Transcranial static magnetic stimulation reduces seizures in a mouse model of Dravet syndrome

Dravet syndrome is a rare form of severe genetic epilepsy characterized by recurrent and long-lasting seizures. It appears around the first year of life, with a quick evolution toward an increase in the frequency of the seizures, accompanied by a delay in motor and cognitive development, and does not respond well to antiepileptic medication. Most patients carry a mutation in the gene SCN1A encoding the α subunit of the voltage-gated sodium channel Nav1.1, resulting in hyperexcitability of neural circuits and seizure onset. In this work, we applied transcranial static magnetic stimulation (tSMS), a non-invasive, safe, easy-to-use and affordable neuromodulatory tool that reduces neural excitability in a mouse model of Dravet syndrome. We demonstrate that tSMS dramatically reduced the number of crises. Furthermore, crises recorded in the presence of the tSMS were shorter and less intense than in the sham condition. Since tSMS has demonstrated its efficacy at reducing cortical excitability in humans without showing unwanted side effects, in an attempt to anticipate a possible use of tSMS for Dravet Syndrome patients, we performed a numerical simulation in which the magnetic field generated by the magnet was modeled to estimate the magnetic field intensity reached in the cerebral cortex, which could help to design stimulation strategies in these patients. Our results provide a proof of concept for nonpharmacological treatment of Dravet syndrome, which opens the door to the design of new protocols for treatment.

Leveraging Physiologically Based Modelling to Provide Insights on the Absorption of Paliperidone Extended-Release Formulation under Fed and Fasting Conditions

Paliperidone was approved by the US FDA in 2006 as an extended-release (ER) tablet (Invega^®) for the once-daily treatment of schizophrenia. This osmotic-controlled release oral delivery system (OROS) offers advantages, such as the prevention of plasma concentration fluctuation and reduced dosing frequency. The administration of the ER after a high-fat/high-calorie meal leads to increased maximum plasma concentration and area under the curve values by 60% and 54%, respectively. Food has various effects on gastrointestinal (GI) physiology, including changed transit times, changed volumes, altered pH in different GI compartments, secretion of bile salts, and increased hepatic blood flow. This may affect solubility, the dissolution rate, absorption, and the pharmacokinetics. The aim of this study was to apply physiologically based absorption modeling (PBAM) to provide insights on paliperidone ER absorption under fed and fasting conditions. The PBAM adequately predicted absorption from the OROS formulation under both conditions. Absorption primarily occurs in the ascending colon and caecum. After a high-fat/high-calorie meal, absorption is increased through the jejunum, ileum, and colon due to either increased solubilization or the better efficiency of the OROS technology. PBAM-guided approaches can improve the understanding of branded drugs and thereby aid in guiding the development of generic formulations or formulation alternatives.

Key Factors in Effective Patient-Tailored Dosing of Fluoroquinolones in Urological Infections: Interindividual Pharmacokinetic and Pharmacodynamic Variability

Fluoroquinolones (FQs) are a critical group of antimicrobials prescribed in urological infections as they have a broad antimicrobial spectrum of activity and a favorable tissue penetration at the site of infection. However, their clinical practice is not problem-free of treatment failure, risk of emergence of resistance, and rare but important adverse effects. Due to their critical role in clinical improvement, understanding the dose-response relation is necessary to optimize the effectiveness of FQs therapy, as it is essential to select the right antibiotic at the right dose for the right duration in urological infections. The aim of this study was to review the published literature about inter-individual variability in pharmacological processes that can be responsible for the clinical response after empiric dose for the most commonly prescribed urological FQs: ciprofloxacin, levofloxacin, and moxifloxacin. Interindividual pharmacokinetic (PK) variability, particularly in elimination, may contribute to treatment failure. Clearance related to creatinine clearance should be specifically considered for ciprofloxacin and levofloxacin. Likewise, today, undesired interregional variability in FQs antimicrobial activity against certain microorganisms exists. FQs pharmacology, patient-specific characteristics, and the identity of the local infecting organism are key factors in determining clinical outcomes in FQs use.

Application of a dual mechanistic approach to support bilastine dose selection for older adults

The objective of this study was to evaluate bilastine dosing recommendations in older adults and overcome the limitation of insufficient data from phase I studies in this underrepresented population. This was achieved by integrating bilastine physicochemical, in vitro and in vivo data in young adults and the effect of aging in the pharmacology by means of two alternative approaches: a physiologically‐based pharmacokinetic (PBPK) model and a semi‐mechanistic population pharmacokinetic (Senescence) model. Intestinal apical efflux and basolateral influx transporters were needed in the PBPK model to capture the observations from young adults after single i.v. (10 mg) and p.o. (20 mg) doses, supporting the hypothesis of involvement of gut transporters on secretion. The model was then used to extrapolate the pharmacokinetics (PKs) to elderly subjects considering their specific physiology. Additionally, the Senescence model was develop starting from a published population PK) model, previously applied for pediatrics, and incorporating declining functions on different physiological systems and changes in body composition with aging. Both models were qualified using observed data in a small group of young elderlies (N = 16, mean age = 68.69 years). The PBPK model was further used to evaluate the dose in older subjects (mean age = 80 years) via simulation. The PBPK model supported the hypothesis that basolateral influx and apical efflux transporters are involved in bilastine PK. Both, PBPK and Senescence models indicated that a 20 mg q.d. dose is safe and effective for geriatrics of any age. This approach provides an alternative to generate supplementary data to inform dosing recommendations in under‐represented groups in clinical trials.

MO647RENOPROTECTIVE EFFECT OF SGLT2 INHIBITORS AFTER FIVE YEARS OF TREATMENT: AN OBSERVATIONAL STUDY

Background and Aims

Sodium-glucose co-transporter 2 (SGLT2) inhibitors, the most recent glucose lowering oral agents, prevent glucose and sodium reabsorption at proximal tubules. These drugs have the potential of nephroprotection by their glucose lowering effects, but also through direct renal effects, such as reducing intraglomerular pressure and suppressing the production of pro-inflammatory and pro-fibrotic factors. Several randomized control trials have demonstrated these effects with slowing chronic kidney disease progression. The aim of our study was to evaluate the effect of SGLT2 inhibitors on estimated glomerular filtration rate throughout five years of treatment.

