Pharmacokinetics of paracetamol and its metabolites in women at delivery and post-partum

AIM

A recent report on intravenous (i.v.) paracetamol pharmacokinetics (PK) showed a higher total clearance in women at delivery compared with non-pregnant women. To describe the paracetamol metabolic and elimination routes involved in this increase in clearance, we performed a population PK analysis in women at delivery and post-partum in which the different pathways were considered.

METHODS

Population PK parameters using non-linear mixed effect modelling were estimated in a two-period PK study in women to whom i.v. paracetamol (2 g loading dose followed by 1 g every 6 h up to 24 h) was administered immediately following Caesarean delivery and in a subgroup of the same women to whom single 2 g i.v.loading dose was administered 10-15 weeks post-partum.

RESULTS

Population PK analysis was performed based on 255 plasma and 71 urine samples collected in 39 women at delivery and in eight of these 39 women 12 weeks post-partum. Total clearance was higher in women at delivery compared with 12th post-partum week (21.1 vs. 11.7 l h⁻¹) due to higher clearances to paracetamol glucuronide (11.6 vs. 4.76 l h⁻¹), to oxidative metabolites (4.95 vs. 2.77 l h⁻¹) and of unchanged paracetamol (1.15 vs. 0.75 l h⁻¹). In contrast, there was no difference in clearance to paracetamol sulphate.

CONCLUSION

The increased total paracetamol clearance at delivery is caused by a disproportional increase in glucuronidation clearance and a proportional increase in clearance of unchanged paracetamol and in oxidation clearance, of which the latter may potentially limit further dose increase in this patient group.

Developmental pharmacokinetics of propylene glycol in preterm and term neonates

AIM

Propylene glycol (PG) is often applied as an excipient in drug formulations. As these formulations may also be used in neonates, the aim of this study was to characterize the pharmacokinetics of propylene glycol, co-administered intravenously with paracetamol (800 mg PG/1000 mg paracetamol) or phenobarbital (700 mg PG/200 mg phenobarbital) in preterm and term neonates.

METHODS

A population pharmacokinetic analysis was performed based on 372 PG plasma concentrations from 62 (pre)term neonates (birth weight (bBW) 630-3980 g, postnatal age (PNA) 1-30 days) using NONMEM 6.2. The model was subsequently used to simulate PG exposure upon administration of paracetamol or phenobarbital in neonates (gestational age 24-40 weeks).

RESULTS

In a one compartment model, birth weight and PNA were both identified as covariates for PG clearance using an allometric function (CL(i) = 0.0849 × {(bBW/2720)(1.69) × (PNA/3)(0.201)}). Volume of distribution scaled allometrically with current bodyweight (V(i) = 0.967 × {(BW/2720)(1.45)}) and was estimated 1.77 times higher when co-administered with phenobarbital compared with paracetamol. By introducing these covariates a large part of the interindividual variability on clearance (65%) as well as on volume of distribution (53%) was explained. The final model shows that for commonly used dosing regimens, the population mean PG peak and trough concentrations range between 33-144 and 28-218 mg l(-1) (peak) and 19-109 and 6-112 mg l(-1) (trough) for paracetamol and phenobarbital formulations, respectively, depending on birth weight and age of the neonates.

CONCLUSION

A pharmacokinetic model was developed for PG co-administered with paracetamol or phenobarbital in neonates. As such, large variability in PG exposure may be expected in neonates which is dependent on birth weight and PNA.

Biochemical tolerance during low dose propylene glycol exposure in neonates: A formulation-controlled evaluation

Background and purpose of the study

Propylene glycol (PG) is a frequently co-administered solvent in formulations administered to neonates, but reports on its (in)tolerance are limited. We aimed to report on renal, metabolic and hepatic tolerance before, during and following intravenous (iv) PG-paracetamol exposure and compared these data with similar datasets reported in literature on neonates exposed to PG without paracetamol or paracetamol without PG.

