2. Antihistamine
Description
Antihistamines are a class of drugs commonly
taken over the counter, such as
diphenhydramine. Antihistamines block the
release of histamine to prevent or relieve
symptoms of seasonal allergies, motion
sickness, nausea, vomiting, and dizziness (Mayo
Clinic, n.d.).
There are two generations of antihistamines with
varying degrees of anticholinergic side effects
(Cho et al., 2018).
There are counter medications combined with
antihistamines such as Tylenol PM, which could
make it less obvious to some individuals they are
taking an antihistamine (Hoskins, 2011).
3. Over the Counter Antihistamines
Types and Ingredients
First-Generation Antihistamines
First-generation antihistamines
contraindicated by the Beers Criteria
include:
Brompheniramine (Dimetane)
Chlorpheniramine (Chlor-Trimeton)
Clemastine (Tavist)
Diphenhydramine (Benadryl)
Diphenhydramine combined with
acetaminophen (Tylenol PM)
(Fick et al., 2015)
Second-Generation Antihistamines
Second-generation antihistamines are
now the first choice due to less
anticholinergic side effects that
include:
Cetirizine (Zyrtec)
Fexofenadine (Allegra)
Loratadine (Claritin)
(Family Doctor, n.d)
4. Key
Information
First-generation antihistamines have more adverse effects
because they cross the blood-brain barrier and react with other
receptors for increased anticholinergic side effects such as
sedation and reduced kidney clearance in the elderly (Cho et al.,
2018).
Taking antihistamines are the most common source of an
anticholinergic overdose related to multiple medications with
anticholinergic properties (Broderick et al., n.d.).
Adverse central nervous system effects include drowsiness,
fatigue, dizziness, cognitive impairment, agitation, and
hallucinations (Broderick et al., n.d.).
It is essential to consider the patient’s renal function due to an
age-related decrease in medication clearance, the potential for
urinary frequency, difficult urination, or urinary retention
(Broderick et al., n.d.).
Geriatric have increased sensitivity to first-generation
antihistamines causing symptoms such as confusion, difficult
urination, drowsiness, feeling faint, constipation, nightmares,
excitement, nervousness, restlessness, irritability, or excessive
dryness to mouth, nose, or throat (Hoskins, 2011; Mayo Clinic,
n.d.).
5. Adverse Effects and Beers Criteria
First Generation Antihistamines
In adults age 65 and older, the Beers Criteria
recommends against the use of first-
generation over the counter antihistamines
due to high anticholinergic effects such as
reduced clearance, confusion, dry mouth,
and constipation(Fick et al., 2015).
Overdose of sedating antihistamines can
cause over-sedation, seizures,
anticholinergic signs, and cardiac conduction
abnormalities (Randall & Hawkins, 2018).
Possible adverse respiratory responses
include thickening of bronchial secretions,
tightness of chest, wheezing, and nasal
stuffiness (NIH U.S. National Library of
Medicine, n.d.).
Second Generation Antihistamines
The second-generation antihistamines are
typically safer with less sedative effects, but
individuals can experience adverse effects in
high doses such as tachycardia, drowsiness,
agitation, gastrointestinal effects, and
headache (Randall & Hawkins, 2018).
6. Patient Education
Instruct patients to have a current list that includes prescriptions, over the counter
medications, and herbal remedies for review to avoid drug interactions (Pérez-
Jover et al., 2018).
Provide verbal and written age-appropriate instructions regarding anticholinergic
side effects and drug interactions (Broderick et al., n.d.).
Instruct patients to read labels and check the active ingredients to prevent an
anticholinergic overdose (Broderick et al., n.d.).
Instruct patients to check with their pharmacist for drug interactions and
contraindications when choosing an over the counter medication (Broderick et al.,
n.d.).
For allergy symptoms, instruct patients to take a second-generation antihistamines
such as fexofenadine (Allegra) to prevent excessive drowsiness.
Provide patient education regarding the increased risk for falls and fractures from
taking first-generation antihistamines like diphenhydramine (Cho et al., 2018).
7. References
Broderick, E., Metheny, H., & Crosby, B. (n.d.). Anticholinergic toxicity. NCBI: StatPearls.
Retrieved June 20, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK534798/
Cho, H., Myung, J., Suh, H. S., & Kang, H. Y. (2018). Antihistamine use and the risk of
injurious falls or fracture in elderly patients: A systematic review and meta-analysis.
Osteoporosis International, 29(10), 2163–2170. https://doi.org/10.1007/s00198-018-
4564-z
Family Doctor. (n.d.). Antihistamines: Understanding your OTC options. Familydoctor.org
American Academy of Family Physicians. Retrieved June 21, 2020, from
https://familydoctor.org/antihistamines-understanding-your-otc-options/?adfree=true
Fick, D. M., Semia, T. P., Beizer, J., Brandt, N., Dombrowski, R., DuBeau, C. E., Eisenberg, W.,
Epplin, J. J., Flanagan, N., Giovannetti, E., Hanlon, J., Hollmann, P., Laird, R., Linnebur,
S., Sandh, S., & Steinman, M. (2015). American geriatrics society 2015 updated beers
criteria for potentially inappropriate medication use in older adults. Journal of the
American Geriatrics Society, 63(11), 2227–2246. https://doi.org/10.1111/jgs.13702
Hoskins, B. L. (2011). Safe prescribing for the elderly. The Nurse Practitioner, 36(12), 47–52.
https://doi.org/10.1097/01.npr.0000407605.53599.a6
8. References Continued
Mayo Clinic. (n.d.). Drugs and supplements: Antihistamine (oral route, parenteral route, rectal
route). Retrieved June 20, 2020, from https://www.mayoclinic.org/drugs-
supplements/antihistamine-oral-route-parenteral-route-rectal-route/before-using/drg-
20070373
NIH U.S. National Library of Medicine. (n.d.). Dailymed. NIH U.S. NATIONAL LIBRARY OF
MEDICINE: DAILYMED. Retrieved June 21, 2020, from
https://dailymed.nlm.nih.gov/dailymed/search.cfm?labeltype=all
Pérez-Jover, V., Mira, J., Carratala-Munuera, C., Gil-Guillen, V., Basora, J., López-Pineda, A.,
& Orozco-Beltrán, D. (2018). Inappropriate use of medication by elderly, polymedicated,
or multipathological patients with chronic diseases. International Journal of
Environmental Research and Public Health, 15(2), 310.
https://doi.org/10.3390/ijerph15020310
Randall, K. L., & Hawkins, C. A. (2018). Antihistamines and allergy. Australian Prescriber,
41(2), 42–45. https://doi.org/10.18773/austprescr.2018.013
