Impact of Solutol HS 15 on the pharmacokinetic behaviour of colchicine upon intravenous administration to male Wistar rats

A novel lipophenol quercetin derivative to prevent macular degeneration: Intravenous and oral formulations for preclinical pharmacological evaluation

Drugs with properties against oxidative and carbonyl stresses are potential candidates to prevent dry age-related macular degeneration (Dry-AMD) and inherited Stargardt disease (STGD1). Previous studies have demonstrated the capacity of a new lipophenol drug: 3-O-DHA-7-O-isopropyl-quercetin (Q-IP-DHA) to protect ARPE19 and primary rat RPE cells respectively from A2E toxicity and under oxidative and carbonyl stress conditions. In this study, first, a new methodology has been developed to access gram scale of Q-IP-DHA. After classification of the lipophenol as BCS Class IV according to physico-chemical and biopharmaceutical properties, an intravenous formulation with micelles (M) and an oral formulation using lipid nanocapsules (LNC) were developed. M were formed with Kolliphor® HS 15 and saline solution 0.9 % (mean size of 16 nm, drug loading of 95 %). The oral formulation was optimized and successfully allowed the formation of LNC (25 nm, 96 %). The evaluation of the therapeutic potency of Q-IP-DHA was performed after IV administration of micelles loaded with Q-IP-DHA (M-Q-IP-DHA) at 30 mg/kg and after oral administration of LNC loaded with Q-IP-DHA (LNC-Q-IP-DHA) at 100 mg/kg in mice. Results demonstrated photoreceptor protection after induction of retinal degeneration by acute light stress making Q-IP-DHA a promising preventive candidate against dry-AMD and STGD1.

Regorafenib loaded self-assembled lipid-based nanocarrier for colorectal cancer treatment via lymphatic absorption

Oral chemotherapy can improve the life quality of patients; however, the therapeutic effects are limited by low bioavailability and rapid in vivo elimination of anticancer drugs. Here, we developed a regorafenib (REG)-loaded self-assembled lipid-based nanocarrier (SALN) to improve oral absorption and anti-colorectal cancer efficacy of REG through lymphatic absorption. SALN was prepared with lipid-based excipients to utilize lipid transport in the enterocytes and enhance lymphatic absorption of the drug in the gastrointestinal tract. The particle size of SALN was 106 ± 10 nm. SALNs were internalized by the intestinal epithelium via the clathrin-mediated endocytosis, and then transported across the epithelium via the chylomicron secretion pathway, resulting in a 3.76-fold increase in drug epithelial permeability (P_app) compared to the solid dispersion (SD). After oral administration to rats, SALNs were transported by the endoplasmic reticulum, Golgi apparatus, and secretory vesicles of enterocytes and were found in the lamina propria of intestinal villi, abdominal mesenteric lymph, and plasma. The oral bioavailability of SALN was 65.9-fold and 1.70-fold greater than that of the coarse powder suspension and SD, respectively, and was highly dependent on the lymphatic route of absorption. Notably, SALN prolonged the elimination half-life of the drug (9.34 ± 2.51 h) compared to the solid dispersion (3.51 ± 0.46 h), increased the biodistribution of REG in the tumor and gastrointestinal (GI) tract, decreased biodistribution in the liver, and showed better therapeutic efficacy than the solid dispersion in colorectal tumor-bearing mice. These results demonstrated that SALN is promising for the treatment of colorectal cancer via lymphatic transport and has potential for clinical translation.

