An 8-year-old spayed female Border Collie is presented in...

This is a critical emergency, and your immediate action is commendable. The fact that the patient is in continuous generalized tonic-clonic seizures for 20 minutes, refractory to initial IV midazolam, signifies true status epilepticus. Furthermore, with a therapeutic phenobarbital trough level, simply increasing the oral phenobarbital dose won't provide the rapid control needed, and adding more phenobarbital acutely carries risks.

For emergency management of refractory status epilepticus in a canine patient who has failed benzodiazepine therapy and is already on therapeutic phenobarbital, intravenous levetiracetam is an excellent next-line choice.

Here's the recommended protocol:

1. Levetiracetam (Keppra)

* Rationale: Levetiracetam has a rapid onset of action when given intravenously, has a wide safety margin, and does not significantly interact with phenobarbital metabolism. It's an excellent choice for immediate seizure control without adding further CNS depression that might occur with additional phenobarbital.
* Dosing Protocol:
* Levetiracetam (canine): Administer 60 mg/kg IV over 5-10 minutes.
* This is a loading dose aimed at rapidly achieving therapeutic concentrations.
* Monitoring: While there's no routine therapeutic drug monitoring for levetiracetam, closely observe for seizure cessation. Side effects are minimal, typically mild sedation or transient inappetence.
* Maintenance: Once the patient is stable and seizures are controlled, you would transition to maintenance dosing, typically 20-30 mg/kg PO q8h (standard release) or 30-40 mg/kg PO q12h (extended release, do NOT split tablets).

2. Phenobarbital (as an additional option, with caution)

While the patient is already on phenobarbital, if levetiracetam alone doesn't break the seizure, or if you prefer to use a second drug concurrently, an additional IV bolus of phenobarbital can be considered, but with careful monitoring.

* Rationale: Phenobarbital is a potent AED, and an IV loading dose can rapidly increase its brain concentration. However, given the patient's existing therapeutic trough, this carries a higher risk of adverse effects.
* Dosing Protocol:
* Phenobarbital (canine): Administer 4 mg/kg IV slowly, over 10-15 minutes.
* You can repeat this dose every 20-30 minutes to effect, but the total cumulative dose should generally not exceed 24 mg/kg in a 24-hour period, especially considering the patient is already on phenobarbital.
* Monitoring: Closely monitor for respiratory depression, hypotension, and profound sedation. These are significant risks with rapid IV phenobarbital administration, particularly in a patient already receiving it. Respiratory support (intubation, ventilation) should be readily available.

3. If Seizures Persist (Refractory Status Epilepticus)

If the patient remains seizing after appropriate doses of both levetiracetam and additional phenobarbital, you are dealing with truly refractory status epilepticus. At this point, continuous IV infusions are typically required to induce a burst suppression pattern on EEG, essentially putting the brain to sleep to stop the seizure activity.

* Propofol CRI: 0.1–0.6 mg/kg/min IV CRI (after a bolus of 1-2 mg/kg). This requires intubation and ventilatory support.
* Ketamine CRI: 0.5 mg/kg IV bolus, then 0.5-1.0 mg/kg/hr IV CRI (emerging evidence for refractory status, less respiratory depression than propofol).

Supportive Care is Paramount

Regardless of the drug choice, remember the critical supportive care measures for any patient in status epilepticus:

* IV Fluids: Maintain hydration and support blood pressure.
* Glucose: Check blood glucose immediately. Correct hypoglycemia with dextrose if present. Seizing patients rapidly deplete glucose stores.
* Temperature Management: Seizures generate significant heat. Monitor core body temperature and actively cool if hyperthermic (>106°F).
* Prevent Self-Trauma: Protect the patient from injuring themselves during the seizure.
* Electrolytes: Monitor for electrolyte derangements.

In summary, for this Border Collie, I would proceed with intravenous levetiracetam at 60 mg/kg IV over 5-10 minutes as the primary next step. Be prepared to follow with additional phenobarbital IV or move to CRI anesthetics if seizures are not controlled. This patient has a high likelihood of having a structural lesion given her age and presentation, so once stabilized, an MRI and CSF analysis will be strongly indicated to determine the underlying cause of her refractory seizures.