EP0589020A4

EP0589020A4 - Verapamil hcl formulation and other ophthalmic solutions with buffer system for ocular administration

Info

Publication number: EP0589020A4
Application number: EP19930908438
Authority: EP
Inventors: Richard L Giovanoni
Original assignee: COOPERVISION PHARMACEUTICALS Inc; COOPERVISION PHARMA
Current assignee: COOPERVISION PHARMACEUTICALS Inc; COOPERVISION PHARMA
Priority date: 1992-03-18
Filing date: 1993-03-18
Publication date: 1994-07-06
Also published as: WO1993018764A3; CZ260093A3; EP0589020A1; HUT67631A; WO1993018764A2; SK143893A3; CA2102110A1; AU3926093A

Abstract

An aqueous ophthalmic solution is disclosed in which one or more acive ingredients in ionized form are gradually brought to undissociated, free base form by lacrimal solution acting against the affect of a plurality of buffers. The affect of each buffer is overcome sequentially by the lacrimal fluid. A preferred formulation includes verapamil HCl as the active ingredient in ionized form and includes as buffers: boric acid at 2.8 %, disodium edetate at 0.18 %, dextrose at 0.3 %, and polyvinylpyrrolidone at 2.0 %.

Description

5 VERAPAMIL HCL FORMULATION AND OTHER OPHTHALMIC SOLUTIONS

WITH BUFFER SYSTEM FOR OCULAR ADMINISTRATION

1

FIELD OF THE INVENTION , The invention relates generally to ophthalmic compositions containing an active ingredient.

10 BACKGROUND OF THE INVENTION

Ophthalmic solutions are primarily aqueous-based pharmaceuticals designed for topical application to the external surface of the eye. They are indicated for a variety of pathological conditions in addition to being used

15 as diagnostic aids to allow visualization of external ocular structures and abnormalities not readily apparent to casual observation by eye-care practitioners.

Consequently, active ingredients of ocular solutions can include anesthetics, mydriatics (agents that dilate the

20 pupil) , iotics (agents that constrict the pupil) , anti- infectives, diagnostics (such as dyes to visualize nonviable, ocular surface areas as well as other surface abnormalities) , astringents, demulcents and lubricants for temporary relief of ocular discomfort, as well as anti-inflammatory agents and

25 other ingredients designed to elicit specific pharmacological effects.

The basic product-related requirements for an acceptable ophthalmic solution are sterility, clarity and freedom from particulates large enough to cause irritation and/or ocular

30 damage. Additionally, the aqueous vehicle of the ophthalmic product should provide an environment that promotes stability for the active ingredient(s) . Furthermore, the resultant ophthalmic solution (active and inactive ingredients) should not be significantly uncomfortable upon application to the «35 eye. An uncomfortable ocular solution has two major disadvantages. First, it does not promote patient compliance when used outside the professional setting, thereby jeopardizing the outcome of the therapeutic regimen. Second, an uncomfortable ophthalmic solution causes irritation to the eye, albeit transitory, which triggers the protective response of excessive tearing. Overt tearing in response to ocular irritation is designed to wash out what the body perceives as ocular irritants. Unfortunately, if the ophthalmic medication is perceived as an irritant, its dwell time on the eye is reduced by the tearing, thereby compromising its desired effect. Since one mediator of comfort is pH, emphasis has traditionally been placed on buffering ocular solutions to specific pH ranges to provide maximum comfort and greatest serviceability of the solution. The pH of normal tear (lacrimal) fluid is approximately 7.2-7.4 with variations being associated with different pathologies. A significantly uncomfortable condition occurs when pH exceeds 8 or is under 5. Thus, it has long been maintained that if eye solutions can be adjusted to pH ranges that approximate those of normal tears, the resulting solution will be less irritating upon use. Discomfort of ocular solutions, when it does occur, is typically related to properties of the active ingredient(s) . Certain chemicals, as well as certain chemical groups, are generally irritating upon ocular instillation. However, in some situations a pH range outside the

