Acetaminophen, codeine, and doxylamine

PHARMACOLOGIC CATEGORY Analgesic, OpioidAntihistamine
DOSING: ADULTS — Oral: 1-2 tablets every 4 hours as needed; total dose should not exceed 12 tablets in a 24-hour period
DOSING: PEDIATRIC — Refer to adult dosing.
DOSING: RENAL IMPAIRMENT — No dosage adjustment required.
DOSING: HEPATIC IMPAIRMENT Acetaminophen: Use with caution. Limited, low-dose therapy usually well tolerated in hepatic disease/cirrhosis. However, cases of hepatotoxicity at daily acetaminophen dosages <4 g/day have been reported. Avoid chronic use in hepatic impairment.
Codeine: Dosage adjustment of codeine is probably necessary in hepatic insufficiency; no specific guidelines available.
DOSAGE FORMS — Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [CAN] = Canadian brand name
Tablet: Mersyndol® With Codeine [CAN]: Acetaminophen 325 mg, codeine 8 mg, and doxylamine 5 mg [not available in the U.S.]
DOSAGE FORMS: CONCISE — [CAN] = Canadian brand name
Tablet: Mersyndol® With Codeine [CAN]: Acetaminophen 325 mg, codeine 8 mg, and doxylamine 5 mg [not available in the U.S.]
USE — Relief of headache, cold symptoms, neuralgia, and muscular aches/pain
ADVERSE REACTIONS SIGNIFICANT — See individual agents.
CONTRAINDICATIONS — Hypersensitivity to acetaminophen, codeine, doxylamine, or any component of the formulation; significant respiratory depression (in unmonitored settings); acute or severe bronchial asthma; hypercapnia
WARNINGS / PRECAUTIONS Concerns related to adverse effects: CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving). Hepatotoxicity: Acetaminophen may cause severe hepatic toxicity on acute overdose; in addition, chronic daily dosing in adults has resulted in liver damage in some patients. Phenanthrene hypersensitivity: Use with caution in patients with hypersensitivity reactions to other phenanthrene-derivative opioid agonists (hydrocodone, hydromorphone, levorphanol, oxycodone, oxymorphone).
Disease-related concerns: Adrenal insufficiency: Use with caution in patients with adrenal insufficiency, including Addison's disease. Cardiovascular disease: Use with caution in patients with cardiovascular disease (including hypertension/hypotension and tachycardia). CNS depression/coma: Use with caution in patients with CNS depression or coma. Drug abuse: Use with caution in patients with a history of drug abuse or acute alcoholism; potential for drug dependency exists. Tolerance, psychological and physical dependence may occur with prolonged use. Ethanol use: Use with caution in patients with alcoholic liver disease; consuming 3 alcoholic drinks/day may increase the risk of liver damage. G6PD deficiency: Use with caution in patients with known G6PD deficiency. Gastrointestinal motility disorders: Use with caution in patients with gastrointestinal motility disorders; avoid in paralytic ileus. Glaucoma: Use with caution in patients with angle-closure glaucoma and/or increased intraocular pressure. Head trauma: Use with extreme caution in patients with head injury, intracranial lesions, or elevated intracranial pressure; exaggerated elevation of ICP may occur. Prostatic hyperplasia/urinary stricture: Use with caution in patients with prostatic hyperplasia and/or urinary stricture. Pyloroduodenal obstruction: Use with caution in patients with pyloroduodenal obstruction (including stenotic peptic ulcer). Seizure disorder: Use with caution in patients with a history of seizure disorder. Thyroid dysfunction: Use with caution in patients with thyroid dysfunction.
Concurrent drug therapy issues: Sedatives: Effects may be potentiated when used with other sedative drugs or ethanol.
Special populations: Debilitated patients: Use with caution in debilitated patients; there is a greater potential for critical respiratory depression, even at therapeutic dosages. Elderly: Use with caution in the elderly; may be more sensitive to adverse effects. Pediatrics: Safety and efficacy have not been established in children <12 years of age. Surgical patients: Use with caution in postoperative patients following thoracotomy or laparotomy due to suppression of cough.
