First Generation Antihistamines
Place in Therapy
Place in Therapy
First generation antihistamines block histamine from binding to histamine 1 receptors and also block mucus and gland secretion which are part of the parasympathetic system. (1) Older studies with poor data collection did not see a benefit in the nasal symptoms of a cold when first generation antihistamines were used however more recent studies using more objective data showed some benefit. Newer studies looked at day-to-day variation of symptoms and concluded that first generation antihistamines are effective in reducing nasal symptoms of rhinorrhea and sneezing, as was determined in the studies by measuring nasal discharge weight from tissues used by participants.(2) Due to the increased side effects first generation antihistamines would not be first line but does have proven efficacy in reducing symptoms of rhinorrhea and sneezing in patients with nasal symptoms of a cold.(1,2)
Safety
First generation antihistamines should be avoided in geriatric patients due to significant anticholinergic side effects and should not be used in children under the age of 6 according to Health Canada.(1) They should be used with caution during pregnancy as it does cross the placenta and although there hasn't been an increased risk of birth defects there have been adverse effects such as respiratory depression and withdrawal symptoms in newborns. Antihistamines should also be avoided during lactation because it enters breast milk. (4,5,6) It should also be used with caution in patients with narrow-angle glaucoma, benign prostatic hypertrophy, heart disease, bladder neck obstruction, hyperthyroidism. (1)
References
First generation antihistamines block histamine from binding to histamine 1 receptors and also block mucus and gland secretion which are part of the parasympathetic system. (1) Older studies with poor data collection did not see a benefit in the nasal symptoms of a cold when first generation antihistamines were used however more recent studies using more objective data showed some benefit. Newer studies looked at day-to-day variation of symptoms and concluded that first generation antihistamines are effective in reducing nasal symptoms of rhinorrhea and sneezing, as was determined in the studies by measuring nasal discharge weight from tissues used by participants.(2) Due to the increased side effects first generation antihistamines would not be first line but does have proven efficacy in reducing symptoms of rhinorrhea and sneezing in patients with nasal symptoms of a cold.(1,2)
Safety
First generation antihistamines should be avoided in geriatric patients due to significant anticholinergic side effects and should not be used in children under the age of 6 according to Health Canada.(1) They should be used with caution during pregnancy as it does cross the placenta and although there hasn't been an increased risk of birth defects there have been adverse effects such as respiratory depression and withdrawal symptoms in newborns. Antihistamines should also be avoided during lactation because it enters breast milk. (4,5,6) It should also be used with caution in patients with narrow-angle glaucoma, benign prostatic hypertrophy, heart disease, bladder neck obstruction, hyperthyroidism. (1)
References
- Roy, H. Viral Rhinitis, Influenza, Sinusitis and Pharyngitis. In: Patient Self Care. 2nd ed. Ottawa, On: Canadian Pharmacists Association; 2010: 187-203.
- Gwaltney JM Jr, Druce HM. Efficacy of brompheniramine maleate treatment for rhinovirus colds. Clin Infect Dis 1997; 25:1188–94.
- Diphenhydramine. Lexi-Drugs Online. Hudson, OH: Lexi-Comp, Inc. Updated March 3, 2014. Available from: http://online.lexi.com.proxy.lib.uwaterloo.ca/lco/action/doc/retrieve/docid/patch_f/1827019. Accessed March 14, 2014.
- Lynch T. Respiratory Disorders: Viral Rhinitis. In: Gray Jean, editor. e-Therapeutics+ [Internet]. Ottawa (ON): Canadian Pharmacists Association; 2007 [updated Sep 2006; cited 2014 Mar 14]. Available from: http://www.e-therapeutics.ca.
- Brompheniramine. Lexi-Drugs Online. Hudson, OH: Lexi-Comp, Inc Updated February 19, 2014. Available from: http://online.lexi.com.proxy.lib.uwaterloo.ca/lco/action/doc/retrieve/docid/patch_f/92. Accessed Mar 14, 2014.
- Chlorpheniramine. Lexi-Drugs Online. Hudson, OH: Lexi-Comp, Inc Updated March 28, 2014. Available from: http://online.lexi.com.proxy.lib.uwaterloo.ca/lco/action/doc/retrieve/docid/patch_f/6590. Accessed Mar 14, 2014.