The bioequivalence of a single intravenous administration of the anesthetic alfaxalone in cyclodextrin versus alfaxalone in cyclodextrin plus preservatives in cats.

To demonstrate the bioequivalence of alfaxalone in cyclodextrin (Reference Product) to a formulation of alfaxalone in cyclodextrin also containing the preservatives ethanol, chlorocresol, and benzethonium chloride (Test Product) when administered for the purpose of inducing anesthesia in the cat. Blinded, single-dose, randomized, two-period, two-sequence, cross-over bioequivalence study with a 7-day washout period between treatments. Twenty-four (12 neutered males and 12 intact females), healthy, adult cats weighing 4.1±0.9 kg. Cats were administered 5 mg/kg IV of alfaxalone in the Reference or Test Product using a randomized cross-over design. One-milliliter venous blood samples were collected at predetermined time points to 12 hr after drug administration to determine alfaxalone plasma concentration over time. Alfaxalone concentrations were determined by a validated analytical testing method using HPLC-MS/MS. Plasma profiles of alfaxalone concentration against time were analyzed by noncompartmental analysis. The pivotal variables for bioequivalence were AUClast and Cmax . Equivalence was achieved if the 90% confidence interval for AUClast and Cmax fell into the asymmetric ±20% interval (0.80-1.25). Physiological variables, quality of anesthesia visual analog scale (VAS) scoring and anesthetic event times were recorded. ANOVA or ANCOVA (single time point), RMANOVA or RMANCOVA (multiple time point) was used for normally distributed data. GLIMMIX was used for nonnormally distributed data. VAS scores were analyzed as for blood bioequivalence data. Variables were evaluated for safety and assessed at alpha = 0.10. Cmax and AUClast for Reference and Test Products were statistically bioequivalent. No physiological variables except for a drug by time interaction for respiratory rate differed between treatment groups, and this difference was not clinically relevant. No anesthetic event times or VAS scores for quality of anesthesia were different between treatment groups. Neither formulation caused pain upon injection. The Reference and Test Products are pharmaceutically bioequivalent formulations when administered as a single intravenous administration for the purpose of induction of anesthesia in cats.

Alphaxalone Reformulated: A Water-Soluble Intravenous Anesthetic Preparation in Sulfobutyl-Ether-ß-Cyclodextrin.

BACKGROUND: Alphaxalone is a neuroactive steroid anesthetic that is poorly water soluble. It was formulated in 1972 as Althesin® using Cremophor® EL, a nonionic surfactant additive. The product was a versatile short-acting IV anesthetic used in clinical practice in many countries from 1972 to 1984. It was withdrawn from clinical practice because of hypersensitivity to Cremophor EL. In the investigations reported here, we compared the properties of 3 anesthetics: a new aqueous solution of alphaxalone dissolved in 7-sulfobutyl-ether-ß-cyclodextrin (SBECD, a water-soluble molecule with a lipophilic cavity that enables drug solubilization in water); a Cremophor EL preparation of alphaxalone; and propofol. METHODS: Two solutions of alphaxalone (10 mg/mL) were prepared: one using 13% w/v solution of SBECD in 0.9% saline (PHAX) and the other a solution of alphaxalone prepared as described in the literature using 20% Cremophor EL (ALTH). A solution of propofol (10 mg/mL; PROP) in 10% v/v soya bean oil emulsion was used as a comparator anesthetic. Jugular IV catheters were implanted in male Wistar rats (180-220 g) under halothane anesthesia. Separate groups of 10 implanted rats each were given IV injections of PHAX, ALTH, or PROP from 1.2 mg/kg to lethal doses. Doses of each drug that caused anesthesia (loss of righting reflex and response to tail pinch) and lethality in 50% of rats were calculated by probit analysis. The drugs were also compared for effects on arterial blood pressure and heart rate. RESULTS: IV PHAX, ALTH, and PROP caused dose-related sedation and anesthesia, with 50% effective dose (ED50) values for loss of righting reflex being 2.8, 3.0, and 4.6 mg/kg, respectively. PROP led to death in 10 of 10 rats at doses >30 mg/kg (50% lethal dose (LD50) = 27.7 mg/kg). A dose of alphaxalone 53 mg/kg as ALTH caused 10 of 10 rats to die (LD50 = 43.6 mg/kg), whereas none died when given the same doses of alphaxalone formulated in SBECD. PHAX caused 20% lethality at the maximal dose tested of 84 mg/kg. PHAX caused less cardiovascular depression than PROP. Control experiments with the 3 drug-free vehicles showed no effects. CONCLUSIONS: Alphaxalone caused fast-onset anesthesia at the same dose for both formulations (PHAX and ALTH). The use of SBECD as a drug-solubilizing excipient did not alter the anesthetic effect of alphaxalone, but it did increase the therapeutic index of alphaxalone in PHAX compared with ALTH. PHAX has a higher safety margin than the propofol lipid formulation and also the alphaxalone formulation in Cremophor EL (ALTH).

