SHIPMAN

Short Term Topical Tetracaine Is Highly Efficacious for the Treatment of Pain Caused by Corneal Abrasions: A Double Blind Randomised Clinical Trial

Shipman S et al. Ann Emerg Med. 2021; 77:338-344. doi:xxx]

Clinical Question

  • In adults presenting to the ED with a corneal abrasion is topical tetracaine more effective than placebo to control pain at a 24-48 hour follow up appointment?

Background

  • Corneal abrasions are examined in ED after immediately alleviating pain with a topical anaesthetic, but patients are sent home with none after fears of complications
  • Complications have been mainly reported in case reports and series and include corneal ulcerations, keratitis, hypopyon and delayed healing
  • Despite this, various studies have suggested safety in topical anaesthetic use for 24-48hours
  • No high quality studies looking at efficacy of corneal local anaesthetic use

Design

  • Prospective randomised double blind, placebo controlled trial
  • Randomisation in a 1:1 ratio to receive tetracaine or placebo
  • Concealed allocation by computer generated random number generator then sequentially numbered opaque sealed envelopes
  • 60 patients per group would have a 95% power to detect a minimum clinical difference in pain scores of 1.5cm on a 10cm numeric rating scale (NRS)

Setting

  • Single centre urban community ED in Oklahoma City (USA), that sees 86,000 patients a year
  • Data collected Jan 2015- Sep 2017

Population

  • Inclusion:
    • 18-80yrs old presenting with a corneal abrasion
  • Exclusion:
    • Contact lens wearers
    • Previous corneal surgery on affected eye
    • >36 hrs post injury
    • Grossly contaminated FB/co-existing ocular infection
    • Retained FB
    • Penetrating eye injury
    • Immunosuppression
    • Allergy to study medications
    • Inability to attend follow up
    • Injury requiring urgent ophthalmology evaluation (large or complicated abrasions with visual loss, corneal ulcers or lacerations)
    • Inability to speak fluent English or Spanish
  • Baseline clinical and demographic characteristics (Tetracaine vs Placebo)
    • Male: 61% vs 58%
    • Median Age: 35 vs 38
    • Baseline NRS pain rating: 7 vs 7
    • Mechanism:
      • Metalic FB: 14% vs 9%
      • Other FB: 29% vs 25%
      • Direct trauma: 17% vs 34%
      • Unknown: 40% vs 32%
    • Language spoken
      • English: 97% vs 97%
      • Spanish: 3% vs 3%

Intervention

  • Tetracaine 0.5%
    • 1 drop every 30mins PRN for maximum 24 hours
    • A single 2ml bottle

Control

  • A balanced artificial tear solution
    • Trade name: Systane
    • 1 drop every 30mins PN for maximum 24 hours
    • 4 separate 0.5ml ampules

Management common to both groups

  • All patients also given:
    • Antibiotic drops mixture of polymyxin B/trimethoprim 2 drops 4 hourly
    • A prescription for hydrocodone/paracetamol 7.5/325mg PRN for breakthrough pain
  • Patients asked to record:
    • Pain measurements on NRS before and 2mins after use of study drops
    • Amount of hydrocodone taken between discharge and ED follow up
  • All patients followed up at 24-48 hours by a blinded EM physician who:
    • Examined under slit lamp looking for persistence/delayed healing or complications- if present referred to blinded study ophthalmologist
    • Asked for an overall NRS score after using study drops
    • Collected study drops at this appointment to prevent prolonged use
  • All patients were asked to then be followed up with a blinded study ophthalmologist at 1 week

Outcome

  • Primary outcome: Overall NRS pain score measured at the patient’s initial ED follow up at 24-48hours was significantly lower in the tetracaine group
    • NRS score 1 vs 8; difference of 7; CI 6-8; P<.001
    • Change to NRS from baseline score:
      • Tetracaine 6; 95% CI 5-7
      • Placebo 0; 95% CI 0-0
  • Secondary outcomes: Patients in tetracaine group ingested less hydrocodone then in placebo group
    • 1 in tetracaine group vs 7 in placebo. Difference 6; CI 4-6
  • Adverse effects between groups were non significant
    • 3.6% in tetracaine group vs 11% in placebo. CI -2.9 to 18
  • Number of patients with small residual corneal abraision at 24-48 hour follow up – no significant difference
    • 18% in tetracaine group vs 11% in placebo. CI -6.4 to 20.4

Authors’ Conclusions

  • Short term topical tetracaine is safe and efficacious as an analgesic for corneal abrasions, is associated with less hydrocodone use compared with placebo

Strengths

  • Randomised controlled
  • Reasonable attempts to blind both patients and physicians involved
  • Intention to treat methodology
  • Despite single centre still has external validity

Weaknesses

  • No mention of how they selected patients, all physicians where trained to recruit which was possible 24/7 but no mention of whether all were assessed for eligibility i.e. likely convenience sample
  • Blinding is limited given:
    • Physician enrolling – tetracaine and placebo arm had different number of ampoules/bottles in envelopes ( 1 in tetracaine vs 4 in placebo). Envelope unlikely to fully mask this
    • Patient- will be able to calculate if they had been allocated study group given they will recognise that tetracaine stings when first applied
  • Only 20% in study arm and 18% in control attended 1wk follow up with ophthalmologist. Despite this:
    • They did attempt to contact all that didn’t attend by either phone or searching local electronic records or both
    • 95% in the study arm and 93% control arm did attend the 24-48hr ED follow up where the necessary primary outcome data was collected
  • Secondary endpoint of adverse effects:
    • May lack reliability as description of healing corneal abrasion is subjective.  Physician initially assessing is likely to be different to physician reviewing at ED follow up
    • No standardised approach thus difficult to ensure consistency of results.
    • This study is not powered for safety
  • Registered on clinicaltrials.gov only after study had been completed

The Bottom Line

  • This study indicates tetracaine is more effective in providing analgesia compared to commonly used alternative- artificial tears with a significant difference in NRS scores at 24-48hours. This specific study has not been powered for safety and should not be used for this. Other studies have however shown safety for short term use
  • As a result of this combined information I will selectively start prescribing topical tetracaine for patients with simple uncomplicated corneal abrasions that I am confident will follow advice on use being short term only

External Links

Metadata

Summary author: Halah Zareian @DocHZ
Summary date: 3/3/21
Peer-review editor: David Slessor

Image by: Rudy and Peter Skitterians from Pixabay

 

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