Volumetric absorptive microsampling as an alternative sampling strategy for the determination of paracetamol in blood and cerebrospinal fluid.

In the field of bioanalysis, dried matrix spot sampling is increasingly receiving interest, as this alternative sampling strategy offers many potential benefits over traditional sampling, including matrix volume-sparing properties. By using a microsampling strategy, e.g., volumetric absorptive microsampling (VAMS), the number of samples that can be collected from a patient can be increased, as a result of the limited sample volume that is required per sample. To date, no VAMS-based methods have been developed for the quantification of analytes in cerebrospinal fluid (CSF). The objective of this study was to develop and validate two LC-MS/MS methods for the quantification of paracetamol in dried blood and dried CSF, with both matrices sampled using VAMS. Both methods were fully validated based on internationally accepted guidelines. Paracetamol was chromatographically separated from its glucuronide and sulfate metabolites and no carry-over or unacceptable interferences were detected. The total precision (%RSD) was below 15% for all QC levels and accuracy (%bias) was below 7% (17% for the LLOQ of aqueous VAMS). The influence of the hematocrit on the recovery of blood VAMS samples appeared to be limited within the hematocrit range of 0.21 to 0.62. The blood VAMS samples were stable for 1 week if stored at 50 °C, and for at least 8 months when stored between - 80 °C and room temperature. The aqueous VAMS samples were stable for at least 9 months when stored between - 80 and 4 °C, and for 1 month when stored at room temperature. Application of the methods on external quality control material and analysis of patient samples demonstrated the validity and utility of the methods and provided a proof of concept for the analysis of CSF microsamples obtained via VAMS devices. Graphical abstract ᅟ.

Comparative Plasma and Cerebrospinal Fluid Pharmacokinetics of Paracetamol After Intravenous and Oral Administration.

BACKGROUND: We compared plasma and cerebrospinal fluid (CSF) pharmacokinetics of paracetamol after intravenous (IV) and oral administration to determine dosing regimens that optimize CSF concentrations. METHODS: Twenty-one adult patients were assigned randomly to 1 g IV, 1 g oral or 1.5 g oral paracetamol. An IV cannula and lumbar intrathecal catheter were used to sample venous blood and CSF, respectively, over 6 hours. The plasma and CSF maximum concentrations (Cmax), times to maximum concentrations (Tmax), and area under the plasma and CSF concentration-time curves (AUCs) were calculated using noncompartmental techniques. Significance was defined by P < .0167 (Bonferroni correction for 3 comparisons for each parameter). Probability (X < Y) (p″) with Bonferroni corrected 95% confidence intervals (CIs) were calculated (CIs including 0.5 meet the null hypothesis). Results are presented as median (range) or p″ (CI). P values are listed as 1 g IV vs 1 g orally, 1 g IV vs 1.5 g orally and 1 g orally vs 1.5 g orally, respectively. RESULTS: Wide variation in measured paracetamol concentrations was observed, especially in the oral groups. The median plasma Cmax in the 1 g IV group was significantly greater than the oral groups. In contrast, the median CSF Cmax was not different between groups. The median plasma Tmax in the 1 g IV group was 105 and 75 minutes earlier than in the 1 and 1.5 g oral groups. The median CSF Tmax was not significantly different between groups. The median plasma AUC (total) was not significantly different between groups; however, in the first hour, the median plasma AUC was significantly greater in the IV group than in the oral groups. In the second hour, there was no difference between groups. The median CSF AUC (total) did not significantly differ between groups; however, in the first hour, the median CSF AUC was significantly greater in the IV compared with the orally groups. In the second hour, there was no difference between groups. Our analysis indicated that the median Cmax, Tmax, and AUC values lacked precision because of small sample sizes. CONCLUSIONS: Peak plasma concentrations were greater and reached earlier after IV than oral dosing. Evidence for differences in CSF Cmax and Tmax was lacking because of the small size of this study.

