The 16
th
-century physician, Paracelsus, commented that the only difference between a drug
and a poison is dose. With the possible exception of cancer chemotherapy agents, this
observation is nowhere as true as with narrow-therapeutic-margin antiepileptic drugs. If we
could deliver an antiepileptic drug in high concentrations specifically to the region of brain
involved in producing seizures, then the therapeutic-to-toxic ratio might substantially be
improved.
Investigators working with animal models of epilepsy have long delivered various putative
anti-seizure medicines to different regions of animal brain, summarized in Table 2.
In 1997, Fisher and associates
56
showed that interictal spikes and seizures produced by the
convulsant GABA-antagonist, bicuculline methiodide (BMI) applied to rat cortex could be
reduced by local perfusion of diazepam (Figure 3).
Delivery of diazepam to a BMI-induced cortical seizure focus based upon an on-line seizure
detection algorithm
57
can truncate seizures and prevent other seizures in a rat.
Diazepam is not itself a practical drug for perfusion on human brain, because of its alkalinity
and depression of cardiorespiratory centers. Better candidates for focal brain perfusion to
stop seizures include adenosine
58
, muscimol
59
or pentobarbital
60
. Greater penetration of
perfused drug can be achieved by pressurizing the infusion catheter to produce bulk
convection
61
.
Another strategy to distribute infused drug widely is to deliver it to the ventricular system.
Serralta
62
showed that continuous introcerebroventricular infusion of valproic acid in the rat
suppressed seizures with minimal side effects. Oommen and the current author
63
showed
efficacy against flurothyl-induced seizures after five days of gabapentin infusion into
ventricles with an osmotic pump. A clinical trial of ventricular perfusion of antiepileptic
medication is about to be started by ICVRx®. Safety and efficacy will need to be shown by
clinical trials, and the ideal agent to use is not yet established