Increase In Plasma AUC Research Articles

Brain targeted lactoferrin coated lipid nanocapsules for the combined effects of apocynin and lavender essential oil in PTZ induced seizures.

Apocynin (APO) is a plant derived antioxidant exerting specific NADPH oxidase inhibitory action substantiating its neuroprotective effects in various CNS disorders, including epilepsy. Due to rapid elimination and poor bioavailability, treatment with APO is challenging. Correspondingly, novel APO-loaded lipid nanocapsules (APO-LNC) were formulated and coated with lactoferrin (LF-APO-LNC) to improve br ain targetability and prolong residence time. Lavender oil (LAV) was incorporated into LNC as a bioactive ingredient to act synergistically with APO in alleviating pentylenetetrazol (PTZ)-induced seizures. The optimized LF-APO-LAV/LNC showed a particle size 59.7 ± 4.5 nm with narrow distribution and 6.07 ± 1.6mV zeta potential) with high entrapment efficiency 92 ± 2.4% and sustained release (35% in 72 h). Following subcutaneous administration, LF-APO-LAV/LNC brought about ⁓twofold increase in plasma AUC and MRT compared to APO. A Log BB value of 0.2 ± 0.14 at 90 min reflects increased brain accumulation. In a PTZ-induced seizures rat model, LF-APO-LAV/LNC showed a Modified Racine score of 0.67 ± 0.47 with a significant increase in seizures latency and decrease in duration. Moreover, oxidant/antioxidant capacity and inflammatory markers levels in brain tissue were significantly improved. Histopathological and immunohistochemical assessment of brain tissue sections further supported these findings. The results suggest APO/LAV combination in LF-coated LNC as a promising approach to counteract seizures.

Overcoming drug resistance with a docetaxel and disulfiram loaded pH-sensitive nanoparticle.

Previous studies have demonstrated that breast cancer cells deploy a myriad array of strategies to thwart the activity of anticancer drugs like docetaxel (DTX), including acquired drug resistance due to overexpression of drug-efflux pumps like P-glycoprotein (P-gp) and innate drug resistance by cancer stem cells (CSCs). As disulfiram (DSF) can inhibit both P-gp and CSCs, we hypothesized that co-treatment of DTX and DSF could sensitize the drug-resistant breast cancer cells. To deliver a fixed dose ratio of DTX and DSF targeted to the tumor, a tumor extracellular pH-responsive nanoparticle (NP) was developed using a histidine-conjugated star-shaped PLGA with TPGS surface decoration ([DD]NpH-T). By releasing the encapsulated drugs in the tumor microenvironment, pH-sensitive NPs can overcome the tumor stroma-based resistance against nanomedicines. In in-vitro studies, [DD]NpH-T exhibited increased drug release at pH 6.4, improved penetration in a 3D tumor spheroid, reduced serum protein adsorption, and enhanced cytotoxic efficacy against both innate and acquired DTX-resistant breast cancer cells. In in-vivo studies, a significant increase in plasma AUC and tumor drug delivery was observed with [DD]NpH-T, which resulted in an enhanced in-vivo anti-tumor efficacy against a mouse orthotopic breast cancer, with a significantly increased intratumoral ROS and apoptosis, while decreasing P-gp expression and prevention of lung metastasis. Altogether, the current study demonstrated that the DTX and DSF combination could effectively target multiple drug-resistance pathways in-vitro, and the in-vivo delivery of this drug combination using TPGS-decorated pH-sensitive NPs could increase tumor accumulation, resulting in improved anti-tumor efficacy.

Age-Dependent Changes in the Plasma and Brain Pharmacokinetics of Amyloid-β Peptides and Insulin.

Age is the most common risk factor for Alzheimer's disease (AD), a neurodegenerative disorder characterized by the hallmarks of toxic amyloid-β (Aβ) plaques and hyperphosphorylated tau tangles. Moreover, sub-physiological brain insulin levels have emerged as a pathological manifestation of AD. Identify age-related changes in the plasma disposition and blood-brain barrier (BBB) trafficking of Aβ peptides and insulin in mice. Upon systemic injection of 125I-Aβ40, 125I-Aβ42, or 125I-insulin, the plasma pharmacokinetics and brain influx were assessed in wild-type (WT) or AD transgenic (APP/PS1) mice at various ages. Additionally, publicly available single-cell RNA-Seq data [GSE129788] was employed to investigate pathways regulating BBB transport in WT mice at different ages. The brain influx of 125I-Aβ40, estimated as the permeability-surface area product, decreased with age, accompanied by an increase in plasma AUC. In contrast, the brain influx of 125I-Aβ42 increased with age, accompanied by a decrease in plasma AUC. The age-dependent changes observed in WT mice were accelerated in APP/PS1 mice. As seen with 125I-Aβ40, the brain influx of 125I-insulin decreased with age in WT mice, accompanied by an increase in plasma AUC. This finding was further supported by dynamic single-photon emission computed tomography (SPECT/CT) imaging studies. RAGE and PI3K/AKT signaling pathways at the BBB, which are implicated in Aβ and insulin transcytosis, respectively, were upregulated with age in WT mice, indicating BBB insulin resistance. Aging differentially affects the plasma pharmacokinetics and brain influx of Aβ isoforms and insulin in a manner that could potentially augment AD risk.