"comfort zone" of 6.8-7.2 is needed to insure stability and, consequently, the therapeutic effect of the active ingredient(s) in the formulation. Other active chemicals stable in the pH comfort zone can still be irritating as a result of their dissociation properties and profiles. In total, the number of ophthalmics that are uncomfortable upon instillation is significant. They comprise the bulk of those used in the professional setting, especially mydriatics and anesthetics. Additionally, patient orientated, long-term use drugs such as pilocarpine HCl or pilocarpine nitrate is also uncomfortable. Many ophthalmic formulations, therefore, represent a compromise between two seemingly often-at-odds requirements: namely, ingredient stability and patient comfort. Historically, this compromise has centered around adjusting the pH of particular formulations to try and meet the comfort needs of the patient as well as the stability requirements of the ingredien (s) in the formulation. By necessity and practicality, considerations of comfort have always had lesser importance. A review of the dissociation profiles of traditionally uncomfortable ocular medications serves to demonstrate why their physiological and therapeutic activity causes ocular discomfort. Ophthalmic medications are physiologically and therapeutically active in their undissociated (free base) state. Generally, however, their dissociated (ionized) forms (or salts) are used in formulating ophthalmic products since they are the most soluble. Examples of ophthalmic medications that are therapeutically active in their undissociated form but formulated as salts, are set forth in Table 1.

Table 1

Antihistamines Mydriatics antazoline phosphate atr opine sulfate naphazoline phosphate ^•c y c l o p e n t o l a t e hydrochloride pyrilamine aleate homatr o ine hydrobromide tetrahydrozoline hydrochloride p h e n y l e p h r i n e hydrochloride scopolamine hydrobromide

Anesthetics

Anti-Inflammatories benoxinate hydrochloride proparacaine hydrochloride cromolyn sodium tetracaine hydrochloride dexamethasone sodium phosphate prednisolone sodium phosphate Miotics

Anti-Infectives demecariu bromide echothiophate iodide gentamicin sulfate pilocarpine hydrochloride neomycin sulfate pilocarpine nitrates polymyxim B sulfate sulfacetamide sodium

Other timolol maleate betaxolol hydrochloride verapamil hydrochloride

Upon application to the exterior eye surface, these salts are "hydrolyzed," resulting in conversion to the free base form and accompanying anion or cation. The free base is absorbed through the eye and ultimately is responsible for the physiologic activity of the drug. It is the absorption of free base drug that is recognized as the cause of discomfort to the eye. Hydrolytic cleavage of the medication salt occurs because of the eye's remarkable buffering capacity to maintain the surface pH generally between 7.2-7.4. The further away the pH of the applied ocular product is from this physiologic ocular pH range, the more rapid and intensive will be the hydrolytic activity with the potential for accompanying acute, intensive discomfort. The ionized ocular product may be stable in buffer as stored. However, once the buffer capacity of the drug vehicle is "broken," the ionized form is "instantaneously" converted to the undissociated (free base) form. Consequently, more intense, acute discomfort is realized from the use of traditional, uncompromising buffers.

Previous ocular medication vehicles have attempted to address the uncomfortable conversion of dissociated medication to the free base by incorporating uncompromising chemical buffers designed to hold the pH of the ocular surface to that of the product for as long as possible. In cases where the pH of the product differs markedly from that of the eye, such buffers only act to increase the discomfort of the product by eliciting an overt physiological buffering response by ocular fluids released from the lacrimal gland as schematically illustrated in Fig. 1.

