PROMETHAZINE

Promethazine is a phenothiazine antihistamine.

Mechanism of action

• Promethazine antagonizes the central and peripheral effects of histamine medicated by histamine H, receptors,
• Antihistamines competitively antagonize most of the smooth muscle stimulating actions of histamine on the Hi receptors of the gastrointestinal tract, uterus, large blood vessels, and bronchial muscle. Increased capillary permeability and edema formation, flare, and pruritus, resulting from actions of histamine on H, receptors, are also effectively antagonized.
• Promethazine appears to act by blocking H; receptor sites, preventing the action of histamine on the cell.
• Promethazine rapidly crosses the blood-brain barrier and it is thought that the sedative effects of antihistamines are due to the blockade of H_{1} receptors in the brain
• The antiemetic effect of promethazine may be due to the blockade of dopaminergic receptors in the Chemoreceptor Trigger Zone (CTZ) of the medulla.

Indication:

• Symptomatic treatment of various allergic conditions, including itching, sneezing, itchy skin rashes, etc.
• Nausea & vomiting
• Motion sickness
• Analgesic adjunct for control of postoperative pain, anesthetic adjunct
• Sedation

Dose

1. Adults

• Hypersensitivity reactions: PO:25mg to 50mg as a single dose at night; or
• Up to 60mg per day in divided doses.
• Hypnotic (hydrochloride): 20 mg hs (PO)
• Nausea and vomiting (hydrochloride, theoclate: Up to 25 mg tid/qid (po)
• All indications except nausea and vomiting (hydrochloride):IM,IV, 25 to 50 mg (Maximum of 100 mg per 24 hours)
• Nausea and vomiting (hydrochloride): 12.5 to 25 mg every 4 hours (Maximum 100mg/24 hours) IM/IV.

Children:

• Hypersensitivity reactions (hydrochloride)
  • 2 to 5 years 5 to 15 mg daily (po).
  • 5 to 10 years 10 to 25 mg daily (po).
     
• Hypnotic (hydrochloride)

  • 2 to 5 years 15 to 20 mg hs (po).

  • 5 to 10 years 20 to 25 mg hs (po)
     

• Motion sickness(hydrochloride)

  • 2 to 5 years 5 mg (po).

  •  

    5 to 10 years 10 mg (po).
     

• Motion sickness(theoclate)
  • 5 to 10 years 12.5 mg (po).

• All indications (hydrochloride)
  • 5 to 10 years 6.25 to 12.5 mg

Contraindication

• Narrow-angle glaucoma, premature & term infants,stenosing peptic ulcer, pyloroduodenal obstruction, paralytic ileus, prostatic hypertrophy, bladder neck obstruction, epilepsy, bone marrow depression, Reye's syndrome, encephalopathy, hepatic diseases.

Side effect

• CNS depression, sedation, confusion, fatigue, excitation, irregular respiratory depression, extrapyramidal reactions, dystonia, blurred apnea, vision, dry mouth, GI upset, constipation, hypotension, tinnitus, tachycardia

Nursing consideration

• The potential for gastric distress can be reduced when an oral dosage is taken with food, milk, or a full glass of water.
• Injections administered intramuscularly (IM) should be made deep into significant muscle mass. Substitute injection locations and monitor regularly.
• The effect might be a sedative. The patient should refrain from driving or engaging in other potentially hazardous activities until a response to medicine is determined.
• Keep an eye on the lung capacity of patients, especially young ones, who are experiencing breathing difficulties.
• Take the first dosage 30-60 minutes before you leave, and repeat every 8-12 hours as necessary.