Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
PROMETHAZINE W/ CODEINE vs ALAVERT
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Codeine is a prodrug converted to morphine, a mu-opioid receptor agonist, which inhibits nociceptive transmission; promethazine is a phenothiazine derivative with H1-receptor antagonism, anticholinergic, and antiemetic effects.
Loratadine is a selective inverse agonist of peripheral histamine H1 receptors, preventing histamine-mediated effects in allergic reactions.
Relief of mild to moderate pain,Cough suppression
Seasonal allergic rhinitis,Perennial allergic rhinitis,Chronic idiopathic urticaria
10 m L (1 mg codeine, 6.25 mg promethazine per 5 m L) orally every 4-6 hours as needed for cough. Maximum: 60 m L per day. Do not exceed 5 days.
10 mg orally once daily; for PRN use, 10 mg orally every 4-6 hours as needed, not to exceed 24 mg/day.
Promethazine: 10-19 hours (terminal). Codeine: 2.5-3.5 hours (terminal); prolonged in renal impairment.
Terminal elimination half-life of loratadine is 8–11 hours; its active metabolite desloratadine has a half-life of 17–24 hours. The longer half-life of desloratadine contributes to sustained antihistaminic effect.
Codeine: Hepatic via CYP2D6 (to morphine), CYP3A4 (to norcodeine); Promethazine: Hepatic via CYP2B6, CYP2D6, and glucuronidation.
Primarily metabolized by CYP3A4 and CYP2D6 to active metabolite descarboethoxyloratadine.
Promethazine: renal (70% as metabolites, <1% unchanged), fecal (20-30%). Codeine: renal (90%, of which 5-10% unchanged, rest as metabolites), fecal (minor).
Approximately 40% of the dose is excreted in urine (25% as unchanged drug and 15% as active metabolite desloratadine) and 40% in feces (as metabolites).
Promethazine: 93% (primarily to albumin). Codeine: 7-25% (to albumin).
Loratadine: 97–99% bound to plasma proteins (primarily albumin and alpha-1-acid glycoprotein). Desloratadine: 82–87% bound.
Promethazine: 5-14 L/kg (extensive tissue distribution). Codeine: 3-6 L/kg (widely distributed).
Loratadine: approximately 120 L (1.7 L/kg for a 70 kg adult), indicating extensive tissue distribution. Desloratadine: 30–40 L/kg.
Promethazine: oral 25% (due to first-pass metabolism), IM ~88%. Codeine: oral 50-70% (converted to morphine via CYP2D6), IM ~80%.
Oral bioavailability is low (approximately 40–50%) due to extensive first-pass metabolism. Food increases bioavailability by 40% but does not affect clinical efficacy.
e GFR 30-59 m L/min: Administer every 6 hours; e GFR 15-29 m L/min: Administer every 8 hours; e GFR <15 m L/min: Avoid use or consider extended interval due to accumulation of codeine metabolites.
For GFR 30-50 m L/min: 10 mg every 48 hours. For GFR <30 m L/min or on dialysis: avoid use or adjust to 10 mg every 72 hours with close monitoring.
Child-Pugh A: No adjustment; Child-Pugh B: Reduce dose by 50% or extend interval; Child-Pugh C: Avoid use due to risk of hepatic encephalopathy and impaired codeine metabolism.
Child-Pugh A: no adjustment. Child-Pugh B: 10 mg every 48 hours. Child-Pugh C: avoid use or 10 mg every 72 hours.
Use not recommended in children <12 years due to risk of respiratory depression. For ages 12-18: 10-15 m L (with caution) every 4-6 hours as needed. Weight-based dosing: 0.5-1 mg/kg/dose of codeine (max 60 mg/day) with promethazine 0.25-0.5 mg/kg/dose (max 25 mg/dose).
Age 6-11 years: 5 mg orally once daily; for PRN use, 5 mg every 4-6 hours, max 15 mg/day. Age ≥12 years: 10 mg orally once daily or 10 mg every 4-6 hours PRN, max 24 mg/day.
