Vaginal Delivery Systems and Their Methods of Preparation and Use

I. Field of the Invention

The present invention is directed to delivery systems which are suitable for use in the vaginal cavity. Specifically, the invention is concerned with vaginal preparations which demonstrate the controlled-release of active agents for an extended period of time to a site of action or absorption.

II. Description of the Prior Art

One of the main disciplines of medicine is the treatment of the female reproductive system for the prevention, treatment, mitigation, diagnosis and cure of diseases and the prevention of conception. Usually, this involves the delivery of active agents to the vaginal cavity and its environs. Systems to effect the delivery of such agents are usually in the form of gels, foams, creams, suppositories and quick dissolving tablets. These delivery systems, regardless of formulation or method of manufacture, have not demonstrated the ability to deliver active agents in a controlled manner within the vaginal cavity for periods of three hours or longer.

The vaginal cavity is subject to conditions which render it a target for disease and infection; however, it is extremely difficult to deliver an active agent to this area for an extended period of time. The vaginal cavity exhibits an aqueous environment containing secreting glands whose fluids create an acidic pH in the range of 4.5 to 5.5. The environment of the vagina is conducive to the growth of bacteria, fungi, yeast and other microorganisms since it is warm, moist and dark. It is also the vestibule for menstrual debris and the residual seminal fluid from sexual intercourse. The crevices of the vaginal cavity facilitate the retention of undesirable bacteria, fungi, yeast and other microorganisms, as well as the debris from menstruation and sexual intercourse. The vaginal cavity is also subject to considerable physical deformation, such as during sexual intercourse or during the insertion of tampons. Active agents which have pharmaceutical qualities have been developed and approved for use in the treatment of afflictions of the vaginal cavity and the prevention of conception. These include fungicides, spermicides, etc. Although pharmaceutically active agents have been developed, it has been difficult to achieve optimal potential effectiveness from these agents due to the inadequacy of currently available delivery systems. No system which is approved or even suitable for use in the vaginal cavity has been shown to release a pharmaceutically active agent for periods of three hours or longer. This also is true of aesthetically oriented systems, such as acidifiers and deodorants. The gels, foams, creams, suppositories and tablets that are presently used as vaginal delivery systems breakdown almost immediately following insertion into the vaginal cavity and have minimal bioadherence to the vaginal walls. This is believed due to their water miscibility and/or their lack of physical stability at 37.degree. C. (body temperature). Thus, they exhibit limited effectiveness since they rapidly release their active agents in an uncontrolled manner. Conventional dosage forms are frequently discharged as an offensive leakage and drippage along with the minute vaginal secretions that are a normal physiological function.

The present invention is advantageous in that it provides a system for the delivery of an active agent in a controlled manner in the vaginal cavity for an extended period of at least three hours. The system may take the form of a multi-phase liquid or semi-solid which is easily introduced into the vaginal cavity but does not seep from this body cavity in an offensive manner.

The invention provides vaginal delivery systems which release an active agent to a site of absorption or action in a controlled manner and are bioadherent to the vaginal surfaces. The invention also provides vaginal delivery systems which release an active agent to a site of absorption or action in a controlled manner for at least three hours and are bioadherent to the vaginal surfaces comprising unit cells having lipoidal external phases and nonlipoidal internal phases.

Further, the invention provides methods of preparing vaginal delivery systems which release an active agent to a site of absorption or action in a controlled manner and which are bioadherent to the vaginal surfaces comprising the mixing of lipoidal and nonlipoidal media with an emulsifier. Finally, the invention is concerned with a method of treatment, prophylaxis, cure or mitigation of diseases of the vagina, urinary tract, cervix or other female reproductive organ; of prevention or inducement of conception; of obtaining aesthetic or cosmetic effect; of diagnosis; of systemic drug therapy; or of sexual determination of offspring comprising the introducing into the vaginal cavity of an active agent which is contained within a bioadherent, controlled-release, vaginal delivery system.

