Solubility Prediction of Satranidazole in Propylene Glycol-Water Mixtures Using Extended Hildebrand Solubility Approach

Extended Hildebrand solubility approach is used to estimate the solubility of satranidazole in binary solvent systems. The solubility of satranidazole in various propylene glycol-water mixtures was analyzed in terms of solute-solvent interactions using a modified version of Hildebrand-Scatchard treatment for regular solutions. The solubility equation employs term interaction energy (W) to replace the geometric mean (δ₁δ₂), where δ₁ and δ₂ are the cohesive energy densities for the solvent and solute, respectively. The new equation provides an accurate prediction of solubility once the interaction energy, W, is obtained. In this case, the energy term is regressed against a polynomial in δ₁ of the binary mixture. A quartic expression of W in terms of solvent solubility parameter was found for predicting the solubility of satranidazole in propylene glycol-water mixtures. The expression yields an error in mole fraction solubility of ~3.74%, a value approximating that of the experimentally determined solubility. The method has potential usefulness in preformulation and formulation studies during which solubility prediction is important for drug design.     

Extended hildebrand solubility approach: satranidazole in mixtures of dioxane and water

The extended Hildebrand solubility parameter approach is used to estimate the solubility of satranidazole in binary solvent systems. The solubility of satranidazole in various dioxane-water mixtures was analyzed in terms of solute-solvent interactions using a modified version of Hildebrand-Scatchard treatment for regular solutions. The solubility of satranidazole in the binary solvent, dioxane-water shows a bell-shaped profile with a solubility maximum well above the ideal solubility of the drug. This is attributed to solvation of the drug with the dioxane-water mixture, and indicates that the solute-solvent interaction energy is larger than the geometric mean (δ(1)δ(2)) of regular solution theory. The new approach provides an accurate prediction of solubility once the interaction energy is obtained. In this case, the energy term is regressed against a polynomial in δ(1) of the binary mixture. A quartic expression of W in terms of solvent solubility parameter was found for predicting the solubility of satranidazole in dioxane-water mixtures. The method has potential usefulness in preformulation and formulation studies during which solubility prediction is important for drug design.     

A Study on Improvement of Solubility of Rofecoxib and its effect on Permeation of Drug from Topical Formulations

Rofecoxib, a practically insoluble cox-2 selective nonsteroidal antiinflammatory agent was subjected to improvement in solubility by preparing its binary mixtures with β cyclodextrin using various methods such as physical mixing, co-grinding, kneading with aqueous methanol and co-evaporation from methanol-water mixture. Characterization of the resulting binary mixtures by differential scanning calorimetry and X-ray diffraction studies indicated partial amorphization of the drug in its binary mixtures. In vitro dissolution studies exhibited remarkable increase in rate and extent of dissolution of the drug from its complexes with β -cyclodextrin. Pure rofecoxib as well as its co-ground binary mixture were formulated as aqueous gels for topical application. In vitro skin permeation of rofecoxib from formulation containing rofecoxib-cyclodextrin complex was significantly higher (p<0.05) at 1, 2, 12, 18 and 24 hr as compared to formulation containing pure rofecoxib. This could be attributed to better solubility of binary mixture in the aqueous gel vehicle leading to greater concentration gradient between the vehicle and skin and hence higher flux of the drug.     

Formulation and characterization of eprosartan mesylate and β-cyclodextrin inclusion complex prepared by microwave technology

The goal of this work was to improve the aqueous solubility and dissolution rate of eprosartan mesylate by preparing inclusion complex of drug with β-cyclodextrin (β-CD) by microwave technique. In order to determine the solubility of eprosartan, phase solubility was determined and dissolution study was also conducted. Further, analytical techniques for instance, particle size distribution, differential scanning calorimetry, powder X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy were used for the characterization of inclusion complex. In addition, the binding pattern of eprosartan with the β-CD was investigated by molecular modeling study. Phase solubility study revealed that approximately 4.48 folds improvement in the solubility of drug was noted with β-CD (10 mM). The estimated stability constant (K_c) values for eprosartan:β-CD binary mixture was found to be 280.78 M^–1. The prepared inclusion complex of drug with β-CD presented better drug release profile (62.96 ± 2.01% in 1 h) as compared to their physical mixture (41.41 ± 1.77% in 1 h) or drug per se (29.97 ± 3.13%). The inclusion complex demonstrated different features and properties from pure drug, and we inferred that this could be due to the inclusion of drug into cyclodextrin cavity that confirmed by different analytical method. Molecular modeling study demonstrated a good affinity of eprosartan to entangle to β-CD. The outcomes have shown that guest molecule has many significant interactions with the host molecule. These observations are very interesting and may be a valuable approach to improve the solubility and in turn the bioavailability of eprosartan.     

