Topical Eyedrops

Administration and Dosage

Although many alternate experimental methods have been tried, eyedrops remains the major method of administration for the topical ocular route. The usual method of self-administration is to place the eyedrop from a dropper or dropper bottle into the lower cul-de-sac by pulling down the eyelid, tilting the head backward, and looking at the ceiling after the tip is pointed close to the sac and applying a slight pressure to the rubber bulb or plastic bottle to allow a single drop to form and fall into the eye. Most people become quite adept at this method with some practice and may develop their own modifications. However, elderly, arthritic, low-vision, and glaucoma patients often have difficulty in self-administration and may require another person to instill the drops.

The pharmacist should instruct patients to keep in mind the following considerations in administering drops to help improve the accuracy and consistency of dosage and to prevent contamination: be sure that the hands are clean; do not touch the dropper tip to the eye, surrounding tissue, or any surface; prevent squeezing or fluttering of lids, which causes blinking; place the drop in the conjunctival sac, not on the globe; and close the lids for several moments after instillation. The administration of eyedrops to young children can be a difficult task. A way to simplify the task involves the parent's sitting on the floor or a flat surface and placing the child's head firmly between the parent's thighs and crossing legs over the child's lower trunk and legs. The parent's hands are then free to lower the eyelid and administer the drops.

In addition to the proper technique to administer eyedrops, the pharmacist may need to explain to the patient the correct technique for temporary punctal occlusion. Punctal occlusion is usually reserved for use with potent drugs, which can have adverse systemic effects from topical ocular administration such as with ocular P-blockers. Tear fluid drains into the nasolacrimal duct via the puncta located on the medial portion of the eyelid, and fluid is directed into the puncta by the blinking action of the lids. The nasal meatus is a highly vascular area within the nasal cavity, which receives the fluid of the nasolacrimal duct, and drugs contained in tears can be absorbed into the systemic circulation from this area as well as from gastrointestinal absorption. Punctal occlusion can be performed immediately after instillation of an eyedrop by closing the eye and placing a finger between the eyeball and the nose and applying pressure for several minutes.

Eyedrops are one of the few dosage forms that are not administered by exact volume or weight dosage, yet this seemingly imprecise method of dosing is quite well established and accepted by ophthalmologists. The volume of a drop is dependent on the physicochemical properties of the formulation, particularly surface tension, the design and geometry of the dispensing office, and the angle at which the dispenser is held in relation to the receiving surface. The manufacturer of ophthalmic products controls the tolerances necessary for the dosage form and dispensing container to provide a uniform drop size. How precise does the actual dose have to be? As noted earlier, the normal tear volume is about 7 |iL, and with blinking about 10 |iL can be retained in the eye. Approximately 1.2 |iL of tear fluid is produced per minute, for about a 16% volume replacement per minute. Commercial ophthalmic droppers deliver drops from about 30 to 50 |iL/drop. Therefore, the volumes delivered normally are more than threefold in excess of that that the eye can hold, and the fluid that does remain in the eye is continuously being removed until the normal tear volume is attained. It can be seen, then, that the use of more than one drop per dose must take into account the fluid volume and dynamics of the lacrimal system of the eye. If the effect of multiple drops is desired, they should be administered one drop at a time with a three- to five-minute interval in between dosings. Some doctors may prescribe more than one drop per dose to ensure that the patients retains at least one drop in the eye.

Dosage Forms

Solutions The two major physical forms of eyedrops are aqueous solutions and suspensions. Nearly all the major ophthalmic therapeutic agents are water soluble or

Table 3 Effects of Salt Form on Product Properties

Salt form

Discomfort reaction

pH range

Buffer capacity

Epinephrine hydrochloride

Mild to moderate stinging

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