A commercial preparation containing phenazopyridine hydrochloride was observed to cause an acute reduction of tear secretion in two dogs, resulting in severe keratoconjunctivitis sicca. Similar results were obtained experimentally by treating three dogs with pure phenazopyridine. No disturbance of tear flow was seen in two experimentally treated cats.
Bryan GM, Slatter DH. Keratoconjunctivitis Sicca Induced by Phenazopyridine in Dogs. Arch Ophthalmol. 1973;90(4):310-311. doi:10.1001/archopht.1973.01000050312015