Gabapentin enacarbil

Restless Legs Syndrome

Gabapentin enacarbil is used to treat adults with moderate-to-severe primary Restless Legs Syndrome (RLS). This condition is characterized by an uncontrollable urge to move the legs, often accompanied by uncomfortable sensations like tingling or crawling. These symptoms typically worsen in the evening or at night, which can interfere with sleep and daily activities.

Postherpetic Neuralgia

This medication is also indicated for the management of postherpetic neuralgia (PHN) in adults. PHN is a type of chronic nerve pain that occurs in the area where a shingles (herpes zoster) rash was previously located. The pain results from damage to the nerves caused by the varicella-zoster virus.

Usage Considerations

It is important to note that gabapentin enacarbil is an extended-release prodrug of gabapentin. Although it is converted into gabapentin once inside the body, it is not interchangeable with other gabapentin products, such as those used to treat epilepsy or different types of nerve pain. The way the body absorbs and uses this specific formulation is different from other versions of the drug.

Conversion into Gabapentin

Gabapentin enacarbil is known as a prodrug. This means that when you take the medication, it is not yet active. Once it enters the body, enzymes in the digestive tract convert it into gabapentin, which is the active medicine that treats symptoms. This specific formulation is designed to be absorbed more efficiently by the body than standard gabapentin.

How It Affects the Nervous System

The exact way gabapentin works to treat restless legs syndrome or nerve pain after shingles is not completely understood. However, researchers believe it interacts with the central nervous system in the following ways:

• Calcium Channel Binding: The medication binds to specific sites on voltage-gated calcium channels in the brain and spinal cord. This action is thought to help regulate the release of neurotransmitters, which are chemicals that nerves use to communicate.
• Reducing Nerve Signals: By affecting these channels, the drug may decrease the transmission of pain signals and calm overactive nerves.

Although gabapentin is structurally similar to a natural brain chemical called gamma-aminobutyric acid (GABA), it does not bind to GABA receptors or change the way GABA is used in the brain. Instead, it focuses on stabilizing electrical activity in the nerves to provide relief.

Common Side Effects

Many people using this medication experience mild side effects. These may include:

• Drowsiness or sleepiness
• Dizziness
• Feeling tired or weak
• Headache
• Nausea
• Irritability

Serious Side Effects

While less common, some side effects require immediate medical attention. Contact a healthcare provider right away if you experience:

• Breathing problems: Serious, life-threatening breathing issues can occur, especially in older adults, people with existing lung disease, or those taking other medications that cause sleepiness, such as opioids.
• Mood or behavior changes: New or worsening depression, anxiety, irritability, agitation, panic attacks, or thoughts of self-harm.
• Severe allergic reactions: Swelling of the face, lips, tongue, or throat; skin rash; hives; or difficulty swallowing.
• Extreme coordination issues: Severe dizziness or sleepiness that makes it dangerous to drive or perform daily tasks.
• Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): A serious reaction that may include fever, rash, and swollen lymph nodes.

This is not a complete list of possible side effects. Always consult with a healthcare professional about any new or unusual symptoms while taking this medication.

Respiratory Depression

Serious and potentially life-threatening breathing difficulties may occur in individuals taking gabapentin enacarbil. This risk is highest for older adults, people with existing lung conditions such as chronic obstructive pulmonary disease (COPD), and those taking other medications that slow breathing, such as opioids or other central nervous system depressants.

Suicidal Thoughts and Behavior

As with other antiepileptic medications, gabapentin enacarbil may increase the risk of suicidal thoughts or actions. It is important to monitor for any new or worsening depression, anxiety, restlessness, or unusual changes in mood or behavior.

Dizziness and Somnolence

Significant drowsiness and dizziness are common side effects. These effects can impair the ability to drive or operate heavy machinery safely. These activities should be avoided until it is clear how the medication affects an individual's alertness and coordination.

Hypersensitivity and Serious Reactions

Rare but serious allergic reactions, such as Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), have been reported. These reactions can affect multiple organs and may present with symptoms like fever, rash, or swollen lymph glands.