Methods

Renal (diuresis, creatinemia, sodium), metabolic (Base Excess, Anion Gap, lactate, bicarbonate) and hepatic (liver enzymes, bilirubinemia) indicators before, during and following iv paracetamol-PG exposure in neonates as included in the PARANEO (paracetamol in neonates) study (intra-individual trends, ANOVA) were collected and analysed. Comparison with observations collected in cases exposed to either iv phenobarbital-PG or iv paracetamol-mannitol (inter-individual comparison, Mann Whitney-U test) were made.

Results

PG exposure (median 34.1 mg/kg/24 h) did not affect postnatal renal, metabolic and hepatic adaptations in 60 cases exposed to paracetamol-PG. These indicators were similar when compared to 29 cases exposed to phenobarbital-PG or 172 cases exposed to paracetamol-mannitol.

Major conclusion

Based on observations in 89 neonates, low dose PG exposure was tolerated well. Studies on PG pharmacokinetics and its covariates are needed to estimate the upper level of PG tolerance in neonates.

A randomized clinical trial comparing point-of-care platelet function assays and bleeding time in healthy subjects treated with aspirin or clopidogrel

Traditional assays of the coagulation status of patients, bleeding time assessment (BT) and light transmission aggregometry (LTA), are useful in clinical drug development. However, these assays are both labor intensive and expensive. BT results can be operator dependent and by its nature can inhibit subject enrollment in a clinical trial. The preparation of platelet-rich plasma necessary for LTA requires specialized training and laboratory support. Alternatives to these methods are desirable. The goal of this study was identification of a quantitative, easy-to-use, point-of-care device with minimal technical variables that could facilitate assessment of platelet aggregation in clinical drug development. This was a double-blind, placebo-controlled, randomized, three-period cross-over study in healthy volunteers designed to compare the abilities of BT, LTA, and three point-of-care devices, Multiplate®, Platelet Function Analyzer-100®, and VerifyNow® to quantitate the effects on platelet function of 3 days of treatment with aspirin, clopidogrel, or placebo. The effect size (difference in treatment means divided by the pooled standard deviations [SD]) of the three point-of-care devices was greater than or similar to BT and LTA for all treatment comparisons examined. VerifyNow® had the highest effect size comparing ASA to placebo. Multiplate® had the highest effect size comparing clopidogrel to placebo. From this study, we conclude that any one of the three simple-to-use point-of-care devices can reliably assess the treatment effect of ASA and CLP on platelet function in comparison with BT or LTA at the study population level

Transplacental transfer of paclitaxel, docetaxel, carboplatin, and trastuzumab in a baboon model

BACKGROUND

The paucity of data on fetal effects of prenatal exposure to chemotherapy prompted us to study the transplacental transport of commonly used anticancer agents in a pregnant baboon model.

METHODS

Single or combination chemotherapy with paclitaxel, docetaxel, carboplatin, and trastuzumab was administered to 9 baboons at a mean (SD) gestational age of 117 (26) days (paclitaxel, 100 mg/m2 [n = 2]; docetaxel, 100 mg/m2 [n = 2]; paclitaxel, 175 mg/m2 with carboplatin, area under the curve of 6 at standard dosage [n = 2] and 50% dosage [n = 1]; docetaxel, 75 mg/m2 with carboplatin, area under the curve 6 [n = 1]; and docetaxel, 75 mg/m2 with trastuzumab, 8 mg/kg [n = 1]). Serial fetal and maternal blood samples, amniotic fluid, maternal urine, and fetal and maternal tissue samples were collected for the first 76 hours after drug infusion. Levels of carboplatin were determined by atomic absorption spectrometry, docetaxel and paclitaxel by high-performance liquid chromatography, and trastuzumab by enzyme-linked immunosorbent assay.

