period, while the MAP decreased by 3 mmHg 5 min after midazolam administration compared to baseline values. A non-significant fall in TcPCO2 was seen at 20 min. Mean CBFV decreased from the baseline by 12% at 5 min, then returning to predose values. Midazolam concentrations were in the range shown to be effective in sedation of paediatric intensive care infants with the elimination being delayed in comparison to older children.

CONCLUSIONS

As only minor cerebral and haemodynamic effects were found with the use of midazolam in stable ventilated preterm infants, it appears to be a safe, short-term sedative agent.

Population pharmacokinetics and pharmacodynamics of oral levodopa in parkinsonian patients

OBJECTIVE

The population pharmacokinetics and pharmacodynamics of a standardised oral test dose of levodopa have been determined in patients with mild to severe Parkinson's disease using parametric, non-linear mixed effect modelling with the program NON-MEM. Levodopa plasma concentration data and motor effect behaviour (tapping times) were obtained from 46 patients, for whom a total of 970 observations were available (approximately 21 pharmacokinetic and pharmacodynamic observations per patient). The pharmacokinetic-pharmacodynamic model used was a one-compartment first-order absorption model linked to the sigmoid EMax representation of the Hill equation via an equilibration rate-constant, ke0. The model was also tested via a reduction in the number of pharmacokinetic and pharmacodynamic data points to a total of four to eight per patient.

RESULTS

In the final regression models the Hoehn and Yahr (HY) status of the patient and duration of disease (DUR) were found to be important determinants of the pharmacodynamic parameters for levodopa. The pharmacokinetic parameters were not significantly affected by any covariates. A test group of 16 additional parkinsonian patients was used to evaluate the predictive performance of the population parameters. The predictive performance of the pharmacokinetic-pharmacodynamic modelling using the full and reduced data sets was evaluated in NONMEM using posthoc, Bayesian forecasting. Statistically insignificant bias existed among predicted and observed levodopa concentrations, whereas the pharmacodynamic model underpredicted the observed tapping times. There was little difference in the pharmacokinetic-pharmacodynamic predictive performance among results for the full and the reduced data sets.

CONCLUSION

In a clinical setting knowledge of the population pharmacokinetic and pharmacodynamic parameters for oral levodopa may prove useful in estimating the duration of the drug's beneficial motor activity in patients with mild to severe Parkinson's disease (Hoehn and Yahr status I-IV).

Interaction of norfloxacin with divalent and trivalent pharmaceutical cations. In vitro complexation and in vivo pharmacokinetic studies in the dog

The formation constants of the fluoroquinolones norfloxacin and ciprofloxacin with Mg2+ (log beta 1 = 2.97(4), log beta 2 = 5.6(2)), Zn2+ (log beta 1 = 3.77(2), log beta 2 = 7.59(3)), and Fe2+ (log beta 1 = 3.99(5), log beta 2 = 7.2(5)) were determined by potentiometric titration. The pH at which precipitation occurred in the titration solutions was compared for the metal ions Ca2+, Mg2+, Zn2+, Fe2+, Cu2+, and Al3+. The formation constants were used to predict a rank order of metals that may be expected to hinder the gastrointestinal absorption of the fluoroquinolones, in vivo. The effects of metal ions on the pharmacokinetics of orally-administered norfloxacin in the dog were investigated. Norfloxacin (12 mg/kg) was administered alone or with equimolar doses of each of the chloride salts of Ca2+, Mg2+, Zn2+, Fe2+, and Al3+. Statistically significant reductions in serum norfloxacin concentrations were observed after analysis by HPLC. The Cmax was reduced 29-85%, while the area under the norfloxacin serum concentration-time curve (AUC0-infinity) was reduced by 29-79%. The extent of the reduction in AUC0-infinity was correlated with the magnitude of the formation constant of the 1:1 norfloxacin:metal chelate complex for the divalent metal ions. On coadministration of 12 mg/kg norfloxacin with various doses of Mg2+ (chloride) the AUC0-infinity and Cmax decreased with increasing Mg2+ dose. The interaction peaked at a Mg2+:norfloxacin ratio of 1:2 suggesting the formation of a 1:2 Mg:norfloxacin complex. Formation constant data were used to simulate the percentage of norfloxacin complexed at pH 6.5. Combinations of metal ion and norfloxacin which result in only a small extent (< 20%) of norfloxacin complex formation can result in relatively large decreases in oral bioavailability of this antimicrobial agent.

