Retigabine (

INN Inns are generally establishments or buildings where travelers can seek lodging, and usually, food and drink. Inns are typically located in the country or along a highway; before the advent of motorized transportation they also provided accommo ...

) or ezogabine (

USAN 280px, "Samguk Sagi" Book 04. Silla's Records. In 512, Usan-guk（于山國）was Ulleungdo（鬱陵島） Usan-guk, or the State of Usan, occupied Ulleung-do and the adjacent islands during the Korean Three Kingdoms period. According to th ...

) is an

anticonvulsant Anticonvulsants (also known as antiepileptic drugs or recently as antiseizure drugs) are a diverse group of pharmacological agents used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of b ...

used as an adjunctive treatment for

partial Partial may refer to: Mathematics * Partial derivative, derivative with respect to one of several variables of a function, with the other variables held constant ** ∂, a symbol that can denote a partial derivative, sometimes pronounced "partial ...

epilepsies Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...

in treatment-experienced adult patients. The drug was developed by

Valeant Pharmaceuticals Bausch Health Companies Inc. (formerly Valeant Pharmaceuticals International, Inc.) is a Canadian multinational specialty pharmaceutical company based in Laval, Quebec, Canada. It develops, manufactures and markets pharmaceutical products and ...

and

GlaxoSmithKline GSK plc, formerly GlaxoSmithKline plc, is a British multinational pharmaceutical and biotechnology company with global headquarters in London, England. Established in 2000 by a merger of Glaxo Wellcome and SmithKline Beecham. GSK is the ten ...

. It was approved by the

European Medicines Agency The European Medicines Agency (EMA) is an agency of the European Union (EU) in charge of the evaluation and supervision of medicinal products. Prior to 2004, it was known as the European Agency for the Evaluation of Medicinal Products or Euro ...

under the trade name Trobalt on March 28, 2011, and by the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...

(FDA), under the trade name Potiga, on June 10, 2011. Production was discontinued in June 2017. Retigabine works primarily as a

potassium channel opener A potassium channel opener is a type of drug which facilitates ion transmission through potassium channels. Examples Some examples include: *Diazoxide vasodilator used for hypertension, smooth muscle relaxing activity *Minoxidil vasodilator us ...

—that is, by activating a certain family of

voltage-gated potassium channel Voltage-gated potassium channels (VGKCs) are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized ce ...

s in the brain. This

mechanism of action In pharmacology, the term mechanism of action (MOA) refers to the specific biochemical interaction through which a drug substance produces its pharmacological effect. A mechanism of action usually includes mention of the specific molecular targe ...

is unique among antiepileptic drugs, and may hold promise for the treatment of other neurologic conditions, including

tinnitus Tinnitus is the perception of sound when no corresponding external sound is present. Nearly everyone experiences a faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearin ...

migraine Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few hou ...

and

neuropathic pain Neuropathic pain is pain caused by damage or disease affecting the somatosensory system. Neuropathic pain may be associated with abnormal sensations called dysesthesia or pain from normally non-painful stimuli (allodynia). It may have continuous ...

. The manufacturer withdrew retigabine from clinical use in 2017.

Adverse effects

The

adverse effects An adverse effect is an undesired harmful effect resulting from a medication or other intervention, such as surgery. An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. The term complica ...

found in the Phase II trial mainly affected the central nervous system, and appeared to be dose-related. The most common adverse effects were

drowsiness Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a common medical c ...

and

vertigo Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...

, confusion, and

slurred speech Dysarthria is a speech sound disorder resulting from neurological injury of the motor component of the motor–speech system and is characterized by poor articulation of phonemes. In other words, it is a condition in which problems effectively ...

. Less common side effects included

tremor A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, fa ...

, memory loss,

gait Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. Di ...

disturbances, and

double vision Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often v ...

. In 2013 FDA warned the public that Potiga (ezogabine) can cause blue skin discoloration and eye abnormalities characterized by pigment changes in the retina. FDA does not currently know if these changes are reversible. FDA is working with the manufacturer to gather and evaluate all available information to better understand these events. FDA will update the public when more information is available. Psychiatric symptoms and difficulty urinating have also been reported, with most cases occurring in the first 2 months of treatment.

Interactions

Retigabine appears to be free of

drug interaction Drug interactions occur when a drug's mechanism of action is disturbed by the concomitant administration of substances such as foods, beverages, or other drugs. The cause is often the inhibition of the specific receptors available to the drug, ...

s with most commonly used anticonvulsants. It may increase metabolism of

lamotrigine Lamotrigine, sold under the brand name Lamictal among others, is a medication used to treat epilepsy and stabilize mood in bipolar disorder. For epilepsy, this includes focal seizures, tonic-clonic seizures, and seizures in Lennox-Gastaut synd ...

(Lamictal), whereas

phenytoin Phenytoin (PHT), sold under the brand name Dilantin among others, is an anti-seizure medication. It is useful for the prevention of tonic-clonic seizures (also known as grand mal seizures) and focal seizures, but not absence seizures. The intr ...

