What is gabapentin

Gabapentin is an anticonvulsant medication structurally related to the inhibitory central nervous system (CNS) neurotransmitter gamma-aminobutyric acid (GABA); gabapentin also possesses analgesic activity. Gabapentin enacarbil (Horizant) is a prodrug of gabapentin. Conventional (immediate-release) preparations of gabapentin (Neurontin) are used in the management of seizure disorders in people who have epilepsy and in the treatment of postherpetic neuralgia. Gabapentin enacarbil (Horizant) is commercially available as an extended-release tablet formulation for once-daily administration is also used to relieve the pain of postherpetic neuralgia (the burning, stabbing pain or aches that may last for months or years after an attack of shingles) and primary restless legs syndrome (a condition that causes discomfort in the legs and a strong urge to move the legs, especially at night and when sitting or lying down).

Gabapentin is sometimes used to relieve the pain of diabetic neuropathy (numbness or tingling due to nerve damage in people who have diabetes), and to treat and prevent hot flashes (sudden strong feelings of heat and sweating) in women who are being treated for breast cancer or who have experienced menopause (”change of life”, the end of monthly menstrual periods).

Occasionally, gabapentin is used to treat migraine headaches.

Gabapentin may be prescribed for other uses; ask your doctor or pharmacist for more information. Gabapentin can also be formulated as an aqueous solution for injection. This formulation is not available commercially or licensed for treatment of any type of neuropathic pain or fibromyalgia.

Gabapentin is also used in veterinary medicine in the treatment of seizures and as an analgesic for treating chronic pain in small animals.

Key facts

• Gabapentin is an anticonvulsant that is used to treat seizures by reducing the abnormal electrical activity in the brain.
• Gabapentin relieves the pain of postherpetic neuralgia by changing the way the body senses pain. It is not known exactly how gabapentin works to treat restless legs syndrome.
• With nerve pain and migraine, gabapentin is thought to interfere with pain messages traveling through the brain and down the spine to block pain.
• Gabapentin at a dose of 1800 to 3600 mg daily (1200 to 3600 mg gabapentin encarbil) can provide good levels of pain relief to some people with postherpetic neuralgia and peripheral diabetic neuropathy. Evidence for other types of neuropathic pain is very limited ¹.
• It’s usual to take immediate-release gabapentin 3 times a day. You can take it with or without food.
• Most people who take gabapentin don’t get any side effects. The most common ones are feeling sleepy, tired and dizzy. Side effects are usually mild and go away by themselves.
• Gabapentin can also cause anaphylaxis and angioedema after the first dose or at any time during treatment. Signs and symptoms in reported cases have included difficulty breathing, swelling of the lips, throat, and tongue, and hypotension requiring emergency treatment. Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multiorgan hypersensitivity, has occurred with gabapentin.
• Antiepileptic drugs, including gabapentin increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Patients treated with any antiepileptic drugs for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.
• It takes at least a few weeks for gabapentin to work.
• You don’t need to have epilepsy for gabapentin to help with pain or migraine.
• The most common brand name for gabapentin is Neurontin and gabapentin extended-release tablets is Horizant.

How long does it take for gabapentin to work?

It takes a few weeks for gabapentin to work properly. You may still have seizures or pain during this time.

Can I drink alcohol with gabapentin?

Yes, you can drink alcohol with gabapentin. However, it may make you feel sleepy or tired.

During the first few days of taking gabapentin, it might be best to stop drinking alcohol until you see how the medicine affects you.

Can I drive or ride a bike whilst taking gabapentin medication?

You may feel sleepy, tired or dizzy when you first start taking gabapentin. This may also happen if your dose has increased. If this happens to you, don’t drive or ride a bike until you feel more alert.

If you have epilepsy, you’re not allowed to drive until you’ve had no seizures for 1 year, or if you only have seizures while you are asleep. You are also not allowed to drive if your epilepsy medicine has changed and for 6 months after.

Will my gabapentin dose go up or down?

To prevent side effects, your doctor will prescribe a low dose to start with and then increase it over a few days.

Once you find a gabapentin dose that suits you, it will usually stay the same.

How long will I take gabapentin for?

If you have epilepsy, it’s likely that once your illness is under control you will still need to take gabapentin for many years.

If you have nerve pain, it’s likely that once the pain has gone you will continue to take gabapentin for several months to stop it coming back.

Is it safe to take gabapentin for a long time?

There’s no evidence that gabapentin has lasting harmful effects even if you take it for many months or years.

Can I get addicted to gabapentin?

Some people have become addicted to gabapentin after taking it for a long time. If this happens, you will have withdrawal symptoms after you stop taking the medicine.