A multiplex HRMS assay for quantifying selected human plasma bile acids as candidate OATP biomarkers.

Selected bile acids (BAs) in plasma have been proposed as endogenous probes for assessing drug-drug interactions involving hepatic drug transporters such as the organic anion-transporting polypeptides (OATP1B1 and OATP1B3). Plasma extracts were analyzed for selected BAs using a triple TOF API6600 high-resolution mass spectrometer. Glycodeoxycholic acid 3-sulfate, glycochenodeoxycholic acid 3-sulfate, glycodeoxycholic acid 3-O-β-glucuronide and glycochenodeoxycholic acid 3-O-β-glucuronide are presented as potential OATP1B1/3 biomarkers. Six BAs are quantified in human plasma using a multiplexed high-resolution mass spectrometry method. Glycodeoxycholic acid 3-sulfate and glycodeoxycholic acid 3-O-β-glucuronide are proposed as potential biomarkers based on observed four- to fivefold increase in plasma AUC (vs placebo), following administration of a compound known to present as an OATP1B1/3 inhibitor in vitro.

Development and optimization of an injectable formulation of copper diethyldithiocarbamate, an active anticancer agent.

Copper diethyldithiocarbamate (Cu(DDC)2) is the active anticancer agent generated when disulfiram (DSF) is provided in the presence of copper. To date, research directed toward repurposing DSF as an anticancer drug has focused on administration of DSF and copper in combination, efforts that have proven unsuccessful in clinical trials. This is likely due to the inability to form Cu(DDC)2 at relevant concentrations in regions of tumor growth. Little effort has been directed toward the development of Cu(DDC)2 because of the inherent aqueous insolubility of the complex. Here, we describe an injectable Cu(DDC)2 formulation prepared through a method that involves synthesis of Cu(DDC)2 inside the aqueous core of liposomes. Convection-enhanced delivery of a Cu(DDC)2 formulation prepared using 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/cholesterol liposomes into a rat model of F98 glioma engendered a 25% increase in median survival time relative to vehicle-treated animals. In a murine subcutaneous MV-4–11 model, treatment resulted in a 45% reduction in tumor burden when compared to controls. Pharmacokinetic studies indicated that the Cu(DDC)2 was rapidly eliminated after intravenous administration while the liposomes remained in circulation. To test whether liposomal lipid composition could increase Cu(DDC)2 circulation lifetime, a number of different formulations were evaluated. Studies demonstrated that liposomes composed of DSPC and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-n-(carboxy[polyethylene glycol]-2000) (95:5) enhanced Cu(DDC)2 concentrations in the circulation as reflected by a 4.2-fold increase in plasma AUC(0−∞) relative to the DSPC/cholesterol formulation. The anticancer activity of this Cu(DDC)2 formulation was subsequently evaluated in the MV-4–11 model. At its maximum tolerated dose, this formulation exhibited comparable activity to the DSPC/cholesterol formulation. This is the first report demonstrating the therapeutic effects of an injectable Cu(DDC)2 formulation in vivo.

Observation of Clinically Relevant Drug Interaction in Chimeric Mice with Humanized Livers: The Case of Valproic Acid and Carbapenem Antibiotics.

