The effect of breastmilk and saliva combinations on the in vitro growth of oral pathogenic and commensal microorganisms

Neonates are exposed to microbes in utero and at birth, thereby establishing their microbiota (healthy microbial colonisers). Previously, we reported significant differences in the neonatal oral microbiota of breast-fed and formula-fed babies after first discovering a primal metabolic mechanism that occurs when breastmilk (containing the enzyme xanthine oxidase) and neonatal saliva (containing highly elevated concentrations of the substrates for xanthine oxidase: xanthine and hypoxanthine). The interaction of neonatal saliva and breast milk releases antibacterial compounds including hydrogen peroxide, and regulates the growth of bacteria. Using a novel in vitro experimental approach, the current study compared the effects of this unique metabolic pathway on a range of bacterial species and determined the period of time that microbial growth was affected. We demonstrated that microbial growth was inhibited predominately, immediately and for up to 24 hr following breastmilk and saliva mixing; however, some microorganisms were able to recover and continue to grow following exposure to these micromolar amounts of hydrogen peroxide. Interestingly, growth inhibition was independent of whether the organisms possessed a catalase enzyme. This study further confirms that this is one mechanism that contributes to the significant differences in the neonatal oral microbiota of breast-fed and formula-fed babies.

Collection and determination of nucleotide metabolites in neonatal and adult saliva by high performance liquid chromatography with tandem mass spectrometry

Saliva contains a number of biochemical components which may be useful for diagnosis/monitoring of metabolic disorders, and as markers of cancer or heart disease. Saliva collection is attractive as a non-invasive sampling method for infants and elderly patients. We present a method suitable for saliva collection from neonates. We have applied this technique for the determination of salivary nucleotide metabolites. Saliva was collected from 10 healthy neonates using washed cotton swabs, and directly from 10 adults. Two methods for saliva extraction from oral swabs were evaluated. The analytes were then separated using high performance liquid chromatography (HPLC) with tandem mass spectrometry (MS/MS). The limits of detection for 14 purine/pyrimidine metabolites were variable, ranging from 0.01 to 1.0μM. Recovery of hydrophobic purine/pyrimidine metabolites from cotton tips was consistently high using water/acetonitrile extraction (92.7-111%) compared with water extraction alone. The concentrations of these metabolites were significantly higher in neonatal saliva than in adults. Preliminary ranges for nucleotide metabolites in neonatal and adult saliva are reported. Hypoxanthine and xanthine were grossly raised in neonates (49.3±25.4; 30.9±19.5μM respectively) compared to adults (4.3±3.3; 4.6±4.5μM); nucleosides were also markedly raised in neonates. This study focuses on three essential details: contamination of oral swabs during manufacturing and how to overcome this; weighing swabs to accurately measure small saliva volumes; and methods for extracting saliva metabolites of interest from cotton swabs. A method is described for determining nucleotide metabolites using HPLC with photodiode array or MS/MS. The advantages of utilising saliva are highlighted. Nucleotide metabolites were not simply in equilibrium with plasma, but may be actively secreted into saliva, and this process is more active in neonates than adults.

Population pharmacokinetics of mefloquine in military personnel for prophylaxis against malaria infection during field deployment

OBJECTIVE

The purpose of this study was to determine the population pharmacokinetics of mefloquine in healthy military personnel during prophylaxis for malaria infections.

METHODS

The subjects were 1,111 Australian soldiers participating in two studies: a randomised double-blinded study (group A, 161 subjects) and an open-label study (group B, 950 subjects). Following a loading dose (250 mg mefloquine base daily, 3 days), subjects received an oral weekly maintenance dose of 250 mg over 6 months. Blood was collected after the last split loading dose then at weeks 4, 8 and 16 for group A, and at weeks 13 and 26 for group B. Plasma mefloquine concentrations were measured by high-performance liquid chromatography (HPLC). Pharmacokinetic modelling was performed using NONMEM.

RESULTS

A two-compartment model with inter-occasion variability (IOV) for clearance satisfactorily described the pharmacokinetics. Typical values were clearance (CL/F, 2.09 l/h), central volume of distribution (V1/F, 528 l), absorption rate constant (KA, 0.24 h(-1)), inter-compartmental clearance (Q/F, 12.5 l/h), peripheral volume of distribution (V2/F, 483 l) and elimination half-life (t (1/2), 14.0 days). Weight had a positive influence on central volume but was insufficient to warrant dosage adjustments. The inter-individual variability (coefficient of variation, CV%) for CL/F and V1/F was 24.4% and 29.6%, respectively. The IOV for CL/F was 17.8%. The proportional residual error (CV%) for groups A and B was 11.5% and 19.5%, respectively, and the additive error standard deviation (SD) was 57 ng/ml and 149 ng/ml, respectively.