Talk to your doctor if you’re concerned about becoming physically dependent on gabapentin.

Will gabapentin affect my fertility?

Gabapentin does not reduce fertility in men or women.

Will gabapentin affect my contraception?

Gabapentin doesn’t affect any type of contraception, including contraceptive pills and the morning after pill.

What if I forget to take gabapentin?

If you forget a dose, take it as soon as you remember. If it is within 2 hours of the next dose, it is better to leave out the missed dose and take your next dose as normal.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If you have epilepsy, it’s important to take this medicine regularly. Missing doses may trigger a seizure.

If you forget doses often, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.

What will happen when I come off gabapentin medication?

Don’t stop taking gabapentin suddenly, even if you feel fine. Don’t stop taking gabapentin without talking to your doctor – you will need to reduce your dose gradually.

Stopping gabapentin suddenly can cause serious problems. If you have epilepsy, stopping gabapentin suddenly can cause seizures that will not stop.

Gabapentin can also build up in the body so that if you’re taking it (for epilepsy, pain or migraine) and stop suddenly, you may have a severe withdrawal syndrome. This can have unpleasant symptoms, including:

• anxiety
• difficulty sleeping
• feeling sick
• pain
• sweating

It’s possible to prevent withdrawal seizures and other symptoms by gradually reducing the dose of gabapentin.

Will recreational drugs affect gabapentin medication?

Gabapentin can intensify the highs of recreational drugs like cannabis and heroin. So, if you use recreational drugs alongside gabapentin, there may be more chance of unpleasant side effects like panic attacks, anxiety and memory loss.

Are there similar medicines to gabapentin?

Pregabalin (also called Lyrica) is a medicine that works in a similar way to gabapentin. Like gabapentin, it’s taken for epilepsy and nerve pain. It can also be taken for anxiety.

However, there are differences between pregabalin and gabapentin. Pregabalin can be taken less often and in different doses to gabapentin.

If you need to change to pregabalin treatment, your doctor will explain how to safely swap from gabapentin.

How does gabapentin work?

Gabapentin is structurally related to GABA. However, it does not bind to GABA_A or GABA_B receptors, and it does not appear to influence synthesis or uptake of GABA.

Gabapentin’s mechanism of action is primarily attributed to its effect on calcium channels located throughout the peripheral and central nervous systems, which modify the release of neurotransmitters and reduce excitability of nerve cells ². This mode of action confers antiepileptic, analgesic, anxiolytic and sedative effects. Research also indicates that gabapentin acts by blocking new synapse formation ³.

Gabapentin has a half‐life of five to seven hours ¹. Gabapentin is absorbed through a saturable transport system, so that absorption is not linear, and the transporter is found only in the proximal small intestine. This means that gabapentin needs to be administered at least three times daily, and may result in plasma trough levels. Two new formulations have attempted to improve the availability of the drug. The first is an extended release, gastro‐retentive formulation, designed to provide continuous delivery at the optimal site of absorption over 8 to 10 hours ⁴. The second uses an extended‐release prodrug (gabapentin encarbil or Horizant) that is absorbed through a high capacity transport system found throughout the intestine, and then undergoes rapid hydrolysis to gabapentin. It is claimed to provide sustained, dose‐proportional gabapentin exposure ⁵, and can be administered twice daily.

Gabapentin special precautions

Before taking gabapentin:

