A 35 y/o male patient is admitted to the medicine ward by the neurology service to work up a seizure disorder and stabilize his medications. His medical history is otherwise unremarkable and his labs are all WNL. To make the titration easier, he was started on carbamazepine suspension.  The patient's serum levels were continually on the low sides. The provider kept increasing the doses over several days. On day seven of therapy the patient appeared lethargic and hypotensive.

What is causing this apparently sudden change in the patient's status?
 

Certainly, you'd do a quick but complete assessment, check vital signs, and a brief physical exam to rule out anything catastrophic. This case's culprit was the carbamazepine suspension and is a real case reported via the AHRQ website.

A suspension, by definition, suspends particles of active drug within some type of viscous vehicle. Left for a period of time, these particles will settle out. How long it takes for a suspension to 'settle out' depends on the drug, the suspending agent, it's viscosity, the manufacturer, etc. If not "Shaken Well", a sub-potent supernatant liquid is the result. In this case, the patient had low serum levels because of
repeated doses of the 'sub-potent' supernatant liquid. Following the patient's serum levels, the physician correctly increased the dose, hoping to get the patient into the therapeutic range. When the nursing staff reached the second half of the bottle, much of the active ingredient from the first half of the bottle was left in the second half of the bottle's volume, creating a super-potent suspension and, subsequently, the toxic serum levels.

Remember, whenever administering an oral suspension, shake the suspension enough to adequately suspend the active drug in the vehicle to assure the desired dose. Other dosage forms to be shaken before dispensing/administering include oral suspensions, ophth or otic suspensions, metered dose inhalers (MDIs), certain injectable suspensions (esp depot injections).

Some possible ways to avoid this kind of error include prescribing tablets or capsules whenever possible and use manufacturer-prepared, commercially available suspensions whenever available.

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