Human in vitro and dog in vitro/in vivo researches indicate that the drug-drug interaction (DDI) of decreased plasma valproic acid (VPA) concentration by co-administration of carbapenem antibiotics is caused by inhibition of acylpeptide hydrolase (APEH)-mediated VPA acylglucuronide (VPA-G) hydrolysis by carbapenems. In this study, we investigated VPA disposition and APEH activities in TK-NOG chimeric mice, whose livers were highly replaced with human hepatocytes, to evaluate the utility of this animal model and the clinical relevance of the DDI mechanism. VPA and VPA-G concentrations in plasma, urinary excretion of VPA-G and APEH activity in humanized livers were measured after co-administration of VPA with meropenem (MEPM) to chimeric mice. After co-administration with MEPM to the chimeric mice, plasma VPA concentration more rapidly decreased than without the co-administration. An increase in plasma AUC and urinary excretion of VPA-G was also observed. APEH activity in humanized livers was strongly inhibited even at 24h after co-administration of MEPM to the chimeric mice. The DDI of VPA with carbapenems was successfully observed in chimeric mice with humanized livers. The DDI was caused by long-lasting inhibition of hepatic APEH-mediated VPA-G hydrolysis by carbapenems, which strongly supports the APEH-mediated mechanism of the clinical DDI. This is the first example showing the usefulness of chimeric mice with humanized livers for evaluation of a DDI via non-cytochrome P450 enzyme.

Leveraging of Rifampicin-Dosed Cynomolgus Monkeys to Identify Bile Acid 3-O-Sulfate Conjugates as Potential Novel Biomarkers for Organic Anion-Transporting Polypeptides.

In the search for novel bile acid (BA) biomarkers of liver organic anion-transporting polypeptides (OATPs), cynomolgus monkeys received oral rifampicin (RIF) at four dose levels (1, 3, 10, and 30 mg/kg) that generated plasma-free Cmax values (0.06, 0.66, 2.57, and 7.79 µM, respectively) spanning the reported in vitro IC50 values for OATP1B1 and OATP1B3 (≤1.7 μM). As expected, the area under the plasma concentration-time curve (AUC) of an OATP probe drug (i.v. 2H4-pitavastatin, 0.2 mg/kg) was increased 1.2-, 2.4-, 3.8-, and 4.5-fold, respectively. Plasma of RIF-dosed cynomolgus monkeys was subjected to a liquid chromatography-tandem mass spectrometry method that supported the analysis of 30 different BAs. Monkey urine was profiled, and we also determined that the impact of RIF on BA renal clearance was minimal. Although sulfated BAs comprised only 1% of the plasma BA pool, a robust RIF dose response (maximal ≥50-fold increase in plasma AUC) was observed for the sulfates of five BAs [glycodeoxycholate (GDCA-S), glycochenodeoxycholate (GCDCA-S), taurochenodeoxycholate, deoxycholate (DCA-S), and taurodeoxycholate (TDCA-S)]. In vitro, RIF (≤100 μM) did not inhibit cynomolgus monkey liver cytosol-catalyzed BA sulfation and cynomolgus monkey hepatocyte-mediated uptake of representative sulfated BAs (GDCA-S, GCDCA-S, DCA-S, and TDCA-S) was sodium-independent and inhibited (≥70%) by RIF (5 μM); uptake of taurocholic acid was sensitive to sodium removal (74% decrease) and relatively refractory to RIF (≤21% inhibition). We concluded that sulfated BAs may serve as sensitive biomarkers of cynomolgus monkey OATPs and that exploration of their utility as circulating human OATP biomarkers is warranted.

Weekly MLN9708, an investigational oral proteasome inhibitor (PI), in relapsed/refractory multiple myeloma (MM): Results from a phase I study after full enrollment.

8514 Background: MLN9708 is an investigational, orally bioavailable, potent, reversible, specific inhibitor of the 20S proteasome that has demonstrated antitumor activity in in vivo models of MM. We report safety, activity and pharmacokinetics (PK) of weekly oral MLN9708 in a phase 1 trial in patients (pts) with relapsed and/or refractory MM after full enrollment (NCT00963820). Methods: Pts received MLN9708 (days 1, 8, 15; 28-day cycles) at 0.24–3.95 mg/m2 (dose-escalation phase) and at the MTD, 2.97 mg/m2, in relapsed and refractory (RR), bortezomib (btz)-relapsed, PI-naïve, and prior carfilzomib (CZ) expansion cohorts. Adverse events (AEs) were graded by NCI-CTCAE v3.0. Response was assessed by IMWG uniform criteria. Results: 60 pts (33 male, median age 64 yrs [40–79]) were enrolled, 32 in the dose-escalation phase and 31 to the expansion cohorts (11 RR, 10 btz-relapsed, 6 PI-naïve, 4 CZ; 2 RR and 1 btz-relapsed pts included from MTD dose-escalation cohort). Median time from MM diagnosis was 4.9 yrs (1.5–18.8). Median number of prior regimens was 6 (2–18), including btz, lenalidomide, thalidomide, and CZ in 83%, 95%, 52%, and 13%, respectively; 76% were refractory to last therapy (17% btz-refractory). At data cut-off (Nov 29, 2012) pts had received a median of 2 cycles (1–11); 5 pts remained on treatment. All-grade/grade ≥3 drug-related AEs were seen in 83%/52% of pts; common drug-related grade ≥3 AEs were thrombocytopenia (33%), diarrhea, neutropenia (17%), decreased appetite, fatigue, and lymphopenia (8%). 6 pts (10%) had drug-related PN (no grade ≥3). 5 pts discontinued due to drug-related AEs; 1 pt died on study due to an unrelated AE. By investigator assessment in 41 evaluable pts, responses included1 VGPR, 5 PR, 1 MR, and 15 with SD. MLN9708 was rapidly absorbed, with a terminal half-life of 4–12 days (supporting weekly dosing) and a proportional increase in plasma AUC with dose (0.8–3.95 mg/m2). PK data were similar across expansion cohorts. Conclusions: Current data suggest weekly oral MLN9708 is generally well tolerated with infrequent PN, and shows activity in this heavily pretreated population with prior exposure to immunomodulatory drugs and btz. Clinical trial information: NCT00963820.