Kolliphor® HS 15 Micelles for the Delivery of Coenzyme Q10: Preparation, Characterization, and Stability

To enhance the stability of coenzyme Q10 (CoQ10), Kolliphor® HS 15 (HS15) was employed as a carrier to build up a stable CoQ10-loaded micelle delivery system. The impact of micellar compositions, the preparation condition, and the preparation method on size characteristics, the solubilization efficiency, and micellar stability were investigated. The optimal preparation conditions were 1:6, 4, 0.2%, 118°C, and 25 min for CoQ10/HS15 mass ratio, pH value, the concentration of glucose, and the sterilization conditions. Upon these conditions, the particle size, polydispersity index (PDI), zeta potential, the entrapment efficiency, drug loading, and the critical micelle concentration (CMC) of CoQ10-loaded micelles were 19.76 nm, 0.112, -3.405 mV, 99.39%, 13.77%, and 5.623 × 10(-4) g/mL, respectively. Differential scanning calorimetry (DSC) analysis collectively corroborated that CoQ10 was entrapped into the micelles in amorphous form. The release pattern of drug was analyzed and proved to follow the first order. Additionally, the samples were exposed to the temperatures of 30°C for 6 months with more significant impact on their stabilities as compared to 4 and 25°C based on particle size and PDI. Under constant humidity with light protection long-term (25 ± 2°C, relative humidity (RH) 60 ± 10%, 18 months) conditions, there was no variation except minor changes of CoQ10 content of the samples. The shelf life of the micellar samples could be predicted as 24 months based on the stability results. Consequently, the CoQ10-loaded micelles showed excellent stabilities below 25°C as a potential drug candidate for further clinical applications.

Cardiotoxic changes of colchicine intoxication in rats: electrocardiographic, histopathological and blood chemical analysis

The microtubule inhibitor colchicine is cardiotoxic and is suggested to impair impulse formation and conduction. However, little is known about the electrocardiographic (ECG) changes induced by colchicine in experimental animals and the detailed pathogenesis of its cardiotoxicity. Therefore, we analyzed cardiotoxicity in colchicine-treated rats using electrocardiographic, histopathological and blood-chemistry approaches. A telemetry device for transmitting ECG data was implanted into male Crl:CD(SD) rats, and ECG tracings were obtained. At 6 weeks of age, 1.25 mg/kg colchicine was injected intravenously once daily for 2 consecutive days, and ECG waveforms and heart rate variability were analyzed. Furthermore, 1.25 mg/kg colchicine or vehicle was injected for 1 or 2 consecutive days in other rats at 6 weeks of age. One day after the final dosing, heart and blood samples were taken for histopathological and bloodchemical examination. ECG analysis revealed a prolonged RR interval, QRS duration, PR interval and QT interval. Heart rate variability analysis showed an increase in high frequency (HF) components as an index of parasympathetic nervous activity. In blood chemical examinations, colchicine induced high levels of parameters of cardiac injury and low levels and/or variations in Ca, inorganic phosphorus, potassium and chloride. Histopathologically, colchicine-treated rats showed eosinophilic granular degeneration and cytoplasmic vacuolation of ventricular myocardial cells but no remarkable change in the atrioventricular node. Not only blood chemical and histopathological changes but also ECG changes were induced in colchicine-treated rats, which indicated a decrease in myocardium excitability and conductivity, and these changes might be related to increased parasympathetic nervous activity and low blood Ca levels.

Can formulation and drug delivery reduce attrition during drug discovery and development-review of feasibility, benefits and challenges

Drug discovery and development has become longer and costlier process. The fear of failure and stringent regulatory review process is driving pharmaceutical companies towards “me too” drugs and improved generics (505(b) (2)) fillings. The discontinuance of molecules at late stage clinical trials is common these years. The molecules are withdrawn at various stages of discovery and development process for reasons such as poor ADME properties, lack of efficacy and safety reasons. Hence this review focuses on possible applications of formulation and drug delivery to salvage molecules and improve the drugability. The formulation and drug delivery technologies are suitable for addressing various issues contributing to attrition are discussed in detail.

