An improved method for specific and quantitative determination of the clopidogrel active metabolite isomers in human plasma

Pharmacokinetic analyses of clopidogrel are hampered by the existence of multiple active metabolite isomers (H1 to H4) and their instability in blood. We sought to retest the pharmacodynamic activities of the four individual active metabolite isomers in vitro, with the ultimate aim of determining the isomers responsible for clopidogrel activity in vivo. In vitro activity was evaluated by measuring binding of [33P]-2-methylthio-ADP on P2Y??-expressing Chinese hamster ovary (CHO) cells and human platelets in platelet-rich plasma (PRP). A stereoselective method that used reverse-phase ultra high-performance liquid chromatography (UHPLC) and tandem mass spectrometry (MS) was developed to measure individual concentrations of the stable 3'-methoxyacetophenone (MP) derivatives of H1-H4. The new method was used to analyze plasma samples from clopidogrel-treated subjects enrolled in a phase I clinical trial. In vitro binding assays confirmed the previously observed biological activity of H4 (IC??: CHO-P2Y??: 0.12 μM; PRP: 0.97 μM) and inactivity of H3, and demonstrated that H1 was also inactive. Furthermore, H2 demonstrated approximately half of the biological activity in vitro compared with H4. Optimisation of UHPLC conditions and MS collision parameters allowed the resolution and detection of the four derivatised active metabolite isomers (MP-H1 to MP-H4). The stereoselective assay was extensively validated, and was accurate and precise over the concentration range 0.5-250 ng/ml. Only MP-H3 and MP-H4 were quantifiable in incurred clinical samples. Based on in vitro pharmacodynamic data and found concentrations, the active metabolite isomer H4 is the only diastereoisomer of clinical relevance for documenting the pharmacokinetic profile of the active metabolite of clopidogrel.     

Sensitivity of Medication Use to Formulary Controls in Medicare Beneficiaries: A Review of the Literature

Background

Several studies have examined the impact of formulary management strategies on medication use in the elderly, but little has been done to synthesize the findings to determine whether the results show consistent trends.

Objective

To summarize the effects of formulary controls (ie, tiered copays, step edits, prior authorization, and generic substitution) on medication use in the Medicare population to inform future Medicare Part D and other coverage decisions.

Methods

This systematic review included research articles (found via PubMed, Google Scholar, and specific scientific journals) that evaluated the impact of drug coverage or cost-sharing on medication use in elderly (aged ≥65 years) Medicare beneficiaries. The impact of drug coverage was assessed by comparing patients with some drug coverage to those with no drug coverage or by comparing varying levels of drug coverage (eg, full coverage vs $1000 coverage or capped benefits vs noncapped benefits). Articles that were published before 1995, were not original empirical research, were published in languages other than English, or focused on populations other than Medicare beneficiaries were excluded. All studies selected were classified as positive, negative, or neutral based on the significance of the relationship (P <.05 or as otherwise specified) between the formulary control mechanism and the medication use, and on the direction of that relationship.

Results

Included were a total of 47 research articles (published between 1995 and 2009) that evaluated the impact of drug coverage or cost-sharing on medication use in Medicare beneficiaries. Overall, 24 studies examined the impact of the level of drug coverage on medication use; of these, 96% (N = 23) supported the association between better drug coverage (ie, branded and generic vs generic-only coverage, capped benefit vs noncapped benefit, supplemental drug insurance vs no supplemental drug insurance) or having some drug coverage and enhanced medication use. Furthermore, 84% (N = 16) of the 19 studies that examined the effect of cost-sharing on medication use demonstrated that decreased cost-sharing was significantly associated with improved medication use.

Conclusion

Current evidence from the literature suggests that restricting drug coverage or increasing out-of-pocket expenses for Medicare beneficiaries may lead to decreased medication use in the elderly, with all its potential implications.Patient access to healthcare resources is an important topic of healthcare discussion, research, and reform in the United States.1,2 Access issues are usually framed in the context of patients having health insurance, as the quality of health insurance facilitates patient access to necessary medical and pharmaceutical therapies.2 Although patient access to medications is essential, formulary management strategies may introduce barriers aimed at restricting utilization, including curbing patient demand by increasing the cost borne by the patient or providing incentives to select lower-cost alternatives. Examples of these strategies include tiered copays, coinsurance, and benefit caps.3,4

