Comparative Pharmacology
Head-to-head clinical analysis: DIPHENHYDRAMINE HYDROCHLORIDE versus PROMETHAZINE DM.
Peer-Reviewed Evidence
Head-to-head clinical analysis: DIPHENHYDRAMINE HYDROCHLORIDE versus PROMETHAZINE DM.
DIPHENHYDRAMINE HYDROCHLORIDE vs PROMETHAZINE DM
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Competitive antagonist of histamine H1 receptors, reducing allergic symptoms; also exerts anticholinergic, sedative, and antiemetic effects via central and peripheral receptor blockade.
Promethazine is a phenothiazine derivative that acts as a histamine H1 receptor antagonist, antiemetic via blockade of dopamine D2 receptors in the chemoreceptor trigger zone, and sedative via central anticholinergic effects. Dextromethorphan is an NMDA receptor antagonist and sigma-1 receptor agonist, suppressing cough by central action on the cough center.
25-50 mg orally or intramuscularly every 4-6 hours as needed; maximum 300 mg per day.
2 teaspoonfuls (10 mL) orally every 4-6 hours, not to exceed 8 teaspoonfuls (40 mL) per 24 hours.
None Documented
None Documented
Terminal elimination half-life 4–10 hours (mean ~7 hours); prolonged in elderly, hepatic impairment, and with CYP2D6 poor metabolizers.
16-19 hours (terminal); note: effect may last longer due to active metabolites and tissue binding
Renal elimination of metabolites accounts for ~60% of the dose; <5% excreted unchanged. Fecal excretion ~40% via bile.
Renal (70-80% as metabolites, <1% unchanged); biliary/fecal (20-30%)
Category A/B
Category A/B
Antihistamine
Antihistamine / Antiemetic