New antiepileptic drugs and non-pharmacological treatments

Development of a dissolution test for lamotrigine in tablet form using an ultraviolet method

A dissolution test for tablets containing 100 mg of lamotrigine was developed and validated. The dissolution test was applied to compare the dissolution profile of Neural® with the reference product Lamictal®. The analysis procedure was carried out using a simple ultraviolet method at 267 nm. After the determination of solubility and sink conditions, the parameters selected were paddles at 50 rpm, 900 mL of 0.01 M hydrochloric acid, and 30 minutes duration (single point). This method was validated for specificity, linearity, accuracy, precision and robustness. Lamotrigine stability was also evaluated in dissolution medium.

Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals

BACKGROUND

Ketogenic diets are used therapeutically to treat intractable seizures. Clinically, it appears that the maintenance of ketosis is crucial to the efficacy of the diet in ameliorating seizures. To understand how ketosis and seizure protection are related, a reliable, noninvasive measure of ketosis that can be performed frequently with minimal discomfort is needed.

OBJECTIVE

The objective was to determine which index, breath acetone or urinary acetoacetate, is more strongly related to the plasma ketones acetoacetate and beta-hydroxybutyrate.

DESIGN

After fasting overnight for 12 h, 12 healthy adults consumed 4 ketogenic meals over 12 h. Blood, breath, and urine samples were collected hourly. Blood was analyzed for plasma acetoacetate and beta-hydroxybutyrate, breath for acetone, and urine for acetoacetate.

RESULTS

By the end of the 12-h dietary treatment, plasma acetoacetate, plasma beta-hydroxybutyrate, and breath acetone had increased 3.5-fold, whereas urinary acetoacetate increased 13-fold when measured enzymatically and 25-fold when measured with urinary ketone dipsticks. Plasma acetoacetate was best predicted by breath acetone (R(2) = 0.70, P < 0.0001). Plasma beta-hydroxybutyrate was equally predicted by breath acetone and urinary acetoacetate (R(2) = 0.54, P = 0.0040).

CONCLUSIONS

Breath acetone is as good a predictor of ketosis as is urinary acetoacetate. Breath acetone analysis is noninvasive and can be performed frequently with minimal discomfort to patients. As an indicator of ketosis in epilepsy patients consuming a ketogenic diet, breath acetone may be useful for understanding the mechanism of the diet, elucidating the importance of ketosis in seizure protection, and ultimately, enhancing the efficacy of the diet by improving patient monitoring.

Selective blockade of N-type calcium channels by levetiracetam

PURPOSE

We investigated the effect of the new antiepileptic drug (AED) levetiracetam (LEV) on different types of high-voltage-activated (HVA) Ca2+ channels in freshly isolated CA1 hippocampal neurons of rats.

METHODS

Patch-clamp recordings of HVA Ca2+ channel activity were obtained from isolated hippocampal CA1 neurons. LEV was applied by gravity flow from a pipette placed near the cell, and solution changes were made by electromicrovalves. Ca2+ channel blockers were used for separation of the channel subtypes.

RESULTS

The currents were measured in controls and after application of 1-200 microM LEV. LEV irreversibly inhibited the HVA calcium current by approximately 18% on the average. With a prepulse stimulation protocol, which can eliminate direct inhibition of Ca2+ channels by G proteins, we found that G proteins were not involved in the pathways underlying the LEV inhibitory effect. This suggested that the inhibitory effect arises from a direct action of LEV on the channel molecule. The blocking mechanism of LEV was not related to changes in steady-state activation or inactivation of Ca2+ channels. LEV also did not influence the rundown of the HVA Ca2+ current during experimental protocols lasting approximately 10 min. Finally, LEV at the highest concentration used (200 microM) did not influence the activity of L-, P- or Q-type Ca2+ channels in CA1 neurons, while selectively influencing the activity of N-type calcium channels. The maximal effect on these channels separated from other channel types was approximately 37%.

CONCLUSIONS

Our results provide evidence that LEV selectively inhibits N-type Ca2+ channels of CA1 pyramidal hippocampal neurons. These data suggest the existence of a subtype of N-type channels sensitive to LEV, which might be involved in the molecular basis of its antiepileptic action.