• tell your doctor and pharmacist if you are allergic to gabapentin, any other medications, or any of the inactive ingredients in the type of gabapentin you plan to take. Ask your pharmacist for a list of the inactive ingredients.
• you should know that gabapentin is available in different forms that may be prescribed for different uses. Ask your doctor to be sure that you are not taking more than one product that contains gabapentin.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: hydrocodone (in Hydrocet, in Vicodin, others), medications that make you feel dizzy or drowsy, morphine (Avinza, Kadian, MSIR, others), and naproxen (Aleve, Anaprox, Naprosyn, others). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• if you are taking antacids such as Maalox or Mylanta, take them at least 2 hours before you take gabapentin tablets, capsules, or solution.
  tell your doctor if you have or have ever had kidney disease. If you will be taking the extended-release tablets, also tell your doctor if you need to sleep during the day and stay awake at night.
• tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking gabapentin, call your doctor.
• if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking gabapentin.
• you should know that gabapentin may make you drowsy or dizzy, may slow your thinking, and may cause loss of coordination. Do not drive a car or operate machinery until you know how this medication affects you, and your doctor agrees that it is safe for you to begin these activities.
• if you are giving gabapentin to your child, you should know that your child’s behavior and mental abilities may change while he or she is taking gabapentin. Your child may have sudden changes in mood, become hostile or hyperactive, have difficulty concentrating or paying attention, or be drowsy or clumsy. Have your child avoid activities that could be dangerous, such as riding a bicycle, until you know how gabapentin affects him or her.
• remember that alcohol can add to the drowsiness caused by this medication.
• you should know that your mental health may change in unexpected ways and you may become suicidal (thinking about harming or killing yourself or planning or trying to do so) while you are taking gabapentin for the treatment of epilepsy, mental illness, or other conditions. A small number of adults and children 5 years of age and older (about 1 in 500 people) who took anticonvulsants such as gabapentin to treat various conditions during clinical studies became suicidal during their treatment. Some of these people developed suicidal thoughts and behavior as early as one week after they started taking the medication. There is a risk that you may experience changes in your mental health if you take an anticonvulsant medication such as gabapentin, but there may also be a risk that you will experience changes in your mental health if your condition is not treated. You and your doctor will decide whether the risks of taking an anticonvulsant medication are greater than the risks of not taking the medication. You, your family, or your caregiver should call your doctor right away if you experience any of the following symptoms: panic attacks; agitation or restlessness; new or worsening irritability, anxiety, or depression; acting on dangerous impulses; difficulty falling or staying asleep; aggressive, angry, or violent behavior; mania (frenzied, abnormally excited mood); talking or thinking about wanting to hurt yourself or end your life; withdrawing from friends and family; preoccupation with death and dying; giving away prized possessions; or any other unusual changes in behavior or mood. Be sure that your family or caregiver knows which symptoms may be serious so they can call the doctor if you are unable to seek treatment on your own.

Who can and can’t take gabapentin

Gabapentin can be taken by adults and children aged 6 years and over.

Gabapentin isn’t suitable for some people:

• Gabapentin capsules contain gelatin so they may not be suitable for vegetarians and vegans.
• Some brands of gabapentin capsules contain lactose, so they may be unsuitable for people who are lactose intolerant.
• Gabapentin liquid contains sodium and potassium. If you are on a controlled sodium or potassium diet, or your kidneys don’t work well, speak to your doctor before taking this liquid.

To make sure gabapentin is safe for you, tell your doctor if you:

• have ever had an allergic reaction to gabapentin or other medicines in the past
• have kidney problems
• have ever misused or been addicted to a medicine
• are trying to get pregnant, are already pregnant or are breastfeeding – gabapentin is usually not recommended in pregnancy or while breastfeeding

Pregnancy and breastfeeding

Gabapentin is not generally recommended in pregnancy. There’s no firm evidence that it’s harmful to an unborn baby but for safety, pregnant women are usually advised to take it only if the benefits of the medicine outweigh the potential harm.

If you take gabapentin for epilepsy and become pregnant, don’t stop the medicine without talking to your doctor first. It’s very important that epilepsy is treated during pregnancy as seizures can harm you and your unborn baby.

If you’re trying to get pregnant or have become pregnant you’re routinely recommended to take at least 400mcg of a vitamin called folic acid everyday. It helps the unborn baby grow normally.

Pregnant women who take gabapentin are recommended to take a higher dose of folic acid. Your doctor might prescribe a high dose of 5mg a day for you to take during the first 12 weeks of pregnancy.

If you take gabapentin around the time of giving birth, your baby may need extra monitoring for a few days after they’re born because they may have gabapentin withdrawal symptoms.

Gabapentin and breastfeeding

Usually, you can breastfeed while taking gabapentin.

Check with your doctor first though if your baby is premature or has kidney problems.

Cautions with other medicines

There aren’t usually any problems mixing gabapentin with other medicines.

Some indigestion remedies, called antacids, reduce the amount of gabapentin that the body takes in so it doesn’t work as well. To stop this happening, take an antacid at least 2 hours before or after your dose of gabapentin.

For safety, tell your doctor if you’re taking these medicines before you start gabapentin treatment:

• strong painkillers such as morphine – these can increase the tiredness and dizziness you can feel when you start gabapentin
• antidepressants such as amitriptyline or fluoxetine
• antipsychotic medicines for mental health problems like schizophrenia or bipolar disorder
• a medicine to prevent malaria called mefloquine
• a weight loss medicine called Orlistat – it may stop gabapentin working as well

Mixing gabapentin with herbal remedies or supplements

• There are no known problems with taking herbal remedies and supplements with gabapentin.

What is gabapentin used for?

Gabapentin is used primarily to treat epilepsy.