Saliva as a valid alternative to serum in monitoring intravenous caffeine treatment for apnea of prematurity

Caffeine is a potentially useful alternative to theophylline for the treatment and prevention of apnea of prematurity because of its lower toxicity and longer terminal half-life. Monitoring of salivary caffeine concentrations is less invasive than blood sampling, especially in very sick premature neonates. Caffeine citrate-3 mg/kg, 15 mg/kg, or 30 mg/kg-was administered once daily for 7 days in a randomized, parallel design to 59 newborn, premature infants with an initial loading dose of twice the maintenance dose. Serum and saliva samples (131 pairs) were collected and assayed by high-performance liquid chromatography (HPLC) for caffeine content. Measurable caffeine concentrations in serum ranged from 0.28 to 93.3 mg/L and in saliva from 0.35 to 91.5 mg/L. The mean ratio of the saliva-to-serum concentrations was 0.924. There was no significant difference in precision between the serum and salivary data. The mean serum caffeine concentration was 29.9 mg/L, and the mean salivary concentration was 27.7 mg/L, indicating a small negative bias for saliva versus serum monitoring. Salivary caffeine concentration monitoring is a satisfactory alternative to blood sampling across a wide range of caffeine doses used to treat apnea.

Copper(II) complexes of the fluoroquinolone antimicrobial ciprofloxacin. Synthesis, X-ray structural characterization, and potentiometric study

Reaction of the fluoroquinolone antimicrobial ciprofloxacin with copper(II) nitrate in the presence of 2,2'-bipyridine resulted in the isolation of the complex [Cu(cip)(bipy) (Cl)0.7(NO3)0.3] (NO3).2H2O. Reaction of an aqueous solution of ciprofloxacin.HCl and NaCl with CuCl2 at pH 5.0 resulted in the isolation of [Cu(cip)2]Cl2.11H2O. The complex [Cu(cip) (bipy)(Cl)0.7(NO3)0.3] (NO3).2H2O crystallizes in the monoclinic space group P2(1)/n, with a = 13.955(8), b = 14.280(8), c = 14.192(6) A, beta = 93.10(4) degrees, Z = 4 with R = 0.046. The selective broadening of resonances in the 13C NMR spectrum of ciprofloxacin by the addition of Cu2+(aq) was employed to probe metal ion binding sites in the ligand. The protonation constants of norfloxacin and ciprofloxacin, and the formation constants with copper(II), were determined by potentiometric titrations at 25 degrees C. The additions of ciprofloxacin to metal to form ML and ML2 complexes exhibit stepwise formation constants of log K1 6.2(1) and log K2 11.1(3), respectively.

Theophylline population pharmacokinetics from routine monitoring data in very premature infants with apnoea

1. Theophylline is commonly used in neonatology for the treatment and prophylaxis of apnoea of prematurity, and during ventilator weaning. 2. NONMEM was used to study the population pharmacokinetics of intravenous and oral theophylline from retrospective drug monitoring data in 82 premature neonates, weighing < 1500 g at birth, and < or = 32 weeks gestational age. 3. Clearance (CL), volume of distribution (V), and oral bioavailability (F1) from liquid preparations were modelled alone, and under the influence of demographic and clinical covariates, assuming a 1-compartment model with first-order elimination. 4. The final population models with influential co-variates were as follows: CL (1h-1) = 0.0000123 *body weight (g) + 0.000377 *postnatal age (days); V (1) = 0.000937 *body weight (g); F = 0.918. 5. The CL was lower and V was higher than previously reported for less premature neonates, term babies, and older children. 6. Predictive performance of the population models was evaluated by Bayesian forecasting in a similar, but independent cohort of 30 infants. There was statistically insignificant bias and imprecision between measured and predicted serum theophylline concentrations. 7. Based on the validated population models, recommended maintenance theophylline dosages are provided for infants aged between 2 and 50 days, and weighing 700 to 2000 g.

Rapid and economical high-performance liquid chromatographic method for the determination of norfloxacin in serum using a microparticulate C18 guard cartridge

A rapid and economical high-performance liquid chromatographic assay is described for norfloxacin in serum. Samples (100 microliters) containing N-ethylnorfloxacin as the internal standard were extracted into 1 ml of chloroform. Chromatography was performed at 30 degrees C on a 40 x 3.2 mm I.D. C18 guard cartridge (3 microns spherical particles) using a mobile phase of 11% (v/v) acetonitrile in 0.01 M phosphate buffer (pH 2.5) containing 0.001 M triethylamine, and pumped at 1 ml/min. Detection was at 279 nm. The retention times of norfloxacin and internal standard were 1.9 and 2.9 min, respectively. Calibration curves were linear (r > 0.999) from 0.1 mg/l to at least 2.0 mg/l. Within-day and between-day precision (C.V.) were 8.6% or less, and accuracy was 5.3% or less. Absolute assay recovery of norfloxacin was over 70%.

