Antinociceptive Agents as General Anesthetic Adjuncts: Supra-additive and Infra-additive Interactions

The hypothesis "General anesthesia consists of producing both loss of consciousness and the inhibition of noxious stimuli reaching the brain and causing arousal" was used as a basis for the review of published data on general anesthetic interactions with antinociceptive agents: opioids, α 2 adrenergic agonists, and systemic sodium channel blockers. This review is focused on a specific type of anesthetic interaction-the transformation of antinociceptive agents into general anesthetic adjuncts. The primary aim is to answer 2 questions. First, how does an antinociceptive agent transform the effect of an anesthetic in providing a certain component of anesthesia-hypnosis, immobility, or hemodynamic response to noxious stimulation? Second, does a combination of an anesthetic with an adjunct result in a simple summation of their respective effects or in a supra-additive or infra-additive interaction? The Medline database was searched for data describing the interactions of antinociceptive agents and general anesthetics. The following classes of antinociceptive agents were considered: opioids, α 2 adrenergic agonists, and systemic sodium channel blockers. Drugs used in combination with antinociceptive agents were general anesthetics and benzodiazepines. The following terms related to drug interactions were used: anesthetic interactions, synergy, antagonism, isobolographic analysis, response surface analysis, and fractional analysis. The interactions of antinociceptive agents with general anesthetics result in a decrease of general anesthetic requirements, which differ for each of the components of general anesthesia: hypnosis, immobility, and hemodynamic response to noxious stimulation. Most studies of the nature of anesthetic interactions are related to opioid-general anesthetic combinations, and their conclusions usually confirm supra-additivity.

Components of General Anesthesia: History of the Concept Transformation

The concept that the state of general anesthesia consists of a number of components representing the distinct and desired central effects of general anesthetics was formulated when it was common to believe that all components of anesthesia have a lipid-centered mechanism of action. The transformation of this concept was associated with changes in our understanding of the mechanisms underlying general anesthetic action. First came the shift from a lipid- to a protein-centered mechanism of action, which opened the way to various molecular targets associated with general anesthesia. Then, it was found that different components of anesthesia may have completely different underlying mechanisms, such as blockade of movement in response to noxious stimulation by isoflurane centers at the spinal cord level, not at the brain, as is the case with other components. The chain of discoveries associated with newfound differences between components of anesthesia accompanied general progress toward a more comprehensive understanding of the mechanism of action of general anesthetics, including anesthetic binding sites, details of receptors and ion channels involved in neurotransmission, and the critical role of neuronal networks. There are several important consequences of our improved understanding. First, a single measurement of anesthetic depth (eg, minimum alveolar concentration index [MAC index]) might not be appropriate for the different component of anesthesia. Second, because the mechanism of action of the components varies, synergy for 1 component does not exclude an additive effect or even antagonism for another component.

Clinical studies that initiated the use of spinal opioids for the treatment of pain: A new approach to historical review

Opioids administered into the spinal space by intrathecal or epidural routes can provide potent and prolonged selective analgesia. Compared to the systemic administration of opioids, spinal administration can bring about analgesia with fewer central and systemic adverse effects. For the past 40 years, spinal opioid analgesia has achieved great popularity in various fields of pain treatment. The aim of this work is to identify clinical studies that initiated the use of spinal opioids for the treatment of pain. To determine the historical role of each of the review's studies we used the combination of two factors: the study priority in terms of the time of its publication and the degree of its acknowl-edgement in the form of citation impact. The date of publication was regarded as the primary factor, but only if the count of citations indicated a sufficient acknowledgement by the other authors. The citation impact was assessed as the initial citation count - for period of five years after the year of article publication - and the total count. The selection of studies most important for the introduction of spinal opioids to clinical practice was based on two factors - the study priority in terms of the time of its publication and the degree of acknowledgement in the form of citation impact. The date of publication was regarded as the primary factor, but only if the citation count was indicative of sufficient acknowledgement by other authors. Analysis of the related data shows that the clinical studies initiating the use of spinal opioids for the treatment of pain belong to two groups of authors - Wang et al. and Behar et al. Both studies were published in 1979 and described delivery of morphine into the spinal space, although the techniques of administration were different: Wang et al. injected morphine intrathecally, Behar et al. administered morphine epidurally. The response to these studies was overwhelming -- close to a dozen reports on this topic were published in 1979 and more than a hundred - in 1980-1981. The total citation response to the Wang et al. article reached 699, and that to Behar et al. - 518. Two earlier records (1900-1901) of the use of intrathecal morphine, by Nicolae Racoviceanu-Pitesti and Otojiro Kitagawa, found no following in medical literature for more than three quarters of a century.

