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Promethazine HCl
Promethazine HCl is an antihistamine used to treat a variety of conditions, including allergies, motion sickness, nausea and vomiting, and as a sedative. It is also used to relieve symptoms of hay fever and cold, such as sneezing, runny nose, and itching. Promethazine belongs to the phenothiazine class, which works by blocking histamine receptors to reduce allergy symptoms and dopamine receptors to control nausea and vomiting.
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Frequently Asked Questions
How long does it take for Promethazine HCl to work?
Promethazine typically begins to work within 20 to 60 minutes after administration, depending on the route (oral, rectal, or injectable).
Can Promethazine HCl be used long-term?
While promethazine is effective for short-term relief of symptoms like nausea and allergies, long-term use should be closely monitored due to the risk of side effects like sedation and tardive dyskinesia.
Is Promethazine safe for children?
Promethazine should not be used in children under 2 years old due to the risk of severe respiratory depression. For older children, use should be carefully monitored by a healthcare provider.
Can I take Promethazine with other medications for nausea?
You should always consult your healthcare provider before combining medications. Promethazine may interact with other antiemetics or sedatives, increasing the risk of side effects.
What should I do if I miss a dose of Promethazine HCl?
Take the missed dose as soon as you remember. If it is close to the time of your next dose, skip the missed dose and resume your regular schedule. Do not double up on doses.
Comprehensive Drug Guide
How Does Promethazine HCl Work?
Promethazine blocks histamine H1 receptors, preventing the binding of histamine, which leads to relief from allergy symptoms. Additionally, it blocks dopamine receptors in the brain, helping to control nausea and vomiting. Promethazine also has sedative properties, making it useful for sleep disorders or calming patients before surgery.
Common Dosages
- Tablets: 12.5 mg, 25 mg, 50 mg
- Oral solution: 6.25 mg/5 mL
- Rectal suppositories: 12.5 mg, 25 mg, 50 mg
- Injection: 25 mg/mL, 50 mg/mL
Typical Dosing
- For allergy symptoms: 25 mg at bedtime or 12.5 mg before meals and at bedtime, depending on the severity of symptoms.
- For motion sickness: 25 mg taken 30 to 60 minutes before travel and repeated every 12 hours as needed.
- For nausea and vomiting: 12.5 to 25 mg every 4 to 6 hours as needed.
- For sedation: 25 to 50 mg before surgery or as directed.
Typical Dosing
FDA Approved Indications
- Allergic reactions (e.g., rhinitis, urticaria)
- Motion sickness
- Nausea and vomiting
- Sedation
- Preoperative or postoperative use to reduce nausea or as a calming agent
Who Shouldn't Take Promethazine HCl?
- Hypersensitivity to promethazine or other phenothiazines
- Severe respiratory depression in pediatric patients younger than 2 years of age
- Comatose states
Advice From The Pharmacist
- Promethazine can cause drowsiness, so avoid activities that require mental alertness, such as driving or operating heavy machinery.
- Take the medication exactly as prescribed by your healthcare provider, and avoid alcohol, as it can enhance sedative effects.
- If using rectal suppositories, store them in a cool place and follow instructions carefully when inserting.
- If you experience symptoms such as confusion, severe dizziness, or difficulty breathing, contact your healthcare provider immediately.
Side Effects of Promethazine HCl
Common Side Effects
- Drowsiness
- Dizziness
- Dry mouth
- Blurred vision
- Constipation
Uncommon/Severe Side Effects
- Severe allergic reactions (e.g., rash, swelling, difficulty breathing)
- Neuroleptic malignant syndrome (fever, muscle rigidity, altered mental status)
- Severe respiratory depression (especially in children under 2 years old)
Risks and Warnings of Promethazine HCl
- Respiratory Depression: Promethazine can cause severe breathing problems in children under 2 years old, so it is contraindicated in this population.
- Sedation: The sedative effects of promethazine can be profound, particularly when combined with alcohol or other sedatives, leading to impaired motor skills or extreme drowsiness.
- Neuroleptic Malignant Syndrome: Although rare, promethazine can cause a life-threatening condition known as neuroleptic malignant syndrome, characterized by fever, muscle stiffness, and confusion.
Interactions with Promethazine HCl
Common Drug Interactions
- CNS depressants (e.g., alcohol, opioids, benzodiazepines): These can enhance the sedative effects of promethazine, increasing the risk of severe drowsiness and respiratory depression.
- Anticholinergic drugs: Promethazine can increase side effects like dry mouth, constipation, and urinary retention.
- MAO inhibitors: These can increase the risk of severe side effects, including serotonin syndrome.
Common Food Interactions
Alternatives to Promethazine HCl
- Meclizine (Antivert®): Used for motion sickness and nausea, with less sedative effect than promethazine.
- Ondansetron (Zofran®): A non-phenothiazine antiemetic used for nausea and vomiting, particularly in chemotherapy patients.
- Diphenhydramine (Benadryl®): Another antihistamine used for allergy relief and sedation, often available over-the-counter.
