Margareta Hammarlund-Udenaes

A comprehensive pharmacist intervention to reduce morbidity in patients 80 years or older: a randomized controlled trial.

BACKGROUND Patients 80 years or older are underrepresented in scientific studies. The objective of this study was to investigate the effectiveness of interventions performed by ward-based pharmacists in reducing morbidity and use of hospital care among older patients. METHODS A randomized controlled study of patients 80 years or older was conducted at the University Hospital of Uppsala, Uppsala, Sweden. Four hundred patients were recruited consecutively between October 1, 2005, and June 30, 2006, and were randomized to control (n = 201) and intervention (n = 199) groups. The interventions were performed by ward-based pharmacists. The control group received standard care without direct involvement of pharmacists at the ward level. The primary outcome measure was the frequency of hospital visits (emergency department and readmissions [total and drug-related]) during the 12-month follow-up period. RESULTS Three hundred sixty-eight patients (182 in the intervention group and 186 in the control group) were analyzed. For the intervention group, there was a 16% reduction in all visits to the hospital (quotient, 1.88 vs 2.24; estimate, 0.84; 95% confidence interval [CI], 0.72-0.99) and a 47% reduction in visits to the emergency department (quotient, 0.35 vs 0.66; estimate, 0.53; 95% CI, 0.37-0.75). Drug-related readmissions were reduced by 80% (quotient, 0.06 vs 0.32; estimate, 0.20; 95% CI, 0.10-0.41). After inclusion of the intervention costs, the total cost per patient in the intervention group was

On The Rate and Extent of Drug Delivery to the Brain

230 lower than that in the control group. CONCLUSION If implemented on a population basis, the addition of pharmacists to health care teams would lead to major reductions in morbidity and health care costs.

AAPS-FDA workshop white paper: Microdialysis principles, application, and regulatory perspectives

To define and differentiate relevant aspects of blood–brain barrier transport and distribution in order to aid research methodology in brain drug delivery. Pharmacokinetic parameters relative to the rate and extent of brain drug delivery are described and illustrated with relevant data, with special emphasis on the unbound, pharmacologically active drug molecule. Drug delivery to the brain can be comprehensively described using three parameters: Kp,uu (concentration ratio of unbound drug in brain to blood), CLin (permeability clearance into the brain), and Vu,brain (intra-brain distribution). The permeability of the blood–brain barrier is less relevant to drug action within the CNS than the extent of drug delivery, as most drugs are administered on a continuous (repeated) basis. Kp,uu can differ between CNS-active drugs by a factor of up to 150-fold. This range is much smaller than that for log BB ratios (Kp), which can differ by up to at least 2,000-fold, or for BBB permeabilities, which span an even larger range (up to at least 20,000-fold difference). Methods that measure the three parameters Kp,uu, CLin, and Vu,brain can give clinically valuable estimates of brain drug delivery in early drug discovery programmes.

Species Differences in Blood-Brain Barrier Transport of Three Positron Emission Tomography Radioligands with Emphasis on P-Glycoprotein Transport

Many decisions in drug development and medical practice are based on measuring blood concentrations of endogenous and exogenous molecules. Yet most biochemical and pharmacological events take place in the tissues. Also, most drugs with few notable exceptions exert their effects not within the bloodstream, but in defined target tissues into which drugs have to distribute from the central compartment. Assessing tissue drug chemistry has, thus, for long been viewed as a more rational way to provide clinically meaningful data rather than gaining information from blood samples. More specifically, it is often the extracellular (interstitial) tissue space that is most closely related to the site of action (biophase) of the drug. Currently microdialysis (μD) is the only tool available that explicitly provides data on the extracellular space. Although μD as a preclinical and clinical tool has been available for two decades, there is still uncertainty about the use of μD in drug research and development, both from a methodological and a regulatory point of view. In an attempt to reduce this uncertainty and to provide an overview of the principles and applications of μD in preclinical and clinical settings, an AAPS-FDA workshop took place in November 2005 in Nashville, TN, USA. Stakeholders from academia, industry and regulatory agencies presented their views on μD as a tool in drug research and development.

The role of P-glycoprotein in blood-brain barrier transport of morphine: transcortical microdialysis studies in mdr1a (-/-) and mdr1a (+/+) mice.