Progress in analgesic development: How to assess its real merits?

BACKGROUND

Assessing analgesic drugs developed over preceding 50 years demonstrated that very intensive efforts directed at diverse molecular pain targets produced thousands of PubMed articles and the introduction of more than 50 new analgesics. Nevertheless, these analgesics did not have a sufficiently broad spectrum of action and level of effectiveness to demonstrably affect the use of opioids or nonsteroidal anti-inflammatory drugs for the treatment of pain. Analgesics in current are only modestly effective in chronic pain (at least with respect to neuropathic pain), and the widespread application of mu opioid receptor agonists for this purpose culminated in the global "opioid crisis". The introduction of every new drug is regarded as an important success, at least initially. Assessing the merit of a new analgesic is extremely complicated.

OBJECTIVE

The aim of this article is to describe an approach that combines very different categories of drug evaluation - multifactorial approach to assessment of new analgesics. It is based on conclusiveness of clinical trials, novelty of a drug's molecular target, a drug's commercial appeal, and the interest in a drug reflected by scientometric indices.

RESULTS

This approach was applied to analgesics developed in 1982-2016. It shows that although several new agents have completely novel mechanisms of action, all newly approved drugs, and drug candidates, demonstrated the same persistent problems: relatively low therapeutic advantage over previous treatment and narrow spectrum of use in different types of pain, compared to opioids or NSAIDs.

CONCLUSION

The use of the suggested multifactorial approach to drug assessment may provide a better view of the whole spectrum of analgesics advantages and disadvantages.

High-Impact Clinical Studies That Fomented New Developments in Anesthesia: History of Achievements, 1966-2015

The aim of this work is to identify the most influential initial clinical studies that fomented important developments in anesthesiology over the past 50 years. Studies fomenting new development can be selected using vastly different approaches and, therefore, might provide diverse outcomes. In the present work, two basic aspects of study assessments – the stage of development (eg, generation of idea, preclinical studies, clinical trials) and the method of selection (eg, committee vote, various types of citation analysis, method of finding the invention disclosure) – were chosen according to the following model. The stage of development: the initial clinical studies demonstrating the basic advantage of an innovation for providing anesthesia. The method: a combination of two factors – the study priority in terms of the time of its publication and the degree of its acknowledgement in the form of citation impact; the time of study publication was regarded as a primary factor, but only if the study’s citation count was =/>20. The initial high-impact studies were selected for 16 drug-related topics (ketamine, isoflurane, etomidate, propofol, midazolam in anesthesia, vecuronium, alfentanil, atracurium, sevoflurane, sufentanil, rocuronium, desflurane, ropivacaine, remifentanil, dexmedetomidine in anesthesia, and sugammadex), and 9 technique-related topics (ultrasound-guided peripheral nerve block, capnography in anesthesia, target-controlled intravenous anesthesia, pulse oximetry in anesthesia, total intravenous anesthesia, transesophageal echocardiography in anesthesia, combined spinal-epidural anesthesia, and bispectral index). Twenty-five studies were designated the first high-impact studies (one for each topic); 16 are drug-related and 9 are technique-related. Half of the first high-impact studies had a citation count of =/>100, (range: 100 to 555). The citation count of the other half of high-impact studies did not reach the 100-citation threshold (range: 41 to 97). If a selected first high-impact study had a citation count <100, a next-on-timeline, additional study with citation count =/>100 was also selected; (range: 100 to 344). The present results show that an initial high-impact clinical study on a new development in anesthesiology can be determined and that related citations usually vary from one hundred to five hundred.

Academic Interest in Pain: Comparison of Four Specialties With Long-Standing Involvement in Pain Medicine

PURPOSE

One of the most interesting signs of growth in a medical specialty is the addition of pain medicine as a clinical subspecialty to it. The aim of this study was to analyze publication-based academic interest in pain medicine among clinical specialties with long-standing involvement in pain management.

