Spray-dried raloxifene submicron particles for pulmonary delivery: Development and in vivo pharmacokinetic evaluation in rats.

Raloxifene hydrochloride (RH) is a selective oestrogen receptor modulator used for the treatment of osteoporosis. Even though 60% of an oral dose is quickly absorbed via the gastrointestinal tract, the absolute bioavailability of RH is only 2-3% in humans due to extensive first-pass metabolism. Various approaches to improve RH bioavailability have been reported over the past few years; however, none have focused on the development of products for pulmonary administration. Therefore, in this study, submicron particles containing RH were produced for pulmonary administration with the aim to limit first-pass metabolism. Powders were produced by vibrational atomisation spray drying with a high process yield (>80%). The drug content was between 440 and 890 mg·g-1, and powders had a high encapsulation efficiency (>95%), mean particle size of 400-700 nm, low residual moisture (<2%) and spherical shape. These powders showed an improved drug dissolution rate compared to the raw RH material. Moreover, they presented high dose uniformity (95-100%), a high in vitro respirable fraction (>55%) and adequate mass median aerodynamic diameter for pulmonary delivery (<5 µm). The pharmacokinetic study in male Wistar rats demonstrated an absolute bioavailability of 47.20% after pulmonary administration of the particles. Therefore, these submicron-sized powders are promising for pulmonary RH delivery as a dry powder medicine.

LC-UV method to assay raloxifene hydrochloride in rat plasma and its application to a pharmacokinetic study

A specific, precise, and accurate LC-UV method was developed and validated to assay raloxifene hydrochloride in rat plasma. Raloxifene was analyzed after liquid-liquid extraction and quantified by reversed phase liquid chromatography (C18 column) using acetonitrile and ammonium acetate buffer 0.05 M (pH 4.0) as mobile phase at a flow rate of 1 mL.min-1 and UV detection at 287 nm. Retention times of raloxifene and internal standard (dexamethasone) were approximately 11 min and 14 min, respectively. Linearity was checked for a concentration range between 25 ng.mL-1 and 1000 ng.mL-1. Intra- and inter-day precision had relative standard deviation lower than 10% and 15%, respectively. Recovery from plasma was higher than 90%. Accuracy values were 98.21%, 99.70%, and 102.70% for lower, medium, and upper limits of quantification, respectively. Limit of quantification was 25 ng.mL-1. Drug stability was analyzed at room temperature using plasma kept in a freezer at -80 °C for 45 days after processing for 6 h and three freeze-thaw cycles. The advantages of the method developed include stability under different conditions and low limit of quantification. Its applicability was confirmed by the analysis of raloxifene levels in plasma samples in a designed pharmacokinetic study in rats after intravenous administration (5 mg.kg-1).

Fast and sensitive HPLC/UV method for cefazolin quantification in plasma and subcutaneous tissue microdialysate of humans and rodents applied to pharmacokinetic studies in obese individuals.

Antimicrobial prophylactic dosing of morbidly obese patients may differ from normal weighted individuals owing to alterations in drug tissue distribution. Drug subcutaneous tissue distribution can be investigated by microdialysis patients and animals. The need for cefazolin prophylactic dose adjustment in obese patients remains under discussion. The paper describes the validation of an HPLC-UV method for cefazolin quantification in plasma and microdialysate samples from clinical and pre-clinical studies. A C18 column with an isocratic mobile phase was used for drug separation, with detection at 272 nm. Total and unbound cefazolin lower limit of quantitation was 5 µg/mL in human plasma, 2 µg/mL in rat plasma, and 0.5 and 0.025 µg/mL in human and rat microdialysate samples, respectively. The maximum intra- and inter-day imprecisions were 10.7 and 8.1%, respectively. The inaccuracy was <9.7%. The limit of quantitation imprecision and inaccuracy were < 15%. Cefazolin stability in the experimental conditions was confirmed. Cefazolin plasma concentrations and subcutaneous tissue penetration were determined by microdialysis in morbidly obese patients (2 g i.v. bolus) and diet-induced obese rats (30 mg/kg i.v. bolus) using the method. This method has the main advantages of easy plasma clean-up and practicability and has proven to be useful in cefazolin clinical and pre-clinical pharmacokinetic investigations.

Simultaneous Semimechanistic Population Analyses of Levofloxacin in Plasma, Lung, and Prostate To Describe the Influence of Efflux Transporters on Drug Distribution following Intravenous and Intratracheal Administration.

