The ototoxic potential of EMLA. A new local anesthetic for the tympanic membrane

Assessing ototoxicity and patients' satisfaction of topical local anaesthesia in myringotomy and ventilation tube insertion

OBJECTIVES

Animal studies have suggested that exposure of the middle ear to topical local anaesthesia may be ototoxic. This study aimed to report sensorineural hearing outcomes and patients' satisfaction in those who underwent myringotomy and ventilation tube insertion using topical local anaesthesia.

METHODS

Twenty-nine patients (32 ears) were operated on. Pre- and post-operative audiology findings were compared. A Likert-type questionnaire on treatment satisfaction was completed at the end of the procedure.

RESULTS

Median patient age was 55 years (range, 27-88 years). Pre- and post-operative bone conduction pure tone averages were 26.76 dB and 25.26 dB respectively (mean reduction of -1.22 dB, 95 per cent confidence interval of -5.91 to 8.13 dB; p = 0.7538). One ear (3 per cent) had a reduction in pure tone average of 10 dB.

CONCLUSION

The results suggest that sensorineural hearing loss is not a complication of ear exposure to topical local anaesthesia during myringotomy and ventilation tube insertion. The procedure was well perceived.

Efficacy of a eutectic mixture of local anesthetics as a topical anesthetic in minor otologic procedures

A eutectic mixture of local anesthetics (EMLA), prepared as a cream, is an oil-in-water emulsion of 2 anesthetic agents lidocaine and prilocaine. Several clinical applications of EMLA cream, its effectiveness as a topical anesthetic, and its safety profile have been previously reported. We report our experience with EMLA cream in 17 adult and 24 pediatric patients. We find EMLA to be the preferred anesthetic for performing minor outpatient otologic procedures in adults. We also find EMLA to be a safe, well-tolerated alternative to general anesthesia in some pediatric patients. Potential cost savings of EMLA cream during pediatric myringotomies in the clinic are also discussed.

Effective anaesthesia for transtympanic electrocochleography

The objective of this study was to quantify the anaesthetic effect of EMLA cream during transtympanic electrocochleography (TTECochG) and thereby to determine if the application of EMLA should be recommended in routine practice of electrocochleography (ECochG). ECochG provides useful information in patients with inner ear fluid disorders. A major concern regarding transtympanic positioning of the electrode in ECochG is patient discomfort. Previous work has suggested that EMLA cream may make this technique more tolerable to patients. A prospective randomized study was performed evaluating the discomfort associated with unilateral TTECochG in a group where EMLA cream was used to anaesthesize the tympanic membrane (n = 24), and in a group where no anaesthesia was used (n = 22). A statistically significant difference was evident between the discomfort ratings of the groups (P < 0.0001, Mann-Whitney U test), the discomfort being greater in the no anaesthesia group. EMLA cream has thus been shown to alleviate the level of discomfort associated with TTECochG and so to be an acceptable modification of this technique.

Eutectic lidocaine/prilocaine cream. A review of the topical anaesthetic/analgesic efficacy of a eutectic mixture of local anaesthetics (EMLA)

Eutectic lidocaine/prilocaine cream 5% is a eutectic mixture of the local anaesthetics lidocaine (lignocaine) 25 mg/g and prilocaine 25 mg/g that provides dermal anaesthesia/analgesia following topical application. The principal indication in which eutectic lidocaine/prilocaine cream has been studied is the management of pain associated with venipuncture or intravenous cannulation, where significantly greater pain relief than placebo, with equivalent efficacy to ethyl chloride spray and lidocaine infiltration, has been demonstrated. In dermatological surgery, eutectic lidocaine/prilocaine cream offers effective pain relief in children undergoing curettage of molluscum contagiosum lesions, and in adults undergoing split-skin graft harvesting. Particular benefit has also been shown with use of eutectic lidocaine/prilocaine cream in association with treatment of condylomata acuminata in both men and women, and it appears to provide a useful alternative to lidocaine infiltration in this context. Further research in such indications as paediatric lumbar puncture, minor otological surgery, and minor gynaecological, urological and andrological procedures is likely to further broaden the profile of clinical use for eutectic lidocaine/prilocaine cream. Eutectic lidocaine/prilocaine cream has a very favourable tolerability profile, transient and mild skin blanching and erythema being the most frequent adverse events to occur in association with its application to skin. The potential for inducing methaemoglobinaemia, attributed to a metabolite of the prilocaine component of the formulation, prohibits its use in infants younger than 6 months. In summary, eutectic lidocaine/prilocaine cream is a novel formulation of local anaesthetics that has proven to be effective and well-tolerated in the relief of pain associated with various minor interventions in adults and children.