CONCLUSION

The typical parameter values were comparable with those estimated in much smaller cohorts of healthy subjects and in malaria patients treated with single-dose mefloquine. The lower unexplained variability in the blinded study suggested these subjects may have been more compliant in taking their medication than soldiers in the open-label study.

Toxicokinetics of the active doxorubicin metabolite, doxorubicinol, in sulphur-crested cockatoos (Cacatua galerita)

The pharmacokinetics of doxorubicinol, a cytotoxic metabolite of the anticancer drug, doxorubicin, were studied in four healthy sulphur-crested cockatoos (Cacatua galerita) after a 20 min intravenous infusion of 2 mg/kg. Plasma doxorubicinol concentrations were measured by HPLC. The pharmacokinetic parameters were estimated using a non-compartmental method. The mean (+/- SD) peak concentration was 8341 +/- 3132 microg/L at 17.5 +/- 5.0 min after the start of the infusion, and doxorubicinol concentrations declined biexponentially to 154.3 +/- 34.5 microg/L, 40 min after the end of the infusion. Systemic clearance was 0.940 +/- 0.473 L/h/kg, mean residence time was 0.165 +/- 0.133 h, and steady-state volume of distribution was 0.123 +/- 0.0526 L/kg. The terminal half-life was 0.660 +/- 0.611 h. Detectible but unquantifiable concentrations of doxorubicinol were present in the plasma ultrafiltrate of two birds during the infusion, indicating very extensive plasma protein binding. Physiological, haematological and biochemical monitoring over 3 weeks showed that doxorubicinol at a single infused dose of 2 mg/kg caused no toxicities of major concern.

A rapid and sensitive microscale HPLC method for the determination of indomethacin in plasma of premature neonates with patent ductus arteriousus

Indomethacin (IND) is the drug of choice for the closure of a patent ductus arteriosus (PDA) in neonates. This paper describes a simple, sensitive, accurate and precise microscale HPLC method suitable for the analysis of IND in plasma of premature neonates. Samples were prepared by plasma protein precipitation with acetonitrile containing the methyl ester of IND as the internal standard (IS). Chromatography was performed on a Hypersil C(18) column. The mobile phase of methanol, water and orthophosphoric acid (70:29.5:0.5, v/v, respectively), was delivered at 1.5 mL/min and monitored at 270 nm. IND and the IS were eluted at 2.9 and 4.3 min, respectively. Calibrations were linear (r>0.999) from 25 to 2500 microg/L. The inter- and intra-day assay imprecision was less than 4.3 % at 400-2000 microg/L, and less than 22.1% at 35 microg/L. Inaccuracy ranged from -6.0% to +1.0% from 35 to 2000 microg/L. The absolute recovery of IND over this range was 93.0-113.3%. The IS was stable for at least 36 h when added to plasma at ambient temperature. This method is suitable for pharmacokinetic studies of IND and has potential for monitoring therapy in infants with PDA when a target therapeutic range for IND has been validated.

Doxorubicin pharmacokinetics following a single-dose infusion to sulphur-crested cockatoos (Cacatua galerita)

OBJECTIVE

To determine the pharmacokinetics of doxorubicin in sulphur-crested cockatoos, so that its use in clinical studies in birds can be considered.

DESIGN

A pharmacokinetic study of doxorubicin, following a single intravenous (i.v.) infusion over 20 min, was performed in four healthy sulphur-crested cockatoos (Cacatua galerita).

PROCEDURE

Birds were anaesthetised and both jugular veins were cannulated, one for doxorubicin infusion and the other for blood collection. Doxorubicin hydrochloride (2 mg/kg) in normal saline was infused i.v. over 20 min at a constant rate. Serial blood samples were collected for 96 h after initiation of the infusion. Plasma doxorubicin concentrations were assayed using an HPLC method involving ethyl acetate extraction, reverse-phase chromatography and fluorescence detection. The limit of quantification was 20 ng/mL. Established non-parametric methods were used for the analysis of plasma doxorubicin data.

