Hydrocodone-Acetaminophen
hydrocodone bitartrate / acetaminophen (Norco, Vicodin, Lortab)
Indications
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Pain severe enough to require an opioid analgesic and for which alternative treatments are inadequate | Adults | Short-term opioid-APAP combination; as-needed or around-the-clock for acute/chronic pain | FDA Approved |
Hydrocodone-acetaminophen is the most widely prescribed opioid combination product in the United States and historically one of the most frequently prescribed medications overall. The combination leverages two complementary analgesic mechanisms: hydrocodone’s mu-opioid receptor agonism for central pain modulation and acetaminophen’s peripheral analgesic and antipyretic effects, producing additive analgesia that permits lower opioid doses. The combination is available in multiple hydrocodone-to-acetaminophen ratios, all limited to 325 mg of acetaminophen per dosage unit per FDA mandate (2011) to reduce hepatotoxicity risk. It is appropriate for moderate-to-moderately-severe pain where non-opioid alternatives have failed or are insufficient. Hydrocodone also possesses antitussive properties, though its combination with acetaminophen is not indicated for cough.
Dosing
Adult Dosing by Formulation Strength
| Strength (HC/APAP) | Dose | Frequency | Max Tablets/Day | Max APAP/Day |
|---|---|---|---|---|
| 2.5/325 mg or 5/325 mg | 1–2 tablets | q4–6h PRN | 8 tablets | 2,600 mg |
| 7.5/325 mg | 1 tablet | q4–6h PRN | 6 tablets | 1,950 mg |
| 10/325 mg | 1 tablet | q4–6h PRN | 6 tablets | 1,950 mg |
| Oral solution (7.5/325 mg per 15 mL) | 1 tablespoon (15 mL) | q4–6h PRN | 6 tablespoons (90 mL) | 1,950 mg |
Special Population Dosing
| Population | Guidance | Key Concern |
|---|---|---|
| Elderly / Debilitated | Start at lowest strength (2.5/325); titrate cautiously | Altered PK, increased respiratory depression risk; Beers Criteria caution |
| Hepatic impairment | Avoid chronic use; limit APAP to ≤2 g/day; reduce hydrocodone dose | APAP hepatotoxicity risk; reduced hydrocodone clearance |
| Renal impairment | Start low; titrate cautiously; extend intervals | Higher hydrocodone plasma concentrations; metabolite accumulation |
| Pediatric | Use and dose determined by physician | Safety/efficacy not established for most formulations; fatal overdose risk |
The maximum daily dose of acetaminophen from all sources must not exceed 4,000 mg in healthy adults (FDA limit), though many guidelines recommend a practical limit of 3,000 mg/day for chronic use and ≤2,000 mg/day in patients with hepatic disease or chronic alcohol use. In 2011, the FDA mandated that all prescription APAP-combination products contain no more than 325 mg of acetaminophen per dosage unit. Always account for ALL sources of acetaminophen (OTC products, other prescriptions) when prescribing. Acetaminophen doses exceeding 4 g/day have been associated with acute liver failure, liver transplant, and death.
Pharmacology
Mechanism of Action
Hydrocodone: A semi-synthetic opioid derived from codeine that functions as a mu-opioid receptor agonist, with additional activity at delta- and kappa-opioid receptors at higher doses. Its analgesic effects are mediated both by the parent compound and by its active metabolite hydromorphone, which has 5–100-fold greater binding affinity for the mu-opioid receptor. Hydrocodone is metabolized by CYP2D6 to hydromorphone (O-demethylation) and by CYP3A4 to norhydrocodone (N-demethylation), with approximately 40% of clearance occurring through non-CYP pathways. Pain relief may correlate more closely with hydromorphone plasma concentrations than with those of the parent compound.
Acetaminophen (APAP): A non-opioid analgesic and antipyretic whose precise mechanism remains incompletely understood. It is thought to act primarily through inhibition of central cyclooxygenase (COX) pathways and activation of the descending serotonergic inhibitory pain pathway. Unlike NSAIDs, acetaminophen has minimal anti-inflammatory activity and does not inhibit peripheral COX at therapeutic doses. Hepatic metabolism produces the reactive intermediate NAPQI (N-acetyl-p-benzoquinone imine) via CYP2E1, which is normally detoxified by glutathione conjugation but can cause hepatocellular necrosis when glutathione stores are depleted (overdose, chronic alcohol use, or malnutrition).
