[Principles of Bayesian statistics and its relationship with applied pharmacokinetics]. / Principios de estadística Bayesiana y su relación con la farmacocinética aplicada.

If one knows the probability of an event occurring in a population, Bayesian statistics allows mo difying its value when there is new individual information available. Although the Bayesian and frequentist (classical) methodologies have identical fields of application, the first one is increasin gly applied in scientific research and big data analysis. In modern pharmacotherapy, clinical phar macokinetics has been used for the expansion of monitoring, facilitated by technical-analytical and mathematical-statistical developments. Population pharmacokinetics has allowed the identification and quantification of pathophysiological and treatment characteristics in a specific patient popu lation, especially in the pediatric and neonatal population and other vulnerable groups, explaining interindividual variability. Likewise, Bayesian estimation is important as a statistical tool applied in pharmacotherapy optimization software when pharmacological monitoring is based on clinical phar macokinetic interpretation. With its advantages and despite its limitations, pharmacotherapeutic op timization based on Bayesian estimation is increasingly used, becoming the reference method today. This characteristic is particularly convenient for routine clinical practice due to the limited number of samples required from the patient and the flexibility it shows regarding blood sampling times for drug quantification. Therefore, the application of Bayesian principles to the practice of clinical phar macokinetics has led to the improvement of pharmacotherapeutic care.

Molecular Epidemiology of ALK Rearrangements in Advanced Lung Adenocarcinoma in Latin America.

OBJECTIVE: Latin American countries are heterogeneous in terms of lung cancer incidence and exposure to potential carcinogens. We evaluated the frequency and clinical characteristics of ALK rearrangements (ALKr) in Latin America. METHODS: A total of 5,130 lung cancer patients from 10 Latin American countries were screened for inclusion. ALKr detection was performed by fluorescence in situ hybridization (FISH), immunohistochemistry (IHC), and real-time reverse transcriptase-polymerase chain reaction (RT-PCR) to assess method variability. Demographic and clinicopathologic characteristics were analyzed. RESULTS: Among the 5,130 patients screened, 8.4% (n = 433) had nonevaluable FISH tests. Evaluable FISH analyses revealed positive ALKr in 6.8% (320/4,697) of the study population, which included patients from 9 countries. ALKr distribution for each country was: Mexico 7.6% (79/1,034), Colombia 4.1% (10/242), Argentina 6.0% (153/2,534), Costa Rica 9.5% (13/137), Panama 4.4% (5/114), Uruguay 5.4% (2/37), Chile 8.6% (16/185), Venezuela 8.9% (13/146), and Peru 10.8% (29/268). RT-PCR showed high positive (83.6%) and negative (99.7%) predictive values when compared to the gold standard FISH. In contrast, IHC only showed a high negative predictive value (94.6%). CONCLUSIONS: Although there is a clear country and continental variability in terms of ALKr frequency, this difference is not significant and the overall incidence of ALKr in Latin America does not differ from the rest of the world.

Twenty-One Novel EGFR Kinase Domain variants in Patients with Nonsmall Cell Lung Cancer.

Somatic sequence variants in the epidermal growth factor receptor (EGFR) kinase domain are associated with sensitivity to tyrosine kinase inhibitors (TKIs) in patients with nonsmall cell lung cancer (NSCLC). Patients exhibiting sequence variants in this domain that produce kinase activity enhancement, are more likely to benefit from TKIs than patients with EGFR wild-type disease. Although most NSCLC EGFR-related alleles are concentrated in a few positions, established protocols recommend sequencing EGFR exons 18-21. In this study, 21 novel somatic variants belonging to such exons in adult Argentinean patients affected with NSCLC are reported. Of these, 18 were single amino acid substitutions (SASs), occurring alone or in combination with another genetic alteration (complex cases), one was a short deletion, one was a short deletion-short insertion combination, and one was a duplication. New variants and different combinations of previously reported variants were also found. Moreover, two of the reported SASs occurred in previously unreported positions of the EGFR kinase domain. In order to characterize the new sequence variants, physicochemical, sequence and conformational analyses were also performed. A better understanding of sequence variants in NSCLC may facilitate the most appropriate treatment choice for this complex disease.

Effects of combinational CYP3A5 6986A>G polymorphism in graft liver and native intestine on the pharmacokinetics of tacrolimus in liver transplant patients: a meta-analysis.