Species differences occur in the brain concentrations of drugs, but the reasons for these differences are not yet apparent. This study was designed to compare brain uptake of three radiolabeled P-glycoprotein (P-gp) substrates across species using positron emission tomography. Brain concentrations and brain-to-plasma ratios were compared; [11C]verapamil in rats, guinea pigs, and monkeys; [11C](S)-(2-methoxy-5-(5-trifluoromethyltetrazol-1-yl)-phenylmethylamino)-2(S)-phenylpiperidine (GR205171) in rats, guinea pigs, monkeys, and humans; and [18F]altanserin in rats, minipigs, and humans. The fraction of the unbound radioligand in plasma was studied along with its metabolism. The effect of P-gp inhibition was investigated by administering cyclosporin A (CsA). Pronounced species differences were found in the brain and brain-to-plasma concentrations of [11C]verapamil, [11C]GR205171, and [18F]altanserin with higher brain distribution in humans, monkeys, and minipigs than in rats and guinea pigs. For example, the brain-to-plasma ratio of [11C]GR205171 was almost 9-fold higher in humans compared with rats. The species differences were still present after P-gp inhibition, although the increase in brain concentrations after P-gp inhibition was somewhat greater in rats than in the other species. Differences in plasma protein binding and metabolism did not explain the species-related differences. The findings are important for interpretation of brain drug delivery when extrapolating preclinical data to humans. Compounds found to be P-gp substrates in rodents are likely to also be substrates in higher species, but sufficient blood-brain barrier permeability may be retained in humans to allow the compound to act at intracerebral targets.

Drug Equilibration Across the Blood—Brain Barrier-Pharmacokinetic Considerations Based on the Microdialysis Method

The aim of this study was to investigate whether blood‐brain barrier transport of morphine was affected by the absence of mdr1a‐encoded P‐glycoprotein (Pgp), by comparing mdr1a (−/−) mice with mdr1a (+/+) mice. Mdr1a (−/−) and (+/+) mice received a constant infusion of morphine for 1, 2 or 4 h (9 nmol/min/mouse). Microdialysis was used to estimate morphine unbound concentrations in brain extracellular fluid during the 4 h infusion. Two methods of estimating in vivo recovery were used: retrodialysis with nalorphine as a calibrator, and the dynamic‐no‐net‐flux method. Retrodialysis loss of morphine and nalorphine was similar in vivo. Unbound brain extracellular fluid concentration ratios of (−/−)/(+/+) were 2.7 for retrodialysis and 3.6 for the dynamic‐no‐net‐flux at 4 h, with corresponding total brain concentration ratios of (−/−)/(+/+) being 2.3 for retrodialysis and 2.6 for the dynamic‐no‐net‐flux. The total concentration ratios of brain/plasma were 1.1 and 0.5 for mdr1a (−/−) and (+/+) mice, respectively. No significant differences in the pharmacokinetics of the metabolite morphine‐3‐glucoronide were observed between (−/−) and (+/+) mice. In conclusion, comparison between mdr1a (−/−) and (+/+) mice indicates that Pgp participates in regulating the amount of morphine transport across the blood‐brain barrier.

In vitro methods for estimating unbound drug concentrations in the brain interstitial and intracellular fluids

AbstractPurpose. The purpose of the study was to investigate the influence of different rates of transport into and out of the brain, including passive and active transport, on unbound brain concentrations and profile in relation to the blood concentration profile. Special emphasis is put on hydrophilic drugs. Methods. Simulations were performed with a model including one body compartment and one brain compartment, with linear or saturable transport into and out of the brain. Comparisons were made with experimental results from microdialysis (MD) studies. Results. Three features were evident when combining the MD results: 1) equilibration across the blood-brain barrier (BBB) is rapid, 2) half-life is similar in brain and blood for most drugs, and 3) unbound brain concentrations seldom reach the level of unbound blood concentrations. A low concentration ratio brain:blood is not mainly caused by a low influx, but rather by different influx and efflux clearances. Active transport out of the brain can explain the results, but also active transport into the brain under certain conditions. A small volume of distribution in brain vs. that in the rest of the body contributes to a rapid equilibration and similar half-lives. Conclusions. Assumptions of slow equilibration of hydrophilic drugs and similar unbound concentrations across the BBB at steady state are contradicted. The results are more in line with recent findings on the presence of P-glycoprotein and other transport mechanisms at the BBB. Non-passive transport across the BBB seems to be the case for almost all drugs studies with MD so far.

