Diphenhydramine Adverse Reactions
- abdominal pain
- agitation
- appetite stimulation
- asthenia
- ataxia
- blurred vision
- confusion
- constipation
- contact dermatitis
- diarrhea
- dizziness
- drowsiness
- dysarthria
- dyskinesia
- dystonic reaction
- fatigue
- hallucinations
- headache
- hypotension
- impaired cognition
- insomnia
- mydriasis
- palpitations
- photosensitivity
- psychosis
- rash (unspecified)
- restlessness
- seizures
- sinus tachycardia
- tardive dyskinesia
- tremor
- urinary retention
- weakness
- xerophthalmia
- xerostomia
Diphenhydramine Adverse Reactions
CNS depression manifested as drowsiness and/or dizziness can occur during therapy with diphenhydramine. Other less frequently occurring CNS effects of sedating antihistamines include asthenia/weakness, confusion, dysarthria (slurred speech), muscular weakness, fatigue, or headache. There is considerable individual patient response to sedative effects, so patients should be warned of the possible impairment of mental acuity. These side effects may disappear after a few days of medication. Geriatric patients may be more predisposed to adverse CNS depressant effects, such as impaired cognition, particularly with higher dosages. Ethanol intake will increase the risk of sedation. In a double-blind study to assess driving performance, diphenhydramine was associated with significantly poorer driving coherence (i.e., the ability to maintain appropriate velocity based on a lead car that varied its speed) compared to ethanol, fexofenadine, or placebo. The study also showed that patients receiving diphenhydramine were more likely to cross the center line of the road than those receiving fexofenadine or placebo. If sedation persists or is severe, a dosage reduction or switching to a non-sedating H1-antagonist may be advisable. Elderly persons and pediatric patients taking sedating antihistamines have the greatest risk of CNS related side effects. Diphenhydramine, like many antihistamines, can cause CNS stimulation, although, this is more likely to occur in children. CNS stimulatory symptoms may include agitation, appetite stimulation, restlessness, insomnia, palpitations, muscle spasms, and in severe cases, seizures. The anticholinergic reactions of insomnia, nervousness or restlessness, irritability, palpitations, and sinus tachycardia may also occur.
Antihistamine overdose has been linked to coma; stimulatory CNS effects such as dyskinesia, dystonic reaction, tardive dyskinesia, tremor, and seizures; and neuropsychiatric effects such as hallucinations or psychosis. Rarely, ataxia and delirium are also seen. Fatalities have been reported with overdose.
Diphenhydramine possesses a significant degree of anticholinergic effects, which can result in thickening of bronchial secretions, xerostomia, urinary retention, insomnia, nervousness, mydriasis, xerophthalmia, and/or blurred vision. Geriatric patients are more susceptible to these adverse reactions, since endogenous cholinergic activity declines with age.
H1-antagonists may cause adverse GI effects including diarrhea, constipation or abdominal pain. The latter adverse reaction may be relieved by taking the drug with meals or milk.
Adverse cardiovascular responses are likely to be associated with the anticholinergic properties or the quinidine-like anesthetic effects of H1-antagonists. These responses can include sinus tachycardia, extrasystoles, palpitations, and/or cardiac arrhythmias. Alpha-adrenergic blockade can lead to symptoms of hypotension. Hypertension can also occur, but is usually not of clinical significance.
Dermatological adverse effects of diphenhydramine may include rash (unspecified), urticaria, or photosensitivity. Topical application of diphenhydramine can cause contact dermatitis through a T-cell mediated response. Although this reaction can occur following systemic administration, it is most commonly the result of topical use of the drug. A hypersensitivity reaction through hapten formation has also been noted. Once this reaction has occurred, cross-sensitivity between topically and orally administered diphenhydramine may be seen.
[ Last revised: 12/11/2002 6:06:00 PM ]
References
. Weiler JM, Bloomfield JR, Woodworth GG, et al. Effects of fexofenadine, diphenhydramine, and alcohol on driving performance: a randomized, placebo controlled trial in the Iowa driving simulator. Ann Intern Med 2000:132:354 - 363.
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