Gabapentin is also taken pain caused by damage to nerves (neuropathic pain). Nerve pain can be caused by different illnesses including diabetes and shingles (postherpetic neuralgia – the burning, stabbing pain or aches that may last for months or years after an attack of shingles) or it can happen after an injury. Gabapentin at doses of 1800 mg to 3600 mg daily (1200 mg to 3600 mg gabapentin encarbil) can provide good levels of pain relief to some people with postherpetic neuralgia and peripheral diabetic neuropathy ¹.

Gabapentin is not normally used to treat acute pain due to injury or pain after an operation; it is debatable whether gabapentin is an effective pain medicine under such circumstances ⁶, because gabapentin 250 mg is not clinically useful as a stand‐alone analgesic in established acute postoperative pain and gabapentin is inferior to commonly used analgesics (e.g., NSAID (naproxen) or opioid (hydrocodone) analgesics) ⁶.

Gabapentin is sometimes used to relieve the pain of diabetic neuropathy (numbness or tingling due to nerve damage in people who have diabetes), and to treat and prevent hot flashes (sudden strong feelings of heat and sweating) in women who are being treated for breast cancer or who have experienced menopause (”change of life”, the end of monthly menstrual periods). Talk to your doctor about the risks of using gabapentin for your condition.

Occasionally, gabapentin is used to treat migraine headaches.

Gabapentin is also used in veterinary medicine in the treatment of seizures and as an analgesic for treating chronic pain in small animals.

Gabapentin for chronic pain

Neuropathic pain comes from damaged nerves. It is different from pain messages that are carried along healthy nerves from damaged tissue (for example, from a fall or cut, or arthritic knee) ⁷. Neuropathic pain is often treated by different medicines (drugs) to those used for pain from damaged tissue, which we often think of as painkillers. Medicines that are sometimes used to treat depression or epilepsy can be effective in some people with neuropathic pain. One of these is gabapentin. Gabapentin at doses of 1800 mg to 3600 mg daily (1200 mg to 3600 mg gabapentin encarbil) can provide good levels of pain relief to some people with postherpetic neuralgia and peripheral diabetic neuropathy ⁸. Evidence for other types of neuropathic pain is very limited ⁸. The outcome of at least 50% pain intensity reduction is regarded as a useful outcome of treatment by patients and the achievement of this degree of pain relief is associated with important beneficial effects on sleep interference, fatigue, and depression, as well as quality of life, function, and work ⁸. Around 3 or 4 out of 10 participants achieved this degree of pain relief with gabapentin, compared with 1 or 2 out of 10 for placebo. Over half of those treated with gabapentin will not have worthwhile pain relief but may experience adverse events ⁸.

Gabapentin for pain in adults with fibromyalgia

There is no good evidence to support or contradict the suggestion that gabapentin at daily doses of 1200 to 2400 mg reduces pain in fibromyalgia ⁹. The evidence that gabapentin improves pain or other symptoms of fibromyalgia is weak and of very low quality. At best it may benefit a few people with the condition ⁹. As fibromyalgia can respond to the same medicines as neuropathic pain, it has been used off‐license for the treatment of fibromyalgia. Pregabalin, which is closely related to gabapentin, is licensed for treatment of fibromyalgia in the USA ⁹. Fibromyalgia is a complex disorder characterised by widespread pain, fatigue, poor sleep, low mood, and other bodily symptoms. Common pain‐relieving medicines such as paracetamol and ibuprofen are not usually considered effective. Antiepileptic drugs are commonly used to treat fibromyalgia, but there is uncertainty about how good they are.

Gabapentin dosage

Gabapentin is a prescription medicine. It’s important to take gabapentin as advised by your doctor. Gabapentin comes as a capsule, a tablet, an extended-release (long-acting) tablet, and an oral solution (liquid) to take by mouth.

The usual dose of gabapentin to:

• treat epilepsy in adults and older children (aged 12 years and over) is between 900mg and 3,600mg a day split into 3 doses
• treat nerve pain in adults is between 900mg and 3,600mg a day split into 3 doses
• prevent migraine in adults varies but can be up to 2,400mg a day split into 3 doses

The dose of gabapentin used to treat epilepsy in younger children (aged 6 to 12 years) varies depending on their weight.

If you’re taking gabapentin as a liquid, 1ml is usually the same as taking a 50mg tablet or capsule.

How to take gabapentin

Gabapentin capsules, tablets, and oral solution are usually taken with a full glass of water (8 ounces [240 milliliters]), with or without food, three times a day. If you or your child are taking a liquid gabapentin, it will come with a plastic syringe or spoon to measure your dose. If you don’t have a syringe or spoon, ask your pharmacist for one.

