In Summary, for those who took the antibiotics:

Benefits in NNT

  • 85% saw no benefit
  • 15% were helped by being clinically cured within 2 to 5 days of treatment
  • 1 in 7 were helped (clinical cure at 2-5 days)

Harms in NNT

  • 0% were harmed by medication adverse reactions
  • None were harmed (medication adverse reaction)

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Source: Sheik A, Hurwitz B. Antibiotics versus placebo for acute bacterial conjunctivitis. Cochrane Database Syst Rev. 2006;(2):CD001211. PMID: 16625540.

Efficacy Endpoints: Clinical cure among patients treated with topical antibiotics

Harm Endpoints: Adverse Medication Events

Narrative: Traditionally antibiotics are considered in bacterial conjunctivitis to reduce relapse, speed recovery, and prevent complications that occur due to contiguous spread of the infection. There are five major randomized, placebo-controlled trials that address efficacy of antibiotics. In these double-blinded studies, 1034 subjects presenting within 10 days of symptom onset received either topical antibiotics or placebo. The review examined both clinical and microbiologic cure rates, but we decided to only analyze and report the patient-oriented outcome of clinical cure in this summary.

Clinical signs of conjunctivitis resolved more quickly among subjects taking antibiotics, however most cases were self-limiting - approximately 65%. The review looked at clinical remission rates of bacterial conjunctivitis in two groups, at 2 to 5 days and 6 to 10 days after starting treatment. Remission rates were highest in the first 2 to 5 days, with an ARR of 14.8%, which corresponds to an NNT of 6.8. Additionally, topical antibiotics had a smaller benefit by days 6 to 10 with an ARR of 8.4%, corresponding to an NNT of 11.9.

Caveats: Of the 5 trials, only two were conducted in a community care population. The remaining three trials were performed in a specialty care environment, raising concerns about referral bias, a bias that occurs when trial subjects represent a sicker or more unusual spectrum of disease than patients seen in common practice. These trials also exhibit important methodological flaws. Inclusion criteria among the trials were heterogeneous with regards to age, diagnostic criteria (for establishing bacterial versus viral infection), and treatment regimens (topical, systemic, and combination treatments were all used). However, the review did not include the patients that received systemic antibiotics in the analysis. Additionally, 2 of the 5 studies evaluated the surrogate marker of bacterial cure rate, instead of the patient-oriented outcome of symptomatic cure. One of these two studies looked only at the bacterial cure rate and the other considered a combined outcome of both bacterial cure and clinical cure. Finally, across the 5 studies 65% of cases in placebo groups resolved spontaneously by day 5, and no adverse outcomes related to spread of infection occurred in either the treatment or placebo groups. Therefore any significant benefit arising from the use of antibiotics in these studies appears to be related to the rate of resolution of the condition, rather than due to prevention of complications. It may take very large trials to detect any benefit in the latter outcome, due to the rarity of complications after common bacterial conjunctivitis.

Author: Virginia M. Stewart, MD and Jarone Lee, MD MPH

Published/Updated: November 7, 2010

  1. The Title Bar

    The title bar is color-coded with our overall recommendation.

    • Green: Benefits outweigh risks.
    • Yellow: Unclear risk/benefit profile.
    • Red: Benefits do not outweigh risks.
    • Black: Obvious harms, no clear benefits.
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