Pharmaceutical excipients influence the function of human uptake transporting proteins

Although pharmaceutical excipients are supposed to be pharmacologically inactive, solubilizing agents like Cremophor EL have been shown to interact with cytochrome P450 (CYP)-dependent drug metabolism as well as efflux transporters such as P-glycoprotein (ABCB1) and multidrug resistance associated protein 2 (ABCC2). However, knowledge about their influence on the function of uptake transporters important in drug disposition is very limited. In this study we investigated the in vitro influence of polyethylene glycol 400 (PEG), hydroxypropyl-β-cyclodextrin (HPCD), Solutol HS 15 (SOL), and Cremophor EL (CrEL) on the organic anion transporting polypeptides (OATP) 1A2, OATP2B1, OATP1B1, and OATP1B3 and the Na(+)/taurocholate cotransporting polypeptide (NTCP). In stably transfected human embryonic kidney cells we analyzed the competition of the excipients with the uptake of bromosulfophthalein in OATP1B1, OATP1B3, OATP2B1, and NTCP, estrone-3-sulfate (E(3)S) in OATP1A2, OATP1B1, and OATP2B1, estradiol-17β-glucuronide in OATP1B3, and taurocholate (TA) in OATP1A2 and NTCP cells. SOL and CrEL were the most potent inhibitors of all transporters with the strongest effect on OATP1A2, OATP1B3, and OATP2B1 (IC(50) < 0.01%). HPCD also strongly inhibited all transport proteins but only for substrates containing a sterane-backbone. Finally, PEG seems to be a selective and potent modulator of OATP1A2 with IC(50) values of 0.05% (TA) and 0.14% (E(3)S). In conclusion, frequently used solubilizing agents were shown to interact substantially with intestinal and hepatic uptake transporters which should be considered in drug development. However, the clinical relevance of these findings needs to be evaluated in further in vivo studies.

CriticalSorb: a novel efficient nasal delivery system for human growth hormone based on Solutol HS15

The absorption enhancing efficiency of CriticalSorb for human growth hormone (MW 22 kDa) was investigated in the conscious rat model. The principle absorption enhancing component of CriticalSorb, Solutol HS15, comprises polyglycol mono- and di-esters of 12-hydroxystearic acid combined with free polyethylene glycol. When administering hGH nasally in rats with increasing concentrations of Solutol HS15, it was found that for a 10%w/v solution formulation a bioavailability of 49% was obtained in the first 2h after administration. Furthermore it was shown that the most effective ratio of Solutol HS15 to hGH was 4:1 on a mg to mg basis. Histopathology studies in rats after 5 days repeated nasal administration showed that Solutol HS15 had no toxic effect on the nasal mucosa. These results have been confirmed in a 6 month repeat nasal toxicity study in rats. It can be concluded that the principle absorption enhancing component of CriticalSorb - Solutol HS15 - is a potent and non- toxic nasal absorption enhancer that warrants further development.

Pharmacokinetics of the fasciocidal drug candidates MT04 and OZ78 in uninfected rats and in vitro pharmacodynamic studies

OZ78 and MT04 are promising drug candidates against fascioliasis (fasciolosis). We determined basic pharmacokinetic (PK) parameters of OZ78 and MT04 in uninfected rats. Rats were treated with single oral doses of 50 mg/kg OZ78 or MT04. Blood samples were withdrawn at selected time points post treatment and the plasma concentrations were quantified by a validated liquid chromatography/mass spectrometry (LC/MS) method. The LC/MS method for MT04 and OZ78, initially developed for sheep plasma analysis, was adapted for rat plasma. In vitro pharmacodynamic studies with Fasciola hepatica incubated in solutions of either test agent complemented our work. The adapted and validated method was precise and accurate to measure OZ78 and MT04 in rat plasma. Accuracies for MT04 ranged from 87.9% to 104.7% with precisions not exceeding 14.3%. Precisions for OZ78 were lower than 9.8% and accuracies were between 88.4% and 105.3%. Following oral administration, maximum plasma concentrations (C max) of MT04 and OZ78 were 49.8 and 70.1 μg/ml after 2.7 h and 1.6 h, respectively (p > 0.05). The estimated area under the plasma time curves (AUCs) were comparable for MT04 and OZ78. Mean elimination half-lives (t1/2) of MT04 and OZ78 covered a range from 1 to 7 h. In vitro studies demonstrated that the fasciocidal activity of MT04 and OZ78 was dependent on the incubation-time, with exposure of flukes for 24 h to the drugs not being sufficient to kill the worms. In conclusion, differences in PK parameters of MT04 and OZ78 were observed in rats. However, further studies (e.g. in infected rats) are necessary to characterize these drugs in greater detail.