METHODS

We assessed the activity within several specialties in the development of an academic foundation for pain medicine by measuring the frequency of the most common pain topics (1998-2017) in academic journals representing such specialties. The selection of materials for the analysis of publication-based academic interest associated with the development of pain medicine followed a three-step process: (1) Medical specialties, limited to those with accredited fellowship training in pain medicine for more than 20 years - anesthesiology, neurology, physiatry, and psychiatry; (2) Pain topics, based on the degree of topic association with the work of pain clinics - a total of 34 topics; (3) Specialty journals, mostly official journals of societies publishing articles representing all aspects of a specialty - four journals per specialty. Specialty-related academic interest was characterized in two dimensions: its breadth (the number of different topics of interest with distinctly high shares of publications) and its intensity (maximal number of publications on a particular topic).

RESULTS

According to the number of topics with a distinctly high share of articles per topic (≥ 5%), the rank order of specialties was as follows (of 34 topics): anesthesiology (22), physiatry (20), neurology (10), and psychiatry (0). Regarding comparative intensity of interest, anesthesiology has prevailing interest in 16 topics (especially in postoperative pain and pharmacologic pain treatment), physiatry in 13 topics (especially in physical methods of pain therapy), and neurology in one topic (headache disorders).

CONCLUSION

Publication-based academic interest in pain management was most intensive in two specialties, anesthesiology and physiatry, with anesthesiology being somewhat more multifaceted, especially in the methods of pain treatment.

Problems with Developments of Breakthrough Analgesics: Recent History via Scientometric Analysis

This study evaluated 13 specific topics representing molecular targets for pain during the period 1982-2016. The evaluation was performed by measuring research efforts via a scientometric approach on one hand and by assessing successful outcomes of these efforts, as indicated by the development of FDA-approved analgesics, on the other. A number of new analgesics were developed during this period, some of them with a completely novel mechanism of action. However, the main problems with approved drugs, as well as drug candidates, are relatively low levels of clinical superiority in effectiveness and narrow spectrum of action in different types of pain, compared to opioids or NSAIDs. The most interesting feature of the scientometric analysis of the 13 analgesic discovery topics is the long-lasting growth in the number of articles. The total number of all PubMed articles persistently increased over each of many 5-year periods in every topic even without any success in the development of new analgesics. Scientometric indices of NIH-supported studies are not better at predicting successes in the discovery of new analgesics than indices applied to all publications without regard to the category of support. Thus, even the highly valued NIH-based funding system did not demonstrate a clear advantage for discovery efforts centered on pain-related molecular targets. The evaluated research efforts did not result in breakthrough analgesics that could demonstrably affect the current use of opioids or NSAIDs. Orthodox thinking-both in research and research funding-might be the main reason for the absence of breakthrough analgesics.

Academic Journals Assessed as Springboards for New Developments: A Study of Leading Anesthesia Journals Over Past 50 Years

PURPOSE

The impact of academic journals on scientific activity can be measured using different approaches. The aim of this study was to assess the leading anesthesia journals as springboards for new developments in the field of anesthesia.

METHODS

The selection of the topics for analysis was based on the degree of increase in the number of articles on a topic that was at the center of specialty interest during 1966-2015. The assessment of a journal's response to a new development was made by measuring the number of initial articles on a related topic. Six leading anesthesia journals were assessed collectively and individually as to whether their responses to new developments were prompt and prominent.

RESULTS

The role of the leading specialty journals in presentation of 28 topics related to prominent new developments in anesthesia was found to depend on the nature of topics and the type of articles. Compared with all PubMed journals publishing articles associated with anesthesia in 1966-2015, the six leading anesthesia journals published 43% of drug-related research articles, 30% of technique-related research articles, and 16% of both drug- and technique-related review articles. Regarding initial publications (on new topics), this group of six journals contributed comparably more articles: from 43% to 84% of drug-related research articles, from 30% to 49% of technique-related research articles, from 16% to 33% of drug-related review articles, and from 16% to 25% of technique-related review articles. The approximate doubling of the shares demonstrates the dominance of this group of journals in the swiftness response to new anesthesia developments. The promptness of reaction to new developments in anesthesia of each of the six leading anesthesia journals was assessed (the combination of drug- and technique-related articles) based on the number of articles published among the first (first 5 plus next 30) on all 28 topics. The ranking order of four journals (with the highest number of all 1966-2015 articles) regarding early publications was (from high to low): Anesthesia & Analgesia, British Journal of Anaesthesia, Anesthesiology, and Anaesthesia.

CONCLUSION

This study assesses six leading anesthesia journals for their function as springboards for new developments in anesthesia over the past 50 years. The dominance of leading journals in initial publications on 28 drug-related and technique-related topics was clearly demonstrated. The results also indicate the possibility of using promptness of response to new advances for quantitative assessment of this aspect of a journal's contribution to the specialty.