ADME Profile
| Parameter | Hydrocodone | Acetaminophen |
|---|---|---|
| Absorption | Oral bioavailability ~25%; Tmax 1.3 ± 0.3 h; Cmax 23.6 ± 5.2 ng/mL (10 mg dose); well absorbed from GI tract; onset 10–20 min | Rapidly and almost completely absorbed from GI tract; bioavailability >85%; Tmax 0.5–1 h |
| Distribution | Distributed throughout body tissues; specific Vd data limited for IR combination products; crosses placenta; detected in breast milk | Distributed throughout most body tissues; protein binding 10–25% (low); Vd ~0.9 L/kg |
| Metabolism | Hepatic: CYP2D6 → hydromorphone (active, 5–100x higher mu-receptor affinity); CYP3A4 → norhydrocodone (major circulating metabolite, minimal CNS penetration); 6-keto reduction to 6α- and 6β-hydrocodol; ~40% via non-CYP pathways | Hepatic conjugation: glucuronidation (~55%) and sulfation (~30%); CYP2E1 → NAPQI (toxic metabolite, ~5–10%); NAPQI detoxified by glutathione conjugation |
| Elimination | t½ ~3.8 h (IR, range 3.3–4.4 h); 7–9 h (ER); ~85% excreted in urine within 24 h (~12% unchanged, 5% norhydrocodone, 4% conjugated hydrocodone, 3% 6-hydrocodol) | t½ 1.25–3 h (prolonged in liver damage/overdose); principally by hepatic conjugation and renal excretion of metabolites; ~3% excreted unchanged |
Side Effects
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Lightheadedness / Dizziness | >10% | Among the most frequently reported effects per FDA PI; more prominent in ambulatory patients |
| Sedation / Drowsiness | >10% | Dose-related; tolerance typically develops within days; warn about driving and hazardous activities |
| Nausea | >10% | Usually resolves within 3–5 days; can be minimized by taking with food and slow titration |
| Constipation | >10% | Does not habituate; proactive bowel regimen mandatory from day 1 of therapy |
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Vomiting | 5–10% | CTZ-mediated; usually habituates; assess for dehydration if persistent |
| Pruritus / Skin rash | 1–5% | Histamine-mediated (hydrocodone) or allergic (APAP); distinguish from true allergy |
| Dysphoria / Euphoria | 1–5% | Euphoria contributes to abuse potential; more common in ambulatory patients without severe pain |
| Urinary retention | 1–5% | Increased detrusor tone; more common in elderly men with prostatic hypertrophy |
| Dry mouth | 1–5% | Encourage oral hydration; long-term use increases dental caries risk |
| Adverse Effect | Component | Typical Onset | Required Action |
|---|---|---|---|
| Respiratory depression | Hydrocodone | First 24–72 h or after dose increase; higher risk with CYP3A4 inhibitors | Naloxone; ventilatory support; dose reduction |
| Hepatotoxicity / Acute liver failure | Acetaminophen | 24–72 h after excessive APAP dose (>4 g/day); earlier with alcohol/malnutrition | N-acetylcysteine (NAC); hepatology consult; assess all APAP sources; may require liver transplant |
| Serotonin syndrome | Hydrocodone | Hours to days with concurrent serotonergic drugs | Discontinue all serotonergic agents; cyproheptadine; supportive care |
| Adrenal insufficiency | Hydrocodone | After ≥1 month of use | Cortisol testing; taper opioid; physiologic steroid replacement |
| Neonatal opioid withdrawal syndrome | Hydrocodone | Hours to days after delivery | Neonatal monitoring; supportive care per neonatology protocols |
| Severe skin reactions (Stevens-Johnson Syndrome, toxic epidermal necrolysis, AGEP) | Acetaminophen (rare) | Days to weeks | Discontinue immediately at first sign of rash; dermatology consultation and supportive care |
This combination product carries two distinct toxicity risks that must be monitored simultaneously. The hydrocodone component poses the risk of respiratory depression and opioid-related adverse effects, while the acetaminophen component poses the risk of dose-dependent hepatotoxicity, which can progress to acute liver failure and death. In overdose, the presentation may be biphasic: early opioid toxicity (respiratory depression, sedation) followed by delayed hepatotoxicity (24–72 h). N-acetylcysteine is the specific antidote for acetaminophen toxicity and is most effective when administered within 8 hours of ingestion. Naloxone is the antidote for the opioid component.