Recently, it has been shown that certain calcium channel blocking agents, especially verapamil, are capable of lowering elevated intraocular pressure when administered topically to the hypertensive eye in solution in a suitable ophthalmic vehicle (Abelson, U.S. Pat. No. 4,981,871, hereby incorporated by reference herein) . However, in practice, it has been difficult to obtain an ophthalmic vehicle for verapamil that will ensure patient compliance. Verapamil represents the classic ophthalmic medication stable in salt form (e.g., as verapamil HCl) in a pH environment below that of ocular fluids. In order to maintain a reasonable shelf life, verapamil HCl ophthalmic solution should preferably be maintained at a pH range of 5.0-5.5. However, without a suitable buffering vehicle, application of verapamil HCl in shelf-stable form to the ocular surface, which is at the physiologic pH of the tearfilm (pH 7.0), results in a degree of stinging that is intolerable for patient compliance.

SUMMARY OF THE INVENTION

In broad scope, the present invention is an ophthalmic composition for topical application to the external surface of the eye, which comprises an active ingredient for effecting a pharmacological change in the eye or as a diagnostic aid in visualizing ocular structures. The active ingredient is applied to the eye in the form of a stable, ionized salt at a pH that is low relative to the pH of lacrimal fluid. The active ingredient is active in its undissociated form as a free base at a pH substantially higher than that in its dissociated form as an ionized salt. Also present are a plurality of buffers in amounts sufficient to arrest the increase in pH of the active ingredient as it changes from a salt to a free base in the presence of the lacrimal fluid. The buffers are differentiated from each other in their buffering capability so that conversion of the active ingredient from dissociated to free base form is moderated and sustained by successive neutralization of different buffers. This gradual formation of free base imparts to the patient a comfort significantly greater than that present when only a single buffer is used and the change in pH as the active ingredient changes from dissociated to free base form is more rapid.

More specifically, it is contemplated that the invention may use a plurality of buffers, e.g., three, four, five or more. Such buffers will be of different buffering capabilities and, if desirable, the same total amounts. In this way the pH of the composition will advance in stages as the buffering capability of each buffer is overcome by the lacrimal fluid and the pH of the composition is raised toward that of the tears. Even more specifically, it is contemplated that a plurality of buffers including boric acid, disodium edetate, and polyvinylpyrrolidone (PVP) be used, the edetate being the weakest and the boric acid the strongest of the weakly dissociated acids to be overcome. Where four buffers are used, dextrose may be the fourth; it is still weaker than the edetate and will be the first to be broken by the tears of the user.

In another aspect, the invention features an ophthalmic composition for topical application to the external surface of the eye comprising verapamil as an active ingredient, in the form of a stable, dissociated salt (verapamil HCl) at a pH that is low compared to the pH of lacrimal fluid. The ophthalmic composition also includes a buffer system comprising a plurality of buffers in amounts sufficient to control the increase in pH of the active ingredient as it changes from a salt to a free base in the presence of the lacrimal fluid. The buffers are differentiated from each other in their buffering capability so that conversion of the active ingredient from dissociated to free base form is moderated and sustained by successive neutralization of different buffers. This gradual formation of free base imparts to the patient a comfort significantly greater than that present when only a single buffer is used and the change in pH as the active ingredient changes from dissociated to free base form is more rapid.

Preferably, the buffers in the buffering system are boric acid at a concentration of 0.5-3.0%, most preferably 2.8%; disodium edetate at a concentration of 0.08-0.5%, most preferably 0.18%; dextrose, at a concentration of 0.1-5.0%, most preferably 0.3%; and polyvinylpyrrolidone at a concentration of 1.0-4.0%, most preferably 2.0%. All concentrations are by weight. The composition may also include a preservative, most preferably benzalkonium chloride.

The ophthalmic composition of the invention serves to moderate the physiological buffering response of the lacrimal fluids. Unlike traditional buffer chemicals which only momentarily adjust the pH of the ocular surface to that of the product then instantly "break" when overpowered by ocular fluids, the composition of the present invention provides a sustained, controlled, degrading, "trenched" buffering response. Instead of attempting to hold a predetermined, product oriented pH environment on the ocular surface, it allows adjustment of the ocular pH by lacrimal fluids over a period of up to approximately 60 seconds. For example, it is contemplated that a composition stored at a pH of about 3 would reach a pH greater than 6.5 after about one minute following application to the eye and would have a pH less than 6.5, even less than 6.0 or 5.5, 30 seconds after installation. This trenched pH change allows sustained, rather than immediate, conversion of the dissociated medication to the undissociated form.

