CODEINE, ASPIRIN, APAP FORMULA NO. 4
Clinical safety rating: avoid
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur especially in CYP2D6 ultra-rapid metabolizers.
Codeine is a prodrug converted to morphine, which acts as a μ-opioid receptor agonist, producing analgesia, cough suppression, and euphoria. Aspirin irreversibly inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis, leading to analgesia, anti-inflammatory, and antipyretic effects. Acetaminophen (APAP) inhibits cyclooxygenase (COX) enzymes, but its central action via cannabinoid receptors may contribute to analgesia and antipyresis.
| Metabolism | Codeine: CYP2D6 metabolizes codeine to morphine (active); CYP3A4 metabolizes to norcodeine; UGT2B7 conjugates morphine. Aspirin: Hydrolyzed to salicylic acid by esterases; salicylic acid conjugated by glucuronidation and oxidation. Acetaminophen: Primarily conjugated by glucuronidation (UGT1A1, UGT1A6, UGT1A9) and sulfation (SULT1A1, SULT1A3); minor oxidation by CYP2E1, CYP1A2, CYP3A4 to toxic NAPQI. |
| Excretion | Codeine: Renal (90% as metabolites, 10% unchanged). Aspirin: Renal (75% as salicyluric acid, 10% as salicyl glucuronides, 10% as gentisic acid, <10% unchanged). Acetaminophen: Renal (90-100% as glucuronide and sulfate conjugates, <5% unchanged). |
| Half-life | Codeine: 2.5-3 hours (terminal half-life); Aspirin: 15-20 minutes (parent drug), 2-3 hours for salicylate at low doses, up to 15-30 hours at high doses (due to saturable metabolism); Acetaminophen: 2-3 hours (therapeutic doses), prolonged in overdose (>4 hours). |
| Protein binding | Codeine: 7-25% (albumin); Aspirin: 80-90% (albumin), desacetylated to salicylate which is 50-80% bound; Acetaminophen: 10-25% (albumin). |
| Volume of Distribution | Codeine: 3-6 L/kg; Aspirin: 0.15-0.2 L/kg (salicylate); Acetaminophen: 0.7-1.0 L/kg. |
| Bioavailability | Codeine: Oral 90% (first-pass effect minimal, but extensive metabolism); Aspirin: Oral 50-70% (presystemic hydrolysis); Acetaminophen: Oral 60-90% (first-pass metabolism saturable at high doses). |
| Onset of Action | Oral: Codeine 30-60 minutes; Aspirin 30-60 minutes; Acetaminophen 30-60 minutes. |
| Duration of Action | Codeine: 4-6 hours; Aspirin: 4-6 hours (analgesic/antipyretic), up to 12 hours (antiplatelet); Acetaminophen: 4-6 hours. |
1-2 tablets orally every 4-6 hours as needed for pain; maximum 8 tablets per day.
| Dosage form | CAPSULE |
| Renal impairment | GFR 30-50 mL/min: reduce dose by 25% or extend interval; GFR <30 mL/min: avoid use due to aspirin and codeine accumulation. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% or extend interval; Child-Pugh C: contraindicated. |
| Pediatric use | Not recommended in children <12 years due to acetaminophen and aspirin content; for age ≥12 years, weight-based: 0.5-1 mg/kg codeine component every 4-6 hours, max 60 mg codeine per dose; aspirin component 10-15 mg/kg every 4-6 hours; limit acetaminophen to <75 mg/kg/day. |
| Geriatric use | Start with lowest effective dose (e.g., 1 tablet every 6 hours); avoid in patients with renal impairment, peptic ulcer disease, or bleeding disorders; monitor for constipation and CNS depression. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur especially in CYP2D6 ultra-rapid metabolizers.