Method

This was a retrospective observational and longitudinal study that included patients diagnosed with DM2 and treated with an iSGLT2 in a Diabetic Clinic. Demographic and clinical variables were collected, including HbA1c, disease duration and cardiovascular risk factors (CVRF). Patient glucose-control therapy as well as RAAS inhibitor drugs were gathered. The estimated Glomerular Filtration Rate (eGFR) by the formula CKD-EPI and albuminuria, using the urinary albumin-to-creatinine ratio, were evaluated at the iSGLT2 introduction date and at 6, 12, 24, 36, 48 and 60 months of treatment. Categorical variables are presented as frequencies and percentages, and continuous variables as means or medians for variables with skewed distributions. All reported p values are two-tailed, with a p value of 0.05 indicating statistical significance. A paired Student’s t-test or paired-sample test were performed for continuous variables and a chi-squared test was performed for categorical variables.

Results

A total of 205 patients, 54,6 % male, mean age 65,4 years, median baseline HbA1c 8,4% and median duration of DM2 14 years were studied. Of all patients, 94,1% had at least 1 CVRF, 71,2% hypertensive, 83,4% dyslipidemia, 48,8% obese, and 25,4% had past/current smoking habits. Regarding glucose-control therapy 17,1% were treated with one drug class and the remaining patients were treated with 2 or more classes. Among the patients 82,0% of them were taking metformin and 51,2% were on insulin therapy. Also, 56,6 % were on a RAAS inhibitor. Overall, 129 (62,9 %) patients received dapaglifozin therapy (5 or 10mg) and 76 (37,1%) empaglifozin (10 or 25mg). Regarding albuminuria at baseline, 37 patients had normal albuminuria (<30mg/g), 18 patients had moderate albuminuria (30-300mg/g) and 6 patients had severe albuminuria (>300mg/g). As for eGFR, 15,6 % patients had an eGFR between 30 and 60 and 84,4% patients had an eGFR greater than 60 ml/min/1,73m2. These clinical features were similar between the patients that received either SGLT2 inhibitor, with the exception of obesity being more prevalent in the dapaglifozin group (55,8 % vs 36,8%, p=0,009). Assessing the eGFR during the 5 years of treatment, a significant decrease was noticed in the first 6 months from an 82,3 to 78,6 ml/min/1,73m2 (p=0,002), followed by a significant increase in the second semester to 82,9 ml/min/1,73m2 (p<0,001). Thereafter there is a slight increase in eGFR throughout the years, to a maximum of 84,1 ml/min/1,73m2 at 24 months and after a slow reduction to 80,6ml/min/1,73m2 in the end of the 5 years of SGLT2 inhibitor use.

Conclusion

This observational study shows that after an initial reduction in eGFR during the first 6 months of treatment, the use of iSGLT2 after five years slowed the decrease in eGFR, similar to what randomized control trials have demonstrated, promoting a renoprotective effect on type 2 diabetic patients.

Management practices for postdural puncture headache in obstetrics: a prospective, international, cohort study

BACKGROUND

Accidental dural puncture is an uncommon complication of epidural analgesia and can cause postdural puncture headache (PDPH). We aimed to describe management practices and outcomes after PDPH treated by epidural blood patch (EBP) or no EBP.

METHODS

Following ethics committee approval, patients who developed PDPH after accidental dural puncture were recruited from participating countries and divided into two groups, those receiving EBP or no EBP. Data registered included patient and procedure characteristics, headache symptoms and intensity, management practices, and complications. Follow-up was at 3 months.

RESULTS

A total of 1001 patients from 24 countries were included, of which 647 (64.6%) received an EBP and 354 (35.4%) did not receive an EBP (no-EBP). Higher initial headache intensity was associated with greater use of EBP, odds ratio 1.29 (95% confidence interval 1.19-1.41) per pain intensity unit increase. Headache intensity declined sharply at 4 h after EBP and 127 (19.3%) patients received a second EBP. On average, no or mild headache (numeric rating score≤3) was observed 7 days after diagnosis. Intracranial bleeding was diagnosed in three patients (0.46%), and backache, headache, and analgesic use were more common at 3 months in the EBP group.

CONCLUSIONS

Management practices vary between countries, but EBP was more often used in patients with greater initial headache intensity. EBP reduced headache intensity quickly, but about 20% of patients needed a second EBP. After 7 days, most patients had no or mild headache. Backache, headache, and analgesic use were more common at 3 months in patients receiving an EBP.

Ethanol Sclerotherapy versus Laparoscopic Surgery for Endometrioma Treatment: A Prospective, Multicenter, Cohort Pilot Study

STUDY OBJECTIVE

To compare the cost-effectiveness of ultrasound (US)-guided aspiration and ethanol sclerotherapy versus laparoscopic surgery for benign-appearing ovarian endometrioma.

DESIGN

Prospective, cohort pilot study.

SETTING

Multiple centers, Spain.

PATIENTS

Forty patients with suspected ovarian endometrioma identified by US, with a maximum diameter of 35 to 100 mm, of whom 33 met inclusion criteria.

INTERVENTIONS

The study group (n = 17) underwent US-guided aspiration plus sclerotherapy with ethanol, and the control group (n = 14) underwent laparoscopic cystectomy.

MEASUREMENTS AND MAIN RESULTS

Recurrence, complications, and direct costs were compared. One of 17 sclerotherapy patients recurred (5.9%) compared with 4 of 14 laparoscopic surgery patients (28.6%) (odds ratio 0.18, 0.01-1.53). No serious adverse effects (Clavien-Dindo ≥ III) were observed in the sclerotherapy group; 1 patient in the surgery group had a Clavien-Dindo IIIb complication. Median hospital direct costs were significantly lower in the sclerotherapy group than those in the surgery group-266 euros versus 2189 euros.

