Casey L. Sayre

Flip-flop pharmacokinetics - delivering a reversal of disposition: challenges and opportunities during drug development

Flip-flop pharmacokinetics is a phenomenon often encountered with extravascularly administered drugs. Occurrence of flip-flop spans preclinical to human studies. The purpose of this article is to analyze both the pharmacokinetic interpretation errors and opportunities underlying the presence of flip-flop pharmacokinetics during drug development. Flip-flop occurs when the rate of absorption is slower than the rate of elimination. If it is not recognized, it can create difficulties in the acquisition and interpretation of pharmacokinetic parameters. When flip-flop is expected or discovered, a longer duration of sampling may be necessary in order to avoid overestimation of fraction of dose absorbed. Common culprits of flip-flop disposition are modified dosage formulations; however, formulation characteristics such as the drug chemical entities themselves or the incorporated excipients can also cause the phenomenon. Yet another contributing factor is the physiological makeup of the extravascular site of administration. In this article, these causes of flip-flop pharmacokinetics are discussed with incorporation of relevant examples and the implications for drug development outlined.

Novel intravaginal nanomedicine for the targeted delivery of saquinavir to CD4+ immune cells.

The goal of this study was to develop and characterize an intravaginal nanomedicine for the active targeted delivery of saquinavir (SQV) to CD4+ immune cells as a potential strategy to prevent or reduce HIV infection. The nanomedicine was formulated into a vaginal gel to provide ease in self-administration and to enhance retention within the vaginal tract. SQV-encapsulated nanoparticles (SQV-NPs) were prepared from poly(lactic-co-glycolic acid) (PLGA) and conjugated to antihuman anti-CD4 antibody. Antibody-conjugated SQV-NPs (Ab-SQV-NPs) had an encapsulation efficiency (EE%) of 74.4% + 3.7% and an antibody conjugation efficiency (ACE%) of 80.95% + 1.10%. Over 50% of total loaded SQV was released from NPs over 3 days. NPs were rapidly taken up by Sup-T1 cells, with more than a twofold increase in the intracellular levels of SQV when delivered by Ab-SQV-NPs in comparison to controls 1 hour post-treatment. No cytotoxicity was observed when vaginal epithelial cells were treated for 24 hours with drug-free Ab-NPs (1,000 μg/mL), 1% HEC placebo gel (200 mg/mL), or 1% HEC gel loaded with drug-free Ab-NPs (5 mg NPs/g gel, 200 mg/mL of gel mixture). Overall, we described an intravaginal nanomedicine that is nontoxic and can specifically deliver SQV into CD4+ immune cells. This platform may demonstrate potential utility in its application as postexposure prophylaxis for the treatment or reduction of HIV infection, but further studies are required.

Vorinostat with sustained exposure and high solubility in poly(ethylene glycol)-b-poly(dl-lactic acid) micelle nanocarriers: Characterization and effects on pharmacokinetics in rat serum and urine

The histone deacetylase inhibitor suberoylanilide hydroxamic acid, known as vorinostat, is a promising anticancer drug with a unique mode of action; however, it is plagued by low water solubility, low permeability, and suboptimal pharmacokinetics. In this study, poly(ethylene glycol)-b-poly(DL-lactic acid) (PEG-b-PLA) micelles of vorinostat were developed. Vorinostats pharmacokinetics in rats was investigated after intravenous (i.v.) (10 mg/kg) and oral (p.o.) (50 mg/kg) micellar administrations and compared with a conventional polyethylene glycol 400 solution and methylcellulose suspension. The micelles increased the aqueous solubility of vorinostat from 0.2 to 8.15 ± 0.60 and 10.24 ± 0.92 mg/mL at drug to nanocarrier ratios of 1:10 and 1:15, respectively. Micelles had nanoscopic mean diameters of 75.67 ± 7.57 and 87.33 ± 8.62 nm for 1:10 and 1:15 micelles, respectively, with drug loading capacities of 9.93 ± 0.21% and 6.91 ± 1.19%, and encapsulation efficiencies of 42.74 ± 1.67% and 73.29 ± 4.78%, respectively. The micelles provided sustained exposure and improved pharmacokinetics characterized by a significant increase in serum half-life, area under curve, and mean residence time. The micelles reduced vorinostat clearance particularly after i.v. dosing. Thus, PEG-b-PLA micelles significantly improved the p.o. and i.v. pharmacokinetics and bioavailability of vorinostat, which warrants further investigation.