PVP and surfactant combined carrier as an effective absorption enhancer of poorly soluble astilbin in vitro and in vivo

Context: Astilbin is considered to be a new and promising immunosuppressant for immune related diseases, but limited in clinical application due to its poor water solubility, difficult oral absorption and low bioavailability.Objective: The present work studied the effect of PVP and surfactant combined carrier on its capability to improve drug absorption.Materials and methods: PVP K30-Tween 80 combined carries was applied into the astilbin solid dispersions, tested both in vivo in beagle dogs and in vitro in transport experiments across Caco-2 cell monolayers.Results and discussion: In the animal studies a many fold increase in plasma AUC was observed for the solid dispersions of drug in PVP K30-Tween 80 combined carries compared to active pharmaceutical ingredient (API). The applicability of Caco-2 monolayers as a tool for predicting the in vivo transport behavior of Astilbin in combination with a solubility enhancing carries was shown. In vitro transport studies confirmed the effect of combined carries on the absorption behavior of the astilbin. MTT studies showed the cell viability gradually decreased with the increase of the drug concentration in a dose dependent manner for astilbin and that in solid dispersions. The permeability and apparent permeability coefficients (Papp) increased with drug in the Caco-2 cell.Conclusion: In this study, it was found that PVP K30 and Tween 80 promoted the permeability of drugs best within a certain amount. For astilbin PVP K30 and surfactant combined carrier had a strong potential to improve oral bioavailability.

Intensified regimen containing rifampicin and moxifloxacin for tuberculous meningitis: an open-label, randomised controlled phase 2 trial

Intensified antibiotic treatment might improve the outcome of tuberculous meningitis. We assessed pharmacokinetics, safety, and survival benefit of several treatment regimens containing high-dose rifampicin and moxifloxacin in patients with tuberculous meningitis in a hospital setting. In an open-label, phase 2 trial with a factorial design in one hospital in Indonesia, patients (aged >14 years) with tuberculous meningitis were randomly assigned to receive, according to a computer-generated schedule, first rifampicin standard dose (450 mg, about 10 mg/kg) orally or high dose (600 mg, about 13 mg/kg) intravenously, and second oral moxifloxacin 400 mg, moxifloxacin 800 mg, or ethambutol 750 mg once daily. All patients were given standard-dose isoniazid, pyrazinamide, and adjunctive corticosteroids. After 14 days of treatment all patients continued with standard treatment for tuberculosis. Endpoints included pharmacokinetic analyses of the blood and cerebrospinal fluid, adverse events attributable to tuberculosis treatment, and survival. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT01158755. 60 patients were randomly assigned to receive rifampicin standard dose (12 no moxifloxacin, ten moxifloxacin 400 mg, and nine moxifloxacin 800 mg) and high dose (ten no moxifloxacin, nine moxifloxacin 400 mg, and ten moxifloxacin 800 mg). A 33% higher dose of rifampicin, intravenously, led to a three times higher geometric mean area under the time-concentration curve up to 6 h after dose (AUC(0-6); 78·7 mg.h/L [95% CI 71·0-87·3] vs 26·0 mg.h/L [19·0-35·6]), maximum plasma concentrations (C(max); 22·1 mg/L [19·9-24·6] vs 6·3 mg/L [4·9-8·3]), and concentrations in cerebrospinal fluid (0·60 mg/L [0·46-0·78] vs 0·21 mg/L [0·16-0·27]). Doubling the dose of moxifloxacin resulted in a proportional increase in plasma AUC(0-6) (31·5 mg.h/L [24·1-41·1] vs 15·1 mg.h/L [12·8-17·7]), C(max) (7·4 mg/L [5·6-9·6] vs 3·9 mg/L [3·2-4·8]), and drug concentrations in the cerebrospinal fluid (2·43 mg/L [1·81-3·27] vs 1·52 mg/L [1·28-1·82]). Intensified treatment did not result in increased toxicity. 6 month mortality was substantially lower in patients given high-dose rifampicin intravenously (ten [35%] vs 20 [65%]), which could not be explained by HIV status or severity of disease at the time of presentation (adjusted HR 0·42; 95% CI 0·20-0·91; p=0·03). These data suggest that treatment containing a higher dose of rifampicin and standard-dose or high-dose moxifloxacin during the first 2 weeks is safe in patients with tuberculous meningitis, and that high-dose intravenous rifampicin could be associated with a survival benefit in patients with severe disease. Royal Dutch Academy of Arts and Sciences, Netherlands Foundation for Scientific Research, and Padjadjaran University, Bandung, Indonesia.