Gabapentin should be taken at evenly spaced times throughout the day and night; no more than 12 hours should pass between doses. For example, first thing in the morning, early afternoon and at bedtime.

The extended-release tablet (Horizant) is taken with food once daily at about 5 PM. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take gabapentin exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Gabapentin extended-release tablets cannot be substituted for another type of gabapentin product. Be sure that you receive only the type of gabapentin that was prescribed by your doctor. Ask your pharmacist if you have any questions about the type of gabapentin you were given.

Swallow the extended-release tablets whole; do not cut, chew, or crush them.

If your doctor tells you to take one-half of a regular tablet as part of your dose, carefully split the tablet along the score mark. Use the other half-tablet as part of your next dose. Properly dispose of any half-tablets that you have not used within several days of breaking them.

If you are taking gabapentin to control seizures or postherpetic neuralgia, your doctor will probably start you on a low dose of gabapentin and gradually increase your dose as needed to treat your condition. If you are taking gabapentin to treat postherpetic neuralgia, tell your doctor if your symptoms do not improve during your treatment.

Gabapentin may help to control your condition but will not cure it. Continue to take gabapentin even if you feel well. Do not stop taking gabapentin without talking to your doctor, even if you experience side effects such as unusual changes in behavior or mood. If you suddenly stop taking gabapentin tablets, capsules, or oral solution, you may experience withdrawal symptoms such as anxiety, difficulty falling asleep or staying asleep, nausea, pain, and sweating. If you are taking gabapentin to treat seizures and you suddenly stop taking the medication, you may experience seizures more often. Your doctor may decrease your dose gradually over at least a week.

Your doctor or pharmacist will give you the manufacturer’s patient information sheet (Medication Guide) when you begin treatment with gabapentin and each time you refill your prescription. Read the information carefully and ask your doctor or pharmacist if you have any questions.

You can also visit the Food and Drug Administration (FDA) website (https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm) or the manufacturer’s website to obtain the Medication Guide.

What should I do if I forget a dose?

If you forget to take gabapentin capsules, tablets, or oral solution, take the missed dose as soon as you remember it. However, if it is almost time for the next dose or if you forget to take gabapentin extended-release tablets, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

What if I take too much?

Taking too much gabapentin by accident can cause unpleasant side effects. These include:

• feeling dizzy or sleepy
• seeing double
• slurring your words
• diarrhea
• passing out

If you need to go to hospital, take the gabapentin packet or leaflet inside it plus any remaining medicine with you.

Adult Dose for Postherpetic Neuralgia

In adults with postherpetic neuralgia, gabapentin medication may be initiated as a single 300 mg dose on Day 1, 600 mg/day on Day 2 (divided twice daily), and 900 mg/day on Day 3 (divided three times daily). The dose can subsequently be titrated up as needed for pain relief to a daily dose of 1800 mg (divided three times daily). In clinical studies, efficacy was demonstrated over a range of doses from 1800 mg/day to 3600 mg/day with comparable effects across the dose range. Additional benefit of using doses greater than 1800 mg/day was not demonstrated.

Gabapentin for Epilepsy

Gabapentin capsules are recommended for add-on therapy in patients 3 years of age and older. Effectiveness in pediatric patients below the age of 3 years has not been established.

Patients > 12 years of age

The effective dose of gabapentin capsules is 900 to 1800 mg/day and given in divided doses (three times a day) using 300 or 400 mg capsules. The starting dose is 300 mg three times a day. If necessary, the dose may be increased using 300 or 400 mg capsules three times a day up to 1800 mg/day. Dosages up to 2400 mg/day have been well tolerated in long-term clinical studies. Doses of 3600 mg/day have also been administered to a small number of patients for a relatively short duration, and have been well tolerated. The maximum time between doses in the three times daily schedule should not exceed 12 hours.

Pediatric Patients Age 3 to 12 years

The starting dose should range from 10 to 15 mg/kg/day in 3 divided doses, and the effective dose reached by upward titration over a period of approximately 3 days. The effective dose of gabapentin capsules in patients 5 years of age and older is 25 to 35 mg/kg/day and given in divided doses (three times a day). The effective dose in pediatric patients ages 3 and 4 years is 40 mg/kg/day and given in divided doses (three times a day). Dosages up to 50 mg/kg/day have been well tolerated in a long-term clinical study. The maximum time interval between doses should not exceed 12 hours.

It is not necessary to monitor gabapentin plasma concentrations to optimize gabapentin capsules therapy. Further, because there are no significant pharmacokinetic interactions among gabapentin capsules and other commonly used antiepileptic drugs, the addition of gabapentin capsules does not alter the plasma levels of these drugs appreciably.

