DIPHENHYDRAMINE
Place in Therapy
Place in Therapy
Diphenhydramine is a first generation antihistamine that is considered second line for the treatment of mild urticaria, including insect bites and stings1. There is limited available evidence regarding the effectiveness of both first and second-generation antihistamines for the treatment of acute urticaria2,3. There is even less evidence comparing the effectiveness of first and second generation antihistamines head to head for the treatment of acute urticaria. Most recommendations concerning treatment for mild urticaria are extrapolated from the primary literature regarding the treatment of chronic urticaria and experimentally histamine induced wheals. Based on this evidence, the expert consensus is that diphenhydramine and second-generation antihistamines provide similar efficacy in the treatment of allergic reactions, including mild urticaria3,4,5.
Although diphenhydramine is considered to be as effective as second generation antihistamines, it is not considered first line treatment for mild urticaria due to its’ side effect profile1,2. First generation antihistamines, including diphenhydramine, tend to cause more sedation and anticholinergic side effects compared to second generation antihistamines1,2,6. Diphenhydramine has been found to impair psychomotor performance and cognitive function after administration of doses equal to or greater than 50mg. The drowsiness and central nervous system effects caused by diphenhydramine are attributed to the blockade of central histaminergic receptors and antagonism of other brain receptors (Ex. serotonergic, cholinergic, and central alpha-adrenergic)2. Second generation antihistamines, on the other hand, exhibit limited transfer across the blood brain and are associated with fewer side effects. There are a few cases where you might consider diphenhydramine first line for the treatment of mild urticaria including cases where patients are experiencing significant itching that keeps them up at night. In this case you might consider starting with a dose of diphenhydramine before bed1.
References:
1. Regier L, Jensen B, Downey S et al. OTC (Over-The-Counter) Products: Allergy-systemic. RxFiles. 2013. Available at: <http://www.rxfiles.ca/rxfiles/uploads/documents/members/CHT-OTCs.pdf >. Accessed June 4, 2014.
2. Banerji A, Long A, Camargo C. Diphenhydramine versus non-sedating antihistamines for acute allergic reactions: A literature review. Allergy and Asthma Proceedings. 2007. 28:418-426.
3. Alper BS. SOAP: Solutions to often asked problems. Choice of antihistamines for urticaria. Archives of Family Medicine. 2000. 9(8): 748-751.
4. Bernstein J, Lang D, Khan D et al. The diagnosis and management of acute and chronic urticaria: 2014 update. Journal of Allergy and Clinical Immunology. 133(5): 1270-1277.
5. Pontasch M, White L, Bradfore J. Oral agents in the management of urticaria: patient perception of effectiveness and level of satisfaction with treatment. Annals of Pharmacotherapy. 1993. 27(6):730-731
6. Grant J, Bernstein D, Buckley C, et al. Double-blind comparison of terfenadine, chlorpheniramine, and placebo in the treatment of chronic idiopathic urticaria. Journal of Allergy and Clinical Immunology. 1988;81:574-579.
Diphenhydramine is a first generation antihistamine that is considered second line for the treatment of mild urticaria, including insect bites and stings1. There is limited available evidence regarding the effectiveness of both first and second-generation antihistamines for the treatment of acute urticaria2,3. There is even less evidence comparing the effectiveness of first and second generation antihistamines head to head for the treatment of acute urticaria. Most recommendations concerning treatment for mild urticaria are extrapolated from the primary literature regarding the treatment of chronic urticaria and experimentally histamine induced wheals. Based on this evidence, the expert consensus is that diphenhydramine and second-generation antihistamines provide similar efficacy in the treatment of allergic reactions, including mild urticaria3,4,5.
Although diphenhydramine is considered to be as effective as second generation antihistamines, it is not considered first line treatment for mild urticaria due to its’ side effect profile1,2. First generation antihistamines, including diphenhydramine, tend to cause more sedation and anticholinergic side effects compared to second generation antihistamines1,2,6. Diphenhydramine has been found to impair psychomotor performance and cognitive function after administration of doses equal to or greater than 50mg. The drowsiness and central nervous system effects caused by diphenhydramine are attributed to the blockade of central histaminergic receptors and antagonism of other brain receptors (Ex. serotonergic, cholinergic, and central alpha-adrenergic)2. Second generation antihistamines, on the other hand, exhibit limited transfer across the blood brain and are associated with fewer side effects. There are a few cases where you might consider diphenhydramine first line for the treatment of mild urticaria including cases where patients are experiencing significant itching that keeps them up at night. In this case you might consider starting with a dose of diphenhydramine before bed1.
References:
1. Regier L, Jensen B, Downey S et al. OTC (Over-The-Counter) Products: Allergy-systemic. RxFiles. 2013. Available at: <http://www.rxfiles.ca/rxfiles/uploads/documents/members/CHT-OTCs.pdf >. Accessed June 4, 2014.
2. Banerji A, Long A, Camargo C. Diphenhydramine versus non-sedating antihistamines for acute allergic reactions: A literature review. Allergy and Asthma Proceedings. 2007. 28:418-426.
3. Alper BS. SOAP: Solutions to often asked problems. Choice of antihistamines for urticaria. Archives of Family Medicine. 2000. 9(8): 748-751.
4. Bernstein J, Lang D, Khan D et al. The diagnosis and management of acute and chronic urticaria: 2014 update. Journal of Allergy and Clinical Immunology. 133(5): 1270-1277.
5. Pontasch M, White L, Bradfore J. Oral agents in the management of urticaria: patient perception of effectiveness and level of satisfaction with treatment. Annals of Pharmacotherapy. 1993. 27(6):730-731
6. Grant J, Bernstein D, Buckley C, et al. Double-blind comparison of terfenadine, chlorpheniramine, and placebo in the treatment of chronic idiopathic urticaria. Journal of Allergy and Clinical Immunology. 1988;81:574-579.