Soluplus® as an effective absorption enhancer of poorly soluble drugs in vitro and in vivo

As many new active pharmaceutical ingredients are poorly water soluble, solubility enhancers are one possibility to overcome the hurdles of drug dissolution and absorption in oral drug delivery. In the present work a novel solubility enhancing excipient (Soluplus®) was tested for its capability to improve intestinal drug absorption. BCS class II compounds danazol, fenofibrate and itraconazole were tested both in vivo in beagle dogs and in vitro in transport experiments across Caco-2 cell monolayers. Each drug was applied as pure crystalline substance, in a physical mixture with Soluplus®, and as solid solution of the drug in the excipient. In the animal studies a many fold increase in plasma AUC was observed for the solid solutions of drug in Soluplus® compared to the respective pure drug. An effect of Soluplus® in a physical mixture with the drug could be detected for fenofibrate. In vitro transport studies confirm the strong effect of Soluplus® on the absorption behavior of the three tested drugs. Furthermore, the increase of drug flux across Caco-2 monolayer is correlating to the increase in plasma AUC and C max in vivo. For these poorly soluble substances Soluplus® has a strong potential to improve oral bioavailability. The applicability of Caco-2 monolayers as tool for predicting the in vivo transport behavior of the model drugs in combination with a solubility enhancing excipient was shown. Also the improvement of a solid dispersion compared to physical mixtures of the drugs and the excipient was correctly reflected by Caco-2 experiments. In the case of fenofibrate the possible improvement by a physical mixture was demonstrated, underscoring the value of the used tool as alternative to animal studies.

Substantiating in vivo magnetic brain tumor targeting of cationic iron oxide nanocarriers via adsorptive surface masking

Cationic magnetic nanoparticles are attractive as potential vehicles for tumor drug delivery due to their favorable interactions with both the tumor milieu and the therapeutic cargo. However, systemic delivery of these nanoparticles to the tumor site is compromised by their rapid plasma clearance. We developed a simple method for in vivo protection of cationic nanocarriers, using non-covalent surface masking with a conjugate of low molecular weight heparin and polyethylene glycol. Surface masking resulted in a 11-fold increase in plasma AUC and a 2-fold increase in the magnetic capture of systemically injected nanoparticles in orthotopic rodent brain tumors. Overall, the described methodology could expand the prospective applications for cationic magnetic nanoparticles in magnetically mediated gene/drug delivery.

A First-in-Man Phase I and Pharmacokinetic Study on CHR-2797 (Tosedostat), an Inhibitor of M1 Aminopeptidases, in Patients with Advanced Solid Tumors