CONCLUSION

Ethanol sclerotherapy seems to be cost-effective for endometrioma and also appears to reduce complications. In this pilot study, recurrence was not higher than with conventional surgery.

Experimental display of the extended polarization coherence theorem

We report experimental results that show the interplay between visibility, distinguishability, and the degree of polarization, as ruled by a recent extension of the polarization coherence theorem (PCT). Theorems of this kind address duality in both quantum and classical scenarios. We particularly focus on the inherent vector nature of the polarization degree of freedom and display various effects that lie beyond the scope of the original PCT. Our results exhibit features that can be shared by quantum and classical phenomena, whenever these phenomena reflect some hidden or exposed coherence.

A predictive pharmacokinetic/pharmacodynamic model of fentanyl for analgesia/sedation in neonates based on a semi-physiologic approach

BACKGROUND AND OBJECTIVES

Fentanyl is a synthetic opioid commonly used as an anesthetic and also increasingly popular as a sedative agent in neonates. Initial dosage regimens in this population are often empirically derived from adults on a body weight basis. However, ontogenic maturation processes related to drug disposition are not necessarily always body weight correlates. We developed a predictive pharmacokinetic/pharmacodynamic model that includes growth and maturation physiologic changes for fentanyl in neonatal care.

METHODS

Key pharmacokinetic variables and principles (protein binding, clearance, distribution) as related to fentanyl pharmacokinetic/pharmacodynamic behavior in adults (tricompartmental model) and to neonatal physiologic data (organ weights and blood flows, body composition, renal and hepatic function, etc.) were used to guide the building of a semi-physiologic ontogenic model. The model applies to a normal-term neonate without any other intervention. Then, extension to a pharmacokinetic/pharmacodynamic link model for fentanyl was made. The final model was evaluated by predicting the time course of plasma concentrations and the effect of a standard regimen of 10.5 μg/kg over a 1-h period followed by 1.5 μg/kg/h for 48 h.

RESULTS

Hepatic clearance was linked to ontogeny of unbound fraction and of α1-acid glycoprotein. All parameters were reduced in the neonate compared to adults but in a differing proportion due to qualitative changes in physiology that are analyzed and accounted for. Systemic clearance (CLS), volume of the central compartment (V1) and steady-state volume of distribution predicted by the model were 0.028 L/min, 1.26 L, and 22.04 L, respectively. Weight-corrected parameters generally decreased in adults compared with neonates, but differentially, e.g., CLS = 0.0093 versus 0.0088 L/min/kg, while V1 = 0.42 versus 0.18 L/kg (neonates vs. adults). Under such complexity a pharmacokinetic/pharmacodynamic model is the appropriate method for rational efficacy targeting. Fentanyl pharmacodynamics in neonates were considered to be similar to those in adults except for the equilibrium rate constant, which was also scaled on an ontogenic basis. The model adequately predicted the reported mean expected concentration-time profiles for the standard regimen.

CONCLUSIONS

Integrated pharmacokinetic/pharmacodynamic modeling showed that the usually prescribed dosage regimens of fentanyl in neonates may not always provide the optimum degree of sedation. The model could be used in optimal design of clinical trials for this vulnerable population. Prospective clinical testing is the reasonable next step.

No time to lose--high throughput screening to assess nanomaterial safety

Nanomaterials hold great promise for medical, technological and economical benefits. Knowledge concerning the toxicological properties of these novel materials is typically lacking. At the same time, it is becoming evident that some nanomaterials could have a toxic potential in humans and the environment. Animal based systems lack the needed capacity to cope with the abundance of novel nanomaterials being produced, and thus we have to employ in vitro methods with high throughput to manage the rush logistically and use high content readouts wherever needed in order to gain more depth of information. Towards this end, high throughput screening (HTS) and high content screening (HCS) approaches can be used to speed up the safety analysis on a scale that commensurate with the rate of expansion of new materials and new properties. The insights gained from HTS/HCS should aid in our understanding of the tenets of nanomaterial hazard at biological level as well as assist the development of safe-by-design approaches. This review aims to provide a comprehensive introduction to the HTS/HCS methodology employed for safety assessment of engineered nanomaterials (ENMs), including data analysis and prediction of potentially hazardous material properties. Given the current pace of nanomaterial development, HTS/HCS is a potentially effective means of keeping up with the rapid progress in this field--we have literally no time to lose.

Effect of P-glycoprotein inhibition on methadone analgesia and brain distribution in the rat

Methadone is an opiate drug that has been identified as an in-vitro substrate of the efflux pump P-glycoprotein (P-gp), active in the intestinal epithelium and in the blood–brain barrier (BBB), among other sites. The objective of this study was to test in vivo, in the rat model, the role of P-gp modulation on the analgesic effect and brain uptake of methadone, as well as identify the most relevant site via dual oral and intravenous (i.v.) experiments. The P-gp specific inhibitor (valspodar or PSC833) was preadministered (10 mg kg−1 i.v.) to test groups. Analgesia was measured using the tailflick test. The ED50 for oral methadone (2, 3, 6 and 8 mg kg−1) decreased three-fold in valspodar groups compared with controls (2.23 + 0.002 mg kg−1 and 6.07 + 0.07 mg kg−1; P < 0.0001). The overall analgesic effect (% antinociception) was elevated 3.1 times in pretreated compared with control rats (90.65% + 0.22 vs 29.23% + 14.0; P < 0.01) after 6 mg kg−1 oral methadone and 2.8 times after i.v. (0.35 mg kg−1) administration (91.75% + 4.27 vs 32.45% + 9.0; P < 0.01). The brain:plasma distribution ratio was higher in pretreated animals and AUCbrain (overall brain concentration) was 6 times higher after oral methadone and 4 times higher after i.v. compared with controls, disproportionally increased relative to plasma, implying an active process at the BBB. P-gp, and hence substrate comedication, plays a critical role in the evolution of the methadone analgesic effect and in its brain uptake, independent of the administration route.

