1st Generation Antihistamines
Place in Therapy
Place in Therapy
First-generation antihistamines elicit their effects symptom relief of allergic rhinitis via blockage of histamine-1-receptor to reduce smooth muscle constriction, mucus secretion, vascular permeability, and sensory nerve stimulation.1 Oral antihistamines are effective in alleviating symptoms such as sneezing, rhinorrhea, nasopharyngeal itching, and ocular symptoms.1,2 First-generation antihistamines have comparable efficacy profile compared to second-generation antihistamines. Some studies have demonstrated greater symptomatic reliefs with first-generation antihistamines than with second-generation antihistamines.3,4 However, use of first-generation antihistamines is limited by their side effect profiles, placing their use as second line after trials with second generation antihistamines.
First-generation antihistamines are more lipophilic than second-generation antihistamines, and therefore easily cross the blood-brain barrier leading to more central nervous system side effects such as sedation. Use of first-generation antihistamines have been associated with reduced vigilance, attention, memory, speed, and performance.2,4 First-generation antihistamines should not be used in patients requiring vigilance at work, and are not the preferred pharmacologic options for elderly because of higher sensitivity to anticholinergic effects and for children where use has been associated with learning impairment.2,4 With regards to pregnancy, chlorpheniramine is considered acceptable but there exist safer alternatives.2 Lastly, first-generation antihistamines are dosed three to four times daily, which could compromise compliance.
References
1. Sur DK, Scandale S. Treatment of allergic rhinitis. Am Fam Physician. 2010;81(12):1440-1446.
2. Keith, P. Respiratory Disorders: Allergic Rhinitis. In: e-Therapeutics (Therapeutic Choices). Ottawa, ON: Canadian Pharmacists Association; 2014. http://www.e-therapeutics.ca. Revised June 2014. Accessed June 20, 2014.
3. Raphael GD, Angello JT, Wu M, Druce HM. Efficacy of diphenhydramine vs desloratadine and placebo in patients with moderate-to-severe seasonal allergic rhinitis. Ann Allergy Asthma Immunol. 2006;96(4):606-612.
4. Wilken JA, Kane RL, Ellis AK, et al. A comparison of the effect of diphenhydramine and desloratadine on vigilance and cognitive function during treatment of ragweed-induced seasonal allergic rhinitis. Ann Allergy Asthma Immunol. 2003;91(4):375-385.
First-generation antihistamines elicit their effects symptom relief of allergic rhinitis via blockage of histamine-1-receptor to reduce smooth muscle constriction, mucus secretion, vascular permeability, and sensory nerve stimulation.1 Oral antihistamines are effective in alleviating symptoms such as sneezing, rhinorrhea, nasopharyngeal itching, and ocular symptoms.1,2 First-generation antihistamines have comparable efficacy profile compared to second-generation antihistamines. Some studies have demonstrated greater symptomatic reliefs with first-generation antihistamines than with second-generation antihistamines.3,4 However, use of first-generation antihistamines is limited by their side effect profiles, placing their use as second line after trials with second generation antihistamines.
First-generation antihistamines are more lipophilic than second-generation antihistamines, and therefore easily cross the blood-brain barrier leading to more central nervous system side effects such as sedation. Use of first-generation antihistamines have been associated with reduced vigilance, attention, memory, speed, and performance.2,4 First-generation antihistamines should not be used in patients requiring vigilance at work, and are not the preferred pharmacologic options for elderly because of higher sensitivity to anticholinergic effects and for children where use has been associated with learning impairment.2,4 With regards to pregnancy, chlorpheniramine is considered acceptable but there exist safer alternatives.2 Lastly, first-generation antihistamines are dosed three to four times daily, which could compromise compliance.
References
1. Sur DK, Scandale S. Treatment of allergic rhinitis. Am Fam Physician. 2010;81(12):1440-1446.
2. Keith, P. Respiratory Disorders: Allergic Rhinitis. In: e-Therapeutics (Therapeutic Choices). Ottawa, ON: Canadian Pharmacists Association; 2014. http://www.e-therapeutics.ca. Revised June 2014. Accessed June 20, 2014.
3. Raphael GD, Angello JT, Wu M, Druce HM. Efficacy of diphenhydramine vs desloratadine and placebo in patients with moderate-to-severe seasonal allergic rhinitis. Ann Allergy Asthma Immunol. 2006;96(4):606-612.
4. Wilken JA, Kane RL, Ellis AK, et al. A comparison of the effect of diphenhydramine and desloratadine on vigilance and cognitive function during treatment of ragweed-induced seasonal allergic rhinitis. Ann Allergy Asthma Immunol. 2003;91(4):375-385.