Kerry S. Estes

An intravenous toxicity study of 2-hydroxypropyl-β-cyclodextrin, a useful drug solubilizer, in rats and monkeys

Abstract The subacute and subchronic intravenous (i.v.) toxicity of 2-hydroxypropyl-β-cyclodextrin (HPCD) was examined in Sprague-Dawley rats and cynomolgus monkeys. After either 14 or 90 days of alternate day dosing with either saline or 200 mg/kg HPCD, no toxicologically meaningful differences were observed in the following parameters: body weight, body weight gain, food consumption, hematology, clinical chemistry, organ weights, organ to brain weight ratio, organ to body weight ratio and macroscopic and microscopic histopathology. Subsequent to these studies, an acute high-dose study was performed in cynomolgus monkeys which indicated that a single i.v. dose of HPCD as high as 10 g/kg was not lethal.

Effect of various cyclodextrins on solution stability and dissolution rate of doxorubicin hydrochloride

Abstract A number of cyclodextrins were examined as to their ability to stabilize doxorubicin in solution and to enhance the rate of its dissolution. 2-Hydroxypropyl-β-cyclodextrin (HPβCD), 2-hydroxypropyl-γ-cyclodextrin (HPγCD) and γ-cyclodextrin (γCD) all acted to decrease degradation of doxorubicin in solution although the γ-cyclodextrin derivatives were decidedly more effective. Lineweaver-Burk analysis indicated that the incorporated anthracycline degraded 6–10-times more slowly than did doxorubicin in systems which did not contain Cyclodextrin. The chemically modified cyclodextrins were also shown to enhance the rate of dissolution of prototype lyophilized formulations. Thus, HPγCD, present in 5-fold excess relative to doxorubicin, acted to decrease dissolution time from 26 min (for a doxorubicin/lactose dosage form) to less than 9 min. Similarly, HPγCD decreased dissolution time for various prototype formulations. Finally, a complex of HPγCD and doxorubicin was found to be less toxic in a dermal extravasation model. These results, along with the accrued toxicity data which suggest HPγCD is innocuous even when given in large doses parenterally, highly support the use of the modified Cyclodextrin as a stabilizing and dissolution-enhancing excipient.

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.

Age-related alterations in dopamine and norepinephrine activity within microdissected brain regions of ovariectomized long evans rats

The ability of several stimuli which augment central catecholamine (CA) neuronal activity to reinitiate estrous cycles in old constant estrous (CE) rats suggests CA neuronal function is impaired with advanced age. We examined the effects of age on dopamine (DA) and norepinephrine (NE) levels and turnover rates within microdissected brain regions of previously normally cycling young (3-4 months old) and middle-aged (10 months old) and CE old (20-22 months old) Long Evans 2 weeks after ovariectomy. Steady-state DA concentrations were significantly decreased in old compared to young rats in the nucleus accumbens (34%), anterior hypothalamic nucleus (54%, NHA ), neurointermediate pituitary lobe (51%, NIL) and median eminence (74%, ME). The rate constant of DA loss, an estimate of neuronal activity, decreased in old versus young rats only in the preoptic area suprachiasmatica (60%, POAs ) and NHA (60%) and was unchanged or augmented in the 7 other regions. In contrast, a decline in DA turnover rate of 29-67% was observed in 6 of 9 regions in middle-aged rats and 45-81% in 5 of 9 regions in old rats. Steady-state NE concentrations similarly were significantly decreased in old versus young rats in the POAs (54%), medial forebrain bundle (44%), nucleus suprachiasmatica (49%) and ME (59%). The rate constant of NE loss progressively decreased with increasing age only in the POAs and was unchanged or augmented in other regions. Turnover rate of NE was decreased from 21 to 98% in 4 of 8 regions from old animals. A strong positive correlation was noted between the rate constant of NE (but not DA) loss measured in young rats and the magnitude of the age-related depletion in NE concentrations within specific brain regions. Collectively these data indicate that with increasing age: CA neuronal function is differentially altered in nuclei located along the preoptico-tuberal pathway; substantial declines in both DA and NE concentrations are the primary contributor to the reduced amine turnover noted in several of these regions; and the observed age-related alterations in CA turnover may contribute to impaired LH response and the persistent hyperprolactinemia in old CE rats.

