Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
DHC PLUS vs PROMETH VC PLAIN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
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.
Promethazine is a phenothiazine derivative that acts as a potent histamine H1 receptor antagonist, blocking allergic reactions; it also has anticholinergic, antiemetic, sedative, and local anesthetic effects.
Relief of acute moderate pain in adults,Off-label: management of diarrhea
FDA: Allergic conditions (rhinitis, urticaria, pruritus), motion sickness, nausea/vomiting, preoperative sedation, postoperative pain control (adjunct),Off-label: Nausea in pregnancy (morning sickness), vertigo, sedation in pediatric procedures
1-2 tablets (dihydrocodeine 40 mg/paracetamol 500 mg per tablet) orally every 4-6 hours as needed, maximum 8 tablets per day.
Adults: 1-2 tablets (each containing Promethazine 6.25 mg and Phenylephrine 5 mg) orally every 4-6 hours; maximum 12 tablets per day.
3.5-5 hours for dihydrocodeine; prolonged in hepatic impairment (up to 8-10 hours) and may require dose adjustment.
Promethazine: terminal half-life 9-16 hours (mean 12 hours) in adults; longer in elderly (13.5-18 hours) and in hepatic impairment. Phenylephrine: half-life 2-3 hours.
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.
Primarily hepatic metabolism via CYP2D6 and other pathways; metabolites include promethazine sulfoxide and N-demethylated derivatives.
Renal: ~90% as glucuronide conjugates, with 10% as unchanged dihydrocodeine and 5-10% as nordihydrocodeine; biliary/fecal: <5%.
Primarily renal; promethazine is excreted in urine as unchanged drug (approximately 6%) and as metabolites (promethazine sulfoxide and N-demethylpromethazine); less than 1% excreted in feces. Phenylephrine is primarily metabolized by MAO and COMT; renal excretion of metabolites and unchanged drug (about 16%).
20-30% bound to albumin.
Promethazine: approximately 93% bound to plasma proteins (mainly albumin). Phenylephrine: approximately 95% bound to plasma proteins (mainly albumin).
1.5 L/kg; reflects moderate tissue distribution due to lipophilicity.
Promethazine: Vd 5-17 L/kg (mean ~12 L/kg), indicating extensive tissue distribution. Phenylephrine: Vd 4-5 L/kg, also widely distributed.
Oral: ~60-70% due to first-pass metabolism; subcutaneous: ~80-90%; rectal: ~70-80%.
Oral promethazine: approximately 25% due to extensive first-pass metabolism. Intramuscular: nearly 100%. Rectal: approximately 70% of oral. Phenylephrine: oral bioavailability is low (about 38%) due to first-pass metabolism by MAO in gut and liver.
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 specific guidelines; use with caution in renal impairment (Cr Cl <30 m L/min) due to potential accumulation of promethazine; consider dose reduction or extended intervals.
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.
Child-Pugh Class A-C: Use with caution; reduce dose or avoid in severe hepatic impairment (Child-Pugh Class C) due to decreased metabolism of promethazine.
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.
Children aged 6-12 years: 1 tablet orally every 4-6 hours; maximum 6 tablets per day. Not recommended for children under 6 years due to risk of respiratory depression.
Initiate with lowest effective dose, 1 tablet every 6-8 hours; maximum 4 tablets per day; monitor for CNS depression and constipation.
Elderly patients: Initiate at lower doses (e.g., 1 tablet orally every 6-8 hours) and titrate carefully; monitor for anticholinergic effects, sedation, and orthostatic hypotension.
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.
Promethazine should not be used in children younger than 2 years due to risk of respiratory depression, including fatalities. Use in children aged 2+ with caution. Not for intra-arterial or subcutaneous injection (risk of severe tissue injury).
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
Risk of respiratory depression (especially in children, elderly, or with CNS depressants); use caution in asthma, sleep apnea, respiratory insufficiency. May impair cognitive/motor function; avoid alcohol. Extrapyramidal symptoms (rare). Caution in glaucoma, prostatic hyperplasia, urinary retention. Use in pregnancy (only if clearly needed).
Hypersensitivity to codeine, homatropine, or any component,Significant respiratory depression,Acute or severe bronchial asthma,Paralytic ileus,Children under 12 years (codeine)
Hypersensitivity to promethazine or phenothiazines; children <2 years; comatose patients; CNS depression (e.g., alcohol, barbiturates); Reye's syndrome (avoid in children with viral illness due to risk of Reye's? – actually contraindicated in patients with suspected Reye's). Also contraindicated for intra-arterial or subcutaneous injection.
Avoid alcohol as it increases sedation and hepatotoxicity risk. High-fat meals may delay absorption but not significantly alter efficacy.
No clinically significant food interactions. However, taking with food may reduce gastrointestinal upset. Avoid grapefruit juice as it may theoretically increase sedation.
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.
First trimester: Avoid. Inadequate studies; animal studies not sufficient. Second/third trimester: Use only if clearly needed; may cause neonatal respiratory depression, irritability, and tremors if used near term.
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.
Promethazine is excreted into breast milk in small amounts; M/P ratio unknown. Caution suggested; avoid in infants with apnea, respiratory issues, or in mothers of preterm infants.
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.
No standard dose adjustment required during pregnancy. Use lowest effective dose; monitor for increased sedation and anticholinergic effects due to physiological changes.
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.
Promethazine is a phenothiazine derivative with antihistamine, antiemetic, sedative, and anticholinergic properties. Administer deep IM if parenteral route required; avoid intra-arterial or subcutaneous injection due to risk of severe tissue damage. Monitor for extrapyramidal symptoms in children and elderly. Use with caution in patients with asthma, COPD, or sleep apnea due to respiratory depression risk. Do not use in children <2 years due to risk of fatal respiratory depression.
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.
Do not drive or operate heavy machinery until you know how this medication affects you, as it can cause drowsiness and dizziness.,Avoid alcohol and other central nervous system depressants while taking this medication.,Take exactly as prescribed; do not exceed recommended dose or duration.,Contact your healthcare provider if you experience difficulty breathing, involuntary muscle movements, or signs of jaundice (yellowing of skin/eyes).
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 DHC PLUS vs PROMETH VC PLAIN, answered by our medical review team.
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.. PROMETH VC PLAIN is a Antihistamine-decongestant combination that works by Promethazine is a phenothiazine derivative that acts as a potent histamine H1 receptor antagonist, blocking allergic reactions; it also has anticholinergic, antiemetic, sedative, and local anesthetic effects.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between DHC PLUS and PROMETH VC PLAIN 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 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.. The standard adult dose of PROMETH VC PLAIN is: Adults: 1-2 tablets (each containing Promethazine 6.25 mg and Phenylephrine 5 mg) orally every 4-6 hours; maximum 12 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 DHC PLUS and PROMETH VC PLAIN 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. 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. PROMETH VC PLAIN is classified as Category C. First trimester: Avoid. Inadequate studies; animal studies not sufficient. Second/third trimester: Use only if clearly needed; may cause neonatal respiratory depression, irritabili. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.