Enthalpy and Entropy Contributions to the Solubility of Sulphamethoxypyridazine in Solvent Mixtures Showing Two Solubility Maxima

The solubility of sulphamethoxypyridazine was measured at several temperatures in mixtures of water: ethanol and ethanol: ethyl acetate. Sulphamethoxypyridazine was chosen as a model drug to compare the solvation effects of proton donor-proton acceptor (water and ethanol) and proton acceptor (ethyl acetate) solvents and mixtures of these solvents because this drug contains functional groups capable of Lewis acid-base interaction. A plot of the mole fraction solubility against the solubility parameter (δ₁) of these solvent mixtures showed two solubility maxima, one at δ₁ = 30·87 MPa^1/2 (20:80 v/v water: ethanol) and another at δ₁ = 20·88 MPa^1/2 (30:70 v/v ethanol: ethyl acetate) at all the temperatures under study. The enthalpies and entropies of mixing as well as the enthalpies and entropies of transfer of sulphamethoxypyridazine from ethanol to water:ethanol and ethanol:ethyl acetate mixtures were calculated to compare solvation characteristics of the solvent mixtures toward the drug. As ethanol is added to water, the entropy increases and the structure of the solvent mixture became less ordered, favouring the interaction of the drug with the solvent mixture. On the other hand, in the case of the ethanol: ethyl acetate mixture, solubility is favoured by the more negative enthalpy values. This way, the same result, i.e. a solubility maximum, is obtained by different routes. In the ethanol: water mixtures, the dissolution process is entropy-controlled while enthalpy is the driving force in the case of ethanol: ethyl acetate mixtures. The two solvent systems show enthalpy-entropy compensation. Water deviates from the linear relationship due possibly to its hydrophobic effect.     

Rapid Delivery of Diazepam from Supersaturated Solutions Prepared Using Prodrug/Enzyme Mixtures: Toward Intranasal Treatment of Seizure Emergencies

Current treatments for seizure emergencies, such as status epilepticus, include intravenous or rectal administration of benzodiazepines. While intranasal delivery of these drugs is desirable, the small volume of the nasal cavity and low drug solubility pose significant difficulties. Here, we prepared supersaturated diazepam solutions under physiological conditions and without precipitation, using a prodrug/enzyme system. Avizafone, a peptide prodrug of diazepam, was delivered with—Aspergillus oryzae (A.O.) protease, an enzyme identified from a pool of hydrolytic enzymes in assay buffer, pH 7.4 at 32°C. This enzyme converted avizafone to diazepam at supersaturated concentrations. In vitro permeability studies were performed at various prodrug/enzyme ratios using Madin-Darby canine kidney II-wild type (MDCKII-wt) monolayers, a representative model of the nasal epithelium. Monolayer integrity was examined using TEER measurement and the lucifer yellow permeability assay. Prodrug/drug concentrations were measured using HPLC. Enzyme kinetics with avizafone-protease mixtures revealed K_M = 1,501 ± 232 μM and V_max = 1,369 ± 94 μM/s. Prodrug-protease mixtures, when co-delivered apically onto MDCKII-wt monolayers, showed 2–17.6-fold greater diazepam flux (S = 1.3–15.3) compared to near-saturated diazepam (S = 0.7). Data for prodrug conversion upstream (apical side) and drug permeability downstream (basolateral side) fitted reasonably well to a previously developed in vitro two compartment pharmacokinetic model. Avizafone-protease mixtures resulted in supersaturated diazepam in less than 5 min, with the rate and extent of supersaturation determined by the prodrug/enzyme ratio. Together, these results suggest that an intranasal avizafone-protease system may provide a rapid and alternative means of diazepam delivery.

