acetaminophen/dextromethorphan/phenylephrine/guaifenesin (OTC)

Frequency Not Defined

Hypertension

Reflex tachycardia

Severe peripheral and visceral vasoconstriction

Dizziness

Drowsiness

Excitability

Headache

Restlessness

Tremor

Dermatologic rash

Nausea

Vomiting

Anemia blood dyscrasias (neutropenia, pancytopenia, leukopenia)

Bilirubin and alkaline phosphatase may increase

Contraindications

Documented hypersensitivity to any of the drugs or components

Cautions

Caution in elderly patients, hyperthyroidism, myocardial disease, bradycardia, partial heart block or severe atherosclerosis when administering phenylephrine; in hypovolemia, phenylephrine use is not a substitute for replacement of blood, fluids and electrolytes, and plasma (promptly restore with loss); dilute IV and administer via large vein; extravasation precautions required

Not for persistent cough associated with chronic bronchitis, smoking, asthma, or accompanied with excessive secretions

Acetaminophen hepatotoxicity possible in chronic alcoholics following various dose levels; severe or recurrent pain or high or continued fever may indicate a serious illness; contained in many OTC products and combined use with these products may result in toxicity due to cumulative doses exceeding recommended maximum dose

Acetaminophen: Risk for rare, but serious skin reactions that can be fatal; these reactions include Stevens-Johnson Syndrome (SJS), toxic epidermal necrolysis (TEN), and acute generalized exanthematous pustulosis (AGEP); symptoms may include skin redness, blisters and rash

Pregnant or breastfeeding patients should seek advice of health professional before using OTC drugs

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Mechanism of Action

Dextromethorphan: Cough suppressant that acts centrally on the cough center in the medulla

Guaifenesin: Increases respiratory tract fluid secretions and helps to loosen phlegm and bronchial secretions

Phenylephrine: Vasoconstrictor and a decongestant that relieves symptoms resulting from irritation of upper respiratory tract tissue; shrinks swollen mucous membranes, reduces nasal congestion and tissue hyperemia

Acetaminophen: Blocks pain impulse generation peripherally and may inhibit the generation of prostaglandin in the CNS; reduces fever by inhibiting the hypothalamic heat-regulating center

Pharmacokinetics

Acetaminophen

• Peak plasma time: 10-60 min (PO immediate release); 60-120 min (PO extended release); 6 hr (PO 500 mg tablet); 8 hr (PO 650 mg extended release tablet)
• Vd: 1 L/kg
• Protein binding: 10-25%
• Metabolism: Liver (microsomal enzyme systems); conjugation (glucuronic acid)
• Half-life: 1.25-3hr
• Excretion: Urine

Dextromethorphan

• Onset: 15-30 min
• Duration: 3-6 hr
• Metabolism: Hepatic P450 enzyme CYP2D6
• Excretion: Urine
• Half-life: 2-4 hr (extensive metabolizers); 24 hr (poor metabolizers)
• Peak plasma time: 2-3 hr

Phenylephrine

• Half-life: 2-3 hr
• Onset: 10-15 min
• Duration: 15 min
• Bioavailability: < 38%
• Excretion: Urine (80-90%)
• Peak plasma time: 0.75-2 hr
• Vd: 26-61 L
• Vdss: 340 L

Guaifenesin

• Half-Life: 1 hr
• Onset: 30 min
• Duration: 4-6 hr
• Metabolism: Liver
• Metabolite: b-(2-methoxyphenoxy) lactic acid
• Excretion: Urine