| FDA category | Positive |
| Breastfeeding | Codeine is excreted into breast milk; M/P ratio is approximately 2.5 for codeine and 2.0 for morphine. Risk of infant opioid toxicity is increased in mothers with CYP2D6 ultra-rapid metabolizer phenotype. ASA is excreted in low amounts but may cause Reye's syndrome; thus caution. APAP is excreted in low amounts (M/P ratio ~0.91–1.42) and is considered compatible with breastfeeding. Combination product should be used with caution; monitor infant for sedation, respiratory depression, poor feeding. |
■ FDA Black Box Warning
WARNING: RISK OF MEDICATION ERRORS; ADDICTION, ABUSE, AND MISUSE; LIFE-THREATENING RESPIRATORY DEPRESSION; ACCIDENTAL INGESTION; ULTRA-RAPID METABOLISM OF CODEINE AND OTHER RISK FACTORS FOR LIFE-THREATENING RESPIRATORY DEPRESSION IN CHILDREN; NEONATAL OPIOID WITHDRAWAL SYNDROME; CYTOCHROME P450 3A4 INTERACTION; CONCOMITANT USE OF BENZODIAZEPINES OR OTHER CNS DEPRESSANTS; RISK FROM CONCOMITANT USE WITH CYP3A4 INHIBITORS OR DISCONTINUATION OF CYP3A4 INDUCERS; RISKS FROM CONCOMITANT USE WITH ALCOHOL; RISK OF REYE'S SYNDROME IN CHILDREN WITH VIRAL ILLNESSES (ASPIRIN); RISK OF GASTROINTESTINAL BLEEDING, ULCERATION, AND PERFORATION (ASPIRIN); RISK OF SEVERE LIVER INJURY (ACETAMINOPHEN).
| Common Effects | cough |
| Serious Effects |
Hypersensitivity to any component, severe respiratory depression, acute or severe bronchial asthma, gastrointestinal obstruction, known CYP2D6 ultra-rapid metabolizers (codeine), children <12 years of age (codeine), children <18 years following tonsillectomy/adenoidectomy (codeine), viral illness in children (aspirin), active peptic ulcer disease, severe liver impairment, severe renal impairment, concomitant use with MAOIs or within 14 days, pregnancy (third trimester for aspirin; prolonged use of opioids may cause neonatal withdrawal), breastfeeding (codeine at high doses).
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| Teratogenic Risk | First trimester: Codeine is associated with increased risk of congenital malformations, particularly cardiac defects, with data suggesting a dose-dependent relationship. Aspirin (ASA) is contraindicated due to risk of neural tube defects and gastroschisis. APAP (acetaminophen) is generally considered low risk but data are conflicting. Second and third trimesters: Codeine may cause fetal dependence and neonatal withdrawal syndrome. ASA use in third trimester is contraindicated due to premature closure of ductus arteriosus, oligohydramnios, and bleeding risk. APAP is considered safe at therapeutic doses. |
| Fetal Monitoring | Maternal: Assess pain control, evaluate for opioid-related adverse effects (respiratory depression, constipation), monitor for bleeding (ASA effect). Monitor liver function and renal function with chronic use. Fetal/neonatal: Serial ultrasound for fetal growth and amniotic fluid volume (ASA effect), fetal echocardiography if available. After delivery, observe neonate for signs of opioid withdrawal (irritability, tremors, poor feeding, seizures). |
| Fertility Effects | Chronic opioid use may disrupt hypothalamic-pituitary-gonadal axis, leading to menstrual irregularities, anovulation, and reduced fertility. Aspirin at high doses may impair implantation; low-dose aspirin may improve fertility in certain conditions (e.g., antiphospholipid syndrome). Acetaminophen has limited evidence for fertility effects; some studies suggest reduced time to pregnancy with intermittent use, but routine use may be associated with ovulatory infertility. |
| Precautions | Respiratory depression, opioid-induced hyperalgesia, adrenal insufficiency, hypotension, seizure, severe hypotension, gastrointestinal obstruction, hepatotoxicity, Reye's syndrome, bleeding risk, renal impairment, hypersensitivity reactions, drug dependence, withdrawal. |