Electronic supplementary material

The online version of this article (doi:10.1208/s12248-014-9596-5) contains supplementary material, which is available to authorized users.KEY WORDS: avizafone enzyme activation, diazepam delivery, hydrophobic drugs, MDCK monolayers, rapid absorption, seizure emergencies, supersaturation     

Predicting the Solubility of Drugs in Solvent Mixtures: Multiple Solubility Maxima and the Chameleonic Effect

Abstract— An approach to reproduce the solubility profile of a drug in several solvent mixtures showing two solubility maxima is proposed in this work. The solubility of sulphamethoxypyridazine was determined at 25°C in several mixtures of varying polarity (hexane: ethyl acetate, ethyl acetate:ethanol and ethanol: water). Sulphamethoxypyridazine was chosen as a model drug because of its proton-donor and proton-acceptor properties. A plot of the mole fraction of the drug vs the solubility parameter of the solvent mixtures shows two solubility peaks. The two peaks found for sulphamethoxypyridazine demonstrate the chameleonic effect as described by Hoy and suggest that the solute-solvent interaction does not vary uniformly from one mixture to another. The different behaviour of the drug in mixtures of two proton-donor and proton-acceptor solvents (alcohol and water), and in mixtures of one proton acceptor (ethyl acetate) and one proton donor-proton acceptor (ethanol) is rationalized in terms of differences in the proton donor-acceptor ability of the solvent mixtures. An approach based on the acidic and basic partial solubility parameters together with the Hildebrand solubility parameter of the solvent mixtures is developed to reproduce the experimental results quantitatively. The equation predicts the two solubility maxima as found experimentally, and the calculated values closely correspond to the experimental values through the range composition of the solvent mixtures. These results show that the chameleonic effect can be described in a quantitative way in terms of Lewis acid-base interactions; this approach can assist the product formulator to choose the proper solvent mixture for a new drug. A good solvent blend should result in a solubility parameter close to that of the drug; the acidic and basic partial solubility parameter values should provide maximum acid-base interaction of the mixed solvent with the drug. The failure in one of these conditions results in decreased solubility. Solubility parameters as well as the acidic and basic parameters are tabulated or they can be obtained from group contribution methods, making easier the evaluation of the best solvent mixture for a drug.     

Aβ oligomer toxicity inhibitor protects memory in models of synaptic toxicity

BACKGROUND AND PURPOSE

Amyloid-β (Aβ) aggregation into synaptotoxic, prefibrillar oligomers is a major pathogenic event underlying the neuropathology of Alzheimer''s disease (AD). The pharmacological and neuroprotective properties of a novel Aβ aggregation inhibitor, SEN1269, were investigated on aggregation and cell viability and in test systems relevant to synaptic function and memory, using both synthetic Aβ_1-42 and cell-derived Aβ oligomers.

EXPERIMENTAL APPROACH

Surface plasmon resonance studies measured binding of SEN1269 to Aβ_1–42. Thioflavin-T fluorescence and MTT assays were used to measure its ability to block Aβ_1–42–induced aggregation and reduction in cell viability. In vitro and in vivo long-term potentiation (LTP) experiments measured the effect of SEN1269 on deficits induced by synthetic Aβ_1–42 and cell-derived Aβ oligomers. Following i.c.v. administration of the latter, a complex (alternating-lever cyclic ratio) schedule of operant responding measured effects on memory in freely moving rats.

KEY RESULTS

SEN1269 demonstrated direct binding to monomeric Aβ_1–42, produced a concentration-related blockade of Aβ_1–42 aggregation and protected neuronal cell lines exposed to Aβ_1–42. In vitro, SEN1269 alleviated deficits in hippocampal LTP induced by Aβ_1–42 and cell-derived Aβ oligomers. In vivo, SEN1269 reduced the deficits in LTP and memory induced by i.c.v. administration of cell-derived Aβ oligomers.

CONCLUSIONS AND IMPLICATIONS

SEN1269 protected cells exposed to Aβ_1–42, displayed central activity with respect to reducing Aβ-induced neurotoxicity and was neuroprotective in electrophysiological and behavioural models of memory relevant to Aβ-induced neurodegeneration. It represents a promising lead for designing inhibitors of Aβ-mediated synaptic toxicity as potential neuroprotective agents for treating AD.     

