LRJ EYE DROPS

Indications

• Allergic rhinitis
• Allergic conjunctivitis
• Urticaria
• Pruritus
• Common cold symptoms

Dosage

Children: For children aged 6 to 12 years, the recommended dose is 12.5 mg every 4 to 6 hours, not exceeding 75 mg in 24 hours. For children aged 2 to 6 years, consult the BNF for Children for appropriate dosing guidelines.

Adults: The usual oral dose for adults is 25 mg to 50 mg every 4 to 6 hours, not exceeding 300 mg in 24 hours.

Mechanism of action

Pheniramine competes with histamine for the histamine H1 receptor, acting as an inverse agonist once bound. This leads to reduced H1 receptor activity, which is responsible for alleviating symptoms such as itching, redness, and edema. Additionally, the inverse agonism of H4 receptors may contribute to its anti-inflammatory properties and further reduce itching.

Pharmacodynamics

Pheniramine antagonizes the effects of histamine, leading to decreased allergic symptoms such as edema, itching, and redness. Its central nervous system activity results in sedation, a characteristic effect of first-generation antihistamines. This dual action makes it effective for both allergy relief and as a mild sedative.

Pharmacokinetics

Pheniramine is absorbed well from the gastrointestinal tract and crosses the blood-brain barrier, leading to its sedative effects. The drug is extensively metabolized in the liver, and its metabolites are excreted primarily through the urine. The onset of action typically occurs within one hour, with a duration of effect lasting several hours.

Adverse effects

• Drowsiness
• Dizziness
• Dry mouth
• Blurred vision
• Constipation
• Urinary retention

Precautions

• Use with caution in patients with glaucoma
• Use with caution in patients with prostatic hypertrophy
• Caution in patients with cardiovascular disease
• May enhance the effects of alcohol and other CNS depressants

Pregnancy

Use only if clearly needed, as there are limited studies on safety.

Breast-feeding

Use with caution, as it may pass into breast milk and affect the infant.

Storage

Store in a cool, dry place, away from direct sunlight.

Formulations

• Tablets
• Syrup

Indications

• Allergic rhinitis
• Nasal congestion
• Ocular irritation

Dosage

Children: Refer to BNF for Children for specific dosing information.

Adults: Refer to BNF for specific dosing information.

Mechanism of action

Tetryzoline selectively activates alpha-1 adrenergic receptors, which are G-protein-coupled receptors that mediate vasoconstriction. This action reduces vascular permeability and alleviates the symptoms of ocular irritation and nasal congestion caused by vasodilation in the conjunctival and nasal capillaries.

Pharmacodynamics

Tetryzoline exhibits vasoconstricting and decongestant effects by constricting small arterioles in the nasal passages and conjunctival blood vessels. It is capable of crossing the blood-brain barrier, which may lead to additional effects such as hypotension, bradycardia, analgesia, hypothermia, sedation, and hypnosis due to its action on alpha-2 adrenoceptors and imidazole receptors.

Pharmacokinetics

The pharmacokinetics of tetryzoline involve absorption, distribution, metabolism, and excretion characteristics typical of sympathomimetic agents. Specific data on half-life, peak plasma concentrations, and elimination routes are not provided in the source material, hence further literature should be consulted for detailed pharmacokinetic parameters.

Adverse effects

• Local irritation
• Burning sensation in the eyes
• Dryness of the nasal mucosa
• Rebound congestion with prolonged use

Precautions

• Use with caution in patients with cardiovascular disease
• Use with caution in patients with hypertension
• Avoid prolonged use to prevent rebound congestion

Pregnancy

Safety in pregnancy has not been established; use only if clearly needed.

Breast-feeding

It is not known whether tetryzoline is excreted in human milk; caution is advised.

Storage

Store at room temperature, away from moisture and heat.

Formulations

• Ophthalmic solution
• Nasal spray

Mechanism of action

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.

Pharmacodynamics

Pheniramine acts as an antagonist to allergic symptoms stemming from inappropriate histamine release to reduce edema, itching, and redness. The same antihistamine effect also produces sedation by acting in the central nervous system.

Mechanism of action

Adrenergic receptors are G-protein-coupled receptors (GPCR) that regulate vascular tone: stimulation of alpha-1 adrenergic receptors leads to vasoconstriction. Ocular redness and nasal congestion often result from vasodilation of nasal, conjunctival, and corneal capillary blood vessels. Activation of alpha-1 adrenergic receptors have been therefore associated with a reduction of symptoms of ocular irritation and nasal congestion. Tetryzoline is a selective agonist of alpha-1 adrenergic receptors, causing vasoconstriction and alleviating ocular and nasal symptoms.

Pharmacodynamics

Tetryzoline is a sympathomimetic amine and an alpha-adrenergic agonist with vasoconstricting and decongestant properties. It works by constricting the smaller arterioles of the nasal passages and conjunctival blood vessels to ameliorate allergic rhinitis, nasal congestion, and ocular irritation. Tetryzoline is known to cross the blood-brain barrier to work on alpha-2 adrenoceptors and imidazole receptors, causing effects like hypotension, bradycardia, analgesia, hypothermia, sedation, and hypnosis.