By avoiding instantaneous conversion of all the ionized medication, the composition allows for gradual conversion of the dissociated form to the undissociated, absorbable form of the active agent. The slower conversion results in lower concentration of undissociated drug on the eye at any one time, thereby lessening or avoiding the discomfort associated with the undissociated drug. Since the eye perceives less to no irritation, the tearing response is lessened, thereby allowing a longer dwell time of the medication on the ocular surface.

Other features and advantages of the invention will be apparent from the following description of the preferred embodiment thereof and from the claims taken in conjunction with the accompanying drawings in which:

Fig. 1 shows a traditional buffer-drug discomfort relationship; and

Fig. 2 shows a drug discomfort relationship in the buffer system of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The Lacrimal Activated Buffer System (LABS) of the invention is designed to control (by moderating) the physiological buffering response of the lacrimal fluids to the pH of stored ophthalmic solutions containing certain active ingredients. Unlike traditional buffered compositions which only momentarily adjust the pH of the ocular surface to that of the product and then instantly "break" when overpowered by ocular fluids, LABS is formulated to provide a sustained, controlled, degrading "trenched" buffering response. Instead of attempting to hold a predetermined product oriented pH environment on the ocular surface, LABS allows continual adjustment of the ocular pH by lacrimal fluids over a period of time which can last up to approximately 60 seconds. Consequently, this trenched pH change allows sustained, rather than immediate, conversion of the dissociated (ionized) form of the active ingredient to its undissociated (nonionized) form. By avoiding instantaneous conversion of all the ionized product, e.g., verapamil HCl, the metered change of the LABS induced pH environment on the eye allows for gradual conversion of the dissociated form to its undissociated, absorbable, therapeutically active form (e.g., verapamil) as schematically illustrated in Fig. 2. This slower conversion results in a lower concentration of undissociated drug on the eye at any one time, thereby lessening or avoiding the discomfort associated with its presence. Since the eye perceives less-to-no irritation, the tearing response is lessened or negated, thereby allowing a longer resident time for the undissociated drug on the ocular surface. The controlled shift in the dissociation/undissociation equilibrium reaction of the active ingredient is mediated by a formulation that utilizes a select number and variety of weak, acidic chemicals that consequently are only mildly dissociated in aqueous media. Most often, these weakly dissociated, acidic chemicals and their preferred concentration ranges include, but are not limited to: Boric Acid, USP grade (0.5-3.0%)

Disodium Edetate, USP grade (0.08-0.5%) Dextrose, USP grade (0.1-5.0%)

Polyvinylpyrrolidone (PVP) , USP grade (1.0-4.0%) All the aforelisted ingredients are recognized and acceptable for ocular pharmaceutical formulations and, indeed, are used in many available eye preparations. Their inclusion, however, is for other reasons not related to their use as explained in this application. For example, boric acid has antimicrobial and uncompromising pH adjusting properties when used alone, disodium edetate and dextrose can chemically stabilize certain ophthalmic active ingredients, and, additionally, disodium edetate exhibits antimicrobial activity. PVP is typically included in formulations to increase viscosity and/or serve as a suspending agent. While concentrations outside the preferred ranges are not ineffectual for influencing dissociation rates of some active, ophthalmic ingredients, these are the concentrations preferred at present. It is preferred that all four of the listed buffering compounds be used together; nevertheless, use of at least two of the buffering compounds in a specific formulation is consistent with providing controlled dissociation of certain active ingredients. The number of buffers and their concentrations is generally related to the discomfort imparted by a specific active ingredient. Additionally, it will be recognized that other organic and/or inorganic chemicals can be used in place of some or all of the common buffers listed. These buffers enjoy the greatest use largely because they are recognized as safe for use in ophthalmic preparations.