Neurosteroid analogues. 15. A comparative study of the anesthetic and GABAergic actions of alphaxalone, Δ16-alphaxalone and their corresponding 17-carbonitrile analogues.

Alphaxalone, a neuroactive steroid containing a 17ß-acetyl group, has potent anesthetic activity in humans. This pharmacological activity is attributed to this steroid's enhancement of γ-amino butyric acid-mediated chloride currents at γ-amino butyric acid type A receptors. The conversion of alphaxalone into Δ(16)-alphaxalone produces an analogue that lacks anesthetic activity in humans and that has greatly diminished receptor actions. By contrast, the corresponding 17ß-carbonitrile analogue of alphaxalone and the Δ(16)-17-carbonitrile analogue both have potent anesthetic and receptor actions. The differential effect of the Δ(16)-double bond on the actions of alphaxalone and the 17ß-carbonitrile analogue is accounted for by a differential effect on the orientation of the 17-acetyl and 17-carbonitrile substituents.

Preemptive Analgesic Effect of Intrathecal Applications of Neuroactive Steroids in a Rodent Model of Post-Surgical Pain: Evidence for the Role of T-Type Calcium Channels.

Preemptive management of post-incisional pain remains challenging. Here, we examined the role of preemptive use of neuroactive steroids with activity on low-voltage activated T-type Ca2+ channels (T-channels) and γ-aminobutyric acid A (GABAA) receptors in the development and maintenance of post-incisional pain. We use neuroactive steroids with distinct effects on GABAA receptors and/or T-channels: Alphaxalone (combined GABAergic agent and T-channel inhibitor), ECN (T-channel inhibitor), CDNC24 (GABAergic agent), and compared them with an established analgesic, morphine (an opioid agonist without known effect on either T-channels or GABAA receptors). Adult female rats sustained the skin and muscle incision on the plantar surface of the right paw. We injected the agents of choice intrathecally either before or after the development of post-incisional pain. The pain development was monitored by studying mechanical hypersensitivity. Alphaxalone and ECN, but not morphine, are effective in alleviating mechanical hyperalgesia when administered preemptively whereas morphine provides dose-dependent pain relief only when administered once the pain had developed. CDNC24 on the other hand did not offer any analgesic benefit. Neuroactive steroids that inhibit T-currents-Alphaxalone and ECN-unlike morphine, are effective preemptive analgesics that may offer a promising therapeutic approach to the treatment of post-incisional pain, especially mechanical hypersensitivity.

Structural basis of neurosteroid anesthetic action on GABAA receptors.

Type A γ-aminobutyric acid receptors (GABAARs) are inhibitory pentameric ligand-gated ion channels in the brain. Many anesthetics and neurosteroids act through binding to the GABAAR transmembrane domain (TMD), but the structural basis of their actions is not well understood and no resting-state GABAAR structure has been determined. Here, we report crystal structures of apo and the neurosteroid anesthetic alphaxalone-bound desensitized chimeric α1GABAAR (ELIC-α1GABAAR). The chimera retains the functional and pharmacological properties of GABAARs, including potentiation, activation and desensitization by alphaxalone. The apo-state structure reveals an unconventional activation gate at the intracellular end of the pore. The desensitized structure illustrates molecular determinants for alphaxalone binding to an inter-subunit TMD site. These structures suggest a plausible signaling pathway from alphaxalone binding at the bottom of the TMD to the channel gate in the pore-lining TM2 through the TM1-TM2 linker. The study provides a framework to discover new GABAAR modulators with therapeutic potential.

The use of differential scanning calorimetry to study drug-membrane interactions.