Population pharmacokinetics of recombinant factor VIII:C (ReFacto) in adult HIV-negative and HIV-positive haemophilia patients

PURPOSE

The aim of this study was to explore possible differences in the pharmacokinetics (PK) of recombinant factor VIII:C (ReFacto - ReFacto ) in HIV+ vs. HIV- patients and also differences in the chromogenic substrate bioassay (CHS) and one-stage clotting (OSC) methods.

METHODS

Twenty-eight haemophilia A adults (20 HIV- and eight HIV+) were assayed with both the CHS and OSC methods. An average of two and six samples were collected per patient for HIV-/+, respectively, after one, and occasionally two more, prophylactic doses (mean 2,003 IU; range 1,000-4,300 IU). The observations were analysed with the mixed-effects (population) compartmental PK modelling package NONMEM (nonlinear mixed-effects modelling) and the FOCE (first-order conditional estimation) method. Base modelling was performed independently for the CHS and OSC bioassays for comparison, and covariate models and simulation tests were done only for the commonly used OSC bioassay. The final covariate model was validated using the bootstrap method. Monte Carlo simulations were used to estimate the expected probability of exceeding 20%, 40% or 60% of normal factor VIII:C in plasma after a single dose, corresponding to required levels for preventing mild, moderate and life-threatening haemorrhages.

RESULTS

One-compartment base-model population PK parameters were [mean parameter (interpatient variability %)] for CHS: clearance (CL) = 2.56 dl h(-1) (33.2%); volume of distribution (V) = 34.8 dl (12.8%); and for OSC: CL = 3.83 dl h(-1) (47.8%), V = 53.7 dl (22.4%). The volumes differed significantly between the CHS and OSC methods (p < 0.0001), and variabilities were higher for OSC. Nevertheless, the empirical half-lives (t(1/2) = l n (2) x V/CL) were similar for CHS and OSC, [(mean +/- standard deviation (SD)], 9.5 +/- 3 h and 10.2 +/- 4 h, respectively. In covariate modelling with the OSC-derived model, HIV status (VIR) was a significant categorical predictor (p < 0.005) for V. The final covariate models with OSC were for CL = 3.93 + 0.09 x (WT-75) and for V = 48.6 x (1 + 0.36 x VIR) + 0.55 x (WT-75); therefore, V for the typical HIV+ patient was 36% higher than for the HIV- patient.

CONCLUSIONS

Both HIV- and HIV+ patients showed 100% success with the 20% threshold at doses >20 IU/kg. HIV- patients receiving >50 IU/kg had a 100% expected chance of success for all thresholds. HIV+ patients for moderate or life-threatening haemorrhage treatment need 10 IU/kg more than the HIV- patient equivalent to have the same probability of success.

The prevalence of radiographic vertebral fractures in Latin American countries: the Latin American Vertebral Osteoporosis Study (LAVOS)

In the first population-based study of vertebral fractures in Latin America, we found a 11.18 (95% CI 9.23-13.4) prevalence of radiographically ascertained vertebral fractures in a random sample of 1,922 women from cities within five different countries. These figures are similar to findings from studies in Beijing, China, some regions of Europe, and slightly lower than those found in the USA using the same standardized methodology.

INTRODUCTION

We report the first study of radiographic vertebral fractures in Latin America.

METHODS

An age-stratified random sample of 1,922 women aged 50 years and older from Argentina, Brazil, Colombia, Mexico, and Puerto Rico were included. In all cases a standardized questionnaire and lateral X-rays of the lumbar and thoracic spine were obtained after informed consent.

RESULTS

A standardized prevalence of 11.18 (95% CI 9.23-13.4) was found. The prevalence was similar in all five countries, increasing from 6.9% (95% CI 4.6-9.1) in women aged 50-59 years to 27.8% (95% CI 23.1-32.4) in those 80 years and older (p for trend < 0.001). Among different risk factors, self-reported height loss OR = 1.63 (95% CI: 1.18-2.25), and previous history of fracture OR = 1.52 (95% CI: 1.14-2.03) were significantly (p < 0.003 and p < 0.04 respectably) associated with the presence of radiographic vertebral fractures in the multivariate analysis. In the bivariate analyses HRT was associated with a 35% lower risk OR = 0.65 (95% CI: 0.46-0.93) and physical activity with a 27% lower risk of having a vertebral fracture OR = 0.73 (95% CI: 0.55-0.98), but were not statistically significant in multivariate analyses

CONCLUSION

We conclude that radiographically ascertained vertebral fractures are common in Latin America. Health authorities in the region should be aware and consider implementing measures to prevent vertebral fractures.

The relation among the diameter of the great saphenous vein, clinical state and haemodynamic pattern of the saphenofemoral junction in chronic superficial venous insufficiency

OBJECTIVE

To find out if there is a relation among the diameter of the great saphenous vein (GSV) when it is incompetent, the clinical gravity of the varicose syndrome and the type of insufficiency of the saphenofemoral junction (SFJ) in patients with chronic venous insufficiency (CVI) by means of duplex exploration.

METHODS

The sample included 145 extremities, 38 normal as a control group and 107 with incompetence of the GSV. According to the results of the Valsalva and Parana manoeuvres in the SFJ, they were distributed into four groups. The diameter of the GSV and the clinical state according to the clinical, aetiological, anatomical and pathological element classification were recorded for each group.

RESULTS

Statistically significant differences were obtained for the diameter and the clinical state in patients with positive manoeuvres with regard to other groups. The diameter was greater and the clinical state more severe (C4, C5 and C6) when two manoeuvres were positive.

CONCLUSIONS

The presence of both positive manoeuvres in the SFJ is related to severe clinical states and greater diameters of the GSV, allowing the establishment of a prognosis of the CVI and the most suitable surgical approach.

Modeling methadone pharmacokinetics in rats in presence of P-glycoprotein inhibitor valspodar

PURPOSE

To quantify the in vivo role of P-glycoprotein (P-gp) in the pharmacokinetics of methadone after intravenous and oral administration, using valspodar as a P-gp inhibitor.

