Development of a physiologically-based pharmacokinetic pediatric brain model for prediction of cerebrospinal fluid drug concentrations and the influence of meningitis.

Different pediatric physiologically-based pharmacokinetic (PBPK) models have been described incorporating developmental changes that influence plasma drug concentrations. Drug disposition into cerebrospinal fluid (CSF) is also subject to age-related variation and can be further influenced by brain diseases affecting blood-brain barrier integrity, like meningitis. Here, we developed a generic pediatric brain PBPK model to predict CSF concentrations of drugs that undergo passive transfer, including age-appropriate parameters. The model was validated for the analgesics paracetamol, ibuprofen, flurbiprofen and naproxen, and for a pediatric meningitis population by empirical optimization of the blood-brain barrier penetration of the antibiotic meropenem. Plasma and CSF drug concentrations derived from the literature were used to perform visual predictive checks and to calculate ratios between simulated and observed area under the concentration curves (AUCs) in order to evaluate model performance. Model-simulated concentrations were comparable to observed data over a broad age range (3 months-15 years postnatal age) for all drugs investigated. The ratios between observed and simulated AUCs (AUCo/AUCp) were within 2-fold difference both in plasma (range 0.92-1.09) and in CSF (range 0.64-1.23) indicating acceptable model performance. The model was also able to describe disease-mediated changes in neonates and young children (<3m postnatal age) related to meningitis and sepsis (range AUCo/AUCp plasma: 1.64-1.66, range AUCo/AUCp CSF: 1.43-1.73). Our model provides a new computational tool to predict CSF drug concentrations in children with and without meningitis and can be used as a template model for other compounds that passively enter the CNS.

Plasma and brain pharmacokinetics of ganoderic acid A in rats determined by a developed UFLC-MS/MS method.

Ganoderic acid A (GAA), an active triterpenoid of the traditional Chinese herbal medicine Lingzhi, has been reported to exhibit antinociceptive, antioxidative, and anti-cancer activities. The present study aims to establish a sensitive and rapid UPLC-MS/MS method for studying the plasma and brain pharmacokinetics of GAA in rats. The analytes were separated on a C18 column eluted with a gradient mobile phase consisting of acetonitrile and 0.1% aqueous formic acid at 0.3mL/min. The eluate was monitored by a mass detector using an MRM (m/z, 515.3-285.1) model in negative electrospray ionization. The calibration curve showed good linearity (r2>0.99), with limits of detection and quantification of 0.25 and 2.00 nmol/L, respectively. The intra- and inter-day precision and accuracy were less than 9.99% and ranged from 97.45% to 114.62%, respectively. The extraction recovery from plasma was between 92.89% and 98.87%. GAA was found to be stable in treated samples at room temperature (22°C) for 12h and in plasma at -20°C for 7d. The developed method was successfully applied to a pharmacokinetic study of GAA in rats. GAA could be rapidly absorbed into the circulation (Tmax, 0.15h) and eliminated relatively slowly (t1/2, 2.46h) after orally dosing, and could also be detected in the brain lateral ventricle (Tmax, 0.25h and t1/2, 1.40h) after intravenously dosing. The absolute oral bioavailability and brain permeability of GAA were estimated to be 8.68% and 2.96%, respectively.

Delivery of ziconotide to cerebrospinal fluid via intranasal pathway for the treatment of chronic pain.

The purpose of the current study was to investigate the plausibility of delivery of ziconotide to the cerebrospinal fluid (CSF) via intranasal administration. Ziconotide was administered either in the form of solution or Kolliphor P 407 gels (KP 407) intranasally in Sprague-Dawley rats. The effect of incorporation of chitosan in the formulation was also investigated. Time course of drug in the CSF was investigated by collecting CSF from cisterna magna. Pharmacokinetics of ziconotide in CSF following intrathecal and intravenous (i.v.) administration of ziconotide was investigated. Upon intrathecal administration the elimination rate constant of ziconotide in CSF was found to be 1.01±0.34h(-1). The Cmax and Tmax of ziconotide in CSF following intravenous administration were found to be 37.78±6.8ng/mL and ~2h respectively. The time required to attain maximum concentration (Tmax) in CSF was less upon intranasal administration (15min) compared to i.v. administration (120min). Presence of chitosan enhanced the overall bioavailability of ziconotide from intranasal solution and gel formulations. The elimination rate constant of ziconotide in CSF following intranasal and intravenous administration of ziconotide solution was found to be 0.54±0.08h(-1) and 0.42±0.10h(-1) respectively. Whereas, intranasal administration of ziconotide in the form of in situ forming gel lowered the elimination rate significantly. These results suggest that intranasal administration could be a potential noninvasive and patient compliant method of delivering ziconotide to CSF to treat chronic pain.

