CORRESPONDENCE
A clinical trial of a topical preparation of miconazole, polymyxin and prednisolone in the treatment of otitis externa in dogs Awanohi Road, RD 2, Albany, New Zealand
A BELL
The treatment of canine otitis externarequires the identifkation and preferably the correction of the primary cause as well as redressing the imbalance between commensals (Mulusseziu and Staphylococcus) and host epithelial defences. Treating this infection without addressing the primary problem is certain to result in recurrence. For this reason I believe the recurrence figures in the clinical trial described by Studdert and Hughes (1991) are illusory. They are also remiss in failing to mention hypersensitivity as an underlying cause. Many students of canine otitis (August 1988; Kowalski 1988; Rosser 1988; Griffin 1990), including some cited by Studdert and Hughes (1991), consider hypersensitivity to be the most common cause. The statement that "there were no obvious factors contributing to the occurrence of otitis externa" gives little confdence that a vigorous work-up for primary causes was undertaken. This despite the fact that 8% of the sample had otitis without infection. While the authors mention the association of Labradors, water and otitis, they do not specifically state that swimming was a routine activity in this colony or whether this activity was altered when the dogs had otitis. How similar is this colony to the dog population at large? I would value the investigators' assessment of this based on a comparisonof the incidenceof otitis and dermatitis in this colony with the incidence in Melbourne dogs. Other questions I would ask of this trial are 1.Were the dogs presenting for the second or more times randomly assigned to the treatment groups? 2.What was the treatment history in this colony? Had all 3 products been extensively and equally used over the previous 5 years or are we to be left with the suspicion that this product is simply the latest "stickyplaster" for ears rather than an inherently better product.
References August JR (1988) Vet Clin North Am 18:731 Griffin C (1990) Inlnfectious Diseases of the Dog and Cat, edited by Green C. Saunders, Philadelphia Kowdski JJ (1988) Vet Clin North Am 18743 Rosser El (1988) Vet ClinNorth Am 18765 Studdett VPandHughes KL(1991)Aust Vet J68193
Veterinary Clinical Centre, The University of Melbourne, Princes Highway, Werribee Vic 3030 Faculty of Veterinary Science, The University of Queensland, Queensland 4072
VP STUDDERT
KL
The trial reported was, we believe, representativeof many cases of naturally occurring otitis externa in dogs and the treatment as
Australian VeterinaryJournal, Vol68, No 9, September 1991
is commonly given. We recognise only 2 major differences between the population of dogs studied and those encountered in most clinical settings. The dogs were all of the same breed, Labrador Retrievers, and a reliable, complete medical history with follow-up was available in each case. Until such time as breed-specific factorspredisposing to otitis extema are identified inlabradors, these dogs could not be viewed as unrepresentative of many other dogs in the community. All of the dogs in which otitis extema was diagnosed were housed individually as pets in private homes, principally in metropolitan Melbourne, from the age of 6 weeks and the disease was acquired during that time. For this reason, environmentaland management factors were as widely varied as for other dogs in the population. Swimmingmay well have occurredforsome, but it was not routine and once the diagnosis was made, was restricted, as would be indicated during the treatment of any dog with otitis extema. Most dogs were kennelled while treatment was administered, ensuring uniform and reliable methods and recording. In all treatment groups, some dogs remained in the kennel and others retumed to their home for varying periods after recovery was documented, but they were all eventually retumed for the follow-up examinations. Clearly, not all 3 preparations had been used equally in the kennels for the 5 years nominated by Dr Bell, as preparation A was only recently registered for use in Australia. Since all of the dogs acquired their disease outside the kennel, and had not previously been treated for otitis extema, this seems irrelevant to the validity of the trial. Dogs were randomly assigned to treatment groups for all courses oftTeatment,with~tregardtoseverityofdisease.Ofthe29unresponsive cases in group B, 12 were crossed over to