BACKGROUND: Many studies have reported reduced tacrolimus dose-adjusted exposure in individuals expressing the CYP3A5*1 allele. A meta-analyses of the current data may help characterize the extent of impact this polymorphism has on tacrolimus pharmacokinetics in adult liver transplant recipients and whether donor or recipient genotype is the most influential factor. METHODS: Structured searches, of studies that evaluated the association between CYP3A5*1 allele and tacrolimus pharmacokinetics in adult liver transplant recipients, were conducted using Embase and Medline. A meta-analysis comparing tacrolimus daily dose, trough concentrations (C0), and dose-adjusted trough concentrations (C0/dose) across the donor and recipient genotype pairs was conducted using a random effects model. RESULTS: Eight studies, involving a total of 694 adult liver transplant recipients, were included. Dose-adjusted tacrolimus trough concentrations were significantly lower in those in whom the donor or recipient expressed a *1 allele compared with those in whom neither the donor nor recipient expressed this allele at 7 days and 2, 3, 6, and 12 months after transplant [standardized mean differences between expressers and nonexpressers of -1.98, -2.12, -2.39, -3.68, and -3.26 (ng/mL)/(mg·kg·d), respectively]. CONCLUSIONS: Results of the meta-analysis demonstrated that, in adult liver transplant patients, CYP3A5 expression in either the donor or recipient resulted in a need for a higher mean tacrolimus daily dose to achieve the target drug exposure. In the immediate posttransplant period, recipient expression of a CYP3A5*1 allele seemed to have the greatest influence on tacrolimus pharmacokinetics with donor expression of a CYP3A5*1 allelle possibly becoming more important with increasing time after transplant.

Ocular pharmacology of topotecan and its activity in retinoblastoma.

PURPOSE: To review the ocular pharmacology and antitumor activity of topotecan for the treatment of retinoblastoma by an evaluation of different routes of administration. METHODS: Systematic review of studies available at PubMed using the keywords retinoblastoma, topotecan, and camptothecins, including preclinical data such as cell lines and animal models, as well as clinical studies in patients with retinoblastoma. RESULTS: Forty-two available studies were reviewed. Evidence of antitumor activity against retinoblastoma as a single agent is based on data on cell lines and a limited number of affected patients with intraocular and extraocular disease when given in a protracted schedule. Evidence of additive or synergistic activity in combination with other agents such as carboplatin, melphalan, and vincristine was reported in preclinical and clinical models. In animal models, pharmacokinetic evaluation of topotecan administered by the periocular route shows that most of the drug reaches the vitreous through the systemic circulation. Topotecan administered by intravitreal injection shows high and sustained vitreal concentrations with limited systemic exposure and lack of retinal toxicity at a dose of up to 5 µg. Topotecan administered intraophthalmic artery shows higher passage to the vitreous compared with periocular administration in a swine model. CONCLUSION: Topotecan alone or in combination is active against retinoblastoma. It shows a favorable passage to the vitreous when given intravenously and intraarterially, and ocular toxicity is minimal by all routes of administration. However, its clinical role, optimal dose, and route of administration for the treatment of retinoblastoma are to be determined.

Ocular and systemic toxicity of intravitreal topotecan in rabbits for potential treatment of retinoblastoma.