RESULTS

During the infusion the mean +/- SD for the Cmax of doxorubicin was 4037 +/- 2577 ng/mL. Plasma concentrations declined biexponentially immediately after the infusion was ceased. There was considerable intersubject variability in all pharmacokinetic variables. The terminal (beta-phase) half-life was 41.4 +/- 18.5 min, the systemic clearance (CI) was 45.7 +/- 18.0 mL/min/kg, the mean residence time (MRT) was 4.8 +/- 1.4 min, and the volume of distribution at steady state (V(SS)) was 238 +/- 131 mL/kg. The extrapolated area under the curve (AUC(0-infinity)) was 950 +/- 677 ng/mL x h. The reduced metabolite, doxorubicinol, was detected in the plasma of all four parrots but could be quantified in only one bird with the profile suggesting formation rate-limited pharmacokinetics of doxorubicinol.

CONCLUSIONS AND CLINICAL RELEVANCE

Doxorubicin infusion in sulphur-crested cockatoos produced mild, transient inappetence. The volume of distribution per kilogram and terminal half-life were considerably smaller, but the clearance per kilogram was similar to or larger than reported in the dog, rat and humans. Traces of doxorubicinol, a metabolite of doxorubicin, were detected in the plasma.

Carboplatin pharmacokinetics following a single-dose infusion in sulphur-crested cockatoos (Cacatua galerita)

OBJECTIVE

To determine the pharmacokinetics of carboplatin in sulphur-crested cockatoos, so that its use in clinical studies in birds can be considered.

DESIGN

A pharmacokinetic study of carboplatin, following a single intravenous (IV) or intraosseus (IO) infusion over 3 min, was performed in six healthy sulphur-crested cockatoos (Cacatua galerita).

PROCEDURE

Birds were anaesthetised and a jugular vein cannulated for blood collection. Carboplatin (5 mg/kg) was infused over 3 min by the IV route in four birds via the contralateral jugular vein, and by the IO route in two birds via the ulna. Serial blood samples were collected for 96 h after initiation of the infusion. Tissue samples from 11 organs were obtained at necropsy, 96 h after carboplatin administration. Total Pt and filterable Pt in plasma and tissue Pt concentrations were assayed by inductively coupled plasma-mass spectrometry. A noncompartmental pharmacokinetic analysis was performed on the plasma data.

RESULTS

The mean +/- SD for the Cmax of filterable Pt was 27.3 +/- 4.06 mg/L and in all six birds occurred at the end of the 3 min infusion, thenceforth declining exponentially over the next 6 h to an average concentration of 0.128 +/- 0.065 mg/L. The terminal half-life (T1/2) was 1.0 +/- 0.17 h, the systemic clearance (CI) was 5.50 +/- 1.06 mL/min/kg and the volume of distribution (Vss) was 0.378 +/- 0.073 L/kg. The extrapolated area under the curve (AUC0-x) was 0.903 +/- 0.127 mg/mL x min; the area extrapolated past the last (6 h) data point to infinite time averaged only 1.25% of the total AUC0-x. The kidneys had the greatest accumulation of Pt (7.04 +/- 3.006 microg/g), followed by the liver (3.08 +/- 1.785 microg/g DM).

CONCLUSIONS AND CLINICAL RELEVANCE

Carboplatin infusion in sulphur-crested cockatoos produced mild, transient alimentary tract signs and the Pt plasma concentration was similar whether carboplatin was given intravenously or intraosseously. Filterable plasma Pt concentrations for carboplatin persisted longer than for cisplatin, due mostly to the difference in systemic clearance between these drugs in sulphur-crested cockatoos. The distribution of tissue Pt after carboplatin administration was similar to that reported for cisplatin in sulphur-crested cockatoos. Despite anatomical, physiological and biochemical differences among animal species, the pharmacokinetic disposition of filterable Pt in the sulphur-crested cockatoo shares some features with the kinetics reported previously in other animals and human beings.

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.