To determine the maximum tolerated dose, dose-limiting toxicity, pharmacokinetics, and preliminary therapeutic activity profile of CHR-2797 (tosedostat), a novel, orally bioavailable inhibitor of the M1 family of aminopeptidases with antiproliferative and antiangiogenic activity in vitro. A phase I study of accelerated titration design that escalated through nine doses (10-320 mg) in patients (Eastern Cooperative Oncology Group performance status, < or =2) with advanced solid tumors. CHR-2797 was administered once daily. Forty patients (median age, 60 years; range, 24-80 years; male, 27; female, 13) were treated in 12 cohorts with once daily doses (10-320 mg). Dose-limiting toxicities were thrombocytopenia, dizziness, and visual abnormalities in one patient, and anemia, blurred vision, and vomiting in a second patient at 320 mg, resulting in an inability to complete 28 days of study drug. The most commonly observed toxicities were fatigue, diarrhea, peripheral edema, nausea, dizziness, and constipation. One patient had a partial response (renal cell carcinoma) and four patients had stable disease for >6 months. CHR-2797 and its active metabolite, CHR-79888, show dose-proportional increases in plasma AUC and C(max). The terminal half-life for CHR-2797 is approximately 1 to 3.5 hours and between 6 and 11 hours for CHR-79888. Intracellular (packed blood cells) exposure to CHR-79888 is consistent with intracellular levels that proved to be efficacious in xenograft models. CHR-2797 is well tolerated and can be safely administered at doses that result in intracellular levels of CHR-79888 that are associated with activity in preclinical models. The recommended dose for single agent therapy in solid tumors is 240 mg/d.

Investigation of the Inhibitory Effects of Various Drugs on the Hepatic Uptake of Fexofenadine in Humans

Fexofenadine (FEX), an H(1)-receptor antagonist, is eliminated from the liver mainly in an unchanged form. Our previous study suggested that organic anion-transporting polypeptide (OATP) 1B3 contributes mainly to the hepatic uptake of FEX. On the other hand, a clinical report demonstrated that a T521C mutation of OATP1B1 increased its plasma area under the plasma concentration-time curve. Several compounds are reported to have a drug interaction with FEX, and some of this may be caused by the inhibition of its hepatic uptake. We determined which transporters are involved in the hepatobiliary transport of FEX by using double transfectants and examined whether clinically reported drug interactions with FEX could be explained by the inhibition of its hepatic uptake. Vectorial basal-to-apical transport of FEX was observed in double transfectants expressing OATP1B1/multidrug resistance-associated protein 2 (MRP2) and OATP1B3/MRP2, suggesting that OATP1B1 as well as OATP1B3 is involved in the hepatic uptake of FEX and that MRP2 can recognize FEX as a substrate. The inhibitory effects of compounds on FEX uptake in OATP1B3-expressing HEK293 cells were investigated, and the maximal degree of increase in plasma AUC of FEX by drug interaction in clinical situations was estimated. As a result, cyclosporin A and rifampicin were found to have the potential to interact with OATP1B3-mediated uptake at clinical concentrations. From these results, most of the reported drug interaction cannot be explained by the inhibition of hepatic uptake of FEX, and different mechanisms such as the inhibition of intestinal efflux should be considered.

Pharmacokinetics of Amiodarone in hyperlipidemic and simulated high fat‐meal rat models

The objective of this study was to examine the effect of a high fat meal and hyperlipidemia on the pharmacokinetic behavior of amiodarone. To evaluate these effects, single doses of amiodarone were administered to rats i.v. (25 mg/kg) or orally (50 mg/kg). Some rats were rendered hyperlipidemic by intraperitoneal doses of poloxamer 407 followed by amiodarone i.v. In other normolipidemic rats, amiodarone was administered i.v. in a fasted state or after the administration of 1% cholesterol in peanut oil. Amiodarone plasma concentrations were considerably (>11-fold) increased in hyperlipidemia. Substantial decreases were noted in the clearance, volume of distribution and unbound fraction (11.6, 23 and 24.7-fold, respectively) in plasma of hyperlipidemic rats. Oral lipid caused a significant increase in plasma AUC(0-infinity) (1.38-fold) and a significant decrease in clearance (1.5-fold) of amiodarone after intravenous doses. Oral consumption of 1% cholesterol in peanut oil significantly increased the plasma AUC (1.83-fold) and bioavailability of amiodarone (1.31-fold) after oral doses. In determining oral bioavailability of lipophilic drugs such as amiodarone in food effect studies, in addition to the increase in absorption of drugs, other factors such as a decrease in clearance due to increases in lipoprotein levels should be taken into account.

In-vitro metabolism of celecoxib, a cyclooxygenase-2 inhibitor, by allelic variant forms of human liver microsomal cytochrome P450 2C9: correlation with CYP2C9 genotype and in-vivo pharmacokinetics.