MATERIALS AND METHODS

Methadone plasma concentrations after intravenous (0.35 mg/kg) and oral (6 mg/kg) administration were analyzed, in absence and presence of valspodar, using nonlinear mixed effects modeling (NONMEM V). Non-parametric bootstrap analysis and posterior predictive check were employed as model evaluation techniques.

RESULTS

The pharmacokinetics of methadone in the rat was successfully modeled using a two-compartmental model with a linear elimination from the central compartment and a first-order absorption process with lag time. Valspodar increased methadone F by 122% (95%CI: 34-269%) and decreased the V ( c ) and V ( p ) by 35% (95%CI: 16-49%) and 81% (95%CI: 63-93%), respectively. No effect of valspodar on other pharmacokinetic parameters was discernible. The non-parametric bootstrap analysis confirmed the absence of bias on the parameter estimates, and visual predictive check evidence the adequacy of the model to reproduce the observed time course of methadone plasma concentrations.

CONCLUSION

Valspodar increased methadone's bioavailability as consequence of P-gp inhibition, which resulted in an increased analgesic effect of methadone.

Time-dependent pharmacokinetics of cyclosporine (Neoral) in de novo renal transplant patients

PURPOSE

A model for the large scale temporal trend in the oral bioavailability of microemulsion cyclosporine (Neoral) (CsA) is established, with dependence on post-(renal) transplantation day (PTD).

METHODS

Twenty de novo adult renal transplant recipients were monitored for CsA administered orally q12 h. A model development group (11 patients, 315 blood concentration samples) was screened at 2 h (C(2); n = 92), 3 h (C(3); n = 56) and at predose troughs (C(min); n = 167) over periods of up to 75 days. The final model was tested in nine patients with C(min) (n = 580) monitored across 4-5 years. The doses varied between 100 and 538 mg with an apparent hyperbolic trend in C(2)/dose vs. PTD. A nonlinear mixed effects modelling (NONMEM) approach was used to obtain population and individual patient one-compartment pharmacokinetic (PK) parameters for oral CsA, which carry implicit the bioavailability (F).

RESULTS

In the final PK model (PK-f) the F was modelled via a simple function for the temporal (days) trend of the bioavailability after transplantation as, F(f) = 1-alpha * exp(-lambda * PTD) resulting in a 28% reduction in the unexplained intra-individual variability. The population PK-f parameters were, for apparent clearance [mean, 95% confidence interval (interindividual CV%)] Cl/F(f) = 17.0 (13.8-20.2) L/h (27%), apparent central compartment volume of distribution, V/F(f) = 134 L (108-160) (28%), and lambda = 0.037/day (0.005-0.069) (120%). The absorption rate k(a) and the parameter alpha were approximated iteratively as 4/h and 0.62 respectively. The PK-f was structurally superior to the base model in explaining part of the within subject (occasion) variability and predicting the exposure surrogates C(2) and C(3). Also, the PK-f was better than the base model with Bayesian fitting of individual profiles in that group.

CONCLUSION

The PTD-dependent relative bioavailability model provides a rational means of steering dose titration of CsA in de novo renal transplantation patients by removing the large scale PK adjustment signal, either through nomograms or as a Bayesian prior.

The Role of Unbound Drug in Pharmacokinetics/Pharmacodynamics and in Therapy

The evolution of research on drug protein binding is discussed with the unbound concentration (Cu) and the unbound fraction (fu) as protagonists. Particular attention is paid to the mechanisms via which alterations in binding affect the pharmacokinetics (PK) and the effect, or independently the pharmacodynamics (PD). Apart from albumin, the important alpha-acid glycoprotein (AGP), as well as specific drug classes and applications in the clinic and development (routine monitoring, cancer and HIV therapy, allometry) are addressed. The flaws with the classical method of indirectly calculating the Cu or the unbound PK/PD parameters, based on the fu in vitro, are related to the intrinsic complexity and variability in the outcomes. Increased focus is urged on directly estimating the unbound PK/PD and also on using population statistical methods.

Bicompartmental kinetics of tobramycin analysed with a wide range of covariates

The pharmacokinetics of tobramycin was studied in adult patients (N = 151) admitted either for initial suspicion of Gram-negative infection or for prophylaxis. In addition to age, weight, height and creatinine clearance (CrCL), a range of other covariates were also analysed, including type of pathology, co-medication, fever, sex and ethnicity (Basque or not). All patients received 100mg tobramycin every 8 h and samples were collected at three time points after the first dose and at two time points after the fourth dose and assayed with a fluorescence polarisation immunoassay. The population mixed effects bicompartmental parameters were obtained from 725 concentration measurements using NONMEM, FOCE method, and were: systemic clearance, CL = 6.03 L/h (between-subject coefficient of variation (CV) %, 29.4%); volume of distribution, V = 15.04 L (7.3%); and intercompartmental constants, k(12) = 0.192 h(-1) (56%) and k(21) = 0.55 h(-1) (no CV% determined). Covariate modelling was performed within NONMEM. Two alternative significant covariate models (Models 1 and 2) are proposed, with functions of CrCL and/or sex (Model 2). However, for clinical purposes, differentiation by sex is insignificant. Model 1 is for CL = 3.1 + 0.05.CrCLL/h (17.3%); V = 14.6 L (12%); k(12) = 0.224 h(-1) (63%) and k(21) = 0.468 h(-1). Stochastic simulation was used to predict the expected concentration 95th percentiles after the recommended 7 mg/kg dose and for minimum inhibitory concentration (MIC) = 1 mg/L, as well as alternative once-daily dosing regimens for MIC = 2 mg/L. It is seen that once-daily high-dose tobramycin is an appropriate strategy with respect to pharmacodynamic indices, C(peak)/MIC or AUC/MIC (where C(peak) is the peak plasma concentration and AUC is the area under the concentration-time curve).

