Diphenhydramine: Difference between revisions
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{{MedTemplate | {{MedTemplate | ||
| generic | | generic = Diphenhydramine (hydrochloride; citrate) | ||
| brand | | brand = Benadryl (oral, injectable, topical), Banophen, Sominex (sleep aid), ZzzQuil, Aler-Dryl | ||
| structure | | structure = | ||
| classes | | classes = [[:Category:Antihistamines|First-generation antihistamine (ethanolamine)]], [[:Category:Anticholinergics|Anticholinergic]], [[:Category:Sleep aids|Sleep aid]], [[:Category:Antiemetics|Antiemetic]] | ||
| | | uses = <vote slug="allergic-conditions-use">Allergic conditions including urticaria and seasonal allergies (OTC and FDA)</vote>, <vote slug="motion-sickness-use">Motion sickness (OTC, FDA)</vote>, <vote slug="insomnia-otc-use">Insomnia, short-term (OTC, FDA)</vote>, <vote slug="acute-dystonia-emergency-use">Acute dystonic reaction from neuroleptics (off-label, IV emergency)</vote>, <vote slug="anaphylaxis-adjunct-use">Anaphylaxis adjunct (FDA, IV; not a substitute for epinephrine)</vote>, <vote slug="parkinson-disease-anticholinergic-use">Parkinson disease tremor (off-label, anticholinergic effect)</vote> | ||
| starting_dose = Allergy: 25-50 mg PO every 4-6 hours. Insomnia: 25-50 mg PO at bedtime. IV (acute dystonia, severe allergic reaction): 25-50 mg slow IV push | |||
| starting_dose | | preparations = Tablets 25, 50 mg; capsules; liquid; chewable; topical cream/gel; injection 50 mg/mL | ||
| preparations | | fda_max = 300 mg/day (oral) | ||
| | | pill_id = | ||
| | | routes = Oral, IV, IM, topical | ||
| onset = 15-30 minutes (oral); 1-2 minutes (IV) | |||
| | | duration = 4-6 hours | ||
| | | halflife = 4-8 hours (longer in elderly, 9-13 hours)<ref name="benadryl-label">FDA Prescribing Information, Benadryl (diphenhydramine hydrochloride), Johnson & Johnson/various, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/010661s045lbl.pdf</ref> | ||
| | | bioavailability = ~40-60% (oral, with significant first-pass)<ref name="benadryl-label" /> | ||
| | | pregnancy = Older agent with substantial use experience; broadly considered safe in pregnancy<ref name="benadryl-label" /> | ||
| legal = [[USLegal:Over-the-counter|OTC]] for most oral and topical formulations; [[USLegal:Prescription only|Rx-only]] for injectable | |||
| | | mechanism = <vote slug="diphenhydramine-mech-claim">First-generation H1 histamine receptor antagonist with substantial central nervous system penetration and '''strong muscarinic acetylcholine receptor antagonism'''. The H1 blockade produces antihistamine and antiemetic effects; the muscarinic blockade produces sedation, anticholinergic burden (dry mouth, blurred vision, urinary retention, cognitive impairment), and at supratherapeutic doses, anticholinergic delirium with classic toxidrome ("blind as a bat, mad as a hatter").</vote> Major Beers-list concern in elderly patients for cognitive and fall risks. CYP2D6 substrate. At massive overdose, also produces sodium channel blockade with cardiac toxicity<ref name="benadryl-label" />. | ||
| | <effect ref="dry-mouth" author="MDElliottMD"/> | ||
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}} | }} | ||
== References == | |||
<references /> | |||
[[Category:Antihistamines]] | [[Category:Antihistamines]] | ||
[[Category:Anticholinergics]] | |||
[[Category:Sleep aids]] | |||
[[Category:Antiemetics]] | |||
Latest revision as of 07:32, 23 May 2026
Diphenhydramine (hydrochloride; citrate)
Benadryl (oral, injectable, topical), Banophen, Sominex (sleep aid), ZzzQuil, Aler-Dryl
Experience
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Problems
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Effects
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Relevant Literature
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Pharmacy
Starting dose
Allergy: 25-50 mg PO every 4-6 hours. Insomnia: 25-50 mg PO at bedtime. IV (acute dystonia, severe allergic reaction): 25-50 mg slow IV push
Preparations
Tablets 25, 50 mg; capsules; liquid; chewable; topical cream/gel; injection 50 mg/mL
US FDA Max
300 mg/day (oral)
Common uses
Classification(s)
Pharmacology
Routes
Oral, IV, IM, topical
Onset
15-30 minutes (oral); 1-2 minutes (IV)
Duration
4-6 hours
Half-life
4-8 hours (longer in elderly, 9-13 hours)[1]
Bioavailability
~40-60% (oral, with significant first-pass)[1]
Pregnancy
Older agent with substantial use experience; broadly considered safe in pregnancy[1]
Purported mechanism
First-generation H1 histamine receptor antagonist with substantial central nervous system penetration and strong muscarinic acetylcholine receptor antagonism. The H1 blockade produces antihistamine and antiemetic effects; the muscarinic blockade produces sedation, anticholinergic burden (dry mouth, blurred vision, urinary retention, cognitive impairment), and at supratherapeutic doses, anticholinergic delirium with classic toxidrome ("blind as a bat, mad as a hatter").0 Major Beers-list concern in elderly patients for cognitive and fall risks. CYP2D6 substrate. At massive overdose, also produces sodium channel blockade with cardiac toxicity[1].
Dry mouth 100% -67.0 (n=1) no reports yet
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References
- ↑ 1.0 1.1 1.2 1.3 FDA Prescribing Information, Benadryl (diphenhydramine hydrochloride), Johnson & Johnson/various, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/010661s045lbl.pdf