Involvement of brain opioid receptors in the anti-allodynic effect of hyperbaric oxygen in rats with sciatic nerve crush-induced neuropathic pain

Earlier research has demonstrated that hyperbaric oxygen (HBO2) can produce an antinociceptive effect in models of acute pain. Recent studies have revealed that HBO2 can produce pain relief in animal models of chronic pain as well. The purpose of the present investigation was to ascertain whether HBO2 treatment might suppress allodynia in rats with neuropathic pain and whether this effect might be blocked by the opioid antagonist naltrexone (NTX). Male Sprague Dawley rats were subjected to a sciatic nerve crush under anesthesia and mechanical thresholds were assessed using an electronic von Frey anesthesiometer. The time course of the HBO2-induced anti-allodynic effect in different treatment groups was plotted, and the area-under-the-curve (AUC) was determined for each group. Seven days after the nerve crush procedure, rats were treated with HBO2 at 3.5 atm absolute (ATA) for 60 min and exhibited an anti-allodynic effect, compared to nerve crush-only control rats. Twenty-four hours before HBO2 treatment, another group of rats was implanted with Alzet(®) osmotic minipumps that continuously released NTX into the lateral cerebral ventricle for 7 days. These NTX-infused, HBO2-treated rats exhibited an allodynic response comparable to that exhibited by rats receiving nerve crush only. Analysis of the AUC data showed that HBO2 significantly reduced the nerve crush-induced allodynia; this anti-allodynic effect of HBO2 was reversed by NTX. These results implicate opioid receptors in the pain relief induced by HBO2.

Quantification of Three Chiral Flavonoids with Reported Bioactivity in Selected Licensed Canadian Natural Health Products and US Marketed Dietary Supplements

PURPOSE Research indicating potentially beneficial bioactivity of flavonoids has produced a market and demand for natural health products and dietary supplements containing flavonoids. Implementation of the Canadian natural health product (NHP) regulations in January of 2004 increased regulation and oversight of NHP manufacture and marketing leading many consumers and clinicians to assume a similar pathway of development and approval to over-the-counter or prescription drugs. METHODS Three stereospecific liquid chromatograph/mass spectrometry (LC/MS) methods were used to assess the flavonoids, liquiritigenin, pinocembrin, and pinostrobin, in selected Canadian licensed NHPs and US marketed dietary supplements. RESULTS The present study quantifies bioactive flavonoids in these products and notes variability in flavonoid content. CONCLUSIONS Efficacy and safety of NHPs and dietary supplements should not be assumed due to differences in criteria for NHP licensure by Health Canada as well as variation of flavonoid content between manufacturers and products with similar indications for use.

Chiral analytical method development and application to pre-clinical pharmacokinetics of pinocembrin

An analytical method enabling the detection and quantification of the individual enantiomers of racemic (±) pinocembrin is required to fully characterize its pharmacokinetic disposition. Direct resolution of the enantiomers of pinocembrin was achieved using a novel and simple reversed-phase high-performance liquid chromatography method with electrospray ionization and detection by mass spectrometry in rat serum. A Chiralcel® AD-RH column was employed to perform baseline separation with electrospray positive-mode ionization with selected ion monitoring detection. The standard curves were linear from 0.5 to 100 µg/mL for each enantiomer. The limit of quantification was 0.5 µg/mL. The assay was applied successfully to stereoselective serum disposition of pinocembrin enantiomers in rats. Pinocembrin enantiomers were detected in serum. Both enantiomers had a serum half-life of ~15 min in rats. Similar values of volume of distribution between the enantiomers were also observed: 1.76 L/kg for S-pinocembrin and 1.79 L/kg for R-pinocembrin. Total clearance was 5.527 L//h/kg for S-pinocembrin and 5.535 L/h/kg for R-pinocembrin, and the area under the curve was 1.821 µg h/mL for S-pinocembrin and 1.876 µg h/mL for R-pinocembrin. The large volume of distribution coupled with the short serum half-life suggests extensive distribution of pinocembrin into the tissues.

Quantification of cefazolin in serum and adipose tissue by ultra high performance liquid chromatography-Tandem mass spectrometry (UHPLC–MS/MS): application to a pilot study of obese women undergoing cesarean delivery

Higher doses of cefazolin are required in obese patients for preoperative antibiotic prophylaxis, owing to its low lipophilicity. An ultra high performance liquid chromatography-tandem mass spectrometry method was developed to quantify cefazolin in serum and adipose tissue from 6 obese patients undergoing cesarean delivery, and using stable-isotope labeled cefazolin as an internal standard. The method has a 2μg/g lower limit of quantitation. The concentration in adipose tissue was 3.4±1.6μg/mL, which is less than half of the reported minimum inhibitory concentration of 8μg/mL for cefazolin. Serum cefazolin concentrations were more than 30-fold higher than in adipose tissue.

