Diphenhydramine HCl Facts

Diphenhydramine hydrochloride (HCl) is an antihistamine that has drying (anticholinergic) and sedative or sleep-inducing effects. It works by battling histamine for receptor sites in affected cells. Diphenhydramine HCl is a white, crystalline, odorless powder that is soluble in both alcohol and water. It is used to treat all types of allergic reactions, as well as motion sickness, Parkinson's disease and sleeping problems. However, diphenhydramine HCl can produce a number of potential side effects, and may interact adversely with other drugs.

Uses

• Diphenhydramine HCl is used primarily to treat allergic reactions or conjunctivitis caused by food, reactions to blood or plasma transfusions, skin reactions such as angioedema and urticaria, dermatographism (or hives: red itchy, irritating bumps) and antigen-induced anaphylactic reactions that are extremely severe.

  It is also used to treat motion sickness, both actively and preventively, and to treat Parkinson's disease, including drug-induced Parkinson's disease. Diphenhydramine HCl is a gentler alternative to harsher Parkinson's medications, and is used primarily by elderly individuals and individuals with mild symptoms. The drug can also be used to aid in sleep.

Dosage

• The specific dosage of diphenhydramine HCl a patient should take varies on a case-by-case basis. According to drugs.com, in general, adults should take 25 to 50 milligrams, three to four times daily. If it is being used as a sleep-aid, an individual should take 50 milligrams before going to sleep. For children over 20 pounds in weight, drugs.com recommends a dosage of 12.5 or 25 milligrams three or four times daily. In no cases should the daily maximum dosage exceed 300 milligrams.

Duration

• Diphenhydramine HCl is most often administered orally and is absorbed quickly into the body. The most activity occurs generally an hour after the drug has been taken. The average dose of diphenhydramine HCl is effective for between four and six hours. The drug is distributed widely throughout the body, including the central nervous system. In general, diphenhydramine HCl completely disappears from the body 24 hours after it is administered.

Precautions

• According to drugs.com, newborns, nursing mothers and individuals with narrow-angle glaucoma, bladder obstructions, peptic ulcers or prostatic hypertrophy should not use diphenhydramine HCl. Patients who have had lower respiratory diseases like asthma, hyperthyroidism, increased intraocular pressure, hypertension or cardiovascular disease should use the drug with caution. Diphenhydramine HCl has been known to interact with alcohol, MAO inhibitors and depressants like tranquilizers and hypnotics.

Reactions

• The most common adverse reactions to diphenhydramine HCl include rash, excessive sweating, urticaria, anaphylactic shock, chills, photosensitivity, and dryness of the nose, throat and mouth. The drug can also cause cardiovascular problems like hypotension and palpitations, hematologic problems like anemia and thrombocytopenia, nervous system problems like dizziness and confusion, and respiratory problems like wheezing and bronchial secretions.