Drug information of Promethazine

Promethazine

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Promethazine is used to relieve or prevent the symptoms of hay fever, allergic conjunctivitis (inflammation of the eye), and other types of allergy or allergic reactions.

Mechanism of effect

Like other H1-antagonists, promethazine competes with free histamine for binding at H1-receptor sites in the GI tract, uterus, large blood vessels, and bronchial muscle.
The relief of nausea appears to be related to central anticholinergic actions and may implicate activity on the medullary chemoreceptor trigger zone.

Pharmacodynamic

Promethazine is an antihistamine and works by blocking a certain natural substance (histamine) that your body makes during an allergic reaction. Its other effects (such as anti-nausea, calming, pain relief) may work by affecting other natural substances (such as acetylcholine) and by acting directly on certain parts of the brain.
it is a phenothiazine , an H1-antagonist with anticholinergic, sedative, and antiemetic effects and some local anesthetic properties. Promethazine is used as an antiemetic or to prevent motion sickness.

Pharmacokinetics

On average, 88% of a promethazine dose is absorbed after oral administration; however, the absolute bioavailability is only 25% because of first-pass clearance. Promethazine hydrochloride is metabolized in the liver. Its half life is 16 to 19 hours.

Drug indications

Rhinorrhea , Motion sickness

Dosage

Adults
Usual Adult Dose for Allergic Reaction, Allergic Rhinitis,Anaphylaxis,Urticaria :
6.25 to 12.5 mg orally or rectally before meals and at bedtime, if necessary, OR 25 mg orally or rectally once a day at bedtime
Parenteral: 25 mg IM or IV once, and may be repeated within 2 hours if necessary
Usual Adult Dose for Light Sedation :
25 to 50 mg orally or rectally once
Parenteral :
-Early stages of labor: 50 mg IM or IV once
-Nighttime sedation: 25 to 50 mg IM or IV once
Usual Adult Dose for Motion Sickness :
Treatment :
25 mg orally, or rectally once, then 12.5 to 25 mg every 4 to 6 hours as needed
Parenteral : 12.5 to 25 mg IM or IV every 4 hours as needed
Prophylaxis :
-Initial day: 25 mg orally or rectally 30 to 60 minutes before traveling, then 8 to 12 hours as needed
Usual Adult Dose for Nausea/Vomiting :
Treatment: 12.5 to 25 mg IM, IV, orally, or rectally every 4 hours as needed
Prophylaxis:25 mg orally every 4 to 6 hours as needed
Pediatrics
Usual Pediatric Dose for Allergic Reaction :
2 years and older :
6.25 to 12.5 mg orally or rectally before meals and at bedtime, as necessary OR 25 mg orally or rectally once a day at bedtime
Usual Pediatric Dose for Motion Sickness:
Treatment and prevention:
12.5 to 25 mg orally or rectally 2 times a day
Usual Pediatric Dose for Nausea/Vomiting(2 years and older):
Treatment:
1.1 mg/kg orally or rectally every 4 to 6 hours as needed
(Maximum dose: 25 mg)
Parenteral: 6.25 to 12.5 mg IM or IV every 4 hours as needed
Prophylaxis: Up to 25 mg orally or rectally every 4 to 6 hours as needed
Usual Pediatric Dose for Sedation(2 years and older) :
Preoperative medication: 1.1 mg/kg IM, IV, orally, or rectally once.

Alerts

Promethazine should not be given to a child younger than 2 years old it can cause severe breathing problems or death in very young children .
• You should not take this medicine if you are allergic to promethazine or to similar medicines( to any other phenothiazines such as chlorpromazine).
• Before using this medication, tell your doctor or pharmacist if you have :
• asthma, chronic obstructive pulmonary disease (COPD), sleep apnea, or other breathing disorder ;a history of seizures; a weak immune system (bone marrow depression); glaucoma; enlarged prostate or problems with urination; stomach ulcer or obstruction; heart disease or high blood pressure; liver disease; adrenal gland tumor (pheochromocytoma); low levels of calcium in your blood (hypocalcemia).

Points of recommendation

Promethazine is often taken at bedtime or before meals.
• For motion sickness, promethazine is usually started within 1 hour before traveling.
• When used for surgery, promethazine is usually taken the night before the surgery.
• Stop using promethazine and call your doctor at once if you have twitching or uncontrollable movements of your eyes, lips, tongue, face, arms, or legs. These could be early signs of dangerous side effects.

Drug contraindications

bowel obstruction , angle-closure glaucoma

Pregnancy level

C

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