Plasma and cerebrospinal fluid pharmacokinetic parameters after single-dose administration of intravenous, oral, or rectal acetaminophen.

BACKGROUND: This is the first study to compare plasma and cerebrospinal fluid (CSF) pharmacokinetics of intravenous (IV), oral (PO), or rectal (PR) formulations of acetaminophen. METHODS: Healthy male subjects (N = 6) were randomized to receive a single dose of IV (OFIRMEV(®) ; Cadence) 1,000 mg (15 minute infusion), PO (2 Tylenol(®) 500 mg caplets; McNeil Consumer Healthcare), or PR acetaminophen (2 Feverall(®) 650 mg suppositories; Actavis) with a 1-day washout period between doses. The 1,300 mg PR concentrations were standardized to 1,000 mg. Acetaminophen plasma and CSF levels were obtained at T0, 0.25, 0.5, 0.75, 1, 2, 3, 4, and 6 hours. RESULTS: IV acetaminophen showed earlier and higher plasma and CSF levels compared with PO or PR administration. CSF bioavailability over 6 hours (AUC(0-6)) for IV, PO, and PR 1 g was 24.9, 14.2, and 10.3 µg·h/mL, respectively. No treatment-related adverse events were reported. One subject was replaced because of premature failure of his lumbar spinal catheter. The mean CSF level in the IV group was similar to plasma from 3 to 4 hours and higher from 4 hours on. Absorption phase, variability in plasma, and CSF were greater in PO and PR groups than variability with IV administration. CONCLUSIONS: These results demonstrate that earlier and greater CSF penetration occurs as a result of the earlier and higher plasma peak with IV administration compared with PO or PR.

A simple and rapid method to collect the cerebrospinal fluid of rats and its application for the assessment of drug penetration into the central nervous system.

Many central nervous system (CNS) drug discovery programs require the successful collection of cerebrospinal fluid (CSF) for assessing CNS penetration and distribution of new chemical entities. The objective of the present investigation was to simplify the technique for collecting maximum CSF from cisterna magna of the rats. Rat was anesthetized with 5% halothane and positioned in a stereotaxic frame. The rat head was flexed downward at approximately 45 degrees , a depressible surface with the appearance of a rhomb between occipital protuberances and the spine of the atlas becomes visible. The 23 G needle was punctured into the cisterna magna for CSF collection without making any incision at this region. The blunt end of the needle was inserted into a 10 in. length of PE-50 tubing and other end of the tubing was connected to a collection syringe. The non-contaminated sample was drawn into the syringe by simple aspiration. This technique is simple and can be performed by one person. The technique has a greater than 95% success rate of CSF collection and it was free of red blood cell contamination. In addition, it yielded 100-120 microL of CSF per rat. This method is simple, effective, and easy to perform and has been successfully applied in preclinical screening of novel chemical entities in neuropharmacotherapy for CNS use. The present method is demonstrated by studying the CSF concentrations of carbamazepine and raclopride.

The association between acetaminophen concentrations in the cerebrospinal fluid and temperature decline in febrile infants.

The objective of this study consisting of a prospective cohort of febrile infants was to describe the correlation between cerebrospinal fluid (CSF) acetaminophen (paracetamol) concentrations and changes in body temperature in febrile infants. Infants, one week to one year of age, with rectal temperature >or=38.0 degrees C, treated with acetaminophen were studied if they underwent a lumbar puncture (LP). Patients received 15 mg/kg of acetaminophen 30 minutes to 4 hours before lumbar puncture was performed. Rectal temperature was documented before acetaminophen administration and at the time of lumbar puncture. Plasma and CSF acetaminophen levels were determined using high-pressure liquid chromatography. Thirty-one infants were studied. In a nonlinear regression, the relationship among acetaminophen concentrations in the CSF, time, and temperature differences is best described by a Lorentzian distribution. The model suggests that a peak effect on temperature is achieved at CSF concentration of 11.9 microg/mL and 182 minutes after acetaminophen administration (P<0.001 and P<0.001, respectively r=0.9 adjusted r square=0.78). Temperature decrement in young febrile infants, treated with acetaminophen, correlates with time and acetaminophen concentrations in the CSF. High concentrations of acetaminophen in the CSF, exceeding a certain level, are not associated with greater temperature decrement.

