Particle size and drug interactions of injectable corticosteroids used in ophthalmic practice

The aim of this study is to compare the particle sizes of commercially available corticosteroids for intralesional injection to manufacturers' specifications and to evaluate changes in size when mixed with other steroids and other commonly used solutions.

The particle sizes of dexamethasone sodium phosphate, methylprednisolone acetate, triamcinolone acetonide, and betamethasone sodium phosphate and beta-methasone acetate were measured with the Coulter counter. Each steroid was mixed with each of the others, lidocaine, and lidocaine with epinephrine, then measured immediately and after 1 hour to determine the effect on particle size.

All steroids showed accurate manufacturer specifications. Dexamethasone showed an increase in particle size when mixed with lidocaine alone, immediately and after 1 hour. Triamcinolone showed an increase in particle size only after 1 hour after mixture with lidocaine alone. Triamcinolone, dexamethasone, and methylprednisolone particles increased in size when mixed with lidocaine and epinephrine. Dexamethasone and triamcinolone showed an additional increase in size when allowed to sit for 1 hour after mixture with lidocaine and epinephrine. Mixing steroids caused no increase in particle size.

Because an increase in the number of particles greater than 20 microns in a solution also increases the likelihood of vascular occlusion, the authors urge care in the mixing of these drugs, especially with lidocaine and epinephrine. If mixture is necessary, the authors recommend that injection take place immediately subsequent.