Exemplarily, other weakly dissociating acidic substances such as alginic acid, cyclamic acid, edetate calcium disodium, gluronic acid, and sorbic acid may be used in proper concentrations in formulations according to the invention.

Likewise, concomitant use of a strong base such as sodium hydroxide and/or strong acid such as hydrochloric acid is consistent for inclusion into the preferred embodiments in order to bring the formulation to the appropriate final pH range for optimal shelf stability.

In addition, pharmaceutically acceptable antimicrobial preservatives can be included. Examples of compatible preservatives include, but are not limited to benzalkonium chloride, edetate disodium, phenylmercuric nitrate, silver protein salts, sorbic acid, and thimerosal. It will be apparent from this list that certain agents may serve a dual function as a preservative and a buffer. The choice of preservative is contingent on the active ingredients present and profile of the buffers used. In the preferred embodiment of the invention the LABS formulation is used to act as a comfort vehicle for verapamil HCl, and the preferred concentrations of the buffering ingredients are as follows:

Additionally, benzalkonium chloride (BAC) is included in the preferred LABS formulation. BAC serves as an antimicrobial agent to maintain the sterility of the packaged solution in multidose containers. If the solution is packaged in unit-of-use (one time use containers) , the BAC is omitted from the formulation since it does not contribute to the flexible buffering properties of the formulation.

The mechanism of action of the LABS formulation is based on the capability of its ingredients to be buffered up to the physiologic pH range of ocular fluids concurrent with the "uncomfortable" active ingredient(s) . Being weakly acidic chemicals, each of the LABS ingredients offers a different degree of weak resistance to the buffering activity of ocular fluid. The LABS ingredient having the weakest resistance (least buffering properties) is neutralized first. Neutralization of the other buffering ingredients continues from the second weakest to the ingredient having most resistance to pH change. Specifically, if the four common buffers of the preferred embodiment are present, the theoretical order of neutralization of this formulation is: dextrose—»disodium edetate—→^'PVP 'boric acid

(weakest "Strongest) based on their in vitro buffering capacities.

Therefore, as each LABS ingredient is neutralized

(buffered to approximately pH 7.0) the pH of the ocular fluids gradually rises. As the pH rises (or as acidity is reduced) more of the dissociated product, e.g., verapamil HCl, is converted, hydrolytically, to undissociated product, e.g., absorbable verapamil free base. Because this conversion is moderated and sustained by successive neutralization of LABS ingredients (the trench buffer phenomenon) , the ocular discomfort associated with instantaneous, total conversion to free base is largely reduced or negated. The average concentration of free base gradually rises as the ocular surface pH rises (due to neutralization of LABS ingredients) until it reaches maximum concentration and then diminishes. It follows, therefore, that the plurality of buffers must be qualitatively and quantitatively custom tailored to the dissociation profile of the active ingredients present in a specific formulation.

Three factors are simultaneously in play that help avoid overt free base concentration on the ocular surface: 1) as the free base forms, it is absorbed away from the ocular surface into interior eye tissue, 2) the tearfilm activity constantly removes drug product from the ocular surface, and

3) the free base is formed gradually.

The first two phenomena are common to instillation of all eye drops; however, it is the third phenomenon that distinguishes the activity of LABS from other buffer compositions used to impart comfort to ocular preparations.