Recent History of Publication-Based Academic Interest in General Anesthetics

PURPOSE

The aim of this study was to determine how interest in various general anesthetics among the authors of academic publications changed over the past 50 years.

METHODS

Publication-based academic interest were analyzed using specific scientometric indices: popularity index (PI), top journal selectivity index (TJSI), and index of change (IC). Terms used for searches were the names of drugs belonging to two pharmacological classes of general anesthetics - inhaled and intravenous. Only those that had a PI value > 2.0 during at least one of the 10 five-year periods, from 1967 to 2016, were selected.

RESULTS

The PI, an index of comparative popularity, reflects a consistent decline in academic interest over time in both classes of general anesthetics. Over the past 25 years, the PI of inhaled anesthetics decreased by 52 %, and that of intravenous anesthetics fell by 32%. At the same time, the PI of anesthesia management increased by 167%. Among individual anesthetics, the most impressive change was a profound decline in halothane's PI, from 22.9 in 1972-1976 to 0.5 in 2012-2016. The interest in halothane was gradually supplanted by that in new agents, initially by enflurane, followed by isoflurane and finally, sevoflurane. The next meaningful change was the gradual rise in sevoflurane's PI to surpass that of isoflurane. The most dramatic change among the PIs of intravenous anesthetics was associated with the introduction of propofol: an increase from 1.8 to its maximum of 13.6.

CONCLUSIONS

The study revealed a constant decline over time in academic interest in the pharmacological basis of general anesthesia relative to all fields of anesthesia combined.

What Can Big Data on Academic Interest Reveal about a Drug? Reflections in Three Major US Databases

The different stages of the life cycle of a drug - 'prenatal' stage, birth of a drug, rapid growth, maturity and stability, decline, and status before 'death' - are reflected in the three following databases: journal articles (PubMed-www.ncbi.nlm.nih.gov/pubmed); patents (US Patent Office-http://partfl1.uspto.gov/netahtml/PTO/search-adv.htlm); and approved drugs (FDA - www.accessdata.fda.gov/scripts/cder/drugsatfda/index/cfm). These databases are huge, from authoritative sources, correctly classified, and they properly link different datasets. Analysis of such data can uncover hidden patterns important for the assessment of drug status and may also yield some predictions regarding its future prospects. Drug-related, publication-based academic bibliographic records are especially numerous and support the development of various scientometric indices. In combination with information from other types of databases, they can outline various trends in pharmacology. Scientometric indices can be classified into those indicating a change in the status of a drug, and those assessing the chances for success, or even drug discontinuation. Here, we present big data analytics on publication-based academic interest in two segments: (i) description of scientometric indices and (ii) their applications for the assessment of the status of a drug.

Publication-Based Academic Interest in Drugs and Techniques for Treatment of Postoperative Pain, 1975-2015

PURPOSE

The aim of this study was to determine how drugs and their administration techniques, introduced over the past 40 years and still popular now, influenced publication-based academic interest in the treatment of postoperative pain.

METHODS

Specific scientometric indices-popularity index (PI), top journal selectivity index (TJSI), and index of change (IC)-were used. Of the 61 terms searched, only those that had a PI value ≥1.0 during the 2011-2015 period were selected. They include eight drugs-bupivacaine, fentanyl, ropivacaine, acetaminophen, tramadol, remifentanil, and dexamethasone-and five techniques-patient-controlled analgesia, epidural opioids, ultrasound-guided nerve blocks, continuous nerve blocks, and transversus abdominis plane block (presented according to their decreasing PI value in each category).

RESULTS

Four of these drugs or techniques with the highest PI in 2011-2015 also held top positions even 20 years earlier: in 1991-1995, the PI for bupivacaine was 9.1; fentanyl, 6.6; patient-controlled analgesia, 10.4; and epidural opioids, 6.8. Since that time, their PI values slowly decreased, for the first three items by approximately 50% and much more than that (85%) with epidural opioids. Nevertheless, to this day, they continue to hold the highest degree of publication-based academic interest. The TJSI can be regarded as an index of expectations at the time of articles publication. With bupivacaine, fentanyl, patient-controlled analgesia, and epidural opioids, the TJSI exceeded the specific high threshold of 10.0 for a very long time. The TJSIs of acetaminophen, ketamine, and dexamethasone were increased with the advent of new expectations regarding the treatment of postoperative pain using these old agents.

