N. Bodor

A NON-SURFACTANT FORMULATION FOR ALFAXALONE BASED ON AN AMORPHOUS CYCLODEXTRIN : ACTIVITY STUDIES IN RATS AND DOGS

Abstract The steroid anesthetic, alfaxalone, is commercially available for veterinary use in a formulation containing Cremophor-EL® and alfadalone acetate. The allergic sensitivity of some species to this formulation limits its veterinary application and also led to withdrawal of the product for human use. The present studies evaluated alfaxalone formulated as an inclusion complex with a mixture of 2-hydroxypropyl-β-cyclodextrin (HPCD) isomers for anesthetic properties in rats and dogs. Aqueous solutions of alfaxalone-HPCD showed identical anesthetic profiles in rats compared to the commercial formulation. In contrast, the anesthetic response to alfaxalone-HPCD in dogs was not accompanied with massive histamine release and pronounced decrease in respiration and blood pressure seen after the commercial preparation. Anesthesia induction and recovery phases were rapid and uncomplicated after alfaxalone-HPCD. An anaphylactoid-like response did occur in dogs after the same dose of alfaxalone as the commercial preparation. The favorable anesthetic profile of alfaxalone formulated as an HPCD complex together with previous toxicology and stability studies suggest that the steroid may be successfully formulated for intravenous dosing with modified cyclodextrins.

The use of 2-hydroxypropyl-β-cyclodextrin as a vehicle for intravenous administration of dexamethasone in dogs

Abstract Dexamethasone (Dex) was administered to 6 mongrel dogs in a dose of 5 mg/kg as the sodium salt of its phosphate ester or as an inclusion complex in 2-hydroxypropyl-β-cyclodextrin (HPCD). Blood and urine were collected and analyzed for dexamethasone by HPLC. The area under the plasma concentration time curve (AUC) of dexamethasone during the first hour was significantly greater after the administration of the Dex-HPCD complex compared to the phosphate ester prodrug (1.63 ± 0.13 vs 1.04 ± 0.10 μ g h ml −1 ). In addition, the renal clearance (CL ren ) was significantly higher after administration of the HPCD form (0.91 ± 0.20 vs 0.52 ± 0.20 ml min −1 kg −1 ). There was no difference between treatments for other pharmacokinetic parameters of dexamethasone. Hence, intravenous injection of dexamethasone in HPCD allows direct administration of this poorly soluble steroid without any prodrug conversion. The higher plasma levels during the first hour after administration may be advantageous for the treament of emergency situations.

A novel redox system for CNS-directed delivery of estradiol causes sustained LH suppression in castrate rats

A series of 4 studies was conducted to examine the estrogen-like activity of a chemical delivery system (CDS) coupled to estradiol (E2). The CDS is based on a redox system, analogous to the NAD+ in equilibrium NADH coenzyme system and has previously been shown capable of sustained and site specific drug delivery to the central nervous system. The ability of CDS-E2 to suppress luteinizing hormone (LH) in gonadectomized rats was examined as an index of sustained estrogen action. A single dose of CDS-E2 resulted in significantly decreased LH serum levels in castrate rats through at least 24 days while an equimolar dose of E2 resulted in only transient LH decrease. Serum E2 levels were not different between the treatment groups, indicating that peripheral estrogen could not readily explain sustained hormone activity. A dose-response relationship was observed 12 days post-drug treatment in all monitored estrogen activities which showed CDS-E2 is more potent compared to equimolar E2. Further, LH suppression was significantly greater compared to ovariectomized rats treated with equimolar estradiol valerate, while anterior pituitary weights were not different between groups. Together with our previous data, these studies show that CDS-E2 exerts sustained estrogen-like activity which cannot be readily attributed to circulating E2 levels. These findings are consistent with a sustained, brain directed delivery of estrogen.

Drug targeting and retrometabolic drug design approaches Introduction

Abstract Traditional methods for drug design have relied on optimization of drug activity with little regard for drug safety. Such manipulation often produces highly potent derivatives with equally elevated toxicities giving rise to no or disadvantageous changes in the therapeutic index of the derivatives. Inclusion of metabolic and toxicological concerns in the drug design process is embodied in the retrometabolic approach. This systematic methodology employs several schemas to provide for the safe targeting of drugs to defined sites or tissues in the body. The retrometabolic approach can be subdivided into soft drug technologies, which provide for agents that are readily and safely deactivated subsequent to exerting their biological effects, and the chemical delivery systems which through multiple enzymatic conversions provide for site-selective delivery. Examples of these chemical techniques to improved drug design are given including a soft steroid for treating ocular inflammation and a brain-targeting chemical delivery system for peptides.

Chronic weight loss in lean and obese rats with a brain-enhanced chemical delivery system for estradiol

Studies were undertaken to determine the effects on body weight and food intake of a chemical delivery system which preferentially delivers estradiol (E2) to the brain and there serves as a source for the sustained release of the steroid. We injected intravenously various doses of this estradiol-chemical delivery system (E2-CDS), E2-valerate (E2-VAL) or the dimethyl sulfoxide (DMSO) vehicle to young lean male rats and monitored body weight and 24 hr food intake for 39 days postinjection. E2-VAL caused a transient reduction in food intake and body weight gain. By contrast, a single injection of E2-CDS caused a chronic, dose-dependent reduction in the rate of body weight gain. In these lean rats, the duration of reduced body weight gain was not correlated with the observed transient reduction in food intake. In aged, obese male rats, E2-CDS caused a marked and chronic dose-dependent reduction in body weight. In contrast to lean rats, E2-CDS caused a long-term reduction in food intake in obese rats. To evaluate the importance of the E2-CDS-induced reduction in food intake in the observed persistent weight loss in obese rats, E2-CDS was administered to a group of obese rats and a second group which received the DMSO vehicle was pair-fed an equivalent amount of food daily. The resulting weight loss in both groups was equivalent. These results show that the enhanced delivery of E2 to the brain with the E2-CDS causes sustained reduction in the rate of body weight gain in lean rats and persistent weight loss in obese animals.

