title: The intraocular pressure-lowering properties of intravenous paracetamol.
abstract: OBJECTIVE
  The aim of this paper was to investigate the intraocular pressure (IOP)-changing properties of a single standard dose of intravenous (IV) paracetamol and compare it to that of topical timolol, oral acetazolamide, and no treatment.
  
  
  METHODS
  A prospective, randomized, investigator-blind, parallel-group study was conducted in 73 eyes of 52 subjects. Subjects received a single dose of IV paracetamol (1 g), oral acetazolamide (250 mg), topical timolol (0.5%, one drop), or no treatment. Baseline IOP was measured, and the measurement was repeated at 1, 2, 4, and 6 hours after treatment.
  
  
  RESULTS
  Paracetamol reduced IOP from baseline by -10.8% (95% confidence interval [CI]: -4.9% to -16.8%, P=0.146) at 1 hour, -13.3% (95% CI: -8.3% to -18.4%, P=0.045) at 2 hours, -11.8% (95% CI: -5.5% to -18.4%, P=1.000) at 4 hours, and -23.9% (95% CI: -17.8% to -30.1%, P=0.006) at 6 hours after treatment. In the no-treatment group, the change was -2.9% (95% CI: +1.0% to -6.7%, P= referent) at 1 hour, -2.1% (95% CI: +2.9% to -7.2%, P= referent) at 2 hours, -7.6% (95% CI: -3.9% to -11.2%, P= referent) at 4 hours, and -6.9% (95% CI: -3.6% to -10.2%, P= referent) at 6 hours. Acetazolamide reduced IOP by -18.8% (95% CI: -12.7% to -24.8%, P=0.000) at 1 hour, -26.2% (95% CI: -18.2% to -34.2%, P=0.001) at 2 hours, -24.6% (95% CI: -16.9% to -32.3%, P=0.000) after 4 hours, and -26.9% (95% CI: -19.6% to -34.3%, P=0.000) 6 hours after treatment. Timolol reduced IOP by -31.2% (95% CI: -26.7% to -35.7%, P=0.000) at 1 hour, -27.7% (95% CI: -20.7% to -34.8%, P=0.000) at 2 hours, -28.7% (95% CI: -21.1% to -36.2%, P=0.000) at 4 hours, and -21.3% (95% CI: -13.4% to -30.0%, P=0.030) at 6 hours after treatment. The average change in IOP for the no-treatment group was -4.8% (95% CI: -2.6% to -6.9%, P= referent). It was -15.7% (95% CI: -9.3% to -22.1%, P=0.021) for paracetamol, -23.1% (95% CI: -16.4% to -29.8%, P=0.000) for acetazolamide, and -25.3% for the timolol group (95% CI: -19.4% to -31.2%, P=0.000). The maximal change in IOP for the no-treatment group was -9.2% (95% CI: -3.2% to -15.3%, P= referent). It was -25.9% (95% CI: -16.6% to -35.2%, P=0.009) for paracetamol, -33.8% (95% CI: -25.5% to -42.1%, P=0.000) for acetazolamide, and -36.8% (95% CI: -31.0% to -42.5%, P=0.000) for the timolol group.
  
  
  CONCLUSIONS
  Intravenously administered paracetamol shows IOP-lowering properties over the first 6 hours after administration. Clinicians performing IOP measurements in patients who have received IV paracetamol in the preceding 6 hours should interpret these measurements with caution. Further studies are needed to investigate the IOP-changing properties of paracetamol.
authors.affiliation: Division of Ophthalmology, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa.
authors.forename: Henning
authors.initials: H
authors.lastname: van den Heever
authors.affiliation: Division of Ophthalmology, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa.
authors.forename: David
authors.initials: D
authors.lastname: Meyer
keywords: AM404; anandamide; endocannabinoid; ocular hypotensive