Epidural administration of neostigmine-loaded nanofibers provides extended analgesia in rats.

BACKGROUND: In this study, neostigmine-loaded electrospun nanofibers were prepared and then their efficacy and duration of analgesic action were studied after epidural administration in rats by repeated tail flick and formalin tests. METHODS: The neostigmine poly vinyl alcohol (PVA) nanofibers were fabricated by electrospinning methods. The nanofibers (1 mg) were injected into the lumbar epidural space (L5-L6) of rats (n = 6). Cerebrospinal fluid samples of rats were collected 1, 5 and 24 hours after injection and then were sampled once weekly for 4 weeks. Free-neostigmine concentration was measured in the samples spectrophotometrically. Rat nociceptive responses were evaluated by repeated tail-flick and formalin tests for 5 weeks after the nanofibers (1 mg) injection. Locomotor activity of rats was measured in the open-field at the same period. RESULTS: The cerebrospinal fluid concentration of free neostigmine reached 5 µg/ml five hours after injection and remained constant until the end of the experiments. The tail-flick latency of treated rats was significantly (p < 0.01) increased and remained constant up to 4 weeks. Pain scores of the rats in both phases of formalin test were significantly (p < 0.01) reduced during the same periods, Epidural injection of the nanofibers had no effect on locomotor activity of rats in an open-field. CONCLUSIONS: Our results indicate that the neostigmine nanofibers can provide sustained release of neostigmine for induction of prolonged analgesia after epidural administration. High tissue distribution and penetration of the nanofibers in dorsal horn can increase thermal and chemical analgesia duration without altering locomotor activity in rats for 4 weeks.

Can a single dose of 300 mg of pregabalin reach acute antihyperalgesic levels in the central nervous system?

BACKGROUND AND OBJECTIVES: Central spinal cord sensitization can occur during surgery and may lead to persistent pain after surgery. Pregabalin has been shown to decrease central sensitization in experimental pain paradigms, and so the same antihyperalgesic effect of pregabalin may occur during and immediately after surgery. Our study investigated whether a single 300-mg dose of pregabalin in patients has sufficient central nervous system bioavailability to be useful under acute conditions where brain or spinal cord excitability may lead to long-term disease, such as chronic pain. METHODS: Nine patients undergoing primary total knee replacement received pregabalin 300 mg orally, 1 hr before surgery. An intrathecal catheter was inserted for anesthesia, postoperative analgesic drug administration, and cerebrospinal fluid (CSF) sampling. Blood and CSF were then simultaneously sampled at 2, 4, 6, 8, and 24 hrs after oral pregabalin administration. Pregabalin concentration in plasma and CSF was measured using a validated high-pressure liquid chromatography assay. RESULTS: By 2 hrs after pregabalin administration, the CSF pregabalin concentration is high enough (0.115 µg/mL) to have anticonvulsant activity, and by 6 hrs after pregabalin administration, the CSF pregabalin level is high enough (0.359 µg/mL) to reduce central nervous system hypersensitivity. The median time to peak pregabalin concentration in CSF was at 8 hrs. The pregabalin CSF/plasma based on area under the curve (AUC[0-24 hrs]) was 0.098 ± 0.016, and for AUC[0-∞], the ratio was 0.176 ± 0.064. CONCLUSIONS: Sufficient central nervous system drug concentrations are reached after oral administration of pregabalin, suggesting that postoperative pain hypersensitivity can be reduced. Decreasing this acute brain or spinal cord excitability may prevent chronic pain from developing after surgery.

Plasma and cerebrospinal fluid pharmacokinetics of flurbiprofen in children.