Treatment of intraocular retinoblastoma with vitreous seeding is a challenge. Different routes of chemotherapy administration have been explored in order to attaining pharmacological concentrations into the posterior chamber. Intravitreal drug injection is a promissing route for maximum bioavailability to the vitreous but it requires a well defined dose for achieving tumor control while limited toxicity to the retina. Topotecan proved to be a promising agent for retinoblastoma treatment due to its pharmacological activity and limited toxicity. High and prolonged concentrations were achieved in the rabbit vitreous after 5 µg of intravitreal topotecan. However, whether a lower dose could achieve potentially therapeutic levels remained to be determined. Thus, we here study the pharmacokinetics of topotecan after 0.5 µg and the toxicity profile of intravitreal topotecan in the rabbit eye as a potential treatment of retinoblastoma. A cohort of rabbits was used to study topotecan disposition in the vitreous after a single dose of 0.5 µg of intravitreal topotecan. In addition, an independent cohort of non-tumor bearing rabbits was employed to evaluate the clinical and retinal toxicity after four weekly injections of two different doses of intravitreal topotecan (Group A, 5 µg/dose; Group B, 0.5 µg/dose) to the right eye of each animal. The same volume (0.1 ml) of normal saline was administered to the left eye as control. A third group of rabbits (Group C) served as double control (both eyes injected with normal saline). Animals were weekly evaluated for clinical and hematologic values and ocular evaluations were performed with an inverse ophthalmoscope to establish potential topotecan toxicity. Weekly controls included topotecan quantitation in plasma of all rabbits. Electroretinograms (ERGs) were recorded before and after topotecan doses. One week after the last injection, topotecan concentrations were measured in vitreous of all eyes and samples for retinal histology were obtained. Our results indicate that topotecan shows non linear pharmacokinetics after a single intravitreal dose in the range of 0.5-5 µg in the rabbit. Vitreous concentration of lactone topotecan was close to the concentration assumed to be therapeutically active after 5 h of 0.5 µg intravitreal administration. Eyes injected with four weekly doses of topotecan (0.5 or 5 µg/dose) showed no significant differences in their ERG wave amplitudes and implicit times in comparison with control (p > 0.05). Animals showed no weight, hair loss or significant changes in hematologic values during the study period. There were no significant histologic damage of the retinas exposed to topotecan treatments. After intravitreal administration no topotecan could be detected in plasma during the follow-up period nor in the vitreous of treated and control animals after 1 week of the last injection. The present data shows that four weekly intravitreal injection of 5 µg of topotecan is safe for the rabbit eye. Despite multiple injections of 0.5 µg of topotecan are also safe to the rabbit eye, lactone topotecan vitreous concentrations were potentially active only after 5 h of the administration. We postulate promising translation to clinics for retinoblastoma treatment.

Pharmacokinetic analysis of topotecan after superselective ophthalmic artery infusion and periocular administration in a porcine model.

PURPOSE: To characterize the vitreous and plasma pharmacokinetics of topotecan after ophthalmic artery infusion (OAI) subsequent to superselective artery catheterization and to compare it with periocular injection (POI). METHODS: The ophthalmic artery of 4 pigs was catheterized and 1 mg of topotecan infused over a period of 30 minutes. The contralateral eye was subsequently used for administering topotecan by POI. Serial vitreous specimens were obtained by microdialysis and plasma samples collected and assayed for total and lactone topotecan. RESULTS: Maximum total topotecan concentration in the vitreous (median, range) was significantly higher after OAI compared with POI (131.8 ng/mL [112.9-138.7] vs. 13.6 ng/mL [5.5-15.3], respectively; P < 0.005). Median vitreous exposure calculated as area under the curve for total topotecan attained after OAI was significantly higher than after POI (299.8 ng·hour/mL [247.6-347.2] and 48.9 ng·hour/mL [11.8-63.4], respectively; P < 0.05). The vitreous to plasma exposure ratio was 29 after OAI and 3.4 after POI. Systemic exposure for total topotecan was low after both modalities of administration, with a trend to be lower after OAI compared with POI (10.6 ng·hour/mL [6.8-13.4] vs. 18.7 ng·hour/mL [6.3-21.7]; P = 0.54). CONCLUSION: Superselective OAI resulted in significantly higher vitreous concentrations and exposure and a trend toward lower systemic exposure than POI.

Developing a real-world database for oncology: a descriptive analysis of breast cancer in Argentina.