Discontinuation and Withdrawal

Stopping the medication suddenly can lead to withdrawal symptoms, such as insomnia, nausea, or anxiety. In some cases, sudden discontinuation may cause the underlying symptoms to return more severely. A gradual reduction in dosage is typically recommended.

Alcohol Interaction

Consuming alcohol while taking this medication can increase the sedative effects and significantly raise the risk of severe respiratory depression.

Pregnancy

There is limited research on the use of gabapentin enacarbil in pregnant women. In animal studies, high doses of the medication were associated with developmental issues, such as skeletal abnormalities and lower birth weights. Because human data is insufficient, healthcare providers typically only prescribe this medication during pregnancy if the potential benefit to the parent justifies the potential risk to the developing fetus.

If you become pregnant while taking this medication, you are encouraged to talk to your doctor about enrolling in the North American Antiepileptic Drug (NAAED) Pregnancy Registry. This registry collects information to help researchers understand how certain medications affect pregnancy outcomes.

Breastfeeding

Gabapentin, the active form of gabapentin enacarbil, is known to pass into human breast milk. There is currently no clear information on how the drug affects breastfed infants or milk production. If you are breastfeeding or planning to breastfeed, discuss the potential risks and benefits with your healthcare provider to determine the best course of action for you and your baby.

Available Forms

Gabapentin enacarbil is provided as an oral medication in the following form:

• Extended-release tablet: This formulation is designed to release the medication slowly into the body after it is swallowed.

These tablets are intended to be swallowed whole. They should not be crushed, chewed, or broken, as doing so can interfere with the extended-release mechanism of the medication.

FDA Approval and Indications

Gabapentin enacarbil is approved by the U.S. Food and Drug Administration (FDA) for the treatment of two specific conditions in adults:

• Moderate-to-severe primary Restless Legs Syndrome (RLS).
• Postherpetic neuralgia (PHN), which is the chronic nerve pain that can follow a shingles infection.

Safety Communications

The FDA has issued safety alerts regarding the risk of serious breathing difficulties associated with gabapentinoids, the class of drugs that includes gabapentin enacarbil. These respiratory issues are most likely to occur in patients with pre-existing respiratory risk factors, such as chronic obstructive pulmonary disease (COPD) or reduced lung function. The risk is also significantly increased when the medication is used in combination with other central nervous system (CNS) depressants, particularly opioid pain medications.

Healthcare providers are encouraged to monitor patients for signs of respiratory depression and to use the lowest effective dose, especially in elderly patients or those with underlying lung disease.

Regulatory Classification

At the federal level in the United States, gabapentin enacarbil is not classified as a controlled substance. However, because it is a prodrug that is converted into gabapentin within the body, it may be subject to specific monitoring requirements in certain states. Some state jurisdictions have implemented additional oversight or reclassified gabapentin-containing products due to concerns regarding misuse and safety.

Risks of Abrupt Discontinuation

You should not stop taking gabapentin enacarbil without first consulting your healthcare provider. Stopping the medication abruptly can lead to withdrawal symptoms or cause the symptoms of your condition to return. If you are taking this medication for Restless Legs Syndrome (RLS), stopping it suddenly may cause your RLS symptoms to become more severe than they were before treatment.

Potential Withdrawal Symptoms

While specific withdrawal data for the enacarbil formulation is limited, medications in the gabapentinoid class are generally associated with certain symptoms when stopped quickly. These may include:

• Anxiety
• Insomnia or difficulty sleeping
• Nausea
• Pain
• Sweating

Seizure Risk

For patients using gabapentin products for seizure disorders, stopping the medication suddenly can increase the frequency of seizures. In some cases, this can lead to status epilepticus, a serious condition where seizures do not stop. Even if you are taking gabapentin enacarbil for a different condition, such as nerve pain, a gradual taper is usually recommended to ensure safety.

Tapering the Dose

To minimize the risk of withdrawal, healthcare providers typically recommend gradually reducing the dose over a period of at least one week. Your doctor will provide a specific schedule to slowly lower your dosage before you stop the medication entirely. Always follow these instructions carefully and report any new or worsening symptoms during the tapering process.