Pharmacokinetic software for the health sciences: choosing the right package for teaching purposes

Computer assisted learning has an important role in the teaching of pharmacokinetics to health sciences students because it transfers the emphasis from the purely mathematical domain to an 'experiential' domain in which graphical and symbolic representations of actions and their consequences form the major focus for learning. Basic pharmacokinetic concepts can be taught by experimenting with the interplay between dose and dosage interval with drug absorption (e.g. absorption rate, bioavailability), drug distribution (e.g. volume of distribution, protein binding) and drug elimination (e.g. clearance) on drug concentrations using library ('canned') pharmacokinetic models. Such 'what if' approaches are found in calculator-simulators such as PharmaCalc, Practical Pharmacokinetics and PK Solutions. Others such as SAAM II, ModelMaker, and Stella represent the 'systems dynamics' genre, which requires the user to conceptualise a problem and formulate the model on-screen using symbols, icons, and directional arrows. The choice of software should be determined by the aims of the subject/course, the experience and background of the students in pharmacokinetics, and institutional factors including price and networking capabilities of the package(s). Enhanced learning may result if the computer teaching of pharmacokinetics is supported by tutorials, especially where the techniques are applied to solving problems in which the link with healthcare practices is clearly established.

Population pharmacokinetics of perhexiline from very sparse, routine monitoring data

Using NONMEM, the population pharmacokinetics of perhexiline were studied in 88 patients (34 F, 54 M) who were being treated for refractory angina. Their mean +/- SD (range) age was 75 +/- 9.9 years (46-92), and the length of perhexiline treatment was 56 +/- 77 weeks (0.3-416). The sampling time after a dose was 14.1 +/- 21.4 hours (0.5-200), and the perhexiline plasma concentrations were 0.39 +/- 0.32 mg/L (0.03-1.56). A one-compartment model with first-order absorption was fitted to the data using the first-order (FO) approximation. The best model contained 2 subpopulations (obtained via the $MIXTURE subroutine) of 77 subjects (subgroup A) and 11 subjects (subgroup B) that had typical values for clearance (CL/F) of 21.8 L/h and 2.06 L/h, respectively. The volumes of distribution (V/F) were 1470 L and 260 L, respectively, which suggested a reduction in presystemic metabolism in subgroup B. The interindividual variability (CV%) was modeled logarithmically and for CL/F ranged from 69.1% (subgroup A) to 86.3% (subgroup B). The interindividual variability in V/F was 111%. The residual variability unexplained by the population model was 28.2%. These results confirm and extend the existing pharmacokinetic data on perhexiline, especially the bimodal distribution of CL/F manifested via an inherited deficiency in hepatic and extrahepatic CYP2D6 activity.

Population pharmacokinetics of the new antimalarial agent tafenoquine in Thai soldiers

AIMS

To describe the population pharmacokinetics of tafenoquine in healthy volunteers after receiving tafenoquine for malaria prophylaxis.

METHODS

The population consisted of 135 male Thai soldiers (mean age 28.9 years; weight 60.3 kg). All soldiers were presumptively treated with artesunate for 3 days plus doxycycline for 7 days to remove any pre-existing malaria infections. After the treatment regime, 104 soldiers (drug group) received a loading dose of 400 mg tafenoquine base daily for 3 days followed by 400 mg tafenoquine monthly for 5 consecutive months. In the placebo group, 31 soldiers were infected with malaria during the study period. They were re-treated with artesunate for 3 days plus doxycycline for 7 days followed by a loading dose of 400 mg tafenoquine daily for 3 days and then 400 mg tafenoquine weekly for prophylaxis. Blood samples were randomly collected from each soldier on monthly and weekly prophylaxis. Plasma tafenoquine concentrations were measured by h.p.l.c. Population pharmacokinetic modelling was performed using NONMEM.

RESULTS

A one-compartment model was found best to describe the pharmacokinetics of tafenoquine after oral administration. Age and weight influenced volume of distribution (V/F), and subjects who contracted malaria had higher clearance (CL/F), but none of these factors was considered to have sufficient impact to warrant change in dosing. The population estimates of the first-order absorption rate constant (Ka), CL/F and V/F were 0.694 h(-1), 3.20 l h(-1) and 1820 l, respectively. The intersubject variability in these parameters (coefficient of variation, CV%) was 61.2%, 25.3% and 14.8%, respectively. The absorption and elimination half-lives were 1.0 h and 16.4 days, respectively. The residual (unexplained) variability was 17.9%.

CONCLUSIONS

The population pharmacokinetics of orally administered tafenoquine have been determined in Thai soldiers under field conditions. This information, together with its known potent antimalarial activity, portends well for the application of tafenoquine as a useful prophylactic drug or for short-term radical treatment of vivax malaria.

