Ketotifen

Ketotifen is an antihistamine medication and a mast cell stabilizer used to treat allergic conditions such as conjunctivitis (pink eye), asthma, and hives. Ketotifen is available in ophthalmic (eye drops or drug-eluting contact lenses) and oral (tablets or syrup) forms: the ophthalmic form relieves eye itchiness and irritation associated with seasonal allergies, while the oral form helps prevent systemic conditions such as asthma attacks and allergic reactions. In addition to treating allergies, ketotifen has shown efficacy in managing systemic mast cell diseases such as mastocytosis and mast cell activation syndrome (MCAS), which involve abnormal accumulation or activation of mast cells throughout the body. Ketotifen is also used for other allergic-type conditions like atopic dermatitis (eczema) and food allergies.

Ketotifen acts by blocking the H1 histamine receptors, which are found on various cells in the body, such as smooth muscle, endothelium, and nerve cells. This blocking prevents the binding of histamine to these receptors and thus reduces the symptoms of histamine-mediated reactions, such as itching, sneezing, wheezing, and swelling. Ketotifen also prevents the release of histamine and other inflammatory substances from immune cells (mast cells); this action helps reduce symptoms of conditions (including allergic conditions) by blocking the activation of these cells. In addition to its antihistaminic activity, ketotifen also functions as a leukotriene antagonist, which blocks inflammation-causing chemicals known as leukotrienes; it also acts as a phosphodiesterase inhibitor that regulates blood vessel dilation.

Ketotifen can have side effects, including drowsiness, weight gain, dry mouth, irritability, increased nosebleeds when taken orally, and temporary burning or stinging sensations in the eyes when used in the ophthalmic form. Ketotifen has contraindications for individuals with certain medical conditions, such as acute porphyrias or epilepsy. Controversies surrounding ketotifen include its classification as a first-generation or second-generation antihistamine due to varying criteria of classification.

In 2023, it was the 299th most commonly prescribed medication in the United States, with more than 400,000 prescriptions.[6][7]

Medical uses

Ketotifen, an antihistamine medication and a mast cell stabilizer, is most commonly sold as a salt with fumaric acid, ketotifen fumarate, and is available in two forms:

Ketotifen ophthalmic solution (eye drops) relieves and prevents eye itchiness and/or irritation associated with most seasonal allergies. It starts working within minutes after administering the drops. The safety and effectiveness of ketotifen eye drops in children under three years of age have not been established,[12] whereas drug-eluting contact lenses have not been studied in children under eleven years of age.[9]

Drug-eluting contact lenses, which release ketotifen medication, are used to help prevent itchy eyes caused by allergies. The lenses can also correct vision problems, namely, nearsightedness and farsightedness. These lenses are meant for people who don't have red eyes, can comfortably wear contact lenses, and have less than 1 degree of astigmatism.[9]

Oral ketotifen is used to treat asthma, allergic rhinitis, allergic conjunctivitis, atopic dermatitis, chronic urticaria (hives), cold-induced urticaria, cholinergic urticaria, and exercise-induced urticaria.[16][13] It is also used for systemic mast cell diseases such as mastocytosis and mast cell activation syndrome (MCAS), as well as allergic and nonallergic anaphylaxis.[14]

As an antihistamine medication, ketotifen acts by blocking the H1 histamine receptors,[11] which are found on various cells in the body, such as smooth muscle, endothelium, and nerve cells.[17] This blocking prevents the binding of histamine to these receptors and thus reduces the symptoms of histamine-mediated reactions, such as itching, sneezing, wheezing,[18][19] and swelling.[20]

As a mast cell stabilizer to treat MCAS, oral ketotifen prevents the release of histamine and other inflammatory substances from mast cells, which are immune cells that react to allergens. Therefore, ketotifen, by blocking a calcium channel essential for mast cell activation,[21] helps reduce symptoms of conditions typically associated with mast cell activation. These conditions include asthma, hay fever, and conjunctivitis. Calcium channels are proteins in mast cell membranes that allow calcium ions to enter the cell, triggering the release of histamine and other inflammatory substances. When these channels open, calcium floods into the cells, causing them to degranulate.[22][23] Ketotifen inhibits calcium influx into cells,[24][25] reducing mast cell degranulation.[21] In Canada, Europe, and Mexico, oral ketotifen is commonly prescribed for these indications (asthma, hay fever, and conjunctivitis caused by mast cell activation).[26][16][13] In patients with MCAS, ketotifen reduces episodes of flushing, gastrointestinal symptoms (such as abdominal pain, diarrhea), respiratory symptoms (such as wheezing), and other systemic manifestations. Treatment plans for MCAS typically involve a combination of medications targeting different aspects of mast cell activation along with lifestyle modifications to minimize triggers.[27]