Introduction: Registries based on Real-World Data (RWD) are those obtained outside of systematised and randomised clinical trials. They allow the collection of information from a large number of patients and enable the participation of a significant number of professionals. PrecisaXperta is a web platform developed for this purpose with more than 2 years of operation, parameterised for oncology. Its design allows the construction of an epidemiological database in real time and exportable for processing. Objective: To describe the characteristics and operation of this online data recording tool, explain how it was developed and analyse the quality of the information recorded, taking as an example the data obtained for breast cancer. Materials and methods: Physicians, computer scientists and data science analysts participated in the development. Patient data, history, educational level, diagnosis, staging, molecular markers, quality of life, types of treatments, progression and response, imaging, complications, adverse events are some of the fields included. Data treatment in terms of encryption, anonymisation, protection and validation is also explained. The selected breast cancer data for description were processed with medium-level statistical programmes, since the number required to apply Big Data engines is not yet available. Results: From a total of 6,892 solid tumours, 1,892 were breast cancer and 1,654 were selected that complied with a data set minimum elaborated ad hoc. Cases from 13 provinces showed a geolocation bias according to the place of practice of the professionals in the collaborative network. The predominant lack of data was detected in molecular markers (ki67) and correlativity in some lines of treatment. Inconsistencies in dates and therapeutic schemes were also detected. Data curation made it possible to exclude them. The age of the patients was 55.3 ± 11.88 years. At the time of diagnosis, the predominance was in stage I: 36.48% and II 30.06%, with positive hormone receptors in 1,424 (89.96%) cases. The predominant treatments were hormonal (61.54%) and target directed with 30.85% for HER2(+) and 39.14% for HER2(-) accompanied in most cases (85.9%) by some period of chemotherapy. Immunotherapy was much less represented (0.36%). Data were processed, homogenised, pooled and presented and made accessible in a form suitable for application to RWD analyses. Conclusions: PrecisaXperta fulfils this purpose of systematising the information to facilitate its loading with its simple and intuitive interface. From the analysis of the data obtained in breast cancer, it is clear that some fields should be mandatory in order to improve the quality of the information. The results describing the registered breast cancers give us a surface view of the affected population and prepare us to design future studies when we have local Big Data. This type of development, with continuous improvements and online results, will allow with its dissemination, that the participating professionals have information of what happens in the real world, having available in a democratic way, the epidemiology to be able to study, publish and investigate with these data.

Pharmacokinetic analysis of topotecan after intra-vitreal injection. Implications for retinoblastoma treatment.

Topotecan is a promising drug with activity against retinoblastoma, however, attaining therapeutic concentrations in the vitreous humor is still a challenge for the treatment of vitreous seeds in retinoblastoma. Our aim was to characterize topotecan pharmacokinetics in vitreous and aqueous humor, and to assess the systemic exposure after intra-vitreal injection in rabbits as an alternative route for maximizing local drug exposure. Anesthetized rabbits were administered intra-vitreal injections of 5 microg of topotecan. Vitreous, aqueous, and blood samples were collected at pre-defined time points. A validated high-performance liquid chromatography assay was used to quantitate topotecan (lactone and carboxylate) concentrations. Topotecan pharmacokinetic parameters were determined in vitreous, aqueous and plasma using a compartmental analysis. Topotecan lactone concentrations in the vitreous of the injected eye were about 8 ng/mL 48 h after drug administration. The median maximum vitreous, aqueous and plasma total topotecan concentrations (C(max)) were 5.3, 0.68 and 0.21 microg/mL, respectively. The C(max) vitreous/aqueous of treated eyes and the C(max) vitreous/plasma were approximately 8 and 254, respectively. Total topotecan exposure (AUC) in the vitreous of the injected eye was 50 times greater than the total systemic exposure. These findings suggest that intra-vitreal administration of only 5 microg of topotecan reaches significant local levels over an extended period of time while minimizing systemic exposure in the rabbit. Intra-vitreal topotecan administration offers a promising alternative route for enhanced drug exposure in the vitreous humor with potential application for treatment of vitreal seeds in retinoblastoma while avoiding systemic toxicities.

Frequency of CYP3A5 Genetic Polymorphisms and Tacrolimus Pharmacokinetics in Pediatric Liver Transplantation.

The evidence available in the pediatric population is limited for making clinical decisions regarding the optimization of tacrolimus (TAC) in pharmacotherapy. The objective of this study was to estimate the frequency of CYP3A5 genetic polymorphisms and their relationship with tacrolimus requirements in the pediatric population. This was a longitudinal cohort study with a two-year follow-up of 77 patients under 18 years old who underwent a liver transplant during the period 2009-2012 at the J.P. Garrahan Pediatric Hospital. Tacrolimus levels from day five up to two years after the transplant were obtained from hospital records of routine therapeutic drug monitoring. The genotyping of CYP3A5 (CYP3A5*1/*3 or *3/*3) was performed in liver biopsies from both the donor and the recipient. The frequency of CYP3A5*1 expression for recipients was 37.1% and 32.2% for donors. Patients who received an expresser organ showed lower Co/dose, especially following 90 days after the surgery. The role of each polymorphism is different according to the number of days after the transplant, and it must be taken into account to optimize the benefits of TAC therapy during the post-transplant induction and maintenance phases.

Pharmacokinetic study of the variability of indinavir drug levels when boosted with ritonavir in HIV-infected children.