Determination of the angiotensin-converting enzyme inhibitor lisinopril in urine using solid-phase extraction and reversed-phase high-performance liquid chromatography

A simple, accurate and precise high-performance liquid chromatographic method is described for assaying lisinopril in human urine. Urine (1 ml) containing lisinopril and enalaprilat (internal standard) was acidified with 10 microliters of 6 M nitric acid, passed through a Sep-Pak C18 cartridge and eluted with 3 ml of 10% acetonitrile, followed by 6 ml of distilled water. the separations were carried out using a mu Bondapak c18 column with a mobile phase comprising acetonitrile (60 ml), methanol (10 ml) and tetrahydrofuran (10 ml) in 15 mM phosphate buffer (920 ml) at pH 2.90. Separations were performed at 40 degrees C and detection was at 206 nm. Standard calibration plots of lisinopril in urine were linear (r > 0.998) and recovery was greater than 64%. The lowest quantifiable concentration was 0.5 micrograms/ml. Within-day and between-day imprecision (coefficient of variation) ranged from 2.51% to 9.26%, and inaccuracy was less than 8.3%.

Analysis of cisapride in neonatal plasma using high-performance liquid chromatography with a base-stable column and fluorescence detection

A simple, selective, sensitive, and precise high-performance liquid chromatographic plasma assay for the prokinetic drug cisapride is described. Alkalinised samples of plasma (100 microliters) were extracted with 1.0 ml of 10% (v/v) isopropanol in chloroform, dried, redissolved in mobile phase and injected. Chromatography was performed at 20 degrees C by pumping a mobile phase of acetonitrile (370 ml) in pH 5.2, 0.02 M phosphate buffer (630 ml) at 1.0 ml/min through a C8 Symmetry column. Cisapride and the internal standard were detected by fluorescence monitoring at 295 nm (excitation) and 350 nm (emission), and were eluted 5 min and 8 min, respectively, after injection. Calibration plots in bovine serum albumin (3% w/v) were linear (r > 0.999) from 5 to 250 ng/ml. Intra-day and inter-day precision (C.V.) was 9.5%, or less, and the accuracy was within 5.5% of the nominal concentration over the range 8-200 ng/ml. Total assay recovery was above 82%. Endogenous plasma components, the major cisapride metabolite (norcisapride), and other drugs used in neonatal pharmacotherapeutics did not interfere.

Rapid column liquid chromatographic analysis of flucloxacillin in plasma on a microparticulate pre-column

A rapid, sensitive, accurate and precise high-performance liquid chromatographic assay is described for flucloxacillin in plasma. Samples (100 microliters) containing dicloxacillin (internal standard) were extracted with ethyl acetate (2 ml). The mobile phase of acetonitrile (18%, v/v) in phosphate buffer (0.01 M, pH 7) was pumped at 1.2 ml/min through a 40 x 3.2 mm I.D. column (3 microns particles). Detection was at 220 nm. Calibration plots were linear (r > 0.9995) from 0.2 to 40 mg/l. Within-day and between-day coefficients of variation were less than 9% (n = 6). The detection limit was 0.05 mg/l and the limit of quantitation was 0.3 mg/l. Of 24 drugs tested, only phenytoin and carbamazepine may interfere in some patients' samples.

A retrospective study of risk factors of akathisia in terminally ill patients

Akathisia is a distressing disorder that manifests as a state of restlessness and motor agitation. We aim to highlight the problem of akathisia to the palliative care physician by identifying and quantifying risk factors in the terminally ill. A retrospective case-control study was utilized to investigate risk factors for akathisia. Medical records of cases (N = 100) and controls (N = 365) archived in a computerized database were downloaded and risk factors determined using conditional logistic regression analyses. Exposure to pharmacologically similar drugs, such as haloperidol [odds ratio (OR), 18.4; 95% confidence interval (CI), 8.2-41.4], prochlorperazine (OR, 8.1; 95% CI, 3.0-21.8), and promethazine (OR, 3.3; 95% CI, 1.3-8.0), conferred an increased risk. Other significant variables were exposure to morphine (OR, 5.3; 95% CI, 1.9-14.2), sodium valproate (OR, 2.5; 95% CI, 1.0-6.4), and sodium bicarbonate/tartrate (Ural) (OR, 4.2; 95% CI, 1.2-15.3). Highlighting factors that predispose patients to akathisia emphasizes that this syndrome should not be forgotten when treating the terminally ill. It is recommended that those drugs identified should be judicially used and carefully monitored.

