Application of in vitro data in physiologically-based kinetic models for quantitative in vitro-in vivo extrapolation: A case-study for baclofen.

Physiologically-based kinetic (PBK) models can simulate concentrations of chemicals in tissues over time without animal experiments. Nevertheless, in vivo data are often used to parameterise PBK models. This study aims to illustrate that a combination of kinetic and dynamic readouts from in vitro assays can be used to parameterise PBK models simulating neurologically-active concentrations of xenobiotics. Baclofen, an intrathecally administered drug to treat spasticity, was used as a proof-of-principle xenobiotic. An in vitro blood-brain barrier (BBB) model was used to determine the BBB permeability of baclofen needed to simulate plasma and cerebrospinal concentrations. Simulated baclofen concentrations in individuals and populations of adults and children generally fall within 2-fold of measured clinical study concentrations. Further, in vitro micro-electrode array recordings were used to determine the effect of baclofen on neuronal activity (cell signalling). Using quantitative in vitro-in vivo extrapolations (QIVIVE) corresponding doses of baclofen were estimated. QIVIVE showed that up to 4600 times lower intrathecal doses than oral and intravenous doses induce comparable neurological effects. Most simulated doses were in the range of administered doses. This show that PBK models predict concentrations in the central nervous system for various routes of administration accurately without the need for additional in vivo data.

Simultaneous Quantitation of S(+)- and R(-)-Baclofen and Its Metabolite in Human Plasma and Cerebrospinal Fluid using LC-APCI-MS/MS: An Application for Clinical Studies.

Baclofen is a racemic mixture that is commonly used for the treatment for spasticity. However, the optimal dose and dosing interval to achieve effective cerebral spinal fluid (CSF) concentrations of baclofen are not known. Moreover, it is unclear if there are differences in the ability of R- or S-baclofen to cross the blood-brain barrier and achieve effective CSF concentrations. We have validated a liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method with improved selectivity and sensitivity for the simultaneous quantitation of R- and S-baclofen and metabolites in plasma and CSF. Protein precipitation by acetonitrile was utilized to obtain an acceptable recovery of the analytes. The detection and separation of analytes was achieved on a 48 °C-heated Crownpak CR(+) column (150 mm × 4.0 mm, 5µ) with elution using 0.4% formic acid (FA) in water and 0.4% FA in acetonitrile as the mobile phase running at a flow rate of 1.0 mL/min. Accurate quantitation was assured by using this MS/MS method with atmospheric pressure chemical ionization in multiple reaction monitoring (MRM) mode. Therefore, this method is enantioselective, accurate, precise, sensitive, reliable, and linear from 1 to 1500 ng/mL for baclofen and 2 to 4000 ng/mL for the metabolites. An additional method was developed to separate racemic baclofen 3-(4-chlorophenyl)-4 hydroxybutyric acid metabolites for individual concentration determination. Both validated methods were successfully applied to a clinical pharmacokinetic human plasma and CSF study evaluating the disposition of baclofen and metabolites.

Baclofen overdose mimicking brain death.

CONTEXT: Brain death guidelines should be used with caution in patients with drug intoxication. It is often suggested that physicians use five half-lives of a drug when observing a patient with an overdose. We report two cases of baclofen intoxication where brain death was entertained as an explanation for prolonged coma, with arousal seen days later, suggesting that routine use of a 5-half-life observation period is insufficient with baclofen intoxication. CASE PRESENTATION: A 40-year-old woman was found unresponsive by her family. Baclofen was found to be the responsible overdose. The patient had absent brain stem reflexes and was intubated and in the ICU for several days. Although EEG and Apnea test were inconclusive, the patient was thought to be brain dead and organ procurement was arranged. On hospital day 5, the patient started having purposeful movements. The patient had progressive arousal and was eventually transferred without neurologic sequelae to psychiatry. The second patient also had a massive baclofen overdose, had absence of almost all brain stem reflexes and was also intubated and in the ICU. Brain death was felt to be imminent, but the patient began to awake on hospital day 7. DISCUSSION: Our two cases suggest that baclofen intoxication may result in very prolonged and profound coma and may, in fact, mimic brain death. Conclusion. The determination of brain death in the comatose overdose patient must proceed with caution. An adequate period of time to allow drug clearance must be allowed.

Cerebrospinal fluid and spinal cord distribution of hyperbaric bupivacaine and baclofen during slow intrathecal infusion in pigs.