RESULTS

Fetal plasma concentrations of carboplatin averaged 57.5% (14.2%) of maternal concentrations (n = 7). Fetal plasma concentrations were 1.5% (0.8%) of maternal concentrations (n = 7). Immediately after ending the infusion, paclitaxel was not detectable in fetal tissues, whereas, after 3 hours, fetal tissues contained 15% of maternal tissue concentrations.Docetaxel could not be detected in fetal blood samples (n = 9). In the first 3 hours after docetaxel infusion, fetal tissues contained 5.0% to 50.0% of maternal tissue concentrations, whereas equal fetal and maternal tissue concentrations were found after 26 and 76 hours.The transplacental passages of trastuzumab were 85.0% and 3.0%, 2 and 26 hours after trastuzumab infusion, respectively. After 26 hours, amniotic fluid contained 36.4% of the fetal plasma concentration. Fetal tissue concentrations varied between 5.0% and 14.0% of the maternal concentration.

CONCLUSION

Variable plasma and/or tissue concentrations of taxanes, carboplatin, and trastuzumab were encountered in the fetal compartment. These data are important when cancer treatment is considered during pregnancy and underline the need for long-term follow-up of children after prenatal exposure to these cytotoxic agents.

Prospective assessment of short-term propylene glycol tolerance in neonates

INTRODUCTION

Propylene glycol (PG) is an unintentional frequently administered solvent in neonates despite the fact that PG accumulation potentially results in hyperosmolarity, lactic acidosis and renal/hepatic toxicity.

METHODS

Prospective evaluation of renal (diuresis, creatinaemia, sodium), metabolic (base excess, anion gap, lactate, bicarbonate) and hepatic (alanine transaminase, aspartate aminotransferase, direct bilirubinaemia) tolerance to PG in (pre)term neonates following intravenous administration of formulations (paracetamol, phenobarbital, digoxin) that contain PG. Observations from 48 h before up to 48 after the last PG administration were described and compared (paired analysis). Clinical characteristics and observations collected following intravenous PG-paracetamol administration were compared with a historical cohort of neonates in whom similar (renal, hepatic) observations during exposure to a mannitol-containing paracetamol formulation were collected.

RESULTS

5566 observations were collected in 69 neonates before, during and following median PG exposure of 34 mg/kg/24 h (range 14-252). Progressive postnatal adaptation in renal, metabolic and hepatic function was documented, unrelated to the PG exposure. In the subgroup of 40 cases treated with intravenous PG-paracetamol, observations on renal and hepatic function were similar to a historical cohort of published observations following exposure to intravenous mannitol-paracetamol.

CONCLUSIONS

Unintended PG administration (34 mg/kg/24 h) for a maximum of 48 h seems to be tolerated in (pre)term neonates and does not affect short-term postnatal adaptations. Further studies on PG disposition and the level of safe exposure to PG, including long-term safety data in neonates are needed.

The use of diameter distension waveforms as an alternative for tonometric pressure to assess carotid blood pressure

Proper non-invasive assessment of carotid artery pressure ideally uses waveforms recorded at two anatomical locations: the brachial and the carotid artery. Calibrated diameter distension waveforms could provide a more widely applicable alternative for local arterial pressure assessment than applanation tonometry. This approach might be of particular use at the brachial artery, where the feasibility of a reliable tonometric measurement has been questioned. The aim of this study was to evaluate an approach based on distension waveforms obtained at the brachial and carotid arteries. This approach will be compared to traditional pulse pressures obtained through tonometry at both the carotid and brachial arteries (used as a reference) and the more recently proposed approach of combining tonometric readings at the brachial artery with linearly or exponentially calibrated distension curves at the carotid artery. Local brachial and carotid diameter distension and tonometry waveforms were recorded in 148 subjects (119 women; aged 19-59 years). The morphology of the waveforms was compared by the form factor and the root-mean-squared error. The difference between the reference carotid PP and the PP obtained from brachial and carotid distension waveforms was smaller (0.9 (4.9) mmHg or 2.3%) than the difference between the reference carotid PP and the estimates obtained using a tonometric and a distension waveform (-4.8 (2.5) mmHg for the approach using brachial tonometry and linearly scaled carotid distension, and 2.7 (6.8) mmHg when using exponentially scaled carotid distension waves). We therefore recommend to stick to one technique on both the brachial and the carotid artery, either tonometry or distension, when assessing carotid blood pressure non-invasively.

