methdilazine

Action and Spectrum

Actions and Spectrum: 

methdilazine is an antihistamine medication used to treat various allergic conditions, such as hay fever, allergic rhinitis, and allergic skin reactions. It belongs to the first-generation H1 receptor antagonists class, also known as “sedating antihistamines.” methdilazine primarily works by blocking the effects of histamine. By blocking histamine’s action, methdilazine helps to alleviate allergy symptoms. 

• Antihistamine Action: methdilazine competes with histamine for binding to H1 receptors on target cells. Binding to these receptors prevents histamine from exerting its effects, thus reducing symptoms like itching, sneezing, runny nose, and watery eyes commonly associated with allergies. 
• Sedation: One notable characteristic of first-generation antihistamines like methdilazine is their sedative effect. They can cross the BBB (blood-brain barrier) more readily than second-generation antihistamines, which can lead to drowsiness and sedation. This sedative effect is often utilized in over-the-counter sleep aids. 
• Anticholinergic Effects: methdilazine, like other first-generation antihistamines, can have anticholinergic effects. This means it can inhibit the activity of the neurotransmitter acetylcholine in central and peripheral nervous systems. This can result in dry mouth, dry eyes, constipation, and urinary retention, among other potential side effects. 
• Allergy Symptom Relief: By blocking the effects of histamine, methdilazine helps reduce or alleviate the symptoms associated with allergies, such as itching, redness, inflammation, sneezing, and nasal congestion. 

Drug Interaction

Adverse Reaction

Frequency not defined 

Drowsiness 

Paradoxical excitation 

Giddiness 

Headache 

CNS depression 

Urinary retention  

Menstrual disorders 

Dry mouth  

Constipation 

Blood dyscrasias 

Jaundice 

Asthma 

Black Box Warning

Black Box Warning: 

None 

Contraindication / Caution

Contraindication/Caution: 

Contraindication 

• Hypersensitivity: Individuals with a known hypersensitivity or allergy to methdilazine or its components should not use the medication. Allergic reactions can range from mild skin reactions to severe anaphylactic reactions. 
• Narrow-Angle Glaucoma: methdilazine, like other antihistamines with anticholinergic effects, can potentially worsen narrow-angle glaucoma, which affects the eyes. It can increase intraocular pressure and lead to complications. Individuals with narrow-angle glaucoma should avoid methdilazine. 
• Prostate Hypertrophy: methdilazine’s anticholinergic effects can interfere with urinary function, particularly in individuals with prostate hypertrophy (enlarged prostate). It may exacerbate urinary retention and related symptoms. 
• Urinary Retention: Individuals with a history of urinary retention or bladder neck obstruction should not use methdilazine due to its potential to worsen these conditions. 
• Severe Central Nervous System Depression: methdilazine’s sedative effects can be potentiated when taken in conjunction with other central nervous system depressants, such as alcohol, sedatives, tranquilizers, and certain medications used for anxiety or sleep disorders. Combining these substances can lead to excessive drowsiness, impaired coordination, and other adverse effects. 
• Monoamine Oxidase Inhibitors (MAOIs): There is a potential interaction between methdilazine and MAOIs, a class of antidepressant medications. Combining these drugs can lead to serious adverse effects, such as hypertensive crisis. 
• Newborns and Premature Infants: methdilazine is generally not suggested for use in newborns and premature infants due to their susceptibility to sedative effects and potential adverse reactions. 
• Pregnancy and Breastfeeding: Using methdilazine during pregnancy and breastfeeding is generally not advised without careful consideration and supervision by a healthcare provider.  
• Elderly Patients: Elderly individuals may be more susceptible to methdilazine’s sedative and anticholinergic effects.  
• Certain Medical Conditions: Individuals with certain medical conditions, such as epilepsy, asthma, peptic ulcer disease, cardiovascular disease, and liver disease, may require close monitoring or adjustment of the dosage when taking methdilazine. 