(Dilantin) and

carbamazepine Carbamazepine (CBZ), sold under the trade name Tegretol among others, is an anticonvulsant medication used primarily in the treatment of epilepsy and neuropathic pain. It is used as an adjunctive treatment in schizophrenia along with other medi ...

(CBZ, Tegretol) increase the clearance of retigabine. Concomitant use of retigabine and

digoxin Digoxin (better known as Digitalis), sold under the brand name Lanoxin among others, is a medication used to treat various heart conditions. Most frequently it is used for atrial fibrillation, atrial flutter, and heart failure. Digoxin is on ...

may increase serum concentration of the latter. ''In vitro'' studies suggest that the main metabolite of retigabine acts as a

P-glycoprotein P-glycoprotein 1 (permeability glycoprotein, abbreviated as P-gp or Pgp) also known as multidrug resistance protein 1 (MDR1) or ATP-binding cassette sub-family B member 1 (ABCB1) or cluster of differentiation 243 (CD243) is an important protein ...

inhibitor, and may thus increase absorption and reduce elimination of digoxin.

Pharmacology

Mechanism of action

Retigabine acts as a neuronal KCNQ/

Kv7 Tomb KV7 was the final resting place of ancient Egyptian Pharaoh Ramesses II ("Ramesses the Great") of the Nineteenth Dynasty. Location It is located in the Valley of the Kings opposite the tomb of his sons, KV5, and near to the tomb of his son ...

, a mechanism of action markedly different from that of any current anticonvulsants. This mechanism of action is similar to that of the chemically-similar

flupirtine Flupirtine is an aminopyridine that functions as a centrally acting non-opioid analgesic that was originally used as an analgesic for acute and chronic pain but in 2013 due to issues with liver toxicity, the European Medicines Agency restricte ...

, which is used mainly for its analgesic properties. The term "channel opener" refers to a shift in the voltage dependence for channel opening towards more negative potentials. This means that KCNQ/Kv7 channels open at more negative potentials in the presence of Retigabine. Recently, it has also been shown that Retigabine stabilizes the open Kv7.2/7.3 channel, making deactivation slower with little change in voltage dependence. This effect of Retigabine is observed at concentrations below 10 micromolar. A similar effect is observed on the homomeric Kv7.2 channel.

Pharmacokinetics

Retigabine is quickly absorbed, and reaches maximum plasma concentrations between half an hour and 2 hours after a single oral dose. It has a moderately high oral

bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...

(50–60%), a high

volume of distribution In pharmacology, the volume of distribution (VD, also known as apparent volume of distribution, literally, ''volume of dilution'') is the theoretical volume that would be necessary to contain the total amount of an administered drug at the same c ...

(6.2 L/kg), and a

terminal half-life Biological half-life (also known as elimination half-life, pharmacologic half-life) is the time taken for concentration of a biological substance (such as a medication) to decrease from its maximum concentration ( Cmax) to half of Cmax in the bl ...

of 8 to 11 hours. Retigabine requires thrice-daily dosing due to its short half-life. Retigabine is

metabolized Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

in the liver, by ''N''-

glucuronidation Glucuronidation is often involved in drug metabolism of substances such as drugs, pollutants, bilirubin, androgens, estrogens, mineralocorticoids, glucocorticoids, fatty acid derivatives, retinoids, and bile acids. These linkages involve glycosid ...

and

acetylation : In organic chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed ''acetate esters'' or simply '' acetates''. Deacetylation is the oppo ...

. The

cytochrome P450 Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...

system is not involved. Retigabine and its metabolites are excreted almost completely (84%) by the kidneys.

History

Among the newer anticonvulsants, retigabine was one of the most widely studied in the

preclinical In drug development, preclinical development, also termed preclinical studies or nonclinical studies, is a stage of research that begins before clinical trials (testing in humans) and during which important feasibility, iterative testing and drug ...

setting: it was the subject of over 100 published studies before clinical trials began. In preclinical tests, it was found to have a very broad spectrum of activity—being effective in nearly all the

animal model An animal model (short for animal disease model) is a living, non-human, often genetic-engineered animal used during the research and investigation of human disease, for the purpose of better understanding the disease process without the risk of ha ...

s of seizures and epilepsy used: retigabine suppresses seizures induced by electroshock, electrical

kindling Kindling is material for firelighting Kindling may also refer to: * ''Kindling'' (album), a 1973 album by Gene Parsons * ''Kindling'' (film), a 1915 film by Cecil B. DeMille * ''Kindling'' (Mick Farren novel) * ''Ruined City'' (novel) or ''Ki ...

of the

amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...

pentylenetetrazol Pentylenetetrazol, also known as pentylenetetrazole, leptazol, metrazol, pentetrazol (INN), pentamethylenetetrazol, Corazol, Cardiazol, Deumacard, or PTZ, is a drug formerly used as a circulatory and respiratory stimulant. High doses cause convuls ...

kainate Kainic acid, or kainate, is an acid that naturally occurs in some seaweed. Kainic acid is a potent neuroexcitatory amino acid agonist that acts by activating receptors for glutamate, the principal excitatory neurotransmitter in the central nervo ...