Initiate with 5 m L orally every 6-8 hours; titrate cautiously due to increased sensitivity, risk of sedation, and anticholinergic effects. Maximum daily dose: 40 m L. Avoid in patients with significant cognitive impairment.
Initiate at 5 mg orally once daily; may increase to 10 mg once daily if tolerated and needed. Caution due to increased risk of anticholinergic effects and impaired renal function.
Warning: Risk of respiratory depression, especially in children; fatal respiratory depression can occur. Codeine is contraindicated in children <12 years and should not be used in children <18 years after tonsillectomy/adenoidectomy. Also, risk of opioid addiction, abuse, and misuse.
None.
Respiratory depression, risk of opioid-induced hyperalgesia, severe hypotension, seizures in patients with porphyria, sedation and impaired motor skills, risk of serotonin syndrome when combined with serotonergic drugs, avoid abrupt discontinuation, use caution in elderly, hepatic/renal impairment, and respiratory disorders.
Avoid use in patients with severe hepatic impairment,Renal impairment may require dose adjustment,Caution in elderly patients due to increased anticholinergic sensitivity
Hypersensitivity to codeine, promethazine, or any phenothiazine; children <12 years; postoperative management in children <18 years following tonsillectomy/adenoidectomy; significant respiratory depression; acute or severe bronchial asthma; GI obstruction; concurrent use of MAOIs or within 14 days.
Hypersensitivity to loratadine or any component of the formulation
Avoid alcohol; may enhance sedative effects. No specific food restrictions, but high-fat meals may delay absorption.
Grapefruit juice may slightly increase loratadine absorption but not clinically significant. No specific dietary restrictions. Alcohol may increase CNS depression.
PROMETHAZINE W/ CODEINE is contraindicated during all trimesters. First trimester: codeine is associated with increased risk of congenital malformations (cardiac, cleft palate) due to opioid receptor activation. Promethazine may cause mild neural tube defects. Second/third trimesters: codeine can cause fetal opioid dependence and neonatal abstinence syndrome; promethazine may cause respiratory depression and thrombocytopenia in neonates. Chronic use may lead to preterm birth and low birth weight. Do not use during labor and delivery due to risk of respiratory depression in the neonate.
ALAVERT (loratadine) is FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic effects, but no adequate, well-controlled studies in pregnant women. Based on available human data, first trimester exposure does not show increased risk of major malformations. Second and third trimester risks are not established, but adverse fetal outcomes are unlikely given lack of placental transfer concerns.
Breastfeeding not recommended. Codeine is excreted into breast milk with a milk-to-plasma (M/P) ratio of approximately 2.5-3.0 (for morphine, codeine active metabolite). In mothers who are CYP2D6 ultra-rapid metabolizers, codeine can lead to life-threatening respiratory depression in infants. Promethazine is excreted in low amounts but may cause sedation and apnea in neonates.
Loratadine is excreted into human breast milk. The milk-to-plasma ratio is approximately 1.17, with low relative infant dose (<2% of maternal weight-adjusted dose). Considered compatible with breastfeeding, but monitor infant for drowsiness or irritability. Caution in premature infants or those with renal impairment.
Pregnancy is a contraindication; thus, dosing adjustments are not applicable. If unavoidable, use the lowest effective dose for the shortest duration, but no safe dose established. Avoid during third trimester due to risk of neonatal respiratory depression. Codeine pharmacokinetics in pregnancy: increased clearance due to enhanced hepatic blood flow and CYP2D6 induction, but this is not a basis for dose adjustment as risk outweighs benefit.
No dose adjustment is routinely recommended for pregnancy. Pharmacokinetic changes during pregnancy (increased volume of distribution, hepatic metabolism) are not significant enough to require dose changes for loratadine. Standard adult dose (10 mg once daily) can be used.