If gabapentin capsules are discontinued and/or an alternate anticonvulsant medication is added to the therapy, this should be done gradually over a minimum of 1 week.

Gabapentin side effects

Most people who take gabapentin don’t have too much trouble with side effects.

Common side effects

These common side effects may happen in more than 1 in 100 people. They’re usually mild and go away by themselves.

Keep taking the medicine but talk to your doctor if these side effects bother you or don’t go away:

• tiredness or feeling sleepy
• dizziness or losing your co-ordination
• feeling or being sick (nausea or vomiting)
• getting more infections than usual
• memory problems
• mood changes
• swollen arms and legs
• blurred vision
• dry mouth
• difficulties for men getting an erection
• weight gain – gabapentin can make you feel hungry

Serious side effects

Very few people taking gabapentin have serious problems.

Tell a doctor straight away if you have a serious side effect, including:

• thoughts of harming or killing yourself – a small number of people taking gabapentin have had suicidal thoughts, they can happen after only a week of treatment
• yellowing of your skin or whites of your eyes – these may be warning signs of jaundice
• unusual bruises or bleeding – these may be warning signs of a blood disorder
• long-lasting stomach pain, feeling sick or vomiting – these may be warning signs of an inflamed pancreas
• muscle pain or weakness and you are having dialysis treatment because of kidney failure

Serious allergic reaction

In rare cases, it’s possible to have a serious allergic reaction to gabapentin. A serious allergic reaction is an emergency. Contact a doctor straight away if you think you or someone around you is having a serious allergic reaction.

Gabapentin can cause anaphylaxis and angioedema after the first dose or at any time during treatment. Signs and symptoms in reported cases have included difficulty breathing, swelling of the lips, throat, and tongue, and hypotension requiring emergency treatment. You should be instructed to discontinue gabapentin and seek immediate medical care should they experience signs or symptoms of anaphylaxis or angioedema.

The warning signs of a serious allergic reaction are:

• getting a skin rash that may include itchy, red, swollen, blistered or peeling skin
• wheezing
• tightness in the chest or throat
• having trouble breathing or talking
• swelling of the mouth, face, lips, tongue, or throat

Tell your doctor if any of these symptoms are severe or do not go away:

• drowsiness
• tiredness or weakness
• dizziness
• headache
• uncontrollable shaking of a part of your body
• double or blurred vision
• unsteadiness
• anxiety
• memory problems
• strange or unusual thoughts
• unwanted eye movements
• nausea
• vomiting
• heartburn
• diarrhea
• dry mouth
• constipation
• increased appetite
• weight gain
• swelling of the hands, feet, ankles, or lower legs
• back or joint pain
• fever
• runny nose, sneezing, cough, sore throat, or flu-like symptoms
• ear pain
• red, itchy eyes (sometimes with swelling or discharge)

Some side effects may be serious. If you experience any of the following symptoms, call your doctor immediately:

• rash
• itching
• swelling of the face, throat, tongue, lips, or eyes
• hoarseness
• difficulty swallowing or breathing
• seizures

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multiorgan hypersensitivity, has occurred with gabapentin. Some of these reactions have been fatal or life-threatening. Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) typically, although not exclusively, presents with fever, rash, and/or lymphadenopathy, in association with other organ system involvement, such as hepatitis, nephritis, hematological abnormalities, myocarditis, or myositis sometimes resembling an acute viral infection. Eosinophilia is often present. This disorder is variable in its expression, and other organ systems not noted here may be involved. It is important to note that early manifestations of hypersensitivity, such as fever or lymphadenopathy, may be present even though rash is not evident. If such signs or symptoms are present, you should be evaluated by your doctor immediately. Gabapentin should be discontinued if an alternative etiology for the signs or symptoms cannot be established.

These are not all the side effects of gabapentin. For a full list see the leaflet inside your medicines packet. Call your doctor if you have any unusual problems while taking gabapentin.