Other warnings/precautions: Dosage limit: Limit total acetaminophen dose to <4 g/day.
RESTRICTIONS — CDSA-1; Not available in U.S.
DRUG INTERACTIONS Acetaminophen: Substrate (minor) of CYP1A2, 2A6, 2C9, 2D6, 2E1, 3A4; Inhibits CYP3A4 (weak)
Codeine: Substrate of CYP2D6 (major), 3A4 (minor); Inhibits CYP2D6 (weak)
Anticholinergic agents: Central and/or peripheral anticholinergic syndrome can occur when administered with opioid analgesics, phenothiazines and other antipsychotics (especially with high anticholinergic activity), tricyclic antidepressants, quinidine and some other antiarrhythmics, and antihistamines.
Cholinergic agents: Drugs with high anticholinergic activity may antagonize the therapeutic effect of cholinergic agents; includes donepezil, rivastigmine, and tacrine.
CNS depressants: Sedative effects may be additive with CNS depressants; includes ethanol, benzodiazepines, barbiturates, opioid analgesics, and other sedative agents; monitor for increased effect.
CYP2D6 inhibitors: May decrease the effects of codeine. Example inhibitors include chlorpromazine, delavirdine, fluoxetine, miconazole, paroxetine, pergolide, quinidine, quinine, ritonavir, and ropinirole.
Warfarin: The effect of warfarin may be enhanced.
ETHANOL / NUTRITION / HERB INTERACTIONS Ethanol: Avoid ethanol (may increase CNS depression).
Herb/Nutraceutical: Avoid valerian, St John's wort, kava kava, gotu kola (may increase CNS depression).
PREGNANCY IMPLICATIONS — There are no adequate and well-controlled studies in pregnant women. Should not be used in pregnancy unless the potential benefit to the mother justifies possible harm to the fetus.
LACTATION — No data available.
BREAST-FEEDING CONSIDERATIONS — Doxylamine may be excreted in breast milk, potentially resulting in sedative effects in nursing infants.
MONITORING PARAMETERS — Relief of pain, respiratory and mental status, blood pressure, bowel function
TOXICOLOGY / OVERDOSE COMPREHENSIVE — Symptoms of acetaminophen overdose include hepatic necrosis and blood dyscrasias, while opiate overdose may result in respiratory depression. Anticholinergic overdose may result in death, cardiopulmonary arrest, catatonic psychosis, CNS depression or stimulation, elevated CPK, mydriasis, seizures, rhabdomyolysis, or tachycardia.
Activated charcoal is effective at binding certain chemicals, and this is especially true for acetaminophen (use within 2 hours of ingestion).
Acetylcysteine 140 mg/kg orally (loading) followed by 70 mg/kg every 4 hours for 17 doses; therapy should be initiated based upon laboratory analysis suggesting high probability of hepatotoxic potential.
Naloxone 2 mg I.V. (0.01 mg/kg for children) with repeat administration as necessary up to a total of 10 mg; can also be used to reverse the toxic effects of the opiate.
CANADIAN BRAND NAMES — Mersyndol® With Codeine
INTERNATIONAL BRAND NAMES — Mersyndol With Codeine (CA)
MECHANISM OF ACTION — Acetaminophen inhibits the synthesis of prostaglandins in the central nervous system and peripherally blocks pain impulse generation; produces antipyresis from inhibition of hypothalamic heat-regulating center. Codeine binds to opiate receptors in the CNS, causing inhibition of ascending pain pathways, altering the perception of and response to pain; causes cough supression by direct central action in the medulla; produces generalized CNS depression. Doxylamine competes with histamine for H1-receptor sites on effector cells; blocks chemoreceptor trigger zone, diminishes vestibular stimulation, and depresses labyrinthine function through its central anticholinergic activity.
PHARMACODYNAMICS / KINETICS — See individual agents.