Cognitive and Cortical Plasticity Deficits Correlate with Altered Amyloid-�� CSF Levels in Multiple Sclerosis

Cognitive dysfunction is of frequent observation in multiple sclerosis (MS). It is associated with gray matter pathology, brain atrophy, and altered connectivity, and recent evidence showed that acute inflammation can exacerbate mental deficits independently of the primary functional system involved. In this study, we measured cerebrospinal fluid (CSF) levels of amyloid-β₁₋₄₂ and τ protein in MS and in clinically isolated syndrome patients, as both proteins have been associated with cognitive decline in Alzheimer''s disease (AD). In AD, amyloid-β_1–42 accumulates in the brain as insoluble extracellular plaques, possibly explaining why soluble amyloid-β_1–42 is reduced in the CSF of these patients. In our sample of MS patients, amyloid-β_1–42 levels were significantly lower in patients cognitively impaired (CI) and were inversely correlated with the number of Gadolinium-enhancing (Gd+) lesions at the magnetic resonance imaging (MRI). Positive correlations between amyloid-β_1–42 levels and measures of attention and concentration were also found. Furthermore, abnormal neuroplasticity of the cerebral cortex, explored with θ burst stimulation (TBS), was observed in CI patients, and a positive correlation was found between amyloid-β_1–42 CSF contents and the magnitude of long-term potentiation-like effects induced by TBS. No correlation was conversely found between τ protein concentrations and MRI findings, cognitive parameters, and TBS effects in these patients. Together, our results indicate that in MS, central inflammation is able to alter amyloid-β metabolism by reducing its concentration in the CSF and leading to impairment of synaptic plasticity and cognitive function.     

Selective ��4��2 Nicotinic Acetylcholine Receptor Agonists Target Epigenetic Mechanisms in Cortical GABAergic Neurons

Nicotine improves cognitive performance and attention in both experimental animals and in human subjects, including patients affected by neuropsychiatric disorders. However, the specific molecular mechanisms underlying nicotine-induced behavioral changes remain unclear. We have recently shown in mice that repeated injections of nicotine, which achieve plasma concentrations comparable to those reported in high cigarette smokers, result in an epigenetically induced increase of glutamic acid decarboxylase 67 (GAD₆₇) expression. Here we explored the impact of synthetic α₄β₂ and α₇ nAChR agonists on GABAergic epigenetic parameters. Varenicline (VAR), a high-affinity partial agonist at α₄β₂ and a lower affinity full agonist at α₇ neuronal nAChR, injected in doses of 1–5 mg/kg/s.c. twice daily for 5 days, elicited a 30–40% decrease of cortical DNA methyltransferase (DNMT)1 mRNA and an increased expression of GAD₆₇ mRNA and protein. This upregulation of GAD₆₇ was abolished by the nAChR antagonist mecamylamine. Furthermore, the level of MeCP₂ binding to GAD₆₇ promoters was significantly reduced following VAR administration. This effect was abolished when VAR was administered with mecamylamine. Similar effects on cortical DNMT1 and GAD₆₇ expression were obtained after administration of A–85380, an agonist that binds to α₄β₂ but has negligible affinity for α₃β₄ or α₇ subtypes containing nAChR. In contrast, PNU–282987, an agonist of the homomeric α₇ nAChR, failed to decrease cortical DNMT1 mRNA or to induce GAD₆₇ expression. The present study suggests that the α₄β₂ nAChR agonists may be better suited to control the epigenetic alterations of GABAergic neurons in schizophrenia than the α₇ nAChR agonists.     

