PREFRIN-A
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PREFRIN-A (PREFRIN-A).
PREFRIN-A contains phenylephrine, an alpha-1 adrenergic receptor agonist, and acetaminophen, a centrally acting analgesic and antipyretic. Phenylephrine causes vasoconstriction in nasal mucosa, reducing congestion. Acetaminophen inhibits cyclooxygenase (COX) enzymes in the brain, reducing prostaglandin synthesis.
| Metabolism | Phenylephrine undergoes extensive first-pass metabolism by monoamine oxidase (MAO) in the liver and gut; acetaminophen is primarily metabolized by glucuronidation and sulfation, with minor CYP2E1 oxidation to a hepatotoxic metabolite NAPQI. |
| Excretion | Renal: 70-80% as unchanged drug and metabolites; biliary/fecal: 20-30% as metabolites. |
| Half-life | Terminal elimination half-life: 2-4 hours in adults; 6-12 hours in neonates and infants due to immature hepatic metabolism. |
| Protein binding | Phenylephrine: 50-60% bound to albumin and alpha-1-acid glycoprotein; Antazoline: ~20% bound to albumin. |
| Volume of Distribution | Phenylephrine: Vd ~0.5 L/kg (distributes primarily into extracellular fluid); Antazoline: Vd ~2 L/kg (extensive tissue distribution). |
| Bioavailability | Ocular: <1% systemic bioavailability after topical administration; intranasal: 10-20% systemic bioavailability; oral: 2-5% due to first-pass metabolism. |
| Onset of Action | Ocular: 10-30 minutes after topical administration; intranasal: 5-15 minutes. |
| Duration of Action | Ocular: 4-8 hours (decongestant effect); intranasal: 4-6 hours (vasoconstriction). |
1 drop in each affected eye every 3-4 hours as needed, not to exceed 4 times daily.
| Dosage form | SOLUTION/DROPS |
| Renal impairment | No dosage adjustment required for renal impairment. |
| Liver impairment | No dosage adjustment required for hepatic impairment. |
| Pediatric use | Children ≥6 years: 1 drop in each affected eye every 3-4 hours as needed, not to exceed 4 times daily. Children <6 years: not recommended. |
| Geriatric use | Use with caution due to increased risk of systemic absorption and adverse effects; consider lowest effective dose and frequency. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PREFRIN-A (PREFRIN-A).
| Breastfeeding | Phenylephrine: minimal excretion in breast milk; M/P ratio unknown. Pyrilamine: not known if excreted. Antihistamines may cause drowsiness or irritability in infant. Avoid if possible due to lack of safety data. Consider alternative with more data. |
| Teratogenic Risk | Phenylephrine (sympathomimetic) and pyrilamine (antihistamine) combination. No adequate well-controlled studies in pregnant women. Phenylephrine may cause uterine vasoconstriction and reduced placental perfusion; risk of fetal hypoxia in third trimester. Pyrilamine: Class B in pregnancy; animal studies show no fetal harm. Avoid in first trimester due to theoretical risk of vasoconstriction. Use only if benefit outweighs risk. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to phenylephrine, acetaminophen, or any excipients. Severe hypertension or coronary artery disease. Concomitant use or within 14 days of MAO inhibitors.
| Precautions | Avoid use in patients with hypertension, hyperthyroidism, diabetes, or cardiovascular disease. Risk of hepatotoxicity with acetaminophen overdose. Do not exceed recommended dose. Avoid concurrent use with MAO inhibitors. |
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| Fetal Monitoring | Monitor maternal blood pressure and heart rate; phenylephrine may cause hypertension or reflex bradycardia. In third trimester, monitor for uterine activity and fetal heart rate if used long-term or at high doses. |
| Fertility Effects | No known effects on fertility in humans. Animal studies with pyrilamine show no impairment. Phenylephrine may theoretically affect uterine perfusion but no fertility data. |