Electrocardiographic evaluation of healthy dogs treated with ophthalmic solution of timolol maleate 0.5%: preliminary study


  • Riane Moreira Santos Instituto de Biologia do Exército
  • Ceci Ribeiro Leite Universidade Federal Fluminense
  • Fábio de Oliveira Monteiro Universidade Unigranrio
  • Mariana Boechat de Abreu Universidade Federal do Rio de Janeiro
  • Daniel Augusto Barroso Lessa Universidade Federal Fluminense
  • Orlei Justen dos Santos Universidade Federal Fluminense




Glaucoma, Canine, Electrocardiogram


Timolol maleate 0.5% is a drug recommended for glaucoma treatment in dogs. After administration, it is absorbed to systemic circulation and being an antagonist of beta adrenergic receptors it has important systemic side effects on cardiac electrical conduction. The present study evaluated the modification caused by ophthalmic timolol 0.5% in the electrocardiogram. Six clinically normal dogs were selected to participate in two different ophthalmic treatments: in the first one, a placebo (hypromellose 0.5%) was used and in the second one, timolol 0.5% was administered. Each solution was applied twice a day, for 14 days. The electrocardiographic parameters were measured in times: zero, 10, 60, 120, 240, 360 and 720 min after ocular solution instillation in first, seventh and 14th days of each treatment. The differences found in electrocardiogram were more evident between 120 and 240 min after instillation of timolol 0.5% when compared with placebo treatment. The rhythm was irregular, with sinus arrhythmia and sinus bradycardia moments. The RR and PR intervals lengthen notoriously (p < 0.05) from the first day of timolol administration, and are more expressive in the 14th day of treatment. The QT interval demonstrated a few changes, just lengthening noticeably (p < 0.05) in the 14th day of timolol application. The QTc interval did not show expressive change. Despite the changes in the electrocardiogram, no clinical manifestation related to beta-adrenoceptor antagonists were observed. One must consider, however, that the animals studied were healthy and thus, clinical signs could result from the changes implied by the use of timolol in animals with pre-existing heart disease. Therefore, cardiac assessment of patients prior to prescription of ophthalmic timolol is recommended. 


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How to Cite

Santos, R. M., Leite, C. R., Monteiro, F. de O., Abreu, M. B. de, Lessa, D. A. B., & Santos, O. J. dos. (2015). Electrocardiographic evaluation of healthy dogs treated with ophthalmic solution of timolol maleate 0.5%: preliminary study. Brazilian Journal of Veterinary Research and Animal Science, 52(2), 112-119. https://doi.org/10.11606/issn.1678-4456.v52i2p112-119




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