Anticonvulsant Medications for Status Epilepticus

Status epilepticus is a medical emergency with significant morbidity and mortality and, in circumstances where benzodiazepines alone have failed to terminate seizures, has traditionally been treated with anticonvulsants such as phenytoin or phenobarbitone. Other intravenously administered antiepileptics have also been found to be effective.

There is a lack of comparative data on different anticonvulsants and this blinded prospective study “Randomised Trial of Three Anticonvulsant Medications for Status Epilepticus” by Kapur et al. (2019) compares three options: fosphenytoin (a pro drug of phenytoin which is more expensive but more soluble and can be given intravenously faster with fewer extravasation problems and can also be given intramuscularly), valproate and levetiracetam.

Study Details

Patients in the study had to be over 2 years of age, and had to have convulsive status (persistent or recurrent convulsions) for at least 5 minutes, and then more convulsions between 5-30 minutes after an adequate dose of benzodiazepine (5 minutes to have allowed the benzodiazepines to work and less than 30 minutes, after which point another dose of benzodiazepines could have been tried instead). Patients were randomised by stratifying for age.

Patients with major trauma or anoxia, etc., were excluded, as were pregnant women (give levetiracetam and consider magnesium).

The doses of the intravenous anticonvulsants levetiracetam (60 mg/kg) and valproate (40 mg/kg) seemed very high.

The primary successful outcome was absence of clinical seizure activity and improved responsiveness at 60 min after infusion start.

Analysis was based on assuming equal prior probability of success for the three treatments, then using the binomial probability of positive or negative outcome to calculate the posterior probabilities. An iterative method was then used from these three separate probabilities to calculate the probability that a given treatment was better than the other two, or worse than the other two.

The sample size was set on the basis of correctly identifying with 90% probability a difference when one treatment was 15% better than the other two (65% response for the best and 50% response for the other two).

A total of 400 patients were enrolled. The intention to treat population was only 384 because some patients were enrolled more than once. Nearly a third of patients were then excluded because treatment did not follow the protocol, e.g. not status epilepticus such as functional seizures, did not receive the correct amount of benzodiazepine or anticonvulsant or wrong timing with respect to benzodiazepine.

Half the patients were unblinded to avoid suboptimal management.

In the per-protocol population, 47% of patients responded to each of the three treatments, with probability of most effective treatment distributed as follows: levetiracetam (0.34), fosphenytoin (0.35), valproate (0.31). There was also an “adjudicated population” outcome, which was perhaps based on an adjudicator clinician looking retrospectively at the notes, whether following the protocol or having had previous treatment or not, and deciding if the treatment worked. Although the data were similar, it did seem that levetiracetam may have been worse (0.51 versus 0.29 and 0.2) and clearly 0.51 is 31% worse than 0.2 (valproate), which is more than their threshold of meaningful difference of 15% for best treatment.

Secondary outcomes included requirement for admission to ICU (87% for levetiracetam and only 71% for valproate).

Regarding safety, there were 4.7% deaths in the levetiracetam group and 1.6% in the valproate group, with fosphenytoin in the middle. Hypotension, a known issue with phenytoin was 3.2% in the fosphenytion group to a life-threatening degree and only 0.7% for levetiractem and 1.6% for valproate. Cardiac arrhythmia only occurred in one patient. Acute respiratory depression occurred in 12.8 % with fosphenytoin and 8% with levetiracetam and valproate. None of these differences reached significance.

The conclusion was that there was no difference between the drugs.

Journal Club Discussion

The study was welcome as it was on an important practical topic. The group wondered about the high doses used, and whether our own guidelines should reflect these doses. The trial was powered for the primary efficacy outcome and then stopped. However it was always going to be as likely that any differences between the drugs wold lie in their side effects as in their efficacy and it is a shame that the powering did not reflect this so that what may have been real differences in respiratory depression or hypotension never reached significance.

The vagaries of statistics are illustrated by the per-protocol efficacies, which seem identical, and the adjudicator population efficacies, where there was actually a 31% greater chance of levetiracetam being the worst drug compared to valproate.

Negative study results always make us turn to how the study was powered: were there no differences seen because there are no differences, or because too few patients were studied (i.e. too low power)? When powering a study, a judgement must always be made on what level of difference would be considered meaningful, otherwise if accepting any difference as being meaningful it would require an infinite population to prove there is no difference. They chose a meaningful 15% difference for one drug being better than the other two, but if they had chosen one drug worse than the other two, the 31% difference in the adjudicator population would have been more than their set level. There should have been more explanation of their adjudicator population, and perhaps more explanation of the advantage of using Baysian probabilities in addition to a simple comparison of means and standard errors of success rates.

In real practice, there should perhaps be tailoring of treatment to the patient. If a patient is already on therapeutic levels of phenytoin, is more of the same going to be the best choice? If a patient is a female of child bearing potential, is valproate the best choice when the patient often ends up on the oral equivalent of the status treatment they received. On reviewing the data in this study and knowing that the levetiracetam dose was very high, valproate might shade the other two choices, especially in men.

The Journal Club on which this article is based was presented by Dr Katie Yoganathan, SpR in Neurology at Queens Hospital, Romford.

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