Modeling the Solubility of Pharmaceuticals in Pure Solvents and Solvent Mixtures for Drug Process Design

The knowledge of the solubility of pharmaceuticals in pure solvents and solvent mixtures is crucial for designing the crystallization process of drug substances. The first step in finding optimal crystallization conditions is usually a solvent screening. Since experiments are very time consuming, a model which allows for solubility predictions in pure solvents and solvent mixtures based only on a small amount of experimental data is required. In this work, we investigated the applicability of the thermodynamic model perturbed-chain statistical associating fluid theory (PC-SAFT) to correlate and to predict the solubility of exemplary five typical drug substances and intermediates (paracetamol, ibuprofen, sulfadiazine, p-hydroxyphenylacetic acid, and p-aminophenylacetic acid) in pure solvents and solvent mixtures. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4205–4215, 2009     

Agonists at the δ-opioid receptor modify the binding of µ-receptor agonists to the µ-δ receptor hetero-oligomer

BACKGROUND AND PURPOSE

µ- and δ-opioid receptors form heteromeric complexes with unique ligand binding and G protein-coupling profiles linked to G protein α z-subunit (Gα_z) activation. However, the mechanism of action of agonists and their regulation of the µ–δ receptor heteromer are not well understood.

EXPERIMENTAL APPROACH

Competition radioligand binding, cell surface receptor internalization in intact cells, confocal microscopy and receptor immunofluorescence techniques were employed to study the regulation of the µ–δ receptor heteromer in heterologous cells with and without agonist exposure.

KEY RESULTS

Gα_z enhanced affinity of some agonists at µ–δ receptor heteromers, independent of agonist chemical structure. δ-Opioid agonists displaced µ-agonist binding with high affinity from µ–δ heteromers, but not µ receptor homomers, suggestive of δ-agonists occupying a novel µ-receptor ligand binding pocket within the heteromers. Also, δ-agonists induced internalization of µ-opioid receptors in cells co-expressing µ- and δ-receptors, but not those expressing µ-receptors alone, indicative of µ–δ heteromer internalization. This dose-dependent, Pertussis toxin-resistant and clathrin- and dynamin-dependent effect required agonist occupancy of both µ- and δ-opioid receptors. In contrast to µ-receptor homomers, agonist-induced internalization of µ–δ heteromers persisted following chronic morphine exposure.

CONCLUSIONS AND IMPLICATIONS

The µ–δ receptor heteromer may contain a novel δ-agonist-detected, high-affinity, µ-receptor ligand binding pocket and is regulated differently from the µ-receptor homomer following chronic morphine exposure. Occupancy of both µ- and δ-receptor binding pockets is required for δ-agonist-induced endocytosis of µ–δ receptor heteromers. δ-Opioid agonists target µ–δ receptor heteromers, and thus have a broader pharmacological specificity than previously identified.     

Rational formulation engineering of fraxinellone utilizing 6-O-α-D-maltosyl-β-cyclodextrin for enhanced oral bioavailability and hepatic fibrosis therapy

Although Fraxinellone (Frax) isolated from Dictamnus albus L. possessed excellent anti-hepatic fibrosis activity, oral administration of Frax suffered from the inefficient therapeutic outcome in vivo due to negligible oral absorption. At present, the oral formulation of Frax is rarely exploited. For rational formulation design, we evaluated preabsorption risks of Frax and found that Frax was rather stable while poorly dissolved in the gastrointestinal tract (78.88 μg/mL), which predominantly limited its oral absorption. Further solubility test revealed the outstanding capacity of cyclodextrin derivatives (CDs) to solubilize Frax (6.8–12.8 mg/mL). This led us to study the inclusion complexes of Frax with a series of CDs and holistically explore their drug delivery performance. Characterization techniques involving ¹H-NMR, FT-IR, DSC, PXRD, and molecular docking confirmed the most stable binding interactions when Frax complexed with 6-O-α-D-maltosyl-β-cyclodextrin (G₂-β-CD-Frax). Notably, G₂-β-CD-Frax exhibited the highest solubilizing capacity, fast dissolution rate, and superior Caco-2 cell internalization with no obvious toxicity. Pharmacokinetic studies demonstrated markedly higher oral bioavailability of G₂-β-CD-Frax (5.8-fold that of free drug) than other Frax-CDs. Further, long-term administration of G₂-β-CD-Frax (5 mg/kg) efficiently inhibited CCl₄-induced hepatic fibrosis in the mouse without inducing any toxicity. Our results will inspire the continued advancement of optimal oral Frax formulations for anti-fibrotic therapy.     

