What is Oxybuprocaine?
Oxybuprocaine, also known as benoxinate, is an ester-type local anesthetic used primarily as a topical eye drop [1.4.2]. It is applied to the surface of the eye to numb the cornea and conjunctiva, preventing pain during short medical procedures [1.4.1]. Its primary function is to enable ophthalmologists and other healthcare professionals to perform examinations and minor surgeries without causing discomfort to the patient [1.5.3]. Common uses include measuring intraocular pressure (tonometry), fitting contact lenses, and removing superficial foreign bodies from the eye [1.4.1, 1.4.5]. It is also utilized in otolaryngology (ear, nose, and throat) to numb mucous membranes [1.4.2].
Mechanism of Action
Oxybuprocaine works by blocking pain signals in the nerve endings of the eye's surface [1.7.6]. It achieves this by binding to sodium channels in the neuronal membrane and reversibly stabilizing them [1.7.1, 1.7.7]. This action decreases the membrane's permeability to sodium ions, which is essential for initiating and conducting nerve impulses [1.7.2]. By inhibiting this process, oxybuprocaine effectively prevents the depolarization of the nerve cell, thereby blocking the sensation of pain [1.7.1, 1.7.3].
Onset and Duration of Anesthesia
The key to oxybuprocaine's clinical utility is its rapid onset and predictable duration.
How Quickly Does It Work?
After instillation into the conjunctival sac, oxybuprocaine begins to anesthetize the eye very quickly. Maximal corneal anesthesia is typically achieved within approximately 1 minute [1.2.1, 1.2.3]. Some sources indicate the onset can be as fast as 30 seconds [1.2.1]. This rapid action makes it highly efficient for time-sensitive procedures in a clinical setting.
How Long Does the Effect Last?
The anesthetic effect of oxybuprocaine is relatively short-lived, which is ideal for outpatient procedures as it allows for a quick return to normal sensation. The duration of action is generally reported to be between 20 and 30 minutes [1.3.1, 1.3.2]. In some cases, the duration may extend up to 40 minutes [1.3.6]. Studies have shown that corneal sensitivity typically returns to baseline levels after about one hour [1.2.2].
Comparison with Other Topical Anesthetics
Oxybuprocaine is one of several topical anesthetics used in ophthalmology. It is often compared to proparacaine and tetracaine.
| Feature | Oxybuprocaine (Benoxinate) | Proparacaine (Proxymetacaine) | Tetracaine (Amethocaine) |
|---|---|---|---|
| Onset of Action | ~1 minute [1.2.1] | ~30 seconds [1.2.1] | Similar to oxybuprocaine [1.6.7] |
| Potency | Similar to proparacaine [1.6.5] | Potent, similar to tetracaine [1.2.1] | High potency [1.7.7] |
| Duration | 10-30 minutes [1.6.5, 1.3.1] | Similar to oxybuprocaine [1.6.5] | Longest duration of the three [1.6.3] |
| Irritation/Stinging | Causes more stinging than proparacaine but less than tetracaine [1.2.7, 1.6.7] | Best tolerated, least stinging [1.2.7, 1.6.3] | Causes the most stinging and discomfort [1.2.1, 1.6.3] |
Studies comparing the three show that while proparacaine may have the fastest onset and be the most comfortable for the patient, tetracaine provides the longest-lasting effect despite causing more irritation [1.6.3]. Oxybuprocaine offers a balance, with a rapid onset and potency similar to proparacaine, but is considered less irritating to the conjunctiva than tetracaine [1.6.5, 1.6.7].
Potential Side Effects and Precautions
Like all medications, oxybuprocaine can cause side effects. The most common is a transient stinging or burning sensation upon instillation, which usually subsides within 30 seconds [1.3.1, 1.5.3]. Other potential ocular side effects include blurred vision, redness, and itching [1.5.2, 1.5.6].
Important Precautions:
- Prolonged Use: Oxybuprocaine is intended for short-term use by a healthcare professional only. Frequent or prolonged, uncontrolled use can lead to severe and irreversible corneal damage, including keratitis and corneal opacification [1.3.2, 1.5.4, 1.5.5].
- Protection: The anesthetized eye should be protected from dust, bacterial contamination, and injury, as the natural blink reflex and pain sensation are absent [1.3.6, 1.5.3].
- Contact Lenses: Contact lenses must be removed before the drops are administered and should not be reinserted until the anesthetic effect has completely worn off (at least one hour) to prevent corneal damage [1.4.8].
- Allergies: It should not be used in patients with a known hypersensitivity to oxybuprocaine or other ester-type local anesthetics [1.4.8]. Allergic reactions are rare but can occur [1.5.6].
Conclusion
Oxybuprocaine is a fast-acting and effective topical anesthetic essential for many ophthalmic procedures. It typically works within one minute and provides reliable anesthesia for 20 to 30 minutes. Its pharmacological profile offers a valuable balance of rapid onset, adequate duration, and moderate patient comfort compared to other common topical agents like proparacaine and tetracaine. Due to the risk of serious corneal damage with improper use, it must always be administered under the supervision of a qualified healthcare professional.
For more detailed information, you can review resources from governmental health authorities such as Medsafe.