Altered dose-to-effect of propofol due to pharmacokinetics in rats with experimental diabetes mellitus

Pathology related alterations in the pharmacokinetics or the pharmacodynamics of propofol could contribute to the observed large variability in the hypnotic dose. We have tested the influence of diabetes mellitus on the induction dose and the pharmacokinetics and pharmacodynamics of propofol in rats. Diabetes was induced in rats by administration of streptozotocin (60 mg kg(-1), i. p.) while control rats received vehicle intraperitoneally. All animals had glucose, cholesterol, triglycerides and albumin levels measured. In-vitro protein binding was determined by ultrafiltration. Rats were randomly split into set 1 (dose-concentration-effect study) with control and streptozotocin rats, and set 2 (pharmacokinetic study), with control and streptozotocin rats. Rats in the effect set received either a variable infusion of 6 mg kg(-1) min(-1) propofol until onset (induction dose) of the hypnotic effect (loss of the righting reflex), or a 15 mg kg(-1) bolus to assess offset time (recovery of the righting reflex). Blood (C(blood)) and brain (C(brain)) propofol concentrations at onset and offset were assayed by HPLC. In the pharmacokinetic study, propofol was administered intravenously at 6 mg kg(-1) min(-1) for 2 min. Arterial blood samples were collected between 0.5 and 540 min and assayed for propofol. A mixed effects compartmental pharmacokinetic modelling method (NONMEM) was used to analyse the observations and variabilities. The dose necessary for onset differed between streptozotocin and controls, and so did the pharmacokinetics with two- and three-compartment descriptions, respectively. C(blood) and C(brain) at onset and offset were similar, possibly rejecting changes in pharmacodynamics. The total and unbound volume of distribution was significantly lower in the streptozotocin group with no differences in clearance (CL) between streptozotocin and controls, (mean (inter-animal CV%)) CL = 0.026 (17%) and 0.025 (62%) L min(-1), respectively. Individual Bayes Vd(ss) (volume of distribution at steady state) were different, (mean (s. d.)) Vd(ss) = 7.7 (2.67) and 1.11 (0.09) L, respectively. The pharmacokinetic model was validated by comparison with the data from set 1. Simulations of total and unbound C(blood), for both groups, at the hypnotic dose for the controls, revealed differences throughout the time course of the pharmacokinetics. The difference observed in the induction dose of propofol to streptozotocin and control rats was due to alterations in the pharmacokinetics, secondary to the pathology.

Alpha‐1‐acid glycoprotein directly affects the pharmacokinetics and the analgesic effect of methadone in the rat beyond protein binding

Methadone is a basic drug highly bound to alpha1-acid glycoprotein (AGP), a plasma protein that increases in several pathological situations. Our aims were to evaluate the processes (pharmacokinetics-PK and/or pharmacodynamics-PD) associated with changes of methadone analgesia under conditions of increased AGP, and whether these changes are dependent on binding, secondary to a pathology, or directly attributable to AGP. AGP levels, in rats, were increased by two different methods: (a) experimental inflammation with turpentine oil (TP), and (b) by directly infusing the protein (exo-AGP). Both had a corresponding control group. Tail-flick analgesia and PK were evaluated after methadone dose (0.35 mg/kg i.v.). Bicompartmental PK parameters as well as interanimal and assay variabilities were estimated using NONMEM. The relationship between Cp and analgesic effect (PD) was analyzed with WINNONLIN. AGP levels in both pretreated groups (TP and exo-AGP) were significantly increased, and the unbound fraction (fu) was decreased, compared to controls. All PK parameters were lower in the pretreated groups, but in exo-AGP the difference was maintained even when corrected by fu. Paradoxically, also in exo-AGP the analgesic effect was practically nonexistent, although the unbound Cp remained high, possibly associated to a change in the PD. AGP appears responsible for alterations in both PK and PD, beyond protein binding and inflammatory processes.

Influence of formulation on propofol pharmacokinetics and pharmacodynamics in anesthetized patients

BACKGROUND

In anesthesia with propofol, variability persists besides sophisticated effect targeting. Drug formulation may be another factor. We have analyzed, retrospectively, the pharmacokinetics (PK) and pharmacodynamics (PD) in monitored surgery patients anesthetized with one each of five formulations of propofol.

METHODS

Propofol 1% ('form' 1: Diprivan(Zeneca Limited, Macclesfield, UK), 2: Recofol(Schering Espana, Madrid, Spain), 3: Ivofol(Juste, Madrid, Spain), 4: Propofol Abbott (Abbott Laboratories, Madrid, Spain), 5: Fresenius (Fresenius Kabi Espana, Barcelona, Spain)) was administered to 77 ASA I-II patients of age [mean (range) 44 (18-65) years]. Induction of anesthesia was with varying propofol doses up to endpoints of either 60 on the Bispectral Index system (BIS) in group I (n = 48, model development) or standard clinical signs in group II (n = 29, validation). Maintenance was with three 10-min infusions of 10, 8 and 6 mg kg(-1) h(-1). Three blood samples were obtained from each subject, immediately after induction, and at 15 and 30 min on maintenance, with BIS and hemodynamic variables recorded at these times also. Total and free blood concentrations (Cb) of propofol were determined with HPLC. Pharmacokinetic and PD models with link equilibration rate ke0, were studied with a mixed-effects procedure (NONMEM).

RESULTS

The induction dose (group I) showed large interindividual variability [mean (range) 163 (90-290 mg)] that correlated significantly with age, basal systolic blood pressure and formulation. The PK of propofol (basic model) was described by a one-compartment model with (typical value [interindividual coefficient of variation percent (CV%)]) CL=2.30 l min(-1) (27%) and V=8.40 l (80%). Weight (WT) and formulation, within NONMEM, were found to be significant covariates for CL and V, reducing their CV% to 25% and 74%, respectively. The final PK/PD model, which includes formulation, showed a 50% reduction in the CV% for both the ke0 and the residual error. This PK/PD model was validated in group II with 33% precision and no bias.

CONCLUSION

The PK and PD are not equal for all formulations, which contributes to an increase in variability of the observed effect.

