The present study was undertaken to determine if estrogens protect female rats from the neurodegenerative effects of middle cerebral artery (MCA) occlusion. The rats were ovariectomized and 7 or 8 days later various estrogen preparations were administered before or after MCA occlusion. Pretreatment with 17beta-estradiol (17beta-E2) or a brain-targeted 17beta-E2 chemical delivery system (CDS) decreased mortality from 65% in ovariectomized rats to 22% in 17beta-E2-treated and 16% in 17beta-E2 CDS-treated rats. This marked reduction in mortality was accompanied by a reduction in the ischemic area of the brain from 25.6+/-5.7% in the ovariectomized rats to 9.8+/-4% and 9.1+/-4.2% in the 17beta-E2-implanted and the 17beta-E2 CDS-treated rats, respectively. Similarly, pretreatment with the presumed inactive estrogen, 17alpha-estradiol, reduced mortality from 36 to 0% and reduced the ischemic area by 55 to 81%. When administered 40 or 90 minutes after MCA occlusion, 17beta-E2 CDS reduced the area of ischemia by 45 to 90% or 31%, respectively. In summary, the present study provides the first evidence that estrogens exert neuroprotective effects in an animal model of ischemia and suggests that estrogens may be a useful therapy to protect neurons against the neurodegenerative effects of stroke.

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A BSTRACTDespite its apparent easy accessibility, the eye is, in fact, well protected against the absorption of foreign materials, including therapeutic agents, by the eyelids, by the tearfl ow, and by the permeability barriers imposed by the cornea on one side and the blood-retinal barrier on the other. Most existing ophthalmic drugs were adapted from other therapeutic applications and were not specifi cally developed for the treatment of eye diseases; hence, they are not well suited to provide eye-specifi c effects without causing systemic side effects. A real breakthrough in the area of ophthalmic therapeutics can be achieved only by specifi cally designing new drugs for ophthalmic applications to incorporate the possibility of eye targeting into their chemical structure. Possibilities provided along these lines by designing chemical delivery systems (CDSs) and soft drugs within the framework of retrometabolic drug design are reviewed here. Both are general concept applicable in almost any therapeutic area. This review will concentrate on ␤ -adrenergic agonists and anti-infl ammatory corticosteroids, where clinical results obtained with new chemical entities, such as betaxoxime, adaprolol, loteprednol etabonate, and etiprednol dicloacetate, exist to support the advantages of such metabolism-focused, ophthalmic-specifi c drug design approaches.K EYWORDS: beta-blockers , corticosteroids , eye-targeted delivery , glaucoma , intraocular pressure , oxime OCULAR DRUG DESIGN AND DELIVERY: CHALLENGESFor the therapeutic treatment of most ocular problems, topical administration clearly seems the preferred route, because for systemically administered drugs, only a very small fraction of their total dose will reach the eye from the general circulatory system. Even for this fraction, distribution to the inside of the eye is further hindered by the blood-retinal barrier (BRB), which is almost as effective as the blood-brain barrier (BBB) in restricting the passage of xenobiotics from the blood stream. 1 At fi rst sight, the eye seems an ideal, easily accessible target organ for topical treatment. However, the eye is, in fact, well protected against absorption of foreign materials, fi rst by the eyelids and tear-fl ow and then by the cornea, which forms the physical-biological barrier. When any foreign material or medication is introduced on the surface of the eye, the tear-fl ow immediately increases and washes it away in a relatively short time. Under normal conditions, the eye can accommodate only a very small volume without overfl owing. Commercial eyedrops have a volume of ~30 L, which is about the volume of the conjunctival sac in humans; however, after a single blink, only an estimated 10 L remains. 2 Consequently, there is a window of only ~5 to 7 minutes for any topically introduced drug to be absorbed, and in many cases, no more than 2% of the medication introduced to the eye will actually be absorbed. 2-4 The rest will be washed away and absorbed through the nasolacrimal duct and the mucosal membranes of the nasa...

Soft drug design represents a new approach aimed to design safer drugs with an increased therapeutic index by integrating metabolism considerations into the drug design process. Soft drugs are new therapeutic agents that undergo predictable metabolism to inactive metabolites after exerting their therapeutic effect. Hence, they are obtained by building into the molecule, in addition to the activity, the most desired way in which the molecule is to be deactivated and detoxified. In an attempt to systematize and summarize the related work done in a number of laboratories, including ours, the present review presents an overview of the general soft drug design principles and provides a variety of specific examples to illustrate the concepts. A number of already marketed drugs, such as esmolol, remifentanil, or loteprednol etabonate, resulted from the successful application of such design principles. Many other promising drug candidates are currently under investigation in a variety of fields including possible soft antimicrobials, anticholinergics, corticosteroids, ␤-blockers, analgetics, ACE inhibitors, antiarrhythmics, and others. Whenever possible, pharmacokinetic and pharmacodynamic properties are briefly summarized and compared to those of other compounds used in the same field.

Strategies for the design of safer drugs are discussed. The various classes of "soft drugs" are designed to avoid undesired metabolic disposition (primarily various oxidative routes, occurring via possible toxic intermediates) and to be metabolized by a predictable manner with controlled rates. As a first example for the "soft analogue" type drugs, a new class of antimicrobial, surface-active quaternary salts of the type RCOOCHR1--N+ comes from X- was developed. These "soft" quaternary salts are isosteric analogues of known "hard" quaternary surfactants and are characterized by predictable and controllable cleavage (metabolism) to nontoxic components, while showing good activity against a wide range of bacteria. Due to their soft nature (low toxicity), the new antimicrobials are much safer than the conventional, hard analogues.

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Soft drug design represents a new approach aimed to design safer drugs with an increased therapeutic index by integrating metabolism considerations into the drug design process. Soft drugs are new therapeutic agents that undergo predictable metabolism to inactive metabolites after exerting their therapeutic effect. Hence, they are obtained by building into the molecule, in addition to the activity, the most desired way in which the molecule is to be deactivated and detoxified. In an attempt to systematize and summarize the related work done in a number of laboratories, including ours, the present review presents an overview of the general soft drug design principles and provides a variety of specific examples to illustrate the concepts. A number of already marketed drugs, such as esmolol, remifentanil, or loteprednol etabonate, resulted from the successful application of such design principles. Many other promising drug candidates are currently under investigation in a variety of fields including possible soft antimicrobials, anticholinergics, corticosteroids, β‐blockers, analgetics, ACE inhibitors, antiarrhythmics, and others. Whenever possible, pharmacokinetic and pharmacodynamic properties are briefly summarized and compared to those of other compounds used in the same field. © 2000 John Wiley & Sons, Inc. Med Res Rev, 20, No. 1, 58–101, 2000.

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