Topical anesthetic

A topical anesthetic is a local anesthetic that is used to numb the surface of a body part. They can be used to numb any area of the skin as well as the front of the eyeball, the inside of the nose, ear or throat, the anus and the genital area.^[1] Topical anesthetics are available in creams, ointments, aerosols, sprays, lotions, and jellies. Examples include benzocaine, butamben, dibucaine, lidocaine, oxybuprocaine, pramoxine, proparacaine, proxymetacaine, and tetracaine (also named amethocaine) all derived from the natural chemical cocaine from the coca plant which is still used for some medical procedures such as rhinoplasties.

Usage

Topical anesthetics are used to relieve pain and itching caused by conditions such as sunburn or other minor burns, insect bites or stings, poison ivy, poison oak, poison sumac, and minor cuts and scratches.^[2]

Topical anesthetics are used in ophthalmology and optometry to numb the surface of the eye (the outermost layers of the cornea and conjunctiva) to:

Perform a contact/applanation tonometry.
Perform a Schirmer's test (The Schirmer's test is sometimes used with a topical eye anesthetic, sometimes without. The use of a topical anesthetic might impede the reliability of the Schirmer's test and should be avoided if possible.).
Remove small foreign objects from the uppermost layer of the cornea or conjunctiva. The deeper and the larger a foreign object which should be removed lies within the cornea and the more complicated it is to remove it, the more drops of topical anesthetic are necessary prior to the removal of the foreign object to numb the surface of the eye with enough intensity and duration.

In dentistry, topical anesthetics are used to numb oral tissue before administering a dental local anesthetic due to the entry of the needle into the soft tissues of the oral cavity. ^[3]

Some topical anesthetics (e.g. oxybuprocaine) are also used in otolaryngology.

Topical anesthetics are now commonly used in the temporary relief of premature ejaculation when applied to the glans (head) of the penis. Benzocaine or lidocaine are typically used for this purpose as they are available OTC (lidocaine is more powerful than benzocaine).

Duration of topical

The duration of topical anesthesia might depend on the type and amount applied, but is usually about half an hour.

Abuse when used for ocular pain relief

When used excessively, topical anesthetics can cause severe and irreversible damage to corneal tissues^[4]^[5]^[6]^[7]^[8] and even loss of the eye.^[9] The abuse of topical anesthetics often creates challenges for correct diagnosis in that it is a relatively uncommon entity that may initially present as a chronic keratitis masquerading as acanthamoeba keratitis or other infectious keratitis.^[4]^[5]^[7]^[9]^[10] When a keratitis is unresponsive to treatment and associated with strong ocular pain, topical anesthetic abuse should be considered,^[7] and a history of psychiatric disorders and other substance abuse have been implicated as important factors in the diagnosis.^[4]^[9]^[10] Because of the potential for abuse, clinicians have been warned about the possibility of theft and advised against prescribing topical anesthetics for therapeutic purposes.^[5]^[9]

Some patients who suffer from eye pain, which is often considerably strong neuropathic pain caused by the irritation of the nerves within the cornea and/or conjunctiva, unfortunately try to illegally obtain oxybuprocaine or other eye anesthetics (for example by stealing them at their ophthalmologist or optometrist, by forging medical prescriptions or by trying to order it via an online pharmacy) and secretly use the substance to numb their eye pain, often ending up with irreversible corneal damage or even destruction (which is a vicious cycle and causes even much more pain). Often, such patients finally require corneal transplantation.

In case of prolonged or chronic eye pain, especially neuropathic eye pain, it is highly advisable to use centrally acting substances like anticonvulsants (pregabalin, gabapentin and in more serious cases carbamazepine) or antidepressants (for example SSRIs or the tricyclic antidepressant amitriptyline). Even very small amounts of an anticonvulsant and/or an antidepressant can almost completely stop eye pain and does not damage the eye at all.

