A comparison of the anticonvulsant effects of propofol and thiopentone against pentylenetetrazol-induced convulsions in the rat

Comparison between the effect of propofol and midazolam on picrotoxin-induced convulsions in rat

Propofol is a short acting intravenous anesthetic that has been used in the treatment of status epileptics. However, the occurrence of seizures in epileptic and non-epileptic patients during recovery from propofol induced anesthesia suggests that propofol may have proconvulsant effects. We have previously shown that propofol displays anticonvulsant effects against picrotoxin (PTX) induced seizures during its peak sedative effects. The purpose of the present study was to compare the time course of the effect of intravenous administration of various doses (2.5, 5, and 10 mg/kg) of propofol and midazolam on PTX-induced seizures in adult female Sprague-Dawley rats. The latency to onset of clonic seizures induced by intraperitoneal injection of PTX was significantly increased by the highest dose of propofol and all doses of midazolam, suggesting that both agents display anticonvulsant effects. The anticonvulsant effects of propofol (10 mg/kg) lasted about 20 min and PTX-induced clonic seizures were observed thereafter and peaked within 30 min post drug administration. Clonic seizures progressed rapidly to tonic seizures leading to high rate of PTX-induced mortality. In midazolam (10 mg/kg) treated rats, clonic seizures were observed 25 min after drug administration and the number of rats exhibiting clonic seizures was highest within 40 min. However, clonic seizures did not progress into tonic seizures and thus, PTX-induced seizure related mortality was significantly reduced. In conclusion, this study provides further evidence for the anticonvulsant effects of propofol and midazolam against PTX-induced seizures. Furthermore, the data of the current study showed that midazolam was more effective than propofol against PTX-induced tonic seizures.

Seizure protection by intrapulmonary delivery of propofol hemisuccinate

The lung provides a portal of entry for drug delivery that could be used to administer anticonvulsant substances to prevent or abort seizures. Here, we demonstrate that intrapulmonary propofol hemisuccinate (PHS) rapidly confers seizure protection in various rodent chemoconvulsant models. Propofol is a powerful anticonvulsant substance at subanesthetic doses, but it is a viscous, water-immiscible oil that is not suitable for intrapulmonary administration. We found that PHS can be formulated as an aqueous solution that is well tolerated when instilled into the lung. High-dose intraperitoneally administered PHS induced loss-of-righting reflex in rats and mice. The onset of action of PHS was delayed in comparison with propofol, suggesting that conversion to propofol is required for activity. A lower dose of PHS (40 mg/kg i.p.) did not cause general anesthesia but protected against pentylenetetrazol (PTZ)-induced seizures in rats. Intrapulmonary administration of an aqueous PHS solution via a tracheal cannula at lower doses (5 and 10 mg/kg) conferred equivalent seizure protection without acute motor toxicity. In mice, intraperitoneal PHS (60-80 mg/kg) was associated with an elevation in PTZ, bicuculline, picrotoxin, and kainic acid seizure thresholds. Intratracheal PHS was markedly more potent, producing seizure threshold elevations at doses of 10 to 15 mg/kg. In the PTZ threshold model in mice, PHS was active at 5 min, maximally active at 10 min, and no longer active at 20 min. Intratracheal PHS also prolonged the onset of 4-aminopyridine-induced convulsions but did not affect the threshold for N-methyl-D-aspartate-induced convulsions. We conclude that intratracheal administration of an aqueous solution of PHS, a putative propofol prodrug, provides potent seizure protection of rapid onset and brief duration. Intrapulmonary PHS may be useful for preventing the spread of seizures or aborting seizure clusters without causing prolonged sedation.

Anesthetic management of the patient with epilepsy or prior seizures

PURPOSE OF REVIEW

Epilepsy is a clinical disorder of paroxysmal recurring seizures, the diagnosis excluding alcohol or drug withdrawal seizures or such recurring exogenous events as repeated insulin-induced hypoglycemia. Epilepsy has a profound impact on each individual diagnosed with this disease.

RECENT FINDINGS

New antiepileptic drugs (AEDs) have been a major change in the approach to management of patients with epilepsy. These drugs tend to have fewer significant drug interactions and less severe side effects. Nonetheless, first-generation AEDs are still widely used. Propofol and desflurane have reliable anticonvulsant effects, whereas remifentanil in larger doses and sevoflurane appear to support epileptiform activity, although the clinical significance of these observations is unclear.

SUMMARY

The primary concerns for providing anesthesia to the patient with epilepsy are the capacity of anesthetics to modulate or potentiate seizure activity and the interaction of anesthetic drugs with AEDs. Proconvulsant and anticonvulsant properties have been reported for virtually every anesthetic such that these properties become elements of the anesthetic plan in the patient with epilepsy. Moreover, AEDs have many physiologic and pharmacologic effects that can have an impact on an anesthetic.