Population pharmacokinetics of tacrolimus in children who receive cut-down or full liver transplants

BACKGROUND

The aim of this study was to investigate the population pharmacokinetics of tacrolimus in pediatric liver transplant recipients and to identify factors that may explain pharmacokinetic variability.

METHODS

Data were collected retrospectively from 35 children who received oral immunosuppressant therapy with tacrolimus. Maximum likelihood estimates were sought for the typical values of apparent clearance (CL/F) and apparent volume of distribution (V/F) with the program NONMEM. Factors screened for influence on the pharmacokinetic parameters were weight, age, gender, postoperative day, days since commencing tacrolimus therapy, transplant type (whole child liver or cut-down adult liver), liver function tests (bilirubin, alkaline phosphatase [ALP], aspartate aminotransferase [AST], gamma-glutamyl transferase [GGT], alanine aminotransferase [ALT]), creatinine clearance, hematocrit, corticosteroid dose, and concurrent therapy with metabolic inducers and inhibitors of tacrolimus.

RESULTS

No clear correlation existed between tacrolimus dosage and blood concentrations (r2=0.003). Transplant type, age, and liver function test values were the most important factors (P<0.01) that influenced the pharmacokinetics of tacrolimus. CL/F estimates were greater in whole liver recipients, decreased with increasing patient age and AST values, and increased with increasing GGT values. Average parameter estimates were CL/F=5.75 L/h (cut-down liver), CL/F=44 L/h (whole liver), and V/F=617 L. Marked intersubject variability (CV%=110% to 297%) and residual variability (CV%=42%) was observed.

CONCLUSIONS

Pharmacokinetic information obtained in this study may assist physicians in making individualized dosage decisions in regard to tacrolimus in pediatric liver transplant recipients. Children who received a whole child's liver appeared to retain "pediatric" clearance, whereas those who received a cut-down adult liver had "adult" clearances (on average 7-fold less).

Population pharmacokinetics of magnesium in preeclampsia

OBJECTIVE

The purpose of this study was to determine the population pharmacokinetics of magnesium from sparse observational data in patients with preeclampsia.

STUDY DESIGN

Serum magnesium concentrations (1-11 per patient) were obtained retrospectively from the records of 116 patients with preeclampsia who had a loading dose of magnesium sulfate (16 or 20 mmol), followed by a maintenance dose (1 mmol/h) over an average of 28 hours. Population clearance, volume of distribution, and the baseline magnesium concentration were estimated using the NONMEM program.

RESULTS

The following population typical values, together with the interpatient variability (expressed as coefficient of variation) were obtained with the use of a 1-compartment model: systemic clearance, 4.28 L/h (37.3%); volume of distribution, 32.3 L (32.1%); baseline concentration, 0.811 mmol/L (18.5%). The average half-life was 5.2 hours. Clonus was not obtunded in 4 patients whose serum magnesium concentrations were similar to the average concentration of 1.7 mmol/L. The variability remaining unexplained after the population model was fitted to the data was 6.5% to 10.8%.

CONCLUSION

This study extended knowledge of the pharmacokinetic disposition of magnesium in preeclampsia. The results are potentially useful for the calculation of loading and maintenance doses, particularly when the relationship between serum concentration and effect in preeclampsia is clarified.

Population pharmacokinetics of tacrolimus in Asian paediatric liver transplant patients

AIMS

The purpose of this study was to describe the population pharmacokinetics of intravenous and oral tacrolimus (FK506) in 20 Asian paediatric patients, aged 1-14 years, following liver transplantation and to identify possible relationships between clinical covariates and population parameter estimates.

METHODS

Details of drug dosage histories, sampling times and concentrations were collected retrospectively from routine therapeutic drug monitoring data accumulated for at least 4 days after surgery. Before analysis, patients were randomly allocated to either the population data set (n = 16) or a validation data set (n = 4). The population data set was comprised of 771 concentration measurements of patients admitted over the last 3 years. Population modelling using the nonlinear mixed-effects model (NONMEM) program was performed on the population data set, using a one-compartment model with first-order absorption and elimination. Population average parameter estimates of clearance (CL), volume of distribution (V) and oral bioavailability (F) were sought; a number of clinical and demographic variables were tested for their influence on these parameters.

