In addition to oral dosage forms, antihistamines come as creams, lotions, nasal sprays, and eye drops; the latter to relieve symptoms associated with allergic conjunctivitis.Other types of allergy drugs include: Corticosteroids: These come as nasal sprays, topical creams and ointments, tablets, injectables and eye preparations. Mast cell stabilizers: These can help prevent allergic reactions from happening when taken regularly.A 1985 review of antihistamine pharmacokinetics found that the elimination half-life of diphenhydramine ranged between 3.4 and 9.3 hours across five studies, with a median elimination half-life of 4.3 hours. Analogues of diphenhydramine include orphenadrine, an anticholinergic, nefopam, an analgesic, and tofenacin, an antidepressant.
Antihistamines used to treat allergy symptoms fall into two broad categories: sedating and non-sedating.
Allergies occur when the body's immune system responds to a substance it considers an "invader." Substances that provoke the immune system into an allergic response are known as allergens. What might trigger a life-threatening allergic response in one person might cause absolutely no harm in another.
The physiological mechanism of allergic reactions is the same, however, in everyone.
Diphenhydramine is a first-generation antihistamine used to treat a number of conditions including allergic symptoms and itchiness, the common cold, insomnia, motion sickness, and extrapyramidal symptoms.
Topical formulations of diphenhydramine are available, including creams, lotions, gels, and sprays.