In patients receiving long-term topical therapy, local toxic or hypersensitivity reactions to the active agent or preservatives may develop (Figure 7–8), especially if there is inadequate tear secretion Preservatives in contact lens cleaning solutions may produce similar problems Burning and soreness are exacerbated by drop instillation or contact lens insertion; occasionally, fibrosis and scarring of the conjunctiva and cornea may occur Preservative-free topical medications, increasingly used in the treatment of glaucoma, and preservative-free contact lens solutions are available An antibiotic instilled into the eye can sensitize the patient to that drug and cause an allergic reaction upon subsequent systemic administration Potentially fatal anaphylaxis is known to occur in up to 0 3% of patients after intravenous fluorescein for fluorescein angiography Anaphylaxis also has been reported after topical fluorescein 6 Systemic Effects of Ocular Drugs The systemic absorption of certain topical drugs (through the conjunctival vessels and lacrimal drainage system) must be considered when there is a systemic medical contraindication to the use of the drug Ophthalmic solutions of the nonselective beta-blockers, eg, timolol, may worsen bradycardia, heart failure, or asthma Phenylephrine eye drops may precipitate hypertensive crises and angina Also to be considered are adverse interactions between sys- temically administered and ocular drugs Using only 1 or 2 drops at a time