Caution 

• Sedation: methdilazine is known to cause drowsiness and sedation, particularly in higher doses. Individuals taking methdilazine should exercise caution when driving, operating machinery/engaging in activities that require mental alertness until they know how the drug affects them. 
• Central Nervous System Effects: In addition to sedation, methdilazine can cause other central nervous system effects, including dizziness, confusion, and impaired coordination. Elderly individuals and those taking other sedative medications are at a greater risk of experiencing these effects. 
• Alcohol and Other Depressants: Combining methdilazine with alcohol or other central nervous system depressants can intensify the sedative effects and increase impairment. It’s advisable to avoid alcohol and consult a healthcare provider before using other medications that may interact with methdilazine. 
• Anticholinergic Effects: methdilazine’s anticholinergic effects can lead to dry mouth, blurred vision, urinary retention, and also constipation. Individuals should stay hydrated, use lubricating eye drops if needed, and address any discomfort caused by these effects. 
• Glaucoma: methdilazine can increase intraocular pressure and worsen glaucoma. Individuals with a history of glaucoma or increased intraocular pressure should use methdilazine cautiously and under the guidance of an eye specialist. 
• Prostate Enlargement: Men with prostate enlargement (benign prostatic hyperplasia) should be cautious when using methdilazine due to the risk of exacerbating urinary symptoms. 
• Children and the Elderly: Children and older adults may be more sensitive to the effects of methdilazine. Careful dosing and monitoring are essential in these populations. 
• Allergic Reactions: Allergic reactions to methdilazine can occur, although rare. If you experience any signs of an allergic reaction, like rash, itching, swelling, severe dizziness, or difficulty breathing, seek medical attention immediately. 
• Pregnancy and Breastfeeding: The use of methdilazine during pregnancy and breastfeeding should be discussed with a healthcare provider.  
• Underlying Medical Conditions: Individuals with certain medical conditions, such as cardiovascular disease, epilepsy, and liver impairment, should use methdilazine cautiously and under medical supervision. 
• Long-Term Use: Prolonged use of methdilazine can lead to tolerance and reduced effectiveness. Using methdilazine for short periods is generally recommended to manage acute symptoms. 

Pregnancy / Lactation

Pregnancy consideration:  

US FDA pregnancy category: Not assigned. 

Lactation:   

Excreted into human milk: Not known. 

Pregnancy category: 

• Category A: well-controlled and Satisfactory studies show no risk to the fetus in the first or later trimester. 
• Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women. 
• Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.    
• Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.    
• Category X: Drugs listed in this category outweigh the risks over benefits. Hence, these categories of drugs need to be avoided by pregnant women.    
• Category N: There is no data available for the drug under this category. 

Pharmacology

Pharmacology: 

methdilazine is a first-generation H1 receptor antagonist, or antihistamine, with pharmacological actions centered on blocking the effects of histamine at H1 receptors. By competitively binding to these receptors on target cells, it inhibits histamine-mediated responses, thus mitigating symptoms like sneezing, runny nose, and watery eyes characteristic of allergic reactions.

Notably, methdilazine possesses sedative and anticholinergic properties due to its ability to cross the BBB (blood-brain barrier) and influence central and peripheral cholinergic pathways, which can result in drowsiness, dry mouth, blurred vision, and other related effects. 

Pharmacodynamics: 

Mechanism of action: methdilazine is a first-generation antihistamine, and its mechanism of action is centered around its ability to block the effects of the histamine at H1 receptors.  

• Histamine Release in Allergic Reactions: When the body encounters an allergen, such as pollen or pet dander, mast cells, and basophils release histamine as part of the immune response. Histamine binding to H1 receptors on various cells leads to the characteristic symptoms of allergies, like sneezing, runny nose, and watery eyes. 
• Antagonism of H1 Receptors: methdilazine is an H1 receptor antagonist, which competes with histamine for binding to H1 receptors on target cells. By binding to these receptors, methdilazine prevents histamine from attaching to and activating them. 
• Blockade of Histamine Effects: When methdilazine occupies the H1 receptors, histamine cannot bind to them. As a result, the histamine-mediated responses that lead to allergy symptoms are inhibited. This blockade of H1 receptors reduces itching, sneezing, nasal congestion, and other allergic reactions. 
• Sedative and Anticholinergic Effects: methdilazine’s action is not limited to H1 receptors. It can also interact with other receptors, leading to its sedative and anticholinergic effects. methdilazine can cross the blood-brain barrier and bind to central nervous system receptors, contributing to its drowsiness-inducing properties. Additionally, its anticholinergic activity can lead to dry mouth, blurred vision, and constipation. 

Pharmacokinetics: 

Absorption 

methdilazine is usually administered orally as tablets or syrup. It is generally absorbed from the gastrointestinal tract after oral administration. The onset of action is relatively quick, usually within 1 to 2 hours. 

