Usage
-
Medical Conditions: Methdilazine is prescribed for the symptomatic relief of pruritus (itching) associated with various dermatoses (skin conditions) like urticaria (hives), eczema, and allergic reactions. It can also alleviate allergic symptoms like sneezing, runny nose, and itchy eyes associated with hay fever (allergic rhinitis). Additionally, it may be used to prevent and treat motion sickness and as a mild sedative for nausea, vomiting, and dizziness.
-
Pharmacological Classification: Methdilazine is classified as a first-generation phenothiazine antihistamine with anticholinergic properties.
-
Mechanism of Action: Methdilazine primarily acts as an H1 receptor antagonist, blocking the action of histamine, a chemical mediator responsible for allergic symptoms. Its anticholinergic properties contribute to its efficacy in treating motion sickness by inhibiting muscarinic receptors in the brain’s vomiting center.
Alternate Names
- International/Other Brands: Dilosyn, Tacaryl, Anergan, Antinaus, Histantil, Panectyl, Pentazine, Phenazine, Phencen, Phenergan, Phenerzine, Phenoject, Pro-Med, Promacot, Promet, Prorex, Prothazine, Shogan, Tacazyl, Tacryl, Temaril, V-Gan-25.
How It Works
-
Pharmacodynamics: Methdilazine binds to H1 receptors, preventing histamine from binding and exerting its effects like itching, vasodilation, and increased mucus production. Its anticholinergic action inhibits the effects of acetylcholine, reducing smooth muscle contractions and glandular secretions. It also crosses the blood-brain barrier, resulting in sedative effects.
-
Pharmacokinetics:
- Absorption: Methdilazine is well-absorbed after oral administration.
- Metabolism: Primarily metabolized in the liver.
- Elimination: Excreted primarily through the kidneys and bile.
-
Mode of Action: Competitive antagonism at histamine H1 receptors and muscarinic receptors.
-
Receptor Binding, Enzyme Inhibition, or Neurotransmitter Modulation: Binds to H1 and muscarinic receptors.
Dosage
Standard Dosage
Adults:
- 8-16 mg orally, two to four times daily.
Children:
- Dosage is based on the child’s weight and age and should be determined by a physician. Typically lower than adult doses.
Special Cases:
- Elderly Patients: Start with the lowest dose and increase cautiously as needed, monitoring for side effects.
- Patients with Renal Impairment: Dose adjustment is necessary in patients with severe renal impairment.
- Patients with Hepatic Dysfunction: Caution is advised; dose adjustment may be required.
- Patients with Comorbid Conditions: Use with caution in patients with glaucoma, prostatic hypertrophy, cardiovascular disease, asthma, or other respiratory disorders. Close monitoring and dose adjustment may be needed.
Clinical Use Cases
Specific dosage recommendations for clinical settings like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations are not well-established and should be determined by a physician based on the individual patient’s needs.
Dosage Adjustments
Dose adjustments are necessary for patients with renal or hepatic impairment, and patients with certain comorbid conditions. Genetic polymorphisms affecting drug metabolism should be considered.
Side Effects
Common Side Effects
- Drowsiness
- Dry mouth
- Dizziness
- Blurred vision
- Constipation
- Headache
- Gastrointestinal disturbances (nausea, vomiting)
Rare but Serious Side Effects
- Confusion
- Hallucinations
- Seizures
- Cardiac arrhythmias
- Difficulty urinating
- Allergic reactions (rash, itching, swelling)
Long-Term Effects
- Potential for tardive dyskinesia with prolonged use.
Adverse Drug Reactions (ADR)
- Severe allergic reactions (anaphylaxis)
- Neuroleptic malignant syndrome
Contraindications
- Hypersensitivity to methdilazine or other phenothiazines.
- Narrow-angle glaucoma
- Urinary retention
- Gastrointestinal obstruction
- Paralytic ileus
- Newborn infants
Drug Interactions
- CNS depressants: Alcohol, barbiturates, benzodiazepines – Increased sedation and risk of respiratory depression.
- Anticholinergic drugs: Antidepressants, antipsychotics, medications for Parkinson’s disease – Exacerbated anticholinergic side effects.
- MAOIs: Prolonged and intensified anticholinergic effects.
- Other: Consult a drug interaction checker for a comprehensive list of potential interactions, as methdilazine has many reported drug interactions.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: C (Consult a doctor if pregnant or planning pregnancy.)
- Fetal Risks: Limited data available. Potential for fetal harm.
- Breastfeeding: Limited information available. Potential for neonatal exposure. Consult a doctor if breastfeeding.
- Safer Alternatives: Discuss safer alternatives with a doctor.
Drug Profile Summary
- Mechanism of Action: H1 receptor antagonist, anticholinergic.
- Side Effects: Drowsiness, dry mouth, blurred vision, dizziness, constipation.
- Contraindications: Hypersensitivity, narrow-angle glaucoma, urinary retention, GI obstruction, newborns.
- Drug Interactions: CNS depressants, anticholinergic drugs, MAOIs.
- Pregnancy & Breastfeeding: Consult a doctor.
- Dosage: 8-16 mg orally, two to four times daily (adults). Pediatric dosage adjusted based on weight/age.
- Monitoring Parameters: Monitor for side effects, especially in elderly patients.
Popular Combinations
Information on popular drug combinations is not consistently documented. Combining methdilazine with other medications requires careful consideration of potential interactions.
Precautions
- General Precautions: Screen for allergies, existing medical conditions, and concurrent medications.
- Specific Populations: See “Special Cases” under Dosage.
- Lifestyle Considerations: Avoid alcohol. Caution with driving or operating machinery due to potential drowsiness and blurred vision.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Methdilazine?
A: 8-16 mg orally, two to four times daily for adults. Pediatric dosage is adjusted based on weight and age.
Q2: What are the common side effects of Methdilazine?
A: Drowsiness, dry mouth, dizziness, blurred vision, constipation, headache, gastrointestinal disturbances.
Q3: Is Methdilazine safe to use during pregnancy?
A: Pregnancy Safety Category C. Consult a doctor before use during pregnancy.
Q4: Can I take Methdilazine while breastfeeding?
A: Limited information available. Consult a doctor before use during breastfeeding.
Q5: What are the serious side effects of Methdilazine?
A: Confusion, hallucinations, seizures, cardiac arrhythmias, difficulty urinating, allergic reactions.
Q6: What medications should be avoided while taking Methdilazine?
A: CNS depressants, anticholinergic drugs, MAOIs. Consult a drug interaction checker for a comprehensive list.
Q7: What conditions is Methdilazine contraindicated in?
A: Hypersensitivity, narrow-angle glaucoma, urinary retention, GI obstruction, paralytic ileus, newborns.
Q8: How does Methdilazine work?
A: It’s an H1 receptor antagonist and anticholinergic agent, blocking histamine’s effects and reducing allergic symptoms and motion sickness.
Q9: Can Methdilazine be used in children?
A: Yes, but the dosage must be adjusted based on weight and age. It’s not recommended for newborns.
Q10: Does Methdilazine interact with alcohol?
A: Yes, alcohol can increase the sedative effects of Methdilazine. It’s best to avoid alcohol while taking this medication.