The present invention is directed to vaginal delivery systems. The systems are characterized by their ability to deliver agents to a specific site, the vaginal cavity, in a controlled manner over a prolonged period of time. The systems are bioadherent to the epithelial tissue and are comprised of at least two phases. The systems when in a vaginal environment retain their integrity and display physical stability for an extended residence time within the vaginal cavity.

As discussed above, the vaginal cavity produces an aqueous environment which is conducive to the growth of bacteria, fungi, yeast and microorganisms. The systems of the prior art are not optimally effective for treating such conditions either due to their water miscibility, lack of bioadhesion, or lack of physical stability in the vaginal environment of 37.degree. C. The vaginal cavity as defined herein not only includes the vagina, but also associated surfaces of the female urinary tract, such as, the ostium of the urethra. Delivery systems are a combination of non-active ingredients which serve to solubilize, suspend, thicken, dilute, emulsify, stabilize, preserve, protect, color, flavor and fashion an active agent into an acceptable and efficacious preparation for the safe and convenient delivery of an accurate dose of said active agent.

It is important that a system not only release an active agent, but that it release the agent in a controlled manner to a site of optimal absorption or action. That is, an agent is made available for absorption, pharmacological or other effect at a site of absorption or action, in an amount sufficient to cause a desired response consistent with the intrinsic properties of the agent and which provides for maintenance of this response at an appropriate level for a desired period of time. Thus, the systems described herein are characterized by the controlled release of an active substance from a delivery system at a receptor site, site of action, site of absorption, or site of use and the achievement of the desired effect at that site. The systems of the invention are not miscible in water and are not harmful for use in the vaginal cavity.

The systems are comprised of unit cells. These unit cells are the basic, nondivisible, repeating unit of the systems. The unit cells have internal and external phases which represent the internal and external phases of the systems. The systems may be described in conventional classifications, such as emulsions, emulsions/dispersions, double emulsions, suspensions within emulsions, suppositories, foams, etc. The systems are usually in the form of emulsions either of medium or high internal phase ratio, preferably greater than 70% and more preferably greater than 75% by volume. The delivery systems are liquids or semi-solids with viscosities that range from 5,000 to 750,000 centipoise, preferably 350,000 to 550,000 centipoise. The systems in order to adhere to the vaginal cavity must have sufficient viscosity to retain their integrity.

The unit cells have an internal phase which may be discontinuous and which is nonlipoidal. The nonlipoidal character of the phase renders it miscible with water. Preferably the internal phase comprises water, glycerine, or combinations thereof. Generally, it is desirable that the internal phase be of high osmotic pressure. The internal phase may be multiphasic and may be a solution, suspension, emulsion or combination thereof and it contains at least a portion of the active agent. Also, the internal phase may contain suspended solids, emulsions, osmotic enhancers, extenders and diluants, as well as fragrances, colors, flavors, and buffers.

The unit cells also have an external phase. This phase is lipoidal and is the continuous phase of the systems. The term lipoidal pertains to any of a group of organic compounds comprising the neutral fats, fatty acids, waxes, phosphatides, petrolatum, fatty acid esters of monoprotic alcohols and mineral oils having the following common properties: insoluble in water, soluble in alcohol, ether, chloroform or other fat solvents, and which exhibit a greasy feel. Examples of oils suitable for use in these delivery systems are mineral oils with viscosities of 5.6 to 68.7 centistokes, preferably 25 to 65 centistokes, and vegetable oils illustrated by coconut, palm kernel, cocoa butter, cottonseed, peanut, olive, palm, sunflower seed, sesame, corn, safflower, rape seed, soybean and fractionated liquid triglycerides of short chain (naturally derived) fatty acids. This external phase may also contain fragrances, colors, flavors, and buffers.