Comparison of the pharmacokinetic properties of vancomycin, linezolid, tigecyclin, and daptomycin

The rapid antibiotic resistance development has created a major demand for new antimicrobial agents that can combat resistant strains such as methicillin-resistant S. aureus (MRSA). Until a short time ago, the glycopeptide vancomycin was the only therapeutic choice in this situation. However, in recent years some newer agents with different mechanisms of actions have been added to the arsenal, and more are on the horizon. For a successful therapy it is of vital importance that these compounds are used judiciously and dosed appropriately. The present article reviews the pharmacokinetic properties of vancomycin, linezolid, tigecycline and daptomycin. The first major difference between these compounds is their oral bioavailability. Only linezolid can be administered orally, whereas vancomycin, daptomycin and tigecycline are limited to parenteral use. Once in the body, they show very different disposition. Daptomycin has a very small volume of distribution of 7L indicating very little tissue distribution whereas tigecycline has a very large volume of distribution of 350-500 L. Vancomycin and linezolid are in-between with volumes of distribution of approximately 30 and 50 L, close to total body water. However, studies have shown that linezolid shows better tissue penetration than vancomycin. Newer studies using microdialysis, a new technique that allows direct monitoring of unbound tissue levels, support this finding. As far as drug elimination, daptomycin and vancomycin are mainly eliminated into the urine and require dosing adjustments in renally impaired patients, whereas tigecycline is eliminated into the bile and linezolid is metabolized so that in renal patients no dosing adjustments are needed for these compounds. Although the elimination pathways are very different, the resulting half-lives of linezolid, vancomycin, and daptomycin are not greatly different and vary from 4-8 h. Tigecycline, however, has a much longer half-life of up to 1-2 days due to the slow redistribution from tissue binding sites.

High-Performance Liquid Chromatographic Assay of a Central Nervous System (CNS)-Directed Estradiol Chemical Delivery System and Its Application After Intravenous Administration to Rats

A redox-based chemical delivery system for estradiol (E2-CDS) has been shown capable of sustained and brain-selective delivery of estradiol (E2). A re versed-phase high-performance liquid chromatographic (HPLC) method is presented for the analysis of E2-CDS and its oxidized quaternary metabolite (E2-Quat) in biological fluids or tissues. The assay utilizes a precolumn enrichment technique and detects plasma levels down to 10 ng/ml E2-Quat and 20 ng/ml E2-CDS. Sample preparation is rapid and simple. Samples are homogenized with acetonitrile, then centrifuged, and the supernatant is directly injected into the HPLC system. A water delivering pump injects the sample on a precolumn where the drug is concentrated. The mobile phase backflushes the retained compound onto the analytical column. At the same time, another sample can be injected onto a second precolumn. This alternating precolumn sample enrichment technique allows the injection of large volumes, up to 1800 µl. Plasma and tissue samples of rats collected after i.v. administration of a single 15-mg/kg E2-CDS dose were analyzed for E2-CDS and E2-Quat by this procedure. The results show sustained brain levels of E2-Quat and prolonged half-life in brain compared to six peripheral tissues measured. These data support the concept of brain-targeted delivery using redox carrier systems of this type.

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.

A dihydropyridine conjugate which generates high and sustained levels of the corresponding pyridinium salt in the brain does not exhibit neurotoxicity in cynomolgus monkeys

Many drugs can be selectively delivered to the brain by using a dihydropyridine in equilibrium pyridinium salt chemical delivery system (CDS). The interaction of these systems with central dopaminergic function was examined in this communication. Castrate female Sprague-Dawley rats when treated with a CDS for estradiol (i.e. 3-hydroxy-17 beta-[( (1-methyl-1,4-dihydropyridin-3-yl)carbonyl]oxy) estra-1,3,5(10)-triene or E2CDS) exhibit sustained and profound suppression of serum levels of leuteinizing hormone (LH). Treatment of rats with pargyline (80 mg/kg) prior to E2CDS (2 mg/kg) did not mitigate the biological effectiveness of this estrogen indicating at least indirectly that monoamine oxidate (MAO) was not involved in the CDS activation. In a more direct examination, cynomolgus monkeys treated with various repeated doses of E2CDS (cumulative doses of 0.2-40.0 mg/kg) demonstrated neither impaired motor function nor depleted striatal dopamine concentrations. The latter parameter was measured using liquid chromatographic-electrochemical analysis. These experiments support the contention that the CDS is not neurotoxic and further strengthens the strict structure-activity requirements for MPTP-induced neurotoxicity.