The aim of this work is to: (1) assess therapeutic drug monitoring of indinavir (IDV) during clinical routine practice in HIV-infected children, whose antiretroviral treatment includes IDV boosted with ritonavir (RTV), and (2) describe a possible relationship between IDV pharmacokinetics and MDR1 genotypes. In 21 ambulatory pediatric patients receiving IDV plus RTV, IDV plasma levels and MDR1 genotypes on exon 26 (C3435T) were determined. Nine of the 21 patients initially receiving 250 mg/m(2) IDV yielded trough levels below 0.10 microg/ml (median: 0.21, range: 0.04-1.31 microg/ml). When the dosage was increased to 400 mg/m(2) IDV plus 100 mg/m(2) RTV b.i.d., all, except 1 patient, achieved levels above 0.10 microg/ml. Pharmacokinetic analysis showed higher volume of distribution median values related to the C/C genotype in comparison with C/T or T/T genotypes for exon 26 (4.57 vs. 1.20 and 1.50 l/kg, respectively; p = 0.002). Although a higher median value of clearance was observed with the C/C genotype, the difference was not statistically significant (1.43 vs. 0.27 and 0.42 l/h, respectively; p = 0.052). These results may be explained by a reduced absorption of the drug, related with lower plasma IDV levels in patients carrying the C/C genotype in exon 26.

Indinavir-loaded pH-sensitive microparticles for taste masking: toward extemporaneous pediatric anti-HIV/AIDS liquid formulations with improved patient compliance.

The aim of this work was to develop indinavir pediatric anti-HIV/AIDS formulations enabling convenient dose adjustment, ease of oral administration, and improved organoleptic properties by means of the generation of drug-loaded microparticles made of a polymer that is insoluble under intake conditions and dissolves fast in the stomach in order to completely release the active agent. Indinavir-loaded microparticles made of a pH-dependent polymeric excipient soluble at pH < 5, Eudragit E100, were prepared using a double emulsion solvent diffusion technique and the in vitro release profiles characterized. Finally, taste masking properties were evaluated in blind randomized sensory experiments by ten healthy human volunteers. The use of a w/o/o emulsion system resulted in indinavir loads around 90%. Thermal analysis of the microparticles by differential scanning calorimetry revealed that indinavir appeared mainly dispersed at the molecular level. Concentrations of residual organic solvents as determined by gas chromatography were below the upper limits specified by the European Pharmacopeia for pharmaceutical oral formulations. Then, the behavior of drug-containing microparticles in aqueous media at different pH values was assessed. While they selectively dissolved in gastric-like medium, in tap water (intake conditions), the matrix remained almost unchanged and efficiently prevented drug dissolution. Finally, sensoring taste tests performed by volunteers indicated that systems with indinavir loads approximately 15% displayed acceptable taste. This work explored the production of indinavir-containing microparticles based on a common pharmaceutical excipient as a means for the improvement of medicines of drugs involved in the treatment of HIV/AIDS. For systems containing about 15% drug, taste studies confirmed the acceptability of the formulation. In pediatric regimes, this composition would require an acceptable amount of formulation (0.7-1.5 g).

Lymphocyte P-glycoprotein variability in healthy individuals.

The aim of the present work was to describe the distribution of lymphocyte P-glycoprotein activity on a population of healthy individuals, taking also into account sex and age. P-glycoprotein activity in lymphocytes was measured by the Rhodamine 123 efflux assay using flow cytometry, in the presence and absence of verapamil, a P-glycoprotein inhibitor. We obtained a range of P-glycoprotein activity from 1.04 to 3.79. The distribution of the activity in the population studied was better described by a bimodal model, according with the Kolmogorov-Smirnov test. The frequency adjusted to the following equation: F = 0.70 N (2.11; 0.43) + 0.30 N(3.29; 0.26), in which 0.70 and 0.30 represented the proportion of each group, and 0.43 and 0.26 were the standard deviations of the activity of each group, respectively. The study of the relationship between subjects' age and P-glycoprotein activity showed no statistical significance. When healthy volunteers were separated according to sex, similar distributions were observed, although for men an increase in proportion of higher P-glycoprotein function group was observed. The variability observed in the population studied was important, with some volunteers with very scarce activity and some with a fourfold higher activity. Characterization of P-glycoprotein functionality in the population represents a useful contribution to the beginning of pharmacological treatments that consider its effect on pharmacokinetics and pharmacodynamics of individualized patients.