Plasma and brain pharmacokinetic profile of cannabidiol (CBD), cannabidivarine (CBDV), Δ⁹-tetrahydrocannabivarin (THCV) and cannabigerol (CBG) in rats and mice following oral and intraperitoneal administration and CBD action on obsessive-compulsive behaviour

RATIONALE

Phytocannabinoids are useful therapeutics for multiple applications including treatments of constipation, malaria, rheumatism, alleviation of intraocular pressure, emesis, anxiety and some neurological and neurodegenerative disorders. Consistent with these medicinal properties, extracted cannabinoids have recently gained much interest in research, and some are currently in advanced stages of clinical testing. Other constituents of Cannabis sativa, the hemp plant, however, remain relatively unexplored in vivo. These include cannabidiol (CBD), cannabidivarine (CBDV), Δ(9)-tetrahydrocannabivarin (Δ(9)-THCV) and cannabigerol (CBG).

OBJECTIVES AND METHODS

We here determined pharmacokinetic profiles of the above phytocannabinoids after acute single-dose intraperitoneal and oral administration in mice and rats. The pharmacodynamic-pharmacokinetic relationship of CBD (120 mg/kg, ip and oral) was further assessed using a marble burying test in mice.

RESULTS

All phytocannabinoids readily penetrated the blood-brain barrier and solutol, despite producing moderate behavioural anomalies, led to higher brain penetration than cremophor after oral, but not intraperitoneal exposure. In mice, cremophor-based intraperitoneal administration always attained higher plasma and brain concentrations, independent of substance given. In rats, oral administration offered higher brain concentrations for CBD (120 mg/kg) and CBDV (60 mg/kg), but not for Δ(9)-THCV (30 mg/kg) and CBG (120 mg/kg), for which the intraperitoneal route was more effective. CBD inhibited obsessive-compulsive behaviour in a time-dependent manner matching its pharmacokinetic profile.

CONCLUSIONS

These data provide important information on the brain and plasma exposure of new phytocannabinoids and guidance for the most efficacious administration route and time points for determination of drug effects under in vivo conditions.

Formulation of a stable and high-loaded quercetin injectable emulsion

The purpose of this paper was to prepare a stable and high-loaded quercetin emulsion with the quercetin-phospholipid complex. The complex was analyzed by FT-IR and SEM. Quercetin and soybean lecithin were reacted in dichloromethane at a ratio of 1:2.5 for 2 h at 40°C to prepare the complex. The optimum quercetin emulsion formulation consisted of (according to quality percentage), the complex (quercetin 0.06% in the emulsion), miglyol 812 10%, soybean oil 2%, solutol HS 15 1.2%, cremophor ELP 0.4%, vitamin E 0.2%, oleic acid 0.5%, glycerol 2.5%. The quercetin emulsion was sterilized at 121°C for 15 min. The drug content and particle size distribution of the emulsion before and after sterilization were almost unchanged. The results of accelerate stability (stored at 40°C over one month) and short-time stability (stored at room temperature over six months) tests showed that the quercetin emulsion had enough physicochemical stability to undergo storage. The histopathological examination for rabbit ear vein irritation test indicated that the quercetin emulsion produced no more irritation than normal saline.

Physiological modeling to understand the impact of enzymes and transporters on drug and metabolite data and bioavailability estimates

PURPOSE

To obtain mathematical solutions that correlate drug and metabolite exposure and systemic bioavailability (F (sys)) with physiological determinants, transporters and enzymes.

METHODS

A series of physiologically-based pharmacokinetic (PBPK) models that included renal excretion and sequential metabolism within the intestine and/or liver as metabolite formation organs were developed. The area under the curve for drug (AUC) and formed metabolite (AUC{mi,P}) were solved by matrix inversion.