preparation A (all recovered with no recurrences), 15 to preparation C (13 recovered, but 7 had reammces) and 2 to other preparations (one recovered). Of the 5 unresponsive cases in group C, 2 were crossed over to preparation A@othrecoveredwithout recurrence), one topreparation B (unresponsive)and then preparation A (responded) and 2 to another preparation(bothresponded).Recmences weretreatedwiththesarw preparation in 48% and a merent one in 52% of cases. This information was removed fromthe original report during editing. We share the view of Dr Bell and others that otitis extema in dogs often has an underlying cause that should be corrccted. However, in many clinical cases none is apparent at the t i e of initial examination and treatment. By stating that no contributing causes were identified in the cases reported, we include any historical or physical evidence of hypersensitivity disease, either concurrently or subsequently. Considering his views on this subject, the 'vigorous work-up for primary causes' suggested by Dr Bell probably would include allergen skin testing. We do not believe that it is practical to expect that every primary case of otitis extema, without other supporting evidence, will undergo such investigation. Claims that hypersensitivityis responsiblefor most cases of otitis externa are usually applied to chronic or persistent cases; in those, such methods may be indicated. To have included other forms of treatment for our cases with recurrences would have prevented this frombeiig a comparativestudy of the effects of topical preparations as they are commonly used. In many reports and surveys of otitis extema in dogs, bacterial and fungal cultures are negative in up to 30%of cases. Failure to isolate organism from ears is suggestive, but not conclusive evidence, of otitis without infection. While these cases may representnon-infectious causes, such as hypersensitivity, a small percentage as occurredin this report, may also occur for technical reasons, especially during transport to the laboratory. Dr Bell's- questions largely overlook the fact that this was a clinical trial and not a study of the aetiological factors contributing to otitis extema in dogs. By treating a varied, but large population of dogs and randomly assigning them to 3 different treatment groups, these variableswould have been present equally in all. It is difficult to see how any of the factors he is trying to identify would have affected only one group. The results
313
A clinical trial of a topical preparation of miconazole, polymyxin and prednisolone in the treatment of otitis externa in dogs Awanohi Road, RD 2, Albany, New Zealand
A BELL
The treatment of canine otitis externarequires the identifkation and preferably the correction of the primary cause as well as redressing the imbalance between commensals (Mulusseziu and Staphylococcus) and host epithelial defences. Treating this infection without addressing the primary problem is certain to result in recurrence. For this reason I believe the recurrence figures in the clinical trial described by Studdert and Hughes (1991) are illusory. They are also remiss in failing to mention hypersensitivity as an underlying cause. Many students of canine otitis (August 1988; Kowalski 1988; Rosser 1988; Griffin 1990), including some cited by Studdert and Hughes (1991), consider hypersensitivity to be the most common cause. The statement that "there were no obvious factors contributing to the occurrence of otitis externa" gives little confdence that a vigorous work-up for primary causes was undertaken. This despite the fact that 8% of the sample had otitis without infection. While the authors mention the association of Labradors, water and otitis, they do not specifically state that swimming was a routine activity in this colony or whether this activity was altered when the dogs had otitis. How similar is this colony to the dog population at large? I would value the investigators' assessment of this based on a comparisonof the incidenceof otitis and dermatitis in this colony with the incidence in Melbourne dogs. Other questions I would ask of this trial are 1.Were the dogs presenting for the second or more times randomly assigned to the treatment groups? 2.What was the treatment history in this colony? Had all 3 products been extensively and equally used over the previous 5 years or are we to be left with the suspicion that this product is simply the latest "stickyplaster" for ears rather than an inherently better product.