Differential-scanning calorimetry is a thermodynamic technique widely used for studying drug-membrane interactions. This chapter provides practical examples on this topic, highlighting the caution to be taken in analyzing thermal data as well as scientific information that can be derived by the proper use of the technique. An example is given using model bilayers containing high concentration of the anesthetic steroid alphaxalone. It is shown that the breadth of the phase transitions and the maximum of the phase-transition temperature of the bilayer depend on the equilibration conditions before acquiring the thermal scan. In addition, the quality of the thermo-gram depends on its perturbation and incorporation effects; for dissecting these effects, a complementary technique such as solid-state nuclear magnetic resonance spectroscopy is necessary. Differential-scanning calorimetry is a useful technique to study the interdigitation effect of a drug by monitoring DeltaH changes. Cholesterol, a main constituent of membrane bilayers, appears to disrupt the interdigitating effect. In general, the thermal effects of the drug incorporated into a membrane bilayer depends on the drug stereoelectronic properties.

Synthesis and pharmacological evaluation of neurosteroid photoaffinity ligands.

Neuroactive steroids are potent positive allosteric modulators of GABAA receptors (GABAAR), but the locations of their GABAAR binding sites remain poorly defined. To discover these sites, we synthesized two photoreactive analogs of alphaxalone, an anesthetic neurosteroid targeting GABAAR, 11ß-(4-azido-2,3,5,6-tetrafluorobenzoyloxy)allopregnanolone, (F4N3Bzoxy-AP) and 11-aziallopregnanolone (11-AziAP). Both photoprobes acted with equal or higher potency than alphaxalone as general anesthetics and potentiators of GABAAR responses, left-shifting the GABA concentration - response curve for human α1ß3γ2 GABAARs expressed in Xenopus oocytes, and enhancing [3H]muscimol binding to α1ß3γ2 GABAARs expressed in HEK293 cells. With EC50 of 110 nM, 11-AziAP is one the most potent general anesthetics reported. [3H]F4N3Bzoxy-AP and [3H]11-AziAP, at anesthetic concentrations, photoincorporated into α- and ß-subunits of purified α1ß3γ2 GABAARs, but labeling at the subunit level was not inhibited by alphaxalone (30 µM). The enhancement of photolabeling by 3H-azietomidate and 3H-mTFD-MPAB in the presence of either of the two steroid photoprobes indicates the neurosteroid binding site is different from, but allosterically related to, the etomidate and barbiturate sites. Our observations are consistent with two hypotheses. First, F4N3Bzoxy-AP and 11-aziAP bind to a high affinity site in such a pose that the 11-photoactivatable moiety, that is rigidly attached to the steroid backbone, points away from the protein. Second, F4N3Bzoxy-AP, 11-aziAP and other steroid anesthetics, which are present at very high concentration at the lipid-protein interface due to their high lipophilicity, act via low affinity sites, as proposed by Akk et al. (Psychoneuroendocrinology2009, 34S1, S59-S66).

Topography of alphaxalone and delta 16-alphaxalone in membrane bilayers containing cholesterol.

We have used small-angle X-ray diffraction and differential scanning calorimetry (DSC) to study the topographies of alphaxalone and its biologically inactive analog delta 16-alphaxalone in dimyristoylphosphatidylcholine (DMPC) and DMPC/cholesterol model membranes. Diffraction patterns were obtained and analyzed for preparations of bilayers without and with the steroids. Temperature dependence of the total period repeat distance (d-spacing) allowed us to identify equivalent temperatures at which the preparations had similar d-spacing and were in the same mesomorphic state. The combination of X-ray and DSC data showed that the anesthetic steroid alphaxalone broadens the membrane phase transition and increases the ratio of gauche: trans conformers in the membranes in contrast to the inactive steroid delta 16-alphaxalone which affects the membranes only marginally. In model DMPC membranes alphaxalone and delta 16-alphaxalone are located near the bilayer interface. This location is maintained by alphaxalone when cholesterol is incorporated in the bilayer as evidenced by the X-ray measurements. However, when delta 16-alphaxalone is incorporated in cholesterol containing bilayers, a decrease in the electron density profile of the preparation is observed. This can be explained by invoking the formation of a delta 16-alphaxalone-cholesterol complex. The delta 16-alphaxalone complex shows no periodicity and is therefore, not detected in the X-ray diffraction experiment. Presumably, this complex forms aggregates either on the surface or inside the bilayer. This explanation corroborates DSC results which show that delta 16-alphaxalone sharpens the phase transition of DMPC/cholesterol preparations, an indication that some cholesterol is excluded from the bilayer preparation after the addition of the biologically inactive steroid.