AIMS: This study was designed to characterize paediatric pharmacokinetics and central nervous system exposure of flurbiprofen. METHODS: The pharmacokinetics of flurbiprofen were studied in 64 healthy children aged 3 months to 13 years, undergoing surgery with spinal anaesthesia. Children were administered preoperatively a single dose of flurbiprofen intravenously as prodrug (n= 27) or by mouth as syrup (n= 37). A single cerebrospinal fluid (CSF) sample (n= 60) was collected at the induction of anaesthesia, and plasma samples (n= 304) before, during and after the operation (up to 20 h after administration). A population pharmacokinetic model was built using the NONMEM software package. RESULTS: Flurbiprofen concentrations in plasma were well described by a three compartment model. The apparent bioavailability of oral flurbiprofen syrup was 81%. The estimated clearance (CL) was 0.96l h(-1) 70 kg(-1) . Age did not affect the clearance after weight had been included as a covariate. The estimated volume of distribution at steady state (V(ss) ) was 8.1 l 70 kg(-1) . Flurbiprofen permeated into the CSF, reaching concentrations that were seven-fold higher compared with unbound plasma concentrations. CONCLUSIONS: Flurbiprofen pharmacokinetics can be described using only weight as a covariate in children above 6months, while more research is needed in neonates and in younger infants.

Mechanisms involved in the antinociception induced by systemic administration of guanosine in mice.

BACKGROUND AND PURPOSE: It is well known that adenine-based purines exert multiple effects on pain transmission. However, less attention has been given to the potential effects of guanine-based purines on pain transmission. The aim of this study was to investigate the effects of intraperitoneal (i.p.) and oral (p.o.) administration of guanosine on mice pain models. Additionally, investigation into the mechanisms of action of guanosine, its potential toxicity and cerebrospinal fluid (CSF) purine levels were also assessed. EXPERIMENTAL APPROACH: Mice received an i.p. or p.o. administration of vehicle (0.1 mM NaOH) or guanosine (up to 240 mg x kg(-1)) and were evaluated in several pain models. KEY RESULTS: Guanosine produced dose-dependent antinociceptive effects in the hot-plate, glutamate, capsaicin, formalin and acetic acid models, but it was ineffective in the tail-flick test. Additionally, guanosine produced a significant inhibition of biting behaviour induced by i.t. injection of glutamate, AMPA, kainate and trans-ACPD, but not against NMDA, substance P or capsaicin. The antinociceptive effects of guanosine were prevented by selective and non-selective adenosine receptor antagonists. Systemic administration of guanosine (120 mg x kg(-1)) induced an approximately sevenfold increase on CSF guanosine levels. Guanosine prevented the increase on spinal cord glutamate uptake induced by intraplantar capsaicin. CONCLUSIONS AND IMPLICATIONS: This study provides new evidence on the mechanism of action of the antinociceptive effects after systemic administration of guanosine. These effects seem to be related to the modulation of adenosine A(1) and A(2A) receptors and non-NMDA glutamate receptors.

Guanosine prevents thermal hyperalgesia in a rat model of peripheral mononeuropathy.

UNLABELLED: It is well known that adenine-based purines exert multiple effects on pain transmission. Less attention has been given, however, to the antinociceptive effects of guanine-based purines. The aim of this study was to investigate the effects of intraperitoneal administration of guanosine on a rat model of peripheral mononeuropathy. Additionally, investigation of the mechanism of action of guanosine, its general toxicity and measurements of central nervous system purine levels were performed. Rats received an intraperitoneal administration of vehicle (0.1 mM NaOH) or guanosine (up to 120 mg.kg(-1)) in an acute or chronic regimen. Guanosine significantly reduced thermal hyperalgesia on the ipsilateral side of the sciatic nerve ligation. Additionally, guanosine prevented locomotor deficits and body weight loss induced by the mononeuropathy. Acute systemic administration of guanosine caused an approximately 11-fold increase on central nervous system guanosine levels, but this effect was not observed after chronic treatment. Chronic guanosine administration prevented the increase on cortical glutamate uptake but not the decrease in spinal cord glutamate uptake induced by the mononeuropathy. No significant general toxicity was observed after chronic exposure to guanosine. This study provides new evidence on the mechanism of action of guanine-based purines, with guanosine presenting antinociceptive effects against a chronic pain model. PERSPECTIVE: This study provides a new role for guanosine: chronic pain modulation. Guanosine presents as a new target for future drug development and might be useful for treatment of neuropathic pain.

Enhanced antinociceptive response to intracerebroventricular kyotorphin in Pept2 null mice.