CONCLUSIONS

Two important developments related to ultrasound-guided nerve block and continuous nerve block demonstrated only a moderate degree of academic interest. In conclusion, even today, the greatest publication-based academic interest related to postoperative pain is associated with drugs and techniques introduced 40-50 years ago.

Assessing advances in regional anesthesia by their portrayals in meta-analyses: an alternative view on recent progress

BACKGROUND

The aim of this study was to delineate research reflecting advances in regional/local anesthesia where recent clinical progress was clearly defined by meta-analysis.

METHODS

We conducted a search to identify all articles with meta-analyses of randomized clinical trials related to the field of regional/local anesthesia. From 279 titles, after multiple exclusions, 16 meta-analyses on important clinical practice developments with high potential for a positive conclusion on the effectiveness of the treatment were left for the assessment. The assessment was performed in two steps. The first step was related to verification of proof-of-concept: the effect is statistically reliable (p-value, effect size, heterogeneity across different RCTs) and the risk of bias not too high. The second step was devoted to attempts to form an opinion on the real clinical benefits of a new development.

RESULTS

The assessment revealed that seven recent developments passed the proof-of-concept step. At the same time, positive conclusion on real clinical benefits was reached only by one of these seven developments: ultrasound guidance for peripheral nerve blocks (at least with some of the blocks). Meaningful clinical improvements with other developments remains uncertain. The assessment of the relationships between analyzed advancements over the past 30 years and earlier similar developments indicated that their evolution was usually incremental. The most original advancement was found to be the introduction of the transversus abdominis plane block.

CONCLUSION

The assessment of recent advances in regional/local anesthesia, based on the evaluation of related meta-analyses, revealed only incremental progress with mostly marginal benefits. The progress was the most notable with ultrasound guidance for some of peripheral nerve blocks.

Changes in Publication-Based Academic Interest in Local Anesthetics Over the Past 50 Years

PURPOSE

To present the history of changes in academic interest in local anesthetics quantitatively.

METHODS

The changes in publication-based academic interest in local anesthetics were assessed using information from the database of PubMed. The assessment was mostly based on the following indices: general popularity index (GPI), representing the proportion of articles on a drug relative to all articles in the field of regional anesthesia, and specific popularity index (SPI), representing the proportion of articles on a drug relative to all articles in one of the four forms of regional anesthesia: local anesthesia, spinal anesthesia, epidural anesthesia, and peripheral nerve blocks.

RESULTS

The most important general feature of the changes in publication-based academic interest in local anesthetics for the past 50 years was the concentration of this interest on a very limited number of drugs. By 2010-2014, only three anesthetics demonstrated the GPI value above 4.0: bupivacaine (10.1), lidocaine (10.0), and ropivacaine (4.6). All other local anesthetics had GPI declining mostly to less than 1.0 (2010-2014). The rate of change in publication-based academic interest was very slow in both its increase and decline. The most profound change in publication-based academic interests was caused by the introduction of bupivacaine. During a 20-year period (from 1965-1969 to 1985-1989), bupivacaine's GPI increased from 1.3 to 12.9.

CONCLUSION

A slowly developing concentration of publication-based academic interest on a very limited number of local anesthetics was the dominant feature related to this class of anesthetic agents.

Opioid prescriptions for pain and epidemic of overdose death: can the dramatic reduction in anesthesia mortality serve as an example?

The annual number of US deaths from prescription-opioid overdose quadrupled between 1999 and 2010 and in 2010 alone reached 16,651. Deaths from opioid overdose have now surpassed the historic death toll from another drug-related epidemic - anesthesia mortality. In 1954, Beecher and Todd published reliable data on anesthesia-related mortality in the US, estimating the annual number of deaths to be nearly 5,000. Presently anesthesia/anesthetics are reported as the underlying cause in approximately 34 deaths in the US annually. This spectacular decline in anesthesia-related mortality could serve as an example for attempts to curb the epidemic of opioid overdose death. The main reason that led to the dramatic decline in anesthesia-related mortality is the context in which anesthetics are used. It includes training of the anesthesia providers, the introduction of specific standards of patient safety, and anesthesia monitoring. I suggest that the introduction of a similar multifactorial proper context for the use of opioids in the treatment of chronic nonmalignant pain might be the same "game changer" it was for safety in anesthesia.

