Intravenous topiramate: comparison of pharmacokinetics and safety with the oral formulation in healthy volunteers.

PURPOSE: Although oral topiramate (TPM) products are widely prescribed for migraines and epilepsy, injectable TPM is not available for human use. We have developed a solubilized TPM formulation using a cyclodextrin matrix, Captisol with the long-term goal of evaluating its safety and efficacy in neonatal seizures. This study in healthy adult volunteers was performed as required by the U.S. Food and Drug Administration (FDA) to demonstrate the pharmacokinetics and safety prior to initiation of studies involving children. This study allowed investigation of absolute bioavailability, absolute clearance, and distribution volume of TPM, information that could not be obtained without using an intravenous TPM formulation. METHODS: This study was an open-label, two-way crossover of oral and intravenous TPM in 12 healthy adult volunteers. Initially two subjects received 50 mg, intravenously and orally. Following evidence of safety in the first two subjects, 10 individuals received 100 mg doses of intravenous and oral TPM randomly sequenced 2 weeks apart. Blood samples were taken just prior to drug administration and at intervals up to 120 h afterwards. TPM was measured using a validated liquid chromatography-mass spectrometry method. Concentration-time data were analyzed using a noncompartmental approach with WinNonlin 5.2. KEY FINDINGS: All subjects completed the study. The mean (±standard deviation) absolute oral bioavailability was 109% (±10.8%). For intravenous and oral TPM the mean distribution volumes were 1.06 L/kg (±0.29) and 0.94 L/kg (±0.24). Clearances were 1.33 L/h (±0.26) and 1.22 L/h (±0.26). The half-life values were 42.3 h (±6.2) and 41.2 h (±7.5). No changes in heart rate, blood pressure, electrocardiography, or infusion site reactions were observed. Mild central nervous system cognitive adverse events and ataxia occurred between dosing and 2 h post dose with both intravenous and oral administration. With intravenous TPM, these adverse effects occurred as early as during the 15-min intravenous infusion. SIGNIFICANCE: In healthy adults, oral TPM is bioequivalent to intravenous TPM, and infusion of 50-100 mg over 15 min is safe. Neurologic effects occurred during the infusion, demonstrating that TPM rapidly diffuses into the brain, which supports its evaluation for neonatal seizures. Results from this pilot study will inform the design of subsequent studies in children and newborns, including controlled clinical trials intended to assess the efficacy and safety of intravenous TPM for neonatal seizures. In addition, our results provide support for the further development of intravenous TPM as bridge therapy for older children and adults in whom oral TPM therapy is interrupted.

Intravenous topiramate: safety and pharmacokinetics following a single dose in patients with epilepsy or migraines taking oral topiramate.

PURPOSE: Although topiramate is widely prescribed for epilepsy and migraine, there is no intravenous product. We have developed an injectable topiramate formulation in which the drug is solubilized in a cyclodextrin matrix, Captisol(®) (Ligand Pharmaceuticals, Inc., La Jolla, CA). Our long-term goal is to evaluate intravenous topiramate for the treatment of neonatal seizures. Prior to studies in newborns, we carried out an investigation of injectable topiramate's safety and pharmacokinetics in adult patients. METHODS: Twenty adult volunteers with epilepsy or migraine on stable, on maintenance topiramate therapy were given 25 mg of a stable-labeled intravenous topiramate over 10 min, followed by their usual oral doses. Vital signs were taken, electrocardiography studies (ECGs) were recorded, and the infusion sites were periodically examined prior to and up to 24 h after dosing. Blood samples were collected prior to administration and serially for 96 h thereafter. Plasma concentrations of both stable-labeled and regular topiramate were measured using liquid chromatography-mass spectrometry (LC-MS). Concentration-time data were analyzed using a noncompartmental approach with WinNonlin 5.2 (Pharsight Corporation, Mountain View, CA, U.S.A.). KEY FINDINGS: Seven patients experienced one or more of the following minor adverse events including nausea and vomiting (1), tingling around the lips (1), paresthesia in the arms and legs (1), and a mild vasovagal response with intravenous catheter placement (1). Included in the adverse events were four patients with epilepsy who had seizures consistent with their histories. There were no changes in heart rate, blood pressure, or ECG results, and there were no infusion site reactions. Pharmacokinetic parameters (mean ± standard deviation [SD]) determined following the intravenous dose included absolute bioavailability: 110 ± 16%, distribution volume: 0.79 ± 0.22 L/kg, clearance: 2.03 ± 1.07 L/h, and elimination half-life: 27.6 ± 9.7 h. Distribution volume, half-life, and clearance were significantly altered by enzyme-inducing drugs. SIGNIFICANCE: A single 25-mg dose of intravenous topiramate caused minimal infusion site or systemic adverse effects in patients taking oral topiramate. Pharmacokinetic results show that oral topiramate is completely absorbed and that its steady-state elimination half-life is longer than previously assumed, which permits once or twice daily dosing even in the presence of enzyme-inducing drugs. The information from this study can inform the design of subsequent studies in adults, older children, and newborns, including controlled clinical trials intended to determine the efficacy and safety of intravenous topiramate for neonatal seizures.

No difference in extra-axial cerebrospinal fluid volumes across neurodevelopmental and psychiatric conditions in later childhood and adolescence.

BACKGROUND: While autism spectrum disorder has been associated with various organizational and developmental aberrations in the brain, an increase in extra-axial cerebrospinal fluid volume has recently garnered attention. A series of studies indicate that an increased volume between the ages of 6 months and 4 years was both predictive of the autism diagnosis and symptom severity regardless of genetic risk for the condition. However, there remains a minimal understanding regarding the specificity of an increased volume of extra-axial cerebrospinal fluid to autism. METHODS: In the present study, we explored extra-axial cerebrospinal fluid volumes in children and adolescents ages 5-21 years with various neurodevelopmental and psychiatric conditions. We hypothesized that an elevated extra-axial cerebrospinal fluid volume would be found in autism compared with typical development and the other diagnostic group. We tested this hypothesis by employing a cross-sectional dataset of 446 individuals (85 autistic, 60 typically developing, and 301 other diagnosis). An analysis of covariance was used to examine differences in extra-axial cerebrospinal fluid volumes between these groups as well as a group by age interaction in extra-axial cerebrospinal fluid volumes. RESULTS: Inconsistent with our hypothesis, we found no group differences in extra-axial cerebrospinal fluid volume in this cohort. However, in replication of previous work, a doubling of extra-axial cerebrospinal fluid volume across adolescence was found. Further investigation into the relationship between extra-axial cerebrospinal fluid volume and cortical thickness suggested that this increase in extra-axial cerebrospinal fluid volume may be driven by a decrease in cortical thickness. Furthermore, an exploratory analysis found no relationship between extra-axial cerebrospinal fluid volume and sleep disturbances. CONCLUSIONS: These results indicate that an increased volume of extra-axial cerebrospinal fluid may be limited to autistic individuals younger than 5 years. Additionally, extra-axial cerebrospinal fluid volume does not differ between autistic, neurotypical, and other psychiatric conditions after age 4.