Ophthalmic ointments metal particles

The USP has numerous requirements, e.g., ophthalmic solutions [need be] essentially free from foreign particles, suitably compounded and packaged for instillation into the eye, or ophthalmic suspensions [need contain] solid particles dispersed in liquid vehicle intended for application to the eye [1]. Ophthalmic suspensions are required to be made with the insoluble drug in a micronized form to prevent irritation or scratching of the cornea. A finished ophthalmic ointment must be free from large particles and must meet the requirements for leakage and for metal particles under ophthalmic ointments . These and other requirements will be discussed further in subsequent sections. 

The tube can be a source of metal particles and must be cleaned carefully before sterilization. The USP contains a test procedure and limits the level of metal particles in ophthalmic ointments. The total number of metal particles detected under 30 x magnification that are 50 pm or larger in any dimension is counted. The requirements are met if the total number of such particles counted in 10 tubes is not more than 50 and if not more than one tube is found to contain more than 8 such particles. 

Metal Particles This test is required only for ophthalmic ointments. The presence of metal particles will irritate the corneal or conjunctival surfaces of the eye. It is performed using 10 ointment tubes. The content from each tube is completely removed onto a clean 60-mm-diameter petridish which possesses a flat bottom. The lid is closed and the product is heated at 85 °C for 2 h. Once the product is melted and distributed uniformly, it is cooled to room temperature. The lid is removed after solidification. The bottom surface is then viewed through an optical microscope at 30x magnification. The viewing surface is illuminated using an external light source positioned at 45 ° on the top. The entire bottom surface of the ointment is examined, and the number of particles 50 pm or above are counted using a calibrated eyepiece micrometer. The USP recommends that the number of such particles in 10 tubes should not exceed 50, with not more than 8 particles in any individual tube. If these limits are not met, the test is repeated with an additional 20 tubes. In this case, the total number of particles in 30 tubes should not exceed 150, and not more than 3 tubes are allowed to contain more than 8 particles [15]. 

The United States Pharmacopeia USP 36/The National Formulary NF 31 (2013) <751 > Metal particles in ophthalmic ointments. The United States Pharmacopeial Convention, Rockville, pp 334—335... 

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