Age-related changes in pharmacokinetics and pharmacodynamics of lerisetron in the rat: a population pharmacokinetic model

BACKGROUND

The importance of studying the effects of age on the pharmacokinetics and pharmacodynamics of lerisetron - a new 5-hydroxytryptamine-3 (serotonin) receptor antagonist - comes from the facts that lerisetron will be administered to patients that are being treated with cytotoxic drugs and that the elderly frequently suffer from neoplastic diseases.

OBJECTIVE

The present study was designed to explore the effects of age on the pharmacokinetics and pharmacodynamics of lerisetron by using an aged rat model. A mixed-effects population study was carried out in order to analyze the sparse data and to create covariate models which could be used to derive dosage recommendations.

METHODS

Fischer 344 rats (n = 44) were divided into three groups, depending on their age: 5, 13, and 25 months. Blood samples were collected before administration of 200 micro g/kg of lerisetron for measurements of albumin, alpha(1)-acid glycoprotein, and unbound fraction of lerisetron. The lerisetron plasma concentrations were measured by high-performance liquid chromatography. A two-compartment model was fitted to the data using the nonlinear mixed-effects computer program WinNonMix. The population analysis was performed with the complete set of the collected data, and the potential sources of variability in the population parameters were investigated. Additionally, a pharmacodynamic study was performed. The effect of lerisetron (inhibition of the von Bezold-Jarisch reflex) was evaluated in young, adult, and senescent Fischer 344 rats.

RESULTS

The mean values of the individual Bayes estimates of the parameters showed a decrease in total clearance and distribution volume of the central compartment in old rats. The lerisetron free (unbound) fraction remained unchanged among the groups, and there were no significant differences in alpha(1)-acid glycoprotein levels. The concentration-effect relationship was best described by a sigmoid E(max) model. Since the drug concentration in plasma at half-maximal effect (EC(50)) decreased in old rats, an increased sensitivity to the effect of lerisetron in old animals could be expected.

CONCLUSION

Both pharmacokinetic changes (decreased volume of distribution and clearance and increased elimination half-life) and pharmacodynamic alterations (decrease in total and unbound EC(50)) may be responsible for the different responses to lerisetron observed in old rats.

Production of antigen-specific human monoclonal antibodies: comparison of mice carrying IgH/kappa or IgH/kappa/lambda transloci

Here we compare human monoclonal antibody (MAb) production from mouse strains that carry disruptions of their endogenous mouse IgH/IgK loci and harbor human IgM + Igkappa(BABkappa) or human IgM + Igkappa + IgA transloci (BABkappa,lambda). We found that whereas both strains proved effective for the isolation of antigen-specific IgM antibodies, many of the IgM MAbs elicited from BABkappa comprise human mu chains that are associated with mouse lambda chains. In contrast, BABkappa,lambda mice gave rise to fully functional, polymeric human IgM antibodies comprising both human IgH and human IgL chains. Therefore, the inclusion of a human Iglambda translocus (in addition to the human IgH + Igkappa transloci) not only diminishes problems of endogenous mouse Iglambda expression but also provides a strain of mice that yields fully human MAbs to a wide range of antigens, as witnessed by the isolation of MAbs to human blood cells, tumor cell lines, and an immunoglobulin idiotype.

Effect of omeprazole on oral and intravenous RS-methadone pharmacokinetics and pharmacodynamics in the rat

The effect of omeprazole on oral and intravenous (iv) RS-methadone pharmacokinetics and pharmacodynamics was studied in awake, freely moving rats, which were divided in four groups: oral RS-methadone (3 mg/kg) was given (a) to a control group (CO(oral)) (n = 65) and (b) to an omeprazole pretreated group (OP(oral)) (n = 77), and iv RS-methadone (0.35 mg/kg) was administered (c) to a control group (CO(iv)) (n = 86) and (d) to an omeprazole pretreated group (OP(iv)) (n = 86). Omeprazole (2 mg/kg) was given iv 2 h before RS-methadone. Plasma concentrations of RS-methadone (Cp) were determined by high-performance liquid chromatography and analgesic response by tail flick for 0-180 min (oral) and 0-120 min (iv). RS-Methadone rate of absorption (mean +/- SE) was faster in OP(oral) (k(01) = 0.31 +/- 0.04 min(-1)) than in CO(oral) (k(01) = 0.05 +/- 0.007 min(-1)), consequently plasma peak concentrations (C(max)) were greater (197.41 +/- 33.70 ng/mL versus 83.54 +/- 7.97 ng/mL) and the time to reach C(max) (t(max)) was shorter (11.23 +/- 1.32 min versus 39.18 +/- 1.74 min). Mean area under the Cp-time curve (AUC(0-infinity)) and hence bioavailability of oral RS-methadone were increased by omeprazole without significant changes in the elimination. Omeprazole did not affect the pharmacokinetics of iv RS-methadone. The changes of the analgesic effect of RS-methadone as a function of time were similar in all four groups. In the CO(oral) group, Cp and analgesic effect were defined by the E(max) model. The relationship between Cp and drug effect in the OP(oral) group showed a counterclockwise hysteresis (k(e0) of 0.018 +/- 0.006 min(-1)). For the iv groups (CO(iv) and OP(iv)), the Cp-analgesic effect relationship was described by an E(max) sigmoid model and omeprazole did not affect the pharmacodynamic parameters. It is concluded that omeprazole causes an increase in the bioavailability of oral RS-methadone without modifying the analgesic response but affecting the Cp-effect relationship.

Sex specificity in methadone analgesia in the rat: a population pharmacokinetic and pharmacodynamic approach

PURPOSE

To quantify the extent to which a sex-specific dichotomy in the temporal evolution of the analgesic effect, after intravenous (i.v.) methadone injection in the rat, relates to the pharmacokinetics (PK) and pharmacodynamics (PD) that mediate the dose-to-effect pathway.

METHODS

Tail-flick analgesia was measured after i.v. methadone injection (0.35 mg/kg) in female (n = 16) and male (n = 16) Sprague-Dawley rats. The PK were evaluated in separate female (n = 56) and male (n = 56) rats after they had received the same dose of methadone i.v. (0.35 mg/kg). A bicompartmental model described the kinetics and a sigmoid Emax model-related drug effect vs. simulated concentrations (pharmacodynamics) at the times of effect measurement. All model parameters as well as interanimal and assay variabilities were estimated with a mixed-effects population method using the program NONMEM.