Therefore, the buffering system of the invention can be customized to impart comfort to a specific ophthalmic formulation by adjusting the concentration of each buffer and altering the number of buffers. As a result, an almost infinite number of "comfort patterns" can be devised to effect the controlled conversion of dissociated drug to undissociated drug. The degree of comfort required is a function of the dissociation profile of the active ingredients with respect to characteristics and degree of free base formed in an environment approximating or somewhat less than pH 7. Stability of a vast majority of active ophthalmic ingredients is enhanced in this pH range. So, the pharmaceutical product can be adjusted to a pH range where long-term stability is ensured even if it is significantly below the pH of the eye. Consequently, the requirements of stability and comfort can both be addressed without compromising either one. In another embodiment the ophthalmic solution of the invention may be regarded as an aqueous solution of a medicament in an aqueous ophthalmic vehicle containing an amount of an ophthalmologically acceptable acidifying reagent sufficient to maintain the solution at an acidic pH in the range of 4.5-5.5 during storage, and an amount of an ophthalmologically acceptable buffer having a pH range between the pH of the solution and the normal pH of the mammalian eye sufficient to cause the pH of the ocular fluid to return gradually to its normal value after a dose of the ophthalmic vehicle is instilled into the eye.

The ophthalmic vehicle of the invention may be used to formulate medicaments to be administered topically to the eye, when the active ingredients have to be stored at a relatively low pH for stability, but are significantly absorbed only from solutions near physiological pH.

Consequently, the ophthalmic solution of the invention will include an acidifying agent, often referred to in this art as a "buffer", which will adjust the pH of the vehicle to a range suitable for long term storage of the active ingredient, typically pH 4.5-5.5. The acidifying agent will typically be a weak acid, such as boric acid, sorbic acid or the like.

The ophthalmic solution of the invention will include one or more intermediate buffers, i.e., compounds having buffering capacity at a pH between the acidic pH to which the vehicle is adjusted for long-term stability of the active ingredient and the normal pH of the eye, i.e., 7.2-7.4. A buffer solution, as is well known to those skilled in this art, is one which experiences relatively little change in pH when an acid or base is added thereto. Buffer solutions typically comprise an aqueous solution of a substance which can react with added acid or base to prevent a rapid change in pH as the acid or base is added. The theory and practice of using buffers is well known. A suitable buffer may be a mixture of a weak acid and its salt, i.e., a partially neutralized weak acid. Typically, such mixtures exhibit their maximum buffering capacity, i.e., their greatest resistance to change in pH with added acid or base, at a pH at which the acid is about half neutralized. However, buffers may include materials e.g. , water-soluble polymers or organic compounds, for which the theory of their buffering capacity is not so easily expressed mathematically. Nevertheless, such materials can be investigated experimentally and characterized as to their resistance to change in pH when an acid or base is added to an aqueous solution -containing them. Thus, the skilled practitioner can readily identify suitable buffering materials for use in the compositions of this invention. For example, the practitioner may select a buffer mixture derived from a weak acid which will be partially neutralized at the desired buffer pH, i.e., an acid having a pKa close to the chosen buffer pH. Alternatively, the practitioner may make use of the known properties of water-soluble polymers such as poly(vinylpyrrolidone) or organic compounds such as dextrose. Evidently , the practitioner may select one or more ophthalmologically acceptable buffering materials and adjust their concentrations in the ophthalmic solution to achieve the desired gradual neutralization when they are instilled 5 into the eye. In particular, a plurality of intermediate buffers may be used, each having effective buffering action at a different pH within the range from the acidic pH at which the ophthalmic solution is kept to enhance its shelf life and the normal pH of the eye, i.e., in the range of

10 about 4.5 to about 7.2. In such a buffer mixture the pH will rise gradually as the eye neutralizes each buffer material in succession.

Preferred materials usable in the ophthalmic vehicle of the invention include boric acid as an acidifying agent and,

15 as intermediate buffers, disodium edetate, dextrose, and poly(vinylpyrrolidone) (PVP) . Among such buffers, the PVP has been found to have significant buffer capacity at a pH between the original acidic pH of the vehicle, i.e., about 4.5-5.5, and the pH of the lacrimal fluids, i.e., 7.2-7.4.

20 Similarly, the disodium edetate, which has a pKa in this range, will be expected to have buffering capacity in this pH range. Dextrose, as well, can be used a buffer in the pH range slightly acidic relative to the natural pH of the i lacrimal fluids.