NMDA ''N''-methyl--aspartic acid or ''N''-methyl--aspartate (NMDA) is an amino acid derivative that acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor. Unlike ...

, and

picrotoxin Picrotoxin, also known as cocculin, is a poisonous crystalline plant compound. It was first isolated by the French pharmacist and chemist Pierre François Guillaume Boullay (1777–1869) in 1812. The name "picrotoxin" is a combination of the Gree ...

. Researchers hoped this wide-ranging activity would translate to studies in humans as well.

Clinical trials

In a

double-blind In a blind or blinded experiment, information which may influence the participants of the experiment is withheld until after the experiment is complete. Good blinding can reduce or eliminate experimental biases that arise from a participants' expec ...

, randomized, placebo-controlled Phase II clinical trial, retigabine was added to the treatment regimen of 399 participants with partial seizures that were refractory to therapy with other antiepileptic drugs. The frequency with which seizures occurred was significantly reduced (by 23 to 35%) in participants receiving retigabine, and approximately one fourth to one third of participants had their seizure frequency reduced by more than 50%. Higher doses were associated with a greater response to treatment. A Phase II trial meant to assess the safety and efficacy of retigabine for treating

postherpetic neuralgia Postherpetic neuralgia (PHN) is neuropathic pain that occurs due to damage to a peripheral nerve caused by the reactivation of the varicella zoster virus (herpes zoster, also known as shingles). Typically, the nerve pain (neuralgia) is confined t ...

was completed in 2009, but failed to meet its primary

endpoint An endpoint, end-point or end point may refer to: * Endpoint (band), a hardcore punk band from Louisville, Kentucky * Endpoint (chemistry), the conclusion of a chemical reaction, particularly for titration * Outcome measure, a measure used as an e ...

. Preliminary results were reported by Valeant as "inconclusive".

Regulatory approval

The U.S. Food and Drug Administration accepted Valeant's New Drug Application for retigabine on December 30, 2009. The FDA Peripheral and Central Nervous System Drugs Advisory Committee met on August 11, 2010 to discuss the process and unanimously recommended approval of Potiga for the intended indication (add-on treatment of partial seizures in adults). However, the possibility of

urinary retention Urinary retention is an inability to completely empty the bladder. Onset can be sudden or gradual. When of sudden onset, symptoms include an inability to urinate and lower abdominal pain. When of gradual onset, symptoms may include loss of bladd ...

as an adverse effect was considered a significant concern, and the panel's members recommended that some sort of monitoring strategy be used to identify patients at risk of bladder dysfunction. Potiga was approved by the FDA on June 10, 2010, but did not become available on the U.S. market until it had been scheduled by the

Drug Enforcement Administration The Drug Enforcement Administration (DEA; ) is a Federal law enforcement in the United States, United States federal law enforcement agency under the U.S. Department of Justice tasked with combating drug trafficking and distribution within th ...

. In December 2011, the U.S.

(DEA) placed the substance into Schedule V of the

Controlled Substances Act The Controlled Substances Act (CSA) is the statute establishing federal government of the United States, federal drug policy of the United States, U.S. drug policy under which the manufacture, importation, possession, use, and distribution of ...

(CSA), the category for substances with a comparatively low potential for abuse. This became effective 15 December 2011.

Name

The International Nonproprietary Name "retigabine" was initially published as being under consideration by

WHO Who or WHO may refer to: * Who (pronoun), an interrogative or relative pronoun * Who?, one of the Five Ws in journalism * World Health Organization Arts and entertainment Fictional characters * Who, a creature in the Dr. Seuss book '' Horton He ...

in 1996. This was later adopted as the ''recommended'' International Nonproprietary Name (rINN) for the drug, and, in 2005 or 2006, the

USAN Council A United States Adopted Name (USAN) is a unique nonproprietary name assigned to a medication marketed in the United States. Each name is assigned by the USAN Council, which is co-sponsored by the American Medical Association (AMA), the United Sta ...

—a program sponsored by the American Medical Association, the United States Pharmacopeial Convention, and the American Pharmacists Association that chooses nonproprietary names for drug sold in the United States—adopted the same name. In 2010, however, the USAN Council rescinded its previous decision and assigned "ezogabine" as the

United States Adopted Name A United States Adopted Name (USAN) is a unique nonproprietary name assigned to a medication marketed in the United States. Each name is assigned by the USAN Council, which is co-sponsored by the American Medical Association (AMA), the United Stat ...

for the drug. The drug will thus be known as "ezogabine" in the United States and "retigabine" elsewhere.

References

External links

* {{Authority control Anticonvulsants Carbamates Potassium channel openers Fluoroarenes GABAA receptor positive allosteric modulators Withdrawn drugs Orphan drugs