The maximum antihistamine and mast cell stabilizing effect of oral ketotifen is achieved on long-term administration, and a period of at least 6-12 weeks is necessary for a maximum therapeutic effect to start.[28] The sedation side effect decreases over time during such long-term administration, but the antihistamine and mast cell stabilizing properties persist even if administered for 12 months or longer.[29]

In the United States, the Food and Drug Administration (FDA) has not approved an oral formulation of ketotifen; however, oral ketotifen is available through compounding pharmacies with a prescription. Ketotifen eye drops are approved in the US for people who are at least three years of age.[30] In the EU, oral ketotifen (syrup, tablets, and capsules) is authorized for adult use at the national level by individual member states.[31] In the UK, ketotifen is available as tablets and elixir (liquid).[32]

Oral ketotifen can be used as a long-term control medication for asthma and wheeze in children. It has been shown to improve asthma control by reducing the need for bronchodilators, decreasing symptoms, preventing exacerbations, and reducing the use of rescue oral steroids. Ketotifen is effective when used alone or in combination with other medications and serves as an alternative to inhaled therapy for asthma in children, especially for younger children who may have difficulty using inhalers.[33]

One small study in men found that the mean elimination half-life of oral ketotifen is 12 hours.[34] Besides its anti-histaminic activity, it is also a functional leukotriene antagonist[35] (a medication that blocks the action of leukotrienes, which are chemicals that cause inflammation and narrowing of the airways in some allergic and respiratory conditions)[36][37] and a phosphodiesterase inhibitor[38][39] (a medication that blocks the enzymes that regulate the levels of cAMP and cGMP, which are molecules that control blood vessel dilation and smooth muscle relaxation in the body).[40][41]

• 1) in its ophthalmic form (eye drops or drug-eluting contact lenses),[8][9][10] it is used to treat allergic conjunctivitis;[11][12]
• 2) in its oral form (tablets or syrup), it is used to prevent asthma attacks or anaphylaxis,[13][14] as well as various mast cell and allergy disorders.[15][16]

Contraindications

The eye drops are contraindicated for individuals who have a known hypersensitivity to ketotifen or any other ingredient in the formulation, whereas drug-eluting contact lenses are contraindicated for those who experience irritation from wearing contact lenses. Eye drops are not recommended for use in children under three years of age,[42][43][44] whereas drug-eluting contact lenses are not recommended for children under eleven years of age.[9]

For oral ketotifen, the contraindication is for known hypersensitivity to any component of the product. Caution should be taken on the following conditions:[11]

The use of ketotifen eye drops during pregnancy and lactation is considered safe, as absorption through the eye is limited. It is unlikely to cause any adverse effects in breastfeeding infants after maternal use. To minimize the amount of medication transferred to breast milk when using eye drops, the National Institute of Child Health and Human Development advises to apply pressure on the tear duct near the corner of the eye for at least one minute and remove any excess solution with a tissue.[55] Ketotifen safety when taken via the oral route (tablets or syrup) during pregnancy and lactation remains unknown; therefore, it is not recommended to use ketotifen orally during these periods until sufficient safety data becomes available.[55]

• acute porphyrias[45] (a group of rare disorders that occur when the body cannot make enough of a substance called heme, which is needed for red blood cells to carry oxygen; this causes a build-up of chemicals called porphyrins, which can damage the nerves and the skin). Unlike other histamines, ketotifen appears to be relatively safe in acute porphyria, still, caution should be taken.[46]
• epilepsy (a disorder causing recurrent seizures) - [47] ketotifen may increase the risk of seizures,[48]
• pyloroduodenal obstruction[49][50][42] (a condition where the passage of food from the stomach to the small intestine is blocked by something, such as a muscle, an ulcer, a tumor, or a gallstone),[51][52]
• susceptibility to angle-closure glaucoma[53] (a condition where the iris, the colored part of the eye, bulges and blocks the drainage of fluid from the eye, causing high pressure and damage to the optic nerve, which connects the eye to the brain),[54] and
• urinary retention (inability to urinate).[42]

Side effects

Common side effects of ophthalmic use are eye redness and swelling. Less common are eye discharge, eye discomfort, eye pain, hives, increased itching of eyes, and rash. Ophthalmic use of ketotifen may also cause burning, stinging, or itching of the eyes, blurred vision, or increased sensitivity to light.[43]

Side effects of systemic (oral) use include drowsiness, weight gain (5.0 - 5.4 kg), dry mouth, irritability, and increased nosebleeds.[56] Systemic use of ketotifen may also cause abdominal pain, nausea, vomiting, constipation, diarrhea, headache, dizziness, or fatigue. In rare cases, systemic use of ketotifen may cause serious side effects such as anaphylaxis, liver dysfunction, blood disorders, or seizures. Systemic use of ketotifen may interact with other drugs that cause sedation, such as alcohol, antihistamines, opioids, benzodiazepines, or antidepressants. Systemic use of ketotifen may affect the results of some laboratory tests, such as skin tests for allergies or blood glucose levels.[57]