Cardiovascular

• Common (1% to 10%): Peripheral edema, vasodilation, hypertension
• Rare (less than 0.1%): Atrial fibrillation, heart failure, myocardial infarction, cerebrovascular accident, ventricular extrasystoles, bradycardia, premature atrial contraction, pericardial rub, heart block, pericardial effusion, pericarditis
• Postmarketing reports: Cardiac arrest, chest pain, palpitation, tachycardia

Dermatologic

• Common (1% to 10%): Abrasion, facial edema, purpura, rash, pruritus, acne
• Uncommon (0.1% to 1%): Alopecia, eczema, dry skin, increased sweating, urticaria, hirsutism, seborrhea, cyst, herpes simplex
• Rare (less than 0.1%): Stevens-Johnson syndrome, angioedema, erythema multiforme, drug rash (with eosinophilia and systemic symptoms), herpes zoster, skin discolor, skin papules, photosensitive reaction, psoriasis, desquamation, maceration, skin nodules, subcutaneous nodule, melanosis, skin necrosis, local swelling
• Frequency not reported: DRESS/multiorgan hypersensitivity

Endocrine

• Rare (less than 0.1%): Hyperthyroid, hypothyroid, goiter, hypoestrogenism, ovarian failure, epididymitis, cushingoid appearance

Gastrointestinal

• Common (1% to 10%): Diarrhea, dry mouth or throat, constipation, nausea, vomiting, dyspepsia, dental abnormalities, gingivitis, abdominal pain, flatulence
• Uncommon (0.1% to 1%): Glossitis, gum hemorrhage, thirst, stomatitis, increased salivation, gastroenteritis, hemorrhoids, bloody stools, fecal incontinence
• Rare (less than 0.1%): Pancreatitis, dysphagia, eructation, pancreatitis, peptic ulcer, colitis, blisters in mouth, tooth discoloration, perlèche, salivary gland enlarged, lip hemorrhage, esophagitis, hiatal hernia, hematemesis, proctitis, irritable bowel syndrome, rectal hemorrhage, esophageal spasm
• Frequency not reported: Dehydration

Genitourinary

• Common (1% to 10%): Incontinence, impotence
• Uncommon (0.1% to 1%): Hematuria, dysuria, urinary frequency, cystitis, urinary retention, vaginal hemorrhage, amenorrhea, dysmenorrhea, menorrhagia
• Frequency not reported: Breast hypertrophy, gynecomastia, sexual dysfunction (including changes in libido, ejaculation disorders, and anorgasmia)

Hematologic

• Common (1% to 10%): Leucopenia, purpura
• Uncommon (0.1% to 1%): Anemia, lymphadenopathy
• Rare (less than 0.1%): Thrombocytopenia, thrombophlebitis, leukocytosis, lymphocytosis, increased bleeding time
• Frequency not reported: Blood creatine phosphokinase increased, coagulation defect

Hepatic

• Rare (less than 0.1%): Hepatitis, jaundice, elevated liver function tests SGOT (AST), SGPT (ALT), and bilirubin, hepatomegaly, hepatotoxicity

Hypersensitivity

• Very rare (less than 0.01%): Hypersensitivity syndrome, a systemic reaction with a variable presentation that can include fever, rash, hepatitis, lymphadenopathy, eosinophilia, and sometimes other signs and symptoms

Metabolic

• Common (1% to 10%): Weight gain, hyperglycemia
• Postmarketing reports: Hyponatremia

Musculoskeletal

• Common (1% to 10%): Back pain, arthralgia, myalgia, twitching
• Uncommon (0.1% to 1%): Tendonitis, arthritis, joint stiffness, joint swelling
• Frequency not reported: Rhabdomyolysis, myoclonus
• Postmarketing reports: Elevated creatine kinase, rhabdomyolysis

Nervous system

• Very common (10% or more): Somnolence (21%), dizziness (17%), ataxia (13%)
• Common (1% to 10%): Abnormal gait, incoordination, neuralgia, tremor, dysarthria, hyperkinesia, seizures, dysarthria, paresthesia, hypesthesia, coordination abnormal, increased/decreased/absent reflexes, vertigo
• Uncommon (less than 1%): Hypokinesia
• Rare (less than 0.1%): Movement disorders (e.g., choreoathetosis, dyskinesia, dystonia), loss of consciousness
• Frequency not reported: Withdrawal precipitated seizure/status epilepticus
• Postmarketing reports: Movement disorder

Ocular

• Common (1% to 10%): Amblyopia, conjunctivitis, diplopia, nystagmus
• Uncommon (0.1% to 1%): Cataract, dry eyes, eye pain, visual field defect, photophobia, bilateral or unilateral ptosis, eye hemorrhage, hordeolum, eye twitching
• Rare (less than 0.1%): Eye itching, abnormal accommodation, eye focusing problem, watery eyes, retinopathy, glaucoma, iritis, corneal disorders, lacrimal dysfunction, degenerative eye changes, blindness, retinal degeneration, miosis, chorioretinitis, strabismus

Oncologic

• Uncommon (0.1% to 1%): Breast cancer
• Rare (less than 0.1%): Non-Hodgkin’s lymphoma

