The correct dose is 150 mg/day. Diphenhydramine acts
as an inverse agonist at the H1 receptor, thereby reversing the
effects of histamine on capillaries, reducing allergic reaction
symptoms. Given that diphenhydramine is a first-generation
antihistamine, it readily crosses the blood-brain barrier and
inversely agonizes the H1 CNS receptors, resulting in drowsiness,
and suppressing the medullary cough center.
Divided into 3 doses per day, the child should receive
50 mg 3 times a day rather than 25 mg 3 times a day.
Diphenhydramine overdose can cause significant toxicity, ranging
from agitation to cardiac arrhythmias to rhabdomyolysis and
classic anticholinergic toxidrome. Further studies are needed to
investigate the potential treatment of diphenhydramine toxicity
with the use of sodium bicarbonate and intravenous lipid emulsion
Dosage should not be titrated based on symptoms
without consulting a physician. Diphenhydramine can be given by
tablet, capsule, or in solution by mouth; by intramuscular (IM) or
intravenous (IV) injection; or topically. Diphenhydramine is now
available over the counter and it is important for the pharmacist
and nurse practitioner to educate the patient on the safe use of
The mother of a 2-month-old infant brings the child to the clinic for a well-baby
check. She is concerned because she feels only one testis in the scrotal sac.
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