Effects of the anesthetic steroid alphaxalone and its inactive delta 16-analog on the thermotropic properties of membrane bilayers. A model for membrane perturbation.

We have studied in detail the effects of the anesthetic steroid alphaxalone and its inactive analog delta 16-alphaxalone on the thermotropic properties of model membranes using differential scanning calorimetry (DSC). The results obtained showed that, for model membranes from hydrated dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), and egg sphingomyelin, the biologically active analog significantly broadened the phase transition, in contrast to the inactive one which produced only marginal effects. Also, alphaxalone abolished the pretransition in these preparations whereas its delta 16-analog only broadened it. However, in DPPE bilayers almost no differences were observed in the effects produced by the two analogs. These results suggest that the ability of the two steroids to perturb membranes is lipid dependent. Comparisons between the effects of the two steroids on lipid/cholesterol model membranes revealed that delta 16-alphaxalone excluded cholesterol from lipid/cholesterol/delta 16-alphaxalone ternary systems whereas alphaxalone enhanced the effects of cholesterol and reduced the cooperativity in the binary phospholipid/cholesterol system. In an attempt to determine whether the different thermotropic effects of the two steroids on model membranes were due to (a) differences in their ability to perturb the bilayers; (b) different extents of incorporation into the bilayer, solid state 2H-NMR was applied using specifically deuterated steroids. The 2H-NMR data showed that alphaxalone incorporated fully into the membrane bilayer up to a molar concentration of 20%, while its inactive analog did only up to a concentration of 1%. To compare the abilities of the two steroids to perturb membrane preparations when both analogs were present in equal amounts in the membrane, the effects of very low steroid concentrations on DPPC bilayers were studied using DSC. The experiment showed that alphaxalone perturbed the membrane bilayers more effectively than its inactive analog. These results strongly suggest that the small structural differences between the two steroids are responsible for the observed differences in their abilities to perturb membranes, possibly because of differences in the packing of these two molecules within the bilayers.

New evidence that both T-type calcium channels and GABAA channels are responsible for the potent peripheral analgesic effects of 5alpha-reduced neuroactive steroids.

Neurosteroids are potent blockers of neuronal low-voltage activated (T-type) Ca(2+) channels and potentiators of GABA(A) ligand-gated channels, but their effects in peripheral pain pathways have not been studied previously. To investigate potential analgesic effects and the ion channels involved, we tested the ability of locally injected 5alpha-reduced neurosteroids to modulate peripheral thermal nociception to radiant heat in adult rats in vivo and to modulate GABA(A) and T-type Ca(2+) channels in vitro. The steroid anesthetic alphaxalone (ALPX), the endogenous neurosteroid allopregnanolone (3alpha5alphaP), and a related compound ((3alpha,5alpha,17beta)-3-hydroxyandrostane-17-carbonitrile, (ACN)), induced potent, dose-dependent, enantioselective anti-nociception in vivo and modulation of both T-type Ca(2+) currents and GABA(A)-mediated currents in vitro. Analgesic effects of ALPX were incompletely antagonized by co-injections of the GABA(A) receptor antagonist bicuculline. The neurosteroid analogue ((3alpha,5alpha)-3-hydroxy-13,24-cyclo-18,21-dinorchol-22-en-24-ol (CDNC24), a compound with GABAergic but not T-type activity, was not analgesic. However, (3beta,5alpha,17beta)-17-hydroxyestrane-3-carbonitrile (ECN)), which has effects on T-type channels but not on GABA(A) receptors, also induced potent enantioselective peripheral anti-nociception. ECN increased pain thresholds less than ALPX, 3alpha5alphaP and ACN. However, when an ineffective dose of CDNC24 was combined with ECN, anti-nociceptive activity was greatly enhanced, and this effect was bicuculline-sensitive. These results strongly suggest that GABA(A) channels do not contribute to baseline pain transmission, but they can enhance anti-nociception mediated by blockade of T-type Ca(2+) channels. In conclusion, we demonstrate that potent peripheral analgesia induced by 5alpha-reduced neurosteroid is mediated in part by effects on T-type Ca(2+) channels. Our results also reveal a role of GABA-gated ion channels in peripheral nociceptive signaling.