Drug Interactions
Hydrocodone-acetaminophen has a dual interaction profile: pharmacokinetic interactions affecting hydrocodone metabolism (CYP3A4 and CYP2D6) and pharmacodynamic interactions common to all opioids, plus acetaminophen-specific hepatotoxicity interactions.
Monitoring
- Respiratory StatusAt initiation; after dose increases
RoutineMonitor respiratory rate, sedation level, and SpO2 during first 24–72 h and after any dose escalation or addition of CYP3A4 inhibitors. - Hepatic Function (LFTs)Baseline; periodically with chronic use
RoutineALT, AST, bilirubin at baseline. Monitor more frequently in patients with liver disease, chronic alcohol use, or taking >2 g APAP/day. Acetaminophen hepatotoxicity can occur even at recommended doses in susceptible patients. - Total Daily APAP IntakeEach visit
RoutineAudit ALL sources of acetaminophen at every visit: prescription combinations, OTC analgesics, cold/flu products. Max 4 g/day (healthy adults); 2 g/day (liver disease/alcohol). - Pain AssessmentEach visit
RoutineValidated pain scale; re-evaluate risk-benefit at least every 3 months for chronic use; document functional outcomes. - Signs of Misuse / OUDEach visit
RoutinePDMP check before prescribing and periodically; risk assessment at baseline; urine drug testing as indicated. Note: urine may test positive for both hydrocodone and hydromorphone (expected metabolite). - Bowel FunctionEach visit
RoutineInitiate preventive bowel regimen at day 1. Constipation does not habituate. - Renal FunctionBaseline if impaired
Trigger-basedHigher hydrocodone concentrations in renal impairment; monitor for accumulation.
Contraindications & Cautions
Absolute Contraindications
- Significant respiratory depression — in settings without monitoring or resuscitative equipment
- Acute or severe bronchial asthma — in unmonitored settings
- Known or suspected GI obstruction, including paralytic ileus
- Hypersensitivity to hydrocodone or acetaminophen
Relative Contraindications
- Severe hepatic impairment — acetaminophen hepatotoxicity risk dramatically increased; consider opioid without APAP
- Active liver disease or hepatic decompensation — risk of APAP-induced acute liver failure
- Chronic alcohol use (≥3 drinks/day) — synergistic hepatotoxicity with APAP; limit to ≤2 g/day if prescribed
- History of substance use disorder — Schedule II; high abuse potential
Use with Caution
- Elderly or debilitated patients — increased sensitivity; Beers Criteria caution
- Head injury or raised ICP — may elevate ICP; miosis obscures neurological assessment
- COPD or cor pulmonale — reduced respiratory reserve
- CYP2D6 ultra-rapid metabolizers — may produce excessive hydromorphone; monitor closely
Addiction, abuse, and misuse: Hydrocodone exposes patients to risks of addiction, abuse, and misuse, which can lead to overdose and death.
Life-threatening respiratory depression: Serious, life-threatening, or fatal respiratory depression may occur, especially during initiation or dose escalation.
Accidental ingestion: Accidental ingestion of even one dose, especially by children, can be fatal.
Neonatal opioid withdrawal syndrome: Prolonged use during pregnancy can cause life-threatening neonatal withdrawal.
CNS depressant interactions: Concomitant use with benzodiazepines or other CNS depressants may result in profound sedation, respiratory depression, coma, and death.
Cytochrome P450 3A4 interaction: Concomitant use with CYP3A4 inhibitors may increase hydrocodone plasma concentrations and cause potentially fatal respiratory depression. Monitor closely when starting or stopping CYP3A4 inhibitors or inducers.
Hepatotoxicity (acetaminophen): Acetaminophen has been associated with cases of acute liver failure, at times resulting in liver transplant and death. Most cases involve doses exceeding 4,000 mg/day and/or multiple acetaminophen-containing products.
REMS: An opioid analgesic Risk Evaluation and Mitigation Strategy (REMS) is required to ensure benefits outweigh risks of addiction, abuse, and misuse.
Patient Counselling
How to Take
Take hydrocodone-acetaminophen exactly as prescribed, every 4–6 hours as needed for pain. Do not take more tablets per day than prescribed. You may take it with food to reduce stomach upset. Store securely out of reach of children and others. Accidental ingestion by a child can be fatal.