Dose-dependent effects of the CRF(1) receptor antagonist R317573 on regional brain activity in healthy male subjects

BACKGROUND

Corticotropin-releasing factor receptor type 1 (CRF(1)) antagonists have been proposed as therapeutic agents in the treatment of mood and anxiety disorders although clinical evidence supporting their development and understanding of a dose-response relationship has been lacking.

METHODS

We tested two doses of the CRF(1) antagonist R317573 for effects on regional cerebral glucose metabolism (rCMglu) using [(18)F] fluoro-2-deoxy-D: -glucose (FDG) positron emission tomography (PET) following single-dose challenges in a double-blind, placebo-controlled, cross-over design, in 12 healthy male volunteers.

RESULTS

Single 30- and 200-mg doses of R317573 resulted in dose-related changes in rCMglu. Relative increases in rCMglu were observed in frontal cortical regions while relative decreases occurred in the putamen and right amygdala after both doses. Relative decreases occurred in cerebellum and right parahippocampal gyrus following the higher dose.

CONCLUSIONS

R317573 appears to produce acute dose-dependent changes in rCMglu. Effects occurred in regions that may be behaviorally relevant to mood and anxiety disorders. In some regions, these effects may be related to the receptor (target) density. Measuring acute effects on rCMglu with FDG-PET may offer a method for defining pharmacologically active doses for central nervous system targets for which selective radiotracers are lacking.

Cefazolin plasma protein binding saturability during pregnancy

This article aims to document cefazolin (CFZ) plasma binding and its covariates during pregnancy and compare these observations with previously reported observations in nonpregnant adults. Maternal CFZ plasma samples were collected during in utero surgery. The unbound CFZ fraction was reported by median and range. Correlation (Spearman) and multiple regression were used to identify covariates (total CFZ concentration, albuminemia, gestational age) of the unbound CFZ fraction. Observations during pregnancy were compared with observations in nonpregnant adults (unpaired t test, multiple regression). Plasma (N = 130) samples were collected during 30 interventions. The median unbound CFZ fraction was 0.25 (range 0.14-0.41). Correlations between the unbound CFZ fraction and total CFZ plasma concentration (0.46), time after administration (-0.38), albuminemia (-0.39) and gestational age (-0.19) were statistically significant. The median unbound CFZ fraction was higher during pregnancy when compared to observations in nonpregnant adults (0.25 vs. 0.19, P < 0.001). In a multiple-regression model, total plasma CFZ concentration and albuminemia were covariates of the unbound CFZ fraction (r(2) = 0.4). The concept of saturability of CFZ plasma protein binding has been confirmed during pregnancy, but the free CFZ fraction is higher, likely explained by the lower albuminemia during pregnancy.

Relationship of type 1 cannabinoid receptor availability in the human brain to novelty-seeking temperament

CONTEXT

Brain neurochemistry can partially account for personality traits as a variance of normal human behavior, as has been demonstrated for monoamine neurotransmission. Positron emission tomography using fluorine 18-labeled MK-9470 now enables quantification of type 1 cannabinoid receptors (CB1R) in the brain.

OBJECTIVE

To investigate whether there is a relationship between human temperament traits and regional cerebral CB1R availability.

DESIGN

Forty-seven [(18)F]MK-9470 baseline scanning sessions were performed and correlated with the temperament dimensions and subdimensions of the 240-item Cloninger Temperament and Character Inventory.

SETTING

Academic brain imaging center.

PARTICIPANTS

Forty-seven nonsmoking, healthy volunteers (paid). Main Outcome Measure Voxel-based correlation of temperament variables of the inventory with regional CB1R availability.

