Focus on Pharm: Gabapentin
Gabapentin is one of the top 100 drugs prescribed in the US, so there’s a very good chance it will show up on NCLEX or your nursing school exams. Let’s go through the key things you need to know about this medication using the Straight A Nursing DRRUGS framework.
D: Drug Class
Gabapentin (brand name Neurontin) is classified therapeutically in a few different ways. As an anticonvulsant, an analgesic adjunct, and a mood stabilizer. Since the exact mechanism is unknown, Gabapentin is one of those drugs that aren’t in a pharmacologic class. We do know that it has a similar structure to GABA, but it does not bind to the same receptors or influence the uptake or synthesis of GABA. For this reason, you may see it referred to as a GABA-mimetic agent. It binds to voltage-gated calcium channels, which is what we think gives it its ability to prevent seizure, block the detection of painful stimuli and reduce anxiety. Though it does not directly act on dopamine or serotonin receptors, studies do show that gabapentin can increase total blood levels of serotonin in some people.
So it’s a very interesting drug that you will see a lot and for a variety of reasons. We’ll talk more about the uses of gabapentin in a bit.
Next in the DRRUGS framework is R for ROUTES….some drugs have multiple routes of administration so it’s always good to know. But gabapentin is not one of these…it has one route and that is the PO route. It comes in capsules, immediate and extended-release tablets, and oral elixir.
R: Regular Dose Range
The second R in the DRRUGS framework is for the regular dose range. It’s helpful to have a general idea of how this medication is dosed. Though, of course, you will always check doses at the bedside, if the MD orders 8 g gabapentin, I’d want you to know this is a massively large dose even without looking it up.
So the typical dose of gabapentin in adults ranges from 300 to 600 mg given three times per day. However, some patients will need more to achieve the desired result, so doses can go up to 1200 mg given three times per day for a max daily dose of 3600 mg/day. Doses will be lower in adults with renal impairment and in children.
Now, this is where gabapentin gets interesting. Its official and approved uses vary based on the formulation, of which there are three – Neurontin, Gralise, and Horizant. The approved uses are as an adjunct treatment for partial seizure (Neurontin), to treat the pain of postherpetic neuralgia (Neurontin and Gralise), and to manage restless leg syndrome (Horizant). However, gabapentin is often used off-label for a variety of conditions. In fact, one study revealed that 83% of gabapentin prescriptions were for off-label use.
Some of the common reasons gabapentin is prescribed are:
- Neuropathic pain and diabetic neuropathy (this is very common)
- Bipolar disorder and anxiety
- Migraine prevention
- Complex regional pain syndrome
- Trigeminal neuralgia
- Attention deficit disorder
- Seizure secondary to alcohol and drug withdrawal
When your patient is prescribed gabapentin, always make sure you understand why this patient is receiving it. Most of the time it will not be for the standard indicated uses.
What do you need to know about gabapentin to administer it safely?
- Gabapentin will have decreased effectiveness if taken with antacids, so make sure the patient knows to separate these medications by at least two hours..
- Patients taking other CNS depressants will have an increased risk for respiratory and CNS depression if also taking gabapentin. This includes alcohol, antihistamines, sedatives, and opioids.
- Even seemingly harmless things like chamomile, valerian, and kava-kava can potentiate the CNS depressive effects of gabapentin.
- Neurontin and Horizant can be taken without regard to meals.
- Horizant, which is often taken for restless leg syndrome, is generally taken at 5 pm.
- Gralise should be taken with the evening meal for maximum bioavailability.
- Teach your patient that scored tablets can be cut in half if needed. They should take the other half at the next dose and discard any half-tablets that have not been used within a few days.
S: Side Effects
The most common side effects of gabapentin are dizziness, drowsiness, confusion, and depression. I would say clinically what I notice the most is drowsiness and dizziness. The most significant or serious side effects are suicidal ideation, Stevens-Johnson syndrome, rhabdomyolysis, and hypersensitivity reactions including angioedema and anaphylaxis.
- When starting therapy or increasing the dosage, patients should be monitored for depression and suicidal thoughts.
- Assess the patient for fall risk secondary to fatigue and dizziness.
- Assess patient for confusion, reorient as necessary.
- Monitor for life-threatening reactions. Angioedema and anaphylaxis can both cause airway closure. Rhabdomyolysis can lead to acute renal failure, so monitor your patient for muscle pain, weakness, and reddish-brown urine. Stevens-Johnson’s syndrome often starts with flu-like symptoms and progresses to a painful rash, blisters, and sloughing of the skin.
I hope this helps you understand one of the most common medications you will see in the clinical setting. For more pharmacology articles, click on BLOG up at the top, and select PHARMACOLOGY from the drop-down menu.
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Davis’s Drug Guide. (n.d.). Gabapentin. Retrieved October 24, 2021, from https://www.drugguide.com/ddo/view/Davis-Drug-Guide/51346/all/gabapentin?refer=true
Fukada, C., Kohler, J. C., Boon, H., Austin, Z., & Krahn, M. (2012). Prescribing gabapentin off label: Perspectives from psychiatry, pain and neurology specialists. Canadian Pharmacists Journal : CPJ, 145(6), 280-284.e1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3567599/
Peckham, A. M., Evoy, K. E., Ochs, L., & Covvey, J. R. (2018). Gabapentin for off-label use: Evidence-based or cause for concern? Substance Abuse: Research and Treatment, 12, 1178221818801311. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6153543/
Schwenk MD, T. L. (2019, April 2). Markedly increased off-label use of gabapentinoid drugs for pain management. NEJM Journal Watch. https://www.jwatch.org/na48857/2019/04/02/markedly-increased-label-use-gabapentinoid-drugs-pain