What immediate steps should be taken for a teenager who has taken two adult doses of DayQuil (acetaminophen, dextromethorphan, phenylephrine) and may have an acetaminophen overdose?

Management of Teenager Who Took 2 Doses of DayQuil

For a teenager who has taken two adult doses of DayQuil, immediately assess the total acetaminophen dose ingested and obtain a serum acetaminophen level at least 4 hours post-ingestion to determine if N-acetylcysteine (NAC) treatment is needed. 1

Immediate Risk Assessment

Determine the exact acetaminophen dose ingested:

• Each adult DayQuil dose contains 650 mg acetaminophen, so two doses = 1,300 mg total 2
• For teenagers weighing less than 70 kg, calculate mg/kg dose to assess toxicity risk 1
• Toxic threshold: ≥200 mg/kg or ≥10 g (whichever is less) requires emergency department evaluation 1, 3
• For a 50 kg teenager, 1,300 mg = 26 mg/kg, which is below the toxic threshold 3

Key historical details to obtain:

• Exact time of ingestion (critical for nomogram use) 1, 2
• Whether ingestion was intentional or accidental 3
• Any other medications or substances co-ingested 3
• Presence of symptoms: nausea, vomiting, right upper quadrant pain, altered mental status 3

Decision Algorithm for Emergency Department Referral

Immediate ED referral is mandatory if: 3

• Any stated or suspected self-harm intent, regardless of dose 3
• Total acetaminophen dose ≥200 mg/kg or ≥10 g (whichever is less) 1, 3
• Patient exhibits any symptoms consistent with toxicity (repeated vomiting, abdominal tenderness, mental status changes) 3
• Time of ingestion is unknown 2, 3
• More than 36 hours have passed since ingestion AND patient is symptomatic 3

Home observation is appropriate if: 3

• Unintentional ingestion with dose <200 mg/kg 3
• Patient is asymptomatic 3
• Time of ingestion is known and reliable 3
• More than 36 hours post-ingestion AND patient remains completely well 3

Critical Timing for Laboratory Assessment

If ED referral is indicated, the patient must arrive in time for:

• Serum acetaminophen level drawn at exactly 4 hours post-ingestion or as soon as possible thereafter 2, 3
• Do NOT draw levels before 4 hours, as they cannot be interpreted on the Rumack-Matthew nomogram 1, 2
• If time of ingestion is unknown, administer NAC loading dose immediately and obtain level to guide continued treatment 2

Treatment Considerations for Dextromethorphan and Phenylephrine

Dextromethorphan toxicity assessment:

• Two adult DayQuil doses contain approximately 20 mg dextromethorphan per dose = 40 mg total 4
• Toxic threshold is 5-7.5 mg/kg, requiring follow-up every 2 hours for 4 hours 4
• Doses >7.5 mg/kg require ED evaluation 4
• For most teenagers, 40 mg total is below toxic threshold and requires only observation 4
• If patient is taking SSRIs or MAOIs, follow-up every 2 hours for 8 hours due to serotonin syndrome risk 4

Phenylephrine is not typically toxic at therapeutic doses and does not require specific intervention beyond supportive care

NAC Treatment Protocol If Indicated

NAC should be started immediately if: 1, 5

• Acetaminophen level plots above the "possible toxicity" line on Rumack-Matthew nomogram 1, 5
• Time of ingestion is unknown with detectable acetaminophen level 1, 2
• Clinical evidence of hepatotoxicity (elevated AST/ALT) 1, 6

Optimal NAC dosing regimen (IV): 5, 2

• Loading dose: 150 mg/kg over 15 minutes 5
• Second dose: 50 mg/kg over 4 hours 5
• Third dose: 100 mg/kg over 16 hours (total 21-hour protocol) 5

Critical timing considerations:

• NAC within 8 hours: only 2.9% develop severe hepatotoxicity 1, 5
• NAC within 10 hours: 6.1% develop severe hepatotoxicity 1
• NAC after 10 hours: 26.4% develop severe hepatotoxicity 1
• Treatment efficacy diminishes dramatically after 8 hours but should never be withheld, even in late presentations 1, 5

Activated Charcoal Consideration

Activated charcoal (1 g/kg) should be given if: 1

• Patient presents within 4 hours of ingestion 1
• Toxic dose was ingested 1
• No contraindications present (altered mental status, unprotected airway) 1
• Give just prior to starting NAC; do not delay NAC administration 1, 5

Common Pitfalls to Avoid

• Never rely on early liver enzymes (<12 hours) to exclude toxicity—they may be normal despite toxic acetaminophen levels 6
• Do not use the nomogram for repeated supratherapeutic ingestions or unknown time of ingestion 1, 2
• Do not delay NAC while awaiting confirmatory levels if strong suspicion of significant overdose exists 5
• Patients with chronic alcohol use or fasting states may develop toxicity at lower doses 1, 5