Promethazine with codeine is contraindicated in children <6 years due to risk of fatal respiratory depression. Avoid in patients with asthma or COPD. Use with caution with other CNS depressants. Monitor for signs of serotonin syndrome if combined with serotonergic drugs.
Alavert (loratadine) is a non-sedating antihistamine with minimal anticholinergic effects. Onset of action is within 1-3 hours; peak effect at 8-12 hours. Useful for chronic urticaria and allergic rhinitis. Does not cause significant QTc prolongation. Avoid in severe hepatic impairment (Child-Pugh C) without dose adjustment.
May cause drowsiness; avoid driving or operating machinery.,Do not exceed recommended dose; risk of addiction and dependence.,Do not consume alcohol while taking this medication.,Take with food if gastrointestinal upset occurs.,Stop use and seek medical attention if breathing becomes difficult or you experience rash.
Take once daily at the same time, with or without food.,Do not exceed recommended dose to avoid side effects.,May cause mild drowsiness in some patients; avoid driving if affected.,Do not use for acute asthma attacks or lower respiratory symptoms.,Store at room temperature away from moisture and heat.,Notify your doctor if symptoms persist or worsen.
"Promethazine, a phenothiazine derivative with strong anticholinergic and sedative properties, combined with levocabastine, a histamine H1-receptor antagonist, results in additive anticholinergic and central nervous system (CNS) depressant effects. This synergy can lead to excessive sedation, impaired cognitive and motor function, and increased risk of anticholinergic side effects such as dry mouth, urinary retention, and constipation. Clinically, patients may experience heightened drowsiness, dizziness, and confusion, posing risks for falls or accidents, particularly in elderly or debilitated individuals."
"The combination of promethazine and gabapentin enacarbil results in additive central nervous system (CNS) depression, leading to enhanced sedative effects, dizziness, and impaired cognitive or motor function. This interaction is primarily mediated by the synergistic pharmacodynamic actions of both drugs on GABAergic and histaminergic pathways, increasing the risk of excessive sedation, respiratory depression, and falls, particularly in elderly or debilitated patients. Clinical outcomes may include profound drowsiness, confusion, and increased risk of accidental injury, necessitating cautious dose titration and monitoring."
"Gabapentin, a GABA analog with central nervous system depressant effects, interacts pharmacodynamically with the antihistamine and anticholinergic agent Promethazine. Co-administration results in additive sedation, dizziness, and cognitive impairment due to enhanced central nervous system depression. This increases the risk of falls, respiratory depression, and impaired psychomotor function, particularly in elderly patients."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about PROMETHAZINE W/ CODEINE vs ALAVERT, answered by our medical review team.
PROMETHAZINE W/ CODEINE is a Antihistamine / Antiemetic that works by Codeine is a prodrug converted to morphine, a mu-opioid receptor agonist, which inhibits nociceptive transmission; promethazine is a phenothiazine derivative with H1-receptor antagonism, anticholinergic, and antiemetic effects.. ALAVERT is a Second-generation Antihistamine that works by Loratadine is a selective inverse agonist of peripheral histamine H1 receptors, preventing histamine-mediated effects in allergic reactions.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between PROMETHAZINE W/ CODEINE and ALAVERT 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 PROMETHAZINE W/ CODEINE is: 10 m L (1 mg codeine, 6.25 mg promethazine per 5 m L) orally every 4-6 hours as needed for cough. Maximum: 60 m L per day. Do not exceed 5 days.. The standard adult dose of ALAVERT is: 10 mg orally once daily; for PRN use, 10 mg orally every 4-6 hours as needed, not to exceed 24 mg/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 PROMETHAZINE W/ CODEINE and ALAVERT 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. PROMETHAZINE W/ CODEINE is classified as Category A/B. PROMETHAZINE W/ CODEINE is contraindicated during all trimesters. First trimester: codeine is associated with increased risk of congenital malformations (cardiac, cleft palate) due. ALAVERT is classified as Category C. ALAVERT (loratadine) is FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic effects, but no adequate, well-controlled studies in pregnant women. Based on ava. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.