Other

• Very common (10% or more): Fatigue (11%), fever (11%)
• Common (1% to 10%): Asthenia, accidental injury, otitis media, tremor, pain
• Rare (0.01% to 0.1%): Tinnitus
• Very rare (less than 0.01%): Sudden unexplained death in patients with epilepsy
• Frequency not reported: Sleepwalking, withdrawal symptoms, hearing loss, earache, tinnitus, inner ear infection, otitis, taste loss, unusual taste, ear fullness, perforated ear drum, sensitivity to noise, eustachian tube dysfunction, otitis externa, odd smell, labyrinthitis

Psychiatric

• Common (1% to 10%): Abnormal thinking, amnesia, depression, hostility, confusion, emotional liability, anxiety, nervousness, insomnia
• Uncommon (0.1% to 1%): Mental impairment
• Rare (less than 0.1%): Hallucinations
• Frequency not reported: Suicidal behavior and ideation, hypomania

Renal

Rare (less than 0.1%): Acute renal failure

Respiratory

• Common (1% to 10%): Pharyngitis, dyspnea, cough, bronchitis, respiratory infection, rhinitis
• Rare (less than 0.1%): Pulmonary thrombosis, pulmonary embolism
• Frequency not reported: Pseudo-croup, hoarseness

How to cope with side effects

What to do about:

• feeling sleepy, tired or dizzy – as your body gets used to gabapentin, these side effects should wear off. If they don’t wear off within a week or two, your doctor may reduce your dose or increase it more slowly. If that doesn’t work you may need to switch to a different medicine.
• feeling sick (nausea) – take gabapentin with or after a meal or snack. It may also help if you don’t eat rich or spicy food.
• diarrhea and being sick (vomiting) – have small but frequent sips of water. It may also help to take oral rehydration solutions which you can buy from a pharmacy or supermarket to prevent dehydration. Don’t take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor.
• blurred vision – don’t drive for a week
• a dry mouth – chew sugar-free gum or suck sugar-free sweets.
• weight gain – gabapentin can make you hungrier so it can be quite a challenge to stop yourself putting on weight. Try to eat a healthy balanced diet without increasing your portion sizes. Don’t snack on foods that contain a lot of calories, such as crisps, cakes, biscuits and sweets. If you feel hungry between meals, eat fruit and vegetables and low-calorie foods. Regular exercise will also help to keep your weight stable.

Gabapentin overdose

Acute oral overdoses of gabapentin up to 49 grams have been reported. In these cases, double vision, slurred speech, drowsiness, lethargy, and diarrhea were observed. All patients recovered with supportive care. Gabapentin can be removed by hemodialysis. Although hemodialysis has not been performed in the few overdose cases reported, it may be indicated by the patient’s clinical state or in patients with significant renal impairment. Coma, resolving with dialysis, has been reported in patients with chronic renal failure who were treated with gabapentin.

Symptoms of overdose may include the following:

• double vision
• slurred speech
• drowsiness
• diarrhea

Animal studies

A lethal dose of gabapentin was not identified in mice and rats receiving single oral doses as high as 8000 mg/kg. Signs of acute toxicity in animals included ataxia, labored breathing, ptosis, sedation, hypoactivity, or excitation. Gabapentin was administered orally to mice and rats in 2-year carcinogenicity studies. No evidence of drug-related carcinogenicity was observed in mice treated at doses up to 2000 mg/kg/day. In rats, increases in the incidence of pancreatic acinar cell adenoma and carcinoma were found in male rats receiving the highest dose (2000 mg/kg), but not at doses of 250 or 1000 mg/kg/day. When pregnant mice received oral doses of gabapentin (500, 1000, or 3000 mg/kg/day) during the period of organogenesis, increased incidences of skeletal variations were observed at the two highest doses. In studies in which rats received oral doses of gabapentin (500 to 2000 mg/kg/day), during pregnancy, increased incidences of hydroureter and/or hydronephrosis were observed at all doses. Likewise, when pregnant rabbits were treated with gabapentin during the period of organogenesis, an increase in embryo-fetal mortality was observed at all doses tested (60, 300, or 1500 mg/kg). Gabapentin did not demonstrate mutagenic or genotoxic potential in several in vitro and in vivo assays. It was negative in the Ames test and the in vitro HGPRT forward mutation assay in Chinese hamster lung cells; it did not produce significant increases in chromosomal aberrations in the in vitro Chinese hamster lung cell assay; it was negative in the in vivo chromosomal aberration assay and in the in vivo micronucleus test in Chinese hamster bone marrow; it was negative in the in vivo mouse micronucleus assay; and it did not induce unscheduled DNA synthesis in hepatocytes from rats given gabapentin.

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