Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION vs DHC PLUS
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Fexofenadine is a selective peripheral H1-receptor antagonist that inhibits histamine release from mast cells. Pseudoephedrine is a sympathomimetic amine that directly stimulates alpha-adrenergic receptors in the respiratory tract mucosa, causing vasoconstriction and reducing nasal congestion. It also has weak beta-adrenergic activity.
DHC PLUS is a combination of codeine (an opioid agonist) and homatropine (an anticholinergic). Codeine binds to mu-opioid receptors in the CNS, inhibiting ascending pain pathways and altering perception of pain. Homatropine antagonizes muscarinic acetylcholine receptors, reducing GI motility and secretions, which may decrease opioid-induced nausea and vomiting.
Relief of symptoms of seasonal allergic rhinitis (sneezing, rhinorrhea, itchy nose/palate/throat, itchy/watery/red eyes),Relief of nasal congestion associated with seasonal allergic rhinitis,Relief of symptoms of perennial allergic rhinitis,Relief of nasal congestion associated with perennial allergic rhinitis
Relief of acute moderate pain in adults,Off-label: management of diarrhea
1 tablet (fexofenadine 180 mg / pseudoephedrine 240 mg) orally every 24 hours.
1-2 tablets (dihydrocodeine 40 mg/paracetamol 500 mg per tablet) orally every 4-6 hours as needed, maximum 8 tablets per day.
Fexofenadine: terminal half-life 14.4 hours (range 11-17 h, ~4-fold longer than IV due to enterohepatic recirculation); pseudoephedrine: terminal half-life 4.3-8 hours (alkaline urine prolongs to 16 h).
3.5-5 hours for dihydrocodeine; prolonged in hepatic impairment (up to 8-10 hours) and may require dose adjustment.
Fexofenadine is minimally metabolized (≤5% of dose) by the liver, primarily via CYP3A4; other minor pathways involve CYP2D6 and CYP2C9. Pseudoephedrine is partially metabolized in the liver by N-demethylation (CYP2D6) and oxidative deamination.
Codeine is metabolized by CYP2D6 to morphine (active), and by CYP3A4 to norcodeine. Homatropine is metabolized via ester hydrolysis and N-demethylation. Both are excreted renally.
Fexofenadine: ~95% excreted unchanged in feces (80%) and urine (11-12%); pseudoephedrine: ~70-90% excreted unchanged in urine (major route).
Renal: ~90% as glucuronide conjugates, with 10% as unchanged dihydrocodeine and 5-10% as nordihydrocodeine; biliary/fecal: <5%.
Fexofenadine: 60-70% primarily to albumin and α1-acid glycoprotein; pseudoephedrine: negligible protein binding (<20%, mainly to albumin).
20-30% bound to albumin.
Fexofenadine: 5.4-5.8 L/kg (extensive tissue distribution, ~30-40 times plasma volume); pseudoephedrine: 2.6-3.5 L/kg (distributes into body water, crosses blood-brain barrier).
1.5 L/kg; reflects moderate tissue distribution due to lipophilicity.
Fexofenadine: ~33-40% (oral, decreased by fruit juices); pseudoephedrine: ~85-100% (oral, minimally affected by food).
Oral: ~60-70% due to first-pass metabolism; subcutaneous: ~80-90%; rectal: ~70-80%.
GFR 30-49 m L/min: 1 tablet every 24 hours; GFR 15-29 m L/min: 1 tablet every 48 hours; GFR <15 m L/min: contraindicated or not recommended.
GFR 30-50 m L/min: Administer every 6-8 hours; GFR 10-29 m L/min: Administer every 8-12 hours; GFR <10 m L/min: Avoid or use with extreme caution, reduce dose by 50% and monitor for toxicity.
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B). Not studied in severe impairment (Child-Pugh C); use with caution.
Child-Pugh Class A: No adjustment; Child-Pugh Class B: Reduce dose by 50% and extend interval to every 8 hours; Child-Pugh Class C: Avoid use due to risk of paracetamol hepatotoxicity and dihydrocodeine accumulation.
Not recommended for children under 12 years. For age >=12 years: same as adult dosing (1 tablet every 24 hours).
Not recommended for children under 12 years of age. For adolescents (12-18 years): Same adult dosing based on weight, typically 1 tablet every 4-6 hours, maximum 4 tablets per day.
Elderly patients may have reduced renal function; assess renal function prior to use. Initial dose may be adjusted based on renal function. Avoid use in patients with hypertension or cardiovascular disease due to pseudoephedrine.
Initiate with lowest effective dose, 1 tablet every 6-8 hours; maximum 4 tablets per day; monitor for CNS depression and constipation.
None
Warning: Risk of addiction, abuse, and misuse; life-threatening respiratory depression; accidental ingestion; neonatal opioid withdrawal syndrome; interactions with alcohol and CNS depressants; risk of medication errors with codeine; risks from concomitant use with benzodiazepines or other CNS depressants; and risks of use in children under 12 years, and in adolescents with certain respiratory conditions.
Cardiovascular effects (hypertension, palpitations, tachycardia, arrhythmias) especially in patients with pre-existing cardiovascular disease; CNS stimulation (insomnia, nervousness, dizziness, anxiety); risk of ischemic colitis; urinary retention (especially in patients with prostatic hypertrophy); increased intraocular pressure in patients with narrow-angle glaucoma; severe hypertension or coronary artery disease; MAOI use or within 14 days of discontinuation; use in renal impairment requires caution; avoid use with alcohol or other CNS depressants; caution in patients with hyperthyroidism, diabetes mellitus, or angle-closure glaucoma; elderly patients may be more sensitive to side effects.