Distribution 

After absorption, methdilazine is distributed throughout the body via the bloodstream. It can cross the BBB (blood-brain barrier), leading to its sedative effects. The drug’s distribution into tissues contributes to its antihistamine and other pharmacological actions. 

Metabolism 

methdilazine undergoes hepatic (liver) metabolism. It is metabolized by enzymes in the liver, primarily via N-demethylation and hydroxylation pathways. The metabolites formed are typically less active than the parent compound but can still contribute to pharmacological and potential side effects. 

Elimination and Excretion 

The elimination of methdilazine and its metabolites occurs primarily through the kidneys. They are excreted in the urine. The elimination half-life of methdilazine can vary among individuals but is generally in the range of 4 to 8 hours. 

Adminstartion

Administration: 

methdilazine is typically available in tablets or oral syrup, and its administration should be done according to the instructions which is provided by a healthcare professional/as indicated on the medication label.  

• Dosage: The dosage of methdilazine can vary based on factors such as the individual’s age, weight, medical condition, and the formulation of the medication (tablet or syrup). A healthcare provider will determine the recommended dosage, which should be followed precisely. 
• Frequency: methdilazine is usually taken 2 to 4 times a day, depending on the severity of the symptoms and the specific formulation. The healthcare professional will provide the dosing schedule. 
• Timing: methdilazine can be taken with or without food. Although, taking it with food may help diminish stomach discomfort that can sometimes occur. 
• Tablets: If you use methdilazine tablets, swallow them whole with water.  
• Oral Syrup: If you are using methdilazine oral syrup, measure the prescribed amount using a measuring device that comes with the medication. Avoid using household teaspoons, as they may not provide accurate measurements. 
• Duration of Use: methdilazine is often used for short-term relief of allergic symptoms. It’s important to follow your healthcare provider’s prescribed duration of use. Long-term use can lead to diminished effectiveness and potential side effects. 
• Missed Dose: If a dose is missed, taking it as soon as possible is generally recommended. However, if the next scheduled dose is missed, it should be skipped and the following dose should be taken at the appropriate time. It is key to avoid taking a double dose of the drug in order to compensate for the missed dose. 
• Special Instructions: If your healthcare provider has given you specific instructions or precautions, such as taking the medication at a particular time or avoiding certain foods or beverages, follow them. 
• Storage: Store methdilazine tablets or syrup according to the storage instructions provided on the packaging.  
• Discontinuation: Avoid taking methdilazine abruptly without consulting your healthcare provider. They may recommend tapering the dose gradually to prevent any potential withdrawal symptoms or adverse effects. 
• Medical Monitoring: Regular follow-up appointments with your healthcare provider may be necessary to monitor your response to the medication, adjust the dosage if needed, and assess any potential side effects. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: methdilazine 

Why do we use methdilazine? 

methdilazine is an antihistamine medication that treats various allergic conditions and associated symptoms. Its primary use is to alleviate the discomfort caused by allergic reactions and to provide relief from symptoms related to histamine release.  

• Allergic Rhinitis: methdilazine is often used to treat allergic rhinitis and inflammation of nasal passages caused by allergens like pollen, dust mites, or pet dander. It can help relieve symptoms like sneezing, runny nose, nasal congestion, and itching. 
• Hay Fever: Hay fever, also known as seasonal allergic rhinitis, occurs during specific seasons when certain plants release pollen into the air. methdilazine can be used to manage hay fever symptoms, including sneezing, nasal congestion, and itchy or watery eyes. 
• Urticaria (Hives): methdilazine can provide relief from itching, redness, and swelling associated with urticaria, which is characterized by raised, itchy welts on the skin. It is commonly used for acute episodes of hives. 
• Allergic Skin Reactions: methdilazine can help alleviate itching and discomfort caused by allergic reactions that affect the skin, such as contact dermatitis or insect bites. 
• Conjunctivitis: methdilazine can be used to manage the symptoms of allergic conjunctivitis, which is inflammation of the conjunctiva. Symptoms may include redness, itching, and watery eyes. 
• Pruritus (Itching): Itching caused by various allergic or inflammatory conditions can be relieved with methdilazine, helping to reduce discomfort and prevent scratching that could worsen the condition. 
• Other Allergic Symptoms: methdilazine may also be prescribed to address other allergic symptoms, such as itching, sneezing, and runny nose, resulting from exposure to allergens.