RESULTS

The PBPK models revealed that AUC{mi,P} was dependent on dispositional parameters (transport and elimination) for the drug and metabolite. The solution was unique for each metabolite formation organ and was dependent on the type of drug and metabolite elimination organs. The AUC ratio of the formed metabolite after oral and intravenous drug dosing was useful for determination of the fraction absorbed (F (abs)) and not the systemic bioavailability (F (sys)) when either intestine or liver was the only drug elimination organ.

CONCLUSIONS

The AUC ratio of the formed metabolite after oral and intravenous drug dosing differed from that for drug and would not provide F (sys). However, the AUC ratio of the formed metabolite for oral and intravenous drug dosing furnished the estimate of F (abs) when intestine or liver was the only drug metabolic organ.

Targeting of daunomycin using biotinylated immunoliposomes: Pharmacokinetics, tissue distribution andin vitropharmacological effects

Biotinylated immunoliposomes were prepared by a non-covalent (biotin-streptavidin) coupling procedure and conjugated to the OX26 monoclonal antibody directed against the rat transferrin receptor. In vitro, these biotinylated immunoliposomes were used to by-pass P-glycoprotein in multidrug-resistant RBE4 brain capillary endothelial cells and thereby to achieve 2- to 3-fold higher intracellular accumulation of liposomal daunomycin as compared to free drug. The extent of cellular uptake of liposomal daunomycin was dose- and time-dependent, was inhibited by competition with unbound OX26 and was associated with a pharmacological (i.e. cytotoxic) effect. Cytotoxic effects of liposomal formulations of daunomycin, in contrast to the free drug, were apparent only after prolonged incubation periods being indicative of a slow intracellular unpacking and release of liposomal daunomycin. Pharmacokinetics and tissue distribution studies in the rat revealed brain accumulation of daunomycin in OX26-immunoliposomes to higher levels as compared to brain uptake of free daunomycin, or daunomycin incorporated within pegylated liposomes or within unspecific IgG(2a) isotype control immunoliposomes. Such OX26-mediated effects were not observed in other tissues such as spleen, liver, muscle or kidney.

The effects of pharmaceutical excipients on drug disposition

Many new chemical entities are poorly soluble, requiring the use of co-solvents or excipients to produce suitable intravenous formulations for early pre-clinical development studies. There is some evidence in the literature that these formulation components can have significant physiological and physicochemical effects which may alter the distribution and elimination of co-administered drugs. Such effects have the potential to influence the results of pre-clinical pharmacokinetic studies, giving a false impression of a compound's intrinsic pharmacokinetics and frustrating attempts to predict the drug's ultimate clinical pharmacokinetics. This review describes the reported effects of commonly used co-solvents and excipients on drug pharmacokinetics and on physiological systems which are likely to influence drug disposition. Such information will be useful in study design and evaluating data from pharmacokinetic experiments, so that the potential influence of formulation components can be minimised.

Enhancement of drug absorption by noncharged detergents through membrane and P-glycoprotein binding

Noncharged detergents are used as excipients in drug formulations. Until recently, they were considered as inert compounds, enhancing drug absorption essentially by improving drug solubility. However, many detergents insert into lipid membranes, although to different extents, and change the lateral packing density of membranes at high concentrations. Moreover, they bind to the efflux transporter P-glycoprotein (P-gp) and most likely to related transporters and metabolising enzymes with overlapping substrate specificities. If their affinity to P-gp is higher than that of the coadministered drug they act as modulators or inhibitors of P-gp and enhance drug absorption. Inhibition of P-gp and related proteins can, however, cause severe side effects. This paper first reviews the membrane binding propensity of different noncharged detergents (including poloxamers) and discusses their ability to bind to P-gp. Second, literature data on drug uptake enhancement by noncharged detergents, obtained in vivo and in vitro, are analysed at the molecular level. The present analysis provides the tools for an approximate and simple prior estimate of the membrane and P-gp binding ability of noncharged detergents based on a modular binding approach.