L-Kyotorphin (L-KTP), an endogenous analgesic neuropeptide, is a substrate for aminopeptidases and a proton-coupled oligopeptide transporter, PEPT2. This study examined the CSF efflux, antinociceptive response, and hydrolysis kinetics in brain of L-KTP and its synthetic diastereomer D-kyotorphin (D-KTP) in wild-type and Pept2 null mice. CSF clearance of L-KTP was slower in Pept2 null mice than in wild-type animals, and this difference was reflected in greater L-KTP-induced analgesia in Pept2 null mice. Moreover, dose-response analyses showed that the ED50 of L-KTP in Pept2-deficient animals was one-fifth of the value observed in Pept2-competent animals (4 vs. 21 nmol for null vs. wild-type mice, respectively). In contrast, the ED50 of D-KTP was very similar between the two genotypes (9-10 nmol). Likewise, there was little difference between genotypes in slope factor or baseline effects of L-KTP and D-KTP. The enhanced antinociceptive response to L-KTP in Pept2 null mice could not be explained by differences in neuropeptide degradation as Vmax and Km values did not differ between genotypes. Our results demonstrate that PEPT2 can significantly impact the analgesic response to an endogenous neuropeptide by altering CSF (and presumably brain interstitial fluid) concentrations and that it may influence the disposition and response to exogenous peptide/mimetic substrates.

Antinociceptive and hemodynamic effects of a novel alpha2-adrenergic agonist, MPV-2426, in sheep.

BACKGROUND: alpha2-Adrenergic agonists produce analgesia primarily by a spinal action and hypotension and bradycardia by actions at several sites. Clonidine is approved for epidural use in the treatment of neuropathic pain, but its wider application is limited by hemodynamic side effects. This study determined the antinociceptive and hemodynamic effects of a novel alpha2-adrenergic agonist, MPV-2426, in sheep. METHODS: Forty sheep of mixed Western breeds with indwelling catheters were studied. In separate studies, antinociception to a mechanical stimulus, hemodynamic effects, arterial blood gas tensions, cerebrospinal fluid pharmacokinetics, and spinal cord blood flow was determined after epidural, intrathecal, and intravenous injection of MPV-2426. RESULTS: MPV-2426 produced antinociception with greater potency intrathecally (ED50 = 49 microg) than epidurally (ED50 = 202 microg), whereas intravenous administration had no effect. Intrathecal injection, in doses up to three times the ED95, failed to decrease systemic or central arterial blood pressures or heart rate, whereas larger doses, regardless of route, increased systemic arterial pressure. Bioavailability in cerebrospinal fluid was 7% after epidural administration and 0.17% after intravenous administration. Intrathecal MPV-2426, in an ED95 dose and three times this dose, produced a dose-independent reduction in thoracic and lumbar spinal cord blood flow. CONCLUSIONS: MPV-2426 shares many characteristics of other alpha2-adrenergic agonists examined in sheep, but differs from clonidine and dexmedetomidine by lack of antinociception and minimal reduction in oxygen partial pressure after large intravenous and epidural injections. No hemodynamic depression was observed after intrathecal injection at antinociceptive doses. These results suggest this compound may be an effective spinal analgesic in humans with less hypotension than clonidine, although its relative potency to cause sedation was not tested in this study.

Distribution, tolerability and tissue compatibility of intrathecal tizanidine in the sheep.

BACKGROUND: Tizanidine (TZD) is an alpha-2-adrenergic drug with potential spinal analgesic action and could be a substitute or additive for intrathecal (i.t.) opiates in chronic pain treatment. However, long-term tolerability and tissue compatibility are not yet established. METHODS: Three sheep were infused intrathecally with TZD up to 4000 micrograms/d over a time period of up to 440 d using implantable drug administration devices; one control animal was infused with vehicle only; standard values were collected from untreated sheep. CSF samples and blood samples were analyzed to determine pharmacokinetics and systemic redistribution. Behavioral effects were studied. The spinal cord tissue was investigated using standard laboratory histology. RESULTS: Bolus kinetics after i.t. injection of TZD are best described by a two-phase model. Elimination half-lives of TZD in CSF were 15 min and 152 min, respectively. Clearance of TZD from lumbar CSF was 0.48 ml/min. Doses higher than 500 microgram i.t. caused dose-dependent motor inactivity and sleepiness. Continuous i.t. TZD up to 4 micrograms/d was well tolerated regarding behavioral, physical activity, heart rate, muscle counts and total protein were detected both in saline and TZD-treated animals, presumably due to local irritation by the catheter and repeated sampling procedures. Histological evaluation of the spinal cord and adjacent tissues showed no abnormalities. CONCLUSION: The long-term intrathecal infusion of TZD is well tolerated and non-toxic in the sheep. The data favor clinical trials in patients with chronic pain.