In-vitro studies were conducted to assess the impact of CYP2C9 genotype on the metabolism (methyl hydroxylation) and pharmacokinetics of celecoxib, a novel cyclooxygenase-2 inhibitor and CYP2C9 substrate. When compared to cDNA-expressed wild-type CYP2C9 (CYP2C9*1), the Vmax/Km ratio for celecoxib methyl hydroxylation was reduced by 34% and 90% in the presence of recombinant CYP2C9*2 and CYP2C9*3, respectively. These data indicated that the amino acid substitution at position 359 (Ile to Leu) elicited a more pronounced effect on the metabolism of celecoxib than did a substitution at position 144 (Arg to Cys). The Vmax/Km ratio was also decreased in microsomes of livers genotyped CYP2C9*1/*2 (47% decrease, mean of two livers), or CYP2C9*1/*3 (59% decrease, one liver). In all cases, these changes were largely reflective of a decrease in Vmax, with a minimal change in Km. Based on simulations of the in-vitro data obtained with the recombinant CYP2C9 proteins, it was anticipated that the pharmacokinetics of celecoxib (as a much as a five-fold increase in plasma AUC) would be altered (versus CYP2C9*1/*1 subjects) in subjects genotyped heterozygous or homozygous for the CYP2C9*2 (Cys144) or CYP2C9*3 (Leu359) allele. In a subsequent clinical study, the AUC of celecoxib was increased (versus CYP2C9*1/*1 subjects) approximately 2.2-fold (range, 1.6-3-fold) in two CYP2C9*1/*3 subjects and one CYP2C9*3/*3 subject receiving a single oral dose (200 mg) of the drug. In contrast, there was no significant change in celecoxib AUC in two subjects genotyped CYP2C9*1/*2.

Pharmacokinetic interactions of Mentat with carbamazepine and phenytoin.

In the present study, Mentat, a herbomineral psychotropic preparation, was studied for its pharmacokinetic interaction with the commonly used anti-epileptic drugs, carbamazepine and phenytoin. The interaction of carbamazepine and phenytoin with Mentat was studied in rabbits. Thirty two rabbits were divided into four groups of eight each. Animals of Group I were treated with carbamazepine (50 mg/kg b.wt. p.o.), Group II were treated with carbamazepine (50 mg/kg b.wt. p.o.) + Mentat (500 mg/kg b.wt. p.o.), Group III were treated with phenytoin (50 mg/kg b.wt. p.o.) and Group IV were treated with phenytoin (50 mg/kg b.wt. p.o.) + Mentat (500 mg/kg b.wt. p.o.) for a period of 8 days. On day 0 and day 8, plasma carbamazepine and phenytoin levels were estimated at different time intervals. A simultaneous treatment with Mentat resulted in a significant increase in plasma AUC of carbamazepine as well as phenytoin as compared to carbamazepine or phenytoin alone. Cmax and Tmax of carbamazepine and phenytoin also were evaluated. The results suggest that co-administration of Mentat could improve the effectiveness of anti-epileptic drugs due to the increased bioavailability of the latter. However, this has to be done with critical medical supervision to avoid any toxic reactions and preferably with therapeutic drug monitoring (TDM) which could also help in dose optimization.

Blood and plasma lipoprotein distribution and gender differences in the plasma pharmacokinetics of lipid-associated annamycin.

The objectives of this study were to determine the lipoprotein distribution of unbound annamycin and liposomal annamycin within human and rabbit blood and plasma and to evaluate the plasma pharmacokinetics of liposomal annamycin in male and female rabbits following a single intravenous bolus of the compound. Annamycin and liposomal annamycin were incubated in human and rabbit blood and plasma for 60 min. at 37 degrees C. Following incubation blood and plasma samples were assayed by HPLC for drug in each of the lipoprotein and lipoprotein-deficient plasma fractions. To evaluate the plasma pharmacokinetics of liposomal annamycin in male versus female rabbits, a single intravenous bolus dose (5 mg/kg) of liposomal annamycin was administered to male and female rabbits. Sequential blood samples were obtained from the animals following the dose, analyzed for drug, and the pharmacokinetics determined using multicompartmental methods. The incorporation of annamycin into liposomes composed of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol resulted in no significant differences in blood versus plasma lipoprotein drug distribution. Furthermore, no differences in the plasma distribution of liposomal annamycin were observed when the drug was either incubated in vitro for 1 hr or 1 hr following intravenous administration into New Zealand male white rabbits. The plasma clearance and volume of distribution of liposomal annamycin were decreased and a increase in plasma AUC in female as compared to male rabbits following a single intravenous bolus of liposomal annamycin was observed. These findings suggest that the lipoprotein distribution of liposomal annamycin is not different when incubated in blood or plasma and that in vitro liposomal annamycin plasma distribution is similar to in vivo. Furthermore, it appears that the pharmacokinetics of liposomal annamycin are different following administration to male versus female rabbits.