Amide–Amine Replacement in Indole-2-carboxamides Yields Potent Mycobactericidal Agents with Improved Water Solubility

Indolecarboxamides are potent but poorly soluble mycobactericidal agents. Here we found that modifying the incipient scaffold by amide–amine substitution and replacing the indole ring with benzothiophene or benzoselenophene led to striking (10–20-fold) improvements in solubility. Potent activity could be achieved without the carboxamide linker but not in the absence of the indole ring. The indolylmethylamine, N-cyclooctyl-6-trifluoromethylindol-2-ylmethylamine (33, MIC_90Mtb 0.13 μM, MBC_99.9Mtb 0.63 μM), exemplifies a promising member that is more soluble and equipotent to its carboxamide equivalent. It is also an inhibitor of the mycolate transporter MmpL3, a property shared by the methylamines of benzothiophene and benzoselenophene.     

Retrochalcone derivatives are positive allosteric modulators at synaptic and extrasynaptic GABA(A) receptors in vitro

BACKGROUND AND PURPOSE

Flavonoids, important plant pigments, have been shown to allosterically modulate brain GABA_A receptors (GABA_ARs). We previously reported that trans-6,4′-dimethoxyretrochalcone (Rc-OMe), a hydrolytic derivative of the corresponding flavylium salt, displayed nanomolar affinity for the benzodiazepine binding site of GABA_ARs. Here, we evaluate the functional modulations of Rc-OMe, along with two other synthetic derivatives trans-6-bromo-4′-methoxyretrochalcone (Rc-Br) and 4,3′-dimethoxychalcone (Ch-OMe) on GABA_ARs.

EXPERIMENTAL APPROACH

Whole-cell patch-clamp recordings were made to determine the effects of these derivatives on GABA_ARs expressed in HEK-293 cells and in hippocampal CA1 pyramidal and thalamic neurones from rat brain.

KEY RESULTS

Rc-OMe strongly potentiated GABA-evoked currents at recombinant α_1–4β₂γ_2s and α₄β₃δ receptors but much less at α₁β₂ and α₄β₃. Rc-Br and Ch-OMe potentiated GABA-evoked currents at α₁β₂γ_2s. The potentiation by Rc-OMe was only reduced at α₁H101Rβ₂γ_2s and α₁β₂N265Sγ_2s, mutations known to abolish the potentiation by diazepam and loreclezole respectively. The modulation of Rc-OMe and pentobarbital as well as by Rc-OMe and the neurosteroid 3α,21-dihydroxy-5α-pregnan-20-one was supra-additive. Rc-OMe modulation exhibited no apparent voltage-dependence, but was markedly dependent on GABA concentration. In neurones, Rc-Br slowed the decay of spontaneous inhibitory postsynaptic currents and both Rc-OMe and Rc-Br positively modulated synaptic and extrasynaptic diazepam-insensitive GABA_ARs.

CONCLUSIONS AND IMPLICATIONS

The trans-retrochalcones are powerful positive allosteric modulators of synaptic and extrasynaptic GABA_ARs. These novel modulators act through an original mode, thus making them putative drug candidates in the treatment of GABA_A-related disorders in vivo.     

Pharmacokinetics and response of obese patients with chronic hepatitis C treated with different doses of PEG-IFN α-2a (40KD) (PEGASYS®)

AIMS

To evaluate whether higher doses of peginterferon α-2a (40KD) [PEG-IFN α-2a (40KD)] can compensate for lower exposure observed among obese patients with chronic hepatitis C (CHC) treated with the standard dose of PEG-IFN α-2a (40KD).

METHODS

Noncirrhotic, obese (body mass index ≥30 kg m⁻²) patients with CHC participated in a single-centre, open-label study. Patients were randomized to 180 or 270 µg week⁻¹ PEG-IFN α-2a (40KD) + ribavirin (1000/1200 mg day⁻¹) for 48 weeks. Blood samples were collected predose and up to 168 h after the first dose and at week 12 for pharmacokinetic analysis. Trough serum concentrations (C_trough) were determined up to week 24.

