VN June 2021

Vetnuus | Junie 2021 30 Regulars I Ophthalmology Column Ophthalmic antibiotic preparations have been used in cats to treat a variety of problems such as blepharitis, conjunctivitis, keratitis, dacrocystitis, corneal ulceration, keratoconjunctivitis sicca, post-surgical intervention as well as an adjuvant to lubrication of the ocular surface. Appropriate antibiotic selection should ideally be based on clinical signs, cytological sampling or culture and antibiogram but, as we all know, that often it is time consuming and impractical. The result is that the more common antibiotics or combinations areused.Thesemaycontainbacitracin, neomycin, polymixinB, oxytetracycline and doxycycline amongst others. Over a number of years reports and warnings have been made about the association between anaphylactic reactions in cats and these products. A recent review article shed more light on this rare phenomenon. Although antibiotics seem to be the issue, often other products had been used prior to the incident such as fluorescein stain, vaccine administration or other systemic/oral drugs. In this study polymyxin B was always present in all the anaphylactic reactions. There are three real hypotheses for this anaphylaxis problem in cats: • A range of topically applied antibiotics (or combinations) may be responsible for the anaphylactic reactions. • One or more active ingredients are responsible. • Polymixin B alone is responsible. There is no predisposing age, gender, breed, etc. that seems to predispose to the anaphylactic event so one cannot predict a susceptible cat. The study showed that 39% of anaphylaxis cases occurred within 5 minutes of drug application and of these 20% occurred within 60 seconds. This may suggest that it could be a good idea to actually apply the prescribed drug initially in the consult room before the patients departs your facility. Flushing the eyes in the event of a problem was statistically shown to improve survival rate! Anaphylaxis mainly affected respiratory and gastrointestinal systems. The fact that the use of antibiotic preparations in cats may result in fatal consequences leads to the question that one should be using a preparation for a very specific problem. In this study 86% of anaphylactic cases received the medication for “ocular infection”, epiphora or as a lubricant. This is rather alarming as lubricationwouldnot be a true indication tobe using an antibiotic preparation. The most common ocular pathogens in cats are feline herpesvirus, Chlamyophilia felis and Mycoplasma species. Neomycin, polymyxin B and bacitracin have no effect against these pathogens. Tetracyclines in combination with polymyxin B were also associated with anaphylaxis in this study. Improved awareness of the potential for anaphylaxis in cats receiving certain ophthalmic preparations, the limited use of these drugs except when definitely indicated, closer observation following drug administration and improved reporting of toxicity to the relevant authorities should reduce these rare incidences and highlight more rapid and specific therapy and highlight drugs of concern in the future. At the Jhb Animal Eye Hospital we for years have not been dispensing polymixin B or its combinations to cats. It would probably be better to choose a non-polymyxin B antibiotic and a separate NSAID anti-inflammatory if that is required and in rare situations a cortisone separately. v References: • Anaphylaxis events observed within 4h of ocular application of an antibiotic- containing ophthalmic preparation: 61 Cats [1993-2010]. J of Feline Medicine and Surgery [2011] 13, 744-751] • Anaphylaxis to Ophthalmic Medication in a cat. J of Veterinary Emergency and Critical Care [2000] Vol 10, No3, 169-171 Anaphylactic events following antibiotic eye drop administration in cats Dr Antony Goodhead, Specialist Veterinary Ophthalmologist, Johannesburg and Cape Animal Eye Hospitals, (www.animaleyehospital.co.za ) Photo: Alvesgaspar, via Wikimedia Commons