NAPROXEN SODIUM AND DIPHENHYDRAMINE HYDROCHLORIDE
Clinical safety rating: avoid
ACE inhibitors and ARBs may have diminished antihypertensive effect Increases risk of serious cardiovascular thrombotic events and GI bleeding.
Naproxen sodium is a nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis, which mediates inflammation, pain, and fever. Diphenhydramine hydrochloride is a first-generation antihistamine that antagonizes histamine H1 receptors, reducing allergic symptoms and inducing sedation via central H1 blockade.
| Metabolism | Naproxen is extensively metabolized in the liver via CYP2C9 (major) and to a lesser extent by glucuronidation. Diphenhydramine is primarily metabolized in the liver via CYP2D6 (major) and other CYP enzymes, with some N-demethylation. |
| Excretion | Naproxen: renal excretion of naproxen and its metabolites (95% as unchanged drug and conjugated metabolites, primarily 6-O-desmethylnaproxen). Diphenhydramine: renal excretion of unchanged drug and metabolites (primarily as diphenylmethoxyacetic acid); approximately 50-60% eliminated in urine as unchanged drug and metabolites, with a small fraction in feces. |
| Half-life | Naproxen: 12-17 hours (mean ~14 hours); clinically, allows twice-daily dosing for sustained anti-inflammatory effect. Diphenhydramine: 4-10 hours (mean ~7 hours); shorter half-life supports sedative effect for sleep induction. |
| Protein binding | Naproxen: >99% bound to albumin. Diphenhydramine: 78-85% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Naproxen: 0.16 L/kg; high protein binding limits distribution primarily to plasma. Diphenhydramine: 3-4 L/kg; extensive tissue distribution due to lipophilicity. |
| Bioavailability | Naproxen: oral bioavailability ~95%; rapid and complete absorption. Diphenhydramine: oral bioavailability ~50-70% due to first-pass metabolism. |
| Onset of Action | Naproxen: oral, analgesic onset within 1 hour, anti-inflammatory effect within 1-2 weeks. Diphenhydramine: oral, sedative onset within 15-30 minutes, peak effect at 1-3 hours. |
| Duration of Action | Naproxen: analgesic duration up to 12 hours; anti-inflammatory effect lasts 24 hours with continued dosing. Diphenhydramine: sedative effect lasts 4-6 hours, with residual hangover effect possible up to 12 hours. |
| Molecular Weight | Naproxen sodium: 252.24 g/mol (naproxen free acid: 230.26 g/mol); Diphenhydramine hydrochloride: 291.82 g/mol (diphenhydramine base: 255.35 g/mol) |
| Action Class | NSAID (naproxen) and antihistamine (diphenhydramine) |
One tablet (naproxen sodium 220 mg / diphenhydramine hydrochloride 25 mg) orally every 8 hours as needed, not to exceed 2 tablets in 24 hours.
| Dosage form | TABLET |
| Renal impairment | CrCl ≥30 mL/min: No adjustment. CrCl <30 mL/min: Contraindicated (risk of accumulation). |
| Liver impairment | Avoid in severe hepatic impairment (Child-Pugh class C). For mild to moderate impairment, use with caution; no specific dose adjustment established. |
| Pediatric use | Not recommended for use in children under 12 years of age due to safety concerns (risk of Reye's syndrome with diphenhydramine) and lack of data for naproxen in this age group. |
| Geriatric use | Start at lowest dose; elderly patients are more sensitive to NSAID side effects (GI bleeding, renal impairment) and anticholinergic effects (diphenhydramine). Avoid use if possible; if necessary, limit to short-term use with close monitoring. |
| 1st trimester | Avoid use; NSAIDs are generally avoided in first trimester due to potential increased risk of miscarriage and congenital anomalies. Diphenhydramine is considered relatively safe but caution advised. |
| 2nd trimester | Use with caution; NSAIDs may be used but should be limited due to risk of oligohydramnios and premature ductus arteriosus constriction after 20 weeks. Diphenhydramine is generally safe. |
| 3rd trimester | Avoid after 30 weeks; NSAIDs are contraindicated due to risk of premature closure of ductus arteriosus and oligohydramnios. Diphenhydramine may be used if needed, but benefits must outweigh risks. |
Clinical note
ACE inhibitors and ARBs may have diminished antihypertensive effect Increases risk of serious cardiovascular thrombotic events and GI bleeding.