RESULTS

Novelty seeking was inversely correlated with global CB1R availability (r = -0.33, P = .02), with the most significant correlation in the left amygdala (r = -0.41, P = .005). In particular, the subdimension extravagance showed a highly significant inverse correlation to global CB1R availability (r = -0.53, P <.001), most pronounced in the amygdala, anterior cingulate, parietal cortex, and precuneus. Also, disorderliness was inversely correlated with global CB1R availability (r = -0.31, P = .04).

CONCLUSIONS

Low baseline cerebral CB1R availability is related to a high novelty-seeking personality, in particular to extravagance, most pronounced in the amygdala. Further investigation of the functional role of the CB1R is warranted in pathological behavior known to be strongly related to novelty seeking, such as addiction and eating disorders.

Cefazolin pharmacokinetics in maternal plasma and amniotic fluid during pregnancy

OBJECTIVE

To study cefazolin pharmacokinetics in maternal plasma and amniotic fluid during pregnancy.

STUDY DESIGN

Newly collected time-concentrations profiles and reported studies investigating cefazolin disposition (plasma, amniotic fluid) were pooled. Nonlinear mixed effect modeling was applied. A 2-compartment linear disposition model was used to fit cefazolin plasma observations. A third compartment was used to model amniotic fluid concentration.

RESULTS

One hundred eighty-seven plasma and 96 amniotic fluid samples were collected in 82 pregnancies (17-40 weeks gestational age). Cefazolin clearance and distribution estimates were 7.44 L/h and 12.04 L without gestational age-dependent trends in maternal plasma. The equilibration half-life (T(eq)) between plasma and amniotic fluid at term gestational age was 4.4 hours, increased with decreasing gestational age, and was 9.09 times longer in patients with polyhydramnios.

CONCLUSION

Cefazolin clearance and distribution volume are increased during pregnancy. The cefazolin T(eq) depends on gestational age and polyhydramnios. On the basis of these observations, dosing regimes to attain higher amniotic fluid concentrations were formulated.

In vivo characterization and dynamic receptor occupancy imaging of TPA023B, an alpha 2/alpha 3/alpha 5 subtype selective gamma-aminobutyric acid-a partial agonist

BACKGROUND

A novel, high-affinity (.7-2.0 nmol) compound that selectively activates the alpha2, alpha 3, and alpha 5 (but not alpha1) gamma-aminobutyric acid-A (GABA(A)) receptor subtypes, TPA023B (2',6-difluoro-5'-[3-(1-hydroxy-1-methylethyl) imidazo[1,2-b][1,2,4]triazin-7-yl][1,1'-biphenyl]-2-carbonitrile) was pharmacologically characterized and studied by means of positron emission tomography (PET) to determine dynamic occupancies of the benzodiazepine binding site of human brain GABA(A) receptors after a single oral dose.

METHODS

Four healthy male volunteers were studied in a double-blind, randomized placebo-controlled study of which three were given a single dose of 1.5 mg TPA023B and the fourth received placebo. The time course of GABA(A) receptor occupancy was determined with multiple dynamic [(11)C]flumazenil PET studies at pre-dose baseline and 5 and 24 hours after dose. Arterial sampling and full kinetic modeling with a two-compartment model was used to calculate parametric maps of receptor availability (distribution volume V(T)) and of occupancy.

RESULTS

The GABA(A) receptor occupancy as determined from [(11)C]flumazenil V(T) values in all brain regions was reduced homogeneously, on average by 52.5 +/- 1.2% after 5 hours and 46.4 +/- 6.0% after 24 hours. No serious adverse events were encountered in humans.

CONCLUSIONS

Single oral doses of 1.5 mg of TPA023B correspond to average receptor occupancies in neocortical regions of 52% and 46% after 5 and 24 hours, respectively. Provided suitable ligands and quantification methods are available for the appropriate target, quantitative PET offers a unique tool for dynamic in vivo measurement of relevant on-site receptor occupancy.