High incidence of persistent subtherapeutic levels of the most common AEDs in children with epilepsy receiving polytherapy.

BACKGROUND: Low levels of AEDs can be secondary drug-drug interactions or related to irregular intake due to poor treatment adherence. This latter behavior is highly suspected in ambulatory pediatric epileptic patients when controls of AEDs are subtherapeutic. However, it cannot be considered for inpatients during long periods of hospitalization. A few isolated case reports have documented persistent low levels (PLL) of AEDs in hospitalized epileptic children, but no population study has currently been reported. OBJECTIVE: The aim of this study was to document the incidence of PLL of the most common AEDs - phenytoin (PHT), phenobarbital (PHB), valproic acid (VA), and carbamazepine (CBZ) - in pediatric epileptic in- and outpatients (PEP). METHODS: 21,040 plasma levels of the aforementioned AEDs from 3279 PEP were retrospectively analyzed. Plasma levels of AEDs were measured by an automated method using trademarked commercial kits with their corresponding quality control programs. Randomized samples were also controlled by HPLC methods. Only cases with more than 3 controls were included in the study. RESULTS: A high rate of PLL of PHT was detected in in- (71.7%) and outpatients (74.1%), while PLL of PHB, VA, and CBZ were detected in a lower proportion. Rates of PLL of PHT were similar in in- and outpatients. PLL of PHB was more commonly observed in outpatients while PLL of VA and CBZ were more frequently seen in inpatients. In some hospitalized patients receiving polytherapy, PLL of at least one AED were documented during a long time. DISCUSSION: Treatment non-adherence could be present in part of the outpatients, but cannot explain the PLL observed in a group of inpatients as described here. The recently described "pharmacokinetic hypothesis" of pharmaco-resistant epilepsy should be addressed in cases with AEDs-PLL, particularly in hospitalized cases. Perhaps, instead of stopping the subtherapeutic medication, the increasing doses of this AED and/or administration of inhibitors of CYP and P-glycoprotein, could help to achieve its therapeutic range, allowing a better pharmacologic effect and avoiding the development of more severe complications, such as status epilepticus or SUDEP.

Topotecan vitreous levels after periocular or intravenous delivery in rabbits: an alternative for retinoblastoma chemotherapy.

PURPOSE: To determine the extent and the mechanism by which topotecan, a candidate agent for the treatment of retinoblastoma, gains access to the vitreous when administered by periocular injection or intravenous infusion. METHODS: In vivo experiments were conducted in which albino rabbits received 1 mg topotecan by periocular injection (POI group; n = 30) or as a 30-minute intravenous infusion (IV group; n = 16). Plasma and vitreal topotecan concentrations were analyzed during the 10 hours after administration. A population pharmacokinetic model was fit to the data. Additionally, periocular injections were performed postmortem to study the effect of removing the blood vasculature barrier. RESULTS: Potentially active lactone topotecan levels were detected in the vitreous in the POI and IV groups. Both administration schedules induced high total topotecan plasma exposures because of absorption from the periocular depot, though plasma lactone area under the curve (AUC) was significantly higher in the IV group. Similar vitreal concentrations were found in treated and control eyes in the POI group. The transfer from the periocular compartment to the vitreous was negligible. The absence of drug levels in the control eye of the postmortem-injected rabbits confirmed the systemic delivery of topotecan. Local toxicity was not observed. CONCLUSIONS: As a consequence of a favored passage across the blood-retinal barrier, considerable topotecan vitreous levels were detected in a rabbit model after systemic or periocular administration. Transscleral entry in vivo was constrained by rapid clearance from the administration site.

Nimodipine restores the altered hippocampal phenytoin pharmacokinetics in a refractory epileptic model.