BACKGROUND: Despite the widespread use of implanted pumps for continuous intrathecal drug delivery, there have been no studies aimed at defining the effect of baricity and posture on drug distribution in the cerebrospinal fluid and spinal cord during the very slow infusion rates typically used for chronic intrathecal drug administration. METHODS: Intrathecal microdialysis probes were placed at six points along the neuraxis in both the anterior and posterior intrathecal space of anesthetized pigs to permit cerebrospinal fluid sampling. Animals were then positioned either vertically or horizontally (prone), and a hyperbaric solution containing bupivacaine (7.5 mg/ml) and baclofen (2 mg/ml) was infused at 20 microl/h for 6 h, while the cerebrospinal fluid was collected for measurement of drug concentration. At the end of the experiment, the animals were killed, and the spinal cord was removed and divided into 1-cm sections that were further divided into anterior and posterior portions for measurement of drug concentration. RESULTS: Bupivacaine and baclofen distribution was biased caudally in the vertical group and cephalad in the horizontal group. Drug concentration decreased rapidly in the cerebrospinal fluid and spinal cord as a function of distance from the site of administration in both groups, resulting in most drugs being located in very close proximity to the site of infusion. CONCLUSION: Even at very slow infusion rates, drug distribution within the cerebral spinal fluid and spinal cord are affected by baricity/posture. These findings suggest that patient position and solution baricity may be important clinical factors determining the distribution and ultimate efficacy of chronic intrathecal drug infusions.

Cerebrospinal fluid baclofen concentrations in patients undergoing continuous intrathecal baclofen therapy.

The aim of this study was to report concentrations of cerebrospinal fluid (CSF) baclofen in children undergoing chronic intrathecal baclofen (ITB) infusions. CSF baclofen concentrations were analyzed in 53 specimens obtained by intrathecal catheter aspiration from 43 participants (28 males, 15 females; range 3-44y, mean 16y [SD 8y 11mo]), with functioning baclofen pumps and catheters. Daily ITB doses ranged from 70 to 1395 microg per day (mean 607 microg per day [SD 363], median 575). Baclofen concentration was quantified by high-pressure liquid chromatography and confirmed by injection onto a gas chromatograph. CSF baclofen concentrations from children receiving either simple continuous or complex infusions ranged from 0.2 to 20.0 microg/ml (mean 4.64 microg/ml, median 3.3 microg/ml). CSF baclofen concentrations from children receiving simple continuous infusions ranged from 0.5 to 12.9 (mean 4.7 microg/ml, median 3.55 microg/ml). There was no correlation between ITB dosage and CSF baclofen concentration. We conclude that baclofen concentration can be measured to determine if baclofen is present in CSF. However, there appears to be no correlation between the ITB dose infused and the corresponding CSF baclofen level.

Interaction of ventriculoperitoneal shunt and baclofen pump.

OBJECTIVE: The authors present three cases of children with shunted hydrocephalus and intrathecal delivery of baclofen via an implanted pump. Each case illustrates a potential interaction of these devices. MATERIALS AND METHODS: A review of the pertinent charts, operative notes, and discharge summaries was performed, along with examination of the pertinent literature. CONCLUSION: The first case illustrates that a change in the pharmacology or effect of intrathecal baclofen may be caused by a failure of a shunt affecting cerebrospinal fluid clearance. The second case illustrates that patients can have ventricular changes with any procedure that accesses the thecal space, even with a functioning shunt. The third case illustrates that ensuring that a patient's shunt is functional before implantation of a baclofen pump is imperative. As the potential pool of patients with both shunted hydrocephalus and need for intrathecal baclofen grows, clinicians should be aware of potential serious interactions.

Cerebrospinal fluid and spinal cord distribution of baclofen and bupivacaine during slow intrathecal infusion in pigs.

BACKGROUND: Increasing numbers of patients are receiving chronic intrathecal infusions of local anesthetics, baclofen, opioids, and other analgesics via implanted pumps. These infusions typically deliver drugs at rates measured in microliters per hour. However, to date, there have been no studies aimed at characterizing drug distribution within cerebrospinal fluid (CSF) and spinal cord during these slow infusion rates. Therefore, this study was designed to address this knowledge gap. METHODS: Anesthetized pigs were instrumented with eight intrathecal microdialysis probes placed at multiple points along the neuroaxis in both the anterior and posterior intrathecal space to permit continuous CSF sampling for measurement of bupivacaine and baclofen concentrations. Animals were divided into three groups and received bupivacaine and baclofen infusions at 20 or 1,000 microl/h or as a 1,000-microl bolus over 5 min every hour. Drug administration continued for 8 h, at which time the animals were killed, and the spinal cord was removed and divided into 1-cm-long sections that were further divided into anterior and posterior portions for measurement of bupivacaine and baclofen concentrations. RESULTS: In all groups, drug concentration in CSF and spinal cord decreased rapidly as a function of distance from the site of administration, with most drug found within a few centimeters. In addition, there were significant anterior-posterior differences in both CSF and spinal cord drug concentrations. CONCLUSIONS: During slow intrathecal infusion, drug distribution in CSF and spinal cord is severely limited in all groups, although significantly more so in the 20-microl/h infusion group.