Determination of dose-dependent absorption of amoxycillin from urinary excretion data in healthy subjects

Measurement of unchanged drug in urine was used to study the rate and extent of amoxycillin absorption after administration of amoxycillin sodium solution to six healthy subjects in a Latin-Square crossover design. The mean (95% CI) fraction of the dose excreted as unchanged amoxycillin decreased (P < 0.05) from 0.50 (0.44-0.56) after 97 mg amoxycillin sodium (= 0.25 mmol amoxycillin) to 0.23 (0.19-0.27) after 3103 mg (8 mmol), while the mean residence time determined from urinary excretion rate data increased (P < 0.05) from 1.54 (1.32-1.76) h to 2.16 (2.01-2.41) h. Plots of total urinary excretion and initial (0-30 min) excretion of unchanged drug vs dose indicated significant non-linearity above 776 mg doses. Michaelis-Menten parameters describing this relationship with respect to amount absorbed were 3.02 mmol for maximum amount absorbed and 1.93 mmol for amount absorbed at half maximum for 0-30 min. These results support a saturable absorption mechanism for amoxycillin which had clinical implications for high oral amoxycillin doses, and for competition with other drugs having capacity-limited absorption.

Determination of dexamethasone in plasma of premature neonates using high-performance liquid chromatography

A high-performance liquid chromatographic assay is described for dexamethasone in neonatal plasma. Samples (100 microliters) were extracted with ethyl acetate (1.0 ml) containing 50 ng of beclomethasone. The mobile phase of acetonitrile-0.01 M phosphate buffer (pH 7.0) (45:55, v/v) was pumped at a flow-rate of 1.0 ml/min through an Ultrasphere ODS column (5.0 microns particles). Detection was by UV absorbance at 240 nm. Calibration plots were linear (r2 > 0.999) from 10-1000 ng/ml. Within-day and between-day precision (C.V.%, coefficient of variation) between 15-900 ng/ml was 1.21-20.6%. Inaccuracy was 7.7%, or less. The minimum quantifiable concentration (C.V. approximately 20%) was 15 ng/ml. Recovery (20-1000 ng/ml) exceeded 75%. Concomitant neonatal medication did not interfere.

Gentamicin dosing in elderly patients based on bioelectrical impedance analysis

The relationship between gentamicin pharmacokinetics and measures of bioelectrical impedance (BI) in elderly patients was investigated with the aim of developing a potential noninvasive means of individualising gentamicin dosage. Linear regression analyses identified height/resistance2 as a statistically significant predictor of gentamicin distribution volume, V, [adjusted (adj)r2 = 0.53, coefficient of variation (CV) = 15.2%], and resistance/reactance and creatinine clearance (CLcr) as predictors of total systemic clearance, CL, adj r2 = 0.52, CV = 20.1%. Individualisation of gentamicin dosage regimens based on these relationships to achieve steady-state (SS), peak gentamicin concentrations, Css,max, and SS trough concentrations, Css,min, of 7.0 and 1.0 micrograms/ml, respectively, in an independent group of elderly patients resulted in serum gentamicin levels of 5.9 +/- 0.7 and 0.8 +/- 0.4 micrograms/ml. Mean absolute prediction errors averaged 0.7 +/- 0.5 micrograms/ml for Css,max and 0.5 +/- 0.3 micrograms/ml for Css,min. Measures of BI provided the best predictions of Css,max, whereas models based on CLcr alone were the best predictors of Css,min. This technique provides a means of complementing routine pharmacokinetic monitoring of gentamicin pharmacotherapy in the elderly hospitalised patient with reductions in patient discomfort and potential savings in time and cost.