RESULTS

The final optimal population models related clearance to age, volume of distribution to body surface area and bioavailability to body weight and total bilirubin concentration. Predictive performance of this model evaluated using the validation data set, which comprised 86 concentrations, showed insignificant bias between observed and model-predicted blood tacrolimus concentrations. A final analysis performed in all 20 patients identified the following relationships: CL (l h-1) = 1.46 *[1 + 0. 339 * (AGE (years) -2.25)]; V (l) = 39.1 *[1 + 4.57 * (BSA (m2)-0. 49)]; F = 0.197 *[1 + 0.0887 * (WT (kg) -11.4)] and F = 0.197 *[1 + 0.0887 * (WT (kg) -11.4)] * [1.61], if the total bilirubin > or = 200 micromol l-1. The interpatient variabilities (CV%) in CL, V and F were 33.5%, 33.0% and 24.1%, respectively. The intrapatient variability (s.d.) among observed and model-predicted blood concentrations was 5.79 ng ml-1.

CONCLUSIONS

In this study, the estimates of the pharmacokinetic parameters of tacrolimus agreed with those obtained from conventional pharmacokinetic studies. It also identified significant relationships in Asian paediatric liver transplant patients between the pharmacokinetics of tacrolimus and developmental characteristics of the patients.

Factors affecting oral cyclosporin disposition after heart transplantation: bootstrap validation of a population pharmacokinetic model

OBJECTIVE

To determine factors affecting the population pharmacokinetics of oral cyclosporin (CsA) in cardiac allograft recipients during the first 3 weeks after surgery.

METHODS

Data were obtained from routine trough monitoring and from two extra samples drawn during a dosing interval on a randomly selected day. Whole blood CsA concentrations were assayed using high-performance liquid chromatography (HPLC). Approximately equal numbers of patients were prescribed Sandimmun (SAN) or Neoral (NEO) CsA formulations. Parameter values of a one-compartment kinetic model with first-order absorption and elimination were sought together with the inter-patient and intra-patient variances using the NONMEM program.

RESULTS

Improved fits resulted from using the following expression in the model to adjust apparent bioavailability as a function of post-operative day (POD): f= 0.2 + 10 x ABS (POD-5)/[(POD + 7) x 60]. The CsA clearance (CL/f) was found to be influenced by current body weight (WT). There was an absorption lag time of about 35 min with SAN, but zero lag time with NEO. Oral bioavailability (f) was increased by about 35% with concomitant diltiazem and about 18% with NEO. The CL/f was 10% higher during the daytime than at night. The final pharmacokinetic model was validated using 200 bootstrap samples of the original data.

CONCLUSIONS

Using a validated population modelling approach, it was found that a number of factors influence the pharmacokinetics of CsA during the early postoperative period in cardiac transplant patients. These influences affecting oral bioavailability and clearance may need to be taken into account for maintaining appropriate concentrations of CsA in the bloodstream.

Platinum pharmacokinetics in sulphur-crested cockatoos (Cacatua galerita) following single-dose cisplatin infusion

OBJECTIVE

To determine the pharmacokinetics of platinum (Pt) in cockatoos.

DESIGN

A pharmacokinetic study of Pt, following a single i.v. infusion of cisplatin, was done in six healthy sulphur-crested cockatoos (Cacatua galerita).

PROCEDURE

Birds were hydrated for 1 h before and 2 h after a 1-h cisplatin infusion (1 mg/kg, i.v.). Serial blood samples were collected for 96 h after initiation of the infusion and urine was collected for 2 h during the hydration period after cisplatin administration. Tissue samples from 10 organs were obtained at necropsy, 96 h after cisplatin infusion. Total Pt and filterable Pt in plasma, urinary Pt and tissue Pt concentrations were assayed by inductively coupled plasma-mass spectrometry. A noncompartmental pharmacokinetic analysis was performed on the plasma and urine data.

RESULTS

For total Pt and filterable Pt, the respective mean systemic clearances were 0.373 and 0.699 L/kg hourly, the steady state volumes of distribution were 4.19 and 0.356 L/kg, and the mean residence times were 111 and 0.512 h. Total plasma Pt displayed a bi-exponential decay profile with average half-lives of 0.398 and 79.0 h, while filterable Pt had a monoexponential decay with mean half-life of 0.413 h. The renal clearance during the 2-h postinfusion period was 0.167 L/kg hourly. The kidneys had the highest Pt accumulation (4.54 micrograms/g DM).

