We examined Medline, CINAHL, and the Cochrane Controlled Trials Register (last accessed January 2004) using the search terms ‘ear and wax’, ‘earwax’, ‘cerumen’, and ‘trial’.11
We also searched the National Research Register (June 2003) for ongoing studies and accessed Clinical Evidence (June 2003) for the most recent advice and references.9
We scrutinised the references of the identified articles and also those of many review articles on the management of earwax and ear care. We contacted experts in the field, people currently doing research on earwax, some of the authors of the identified trials, the pharmaceutical companies manufacturing the preparations used in the UK, and two companies in the United States (US).
The authors included all randomised trials that evaluated drops used for treating earwax with no restriction on either date or language. Each trial was read independently to assess its eligibility and quality. We excluded non-randomised studies and assessed the quality of the RCTs using the following criteria:
- reported generation of allocation sequence,
- allocation concealment,
- inclusion of all randomised patients, and
- blinding of outcome assessors.12
HOW THIS FITS IN
What do we know?
There are many different preparations available for treating earwax. There is no good evidence about which agent to use or the optimal duration of treatment.
What does this paper add?
If syringing is performed for uncomplicated earwax, there is little to choose between water-based and oil-based preparations, and plain water may suffice. Applying a water-based or oil-based preparation 15–30 minutes prior to syringing is probably as effective as applying it for several days. Non-water-, non-oil-based preparations appear promising for clearing earwax, but several days' treatment is required. Further well-designed randomised studies comparing the three types of agents are needed to fill the current gaps in the evidence.
We used a three-point scale for each criterion (Supplementary Table 1) and defined a high-quality trial as having the maximum score on each of the four criteria. The very few differences in opinion were settled by negotiation.
We classified eardrops into three groups: water-based, oil-based, and non-water-, non-oil-based (). The classification is based on the physical and chemical properties of the preparations, as the mechanisms of action are probably different (M Whitefield, personal communication, 2002). The underlying assumption of the classification is that preparations with similar properties have similar mechanisms of action. There is evidence for this from in vitro studies: water-based preparations have a cerumenolytic activity, whereas oil-based preparations have only a softening effect.13-21
There have been no published in vitro studies using non-water-, non-oil-based preparations (SSL International PLC, personal communication, 2002).
Preparations used in trials.
When urea-hydrogen peroxide (carbamide peroxide, Exterol®
[Dermal oratories Ltd], Otex®
[DDD Ltd]) comes into contact with water, hydrogen peroxide is one of the main products. This has been shown to have powerful cerumenolytic activity in vitro. In the 1940s, both hydrogen peroxide (which breaks down into water) and water were shown to have cerumenolytic activity.15
Cerumenolytics work by hydrating the desquamated sheets of corneocytes, which are the major constituent of cerumen plugs, and subsequently inducing keratolysis with disintegration of the wax.22
The main outcomes assessed were clearing earwax without syringing and successful syringing. Successful syringing was variably defined in studies, but included ease of syringing, clearance of wax, and the ability to see the tympanic membrane afterwards. Using a random effects model, we pooled the results of studies that compared water-based, oil-based, and non-water-, non-oil-based preparations where we could identify suitably similar outcomes, and when we were satisfied that the randomisation procedures were acceptable.23