Oral bioavailability of phenobarbital: a comparison of a solution in Myvacet 9-08, a suspension, and a tablet

Formulation and stability study of an oral paediatric phenobarbital 1% solution containing hydroxypropyl-β-cyclodextrins

OBJECTIVES

Phenobarbital is a barbiturate, used to treat focal and generalised epilepsy. Since the end of marketing of the oral solution KANEURON in 2017, phenobarbital tablets remain the only available dosage form. Development of an oral phenobarbital solution for paediatric use is therefore essential to fulfil clinical needs. A new formulation of phenobarbital with hydroxypropyl-β-cyclodextrins (HPBCD) was developed, and the physicochemical stability of the solution was evaluated.

METHODS

Different excipients have been selected to formulate a solution of phenobarbital. Samples were dosed by High Performance Liquid Chromatography (HPLC) at 216 nm with a LiChroCART C18 endcapped column and mobile phase composed of phosphate buffer pH 3 and methanol (50:50 v/v). Linearity, accuracy, sensibility and specificity of the method were tested, and a forced degradation study was carried out. During stability study, content of phenobarbital, pH, osmolality of the phenobarbital solution and degradation products were followed up for 6 months in line with GERPAC guidelines.

RESULTS

The stability indicating the character of the assay method has been validated. The physicochemical stability study shows that the phenobarbital solution formulated is stable for 6 months, in line with International Conference of Harmonisation (ICH) recommendations Q1A and Q3B (R2) regarding the content of phenobarbital and levels of degradation products (no degradation products >0.01%). Phenobarbital concentration was 101.59±2.6% of initial concentration in refrigerated samples and 101.14±0.5% at 20±5°C. No phenobarbital degradation products (>0.01%) were observed throughout the 6 months. No significant variation of pH or osmolality was observed.

CONCLUSIONS

HPBCD solubilise phenobarbital and create a homogeneous solution. These stability data set the shelf life of this new phenobarbital solution at up to 6 months. A microbiological stability study will be carried out to ensure the possibility of using this solution in children.

Phenobarbital loaded microemulsion: development, kinetic release and quality control

ABSTRACT This study aimed to obtain and characterize a microemulsion (ME) containing phenobarbital (PB). The PB was incorporated in the proportion of 5% and 10% in a microemulsion system containing Labrasol(r), ethanol, isopropyl myristate and purified water. The physicochemical characterization was performed and the primary stability of the ME was evaluated. An analytical method was developed using spectrophotometry in UV = 242 nm. The kinetics of the in vitro release (Franz model) of the ME and the emulsion (EM) containing PB was evaluated. The incorporation of PB into ME at concentrations of 5 and 10% did not change pH and resistance to centrifugation. There was an increase in particle size, a decrease of conductivity and a change in the refractive index in relation to placebo ME. The ME remained stable in preliminary stability tests. The analytical method proved to be specific, linear, precise, accurate and robust. Regarding the kinetics of the in vitro release, ME obtained an in vitro release profile greater than the EM containing PB. Thus, the obtained ME has a potential for future transdermal application, being able to compose a drug delivery system for the treatment of epilepsy.

In vivo evaluation of anticonvulsant and antioxidant effects of phenobarbital microemulsion for transdermal administration in pilocarpine seizure rat model

This study aimed to evaluate a microemulsion system (ME) containing phenobarbital in epilepsy model induced by pilocarpine in rats and to oxidative stress and histologic lesions in hippocampus. The microemulsion was applied to the shaved back of Wistar rats. The animals were divided into the following groups: control group (P400); ME50 40mg/kg, topically-t.p.; ME100, 40mg/kg, t.p.; EM50, 40mg/kg, t.p.; phenobarbital solution 40mg/kg (PS), oral. After 60min, behavioral changes were evaluated for 1h in the model of epileptical crisis induced by pilocarpine. Phenobarbital in microemulsion was able to increase the latency for status epilepticus (SE) (p<0.05), decrease the number of epileptical crisis (ME50: p<0.001; ME100: p<0.01) and decrease mortality rate by 80% compared to P400. In EM50 and PS groups, deaths were decreased by 53.3% and 100% respectively. The ME50 and ME100 groups were able to reduce oxidative stress in experimental animals when compared to the P400. The microemulsion was still capable of reducing neuronal damage in the hippocampal areas. The results of this study come in an innovative way, demonstrating the ability of transdermal ME50 and ME100 to reduce pilocarpine-induced epileptical crisis, oxidative stress, besides neuronal damages.

Comparison of acute lethal toxicity of commonly abused psychoactive substances

AIMS

To determine the acute lethal toxicity of a range of psychoactive substances in terms of the dose customarily used as a single substance for non-medical purposes.

DESIGN AND METHOD

A structured English-language literature search was conducted to identify experimental studies and clinical reports that documented human and non-human lethal doses of 20 abused substances that are distributed widely in Europe and North America. Four inclusion criteria were specified for the reports, and approximately 3000 relevant records were retrieved from search engines at Biosis, Science Citation Index, Google and the National Library of Medicine's Gateway. In order to account for different drug potencies, a 'safety ratio' was computed for each substance by comparing its reported acute lethal dose with the dose most commonly used for non-medical purposes.

FINDINGS

The majority of published reports of acute lethal toxicity indicate that the decedent used a co-intoxicant (most often alcohol). The calculated safety ratios varied between substances by more than a factor of 100. Intravenous heroin appeared to have the greatest direct physiological toxicity; several hallucinogens appeared to have the least direct physiological toxicity.

CONCLUSIONS

Despite residual uncertainties, the substantial difference in safety ratios suggests that abused substances can be rank-ordered on the basis of their potential acute lethality.

Evaluation of cytotoxicity of oils used in coenzyme Q10 Self-Emulsifying Drug Delivery Systems (SEDDS)

The objective of the present study was to develop a suitable method for evaluation of cytotoxicity of the oils used in Self-Emulsified Drug Delivery Systems (SEDDS) using Coenzyme Q10 (Co Q10) as a model compound. For this purpose, three methods of sample preparation were tested, namely (i) suspensions, (ii) homogenization, and (iii) nanoemulsions of oils in Dulbecco's Modified Eagle's Media (DMEM). Studies were carried out by incubating the sample or control with Caco-2 cells grown on transwell insert systems as well as in flat bottom 96-well plates. The cell viability was assessed by using WST-1 and propidium iodide reagents while the monolayer integrity was assessed by mannitol permeability and Trans Epithelial Electrical Resistance (TEER). The cytotoxicity of oils was found to be dependent on the method of sample preparation; nanoemulsions being the least cytotoxic. In conclusion, nanoemulsification is a useful tool for cytotoxicity evaluation of substances, which exhibit poor aqueous/dimethyl sulfoxide (DMSO) solubility.