1. Aschenbrenner, Diane S. MS, RN


* Gabapentin enacarbil (Horizant Extended Release Tablets) has been approved to treat moderate-to-severe restless legs syndrome.


* Gabapentin enacarbil causes significant sedation and dizziness and can have a serious deleterious effect on driving. Patients mustn't drive or operate machinery until the effects of the drug on their performance are well known.



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The Food and Drug Administration (FDA) has approved gabapentin enacarbil (Horizant Extended Release Tablets) to treat moderate-to-severe restless legs syndrome, a disorder that causes a strong urge to move the legs, often with accompanying unpleasant feelings (such as pulling, itching, tingling, burning, or aching). Other drugs approved to treat the condition include dopamine antagonists (such as pramipexole [Mirapex], ropinirole hydrochloride [Requip], and carbidopa with levodopa [Sinemet]); synthetic narcotics (such as oxycodone [Oxycontin and others]); and the benzodiazepine clonazepam (Klonopin and others), which enhances the effects of the neurotransmitter [gamma]-aminobutyric acid (GABA).


Gabapentin enacarbil is a prodrug, meaning that it must go through specific metabolic processes in the body before it becomes an active pharmacologic agent-in this case, gabapentin, an antiepileptic. Gabapentin is also approved for the treatment of postherpetic neuralgia and is used off label for a variety of neuropathic conditions, such as diabetic neuropathy and migraine, and as preemptive therapy for postoperative pain in adults. Gabapentin is structurally related to GABA (an inhibitory neurotransmitter) but has no effect on GABA binding, uptake, or degradation. Gabapentin enacarbil isn't interchangeable with other gabapentin products and won't produce the same therapeutic drug levels. Gabapentin enacarbil, like other gabapentin products, isn't metabolized by the cytochrome P-450 isoenzyme system and is excreted unchanged.


Like other gabapentin products, gabapentin enacarbil has been shown to cause significant sedation (in 20% of patients) and dizziness (in 13% of patients). Gabapentin enacarbil's label carries a strong warning that the drug causes significant driving impairment. Patients shouldn't drive until they've been taking the drug for some time, in order to evaluate its effects, although the label warns that patients' ability to assess their own driving may not be completely accurate. In most patients the sedation and dizziness caused by gabapentin enacarbil are transient, lasting around three or four weeks; in others, however, the sedation may be chronic. The manufacturer recommends that the 600-mg oral daily dose be taken with food, around 5 PM; symptoms are worse at night, and taking the medication in the evening will allow it to reach peak effectiveness when it's needed most. Gabapentin enacarbil isn't recommended in patients who need to sleep in the daytime and be awake at night.


Nurses should instruct patients who begin therapy with gabapentin enacarbil to swallow the drug whole and not to chew or crush it. If a dose is missed in the evening, it should be skipped and not made up the following morning. Patients should be advised to watch for sudden changes in mood; gabapentin enacarbil use has been associated with suicidal thoughts or behavior, as well as with mania.