Tissue distribution of indinavir administered as solid lipid nanocapsule formulation in mdr1a (+/+) and mdr1a (-/-) CF-1 mice

PURPOSE

Due to protease inhibitor (PI) efflux transport by P-glycoprotein (P-gp), insufficient PI concentrations result in low ongoing HIV replication in the so-called virus sanctuaries (brain and testes). The aim of the present study was to evaluate indinavir-loaded nanocapsules (Ind-LNC) including Solutol HS15, an excipient reported to possess in vitro P-gp inhibiting properties, as a means to improve indinavir distribution into brain and testes of mice.

METHODS

Normal mdr1a (+/+) or P-gp-deficient mdr1a (-/-) CF-1 mice were dosed with Ind-LNC (10 mg indinavir/kg, i.v.). At 30 min post-administration, indinavir was determined in plasma, brain, testes, as well as in kidneys, liver, and heart by LC-MS/MS, and tissue/plasma concentration ratios were calculated. Results were compared with those of control groups that received an indinavir solution (Ind-Sol).

RESULTS

Using Ind-Sol, ratios were 21.3- and 3.3-fold higher in brains and testes of mdr1a (-/-) mice than of mdr1a (+/+) mice, respectively, whereas in the other organs ratios were not significantly different between the two substrains. When Ind-LNC was used, a similar [mdr1a(-/-) vs. mdr1a (+/+) mice] trend was observed. Moreover, ratios were found to be significantly increased (1.9-fold increase in average) in most organs (brain and testes in particular) with Ind-LNC compared to Ind-Sol, regardless of the substrain used.

CONCLUSIONS

In agreement with previous works, P-gp governs at least in part indinavir uptake into brain and testes. LNC formulation increased indinavir uptake in brain and testes by mechanisms other than, or additional to, P-gp inhibition.

A technical feasibility study of surfactant-free drug suspensions using octenyl succinate-modified starches

Many new drugs exhibit poor wetting behaviour and low aqueous solubility. This is particularly an issue for preclinical studies like toxicological trials, in which considerably higher doses and volumes are being administered compared to clinical studies. Preclinical vehicles typically contain high levels of surfactants that can exert biological effects. However, the biological inertness of vehicles is pivotal for the application in preclinical studies stressing the need in finding new excipients to solve formulation problems of today's drug discovery. The present study investigated the technical feasibility of surfactant-free suspensions using a new poorly soluble drug as model. It was shown that octenyl succinate-modified starches adequately wetted the drug and homogenous tasteless suspensions were obtained. The polymer xanthan gum was identified as macroscopically compatible gelling agent. Concentration effects of xanthan, drug and different modified starches were studied in a D-optimal design with respect to rheological properties. The suspensions were also tested in an analytical centrifuge using NIR transmission profiles to obtain a measure of sedimentation stability under accelerated conditions. The modified starches exhibited only little influence on the viscosity as well as on the yield point in contrast to the rheological effects of xanthan gum. This gelling agent was the main stabilising excipient as the modified starches hindered to a lesser extent sedimentation. The most stable suspensions displayed convenient flow properties. The viscosity at 100 s(-1) and 25 degrees C was in technically acceptable range of 120-140 mPa s in view of a application via gavage or a syringe in animal studies. The results demonstrated that surfactant-free drug suspensions with excellent technical performance can be obtained using octenyl succinate-modified starches. The vehicles were tasteless and based on the experience of modified starches in the food industry, the vehicles should exhibit good tolerability. The future use of such surfactant-free drug suspensions in toxicological, pharmacokinetic and pharmacodynamic studies will have to determine their advantage in terms of biological inertness.

Colchicine inhibits fracture union and reduces bone strength--in vivo study

INTRODUCTION

Recent studies have demonstrated that Colchicine (CO) prevents heterotopic ossification (HO) after total hip replacement in patients suffering from familial Mediterranean fever (FMF). Other investigators have proved that CO is an in vitro inhibitor of proliferation of osteoblasts and osteosarcoma cells, and is a non-selective mitosis inhibitor and selective inhibitor of mineralization.