The Management of Status Epilepticus

Status epilepticus is a major medical emergency associated with significant morbidity and mortality. Status epilepticus is best defined as a continuous, generalized, convulsive seizure lasting > 5 min, or two or more seizures during which the patient does not return to baseline consciousness. Lorazepam in a dose of 0.1 mg/kg is the drug of first choice for terminating status epilepticus. Patients who continue to have clinical or EEG evidence of seizure activity after treatment with lorazepam should be considered to have refractory status epileptics and should be treated with a continuous infusion of propofol or midazolam. This article reviews current information regarding the management of status epilepticus in adults.

Hyperexcitability and epilepsy associated with disruption of the mouse neuronal-specific K-Cl cotransporter gene

Four genes encode electroneutral, Na+-independent, K-Cl cotransporters. KCC2, is exclusively expressed in neurons where it is thought to drive intracellular Cl- to low concentrations and shift the reversal potential for Cl- conductances such as GABA(A) or glycine receptor channels, thus participating in the postnatal development of inhibitory mechanisms in the brain. Indeed, expression of the cotransporter is low at birth and increases postnatally, at a time when the intracellular Cl- concentration in neurons decreases and gamma-aminobutyric acid switches its effect from excitatory to inhibitory. To assert the significance of KCC2 in neuronal function, we disrupted the mouse gene encoding this neuronal-specific K-Cl cotransporter. We demonstrate that animals deficient in KCC2 exhibit frequent generalized seizures and die shortly after birth. We also show upregulation of Fos, the product of the immediate early gene c-fos, and the significant loss of parvalbumin-positive interneurons, both indicative of brain injury. The regions most affected are the hippocampus and temporal and entorhinal cortices. Extracellular field potential measurements in the CA1 hippocampus exhibited hyperexcitability. Application of picrotoxin, a blocker of the GABA(A) receptor, further increased hyperexcitability in homozygous hippocampal sections. Pharmacological treatment of pups showed that diazepam relieved the seizures while phenytoin prevented them between postnatal ages P4-P12. Finally, we demonstrate that adult heterozygote animals show increased susceptibility for epileptic seizure and increased resistance to the anticonvulsant effect of propofol. Taken together, these results indicate that KCC2 plays an important role in controlling CNS excitability during both postnatal development and adult life.

Propofol sedation produces dose-dependent suppression of lidocaine-induced seizures in rats

The association of propofol with excitatory motor activity, such as myoclonic jerking and opisthotonus, in humans and in animals suggests that it may aggravate clinical seizure activity in some circumstances, although evidence suggests that under other circumstances, propofol inhibits seizure activity. In the current study, we assessed the effect of sedating doses of propofol on lidocaine-induced seizure activity in spontaneously breathing rats receiving no other anesthetics. Adult Sprague-Dawley male rats, 300-400 g, were divided into a control group and three experimental groups representing three graded levels of propofol sedation. The control rats then received a lidocaine infusion at the rate of 150 mg x kg(-1) x h(-1), resulting in a slow, progressive increase in systemic lidocaine concentrations. At the onset of electroencephalographic (EEG) seizure activity, arterial lidocaine concentrations were obtained. The treated rats received propofol according to three different dose schedules: Dose 1 = 10 mg x kg(-1) x h(-1) after a 2.5-mg/kg bolus; Dose 2 = 20 mg x kg(-1) x h(-1) after a 5-mg/kg bolus; Dose 3 = 40 mg x kg(-1) x h(-1) after a 10-mg/kg bolus. After 30 min, a steady level of sedation, dependent on the dose of propofol, was achieved. The lidocaine infusion was then started, and systemic lidocaine levels were obtained at the onset of EEG seizure activity. The lidocaine was continued until the onset of death by cardiac arrest. Plasma lidocaine was measured by gas chromatography. Analysis of variance and Dunnett's t-test were used for comparisons with the control values. Continuous propofol sedation increased the seizure dose of lidocaine from 37.7 +/- 3.5 mg/kg (mean +/- SEM) to 52.5 +/- 2.6 mg/kg (Dose 1, P < 0.05) and 67.9 +/- 8.6 mg/kg (Dose 2, P < 0.05), and completely abolished lidocaine seizures at Dose 3. The lethal dose of lidocaine, 89.4 +/- 10.5 mg/kg control versus 108.7 +/- 10.3 mg/kg (Dose 1), 98.3 +/- 10.1 mg/kg (Dose 2), and 93.5 +/- 10.4 mg/kg (Dose 3) did not differ among groups. The lidocaine levels at seizure threshold were increased in the propofol-treated rats: 16.9 +/- 0.5 microg/mL control versus 19.2 +/- 0.7 microg/mL (Dose 1, P = not significant) and 23.7 +/- 1.8 microg/mL (Dose 2, P < 0.05). Continuous propofol sedation in spontaneously breathing rats receiving no other anesthetics exerts a protective effect against lidocaine-induced seizures in a monotonic, dose-dependent fashion. The cardiac arrest dose of lidocaine is unaffected by propofol under these conditions.