25 Other ophthalmologically acceptable buffers may also be

* used in the vehicle of this invention, e.g., phosphate buffers and citrate buffers, as well as other weakly dissociating acidic substances such as alginic acid, cyclamic acid, edetate calcium disodium, glucuronic acid, sorbic acid and the like.

The amount of intermediate buffer incorporated into the ophthalmic vehicle of the invention should be sufficient to provide enough buffering capacity to cause a relatively slow return of the precorneal lacrimal fluid to the normal physiological pH. The duration of this gradual rise in pH to be chosen for a particular medicament will depend on the particular drug used, the concentration of the drug required for therapeutic purposes, and the propensity of the drug to cause ocular discomfort. Typically a duration of about 60 seconds will provide a period long enough for substantial absorption of the drug while keeping the instantaneous concentration of the free base form small enough to minimize discomfort. However, longer or shorter durations can be effected by adjusting the concentration of the intermediate buffers. The choice of concentration of intermediate buffers for a given drug and therapeutic concentration thereof is a matter that can be easily determined by the skilled practitioner.

Use

Verapamil HCl in the LABS buffer composition can be administered topically to the external surface of the eye to lower elevated intraocular pressure. The effective dose used will vary depending on the particular patient. However, a typical dose will range from about 10 micrograms to about 1 milligram per eye per day.

Typically, the concentration of verapamil HCl in the buffer solution will vary from about 0.1 mg/ml to about 5 mg/ml. Preferably, the concentration of the solution is adjusted to deliver the desired dose of verapamil HCl in a single drop, e.g., of about 40 microliters.

Other embodiments are in the claims.

Claims

What is claimed is: 1. An aqueous, ophthalmic composition for topical application to the external surface of a mammalian eye for lowering elevated intraocular pressure comprising verapamil, said verapamil being applied to the eye in the form of a stable, dissociated salt (verapamil HCl) at a pH that is low compared to the pH of lacrimal fluid at about 7.2 to 7.4; and a pharmaceutically acceptable ophthalmic vehicle buffered at said pH that is low compared to the pH of lacrimal fluid, said vehicle being capable of controlling the increase in pH of said composition in the presence of lacrimal fluid, said vehicle comprising boric acid, at a concentration of 0.5-3.0%; disodium edetate, at a concentration of 0.08-0.5%; dextrose, at a concentration of 0.1-5.0%; and polyvinylpyrrolidone, at a concentration of 1.0-4.0%.

2. The composition of claim 1 wherein in said vehicle the concentration of said boric acid is 2.8%.

3. The composition of claim 1 wherein in said vehicle the concentration of said disodium edetate is 0.18%.

4. The composition of claim 1 wherein in said vehicle the concentration of said dextrose is 0.3%. 5. The composition of claim 1 wherein in said vehicle the concentration of said polyvinylpyrrolidone is 2.0%.

6. The composition of claim 1 wherein said vehicle is a solution and wherein the concentration of said boric acid is 2.8%, the concentration of said disodium edetate is 0.18%, the concentration of said dextrose is 0.3%, and the concentration of said polyvinylpyrrolidone is 2.0%.

7. The composition of any one of claims 1-6 wherein said vehicle further comprises benzalkonium chloride.

8. The composition of claim 1 wherein said vehicle is a solution and wherein the concentration of verapamil HCl in said solution is such that a therapeutically effective amount of said verapamil HCl can be contained in one drop of said solution of about 40 microliters.

9. An aqueous, ophthalmic composition for topical application to the external surface of the eye with reduced discomfort to the patient, comprising: an active ingredient for effecting a pharmacological change in the eye or as a diagnostic aid in visualizing ocular structures, said active ingredient being applied to the eye in the form of a stable, dissociated salt at a pH that is low compared to the pH of lacrimal fluid at about 7.2 to 7.4,, said active ingredient being pharmacologically or diagnostically active in its undissociated form as a free base at a pH substantially higher than that in its dissociated form as an ionized salt, and _ a plurality of buffers in amounts sufficient to arrest the increase in pH of said active ingredient as it changes from a salt to a free base in the presence of said lacrimal fluid, said buffers being differentiated from each other in their buffering capability so that the conversion of said active ingredient from dissociated to free base form is moderated by successive neutralizations of different buffers at different pH levels and the gradual formation of free base imparts to the patient a comfort significantly greater than that present when only a single buffer is used and the change in pH as the active ingredient proceeds from dissociated to undissociated form is a more rapid transition.