Notes

↑ Healthopedia.com
↑ DrLinhart.com
↑ Local Anesthesia for the Dental Hygienist, Logothetis, Elsevier, 2012
1 2 3 Pharmakakis NM, Katsimpris JM, Melachrinou MP, Koliopoulos JX (2002). "Corneal complications following abuse of topical anesthetics". Eur J Ophthalmol 12 (5): 373–8. PMID 12474918.
1 2 3 Varga JH, Rubinfeld RS, Wolf TC, et al. (July 1997). "Topical anesthetic abuse ring keratitis: report of four cases". Cornea 16 (4): 424–9. doi:10.1097/00003226-199707000-00009. PMID 9220240.
↑ Chern KC, Meisler DM, Wilhelmus KR, Jones DB, Stern GA, Lowder CY (January 1996). "Corneal anesthetic abuse and Candida keratitis". Ophthalmology 103 (1): 37–40. doi:10.1016/s0161-6420(96)30735-5. PMID 8628558.
1 2 3 Ardjomand N, Faschinger C, Haller-Schober EM, Scarpatetti M, Faulborn J (November 2002). "[A clinico-pathological case report of necrotizing ulcerating keratopathy due to topical anaesthetic abuse]". Ophthalmologe (in German) 99 (11): 872–5. doi:10.1007/s00347-002-0623-z. PMID 12430041.
↑ Chen HT, Chen KH, Hsu WM (July 2004). "Toxic keratopathy associated with abuse of low-dose anesthetic: a case report". Cornea 23 (5): 527–9. doi:10.1097/01.ico.0000114127.63670.06. PMID 15220742.
1 2 3 4 Rosenwasser GO, Holland S, Pflugfelder SC, et al. (August 1990). "Topical anesthetic abuse". Ophthalmology 97 (8): 967–72. doi:10.1016/s0161-6420(90)32458-2. PMID 2402423.
1 2 Sun MH, Huang SC, Chen TL, Tsai RJ (June 2000). "Topical ocular anesthetic abuse: case report". Chang Gung Med J 23 (6): 377–81. PMID 10958042.

External links

Anesthesia (outline)

Types	General Spinal Epidural Conduction anesthesia Local Topical Intercostal nerve block Sedation / Twilight anesthesia Dental (Inferior alveolar nerve) Neuroleptanalgesic anesthesia

Techniques	Airway management Anesthesia provision in the US Arterial catheter Bronchoscopy Capnography Dogliotti's principle Drug-induced amnesia Intraoperative neurophysiological monitoring Nerve block Penthrox inhaler Tracheal intubation

Scientific Principles	Blood–gas partition coefficient Concentration effect Fink effect Minimum alveolar concentration Second gas effect

Measurements	ASA physical status classification system Baricity Bispectral index Direct Fick method Entropy monitoring Fick principle Goldman index Guedel's classification Mallampati score Neuromuscular monitoring Thyromental distance

Instruments	Anaesthetic machine Anesthesia cart Boyle's machine Gas cylinder Laryngeal mask airway Laryngeal tube Medical monitor Odom's indicator Relative analgesia machine Vaporiser Double-lumen endotracheal tube Endobronchial blocker

Drugs	Benzodiazepine Etomidate General anaesthetic Inhalational anaesthetic Infiltration analgesia Ketamine Local anesthetic Methohexital Methoxyflurane Midazolam Neuraxial blockade Opiate Propofol Thiopental Thiopentone

Complications	Emergence delirium Allergic reactions Anesthesia awareness Local anesthetic toxicity Malignant hyperthermia Perioperative mortality Postanesthetic shivering Postoperative nausea and vomiting Postoperative residual curarization

Fields of study	Cardiothoracic Geriatric Oral sedation dentistry

Professions	Anesthesiologist Anesthesiologist assistant Nurse anesthetist Operating Department Practitioners Certified Anesthesia Technician Certified Anesthesia Technologist Anaesthetic technician

History	A.C.E. mixture Helsinki Declaration for Patient Safety in Anaesthesiology History of general anesthesia History of neuraxial anesthesia History of tracheal intubation

Organizations	American Association of Nurse Anesthetists American Society of Anesthesia Technologists & Technicians American Society of Anesthesiologists Anaesthesia Trauma and Critical Care Association of Anaesthetists of Great Britain and Ireland Association of Veterinary Anaesthetists Australian and New Zealand College of Anaesthetists Australian Society of Anaesthetists International Anesthesia Research Society

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