Two new pregnanone derivatives with strong cytotoxic activity from Pachysandra axillaris.

Two new, bioactive, pregnane-based natural products, pachysanonin (= 3beta,11alpha,12beta)-12-acetoxy-3-(dimethylamino)-11-[(3,4-dimethylpent-3-enoyl)oxy]pregnan-20-one; 1) and pachysanone (= (11alpha,12beta)-12-acetoxy-11-[(3,4-dimethylpent-3-enoyl)oxy]pregnan-3,20-dion; 2) have been isolated from Pachysandra axillaris. Their structures were determined by spectroscopic methods, and, in the case of 2, by single-crystal X-ray crystallography (Figure). Compound 2 showed significant antitumor activity against Lewis lung carcinoma (LCC) tumor cells, with an IC50 value of 0.020+/-0.006 microg/ml, which is equal or even lower than those of the well-known natural antitumor agents harringtonine (0.02), homoharringtonine (0.15), and adriamycin (0.06 microg/ml; positive control).

[Isolation and identification of two new epimer from the mother liquid of megestrol acetate].

AIM: To study the impurity in the drug megestrol acetate. METHODS: Chromatography methods were used to separate the chemical constituents. Their structures were determined by NMR and MS spectral analysis. RESULTS: Two new epimers were isolated from the mother liquid of the drug megestrol acetate. CONCLUSION: These new epimers were identified as 17alpha-acetoxy-2beta,6alpha-dimethylprega-4-ene-3,20-dione (1) and 17alpha-acetoxy-2alpha,6alpha-dimethylprega-4-ene-3,20-dione (2).

5-Alpha-dihydroprogesterone formation in human placenta from 5alpha-pregnan-3beta/alpha-ol-20-ones and 5-pregnan-3beta-yl-20-one sulfate.

5Alpha-dihydroprogesterone (5alpha-DHP) is the immediate precursor of 5alpha-pregnan-3alpha-ol-20-one, a potent anxiolytic/anesthetic agent in all vertebrate animals tested, including humans. The levels of 5alpha-DHP in the plasma of pregnant women are very high; and during the third trimester of pregnancy, the blood production rate of this steroid may exceed 100 mg/24 h. 5Alpha-DHP in maternal plasma, however, cannot be accounted for totally by the metabolism of maternal plasma progesterone. This study was conducted to evaluate the possibility that 5alpha-DHP is synthesized in placenta from 5alpha-pregnan-3alpha/beta-ol-20-ones delivered to the trophoblast via the fetal umbilical blood. In incubations of placental minces with radiolabelled 5alpha-pregnan-3alpha/beta-ol-20-ones, there is extensive epimerization and the intermediate, 5alpha-DHP, is the major product. In other incubations, 5alpha-pregnan-3beta-ol-20-one-sulfate was hydrolysed and the liberated 5alpha-pregnan-3beta-ol-20-one was converted to 5alpha-DHP by homogenates of placental tissue, but 5alpha-pregnan-3beta-ol-20-one-sulfate was not. The oxidation of 5alpha-pregnan-3alpha/beta-ol-20-ones was concentrated in microsome-enriched preparations of placental tissue and the apparent Kms for 5alpha-pregnan-3alpha-ol-20-one and 5alpha-pregnan-3beta-ol-20-one were 3.6 microM and 78 nM, respectively. The Vmaxs for 5alpha-DHP formation from 5alpha-pregnan-3alpha-ol-20-one and 5alpha-pregnan-3beta-ol-20-one were, respectively, 336 pmol/min/mg protein and 9.7 nmol/min/mg protein. These oxidation reactions were supported by both NAD+ and NADP+. We suggest that progesterone, which enters the umbilical circulation from its site of synthesis in the syncytiotrophoblast, is metabolized in the fetus to 5alpha-pregnan-3alpha/beta-ol-ones and to 5alpha-pregnan-3alpha/beta-yl-20-one sulfates. These metabolites of progesterone, 5alpha-pregnan-3alpha/beta-ol-20-one and 5alpha-pregnan-3beta-yl-20-one sulfate, formed in the fetus, serve as plasma-borne substrates for trophoblast formation of 5alpha-DHP. Because of the hemochorioendothelial nature of human placentation, 5alpha-DHP secreted from the trophoblast will preferentially enter the maternal compartment, thus constituting a maternal plasma progesterone-independent source of 5alpha-DHP.