Evaluation of an estradiol chemical delivery system (CDS) designed to provide enhanced and sustained hormone levels in the brain

Abstract While estrogens readily penetrate the blood-brain barrier and exert significant CNS effects, they are not retained by this organ, obligating constant dosing to achieve sustained and pharmacologically relevant brain concentrations. Such a regimen also generates high peripheral levels of the estrogens which have been linked to metabolic disturbance and cancer. Brain-selective targeting would act to increase the safety of administered drugs by sparing non-target-site tissues. A dihydronicotinate-nicotinate redox targetor designed along these lines was found to be successful in maintaining high central levels of estradiol while peripheral levels were rapidly eliminated. In human clinical trials, the estradiol-chemical delivery system (E2-CDS) reduced circulating LH levels to a greater extent than did administered estradiol but caused less of an increase in circulating estradiol blood levels.

A redox system for brain targeted estrogen delivery causes chronic body weight decrease in rats

The effects of 2 redox based carriers for brain directed delivery of estradiol (CDS-E2) and ethinyl estradiol (CDS-EE) on body weight were examined in rats. A single dose of CDS-E2 (3 mg/kg) decreased weight gain in castrate rats for at least 24 days. The dose response of weight gain and LH suppression were compared 12 days and 12 to 25 after CDS-E2 and CDS-EE, respectively, in ovariectomized (OVX) rats. Weight decrease was detected at a lower dose and was significant for longer after drug treatment than LH decrease. Both compounds were more potent than equimolar estradiol or estradiol valerate in reducing weight gain. Intact rats also showed decreased weight gain but were less sensitive to CDS-E2 compared to OVX rats. The effects appeared to be estrogen specific as carrier-linked testosterone had no effect on weight. The mechanisms of sustained and potent drug effects on weight are being explored.

Improved brain delivery of antiviral agents through the use of redox targeting

Abstract The inability to effectively deliver antiviral agents to the brain and central nervous system can be overcome via drug latentiation and, specifically, via a redox chemical delivery system. This approach has been successfully applied to a variety of agents, examples of which are summarized in this review. These include azidothymidine, azidouridine, dideoxydidehydrothymidine, acyclovir, trifluorothymidine, gancyclovir and ribavirin.

Use of a Chemical Redox System for Delivery of Drugs to the Brain: Ethinyl Estradiol

The normally protective function of the blood-brain barrier (BBB) can hinder delivery of therapeutic drug concentrations to the central nervous system (CNS). In addition, several CNS active drugs which can readily penetrate the BBB owing to their lipophilic properties have short biological half-lives and require frequent dosing. A chemical redox-based system of drug-enhanced delivery through the BBB has recently been developed in our laboratories. The method is designed to biomimic the NAD+ e NADH redox system and has been shown to both enhance delivery of drugs to the CNS and to maintain sustained drug levels in this tissue.’** The system utilizes a lipophilic dihydropyridine carrier which is covalently attached to a relatively hydrophilic drug. The drug carrier complex enhances drug penetration through the BBB due to augmented lipophilicity; however, the complex is designed to be metabolically labile. In viw oxidation to the corresponding hydrophilic quaternary salt of the drug complex impedes efRux through the BBB. Excretion from peripheral tissues is conversely facilitated by this oxidation. The resulting “locked-in” drug carrier complex is hydrolyzed to release free drug and the naturally occurring nontoxic carrier metabolite, trigonelline. The rate of hydrolysis, and therefore the duration of drug activity, can be altered by chemical design of the carrier linkage.’.* The present studies applied this chemical delivery system (CDS) to ethinyl estradiol (EE). The EE-CDS was synthesized by reacting EE with nicotinic anhydride, followed by preferential phenolic hydrolysis, quaternization and reduction to yield final product. This method is similar to that previously described from this laborat~ry.‘.~ In viw distribution studies verified that the system was capable of enhanced and sustained brain drug concentrations compared to measured circulating levels. FIGURE 1 illustrates the results of this study. Sprague-Dawley male rats were treated with 7.5 mg/kg EE-CDS via tail vein injection. Blood and brain samples were collected at 0.25, 1, 3, 6, 24 and 48 hr post treatment and analyzed for concentrations of the “locked-in” quaternary salt form of the drug (EQ) and free EE using HPLC methods similar to those previously described.)” As shown in FIGURE 1, EQ levels were

Trifluorothymidine: potential non-invasive diagnosis of herpes simplex infection using 19F nuclear magnetic resonance in a murine hepatitis model

Abstract Trifluorothymidine (TFT) is known to be concentrated in herpes simplex virus (HSV) infected cells in vitro in the form of phosphorylated derivatives. We studied a murine hepatitis model of HSV infection to determine whether this in vitro observation would also be demonstrable in vivo. Following i.v. injection of 100 or 160 mg/kg TFT, TFT was found in significantly higher concentrations in the livers of HSV-2 infected mice than in the livers of uninfected mice, mice infected with murine hepatitis virus (MHV-A59) or mice with hepatitis from carbon tetrachloride treatment. Neither altered renal function, nor altered pharmacokinetics could account for this difference. 19F Nuclear Magnetic Resonance spectroscopy readily detected the 19F from TFT in both liver extracts and whole livers, particularly at higher tissue levels, i.e. > 50 μg/g tissue. If further studies with living animals support these preliminary observations, clinical application could be pursued.