KEY POINTS

• ▸ Many studies have investigated the impact of formulary management (eg, tiered copays, step edits, prior authorization) on medication use (eg, adherence, change in days supply, medication fills) patterns in Medicare beneficiaries, but none has synthesized the findings to arrive at some common trends in this patient population.
• ▸ The present study reviewed 47 studies that had met the study criteria involving medication use by Medicare beneficiaries between 1995 and 2009.
• ▸ Among the 24 studies that investigated the impact of drug coverage on medication use, 23 showed that elderly patients with greater drug coverage are more likely to use their medications as prescribed than those with greater coverage restrictions.
• ▸ Of the 19 studies that examined the effect of cost-sharing on medication use, 16 demonstrated that decreased patient cost-sharing improved medication use.
• ▸ Overall, the evidence shows that more restrictive drug coverage is associated with reduced medication use among Medicare beneficiaries, and fewer restrictions encourage enhanced medication use.
• ▸ Health plans are facing increasing pressures to implement strategies to control costs, including drug costs; nevertheless, restricting access to necessary medications in the elderly may lead to suboptimal clinical outcomes and potentially greater medical expenditures.

The advent of Medicare Part D in 2006 made the federal government the single largest payer of medications in the country, providing coverage to Medicare beneficiaries and the disabled. Although Part D is sponsored by the Centers for Medicare & Medicaid Services (CMS), it is administered by health plans that have the ability to implement restrictions on medication use in the form of drug benefit. Evidence generated from previous studies demonstrate that formulary controls can impact patients'' medication-taking behavior and, ultimately, patient outcomes.4 However, conclusions drawn from these studies were largely based on populations that included nonelderly, commercial, or non-US populations.4 Elderly people could behave differently from younger people in response to formulary controls, given their increased likelihood of comorbidities and greater need for medications to maintain good health.No study to date has collated existing data to assess the consistency in the findings regarding the impact of formulary controls on medication use—defined in this current study as adherence, change in days supply, medication fills, and number of tablets—in the elderly. Synthesizing evidence from previous studies involving elderly populations may help in assisting Medicare and other health plan benefit design guidelines in the future.Therefore, the objective of this study was to summarize the effects of formulary controls on the US elderly (ie, Medicare) population based on previously published studies to generate evidence using earlier research that could be used to make future coverage decisions. Formulary controls included all formulary strategies that use mechanisms such as formulary restrictions and benefit design, including tiered copayments, step edits, prior authorization, and generic substitution.     

Integrating objective gene-brain-behavior markers of psychiatric disorders

There is little consensus about which objective markers should be used to assess major psychiatric disorders, and predict/evaluate treatment response for these disorders. Clinical practice relies instead on subjective signs and symptoms, such that there is a "translational gap" between research findings and clinical practice. This gap arises from: a) a lack of integrative theoretical models which provide a basis for understanding links between gene-brain-behavior mechanisms and clinical entities; b) the reliance on studying one measure at a time so that linkages between markers are their specificity are not established; and c) the lack of a definitive understanding of what constitutes normative function. Here, we draw on a standardized methodology for acquiring multiple sources of genomic, brain and behavioral data in the same subjects, to propose candidate markers of selected psychiatric disorders: depression, post-traumatic stress disorder, schizophrenia, attention-deficit/hyperactivity disorder and dementia disorders. This methodology has been used to establish a standardized international database which provides a comprehensive framework and the basis for testing hypotheses derived from an integrative theoretical model of the brain. Using this normative base, we present preliminary findings for a number of disorders in relation to the proposed markers. Establishing these objective markers will be the first step towards determining their sensitivity, specificity and treatment prediction in individual patients.     

Contemporary management of lipoblastoma

Purpose

Lipoblastoma is a rare, benign, adipose tissue tumor. We report the largest single institution experience managing these uncommon neoplasms.

Methods

We retrospectively reviewed 32 cases of lipoblastoma entered in the pathology database at our institution between January 1991 and August 2005. We conducted a comprehensive literature review of lipoblastoma and summarized the results of the largest series published.

