Comparative Pharmacology
Head-to-head clinical analysis: DIPHENHYDRAMINE versus PHENYLEPHRINE HYDROCHLORIDE AND PROMETHAZINE HYDROCHLORIDE.
Peer-Reviewed Evidence
Head-to-head clinical analysis: DIPHENHYDRAMINE versus PHENYLEPHRINE HYDROCHLORIDE AND PROMETHAZINE HYDROCHLORIDE.
Diphenhydramine vs PHENYLEPHRINE HYDROCHLORIDE AND PROMETHAZINE HYDROCHLORIDE
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Inverse agonist at histamine H1 receptors, blocking histamine-mediated effects in blood vessels, respiratory smooth muscle, and GI tract; also anticholinergic by blocking muscarinic receptors and sedative via central H1 receptor antagonism.
Phenylephrine is a selective alpha-1 adrenergic receptor agonist causing vasoconstriction; promethazine is a phenothiazine derivative that blocks histamine H1 receptors and has anticholinergic, antiemetic, and sedative effects.
25-50 mg orally or intramuscularly every 4-6 hours; maximum 300 mg/day. Intravenous administration: 10-50 mg slow IV push (max 25 mg/min).
IV: 0.1-0.5 mg phenylephrine and 12.5-25 mg promethazine as a single dose.
None Documented
None Documented
Clinical Note
moderateDiphenhydramine + Deferasirox
"The serum concentration of Deferasirox can be increased when it is combined with Diphenhydramine."
Clinical Note
moderateDiphenhydramine + Fluticasone propionate
"The risk or severity of adverse effects can be increased when Diphenhydramine is combined with Fluticasone propionate."
Clinical Note
moderateDiphenhydramine + Tenofovir disoproxil
"The metabolism of Tenofovir disoproxil can be decreased when combined with Diphenhydramine."
Clinical Note
moderateTerminal elimination half-life 4-8 hours in adults; prolonged in hepatic impairment (up to 20 hours) and elderly.
Phenylephrine: 2-3 hours (terminal). Promethazine: 10-14 hours (terminal in adults; prolonged in elderly and hepatic impairment).
Primarily renal (90-95% as metabolites, <5% unchanged). Minor biliary/fecal elimination (<5%).
Phenylephrine: renal (80% as unchanged drug and sulfate conjugates). Promethazine: renal (70-80% as metabolites and unchanged drug), fecal (20-30%).
Category C
Category A/B
Antihistamine
Antihistamine / Antiemetic
Diphenhydramine + Sulfisoxazole
"The metabolism of Sulfisoxazole can be decreased when combined with Diphenhydramine."