RESULTS

The area under the effect-time curve (AUCE0-120) was (mean +/- interanimal SD) 1859+/-346 min in the females, which was significantly lower than the 4871+/-393 min in the males (P < 0.0001). On the contrary, the profiles of concentration vs. time were higher in females and, therefore, corresponded inversely to the effect vs. time-relative magnitudes. The central volume of distribution, V1, was 1.94+/-0.37 l/kg for female rats and 3.01+/-0.33 l/kg for male rats. Also, the central clearance was 0.077+/-0.006 l/min/kg and 0.102+/-0.005 l/min/ kg, respectively, for female and male rats. Both parameters differed significantly between sexes (P < 0.0001). The pharmacodynamic maximum observed effect parameter (Emax) was 37%+/-29% in female rats and 85%+/-16% in male rats, and these values were significantly different (P < 0.0001). The parameter for the concentration eliciting half of Emax (EC50) was 24.1+/-7.5 microg/l in female rats and 20.3+/-2.9 microg/l in male rats, and the Hill-related exponent, gamma, was 6.3+/-3.9 in female rats and 5.5+/-4.1 in male rats. These parameters did not differ significantly (at the P < 0.05 level).

CONCLUSIONS

A sex-specific dichotomy in the methadone antinociceptive effect, in the rat, was not proportionally related to plasma concentrations. Each sex corresponded to a distinct subpopulation of the PK parameters and one of the pharmacodynamic parameters (Emax). When the course of a drug involves PK or PD subpopulations, PK/PD modeling can afford the safest prediction of the effect-time evolution for a particular dose.

Pharmacokinetics and pharmacological effect of lerisetron, a new 5-HT3 antagonist, in rats

The pharmacokinetics of lerisetron, a novel 5HT(3) antagonist, are studied together with its efficacy in inhibiting the serotonin (5-HT)-evoked transient bradycardia reflex (von Bezold-Jarisch reflex) in Sprague Dawley rats. [(14)C]Lerisetron (50, 100, and 200 microg/kg) was given to rats by intravenous (iv) injection and plasma levels of unchanged (UL) and total (unchanged + changed, TL) drug were measured by liquid chromatography with radioactivity monitoring and scintillation counting, respectively. Linearity of UL and TL pharmacokinetics over the dose range was established by noncompartmental analysis. Protein binding of lerisetron was measured in vitro by ultrafiltration. The unbound fraction was 14.4 +/- 1.4%. A nonlinear mixed effects ("population") bicompartmental pharmacokinetic analysis showed that volume of distribution and clearance (CL) were high for both forms of the drug, but CL was significantly smaller for TL [(mean +/- SEM) 0.014 +/- 0.03 L/min for UL versus 0.006 +/- 0.03 L/min for TL, p < 0.05)]. Large interindividual variabilities were observed for both forms. The response to lerisetron administration (inhibition of bradycardia) was evaluated at different doses (2, 3, 5, 6, and 10 microg/kg, iv) at times 2-180 min after dose administration and related to simulated concentrations. Inhibition was 100% 5 min after the 10-microg/kg dose and, 3 h later, it was still > 10%. Response to lerisetron was dose related in the range studied. Pharmacodynamic parameters were estimated by a sigmoid E(max) naive-pooled model. The parameters were also different between the two forms: EC(50) was 0.44 ng/mL (CV = 5.9%) for UL and 0.88 ng/mL (CV = 4.9%) for TL. We conclude that UL and TL pharmacokinetics were linear and that the differences in the kinetics and dynamics between the two forms suggest the presence of at least one metabolite.

Altered disposition and effect of lerisetron in rats with elevated alpha 1-acid glycoprotein levels

PURPOSE

To examine the effect of changes in plasma alpha1-acid glycoprotein (AAG) levels on the pharmacokinetics (PK) and pharmacodynamics (PD) of lerisetron, a novel serotonin 5-HT3 receptor antagonist, in the rat.

METHODS

After subcutaneous administration of turpentine oil, AAG was significantly elevated compared with controls. The PK of unchanged lerisetron (UL; high-performance liquid chromatography with radioactivity monitoring) and total lerisetron (TL; unchanged + changed, scintillation counting) was characterized post intravenous (i.v.) 14C lerisetron (50 microg/kg) in control and turpentine oil pretreated rats. The PK (0-180 min) was described by a two-compartmental model. Protein binding of lerisetron in vitro was measured using an ultrafiltration technique. The effect of lerisetron (5 microg/kg, i.v.) over 180 min was measured in anesthetized rats (control and pretreated) with the Bezold-Jarisch reflex (inhibition of bradycardia after 16 microg/kg serotonin i.v.) as the endpoint. PD parameters were estimated by sigmoid Emax models.

RESULTS

The unbound fraction was significantly diminished in pretreated rats (mean +/- SEM) (6.60 +/- 1.23% vs. control 14.4 +/- 1.40%, P < 0.05). Volume of distribution (V) and clearance for UL and TL were significantly decreased when compared to the controls (P < 0.0001 for UL and P < 0.05 for TL). Plasma clearance based on unbound concentration for UL did not differ between groups but the unbound V and steady-state unbound V remained decreased (P < 0.05 and P < 0.0001). Pretreated rats showed a significantly diminished drug effect: the area under the E-t curve over 180 min was (mean +/- SEM) 5,189 +/- 657.7 in control animals vs. 3,486 +/- 464.4 in the pretreated group (P < 0.05). The EC50 (concentration at half maximum effect) for UL and TL were increased in pretreated rats and were not compensated when the unbound concentration was used.

CONCLUSIONS

An increase in AAG causes alterations in the PK and PD of lerisetron, and because this is not compensated with the unbound concentration, we suggest that mechanisms not linked to protein binding may be involved.