Structure−Brain Exposure Relationships in Rat and Human Using a Novel Data Set of Unbound Drug Concentrations in Brain Interstitial and Cerebrospinal Fluids

Concentrations of unbound drug in the interstitial fluid of the brain are not rapidly measured in vivo. Therefore, measurement of total drug levels, i.e., the amount of drug per gram of brain, has been a common but unheplful practice in drug discovery programs relating to central drug effects. This study was designed to evaluate in vitro techniques for faster estimation of unbound drug concentrations. The parameter that relates the total drug level and the unbound interstitial fluid concentration is the unbound volume of distribution in the brain (Vu,brain). It was measured in vitro for 15 drugs using brain slice uptake and brain homogenate binding methods. The results were validated in vivo by comparison with Vu,brain microdialysis results. The slice method results were within a 3-fold range of the in vivo results for all but one compound, suggesting that this method could be used in combination with total drug levels to estimate unbound interstitial fluid concentrations within reasonable limits. Although successful in 10 of 15 cases, the brain homogenate binding method failed to estimate the Vu,brain of drugs that reside predominantly in the interstitial space or compounds that are accumulated intracellularly. Use of the simple methods described in this article will 1) allow quantification of active transport at the blood-brain barrier in vivo, 2) facilitate the establishment of a relationship between in vitro potency and in vivo activity for compounds acting on central nervous system targets, and 3) provide information on intracellular concentrations of unbound drug.

In Vivo Blood-Brain Barrier Transport of Oxycodone in the Rat: Indications for Active Influx and Implications for Pharmacokinetics/Pharmacodynamics

New experimental methodologies were applied to measure the unbound brain-to-plasma concentration ratio (K(p,uu,brain)) and the unbound CSF-to-plasma concentration ratio (K(p,uu,CSF)) in rats for 43 structurally diverse drugs. The relationship between chemical structure and K(p,uu,brain) was dominated by hydrogen bonding. Contrary to popular understanding based on the total brain-to-plasma concentration ratio (logBB), lipophilicity was not a determinant of unbound brain exposure. Although changing the number of hydrogen bond acceptors is a useful design strategy for optimizing K(p,uu,brain), future improvement of in silico prediction models is dependent on the accommodation of active drug transport. The structure-brain exposure relationships found in the rat also hold for humans, since the rank order of the drugs was similar for human and rat K(p,uu,CSF). This cross-species comparison was supported by K(p,uu,CSF) being within 3-fold of K(p,uu,brain) in the rat for 33 of 39 drugs. It was, however, also observed that K(p,uu,CSF) overpredicts K(p,uu,brain) for highly effluxed drugs, indicating lower efflux capacity of the blood-cerebrospinal fluid barrier compared to the blood-brain barrier.

Methodological Aspects of the Use of a Calibrator in In Vivo Microdialysis–Further Development of the Retrodialysis Method

The blood-brain barrier (BBB) transport of oxycodone was studied in rats. Microdialysis probes were inserted into the striatum and vena jugularis. Ten animals were given a bolus dose followed by a 120-min constant rate infusion to study the steady-state concepts of oxycodone BBB equilibration. Another 10 animals were given a 60-min constant rate infusion to study the rate of equilibration across the BBB. Oxycodone-D3 was used as a calibrator for the microdialysis experiments. The samples were analyzed with a liquid chromatography-tandem mass spectrometry method and a population pharmacokinetic model was used to simultaneously fit all the data using NONMEM. A two-compartment model which allowed for a delay between the venous and arterial compartments best described the pharmacokinetics for oxycodone in blood and plasma, whereas a one-compartment model was sufficient to describe the pharmacokinetics in the brain. The BBB transport of oxycodone was parameterized as CLin and Kp,uu. CLin describes the clearance of oxycodone across the BBB into the brain, whereas Kp,uu describes the extent of drug equilibration across the BBB. CLin across the BBB was estimated to 1910 μl/min · g brain. Kp,uu was estimated to 3.0, meaning that the unbound concentration of oxycodone in brain was 3 times higher than in blood, which is an indication of active influx of oxycodone at the BBB. This is the first evidence of an opioid having an unbound steady-state concentration in brain that is higher than unity, which can explain potency discrepancies between oxycodone and other opioids.