Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Eyedrops and ointments
General information
Eyedrops and ointments are specialized pharmaceutical formulations intended to produce therapeutic concentrations of the active drug in ocular structures; a lower dose can be used than would be necessary to obtain the same effect by systemic administration. They can cause local adverse effects in the eye due either to the active ingredient or to excipients in the liquid or solid vehicle. The excipients included in modern ophthalmic medicines increase the viscosity of the drug, help to maintain it in solution or suspension, and are thought to stay longer on the exterior of the eye, leading to a longer contact time and possibly greater absorption of the drug than is the case with a simple aqueous solution [ ].
Excipients
Methylcellulose is a vehicle used in eyedrops and contact lens solutions. It is non-irritant and has a good refractive index. A 1% solution is well retained in the conjunctival sac. Corneal cultures have been stimulated by methylcellulose, resulting in increased growth of cells [ ]; tear-film break-up time was increased four-fold with 2% methylcellulose. Hydroxypropyl methylcellulose is also used as artificial tears for people with dry eyes [ ].
Petrolatum-mineral oil ointment is retained longer on the eye than other vehicles. The large molecules of the petrolatum-mineral oil-base ointment are not easily removed by blinking, and a component of the corneal tear film is a non-polar oil. Ointments are oil bases and non-polar, which is why they are readily absorbed by the pre-corneal and conjunctival tear films. To maintain drug contact with the eye, patching is recommended [ ].
Polyvinyl alcohol, a synthetic long-chain alcohol, has been used as a component of various ophthalmic drug vehicles. For retaining clear vision and longer drug contact with the eye, polyvinyl alcohol is superior to saline. Polyvinyl alcohol has good drug compatibility and it acts as a wetting agent, lowering surface tension; at a concentration of 1.4% it does not interfere with corneal wound healing [ ].
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here