CONCLUSIONS AND CLINICAL RELEVANCE

Cisplatin infusion in cockatoos was well tolerated and Pt plasma concentrations were similar to those measured during treatment of solid tumours in human patients. Despite anatomical, physiological and biochemical differences among animal species, the pharmacokinetic disposition of Pt in the cockatoo shares some features with the kinetics reported previously in rodents, dogs and human beings.

Measurement of extracellular fluid volume in the neonate using multiple frequency bio-impedance analysis

Bioelectrical impedance analysis may be useful for cot-side monitoring of fluid balance in the neonatal intensive care unit (NICU). However the presence of cardio-respiratory monitoring equipment, non-ideal electrode placement and inability to obtain accurate crown-heel measurements may interfere with the ability to obtain reliable impedance data in this setting. This study aimed to investigate the effects of these factors on impedance analysis and to develop a prediction equation for extracellular fluid volume in the neonate. The study found that cardio respiratory monitoring had no significant effect on multi-frequency impedance measurements. Placement of current delivering electrodes on the ventral rather than dorsal surfaces improved separation of current and voltage electrodes but did not alter impedance results. Contralateral measurements were not significantly different to ipsilateral measurements. In 24 infants, extracellular fluid volume was measured using corrected bromide space (CBS) and simultaneous impedance analysis was performed. There was good correlation between CBS and the impedance quotient FF2/Ro where F is foot length and R0 is resistance at zero frequency. The study concludes that despite many potential difficulties associated with impedance analysis in the NICU, reliable measurements of impedance can be obtained and further work to validate prediction equations for ECF is warranted.

Prediction of aminoglycoside distribution space in neonates by multiple frequency bioelectrical impedance analysis

OBJECTIVE

Aminoglycoside antibiotics have a narrow margin of safety between therapeutic and toxic levels. The current study used multiple frequency bioelectrical impedance analysis to develop prediction equations for gentamicin distribution space in neonates.

METHODS

Gentamicin pharmacokinetic parameters and bioimpedance were measured in 14 infants in the neonatal intensive care unit. Stepwise regression analysis was used to develop predictive models, using impedance quotients (F2/R), weight and gestational age as variables, whose predictive performance was then tested in a second group of ten infants.

RESULTS

The prediction model with the smallest bias and highest concordance correlation was that which included F2/R0 and weight. This bias of 50 ml or 6.7% was less than half of that found using a model including weight alone.

CONCLUSION

A bioelectrical impedance-based prediction equation for prediction of gentamicin distribution space in neonates was produced. Although this prediction equation represents only a small improvement over that using weight alone, this is of clinical significance due to the narrow margin between therapeutic and toxic levels for gentamicin. A clinical trial to confirm the value of this methodology is now warranted.

Reactions of cisplatin hydrolytes with methionine, cysteine, and plasma ultrafiltrate studied by a combination of HPLC and NMR techniques

The reactions of cis-[PtCl(NH3)2(H2O)]+ with L-methionine have been studied by 1D 195Pt and 15N NMR, and by 2D[1H, 15N] NMR. When the platinum complex is in excess, the initial product, cis-[PtCl(NH3)2(Hmet-S)]+ undergoes slow ring closure to [Pt(NH3)2(Hmet-N,S)]2+. Slow ammine loss then occurs to give the isomer of [PtCl(NH3)(Hmet-N,S)]+ with chloride trans to sulfur. When methionine is in excess, a reaction sequence is proposed in which trans-[PtCl(NH3)(Hmet-S)2]+ isomerises to the cis-isomer, with subsequent ring closure reactions leading to cis-[Pt(Hmet-N,S)2]2+. Near pH 7, methionine is unreactive toward cis-[PtCl(OH)(NH3)2]. By contrast, L-cysteine reacts readily with cis-[PtCl(OH)(NH3)2] at pH 7, but there were many reaction products, including bridged species. Cis-[PtCl(OH)(NH3)2] reacts with reduced thiols in ultrafiltered plasma but these are oxidized if the plasma is not fresh or appropriately stored. With very low concentrations of the platinum complexes (35.5 microM), HPLC experiments (UV detection at 305 nm) indicate that the thiolate (probably cysteine) reactions become simpler as bridging becomes less important.