Risk of respiratory depression,CYP2D6 ultrarapid metabolizers: increased toxicity,Anticholinergic effects (e.g., urinary retention, constipation),Use caution in elderly, renal/hepatic impairment,Avoid in patients with severe respiratory conditions
Concurrent use of or within 14 days after discontinuation of monoamine oxidase inhibitors (MAOIs); severe hypertension; severe coronary artery disease; narrow-angle glaucoma; urinary retention; hypersensitivity to any component
Hypersensitivity to codeine, homatropine, or any component,Significant respiratory depression,Acute or severe bronchial asthma,Paralytic ileus,Children under 12 years (codeine)
Fruit juices (apple, orange, grapefruit) significantly reduce fexofenadine absorption; take with water only. Avoid high-fat meals as they may affect pseudoephedrine absorption. No specific restrictions for pseudoephedrine, but avoid excessive caffeine (coffee, tea, cola) to reduce additive stimulant effects.
Avoid alcohol as it increases sedation and hepatotoxicity risk. High-fat meals may delay absorption but not significantly alter efficacy.
FDA Pregnancy Category C. First trimester: No adequate studies, animal studies show potential risk. Second and third trimesters: Risk unknown; associated with increased risk of gastrointestinal atresia and gastroschisis with first trimester pseudoephedrine use. Avoid in preeclampsia due to vasoconstriction.
DHC PLUS (dihydrocodeine/paracetamol): First trimester risk of neural tube defects with paracetamol use is low but not zero; dihydrocodeine may cause respiratory depression in neonate if used near term. Chronic use in third trimester can lead to neonatal opioid withdrawal syndrome.
Lactation Risk Category L3 (Moderately Safe). Fexofenadine excreted in breast milk in low amounts; M/P ratio not established. Pseudoephedrine excreted into breast milk with estimated relative infant dose 4.3% of maternal weight-adjusted dose. May reduce milk production and cause irritability in infants.
Dihydrocodeine and paracetamol are excreted in breast milk in low amounts. M/P ratio for dihydrocodeine is approximately 0.5-1.0. Use with caution; monitor infant for sedation and respiratory depression. Paracetamol is considered compatible with breastfeeding.
Pregnancy increases clearance of fexofenadine; however, no specific dose adjustment recommended. Dose of pseudoephedrine should be limited to lowest effective dose due to potential vasoconstriction. Avoid extended-release formulations in pregnancy if rapid delivery is anticipated.
Increased clearance of dihydrocodeine in pregnancy may require dose adjustment; however, avoid use if possible. Paracetamol pharmacokinetics are minimally altered; standard dosing is acceptable. Short-term use only; avoid high doses of paracetamol (>2g/day) in third trimester.
ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION contains fexofenadine 180 mg and pseudoephedrine 240 mg extended-release. Avoid in severe hypertension, coronary artery disease, narrow-angle glaucoma, urinary retention, and concurrent MAOI use or within 14 days. CNS stimulation possible; monitor for insomnia, nervousness, and dizziness. Not recommended in patients with impaired renal function (Cr Cl < 60 m L/min) due to fexofenadine accumulation. Do not crush or chew tablet.
DHC PLUS contains dihydrocodeine and paracetamol. Avoid in CYP2D6 ultra-rapid metabolizers due to morphine toxicity risk. Use with caution in patients with respiratory compromise, as dihydrocodeine can cause respiratory depression. Monitor liver function with prolonged paracetamol use.
Take one tablet daily with water; do not crush or chew.,Avoid taking with fruit juices (e.g., apple, orange, grapefruit) as they may decrease absorption.,Do not use with other products containing pseudoephedrine or antihistamines.,Stop and consult doctor if symptoms do not improve within 7 days or are accompanied by fever.,Avoid alcohol and sedatives as they may increase dizziness.,Discontinue if signs of hypertension or tachycardia occur.,Contraindicated within 14 days of stopping MAOIs.,Pregnant or nursing women should consult a physician before use.
Do not exceed recommended dose due to paracetamol hepatotoxicity risk.,Avoid alcohol while taking this medication.,May cause drowsiness or dizziness; avoid driving or operating machinery.,Take with food if gastrointestinal upset occurs.,Do not crush or chew extended-release formulations.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION vs DHC PLUS, answered by our medical review team.
ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION is a Antihistamine-Decongestant Combination that works by Fexofenadine is a selective peripheral H1-receptor antagonist that inhibits histamine release from mast cells. Pseudoephedrine is a sympathomimetic amine that directly stimulates alpha-adrenergic receptors in the respiratory tract mucosa, causing vasoconstriction and reducing nasal congestion. It also has weak beta-adrenergic activity.. DHC PLUS is a Antihistamine-Decongestant that works by DHC PLUS is a combination of codeine (an opioid agonist) and homatropine (an anticholinergic). Codeine binds to mu-opioid receptors in the CNS, inhibiting ascending pain pathways and altering perception of pain. Homatropine antagonizes muscarinic acetylcholine receptors, reducing GI motility and secretions, which may decrease opioid-induced nausea and vomiting.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION and DHC PLUS depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION is: 1 tablet (fexofenadine 180 mg / pseudoephedrine 240 mg) orally every 24 hours.. The standard adult dose of DHC PLUS is: 1-2 tablets (dihydrocodeine 40 mg/paracetamol 500 mg per tablet) orally every 4-6 hours as needed, maximum 8 tablets per day.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION and DHC PLUS in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ALLEGRA-D 24 HOUR ALLERGY AND CONGESTION is classified as Category C. FDA Pregnancy Category C. First trimester: No adequate studies, animal studies show potential risk. Second and third trimesters: Risk unknown; associated with increased risk of gas. DHC PLUS is classified as Category C. DHC PLUS (dihydrocodeine/paracetamol): First trimester risk of neural tube defects with paracetamol use is low but not zero; dihydrocodeine may cause respiratory depression in neon. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.