The active agent may be any of those which are approved for or used for the treatment, prophylaxis, cure or mitigation of any disease of the vagina, urinary tract, cervix or other female reproductive organ or inducement of conception; for aesthetic or cosmetic usage, for diagnostic purposes; for systemic drug therapy; or for sex determination of offpsring. The agent must have utility when administered by delivery to all or a portion of the vaginal surfaces. Potential agents are normally well-known due to their need for governmental approval or common usage. At least a portion of the active agent must usually be contained in the internal phase in order to obtain the release characteristics of the systems.

Adjacent unit cells have common external phases. The external phase of the unit cells provides the continuous phase of the system. The unit cells may utilize emulsifiers. Preferably, the emulsifiers are soluble in the lipoidal or external phase. Suitable emulsifiers are those oil miscible surface active compounds which are acceptable for use in foods, pharmaceuticals, and/or cosmetics. Examples of such emulsifiers are low molecular weight polyglycerols which have been esterified with fatty acids or fatty acid esters, or mono and diglyceride mixtures alone or with the addition of metallic soaps, such as, aluminum stearate. The metallic soaps appear to improve the characteristics of some of the emulsions.

The systems can be introduced into the vaginal cavity by the use of conventional applicators or other coating or spraying means. Although the systems are deformable at physiological temperatures, approximately 37.degree. C., they do not lose their integrity as do the systems of the prior art. These delivery systems, unlike other systems are not characterized by offensive leakage from the vaginal cavity following the insertion of the system. Since these systems break down over an extended period, nonaqueous components are either absorbed or released from the vaginal cavity at an unnoticeable rate which makes no significant increase in normal secretions.

The characteristics of these systems are a result of their inherent integrity under vaginal conditions. The systems release the active agent in the vaginal cavity due to diffusion of the active agent, rupture of the unit cells and/or a combination of these two mechanisms. This release of active agent can be linear or non-linear depending on the composition of the system. Factors which effect the release rate are the percentage of active agent contained in each of the phases; and the type of system, such as, emulsion, double emulsion, suspension; thickness of the external membrane; amount and nature of emulsifier in the external phase; osmotic pressure of the internal phase; pH of the internal phase; diffusibility of the active species through the external phase membrane; etc. Within the physiological environment of the vaginal cavity all of the chemical and physical forces present, including fluids, enzymes, pH, chemical balance, temperature, and shear forces from body movement, effect the rate of breakdown of the system. These forces do not destroy the integrity of the systems at the same rate as other systems.

The systems may be prepared by continuous or batch processes. As in preparing conventional emulsions, shear force is applied to the system components by use of homogenizers, mills, impingement surfaces, ultrasound, shaking or vibration. Unlike conventional emulsions, the mixing shear should be at low levels in order to prevent destruction of the system by imparting excess energy. Temperature is not usually a critical factor in the preparation of the systems. The temperatures utilized will be dependent upon the final end product desired.

The systems may be prepared by mixing the internal with the external phase in a planetary-type mixer. Another manner of preparing the system is by use of a continuous mixer which comprises multiple impellers. The external phase is first introduced into the continuous mixer until it reaches the level of the lowest impeller in the mixing chamber. The two phases are then simultaneously introduced through the bottom of the mixer in proper proportion as its impeller or impellers rotate to apply a shear to the components. The finished product emerges through the top of the mixer. The actual speed of the impeller or impellers will vary, depending upon the product produced as will the rate of flow of the two phase streams.

The following examples are illustrative of the invention:

Method of Preparation: The active agent, and ingredients of the internal phase were mixed together at room temperature. The ingredients of the external phase were mixed together in a one-gallon vessel. The internal phase composition was slowly added to the external phase composition as the two phases were mixed together with a split disc stirrer at low shear until the desired viscosity was obtained.

The same products were also prepared by introducing the internal and external phases continuously into the bottom of a mixer following the initial introduction of the external phase. The finished product emerged through the top of the mixer at one liter/minute.

Each of the above compositions following introduction into the vaginal cavity continued to release its active agent at effective levels for a period of between three hours and ten days. Systems of the prior art containing the same active agent had completely released their active agent within a three hour period.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.