Preclinical Pharmacokinetics and Pharmacodynamics and Content Analysis of Gnetol in Foodstuffs

Studies were undertaken to evaluate the bioavailability in rats and content analysis of gnetol in Gnetum gnemon products reported to contain gnetol and to examine the pharmacological properties of gnetol in in vitro models including anti‐inflammatory/analgesic, antidiabetic, anti‐adipogenesis, and anticancer activity. Male Sprague–Dawley rats were cannulated and dosed either intravenously with gnetol (10 mg/kg) or orally (100 mg/kg). Various methanolic extractions of G. gnemon products were quantified. Gnetols effect on cell viability in selected cell lines with or without inflammatory stimulus was assessed. α‐Amylase and α‐glucosidase inhibition was evaluated. Cyclooxygenase (COX)‐1, COX‐2, and histone deacetylase inhibition and adipogenesis inhibition were examined. After oral and intravenous administration, gnetol was detected in both serum and urine as the parent compound and as a glucuronidated metabolite. The bioavailability of gnetol was determined to be 6%. Gnetol is rapidly glucuronidated and is excreted in urine and via nonrenal routes. Gnetol was found to exist as an aglycone and as a glycoside in G. gnemon products. Gnetol showed concentration‐dependent reductions in cell viability in cancer cell lines with greatest activity in colorectal cancer and potent COX‐1, histone deacetylase, and weak COX‐2 activities along with limited reduction in inflammation. Gnetol also possessed concentration‐dependent alpha‐amylase, alpha‐glucosidase, and adipogenesis activities. Pretreatment of mice with gnetol was able to increase the latency period to response in analgesia models. Copyright

Pharmacometrics of 3-methoxypterostilbene: a component of traditional chinese medicinal plants.

3-Methoxypterostilbene is a naturally occurring stilbene with potential in the treatment of diabetes. The preclinical pharmacokinetics and pharmacodynamics of 3-methoxypterostilbene were evaluated in the present study. The right jugular veins of male Sprague-Dawley rats were cannulated. The rats were dosed 10 mg/kg or 100 mg/kg of 3-methoxypterostilbene intravenously (IV) or orally (PO), respectively. Serum and urine samples were analyzed using a previously validated reversed-phase HPLC method. Serum AUC, serum t 1/2, urine t 1/2, Cltotal, and Vd for IV dosing were 48.1 ± 23.8 μg/h/mL, 18.9 ± 10.9 h, 9.54 ± 1.51 h, 47.8 ± 23.7 L/h/kg, and 5.11 ± 0.38 L/kg, respectively (mean ± SEM, n = 4) . Serum AUC, serum t 1/2, urine t 1/2, Cltotal, and Vd for PO dosing were 229 ± 44.6 μg/h/mL, 73.3 ± 8.91 h, 20.6 ± 3.01 h, 0.48 ± 0.008 L/h/kg, and 52.0 ± 10.5 L/kg, respectively (mean ± SEM, n = 4). Bioavailability of the stilbene was determined to be 50.6%  ± 10.0%. A 3-methoxypterostilbene glucuronidated metabolite was detected in both serum and urine. 3-Methoxypterostilbene exhibited antidiabetic activity including α-glucosidase and α-amylase inhibition as well as concentration-dependent antioxidant capacity similar to resveratrol. 3-Methoxypterostilbene also exhibited anti-inflammatory activity. 3-Methoxypterostilbene appears to be a bioactive compound and may be useful in reducing postprandial hyperglycemia.

Stereospecific analytical method development and preliminary in vivo pharmacokinetic characterization of pinostrobin in the rat.

The complete pharmacokinetic disposition of the chiral flavonoid (±) pinostrobin remains unknown without the development of an analytical method of detection and quantitation of its individual enantiomers. Resolution of the enantiomers of pinostrobin was achieved using as simple high-performance liquid chromatographic method. A Chiralpak(®) AD-RH column was employed to perform baseline separation with UV detection at 287 nm. The standard curves were linear ranging from 0.5 to 100 µg/mL for each enantiomer. The limit of quantification was 0.5 µg/mL. Precision and accuracy of the assay was < 15% (RSD) and was with a bias <15% for all points on the calibration curve. The assay was applied successfully to stereoselective serum disposition of pinostrobin enantiomers in rats. Both enantiomers had a serum half-life of ~7 h. They also shared similar values of volume of distribution (V(d) S-pinostrobin, 8.2 L/kg; V(d) R-pinostrobin, 8.9 L/kg), total clearance (S-pinostrobin CL(total), 0.959 L//h/kg; R-pinostrobin CL(total), 1.055 L//h/kg), and area under the curve (S-pinostrobin AUC(inf), 23.16 µg h/mL; R-pinostrobin AUC(inf), 21.296 µg h/mL). The large volume of distribution suggests extensive distribution of pinostrobin into tissues.