ABSTRACT

PURPOSE: Standard intravitreal medication dosages are based on an assumed vitreous cavity volume of 4.0-4.5 mL. However, individual variations in vitreous cavity volume may influence both the efficacy and safety of these medications. This study proposes dosage adjustments for intravitreal medications and gases according to axial length and the corresponding vitreous cavity volume.
METHODS: This descriptive study employed reference guidelines that use axial length to estimate the Axial Length-based Volume of the Vitrectomized Space and the Vitreous Volume EXact table for determining dose adjustments across varying eye sizes. Small eyes (axial length 19-22 mm) have an average vitreous cavity volume of 3.5 mL at an axial length of 20.5 mm; standard-sized eyes (22-25 mm) have 4.8 mL at 23.5 mm; large eyes (25-28 mm) have 6.4 mL at 26.5 mm; and extra-large eyes (28-32 mm) have 8.4 mL at 29.5 mm. The medications considered included anti-infectives, anti-VEGFs, complement inhibitors, recombinant proteases, chemotherapy agents, corticosteroids, and medical gases.
RESULTS: Analysis of intravitreal drug concentrations relative to vitreous cavity volume demonstrated notable variability when a standard dose was administered. Small eyes received about 135% of the concentration intended for a standard-sized eye; large eyes received around 75%; and extra-large eyes received under 60%. The recommended dose adjustments are as follows: for small eyes, administer 70-80% of the standard dose; for large eyes, 130-140%; and for extra-large eyes, 170-180%.
CONCLUSIONS: Tailoring intravitreal drug and gas dosages according to axial length and vitreous cavity volume may enhance intraocular drug distribution, potentially improving both safety and therapeutic outcomes.

Keywords: Intravitreal injections; Axial length; Vitreous body; Drug dosage calculations; Pharmacokinetics; Anti-infective agents

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