Determination of progesterone and some of its neuroactive ring A-reduced metabolites in human serum.

A method for the separation and assay of some ring A-reduced metabolites of progesterone (pregnanediones and pregnanolones) is described. Serum was extracted with an organic solvent, and the extract chromatographed using high performance liquid chromatography (HPLC). A total of 50 fractions was collected for each sample and split using a stream splitter so that 30% was collected in counting vials for recovery while 70% was collected in test tubes which were assayed by radioimmunoassay. An antiserum raised in our laboratory to progesterone-3-CMO-BSA cross-reacted with five of these compounds (5alpha- and 5beta-dihydroprogesterone, 3alpha- and 3beta-5alpha-tetrahydroprogesterone, and 3beta, 5beta-tetrahydroprogesterone). Since pregnenolone eluted with 5alpha, 3beta-tetrahydroprogesterone, pregnenolone was assayed separately and its effect subtracted. Using this method it was shown that picogram to nanogram/ml amounts of these metabolites are present in all human sera. Levels in men were comparable to those of women in the follicular phase of the menstrual cycle. 5alpha-Dihydroprogesterone and 3alpha,5alpha-tetrahydroprogesterone rose substantially in the luteal phase of the menstrual cycle and all rose considerably during pregnancy.

Influence of 5alpha- and 5beta-reduced progestins on the contractility of isolated human myometrium at term.

It is very well known that progesterone induces uterine relaxation on myometrium contractile activity. However, little attention has been paid to the effect induced by its metabolites on human uterine contractility. Therefore, we set out to analyze the potential relaxing effect of some 5alpha- and 5beta-reduced progesterone derivatives on the spontaneous contractility of myometrium from pregnant women. Samples were obtained by caesarian section at 38-40 weeks of pregnancy. Spontaneous uterine contractions were recorded in vitro in the presence of progesterone, or progestins independently, at different non-cumulative microM concentrations. The progestins elicited an immediate relaxing effect that was concentration-dependent. With the exception of two 5alpha-reduced progestins (5alpha and 3beta,5alpha), the remaining progestins used in the present study were more potent than progesterone. The potency order with respect to their IC50 values was: 3alpha,5alpha (35 microM) > 5beta (81 microM) > 3beta,5beta (156 microM) > 3alpha,5beta (205 microM) > P4 (225 microM) > 5alpha (19 mM) > 3beta,5alpha (28 mM). When tissues were washed, the contractile activity was recovered. This rapid and reversible relaxing effect was not blocking by antiprogestin RU 486, suggesting that is not through receptor-mediated genomic action. The metabolites from progesterone may also determine the pattern of motility, ensuring the necessary quiescent environment to prevent abortion during gestation.

Incorporation of alphaxalone into different types of liposomes.

The poor solubility of steroid anaesthetics in water has been a serious drawback in the development of clinically acceptable intravenous formulations. The use of Cremophor EL to solubilize steroids such as alphaxalone led to unacceptable hypersensitivity reactions and consequent withdrawal of this anaesthetic. In principle, liposomes can act as a safe solvent for the intravenous administration of alphaxalone. We report the incorporation of [14C]acetylated alphaxalone in both multilamellar vesicles and stable plurilamellar vesicles prepared from a range of amphiphiles including synthetic polyhydroxyl lipids. For both types of preparations, addition of cholesterol to phosphatidylcholine-based lipids caused an increase in encapsulation efficiency. Maximum encapsulation was achieved with the stable plurilamellar vesicle preparation of 1-stearyl-2-myristylglycerate-3, N-methylglucamine:cholesterol:egg phosphatidylcholine (78%). The rate of efflux of this anaesthetic from a range of liposomes was measured in serum. The highest rate (85% after 30 min) was observed with an equimolar egg phosphatidylcholine:cholesterol stable plurilamellar vesicle preparation. From these studies it can be concluded that liposomes offer a suitable alternative for intravenous delivery of steroidal anaesthetics.

Anaesthetic steroids--a review.