Levofloxacin (LEV) is a broad-spectrum fluoroquinolone used to treat pneumonia, urinary tract infections, chronic bacterial bronchitis, and prostatitis. Efflux transporters, primarily P-glycoprotein (P-gp), are involved in LEV's tissue penetration. In the present work, LEV free lung and prostate interstitial space fluid (ISF) concentrations were evaluated by microdialysis in Wistar rats after intravenous (i.v.) and intratracheal (i.t.) administration (7 mg/kg of body weight) with and without coadministration of the P-gp inhibitor tariquidar (TAR; 15 mg/kg administered i.v.). Plasma and tissue concentration/time profiles were evaluated by noncompartmental analysis (NCA) and population pharmacokinetics (popPK) analysis. The NCA showed significant differences in bioavailability (F) for the control group (0.4) and the TAR group (0.86) after i.t. administration. A four-compartment model simultaneously characterized total plasma and free lung (compartment 2) and prostate (compartment 3) ISF concentrations. Statistically significant differences in lung and prostate average ISF concentrations and levels of kidney active secretion in the TAR group from those measured for the control group (LEV alone) were observed. The estimated population means were as follows: volume of the central compartment (V1), 0.321 liters; total plasma clearance (CL), 0.220 liters/h; TAR plasma clearance (CLTAR), 0.180 liters/h. The intercompartmental distribution rate constants (K values) were as follows: K12, 8.826 h(-1); K21, 7.271 h(-1); K13, 0.047 h(-1); K31, 7.738 h(-1); K14, 0.908 h(-1); K41, 0.409 h(-1); K21 lung TAR (K21LTAR), 8.883 h(-1); K31 prostate TAR (K31PTAR), 4.377 h(-1). The presence of P-gp considerably impacted the active renal secretion of LEV but had only a minor impact on the efflux from the lung following intratracheal dosing. Our results strongly support the idea of a role of efflux transporters other than P-gp contributing to LEV's tissue penetration into the prostrate.

Enhanced penetration of moxifloxacin into rat prostate tissue evidenced by microdialysis.

Moxifloxacin is reported to have increased distribution into the prostate compared with older fluoroquinolones such as norfloxacin and ciprofloxacin, being able to reach tissue-to-plasma concentration ratios greater than unity. However, most of these studies use tissue homogenates derived from biopsy samples, which can lead to overestimation of free concentrations as fluoroquinolones tend to accumulate in the intracellular space. The aim of this study was to investigate moxifloxacin pharmacokinetics in rat prostate interstitial fluid by microdialysis. Tissue pharmacokinetics was assessed by implanting a small microdialysis catheter in the prostate gland. Blood samples were simultaneously collected for assessing plasma pharmacokinetics. Analysis of plasma (N=154) and microdialysis (N=344) concentrations after a single intravenous dose of 6 or 12mg/kg moxifloxacin was conducted in the non-linear mixed-effect modelling software NONMEM v.6 as well by a non-compartmental approach. Moxifloxacin showed a significant tissue distribution in the prostate (AUCprostate,ISF/fu·AUCplasma=1.24±0.37), 59% higher than the value obtained for levofloxacin in a previous study. A three-compartment model with non-linear kinetics could adequately describe moxifloxacin pharmacokinetics in terms of curve fitting and precision in parameter estimation. The developed pharmacokinetic model indicates that passive diffusion and active transport are the mechanisms involved in moxifloxacin distribution to the prostate. These findings suggest that moxifloxacin could be a better alternative to levofloxacin for the treatment of chronic bacterial prostatitis owing to its enhanced tissue penetration and higher AUCtissue/MIC ratios, even though it is not yet approved by the US FDA for this indication.

Validation of an efficient LC-microdialysis method for gemifloxacin quantitation in lung, kidney and liver of rats.

A liquid chromatography method has been established for the reliable determination of unbound gemifloxacin concentrations in kidney, lung and liver microdialysates of rats. Microdialysis probes were inserted into tissues of rats, and then dialysates were collected at regular time intervals after intravenous administration of gemifloxacin (40 mg kg(-1)). A pilot study was performed to assess gemifloxacin penetration in lung, kidney and liver of rats. Gemifloxacin was separated on a C(18) column eluted using triethylamine solution (0.5%, v/v), adjusted to pH 3.0±0.1 with 85% phosphoric acid, methanol and acetonitrile (71:15:14, v/v/v) as mobile phase at a flow rate of 1.1 mL min(-1). The fluorescence detector was set at excitation and emission wavelengths of 344 nm and 399 nm, respectively. The limit of quantitation was found to be 50 ng mL(-1). Linearity was found to be over a concentration range of 50-2000 ng mL(-1). The intra-assay and inter-assay precision and accuracy values were determined from the analysis of six quality control samples. The results obtained at three concentration levels showed R.S.D. values lower than 6.06% and 4.10% for repeatability and intermediate precision, respectively. The accuracy (R.E.%) ranged from 90.0 to 106.5%. The chromatographic run time of each sample was performed in 9 min. Drug stability in microdialysates was shown at room temperature for 8h, after three freeze-thaw cycles, in freezer at -80 °C for 14 days, and in the autosampler after processing for 8h. The relative recoveries determined by extraction efficiency (EE) and retrodialysis (RD) in vitro employing a flow rate of 1.5 µL min(-1) were 29.24±3.67% and 23.67±3.31%, respectively. In vivo recoveries determined by RD in Wistar rats' kidney, lung and liver were 27.69±2.09%, 23.12±3.79% and 17.38±0.68%, respectively. The method was successfully applied to investigate tissue penetration of unbound gemifloxacin into the kidney, lung and liver of rats.