NAPHCON-A
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NAPHCON-A (NAPHCON-A).
Naphcon-A combines naphazoline, an alpha-adrenergic receptor agonist, and pheniramine, a histamine H1-receptor antagonist. Naphazoline constricts conjunctival blood vessels via alpha-adrenergic stimulation, reducing redness and edema. Pheniramine blocks histamine effects, alleviating itching and allergic reactions.
| Metabolism | Naphazoline: primarily metabolized in the liver by oxidative deamination and conjugation. Pheniramine: metabolized in the liver via hydroxylation and conjugation, involving CYP450 enzymes. |
| Excretion | Primarily renal excretion of unchanged drug and metabolites; naphazoline <10% unchanged, antazoline ~30% unchanged. Biliary/fecal elimination negligible. |
| Half-life | Naphazoline: ~2-3 hours; antazoline: ~3-4 hours. Clinical context: ocular administration, systemic absorption minimal. |
| Protein binding | Naphazoline: ~20-30% bound to plasma proteins; antazoline: ~10-20% bound. |
| Volume of Distribution | Naphazoline: ~1.5-2.0 L/kg (extensive tissue distribution); antazoline: ~1.0-1.5 L/kg. |
| Bioavailability | Ocular: low systemic bioavailability due to local administration and vasoconstriction limiting absorption; <5% of dose reaches systemic circulation. |
| Onset of Action | Ocular: within minutes (vasoconstriction and antihistamine effect). |
| Duration of Action | Ocular: 2-4 hours for decongestant effect; antihistamine effect may last up to 6 hours. |
| Molecular Weight | 246.33 |
1-2 drops instilled into the conjunctival sac every 3-4 hours as needed, not to exceed 4 times daily.
| Dosage form | SOLUTION/DROPS |
| Renal impairment | No dose adjustment required for renal impairment. |
| Liver impairment | No dose adjustment required for hepatic impairment. |
| Pediatric use | Children ≥6 years: 1 drop every 3-4 hours as needed; safety and efficacy in children <6 years not established. |
| Geriatric use | No specific dose adjustment; use with caution due to potential increased sensitivity to anticholinergic effects. |
| 1st trimester | Avoid use during first trimester; limited human data but potential risk based on animal studies. |
| 2nd trimester | Use only if clearly needed; no well-controlled studies in pregnant women. |
| 3rd trimester | Avoid use near term; may cause uterine irritability or adverse effects on fetus. |
Clinical note
Comprehensive clinical and safety monograph for NAPHCON-A (NAPHCON-A).
| Placental transfer | Both naphazoline and pheniramine are expected to cross the placenta based on molecular weight and properties; limited direct evidence. |
| Breastfeeding | Naphazoline and pheniramine can be excreted in breast milk; potential for adverse effects in nursing infants, including irritability and drowsiness. Avoid use during breastfeeding or use with caution. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to any componentNarrow-angle glaucomaInfantsUse with MAOIs or within 14 days
| Precautions | Do not use if you have narrow-angle glaucoma. Overuse may cause rebound hyperemia and conjunctivitis medicamentosa. Use with caution in patients with cardiovascular disease, hypertension, hyperthyroidism, or diabetes. |
| Food/Dietary | No known food interactions. Avoid alcohol, which may worsen drowsiness from pheniramine. |
| Clinical Pearls | NAPHCON-A contains naphazoline (vasoconstrictor) and pheniramine (antihistamine). Use with caution in patients with cardiovascular disease, hypertension, hyperthyroidism, or diabetes, as systemic absorption of naphazoline can exacerbate these conditions. Avoid prolonged use (>72 hours) to prevent rebound congestion. Contact lens wearers should remove lenses before instillation and wait at least 15 minutes before reinserting. |
Loading safety data…
| Lactation Rating |
| L3 - Moderately Safe |
| Teratogenic Risk | NAPHCON-A (naphazoline/pheniramine) ophthalmic: Inadequate human data; animal studies not available. Naphazoline is an alpha agonist; systemic exposure minimal with ocular use. Pheniramine is an H1-antihistamine; no evidence of teratogenicity in animal studies. Risk cannot be excluded. Avoid first trimester unless clearly needed. |
| Fetal Monitoring | No specific monitoring required for ophthalmic use. Monitor for maternal ocular adverse effects (e.g., increased intraocular pressure, systemic effects like hypertension or tachycardia). No fetal monitoring needed due to minimal systemic absorption. |
| Fertility Effects | No known effects on fertility from ocular use. Systemic effects unlikely. No data available. |
| Patient Advice | Do not use if you have narrow-angle glaucoma or a known allergy to any ingredients. · Tilt head back, pull down lower eyelid, and squeeze 1-2 drops into the affected eye(s) up to 4 times daily as needed. · Avoid touching the dropper tip to any surface to prevent contamination. · Do not use for more than 3 days without consulting a doctor. · Remove contact lenses before use and wait at least 15 minutes before reinserting. · Seek medical attention if symptoms worsen or persist after 72 hours, or if you experience eye pain or vision changes. |