EMLA in local anaesthesia of the tympanic membrane

An ideal agent for local anaesthesia of the tympanic membrane has been missing so far. Recently, however, a eutectic mixture of lignocaine and prilocaine (EMLA, Astra, Södertälje, Sweden) has proved promising. We compared the anaesthetizing efficacy of EMLA, Bonain's solution (cocain, menthol, phenol ana partes) and Xylocain-spray (Astra, Södertälje, Sweden) in 42 voluntary subjects. EMLA was applied on one tympanic membrane and either one of the other two agents in the other ear of each subject. Small cotton pledgets were used for application. Sensitivity of the ear drum was tested under otomicroscope with a cotton tipped wire before and after each local anaesthesia. Full anaesthesia could be reached with EMLA very significantly (p less than 0.001) more often than with Xylocain and almost significantly (p = 0.057) more often than with Bonain's solution. Most of the test subjects preferred EMLA to Bonain's solution of Xylocain. Undesired side effects, including two tympanic membrane perforations, appeared in most of the ears anaesthetized with Bonain's solution. In the clinical part of the study, EMLA topical anaesthesia was used in 127 minor policlinical tympanic membrane procedures like myringotomy and tympanostomy tube assembling. Eighty-three of the procedures were assessed as painless, 36 unpleasant and 8 painful. A 30-min action time of EMLA was considered sufficient in most cases. No EMLA related side effects appeared. In conclusion, Bonain's solution is recommended to be replaced by EMLA or a corresponding agent for local anaesthesia of the tympanic membrane.

Use of EMLA cream as an analgesic in the management of painful otitis externa

A new application of EMLA cream is described. Relief of pain in otitis externa is difficult and systemic analgesics for this localized condition are often ineffective. Meticulous cleaning of the external auditory meatus is an essential step in the treatment. EMLA cream is an effective analgesic which can be used to relieve pain and anaesthetize the external auditory meatus to allow cleaning in patients with intact tympanic membranes.

Structural effects of the topical lidocaine-prilocaine anesthetic Emla on the tympanic membrane

A eutectic mixture of two anesthetic solutions is that of lidocaine and prilocaine, which is available commercially as Emla (eutectic mixture of local anesthetics). This solution is commonly used in clinics in superficial skin surgery and when inserting intravenous catheters, and we also wanted to determine its surface effects when applied onto the tympanic membranes (TM) of rats and guinea pigs as animal models. The animals were observed by otomicroscopy for 2 weeks up to 5 months after administrations of the anesthetic solution. Tissue specimens were then obtained for light microscopy and fine structural analysis. The application of Emla caused minor structural changes to the rat TM, but hardly any alterations to that of the guinea pig. The changes displayed were an overall increased thickness, with typical submucosal edema but only slight epithelial reaction. In comparison with previous results with lidocaine, phenol and Bonain's solution, Emla seemed to be harmless to the structure of the TM. However, the efficacy of Emla as a topical TM anesthetic remains to be proved in future clinical trials.

Toxic effects on inner ear of noxious agents passing through the round window membrane

The effects on inner ear of Xylocain, EMLA, phenol, endotoxin and hydrocortisone were analysed before treatment and 24 h-6 months after instillation of each drug into the round window (RW) niche, where the substance was left. Inner ear function was determined by repeated auditory brainstem recordings (ABR). All cochleae were analysed morphologically at the light microscopic level. Hydrocortisone, Xylocain and endotoxin caused functional changes without morphological correlates, even at long-term follow-up. In contrast, phenol and EMLA caused both functional impairment and graded morphological damage to the organ of Corti in the basal coil. Outer hair cells (OHC) were more vulnerable than inner hair cells (IHC).