Overdose

The symptoms of ketotifen overdose are dose-dependent and may vary from mild to severe. The onset of symptoms may be delayed for several hours after ingestion, and the duration of symptoms may last for more than 24 hours.[58][59][60]

The most common symptom of ketotifen overdose is significant sedation. Other symptoms may include confusion, disorientation, agitation, hallucinations, ataxia (impairment of voluntary muscle movement), tremor (involuntary regular muscle contraction), myoclonus (involuntary, irregular muscle twitch), nystagmus (dysfunction of eye movement), dysarthria (poor speech), and slurred speech.[58][59][60]

Other symptoms of ketotifen overdose may include tachycardia (fast, pounding, or irregular heartbeat or pulse), hypotension (low blood pressure), convulsions, hyperexcitability (particularly in children), reversible coma, unusual tiredness or weakness, blurred vision, dizziness or fainting, loss of consciousness.[59][60]

The symptoms of ketotifen overdose may be described according to the affected system of the body. The cardiovascular effects of ketotifen overdose may include tachycardia, hypotension, arrhythmias, and cardiac arrest. The respiratory effects may include respiratory depression, sleep apnea, and pulmonary edema. The gastrointestinal effects may include nausea, vomiting, abdominal pain, diarrhea, and pancreatitis. The renal effects may include acute renal failure and urinary retention. The hepatic effects may include hepatitis and jaundice. The hematologic effects may include anemia, leukopenia, thrombocytopenia, and coagulopathy. The neurologic effects of ketotifen overdose may include convulsions, hyperexcitability, coma, and death. The risk of seizures is higher in children, especially those with a history of epilepsy or febrile seizures. The risk of coma and death is higher in adults, especially those with pre-existing medical conditions or concomitant use of other drugs that cause sedation or lower the seizure threshold.[58][59]

In children, ketotifen overdose may lead to toxic encephalopathy with lifelong health consequences. There was a reported case of an overdose in a 4-month-old boy that led to growth retardation and mental deterioration.[61][62][60]

Interactions

In systemic (oral) administration, ketotifen has the potential to enhance the effects of sedatives, hypnotics, antihistamines, and alcohol. Interactions have been observed between oral ketotifen and oral hypoglycemic agents, antihistamines, and medications with sedative properties.[63][64]

Oral ketotifen may interact with amphetamine and benzphetamine, which may decrease the activities of ketotifen.[65][66]

The concomitant use of oral ketotifen with amifampridine, bupropion, donepezil, and pitolisant is not recommended.[67]

In rare instances, patients who have been administered oral ketotifen with oral antidiabetic agents have exhibited a reversible decrease in thrombocyte count. As such, it is recommended to monitor thrombocyte counts in patients who are concurrently taking oral antidiabetic agents.[63][64]

Systemic use of ketotifen may decrease the effectiveness of benzylpenicilloyl polylysine as a diagnostic agent.[65] Ketotifen may affect the results of some laboratory tests, such as skin tests for allergies or blood glucose levels. Ketotifen may interfere with the skin test reactions by suppressing the histamine response, leading to false-negative results.[65]

Ophthalmic use of ketotifen may interact with contact lenses, as the eye drops may contain preservatives that can be absorbed by soft contact lenses and cause eye irritation.[68]

Pharmacology

Chemistry

A close analogue of ketotifen is pizotifen, which is a tricyclic (having three rings of atoms), benzocycloheptene-based compound with antihistamine properties: the only difference between the structures of the compounds is that the ketotifen molecule has an oxygen atom that pizotifen molecule lacks—ketotifen contains a carbonyl group (C=O) in the central (7-membered) ring while pizotifen contains a methylene group (-CH2-) in that position. In both ketotifen and pizotifen, the spatial restriction and reduced degrees of freedom caused by the rings enable optimal binding to H1 receptors by providing shape complementarity and facilitating specific interactions with amino acid residues within the receptor's binding site, which plays a role in the ability of both drugs to effectively bind and modulate H1 receptors, thereby exerting its antihistamine effects.[107]

History

Ketotifen was patented in 1970 and came into medical use in 1976.[108] Ketotifen was developed and patented by Sandoz Pharmaceuticals (a part of Novartis), a Swiss company.[109][110][111]

Ketotifen was approved for medical use in Canada in December 1990.[1] Ketotifen was approved for medical use in the United States in July 1999.[112] A contact lens with ketotifen was approved for medical use in the United States in 2022.[113][114]

Society and culture

Research

External links