Steroids produce anaesthesia besides producing the well known metabolic and hormonal effects. A number of anaesthetic steroids have been synthesized and tried clinically. Hydroxydione, althesin, minaxolone and pregnanolone are among those studied in detail. They act through GABAergic mechanism and are known to be advantageous over barbiturates.

The effects on cardio-respiratory and acid-base variables of a constant rate infusion of alfaxalone-HPCD in sheep.

Alfaxalone in a 2-hydroxypropyl-ß-cyclodextrin (HPCD) formulation is an intravenous (IV) hypnotic agent characterised by the stability of cardiorespiratory effects after a single-bolus administration. The objective of this study was to investigate the cardiovascular, respiratory, and acid-base effects of alfaxalone-HPCD administered during a continuous rate infusion in six Ripollesa sheep. After instrumentation, a 2 mg/kg IV bolus of alfaxalone followed by a continuous infusion of 10 mg/kg/h was administered to the sheep. Heart rate, arterial blood pressure, respiratory rate and arterial blood gases were recorded. Occasional side effects and time to standing were also noted. No significant changes were observed in arterial blood pressure, but during the infusion and the initial stages of recovery, a significant increase in heart rate occurred during the last 120 min of the study. Significant respiratory depression was detected during the infusion period and the first 15 min of recovery. This study showed that a constant rate infusion alfaxalone in un-premedicated sheep produced clinically acceptable haemodynamic results and a mild respiratory depression that may require intermittent positive pressure ventilation.

The effects on cardio-respiratory and acid-base variables of the anaesthetic alfaxalone in a 2-hydroxypropyl-ß-cyclodextrin (HPCD) formulation in sheep.

The objective of this study was to determine the pharmacodynamic effects in sheep of the anaesthetic alfaxalone in a 2-hydroxypropyl-ß-cyclodextrin formulation. Seven Ripollesa sheep, weighing 43.0±6.6 kg, were used in the study. Twenty-four hours after instrumentation, the sheep were anesthetised with alfaxalone (2 mg/kg bodyweight IV) in cyclodextrin. Heart rate, arterial blood pressure, respiratory rate and arterial blood gases were recorded. Alfaxalone administration resulted in minimal cardio-respiratory depression. Time to standing from anaesthesia was 22.0±10.6 min. Apnoea was not observed in any of the sheep. Significant differences from baseline were not observed in respiratory rate or arterial blood pressure. Heart rate increased significantly (P<0.05) immediately after administration, returning to control values at 20 min. The calculated haemoglobin saturation (SO2) decreased significantly during the first 15 min after alfaxalone administration. The arterial pH decreased significantly during the first 30 min of the study, although no significant differences from basal values were observed in the arterial partial pressure of carbon dioxide (PaCO2). The results showed that alfaxalone in 2-hydroxypropyl-ß-cyclodextrin administered as an IV bolus at 2 mg/kg produced minimal adverse effects and an uneventful recovery from anaesthesia in sheep.

Neurosteroid analogues. 16. A new explanation for the lack of anesthetic effects of δ(16)-alphaxalone and identification of a δ(17(20)) analogue with potent anesthetic activity.

This study addresses the hypothesis that the lack of anesthetic activity for (3α,5α)-3-hydroxypregn-16-ene-11,20-dione (Δ(16)-alphaxalone) is explained by the steroid Δ(16) double bond constraining the steroid 20-carbonyl group to a position that prevents it from favorably interacting with γ-aminobutyric acid type A (GABA(A)) receptors. A series of Δ(16) and Δ(17(20)) analogues of Δ(16)-alphaxalone was prepared to evaluate this hypothesis in binding, electrophysiological, and tadpole anesthesia experiments. The results obtained failed to support the hypothesis. Instead, the results indicate that it is the presence of the C-21 methyl group in Δ(16)-alphaxalone, not the location of the constrained C-20 carbonyl group, that prevents Δ(16)-alphaxalone from interacting strongly with the GABA(A) receptor and having anesthetic activity. Consistent with this conclusion, a Δ(17(20)) analogue of Δ(16)-alphaxalone without a C-21 methyl group was found to be very similar to the anesthetic steroid (3α,5α)-3-hydroxypregnane-11,20-dione (alphaxalone) with regard to time of onset and rate of recovery from anesthesia when administered to mice by tail vein injection.