Napcon

Uses

This eye drop is used for the symptomatic treatment of allergic conjunctivitis

Napcon is also used to associated treatment for these conditions: Bacterial Conjunctivitis, Blepharoconjunctivitis, Conjunctivitis, Conjunctivitis allergic, Dacryocystitis, Dacryostenosis, Dermatitis, Eczematous of the Eyelid, Eye Pain, Eye redness, Iritis, Lacrimation, Nasal Allergies, Nasal Congestion, Noninfective conjunctivitis, Otitis Media (OM), Photophobia, Foreign body sensation in eye, Ocular bacterial infections, Ocular vasoconstrictionAllergic Skin Reaction, Allergic urticaria, Anaphylaxis, Angioedema, Burns first degree, Common Cold, Congestion of the Conjunctivas, Dermatitis, Eczematous, Drug hypersensitivity reaction, Flu caused by Influenza, Insect Bites, Neurodermatitis, Ocular Irritation, Red eye, Seasonal Allergic Conjunctivitis, Sunburn, Urticaria

How Napcon works

Naphazoline is a vasoconstrictor that functions by stimulating alpha adrenergic receptors in arterioles leading to decreased congestion at the site of administration.

Naphazoline causes the release of norepinephrine in sympathetic nerves. Norepinephrine binds to alpha adrenergic receptors and causes vasoconstriction. Naphazoline is also a mild beta adrenergic receptor agonist, which can cause rebound vasodilation after the alpha adrenergic stimulation has ended. Naphazoline's release of norepinephrine also triggers a negative feedback loop which decreases production of norepinephrine, which can lead to rhinitis medicamentosa after long term use when naphazoline is stopped.

Pheniramine competes with histamine for the histamine H1 receptor, acting as an inverse agonist once bound. The reduction in H1 receptor activity is responsible for reduced itching as well as reduced vasodilation and capillary leakage leading to less redness and edema. This can be seen in the suppression of the histamine-induced wheal (swelling) and flare (vasodilation) response. Inverse agonism of the H1 receptor in the CNS is also responsible for the sedation produced by first-generation antihistamines like pheniramine. The binding of pheniramine to H4 receptors, and subsequent inverse agonism, may also contribute to reduced itching by antagonizing inflammation.

Dosage

Napcon dosage

Adults and children 6 years of age and older: instill 1 or 2 drops in affected eye(s) up to 4 times daily.

Children under 6 years: ask a doctor.

Side Effects

Blurring of vision, mild stinging and/or irritation, mydriasis and increased or decreased intraocular pressure. When used in high doses in elderly, naphazoline may liberate pigment granules from the iris.

Toxicity

In high doses or when ingested, naphazoline can lead to central nervous system depression (which can progress to coma and death), hypothermia, bradycardia, and death. This effect is especially pronounced in children under 6 years.

Long term use of naphazoline can lead to rhinitis medicamentosa once naphazoline is stopped. This condition is a result of norepinephrine release by naphazoline triggering a negative feedback loop.

Safety and effectiveness in children under 12 has not been established. Studies in elderly patients have yet to be performed. Risk in pregnancy, breast feeding, and on overall fertility have not been established, though pregnant and breast feeding patients should consider the risk and benefit before starting naphazoline treatment.

Case reports involving pheniramine overdosage mention the rare possibility of arrythmias, cutaneous eruptions, and rhabdomyolysis with acute kidney injury. The administration of activated charcoal effectively prevents the absorption of pheniramine as it largely adsorbs to the charcoal, therefore this may be of benefit in cases of overdose if provided early after ingestion.

Precaution

Glaucoma, hypertension, CV abnormalities, DM, hyperthyroidism, infection, or injury. Pregnancy and lactation. Avoid in infants and young children <6 yr. Rebound congestion may occur with prolonged use or overuse. Patient to seek medical advice if there is ocular pain, vision changes, worsening of redness or irritation of the eye or symptoms lasts >72 hr. Remove contact lens before use.

Interaction

Increased pressor effects with maprotiline or TCA. Possibility of severe hypertensive reaction with MAOI.

Volume of Distribution

Distribution data for naphazoline are scarce but imidazoline compounds are distributed throughout the body, and can cross the blood-brain barrier.

Elimination Route

Absorption data for naphazoline are scarce but imidazoline compounds in general are weakly basic and lipophilic, with high bioavailability from the gastrointestinal tract.

The administration of 30.5 mg of free base pheniramine resulted in a Cmax of 173-294 ng/L with a Tmax of 1-2.5 h.

Half Life

Half life has not been determined but effects last for 4 to 8 hours. Other imidazoline compounds have half lives varying from 2 to 12 hours.

The terminal half-life of pheniramine administered via IV is 8-17 h.

Clearance

Clearance data for naphazoline is unavailable.

Elimination Route

Imidazoline compounds undergo some hepatic metabolism but a large fraction of the dose may be excreted unchanged in the urine. Urinary excretion is higher with more acidic urine.

Pheniramine is eliminated by metabolism and via renal excretion. 24.3% of pheniramine is present in the urine as the parent drug.

Pregnancy & Breastfeeding use

Pregnancy Category C. Either studies in animals have revealed adverse effects on the foetus (teratogenic or embryocidal or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the foetus.

Contraindication

Angle closure glaucoma.

Acute Overdose

Symptoms: Agitation and convulsions (especially in children), and restlessness, disorientation and hallucinations in adults. Accidental ingestion in small children has resulted in convulsions and in some cases fatal.

Treatment: No specific antidote; symptomatic and supportive. Gastric lavage may be useful for some time after ingestion. Do not use stimulants. Diazepam or short-acting barbiturates may be used to control convulsions. Vasopressors may be used for hypotension.

Storage Condition

Store at room temperature 20 degrees to 25 degrees C. Protect from light. Use before expiration date marked on the carton or bottle.

Innovators Monograph

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