Comparative in vitro and in vivo bioavailability of naproxen from tablet and caplet formulations

A 500 mg dose of naproxen in a caplet formulation (product A) or a tablet (Naprosyn 500, product B) was administered to 14 fasting healthy subjects on two separate occasions, separated by a 1-2 week washout period in an open, randomized crossover. Blood samples were drawn periodically and plasma naproxen concentrations measured by HPLC. The median time Tmax to reach peak concentration for product A was shorter than that for product B (1.025 h versus 1.5 h) but A and B were similar with respect to median peak plasma concentration Cmax (77.9 mg l-1 versus 71.4 mg l-1), and average area AUC0-infinity under the plasma concentration-time curve (1210.2 mg l-1 h versus 1211.0 mg l-1 h). In vitro parameters (A versus B) of mean dissolution time MDT (5.03 min versus 15.0 min), and time for 70% dissolution T70 (6.67 min versus 20.2 min), differed significantly.

13C N.M.R. and Single-Crystal X-Ray Structural Investigation of the Fluoroquinolone Antimicrobial Drug Norfloxacin 2DCl.D2O

The sites of deuteronation of the molecule norfloxacin.2DCl.D2O have been investigated by 13C n.m.r. and a single-crystal structure determination. The 13C n.m.r. spectrum of norfloxacin (3 M DCl ) displays 14 lines, seven of which display 19F-13C coupling. The observation of 19F-13C coupling for the resonance at 171.0 ppm (J 3.9 Hz) allows positive assignment of this resonance to the keto carbon atom. The position of this resonance was found to be sensitive to [D+]. The crystals of norfloxacin.2DCl.D2O are monoclinic, space group P21/c, with a 8.536(2), b 14.379(3), c 14.985(4) Ǻ, β 93.40(2)°, V 1836.0(7) Ǻ3, and Z = 4. The structure was refined to R 0.039 and Rw 0.041. The n.m.r. study, combined with the structural analysis permits assignment of the sites of deuteronation for this molecule as an oxygen of the carboxylic acid, the external nitrogen of the piperazine ring and the keto oxygen atom.

Pharmacokinetics and absolute bioavailability of cyclosporin following intravenous and abomasal administration to sheep

Cyclosporin A pharmacokinetics were studied following intravenous and abomasal dosing in an open, crossover study in healthy, merino ewes. Five different doses of cyclosporin A were dispersed in milk and administered into the abomasum through a surgically inserted fistula which simulates oral administration. Cyclosporin A was well tolerated. Whole blood concentrations of cyclosporin A were measured by HPLC and mean clearance (0.45 +/- 0.05 L h-1 kg-1), distribution volume (4.4 +/- 2.0 L kg-1), mean residence time (9.6 +/- 4.1 h) and half-life (12.1 +/- 3.1 h) were calculated cyclosporin A was excreted in urine or bile. Area under the curve increased proportionally with doses up to 26.3 mg kg-1, but was curvilinear above this dose. Abomasal bioavailability at 6.4 mg kg-1 was 0.26 +/- 0.09, and mean absorption time was 4.7 +/- 11.1 h. Considerable pharmacokinetic variability was observed, particularly after abomasal administration. Cyclosporin A pharmacokinetics in sheep lie within the values reported in man after renal, bone marrow and cardiac transplantation.

Individual theophylline dosing based on bioelectrical impedance analysis

The role of bioelectrical impedance (BI) analysis in determining slow-release theophylline dosage was evaluated in fifteen healthy subjects given a standard 200 mg dose. Reactance and l/resistance were identified as the most significant predictors of pre-dose, steady-state theophylline concentrations (Css,pre). Compared with doses based on body weight (8.8 mg kg-1 day-1), theophylline doses determined by BI analysis (9.6 +/- 2.4 mg kg-1 day-1) resulted in less biased (mean prediction error = 0.6 vs 1.4) though slightly less precise (mean squared error = 7.1 vs 6.3) Css,pre values. These differences were statistically insignificant (P > 0.05).

High-performance liquid chromatographic determination of amoxicillin in urine using solid-phase, ion-pair extraction and ultraviolet detection

A simple, robust high-performance liquid chromatographic method is described for assaying amoxicillin in urine. Sample clean-up involved solid-phase, ion-pair extraction onto Sep-Pak C18 cartridges followed by elution with acetonitrile (3%, v/v) in pH 4.85 buffer. Separations were performed on an Ultrasphere C18 column with a mobile phase comprising acetonitrile (32.5 ml) and pH 7.1 phosphate buffer (0.01 M, 1000 ml). Peaks were detected at 229 nm. Recovery was greater than 94%. Plots of peak area against urinary amoxicillin concentration were linear (r > 0.999) from 5 to 500 mg/l. Between-day and within-day imprecision (coefficient of variation) ranged between 3.0 and 15.5%. Inaccuracy was 7.1%, or less.