IMPLICATIONS

The i.v. anesthetic drug propofol, given to rats to produce sedation, was found to suppress seizure activity caused by overdosage of the local anesthetic lidocaine.

Propofol inhibits epileptiform activity in rat hippocampal slices

Propofol (2,6 di-isopropylphenol) is an intravenous general anesthetic used widely in neuroanesthesia, as a sedative in intensive care units, and has successfully aborted refractory status epilepticus. We investigated the effects of propofol on epileptiform activity in rat hippocampal slices. Interictal epileptiform activity was produced by bath applying one of the following: picrotoxin (PTX; 10 and 50 microM), bicucculine methiodide (BMI; 10 and 50 microM), 4-aminopyridine (4-AP; 50 microM), 8.5 mM [K+]o or 0 [Mg2+]o artificial cerebrospinal fluid. Propofol was then added in increasing concentrations and the effect on the rate of extracellular field epileptiform discharges was measured. Ictal-like discharges (> 2 Hz for > 2 s) were produced by 7.5 mM [K+]o and pilocarpine (10 microM). Propofol (30 micrograms/ml, 168 microM) completely abolished discharges induced by 8.5 mM [K+]o and at 60 micrograms/ml (337 mM) completely suppressed discharges induced by 4-AP and 0 [Mg2+]o. Propofol was less effective in reducing discharges produced by GABAA/Cl- receptor complex antagonists. Propofol at a concentration of 300 micrograms/ml (1.7 mM) was needed to reduce BMI-induced (50 microM) discharges by 77% and only reduced PTX-induced (50 microM) discharges by 20%. Ictal-like discharges produced by pilocarpine were disrupted by low concentrations of propofol (3-10 micrograms/ml, 16.9-56.2 microM) and the duration of the ictal-like discharge period was significantly reduced. We found that propofol has significant in vitro antiepileptic effects. Additionally, propofol was less effective against GABAA antagonists suggesting that the GABAA receptor complex is the site of its action.

Effects of propofol and thiopentone on picrotoxin convulsive threshold in the rabbit

The purpose of the present study was to examine the effect of intravenous administration of propofol and thiopentone on picrotoxin-induced seizures using the picrotoxin convulsive threshold test in the rabbit. Neither propofol nor thiopentone at a dose of 1.25 mg/kg had any significant effect on picrotoxin seizure threshold. However, at higher doses (2.5, 5, 10 mg/kg) both propofol and thiopentone produced a significant and dose-dependent increase in the picrotoxin convulsive threshold. These findings suggest that propofol is an effective anticonvulsant against picrotoxin-induced seizures in the rabbit.

Comparison of the effects of propofol and thiopental on the pattern of maximal electroshock seizures in the rat

The anticonvulsant effects of propofol and thiopental (thiopentone) were determined by measuring the durations of the various phases of maximal electroshock seizures in the rat. Five min. after intraperitoneal administration of subanaesthetic (6.25, 12.5 and 25 mg/kg) and 50 mg/kg doses of propofol, the 2 highest doses abolished both tonic hindlimb extensor phases (full and partial extension) in all rats and decreased the duration of the total tonic phases of the seizure. Although the lowest dose produced no effect, the 12.5 mg/kg dose decreased the duration of both the full and partial tonic extensor phases and increased the duration of tonic flexion, showing that even this low dose had anticonvulsant activity. Subanesthetic doses of thiopental (5, 10 and 20 mg/kg) produced similar changes in the maximal electroshock seizures except that even the lowest dose also significantly decreased the duration of total extension and total tonus. Postseizure depression was prolonged only by the highest dose of propofol. Thus, even low doses of either propofol or thiopental, that produced only minimal behavioural effects, had marked anticonvulsant effects against electrically induced convulsions in the rat. No evidence of enhanced convulsant maximal electroshock seizures patterns was observed at any dose.

The comparative effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol seizure threshold in the rabbit

The anticonvulsant effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol (PTZ) seizure threshold were studied and compared in the rabbit. The PTZ seizure threshold determined in various rabbit groups during the control phase of conducted experiments, was found to be in the range of 10.1 +/- 2.0 to 13.5 +/- 3.7 mg/kg. Intravenous administration of comparable doses of propofol, thiopental, and diazepam resulted in marked and significant increases in PTZ seizure threshold. At all administered doses (1.25-10.0 mg/kg), propofol was found to be more effective than thiopental in increasing the PTZ threshold dose. However, the anticonvulsant effects of diazepam were more marked than those of propofol, except at a dose of 10 mg/kg where both agents exhibited equipotent activities. These data demonstrate that propofol enjoys a considerable degree of anticonvulsant activity in the rabbit. This anticonvulsant action is greater than that of thiopental at doses ranging from 2.5 to 10 mg/kg and equipotent with diazepam at the 10 mg/kg dose.