The present work was undertaken to examine the central pharmacokinetics of phenytoin (PHT) in an experimental model of epilepsy, induced by administration of 3-mercaptopropionic acid (MP), and possible participation of P-glycoprotein in this model of epilepsy. Repeated seizures were induced in male Wistar rats by injection of 3-MP (45 mg kg(-1), i.p.) during 10 days. Control rats (C) were injected with saline solution. In order to monitor extracellular PHT levels, either a shunt microdialysis probe or a concentric probe was inserted into carotid artery or hippocampus, respectively. All animals were administered with PHT (30 mg kg(-1), i.v.) 30 min after intraperitoneal administration of vehicle (V) or nimodipine (NIMO, 2 mg kg(-1)). No differences were found in PHT plasma levels comparing all experimental groups. In pre-treated rats with V, hippocampal PHT concentrations were lower in MP (maximal concentration, C(max): 2.7+/-0.3 microg ml(-1), p<0.05 versus C rats) than in C animals (C(max): 5.3+/-0.9 microg ml(-1)). Control rats pre-treated with NIMO showed similar results (C(max): 4.5+/-0.8 microg ml(-1)) than those pre-treated with V. NIMO pre-treatment of MP rats showed higher PHT concentrations (C(max): 6.8+/-1.0 microg ml(-1), p<0.05) when compared with V pre-treated MP group. Our results indicate that central pharmacokinetics of PHT is altered in MP epileptic rats. The effect of NIMO on hippocampal concentrations of PHT suggests that P-glycoprotein has a role in reduced central bioavailability of PHT in our epileptic refractory model.

Pharmacokinetic-pharmacodynamic modeling of diltiazem in spontaneously hypertensive rats: a microdialysis study.

INTRODUCTION: The aim of the present work was to study the applicability of a modified E(max) pharmacodynamic model for the pharmacokinetic-pharmacodynamic (PK-PD) modeling of diltiazem in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. METHODS: A "shunt" microdialysis probe was inserted in a carotid artery of anaesthetized SHR and WKY rats for simultaneous determination of unbound plasma concentrations of diltiazem and their effects on mean arterial pressure (MAP) and heart rate (HR) after the intravenous application of 1 and 3 mg kg(-1) of the drug. Correlation between diltiazem plasma levels and their cardiovascular effects was established by fitting the data to a conventional and modified E(max) model. RESULTS: Volume of distribution and clearance of diltiazem was greater in SHR than in WKY animals. A proportional increase of area under curve with dose increment was observed in WKY animals but not in SHR. A good correlation between plasma unbound concentrations of diltiazem and their hypotensive and chronotropic effects was found in both experimental groups using both PK-PD models. The application of the modified E(max) model for PK-PD modeling of diltiazem allowed a more accurate and precise estimation of PK-PD parameters than the E(max) equation do. Chronotropic effect of 3 mg kg(-1) diltiazem was lower in SHR compared to WKY animals. Initial sensitivity (S(0)) to diltiazem chronotropic effect was greater in SHR with regards to WKY animals after administration of 1 mg kg(-1). S(0) to diltiazem hypotensive effect was greater in SHR with regards to WKY animals after administration of both doses of diltiazem. DISCUSSION: Microdialysis sampling is a useful technique for the pharmacokinetic study and pharmacokinetic-pharmacodynamic (PK-PD) modeling of diltiazem. The modified E(max) model allows an accurate estimation of drug sensitivity in conditions when maximal pharmacological response can not be attained. Genetic hypertension induced changes in the pharmacokinetic and PK-PD behavior of diltiazem suggesting that SHR is an interesting animal model for pre-clinical evaluation of calcium channel blockers.

Increased delivery of chemotherapy to the vitreous by inhibition of the blood-retinal barrier.

Treatment of retinoblastoma -a pediatric cancer of the developing retina- might benefit from strategies to inhibit the blood-retinal barrier (BRB). The potent anticancer agent topotecan is a substrate of efflux transporters BCRP and P-gp, which are expressed at the BRB to restrict vitreous and retinal distribution of xenobiotics. In this work we have studied vitreous and retinal distribution, tumor accumulation and antitumor activity of topotecan, using pantoprazole as inhibitor of BCRP and P-gp. We used rabbit and mouse eyes as BRB models and patient-derived xenografts as retinoblastoma models. To validate the rabbit BRB model we stained BCRP and P-gp in the retinal vessels. Using intravitreous microdialysis we showed that the penetration of the rabbit vitreous by lactone topotecan increased significantly upon concomitant administration of pantoprazole (P=0.0285). Pantoprazole also increased topotecan penetration of the mouse vitreous, measured as the vitreous-to-plasma topotecan concentration ratio at the steady state (P=0.0246). Pantoprazole increased topotecan antitumor efficacy and intracellular penetration in retinoblastoma in vitro, but did not enhance intratumor drug distribution and survival in mice bearing the intraocular human tumor HSJD-RBT-2. Anatomical differences with the clinical setting likely limited our in vivo study, since xenografts were poorly vascularized masses that loaded most of the vitreous compartment. We conclude that pharmacological modulation of the BRB is feasible, enhances anticancer drug distribution into the vitreous and might have clinical implications in retinoblastoma. CHEMICAL COMPOUNDS INCLUDED IN THIS MANUSCRIPT: Topotecan (PubChem CID: 60700) Pantoprazole sodium (PubChem CID: 15008962).