| FDA category | Positive |
| Placental transfer | Both naproxen (sodium) and diphenhydramine cross the placenta. Naproxen shows significant transfer; detectable fetal plasma concentrations approximate 10-20% of maternal levels. Diphenhydramine crosses readily, with fetal-to-maternal ratio around 0.5–1.0. |
■ FDA Black Box Warning
Nonsteroidal anti-inflammatory drugs (NSAIDs) cause an increased risk of serious cardiovascular thrombotic events, including myocardial infarction and stroke, which can be fatal. This risk may occur early in treatment and may increase with duration of use. NSAIDs are contraindicated in the setting of coronary artery bypass graft (CABG) surgery.
| Common Effects | inflammation |
| Serious Effects | Gastrointestinal bleeding, ulceration, and perforation, Cardiovascular thrombotic events (e.g., myocardial infarction, stroke), Renal impairment including acute renal failure, Anaphylactic reactions, Severe hepatic reactions including jaundice and fatal hepatitis, Central nervous system depression (e.g., sedation, confusion) especially in elderly, Anticholinergic effects (e.g., urinary retention, blurred vision) |
History of allergic reaction to naproxen, aspirin, or other NSAIDsHistory of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDsActive peptic ulcer disease or gastrointestinal bleedingSevere heart failure (NYHA Class III or IV)Coronary artery bypass graft (CABG) surgery (perioperative pain)Third trimester of pregnancy (after 30 weeks gestation)History of anaphylactoid reactions to diphenhydramine or other antihistamines of similar structure
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| Breastfeeding | Naproxen transfers into breast milk in low amounts; limited infant exposure. Diphenhydramine also transfers; may cause drowsiness or irritability in infants. Use lowest effective dose for shortest duration; monitor infant for sedation. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | First trimester: NSAIDs are associated with increased risk of miscarriage and cardiac defects; diphenhydramine is category B, but data limited. Second trimester: NSAIDs may cause fetal renal effects; diphenhydramine not associated with major malformations. Third trimester: NSAIDs (including naproxen) cause premature closure of ductus arteriosus and oligohydramnios; diphenhydramine may cause neonatal respiratory depression if used near term. Avoid use in third trimester. |
| Fetal Monitoring | Monitor fetal ultrasound for ductus arteriosus and amniotic fluid volume if NSAID used beyond 20 weeks; assess maternal blood pressure, renal function, and signs of bleeding. For diphenhydramine, monitor maternal sedation and fetal heart rate if high doses used. |
| Fertility Effects | NSAIDs may impair female fertility through prostaglandin-mediated effects on ovulation; reversible upon discontinuation. Diphenhydramine has no known significant effect on fertility. |
| Precautions | Cardiovascular risk: Increased risk of serious cardiovascular thrombotic events; use lowest effective dose for shortest duration., Gastrointestinal risk: Increased risk of serious GI adverse events including bleeding, ulceration, and perforation, especially in elderly and those with prior history of ulcers., Renal effects: Use caution in patients with renal impairment or dehydration; avoid use in advanced renal disease., Sedation: Diphenhydramine can cause marked drowsiness; patients should avoid driving or operating machinery., Anticholinergic effects: Diphenhydramine may cause urinary retention, blurred vision, or aggravation of glaucoma., Elderly patients: Increased sensitivity to CNS effects; use caution. |
| Food/Dietary | Avoid alcohol. Take with food or milk to minimize GI irritation. No known food-drug interactions beyond general NSAID and antihistamine precautions. |
| Clinical Pearls | Naproxen sodium (NSAID) and diphenhydramine (first-generation antihistamine) combination is used for nighttime pain relief. Risk of CNS depression increased with alcohol or other sedatives. Avoid in patients with severe cardiovascular disease, history of GI bleeding, or concurrent use of other NSAIDs or anticoagulants. Diphenhydramine may exacerbate urinary retention, glaucoma, or hyperthyroidism. Use lowest effective dose for shortest duration. |
| Patient Advice | Take with food or milk to reduce stomach upset. · Do not exceed recommended dose or use for more than 10 days. · Avoid alcohol while taking this medication. · May cause drowsiness; do not drive or operate machinery until you know how it affects you. · Stop and consult a doctor if you experience signs of stomach bleeding (black/bloody stools, vomit with blood), chest pain, or allergic reaction. |