Paracetamol (acetaminophen) penetrates readily into the cerebrospinal fluid of children after intravenous administration.

INTRODUCTION: The main action of paracetamol (acetaminophen) is presumed to be in the central nervous system. The central nervous system penetration of paracetamol has been described in children with intracranial pathologies but not in children with an intact blood-brain barrier. OBJECTIVE: We investigated the cerebrospinal fluid penetration of paracetamol in 32 healthy children, aged 3 months to 12 years, who were undergoing surgery in the lower body using spinal anesthesia. MATERIALS AND METHODS: In this open-label prospective study, children were given a single intravenous injection of paracetamol (15 mg/kg). Cerebrospinal fluid and venous blood samples were obtained between 5 minutes and 5 hours after injection. Paracetamol concentrations were determined from the cerebrospinal fluid and plasma by using a fluorescence polarization immunoassay. RESULTS: Paracetamol was detected in cerebrospinal fluid from the earliest sample at 5 minutes, although in this sample paracetamol concentration was below the limit of quantification of 1.0 mg/L. Subsequent paracetamol concentrations in cerebrospinal fluid ranged between 1.3 and 18 mg/L (median: 7.2 mg/L), plasma concentrations ranged between 2.4 and 33 mg/L, and cerebrospinal fluid/plasma ratios ranged between 0.06 and 2.0. The highest CSF paracetamol concentration was detected at 57 minutes. CONCLUSIONS: Paracetamol permeates readily into the cerebrospinal fluid of children. This fast and extensive transfer enables the rapid central analgesic and antipyretic action of intravenous paracetamol.

Acetaminophen in cerebrospinal fluid in children.

BACKGROUND: There are few studies describing acetaminophen (APAP) cerebrospinal fluid (CSF) concentrations in children. This current study was undertaken in children--from neonates to adolescents--in order to investigate age-related changes in the plasma to CSF equilibration half-time (Teq) of APAP. METHODS: Children (n=41) 1 week to 18 years of age undergoing (semi) elective surgery for placement or revision of a ventriculo-peritoneal shunt or insertion of a temporary external ventricular drain received a loading dose of 30-40 mg/kg APAP 1 h before scheduled surgery. Blood and CSF samples for APAP concentration analysis were collected during surgery. In those children with a temporary external drain, blood and CSF sampling were extended into the postoperative period. APAP and CSF pharmacokinetics were estimated using non-linear mixed-effects models. Size was standardized to a 70-kg person using allometric "1/4 power models". RESULTS: Median (25-75th percentile) age and weight of the patients included in this study were 12 months (3-62 months) and 10.0 kg (5.8-20.0 kg). Median (25-75th percentile) time between APAP loading dose administration and collection of blood samples and median time (25-75th percentile) between APAP loading dose and collection of CSF were, respectively, 125 min (95-210 min) and 133 min (33-202 min). The population mean Teq, standardized to a 70-kg person, was 1.93 h (CV 43%), an estimate similar to that described in adults (2.1 h). There was no relationship between age and Teq other than that predicted by size. APAP plasma concentrations ranged from 0.0 mg/l to 33.0 mg/l, APAP CSF concentrations ranged from 0.0 mg/l to 21.0 mg/l. CONCLUSION: Size rather than blood-brain-barrier maturation determines Teq changes with age in children. We predict a neonate (3.5 kg), 1-year-old child (10 kg), 5-year-old child (20 kg), 10-year-old child (30 kg) and adult (70 kg) to have Teq values of 0.9, 1, 1.4, 1.6, and 1.93 h, respectively.