Results

Most patients presented with an enlarging, palpable, firm, nontender, mobile mass. The male-to-female ratio was 1.9:1. The anatomical distribution was trunk (n = 12), extremity (n = 12), groin (n = 5), and neck (n = 3). Average age at resection was 2.8 years (range, 2.6 months to 12 years). Thirty-one cases were completely excised, although 1 patient underwent staged partial excision to preserve nerve function. Chromosomal analysis performed in selected patients revealed characteristic aberrations in chromosome 8. Complications included keloid formation (n = 3), wound infection/dehiscence (n = 2), wound seroma (n = 1), and transient brachial plexus neurapraxia (n = 1). Average follow-up was 7.4 months (range, 1 day to 6.5 years); 2 patients were lost to follow-up. There were no recurrences.

Conclusions

A staged approach with meticulous sparing of the neurovascular bundle provides excellent functional outcome for patients with large tumors. Nonmutilating surgical excision is the treatment of choice.     

Physical activity in preschoolers: understanding prevalence and measurement issues

Accurate physical activity quantification in preschoolers is essential to establish physical activity prevalence, dose-response relationships between activity and health outcomes, and intervention effectiveness. To date, best practice approaches for physical activity measurement in preschool-aged children have been relatively understudied. This article provides a review of physical activity measurement tools for preschoolers, an overview of measurement of preschoolers' physical activity, and directions for further research. Electronic and manual literature searches were used to identify 49 studies that measured young children's physical activity, and 32 studies that assessed the validity and/or reliability of physical activity measures with preschool-aged children. While no prevalence data exist, measurement studies indicate that preschool children exhibit low levels of vigorous activity and high levels of inactivity, boys are more active than girls, and activity patterns tend to be sporadic and omnidirectional. As such, measures capable of capturing differing activity intensities in very short timeframes and over multiple planes are likely to have the most utility with this population. Accelerometers are well suited for this purpose, and a number of models have been used to objectively quantify preschoolers' physical activity. Only one model of pedometer has been investigated for validity with preschool-aged children, showing equivocal results. Direct observation of physical activity can provide detailed contextual information on preschoolers' physical activity, but is subjective and impractical for understanding daily physical activity. Proxy-report questionnaires are unlikely to be useful for determining actual physical activity levels of young children, and instead may be useful for identifying potential correlates of activity. Establishing validity is challenging due to the absence of a precise physical activity measure, or 'criterion', for young children. Both energy expenditure (EE) and direct observation have been considered criterion measures in the literature; however, EE is influenced by multiple variables, so its use as a physical activity 'criterion' is not ideal. Also, direct observation is inherently subjective, and coding protocols may result in failure to capture intermittent activity, thereby limiting its utility as a physical activity criterion. Accordingly, these issues must be taken into account where EE or direct observation are used to validate physical activity instruments. A combination of objective monitoring and direct observation may provide the best standard for the assessment of physical activity measurement tools. Ideally, the convergent validity of various physical activity tools should be investigated to determine the level of agreement between currently available measures. The correlational approaches commonly employed in the assessment of physical activity measures do not reveal this relationship, and can conceal potential bias of either measure.     

Roscovitine differentially affects CaV2 and Kv channels by binding to the open state

Roscovitine potently inhibits cyclin-dependent kinases (CDK) and can independently slow the closing of neuronal (CaV2.2) calcium channels. We were interested if this drug could affect other ion channels similarly. Using whole cell recordings, we found that roscovitine specifically slows deactivation of all CaV2 channels (N, P/Q and R) by binding to the open state. This effect had a rapid onset and EC(50)=54, 120 and 54microM for N-, P/Q-, and R-type channels, respectively. Deactivation of other channel types was not slowed, including L-type calcium channels (CaV1.2, CaV1.3), potassium channels (native, Kv4.2, Kv2.1 and Kv1.3), and native sodium channels. However, most of the channels tested were inhibited by roscovitine. The inhibition was characterized by slow development and a lower affinity (EC(50)=100-300microM). Surprisingly, potassium channels were rapidly inhibited with an EC(50)=23microM, which is similar to the EC(50) for roscovitine block of cell division [Meijer, L., Borgne, A., Mulner, O., Chong, J., Blow, J., Inagaki, N., Inagaki, M., Delcros, J., Moulinoux, J., 1997. Biochemical and cellular effects of roscovitine, a potent and selective inhibitor of the cyclin-dependent kinases cdc2, cdk2 and cdk5. Eur. J. Biochem. 243, 527-536]. Potassium current inhibition seemed to result from open channel block. The high potency of these two rapid onset effects makes them complicating factors for ongoing clinical trials and research using roscovitine. Thus, the physiology and pharmacology of slow CaV2 deactivation and potassium channel block must be explored.