Sources
- NORCO (hydrocodone bitartrate and acetaminophen) Tablets — FDA-Approved Prescribing Information (2019). accessdata.fda.govPrimary reference for dosing, boxed warnings, CYP3A4 interaction guidance, contraindications, and acetaminophen hepatotoxicity warnings.
- Hydrocodone Bitartrate and Acetaminophen Tablets — DailyMed. dailymed.nlm.nih.govSource for hydrocodone PK data: Tmax 1.3 h, Cmax 23.6 ng/mL, t½ 3.8 h; acetaminophen PK and adverse reactions.
- FDA Drug Safety Communication: Prescription acetaminophen products to be limited to 325 mg per dosage unit (2011). fda.govFDA mandate limiting APAP per dosage unit in combination products to reduce hepatotoxicity risk.
- Singla A, Sloan P. Pharmacokinetic evaluation of hydrocodone/acetaminophen for pain management. J Opioid Manag. 2013;9(1):71–80. doi:10.5055/jom.2013.0149Comprehensive PK review of the hydrocodone-acetaminophen combination with clinical pharmacokinetic parameters.
- Hutchinson MR, Menelaou A, Foster DJ, et al. CYP2D6 and CYP3A4 involvement in the primary oxidative metabolism of hydrocodone by human liver microsomes. Br J Clin Pharmacol. 2004;57(3):287–297. doi:10.1046/j.1365-2125.2003.02002.xDefinitive study establishing CYP2D6 → hydromorphone and CYP3A4 → norhydrocodone metabolic pathways, and that ~40% of clearance is via non-CYP routes.
- Madadi P, Hildebrandt D, Gong IY, et al. Fatal hydrocodone overdose in a child: pharmacogenetics and drug interactions. Pediatrics. 2010;126(4):e986–e989. doi:10.1542/peds.2009-1907Case report illustrating fatal consequences of CYP3A4 inhibition in a CYP2D6 poor metabolizer, highlighting pharmacogenomic risks.
- Dowell D, Ragan KR, Jones CM, Baldwin GT, Chou R. CDC Clinical Practice Guideline for Prescribing Opioids for Pain — United States, 2022. MMWR Recomm Rep. 2022;71(No. RR-3):1–95. doi:10.15585/mmwr.rr7103a1Current CDC guideline on opioid prescribing for pain; dosing thresholds, monitoring, and risk mitigation.
- American Geriatrics Society 2023 Updated AGS Beers Criteria. J Am Geriatr Soc. 2023;71(7):2052–2081. doi:10.1111/jgs.18372Hydrocodone-acetaminophen among most frequently prescribed medications associated with ER visits in elderly.
- Jaeschke H. Acetaminophen: dose-dependent drug hepatotoxicity and acute liver failure in patients. Dig Dis. 2015;33(4):464–471. doi:10.1159/000374090Review of APAP hepatotoxicity mechanisms including CYP2E1-mediated NAPQI formation and glutathione depletion.
- Overholser BR, Foster DR. Opioid pharmacokinetic drug-drug interactions. Am J Manag Care. 2011;17(Suppl 11):S276–S287. PubMed: 21999760Comprehensive review of opioid CYP-mediated interactions applicable to hydrocodone including CYP3A4/CYP2D6 pathways.
- Hydrocodone and Acetaminophen — StatPearls [Internet]. National Library of Medicine. Updated October 6, 2024. ncbi.nlm.nih.govComprehensive clinical reference covering dosing by formulation, CYP2D6/3A4 metabolism, adverse effects, and monitoring.
- Hydrocodone — StatPearls [Internet]. National Library of Medicine. Updated February 29, 2024. ncbi.nlm.nih.govStandalone hydrocodone reference: pharmacogenomics, half-life (IR ~4 h, ER 7–9 h), renal elimination (~85% in 24 h), and Schedule II classification.
- Darwish M, Yang R, Tracewell W, et al. Effects of renal and hepatic impairment on pharmacokinetics of hydrocodone ER. Clin Pharmacol Drug Dev. 2016;5(2):141–149. doi:10.1002/cpdd.208Study documenting increased hydrocodone exposure in renal and hepatic impairment, informing dose adjustments.
- Pinson GM, Beall JW, Kyle JA. A review of warfarin dosing with concurrent acetaminophen therapy. J Pharm Pract. 2013;26(5):518–521. doi:10.1177/0897190013488802Review of INR elevation risk with regular acetaminophen use in warfarin patients.