METHODS

A double blind prospective study comprised four groups of adult rats. The left posterior tibia in each rat was fractured except in one of the control groups. The study groups were treated with CO 1 mg/kg/day 1 week before, or on the fracture day. The control groups did not receive CO treatment. Six weeks after fracture induction the groups were compared radiographically mechanically and histologically.

RESULTS

Prolonged CO treatment had a significant negative influence on fracture healing according to radiological, clinical, mechanical (p<0.02), and pathological parameters (p<0.0001).

CONCLUSIONS

We were able to demonstrate that prolonged CO treatment reduced bone healing.

In vitro investigation on the impact of Solutol HS 15 on the uptake of colchicine into rat hepatocytes

In the current investigation, the impact of the surface-active formulation ingredient Solutol HS 15 on the uptake of colchicine into freshly isolated rat hepatocytes was investigated using a centrifugal filtration technique through a silicone oil layer. Colchicine is taken up into the cells by an active transport mechanism. When conducting the experiment at 37 degrees C, it was found that at concentrations below its critical micellar concentration (CMC) of 0.021% (0.0003 and 0.003%, w/v), Solutol HS 15 did not impact the uptake of colchicine. By contrast, at a Solutol HS 15 concentration above its CMC (0.03%, w/v), the amount of colchicine taken up into the cells as well as its uptake velocity were significantly decreased. However, in control experiments performed at 4 degrees C, a temperature at which active transport processes should be significantly slowed down, Solutol HS 15 at 0.03% did not affect colchicine uptake and/or its association with the cells. The described findings might be rationalized by inhibition of colchicine transport either due to direct interaction at the transport site or due to alterations of membrane properties in the presence of Solutol HS 15 at concentrations above its CMC. Moreover, a strong molecular interaction between Solutol HS 15 and colchicine as well as an incorporation of colchicine into micelles formed by Solutol HS 15, this way resulting in a limited contact of colchicine with the cells, cannot be excluded as contributors to the observed effect.

Impact of Solutol HS 15 on the pharmacokinetic behavior of midazolam upon intravenous administration to male Wistar rats

The pharmacokinetic profile of midazolam (MDZ) and its major metabolites 1'-OH-midazolam (1'OH-MDZ) and 4-OH-midazolam (4OH-MDZ) was investigated in rats. MDZ was administered intravenously at 5 mg/kg either in the absence (NaCl 0.9%, control group) or in the presence of the surfactant Solutol HS 15, a weak inhibitor of cytochrome P450 3A (CYP3A) activity in vitro (Solutol HS 15-treated group). It was found that the pharmacokinetic profiles of MDZ, 1'OH-MDZ and 4OH MDZ did not differ significantly in the two dosing vehicles (P values above 0.2). MDZ exhibited a high plasma clearance (Cl) of 79 and 92 ml/min/kg (corresponding to a blood Cl of 64 and 75 ml/min/kg), a high volume of distribution (V(d)) of 4.0 and 3.6 l/kg, and an area under the plasma concentration-time curve (AUC(t0-tinf)) of 1062 and 932 h.ng/ml in the control group and in the Solutol HS 15-treated group, respectively. The amount of MDZ excreted unchanged into urine was below 0.01% with both dosing vehicles. AUC(t0-tinf) in the control group was 12.3 h.ng/ml for 1'OH-MDZ and 38.8 h.ng/ml 4OH-MDZ. In the Solutol HS 15-treated group, AUC(t0-tinf) was 14 h.ng/ml for 1'OH-MDZ and 35.4 h.ng/ml for 4OH-MDZ. The metabolite concentrations excreted into urine were below the limit of quantification. In the rat, MDZ has a high blood clearance that is limited by liver blood flow. Therefore, weak CYP3A inhibitors like Solutol HS 15 are not likely to affect the hepatic blood clearance of MDZ in vivo.