Scientometrics of drug discovery efforts: pain-related molecular targets

The aim of this study was to make a scientometric assessment of drug discovery efforts centered on pain-related molecular targets. The following scientometric indices were used: the popularity index, representing the share of articles (or patents) on a specific topic among all articles (or patents) on pain over the same 5-year period; the index of change, representing the change in the number of articles (or patents) on a topic from one 5-year period to the next; the index of expectations, representing the ratio of the number of all types of articles on a topic in the top 20 journals relative to the number of articles in all (>5,000) biomedical journals covered by PubMed over a 5-year period; the total number of articles representing Phase I–III trials of investigational drugs over a 5-year period; and the trial balance index, a ratio of Phase I–II publications to Phase III publications. Articles (PubMed database) and patents (US Patent and Trademark Office database) on 17 topics related to pain mechanisms were assessed during six 5-year periods from 1984 to 2013. During the most recent 5-year period (2009–2013), seven of 17 topics have demonstrated high research activity (purinergic receptors, serotonin, transient receptor potential channels, cytokines, gamma aminobutyric acid, glutamate, and protein kinases). However, even with these seven topics, the index of expectations decreased or did not change compared with the 2004–2008 period. In addition, publications representing Phase I–III trials of investigational drugs (2009–2013) did not indicate great enthusiasm on the part of the pharmaceutical industry regarding drugs specifically designed for treatment of pain. A promising development related to the new tool of molecular targeting, ie, monoclonal antibodies, for pain treatment has not yet resulted in real success. This approach has not yet demonstrated clinical effectiveness (at least with nerve growth factor) much beyond conventional analgesics, when its potential cost is more than an order of magnitude higher than that of conventional treatments. This scientometric assessment demonstrated a lack of real breakthrough developments.

A quest to increase safety of anesthetics by advancements in anesthesia monitoring: scientometric analysis

The aim of this study was to assess progress in the field of anesthesia monitoring over the past 40 years using scientometric analysis. The following scientometric indexes were used: popularity indexes (general and specific), representing the proportion of articles on either a topic relative to all articles in the field of anesthetics (general popularity index, GPI) or the subfield of anesthesia monitoring (specific popularity index, SPI); index of change (IC), representing the degree of growth in publications on a topic from one period to the next; and index of expectations (IE), representing the ratio of the number of articles on a topic in the top 20 journals relative to the number of articles in all (>5,000) biomedical journals covered by PubMed. Publications on 33 anesthesia-monitoring topics were assessed. Our analysis showed that over the past 40 years, the rate of rise in the number of articles on anesthesia monitoring was exponential, with an increase of more than eleven-fold, from 296 articles over the 5-year period 1974–1978 to 3,394 articles for 2009–2013. This rise profoundly exceeded the rate of rise of the number of articles on general anesthetics. The difference was especially evident with the comparison of the related GPIs: stable growth of the GPI for anesthesia monitoring vs constant decline in the GPI for general anesthetics. By the 2009–2013 period, among specific monitoring topics introduced after 1980, the SPI index had a meaningful magnitude (≥1.5) in 9 of 24 topics: Bispectral Index (7.8), Transesophageal Echocardiography (4.2), Electromyography (2.8), Pulse Oximetry (2.4), Entropy (2.3), Train-of-four (2.3), Capnography (1.9), Pulse Contour (1.9), and Electrical Nerve Stimulation for neuromuscular monitoring (1.6). Only one of these topics (Pulse Contour) demonstrated (in 2009–2013) high values for both IC and IE indexes (76 and 16.9, respectively), indicating significant recent progress. We suggest that rapid growth in the field of anesthetic monitoring was one of the most important developments to compensate for the intrinsically low margins of safety of anesthetic agents.

Scientometrics of anesthetic drugs and their techniques of administration, 1984-2013

The aim of this study was to assess progress in the field of anesthetic drugs over the past 30 years using scientometric indices: popularity indices (general and specific), representing the proportion of articles on a drug relative to all articles in the field of anesthetics (general index) or the subfield of a specific class of anesthetics (specific index); index of change, representing the degree of growth in publications on a topic from one period to the next; index of expectations, representing the ratio of the number of articles on a topic in the top 20 journals relative to the number of articles in all (>5,000) biomedical journals covered by PubMed; and index of ultimate success, representing a publication outcome when a new drug takes the place of a common drug previously used for the same purpose. Publications on 58 topics were assessed during six 5-year periods from 1984 to 2013. Our analysis showed that during 2009–2013, out of seven anesthetics with a high general popularity index (≥2.0), only two were introduced after 1980, ie, the inhaled anesthetic sevoflurane and the local anesthetic ropivacaine; however, only sevoflurane had a high index of expectations (12.1). Among anesthetic adjuncts, in 2009–2013, only one agent, sugammadex, had both an extremely high index of change (>100) and a high index of expectations (25.0), reflecting the novelty of its mechanism of action. The index of ultimate success was positive with three anesthetics, ie, lidocaine, isoflurane, and propofol, all of which were introduced much longer than 30 years ago. For the past 30 years, there were no new anesthetics that have produced changes in scientometric indices indicating real progress.