References August JR (1988) Vet Clin North Am 18:731 Griffin C (1990) Inlnfectious Diseases of the Dog and Cat, edited by Green C. Saunders, Philadelphia Kowdski JJ (1988) Vet Clin North Am 18743 Rosser El (1988) Vet ClinNorth Am 18765 Studdett VPandHughes KL(1991)Aust Vet J68193
Veterinary Clinical Centre, The University of Melbourne, Princes Highway, Werribee Vic 3030 Faculty of Veterinary Science, The University of Queensland, Queensland 4072
VP STUDDERT
KL
The trial reported was, we believe, representativeof many cases of naturally occurring otitis externa in dogs and the treatment as
Australian VeterinaryJournal, Vol68, No 9, September 1991
is commonly given. We recognise only 2 major differences between the population of dogs studied and those encountered in most clinical settings. The dogs were all of the same breed, Labrador Retrievers, and a reliable, complete medical history with follow-up was available in each case. Until such time as breed-specific factorspredisposing to otitis extema are identified inlabradors, these dogs could not be viewed as unrepresentative of many other dogs in the community. All of the dogs in which otitis extema was diagnosed were housed individually as pets in private homes, principally in metropolitan Melbourne, from the age of 6 weeks and the disease was acquired during that time. For this reason, environmentaland management factors were as widely varied as for other dogs in the population. Swimmingmay well have occurredforsome, but it was not routine and once the diagnosis was made, was restricted, as would be indicated during the treatment of any dog with otitis extema. Most dogs were kennelled while treatment was administered, ensuring uniform and reliable methods and recording. In all treatment groups, some dogs remained in the kennel and others retumed to their home for varying periods after recovery was documented, but they were all eventually retumed for the follow-up examinations. Clearly, not all 3 preparations had been used equally in the kennels for the 5 years nominated by Dr Bell, as preparation A was only recently registered for use in Australia. Since all of the dogs acquired their disease outside the kennel, and had not previously been treated for otitis extema, this seems irrelevant to the validity of the trial. Dogs were randomly assigned to treatment groups for all courses oftTeatment,with~tregardtoseverityofdisease.Ofthe29unresponsive cases in group B, 12 were crossed over to preparation A (all recovered with no recurrences), 15 to preparation C (13 recovered, but 7 had reammces) and 2 to other preparations (one recovered). Of the 5 unresponsive cases in group C, 2 were crossed over to preparation A@othrecoveredwithout recurrence), one topreparation B (unresponsive)and then preparation A (responded) and 2 to another preparation(bothresponded).Recmences weretreatedwiththesarw preparation in 48% and a merent one in 52% of cases. This information was removed fromthe original report during editing. We share the view of Dr Bell and others that otitis extema in dogs often has an underlying cause that should be corrccted. However, in many clinical cases none is apparent at the t i e of initial examination and treatment. By stating that no contributing causes were identified in the cases reported, we include any historical or physical evidence of hypersensitivity disease, either concurrently or subsequently. Considering his views on this subject, the 'vigorous work-up for primary causes' suggested by Dr Bell probably would include allergen skin testing. We do not believe that it is practical to expect that every primary case of otitis extema, without other supporting evidence, will undergo such investigation. Claims that hypersensitivityis responsiblefor most cases of otitis externa are usually applied to chronic or persistent cases; in those, such methods may be indicated. To have included other forms of treatment for our cases with recurrences would have prevented this frombeiig a comparativestudy of the effects of topical preparations as they are commonly used. In many reports and surveys of otitis extema in dogs, bacterial and fungal cultures are negative in up to 30%of cases. Failure to isolate organism from ears is suggestive, but not conclusive evidence, of otitis without infection. While these cases may representnon-infectious causes, such as hypersensitivity, a small percentage as occurredin this report, may also occur for technical reasons, especially during transport to the laboratory. Dr Bell's- questions largely overlook the fact that this was a clinical trial and not a study of the aetiological factors contributing to otitis extema in dogs. By treating a varied, but large population of dogs and randomly assigning them to 3 different treatment groups, these variableswould have been present equally in all. It is difficult to see how any of the factors he is trying to identify would have affected only one group. The results
313