Postmenstrual age and CYP2D6 polymorphisms determine tramadol o-demethylation in critically ill neonates and infants

To document determinants of O-demethylation in critically ill (pre)term neonates and infants, tramadol (M) and O-demethyl tramadol (M1) concentrations were quantified in eighty-six 24 h urine collections and 168 plasma samples. A significant correlation of urine log M/M1 (0.98, SD 0.66) and plasma log M/M1 (0.78, SD 0.45) with postmenstrual age (PMA) (r = -0.69 and -0.65) was observed. One-way analysis of variance documented a significant decrease in urine log and plasma log M/M1 with increasing CYP2D6 activity score (F value 11.6 and 22.55). PMA and CYP2D6 activity score determined the urine and plasma log M/M1 (R 0.59 and 0.64) in a forward multiple regression model. We therefore conclude that PMA and CYP2D6 polymorphisms determined O-demethylation activity in (pre)term neonates and young infants, illustrating the impact of pharmacogenetics on drug metabolism in neonates although a relevant part of the interindividual varaibility remained unexplained. Besides compound-specific relevance, CYP2D6 iso-enzyme specific data on in vivo ontogeny of O-demethylation can contribute to safer and more effective administration of drugs metabolized by the same route in this population.

The acyclic CB1R inverse agonist taranabant mediates weight loss by increasing energy expenditure and decreasing caloric intake

Cannabinoid 1 receptor (CB1R) inverse agonists are emerging as a potential obesity therapy. However, the physiological mechanisms by which these agents modulate human energy balance are incompletely elucidated. Here, we describe a comprehensive clinical research study of taranabant, a structurally novel acyclic CB1R inverse agonist. Positron emission tomography imaging using the selective CB1R tracer [(18)F]MK-9470 confirmed central nervous system receptor occupancy levels ( approximately 10%-40%) associated with energy balance/weight-loss effects in animals. In a 12-week weight-loss study, taranabant induced statistically significant weight loss compared to placebo in obese subjects over the entire range of evaluated doses (0.5, 2, 4, and 6 mg once per day) (p < 0.001). Taranabant treatment was associated with dose-related increased incidence of clinical adverse events, including mild to moderate gastrointestinal and psychiatric effects. Mechanism-of-action studies suggest that engagement of the CB1R by taranabant leads to weight loss by reducing food intake and increasing energy expenditure and fat oxidation.

[18F]MK-9470, a positron emission tomography (PET) tracer for in vivo human PET brain imaging of the cannabinoid-1 receptor

[(18)F]MK-9470 is a selective, high-affinity, inverse agonist (human IC(50), 0.7 nM) for the cannabinoid CB1 receptor (CB1R) that has been developed for use in human brain imaging. Autoradiographic studies in rhesus monkey brain showed that [(18)F]MK-9470 binding is aligned with the reported distribution of CB1 receptors with high specific binding in the cerebral cortex, cerebellum, caudate/putamen, globus pallidus, substantia nigra, and hippocampus. Positron emission tomography (PET) imaging studies in rhesus monkeys showed high brain uptake and a distribution pattern generally consistent with that seen in the autoradiographic studies. Uptake was blocked by pretreatment with a potent CB1 inverse agonist, MK-0364. The ratio of total to nonspecific binding in putamen was 4-5:1, indicative of a strong specific signal that was confirmed to be reversible via displacement studies with MK-0364. Baseline PET imaging studies in human research subject demonstrated behavior of [(18)F]MK-9470 very similar to that seen in monkeys, with very good test-retest variability (7%). Proof of concept studies in healthy young male human subjects showed that MK-0364, given orally, produced a dose-related reduction in [(18)F]MK-9470 binding reflecting CB1R receptor occupancy by the drug. Thus, [(18)F]MK-9470 has the potential to be a valuable, noninvasive research tool for the in vivo study of CB1R biology and pharmacology in a variety of neuropsychiatric disorders in humans. In addition, it allows demonstration of target engagement and noninvasive dose-occupancy studies to aid in dose selection for clinical trials of CB1R inverse agonists.