Pulmonary bioavailability of leuprolide acetate following multiple dosing to beagle dogs: some pharmacokinetic and preclinical issues

Localized delivery of drugs to the lung has long been known as an effective and rapid modality for treating various pulmonary diseases. Because of its large surface area, the lung serves also as a port of drug entry to the systemic circulation. However, lung deposition of pharmaceutical aerosols is generally less than 100% of the nominal dose. This is due largely to complex biophysical factors associated with filtration mechanisms of the respiratory system (Byron et al, Pharm. Res., 3 (1989) 225–229) and patient factors. The incomplete absorption of pharmaceutical aerosols in the lung may be due in part to mechanical losses of drug during drug administration. For example, some drug is retained usually on the mouth adapter (actuator) of the inhaler during use, and often there is significant loss in the throat as a result of inertial impaction (Ganderton and Jones, Drug Delivery to the Respiratory Tract, Ellis Horwood, 1987; Byron et al., Pharm. Res., 3 (1989) 225–229). Inefficient delivery of drugs to the airways may be the single largest cause for low drug absorption via lung. For peptides, physicochemical characteristics of the drug, stability to metabolizing enzymes, molecular weight, permeability to lung mucosa, and stimulation of the alveolar macrophage clearance mechanism (Forrest, In Morén et al. (Eds), Aerosols in Medicine, Principles, Diagnostics and Therapy, Elsevier, 1985) may be more significant in decreasing the efficiency of absorption from the airways. In a previous study (Adjei et al., Int. J. Pharm., 61 (1990) 135–144), male and female beagle dogs were administered an inhalation solution aerosol formulation of leuprolide acetate at daily dosages of 0, 0.5, 1, and 2 mg for 14 consecutive days. The results demonstrated: (a) significant plasma levels following administration of leuprolide to the lung compared to a placebo aerosol formulation as control; (b) a linear dose-dependent increase in pulmonary bioavailability of leuprolide in the dose range of 0.5–2.0 mg/dog per day; (c) no significant differences in pulmonary absorption between male and female dogs; (d) a corresponding decrease in plasma gonadotropins with sequential increases in plasma leuprolide concentrations; and (e) approx. 50% lower bioavailability on day 14 compared with day 1 of the study. The present study clarifies phenomenologic and pharmacokinetic issues associated with lung delivery of leuprolide acetate. For this study, male and female beagle dogs were administered leuprolide using a suspension aerosol formulation instead of a cosolvent based solution aerosol formulation of the drug (Adjei et al., Int. J. Pharm., 61 (1990) 135–144). The results demonstrated: (a) linear dose-dependent increases in plasma AUC of leuprolide in the dose range of 1.5–9 mg/dog per day; (b) no change in bioavailability with multiple dosage of the aerosol up to 14 days; (c) no toxicologic findings over the 14 day dosing period; and (d) the no-toxic effect level of leuprolide was 9 mgJdog per day. This paper also attempts to explain differences between in vivo performance of the alcohol-based solution aerosol (Adjci et al., Int. J. Pharm., 61 (1990) 135–144) compared with a suspension aerosol formulation of the drug.

Inhibition of first-pass metabolism in cancer chemotherapy: interaction of 6-mercaptopurine and allopurinol.

Earlier studies suggested that the dose of 6-mercaptopurine (6-MP) can be reduced substantially when the drug is given with allopurinol. We studied the effect of allopurinol on the kinetics of oral and intravenous 6-MP. Studies conducted initially in rhesus monkeys and subsequently in man with 6-MP doses of 100 mg/m2 and 75 mg/m2, demonstrated that allopurinol pretreatment resulted in a nearly 400% increase in peak plasma concentration of oral 6-MP in monkeys (from a mean of 0.54 microM to a mean of 2.1 microM) and a 500% increase in man (0.74 microM to 3.7 microM). Allopurinol pretreatment also led to a 300% increase in plasma AUC in monkeys after oral 6-MP (from a mean of 121 microM/min to a mean of 391 microM/min) and a 500% increase in AUC in man (from a mean of 142 microM/min to a mean of 716 microM/min). In contrast, allopurinol pretreatment had no effect on the kinetics of intravenous 6-MP. This difference was found to be due to inhibition of first-pass metabolism of oral 6-MP as the result of the action of allopurinol on liver or intestinal xanthine oxidase. Our results indicate that, although dose reduction of oral 6-MP given in conjunction with allopurinol is appropriate, it is not necessary when 6-MP is injected intravenously.