Simple and sensitive liquid chromatography-tandem mass spectrometry method for determination of the S(+)- and R(-)-enantiomers of baclofen in human plasma and cerebrospinal fluid.

A simple and sensitive liquid chromatography-tandem mass spectrometry (LC/MS/MS) method to determine the enantiomers of the muscle relaxant baclofen in human plasma and cerebrospinal fluid (CSF) has been developed. A commercially available ultrafiltration membrane is used to prepare the sample. A chiral CROWNPAK CR(+) stationary phase column is then used to perform complete resolution of the S(+)- and R(-)-enantiomers of baclofen. This method was used to analyze human plasma and CSF spiked with baclofen, and the calibration curves for both biologic samples were linear over a concentration range of 0.15-150 ng enantiomer/ml. The lower limit of quantification was 0.15 ng enantiomer/ml in both fluids. Finally, the method was tested with an artificial CSF as an alternative to authentic human CSF. The results showed that no matrix effects and no interfering peaks were observed using this artificial CSF.

Toxicology of baclofen continuously infused into the spinal intrathecal space of the dog.

The continuous spinal administration of baclofen has been shown to have therapeutic benefit in the management of spasticity in humans with neuraxial injuries. The present study systematically investigated the potential spinal neurotoxicity of continuous intrathecally-infused baclofen in dogs. Male beagle dogs were prepared with chronic lumbar intrathecal catheters connected to subcutaneously implanted infusion pumps. Three groups of dogs received 28 days of infusion of saline (vehicle: 1 ml/24 hrs; N = 10), 200 micrograms/ml/24 hrs baclofen (N = 10) or 2000 micrograms/ml/24 hrs baclofen (N = 10). A mild, dose-dependent anti-nociception and muscle weakness was observed. Independent assessment of spinal histopathology in dogs sacrificed and perfusion fixed at 28 days of treatment revealed a mild fibrotic reaction to the catheter, but there were no changes distinguishable from vehicle infused animals which could be ascribed to any dose of intrathecal baclofen. Cisternal CSF protein and cells in samples taken at sacrifice were also not different for the three groups. These findings with chronic intrathecally administered baclofen in this dog model jointly support the lack of toxicity of chronic intrathecal baclofen at concentrations up to 2000 micrograms/ml.

Intrathecal baclofen overdose: report of 7 events in 5 patients and review of the literature.

This study is intended to alert the clinician to the insidious symptoms of baclofen overdose, its prevention and treatment. In a group of 43 patients suffering from previously intractable spasticity and a total treatment time of 2,422 weeks, 7 events of intrathecal baclofen overdose happened in 5 patients. On two occasions, a bolus injection caused an overdose (dose 50 and 280 micrograms). The 5 events during continuous infusion intoxication only happened in high dosed patients. The overdose symptoms occurred in one patient when she was lying in supine position (800 micrograms/24 h), in another patient after repair of CSF leakage by an autologous epidural bloodpatch (1,920 micrograms/24 h) and in tolerant patients, once during maximal dose adjustments (2,400 micrograms/24 h) and twice ca. 6 hours following reinitiation of the intrathecal baclofen infusion after a "drug holiday" treatment (27 and 55 micrograms/h). We could not confirm the reported similarity of baclofen overdose with the anticholinergic syndrome. Especially, the bradycardia and hypotension are more in accord with the reported clinical picture of oral baclofen overdose. In the absence of a pure baclofen antagonist and the varying symptoms of intrathecal baclofen, intoxication make rational treatment difficult. We observed that the advised physostigmine therapy is not always effective and safe. The occasionally doubtful antidotal benefits of physostigmine must be weighted against major side-effects. The classical approach of decreasing the absorption of a drug by lowering baclofen levels in the CSF by lumbar puncture drainage was successful. This approach together with conservative symptomatic treatment in an intensive care environment is probably a better and safer alternative than physostigmine alone as an antidote.

CSF baclofen levels after intrathecal administration in severe spasticity.

The pharmacokinetic parameters in the CSF of baclofen given to 4 patients as an intrathecal bolus are reported. Considerable inter-individual variability in the parameters was observed. The elimination half-life ranged from 0.9 to 5 h and the clearance from 0.013 to 0.08 l.h-1. In order to optimize treatment, it is suggested that CSF baclofen levels be matched to changes in Hoffman's monosynaptic reflex (H reflex).

[Choreic dyskinesia and GABA - pharmaco-clinical approach. Preliminary note]. / Discinesie coreiche e Gaba - approccio farmaco-clinico. Nota preliminare.

The effects of Baclofen, a gabamimetic drug, have been studied in 4 patients affected by Huntington's Chorea. The biochemical bases of Chorea are discussed in relation to the HVA modifications in the cerebrospinal fluid induced by the drug. Some interesting data on the extrapyramidal physiology may be achieved with further investigations in a greater group of patients.