Antinociceptive potentiation and attenuation of tolerance by intrathecal co-infusion of magnesium sulfate and morphine in rats.

UNLABELLED: N-methyl-D-aspartate (NMDA) antagonists, such as MK801, delay the development of morphine tolerance. Magnesium, a noncompetitive NMDA antagonist, reduces postoperative morphine requirements. The present study was designed to evaluate the effects of intrathecal co-administration of magnesium sulfate with morphine on antinociceptive potentiation, tolerance, and naloxone-induced withdrawal signs. Magnesium sulfate (40-60 microg/h) co-administration for 7 days, similar to MK801 (10 nmol/h), prevented the decline in antinociceptive response compared with morphine (20 nmol/h). Magnesium sulfate (60 microg/h) produced no antinociception, but co-infused with morphine (1 nmol/h), it resulted in potentiated antinociception compared with morphine throughout the 7-day period. Probe morphine doses after 7-day infusions demonstrated a significantly greater 50% effective dose value for morphine 1 nmol/h (109.7 nmol) compared with saline (10.9 nmol), magnesium sulfate 60 microg/h (10.9 nmol), and magnesium sulfate 60 microg/h plus morphine 1 nmol/h (11.2 nmol), which indicates that magnesium had delayed morphine tolerance. Morphine withdrawal signs after naloxone administration were not altered by the co-infusion of magnesium sulfate. Cerebrospinal fluid magnesium levels after intrathecal magnesium sulfate (60 microg/h) for 2 days increased from 17.0 +/- 1.0 microg/mL to 41.4 +/- 23.6 microg/mL, although serum levels were unchanged. This study demonstrates antinociceptive potentiation and delay in the development of morphine tolerance by the intrathecal coinfusion of magnesium sulfate and morphine in the rat. IMPLICATIONS: The addition of magnesium sulfate, an N-methyl-D-aspartate antagonist, to morphine in an intrathecal infusion provided better analgesia than morphine alone in normal rats. These results suggest that intrathecal administration of magnesium sulfate may be a useful adjunct to spinal morphine analgesia.

Ketorolac penetration into the cerebrospinal fluid of humans.

STUDY OBJECTIVE: To determine the cerebrospinal fluid (CSF): total plasma concentration ratio of ketorolac tromethamine following a single intramuscular (IM) dose. DESIGN: Open, single-dose, IM-administration study. SETTING: General operating theaters of a medical school hospital. PATIENTS: 29 ASA physical status I and II patients scheduled to undergo elective surgery with spinal anesthesia. INTERVENTIONS: Patients were premedicated with ketorolac 90 mg IM formulated as 3 ml of a 3% solution. Between 1 and 4 1/2 hours later, an intravenous infusion of 500 ml of compound sodium lactate was begun. Lumbar puncture was then performed, and 2 ml of CSF was collected prior to administration of the spinal anesthetic. In addition, a 5 ml sample of venous blood was taken within 5 minutes of the CSF sample. MEASUREMENTS AND MAIN RESULTS: Simultaneous plasma and CSF concentrations of ketorolac were measured between 62 and 277 minutes following IM administration in 29 patients undergoing spinal anesthesia. The CSF concentrations were on the order of 1,000 times less than the total plasma concentrations; free concentrations of ketorolac in plasma were estimated to be about 10 times more than those in CSF. There appeared to be no constant time factor relating the appearance of ketorolac in the CSF to its plasma concentration following IM administration. CONCLUSION: Although the sensitivity of central prostaglandin synthetase systems to inhibition is unknown, it is unlikely from this pharmacokinetic data that there is a major central mechanism of analgesia for ketorolac.

[Kyotorphin like substance in human cerebrospinal fluid of patients with persistent pain].

Kyotorphin is an analgesic neuropeptide isolated from the bovine brain in 1979. Further studies showed that kyotorphin produces an analgesia through an increased release of met-enkephalin in the brain and the spinal cord. We showed that it is also found in the human cerebrospinal fluid and the concentrations of kyotorphin in normal human CSF is 1.19 +/- 0.51 pmol.ml-1. We also found that it is lower in patients with persistent pain (0.24 +/- 0.04 pmol.ml-1). Above results suggest that kyotorphin acts as a putative neuromediator and/or an endogenous pain modulator in the human brain.