In one aspect, this invention relates to antimicrobial compositions. More particularly, it relates to the discovery that a broad group of known antimicrobial agents have increased activity, either in terms of spectrum, killing power, or both, when used in combination with the potentiating agents of this invention.
Ordinarily, the activity or killing power of known antimicrobial agents are inhibited in the presence of blood, wound exudates and other proteinaceous matter including serum proteins, together with saliva, sebaceous secretions, nasal and other mucous secretions.
Although it has been realized for some time that antibacterial agents lose their efficacy in the presence of blood, bodily secretions such as milk serum and wound exudates, the cause of this loss of efficacy or inactivation is not as yet fully understood. It has been postulated, however, that the lipophilic character of the antimicrobial agent is responsible for both protein binding and antimicrobial activity. In the presence of such extraneous proteinaceous matter as blood, the antimicrobial agent preferentially binds to the serum proteins or other proteinaceous matter rather than to the bacterial cells. Under conditions where this undesired preferential binding can occur, the antimicrobial agent is either ineffective or its efficacy is so reduced that greatly increased dosage levels are required. The extent of this loss in activity can approach 90 percent or more. For example, the antimicrobial activity of quaternary ammonium compounds can be so suppressed in the presence of proteinaceous body fluids that activity losses in excess of 96 percent have been recorded.
While the lack of precise knowledge and understanding of the inactivation mechanism has hampered the development of topical antimicrobial preparations which are effective in the presence of the inactivating materials above referred to, it has long been a desired and sought for goal to develop antimicrobial compositions that could overcome this inactivation.
Therefore, an important feature of the present invention is to provide compositions which include known antibacterial, antiviral or antifungal agents together with a potentiator for such agents so as to overcome the deactivating effect of proteinaceous substances and to significantly increase the killing efficacy or to extend the antimicrobial spectrum of the antimicrobial agent, or to have both enhancing effects.
Enhancement of drug absorption through the intact skin has been pursued by many investigators in recent times. Most of these studies showed that the stratum corneum of the skin, the uppermost or horny layer, acts as a protective barrier against the exterior environment. The stratum corneum consists of dead cells that are extensively keratinized and dehydrated. Due to the nature of the highly crosslinked and insoluble keratin, the barrier property of this layer changes little upon exposure to various environmental conditions.
Because of the impermeable nature of the stratum corneum, it has been a long desired goal to temporarily modify the barrier property of this layer in order to enhance the penetration of topically applied drugs. Especially in dermatological conditions, topical application of medicaments is preferred over systemic administration, because the topically applied drug directly attacks the affected target cells. Furthermore, topical treatment eliminates systemic side effects that are frequently associated with long term oral therapy.
Previous studies have shown that dimethylsulfoxide (DMSO) can enhance the absorption of topically applied drugs through the stratum corneum. Similarly, dimethyl formamide (DMFA) and N,N-dimethyl-acetamide (DMA) and their derivatives are claimed to do the same. Some of these combinations are described in U.S. Pat. Nos. 3,551,554 and 3,472,931.
Other recent studies on the physico-chemical properties of the stratum corneum and the absorption of topically applied drugs therethrough include: Scheuplein, R. J., J. Invest. Dermatol. 45, 334 (1966); Blank, I. H., J. Invest. Dermatol, 43, 415 (1964); Hadgraft, J. W. and Somers, G. F., J. Parm. Pharmacol. 8, 625 (1956); and Grasso, P. and Lansdown, A. B. G., J. Soc. Cosmet. Chem. 23, 481-521 (1972).
Thus, in accordance with another feature of the present invention, there are provided topical compositions comprising a known medicament, exemplified by the anesthetics, and a potentiator, whereby the penetration of topically applied anesthetic or other agents through the stratum corneum are substantially enhanced. As an example, enhanced penetration of the anesthetic agent by the action of the potentiator or accelerator results in a quicker onset and deeper anesthesia at the treated site, than that which is obtained without the accelerator. Furthermore, anesthesia at the site of application lasts up to several hours. Conventional preparations elicit only surface anesthesia and onset times sometimes extend to hours. Most conventional preparations, moreover, have been reported to be ineffective on intact skin [Adriani, J. and Dalili, H. Anesthesia and Analgesia, Current Researches, Vol. 50, No. 5 (Sept.-Oct. 1971)].