Nonselective cyclo-oxygenase inhibitors and glomerular filtration rate in preterm neonates

The adverse effects of nonselective cyclo-oxygenase (COX) inhibitors on the immature kidney have been described in newborn rabbits, but it is much more laborious and difficult to study its relative impact on renal function in human neonates. Amikacin clearance was therefore used as surrogate marker to study the impact of nonselective COX-inhibitors on glomerular filtration rate. Clinical characteristics and amikacin clearance of infants on respiratory support were retrospectively collected. Results in neonates in whom either ibuprofen-lysine or acetylsalicylic acid was administered prophylactically to induce closure of a patent asymptomatic ductus arteriosus were compared to infants not cotreated with any COX-inhibitor (Mann-Whitney U-, chi-square tests). Amikacin clearance was calculated in 142 infants, of whom 50 were cotreated with ibuprofen and 33 with acetylsalicylic acid. There were no significant differences in clinical characteristics between the three groups. Compared to controls (0.52, range 0.09-2.33 ml/kg/min), a significant similar decrease in amikacin clearance in infants cotreated with ibuprofen (0.38, range 0.13-0.80 ml/kg/min, p<0.01) or acetylsalicylic acid (0.38, range 0.13-0.78 ml/kg/min, p<0.01) was demonstrated. Using amikacin clearance as marker, a significant and similar reduction in glomerular filtration rate was documented in preterm infants cotreated with ibuprofen or acetylsalicylic acid.

Intra- and interindividual variability of glucuronidation of paracetamol during repeated administration of propacetamol in neonates

BACKGROUND

Major changes in drug clearance and metabolism are observed during infancy, in part based on ontogenic regulation of various metabolic pathways. Since paracetamol provides a good substrate to study UGT (1A6) activity, urinary metabolites of propacetamol were determined in neonates in whom propacetamol was repeatedly administered.

METHODS

Paracetamol glucuronide (APAP-G), paracetamol sulphate (APAP-S) and free paracetamol were determined in urine samples of neonates during repeated administration of propacetamol. Spearman rank and linear multiple regression (MedCalc, Mariakerke, Belgium) were used to study the effect of postnatal age, of postconceptional age and of repeated administration on the relative contribution of APAP-G to overall urine paracetamol (APAP-G+APAP-S+free paracetamol) elimination (G/T ratio).

RESULTS

147 samples were collected in 23 neonates. Molar median G/T ratio was 14% (range 1-53). Besides increasing G/T ratio with increasing postnatal (p<0.0001) and postconceptional age (p<0.01), repeated administration (p<0.01) also correlated with an increasing G/T ratio, and repeated administration remained significant (p<0.01) after correction of postnatal and postconceptional age in a multiple regression model.

CONCLUSION

Major variability in the ontogeny of UGT activity to overall elimination of paracetamol was documented in neonates. Besides postnatal and postconceptional age, a significant effect of repeated administration on UGT activity was documented.

The impact of ibuprofen on renal clearance in preterm infants is independent of the gestational age

The aim of this investigation was to evaluate whether the relative change in renal clearance due to ibuprofen administration depends on the gestational age (GA). Clearance of amikacin was used as a surrogate marker for renal clearance in preterm infants (GA 24-34 weeks, day 1) on respiratory support. Clearance in infants co-treated with ibuprofen was compared to that of infants not co-treated with ibuprofen. Absolute change of clearance in four consecutive cohorts of increasing (<27, 27-28, 29-31, 32-34 weeks) GA and linear correlations of clearance on GA were calculated in both groups. Data were collected from 204 infants, of whom 93 were co-treated with ibuprofen. Mean amikacin clearance was lower (0.48 to 0.59 ml/kg/min, P <0.001) in infants co-treated with ibuprofen. Absolute decrease in mean amikacin clearance (0.10 to 0.14 ml/kg/min) was similar in all four cohorts. Linear correlations of clearance with GA were documented in infants co-treated (y =0.21+0.011x) or not co-treated (y =0.44+0.009x) with ibuprofen. Renal clearance, reflected by amikacin clearance, is decreased by ibuprofen in preterm infants of 24 to 34 weeks GA on respiratory support on the 1st day of life, independent of the GA.