10. The composition as claimed in claim 9, in which said buffers are at least three in number.

11. The composition as claimed in claim 10, in which said buffers are selected from the group consisting of boric acid, disodium edetate, PVP and boric acid. 12. The composition as claimed in claim 11, in which said buffers are boric acid, disodium edetate and PVP.

13. The composition as claimed in claim 9, in which said buffers are at least four in number.

14. The composition as claimed in claim 13, in which said buffers are boric acid, disodium edetate, PVP and boric acid.

15. An aqueous, ophthalmic composition for topical application to the external surface of the eye with reduced discomfort to the patient, comprising: an active ingredient selected from the group consisting of antihistamines, anesthetics, miotics, mydriatics, anti- inflammatories, anti-infectives, timolol maleate, betaxolol HCl and verapamil HCl, said active ingredient being applied to the eye in the form of a stable, dissociated salt at a pH that is low compared to the pH of lacrimal fluid at about 7.2 to 7.4, said active ingredient being pharmacologically or diagnostically active in its undissociated form as a free base at a pH substantially higher than that in its dissociated form as an ionized salt, and a plurality of buffers in amounts sufficient to arrest the increase in pH of said active ingredient as it changes from a salt to a free base in the presence of said lacrimal fluid, said buffers being differentiated from each other in their buffering capability so that the conversion of said active ingredient from dissociated to free base form is moderated by successive neutralizations of different buffers at different pH levels and the gradual formation of free base imparts to the patient a comfort significantly greater than that present when only a single buffer is used and the change in pH as the active ingredient proceeds from dissociated to undissociated form is a more rapid transition.

16. The composition as claimed in claim 15, in which said buffers are at least three in number.

17. The composition as claimed in claim 16, in which said buffers are selected from the group consisting of boric acid, disodium edetate, PVP and boric acid.

18. The composition as claimed in cla±m 15, in which said buffers are present in substantially equal amounts.

19. The composition as claimed in claim 15, in which the pH of said solution prior to instillation is about 3.

20. The composition as claimed in claim 19, in which the pH of said solution one minute after instillation is greater than 6.5. 21. The composition as claimed in claim 20, in which the pH of said solution 30 seconds after instillation is less than 6.5.

22. An aqueous ophthalmic composition for topical administration of a medicament to a mammalian eye comprising an ophthalmic medicament in a vehicle comprising an aqueous solution containing an amount of an ophthalmologically acceptable acidifying reagent sufficient to maintain said solution at an acidic pH in the range of 4.5-5.5 during storage, and an amount of an ophthalmologically acceptable buffer having a pH buffering range between the pH of the solution and the normal pH of the mammalian eye sufficient to cause a gradual neutralization of the vehicle by the tears of the eye when a dose of the ophthalmic vehicle is instilled into the eye.

23. The use of an aqueous solution comprising an ophthalmic medicament in an aqueous vehicle containing an amount of an ophthalmologically acceptable acidifying reagent sufficient to maintain said solution at an acidic pH in the range of 4.5-5.5 during storage, and an amount of an ophthalmologically acceptable buffer having a pH buffering range between the pH of the solution and the normal pH of the mammalian eye sufficient to cause a gradual neutralization of the vehicle by the tears of the eye when a dose of the ophthalmic vehicle is instilled into the eye, for the treatment of ophthalmic conditions by topical administration of said solution to the eye.

24. The use of Claim 23 wherein said medicament is verapamil hydrochloride and said solution is used for treating glaucoma.