Scientometric assessment of drugs for chronic pain, 1979-2013: rapid growth of publications, paucity of successful drugs

The aim of this study was to find signs of progress in the pharmacotherapy of chronic pain over the past 35 years using scientometric analysis. The following scientometric indices were used: 1) popularity index, representing the share of articles on a specific drug(s) relative to all articles in the field of chronic pain; 2) index of change, representing the degree of growth in publications on a topic from one period to the next; 3) index of expectations, representing the ratio of the number of articles on a topic in the top 20 journals relative to the number of articles in all (>5,000) biomedical journals covered by PubMed; and 4) index of ultimate success, representing a publication outcome when a new drug takes the place of a common drug previously used for the same purpose. Publications on 55 drugs used in the treatment of chronic pain were assessed during seven 5-year periods, from 1979 to 2013. The rate of rise in the number of publications on chronic pain was exponential, with an increase of nearly ninefold from 2,346 articles over the 5-year period 1979–1983 to 21,095 articles in 2009–2013. However, despite this huge increase in publications, our scientometric analysis did not reveal signs of really successful drugs in this field. For the 2009–2013 period, the popularity index had a meaningful magnitude (from 0.5–2.8) for only 13 of 55 drugs. Five of them were opioids, including morphine, which had the highest index value of all drugs (2.8). None of the drugs had a high index of expectations in 2009–2013. The index of ultimate success was positive only with triptans in the relatively limited area of acute treatment of migraine. As a result, despite rapid growth in the number of publications, our scientometric analysis did not reveal signs of substantial progress in the field of pharmacotherapy for chronic pain.

No evidence of real progress in treatment of acute pain, 1993-2012: scientometric analysis

Over the past 2 decades, many new techniques and drugs for the treatment of acute pain have achieved widespread use. The main aim of this study was to assess the progress in their implementation using scientometric analysis. The following scientometric indices were used: 1) popularity index, representing the share of articles on a specific technique (or a drug) relative to all articles in the field of acute pain; 2) index of change, representing the degree of growth in publications on a topic compared to the previous period; and 3) index of expectations, representing the ratio of the number of articles on a topic in the top 20 journals relative to the number of articles in all (>5,000) biomedical journals covered by PubMed. Publications on specific topics (ten techniques and 21 drugs) were assessed during four time periods (1993–1997, 1998–2002, 2003–2007, and 2008–2012). In addition, to determine whether the status of routine acute pain management has improved over the past 20 years, we analyzed surveys designed to be representative of the national population that reflected direct responses of patients reporting pain scores. By the 2008–2012 period, popularity index had reached a substantial level (≥5%) only with techniques or drugs that were introduced 30–50 years ago or more (epidural analgesia, patient-controlled analgesia, nerve blocks, epidural analgesia for labor or delivery, bupivacaine, and acetaminophen). In 2008–2012, promising (although modest) changes of index of change and index of expectations were found only with dexamethasone. Six national surveys conducted for the past 20 years demonstrated an unacceptably high percentage of patients experiencing moderate or severe pain with not even a trend toward outcome improvement. Thus, techniques or drugs that were introduced and achieved widespread use for acute pain management within the past 20 years have produced no changes in scientometric indices that would indicate real progress and have failed to improve national outcomes for relief of acute pain. Two possible reasons for this are discussed: 1) the difference between the effectiveness of old and new techniques is not clinically meaningful; and 2) resources necessary for appropriate use of new techniques in routine pain management are not adequate.

Long-term opioid treatment of chronic nonmalignant pain: unproven efficacy and neglected safety?

BACKGROUND

For the past 30 years, opioids have been used to treat chronic nonmalignant pain. This study tests the following hypotheses: (1) there is no strong evidence-based foundation for the conclusion that long-term opioid treatment of chronic nonmalignant pain is effective; and (2) the main problem associated with the safety of such treatment - assessment of the risk of addiction - has been neglected.