Clinical study of solid dispersions of itraconazole prepared by hot-stage extrusion

The aim of this study was to investigate the performance of three new solid dispersion formulations of itraconazole in human volunteers in comparison with Sporanox, the marketed form. Solid dispersions made up of itraconazole (40%, w/w) and HPMC 2910, Eudragit E100 or a mixture of Eudragit E100-PVPVA64 were manufactured by hot-stage extrusion and filled in gelatin capsules. The formulations were tested in eight human volunteers in a double blind, single dose, and cross-over study. Concentrations of the drug and its metabolite hydroxyitraconazole in the plasma were determined using HPLC. The in vivo performance was evaluated by comparing the mean area under the plasma concentration-time curves (AUC), the mean maximum plasma concentration (C(max)), and the mean time to reach C(max) (T(max)). The mean bioavailability of itraconazole was comparable after administration of the HPMC solid dispersion, compared to Sporanox, while it was lower after administration of the Eudragit E100 or Eudragit E100-PVPVA64 dispersions. Due to high variability, a significant decrease in AUC and C(max) was only observed for the Eudragit E100-PVPVA formulation. Although the solid dispersions showed different in vitro dissolution behaviour, T(max) values were comparable. The same observations with respect to AUC, C(max) and T(max) could be made for hydroxyitraconazole. The present results indicate that hot-stage extrusion can be considered as a valuable alternative for manufacturing solid dispersions of itraconazole.

Intravenous paracetamol (propacetamol) pharmacokinetics in term and preterm neonates

BACKGROUND

The aim of this study was to describe propacetamol pharmacokinetics in term and preterm neonates to suggest dosing regimens. METHODS. A population pharmacokinetic analysis of paracetamol (acetaminophen) time-concentration profiles in 48 neonates was undertaken using non-linear mixed-effects models. Neonates were given either single (n=30) or multiple doses (n=18) of propacetamol infusion over 15 min. Neonates had a median postnatal age of 1 day (range, 1-76 days). Median post-conceptual age (PCA) was 35 weeks (range, 27-42 weeks), and median weight was 2.4 kg (range, 0.51-4 kg).

RESULTS

The population volume of distribution estimate and between-subject variability (%) for a one-compartment model with zero-order input and first-order elimination was 70.4 l (30.7%)/70 kg. Clearance increased from 2.85 l/70 kg, CV 40.7% at 27 weeks PCA to reach 7.05 l/h per 70 kg by 42 weeks PCA (standardised to a 70-kg person using allometric "1/4-power" models). Between-occasion variability for volume of distribution and clearance were 17.4% and 26%, respectively.

CONCLUSIONS

A mean paracetamol steady-state target concentration above 10 mg/l at trough can be achieved using a loading dose of 40 mg/kg and maintenance doses of 20 mg/kg 6 h in 28-week PCA neonates, 25 mg/kg 6 h at 32 weeks, 30 mg/kg 6 h at 36 weeks and 20 mg/kg 4 h at term (propacetamol doses). Since the role of the oxidative enzyme CYP2E1 and production of the hepatotoxic metabolite N-acetyl-p-benzoquinone-imine still is unknown in premature neonates, lower doses scaled by age-related clearance and centred on a daily dose of 60 mg/kg per day in a child of 6-8 years with a clearance of 0.25 l/h per kg (12.5 l/h per 70 kg) may be more appropriate.