Paracetamol plasma and cerebrospinal fluid pharmacokinetics in children.

AIMS: Paracetamol has a central action for both antipyresis and analgesia. Maximum temperature decrease and peak analgesia are reported at 1-2 h after peak plasma paracetamol concentration. We wished to determine the relationship between plasma and cerebrospinal fluid (CSF) pharmacokinetics in children. METHODS: Concentration-time profiles in plasma and CSF after nasogastric paracetamol 40 mg kg(-1) were measured in nine children who had indwelling ventricular drains. Estimation of population pharmacokinetic parameters was made using both a standard two-stage population approach (MKMODEL) and a nonlinear mixed effect model (NONMEM). Results were standardized to a 70 kg person using an allometric power model. RESULTS: Both approaches gave similar estimates. NONMEM parameter estimates were clearance 10.21 h(-1) (CV 47%), volume of distribution 67.11 (CV 58%) and absorption rate constant 0.77 h(-1) (CV 49%). Cerebrospinal fluid concentrations lagged behind those of plasma. The equilibration half time was 0.72 h (CV 117%). The CSF/plasma partition coefficient was 1.18 (CV 8%). CONCLUSIONS: Higher concentrations in the CSF probably reflect the lower free water volume of plasma. The CSF equilibration half time suggests that CSF kinetics approximate more closely to the effect compartment than plasma, but further time is required for paracetamol to exert its effects. Effect site concentrations equilibrate slowly with plasma. Paracetamol should be given 1-2 h before anticipated pain or fever in children.

Dynorphin A (1-8) analog, E-2078, crosses the blood-brain barrier in rhesus monkeys.

E-2078 is a dynorphin A (1-8) analog, [N-methyl-Tyr1, N-methyl-Arg7-D-Leu8] dynorphin A (1-8) ethylamide. Its ability to cross the blood-brain barrier was examined in rhesus monkeys using matrix-assisted laser desorption/ionization mass spectrometry. In vivo studies were carried out by i.v. injecting E-2078, 10 mg/kg, a dose that had been found to be antinociceptive, to rhesus monkeys. Blood and cerebrospinal fluid samples were collected at various time points after the injection. It was found that E-2078 was stable in vivo in rhesus monkey blood. No biotransformation products were detected in the blood. Mass spectrometric analysis of the cerebrospinal fluid samples collected after E-2078 injection detected the presence of E-2078, indicating that E-2078 had crossed the blood-brain barrier. These findings are consistent with the possibility that systemically administered E-2078 could produce centrally mediated behavioral and physiological effects.

Application of intracerebral microdialysis to study regional distribution kinetics of drugs in rat brain.

1. The purpose of the present study was to determine whether intracerebral microdialysis can be used for the assessment of local differences in drug concentrations within the brain. 2. Two transversal microdialysis probes were implanted in parallel into the frontal cortex of male Wistar rats, and used as a local infusion and detection device respectively. Within one rat, three different concentrations of atenolol or acetaminophen were infused in randomized order. By means of the detection probe, concentration-time profiles of the drug in the brain were measured at interprobe distances between 1 and 2 mm. 3. Drug concentrations were found to be dependent on the drug as well as on the interprobe distance. It was found that the outflow concentration from the detection probe decreased with increasing lateral spacing between the probes and this decay was much steeper for acetaminophen than for atenolol. A model was developed which allows estimation of kbp/Deff (transfer coefficient from brain to blood/effective diffusion coefficient in brain extracellular fluid), which was considerably larger for the more lipohilic drug, acetaminophen. In addition, in vivo recovery values for both drugs were determined. 4. The results show that intracerebral microdialysis is able to detect local differences in drug concentrations following infusion into the brain. Furthermore, the potential use of intracerebral microdialysis to obtain pharmacokinetic parameters of drug distribution in brain by means of monitoring local concentrations of drugs in time is demonstrated.