MINIMS PROXYMETACAINE 0,5 %

Indications

• Local anaesthesia for ophthalmic procedures
• Facilitating cataract surgery
• Minor surgical procedures on the eye, such as the removal of corneal sutures

Dosage

Children: Apply as required, but local anaesthetic eye drops should be avoided in preterm neonates due to the immaturity of their metabolizing enzyme system.

Adults: Apply as required, typically in the form of eye drops.

Mechanism of action

Proxymetacaine hydrochloride works by blocking the conduction of nerve impulses in the cornea. This is achieved through the inhibition of voltage-gated sodium channels in neuronal membranes, preventing the initiation and transmission of nerve impulses, thus resulting in local anaesthesia. The drug’s action is localized to the site of administration, minimizing systemic effects.

Pharmacodynamics

The onset of anaesthesia typically occurs within minutes of administration, with the duration of action lasting approximately 15 to 30 minutes. Proxymetacaine is effective in providing pain relief during minor ocular procedures, making it a suitable choice for situations where short-term local anaesthesia is required.

Pharmacokinetics

Proxymetacaine hydrochloride is rapidly absorbed by the corneal epithelium when administered topically. Its pharmacokinetic profile indicates a swift onset of action, with peak effects occurring shortly after application. The drug is primarily metabolized in the liver, with its metabolites excreted through the kidneys. Due to its local application, systemic effects are minimal, though it is still essential to consider potential absorption in sensitive patients.

Contra-indications

• History of acute narrow-angle glaucoma
• Floppy iris syndrome
• Known hypersensitivity to amide-type local anaesthetics or atropine derivatives
• Preterm neonates

Adverse effects

• Headache
• Hyperemia
• Hypertension
• Keratitis
• Dermatitis
• Eye disorders

Interactions

• Antiarhythmics
• Sympathomimetics
• Vasoconstrictors
• Other local anaesthetics

Precautions

• Conditions where systemic exposure to phenylephrine or lidocaine could be harmful
• Counsel patients about the effects on driving and skilled tasks

Pregnancy

Manufacturer advises avoiding use due to insufficient data; lidocaine crosses the placenta but is not known to be harmful in animal studies.

Breast-feeding

Manufacturer advises avoiding use; lidocaine is present in breast milk in small amounts.

Storage

Store at room temperature, protect from light; avoid freezing. Preservative-free formulations should be used immediately after opening.

Formulations

• Proxymetacaine hydrochloride 5 mg per 1 ml eye drops (Minims)
• Preservative-free unit dose vials may be available

Mechanism of action

The exact mechanism whereby proparacaine and other local anesthetics influence the permeability of the cell membrane is unknown; however, several studies indicate that local anesthetics may limit sodium ion permeability through the lipid layer of the nerve cell membrane. Proparacaine may alter epithelial sodium channels through interaction with channel protein residues. This limitation prevents the fundamental change necessary for the generation of the action potential.

Pharmacodynamics

Proparacaine stabilizes the neuronal membrane by inhibiting the ionic fluxes required for the initiation and conduction of impulses thereby effecting local anesthetic action. More specifically, proparacaine appears to bind or antagonize the function of voltage gated sodium channels.