Pharmacokinetic-pharmacodynamic (PK-PD) modeling of cardiovascular effects of metoprolol in spontaneously hypertensive rats: a microdialysis study.

The present work addressed possible alterations in the pharmacokinetics and the in vivo pharmacodynamic of metoprolol (MET) in spontaneously hypertensive (SH) rats and Wistar Kyoto (WKY) animals by means of the microdialysis technique. The correlation between MET unbound plasma concentrations and its pharmacological effects, such as heart rate and blood pressure change, was also examined in SH and WKY rats by the application of a PK-PD model. MET dialysate concentrations and its chronotropic and blood pressure effect were determined during 3 h after the administration of 3 and 10 mg.kg(-1) of the drug. A PK-PD model with a separate effect compartment was used to analyse the data. A good correlation between plasma MET concentrations and its hypotensive and chronotropic effect was found in all experimental groups. Although a greater maximal effect (E(max)) for the antihypertensive effect of MET was observed in SH rats (WKY: E(max): -17+/-1 mmHg; SH: E(max): -28+/-4 mmHg; P<0.05 versus WKY rats), no differences were found in the concentration yielding half-maximal response (IC(50)) comparing SH (IC(50): 583+/-146 ng x ml(-1)) and WKY animals (IC(50): 639+/-187 ng x ml(-1)). The bradycardic effect of MET was greater in SH rats (E(max): -29+/-1%, P<0.05 versus WKY rats) than in WK animals (E(max): -22+/-2%), but no differences were observed in the IC(50) comparing both experimental groups (WKY: IC(50): 187+/-53 ng x ml(-1); SH: IC(50): 216+/-62 ng x ml(-1)). Pharmacokinetic analysis shows that the volume of distribution of MET was greater in SH rats (Vd: 3.4+/-0.5 l, P<0.05 versus WKY rats) with regard to Wistar Kyoto (WKY) animals (Vd: 1.9+/-0.2 l). The results suggest that the pharmacokinetic behaviour of metoprolol are modified in SH rats, resulting in an increased volume of distribution. A greater maximal efficacy to the hypotensive effect of metoprolol was observed in SH rats, suggesting participation of beta-adrenoceptors in the maintenance of the hypertension. Also, a greater chronotropic response to metoprolol was found in the hypertensive group compared with WKY animals, suggesting that, at least in part, the greater cardiac effect of metoprolol explained the enhanced hypotensive response of the beta blocker in the SH animals.

Pharmacokinetics of Immediate and Sustained Release Cephalexin Administered by Different Routes to Llamas (Lama glama).

We investigate the pharmacokinetics of two different cephalexin formulations administered to llamas by the intravenous (IV), intramuscular (IM), and subcutaneous (SC) routes, the minimum inhibitory concentration (MIC) of cephalexin against some Escherichia coli and staphylococci isolated from llamas, and we apply the PK/PD modelling approach, so that effective dosage recommendations for this species could be made. Six llamas received immediate (10 mg/kg, IV, IM, and SC) and sustained (8 mg/kg IM, SC) release cephalexin. Pharmacokinetic parameters were calculated by noncompartmental approach. Immediate release SC administration produced a significantly longer elimination half-life as compared with the IV and IM administration (1.3 ± 0.2 versus 0.6 ± 0.1 and 0.6 ± 0.1 h, resp.) and higher mean absorption time as compared with the IM administration (1.7 ± 0.5 versus 0.6 ± 0.4 h). Absolute bioavailability was in the range of 72-89% for both formulations and routes of administration. Cephalexin MIC90 values against staphylococci and E. coli were 1.0 and 8.0 µg/mL, respectively. Our results show that the immediate release formulation (10 mg/kg) would be effective for treating staphylococcal infections administered every 8 h (IM) or 12 h (SC), whereas the sustained release formulation (8 mg/kg) would require the IM or SC administration every 12 or 24 h, respectively.