RESULTS

In the 180 µg week⁻¹ group mean ± SD steady-state (week 12) estimates of AUC_0–168 (ng h⁻¹ ml⁻¹), C_max (ng ml⁻¹) and CL/F (l h⁻¹) were 2154 ± 919, 13.8 ± 6.7 and 0.102 ± 0.051, respectively. In the 270 µg week⁻¹ group, estimates were 3374 ± 1844, 23.4 ± 10.7 and 0.090 ± 0.042, respectively. The mean (range) C_trough (ng ml⁻¹) was 11.2 (4.4–18.5) in the 180 µg week⁻¹ group and 16.1 (0.4–44.2) in the 270 µg week⁻¹ group. Overall, 14 of 20 (70%) and 16 of 20 (80%) patients in the 180 µg week⁻¹ and 270 µg week⁻¹ groups were infected with hepatitis C virus genotype 1 or 4. In the 180 µg week⁻¹ and 270 µg week⁻¹ groups 14 of 20 (70%) and 15 of 19 (79%) patients, respectively, achieved a sustained viral response. Safety was similar between groups.

CONCLUSIONS

Mean PEG-IFN α-2a (40KD) exposure was dose proportional from 180 to 270 µg week⁻¹. Increasing PEG-IFN α-2a (40KD) from 180 to 270 µg week⁻¹ achieves higher serum drug exposure in obese patients.     

Role of α1- and α2-GABA(A) receptors in mediating the respiratory changes associated with benzodiazepine sedation

BACKGROUND AND PURPOSE

The molecular substrates underlying the respiratory changes associated with benzodiazepine sedation are unknown. We examined the effects of different doses of diazepam and alprazolam on resting breathing in wild-type (WT) mice and clarified the contribution of α1- and α2-GABA_A receptors, which mediate the sedative and muscle relaxant action of diazepam, respectively, to these drug effects using point-mutated mice possessing either α1H101R- or α2H101R-GABA_A receptors insensitive to benzodiazepine.

EXPERIMENTAL APPROACH

Room air breathing was monitored using whole-body plethysmography. Different groups of WT mice were injected i.p. with diazepam (1–100 mg·kg⁻¹), alprazolam (0.3, 1 or 3 mg·kg⁻¹) or vehicle. α1H101R and α2H101R mice received 1 or 10 mg·kg⁻¹ diazepam or 0.3 or 3 mg·kg⁻¹ alprazolam. Respiratory frequency, tidal volume, time of expiration and time of inspiration before and 20 min after drug injection were analysed.

KEY RESULTS

Diazepam (10 mg·kg⁻¹) decreased the time of expiration, thereby increasing the resting respiratory frequency, in WT and α2H101R mice, but not in α1H101R mice. The time of inspiration was shortened in WT and α1H101R mice, but not in α2H101R mice. Alprazolam (1–3 mg·kg⁻¹) stimulated the respiratory frequency by shortening expiration and inspiration duration in WT mice. This tachypnoeic effect was partially conserved in α1H101R mice while absent in α2H101R mice.

CONCLUSIONS AND IMPLICATIONS

These results identify a specific role for α1-GABA_A receptors and α2-GABA_A receptors in mediating the shortening by benzodiazepines of the expiratory and inspiratory phase of resting breathing respectively.     

Nuances in the Calculation of Amorphous Solubility Enhancement Ratio

The theoretical amorphous solubility enhancement ratio (R_s) can be calculated based on the free energy difference between amorphous and crystalline forms (ΔG_x→a), using several experimentally determined input parameters. This work compares the various approaches for the calculation of R_s and explores the nuances associated with its calculation. The uncertainty of R_s values owing to experimental conditions (differential scanning calorimetry heating rates) used to measure the input parameters was determined for 3 drugs (indomethacin, itraconazole, and spironolactone). The calculated value of R_s was most influenced by the measurement of heat of fusion. The range in values of R_s using the various equations in the literature was within the calculated uncertainty of the theoretical R_s value. Still, all equations appear to overpredict the experimental value of R_s, sometimes by more than a factor of 5, when an experimental value is attainable. Methods for the calculation of ΔG_x→a for molecules undergoing additional phase transitions (other than glass transition and melting) were developed, employing itraconazole as a model drug. In addition, the influences of enthalpy relaxation and entropy of mixing for racemic compounds on R_s were also considered. These additional corrections improved agreement between theoretical and experimental R_s.