A procedure for generating bootstrap samples for the validation of nonlinear mixed-effects population models

A method is presented for automated preparation of bootstrap data samples and their presentation to NONMEM for use in the validation of population pharmacokinetic or pharmacodynamic models, which have been developed with relatively small numbers of subjects. The bootstrap sampling procedure involves the use of an MS-DOS batch file and a script file for use with the public-domain text processing program, AWK, which is a single EXE file (48k in size for the version used in this report). A UNIX version of AWK is also available and UNIX users can adapt the process to their needs. Its use obviates the need for expensive, high-end statistical packages and associated script files written using in-built programming languages. The method can easily be adapted to bootstrap sampling requirements in other biomedical modelling applications.

Development of HPLC conditions for valid determination of hydrolysis products of cisplatin

In water, the antineoplastic drug cisplatin, cis-[PtCl2(NH3)2] (1) hydrolyses slowly to the aqua complexes cis-[Pt(NH3)2Cl(H2O)]+ (2) and, to a small extent, cis-[Pt(NH3)2(H2O)2]2+ (3), which are thought to play an important role in the metabolism of cisplatin. HPLC is a useful technique for monitoring 2 and 3, but only if the components of the mobile phase used in the reverse phase HPLC technique are unreactive toward these aqua complexes under the conditions of the experiment. 15N Nuclear magnetic resonance (NMR) with samples highly enriched (>98%) in 15N has been used to check the reactivity of 2 and 3 toward substances commonly used as components of the mobile phase. The results reported herein indicate that acetonitrile, often used as an organic modifier, reacts readily with 2 and 3. Methanol, also commonly employed, is much less reactive. Carboxylic acids RCO2H (R = CH3, H, CF3), which are frequently used to adjust pH of the mobile phase, also react readily with 2 and 3. Trifluoromethanesulfonic acid ("triflic acid"), CF3SO3H, is unreactive. Neither hexanesulfonic acid nor sodium dodecyl sulfate (SDS), used as "ion-pairing agents", reacts significantly with 2 or 3 under the experimental conditions, but SDS gives better peak separation. Commercial SDS must, however, be purified from chloride contamination. From our studies, optimal conditions for HPLC separation of 1, 2, and 3, with a C18 stationary phase at 37 degrees C, require an aqueous mobile phase with 3% v/v methanol, 0.05 mM SDS, and pH 2.5 (adjusted with triflic acid). This technique was then used to measure levels of 1, 2, and 3 in ultrafiltered serum after incubation for various times with cisplatin at 37 degrees C.

Population pharmacokinetic modeling in very premature infants receiving midazolam during mechanical ventilation: midazolam neonatal pharmacokinetics

BACKGROUND

Midazolam is used widely as a sedative to facilitate mechanical ventilation. This prospective study investigated the population pharmacokinetics of midazolam in very premature infants.

METHODS

Midazolam (100 microg/kg) was administered as a rapid intravenous bolus dose every 4-6 h to 60 very premature neonates with a mean (range) gestational age of 27 weeks (24-31 weeks), a birth weight of 965 g (523-1,470 g), and an age of 4.5 days (2-15 days). A median (range) of four (one to four) blood samples, 0.2 ml each, were drawn at random times after the first dose or during continuous treatment, and concentrations of midazolam in serum were assayed by high-performance liquid chromatography. A population analysis was conducted using a two-compartment pharmacokinetic model using the NONMEM program.

RESULTS

Average parameter values (interpatient percent coefficient of variation) for infants with birth weights 1,000 g or less were total systemic clearance (Cl(T)) = 0.783 ml/min (83%), intercompartmental clearance (Cl(Q)) = 6.53 ml/min (116%), volume of distribution of the central compartment (V1) = 473 ml (70%), and volume of distribution of the peripheral compartment (V2) = 513 ml (146%). For infants with birth weights more than 1,000 g they were as follows: Cl(T) = 1.24 ml/min (78%), Cl(Q) = 9.82 ml/min (98%), V1 = 823 ml (43%), and V2 = 1,040 ml (193%). The intrapatient variability (percent coefficient of variation) in the data was 4.5% at the mean concentration midazolam in serum of 121 ng/mL.

CONCLUSIONS

Serum concentration-time data were used in modeling the population pharmacokinetics of midazolam in very premature, ventilated neonates. Clearance of midazolam was markedly decreased compared with previous data from term infants and older patients. Infants weighing less than 1,000 g at birth had significantly lower clearance than those weighing more than 1,000 g.

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.