METHODS

Scientometric analysis of the articles representing clinical research in this area was performed to assess (1) the quality of presented evidence (type of study); and (2) the duration of the treatment phase. The sufficiency of representation of addiction was assessed by counting the number of articles that represent (1) editorials; (2) articles in the top specialty journals; and (3) articles with titles clearly indicating that the addiction-related safety is involved (topic-in-title articles).

RESULTS

Not a single randomized controlled trial with opioid treatment lasting >3 months was found. All studies with a duration of opioid treatment ≥6 months (n = 16) were conducted without a proper control group. Such studies cannot provide the consistent good-quality evidence necessary for a strong clinical recommendation. There were profound differences in the number of addiction articles related specifically to chronic nonmalignant pain patients and to opioid addiction in general. An inadequate number of chronic pain-related publications were observed with all three types of counted articles: editorials, articles in the top specialty journals, and topic-in-title articles.

CONCLUSION

There is no strong evidence-based foundation for the conclusion that long-term opioid treatment of chronic nonmalignant pain is effective. The above identified signs indicating neglect of addiction associated with the opioid treatment of chronic nonmalignant pain were present.

An early indicator of drug success: Top Journal Selectivity Index

The Top Journal Selectivity Index (TJSI) is a scientometric index reflecting the potential importance of a new drug. It represents the ratio of the number of all types of articles on a particular drug in the top 20 journals relative to the number of articles in all (>5,000) biomedical journals covered by Medline over the 5 years since the drug’s introduction. The TJSI can be an indicator of a drug’s potential for sustained use: a higher score increases the probability of continuing success.

Chronic postsurgical pain: still a neglected topic?

Background

Surgical injury can frequently lead to chronic pain. Despite the obvious importance of this problem, the first publications on chronic pain after surgery as a general topic appeared only a decade ago. This study tests the hypothesis that chronic postsurgical pain was, and still is, represented insufficiently.

Methods

We analyzed the presentation of this topic in journal articles covered by PubMed and in surgical textbooks. The following signs of insufficient representation in journal articles were used: (1) the lack of journal editorials on chronic pain after surgery, (2) the lack of journal articles with titles clearly indicating that they are devoted to chronic postsurgical pain, and (3) the insufficient representation of chronic postsurgical pain in the top surgical journals.

Results

It was demonstrated that insufficient representation of this topic existed in 1981–2000, especially in surgical journals and textbooks. Interest in this topic began to increase, however, mostly regarding one specific surgery: herniorrhaphy. It is important that the change in the attitude toward chronic postsurgical pain spreads to other groups of surgeries.

Conclusion

Chronic postsurgical pain is still a neglected topic, except for pain after herniorrhaphy. The change in the attitude toward chronic postsurgical pain is the important first step in the approach to this problem.

Local anesthetic blockade of peripheral nerves for treatment of neuralgias: systematic analysis

BACKGROUND

Nerve blocks with local anesthetics have been used in the diagnosis and treatment of neuralgias. Usually these blocks were administered in combination with corticosteroids and other drugs that can be effective by themselves. Although lasting benefits from nerve blocks in neuralgias have long been described, definitive evidence is lacking. We had the following objectives in this systematic review: to analyze the evidence behind the practice of peripheral nerve blockade with local anesthetics in patients with neuralgias and radicular pain syndromes; to assess the duration of pain relief after conduction block resolution; and to evaluate the effectiveness of the treatment of these syndromes with a series of blocks.

METHODS

We searched Medline, Embase, narrative reviews, and book chapters. Only articles published in English were collected. The list of 3347 identified articles was reduced to 39 articles that were read entirely, 12 of which met inclusion criteria.

RESULTS

Twelve included articles were analyzed. Each can be classified as a single case report or case series; there were no controlled studies among them. Nine reports assessed a single block outcome; all recorded pain relief beyond the duration of conduction blockade. Those 9 reports represented a total of 69 patients, 30 of whom had complete pain relief and 10 had relief ≥50%. Seven reports with the assessment of continuous pain ≥1 week after a single block reported complete or profound pain relief in 11 of 17 patients. All 3 reports with the assessment of a series of blocks in a large number of patients (total of 270) reported overall positive results.

CONCLUSION

Because all reviewed articles were only single case reports or case series, no reliable conclusion could be drawn concerning the effectiveness of nerve blocks with local anesthetics in neuralgia. However, 2 features of the analyzed reports-the large magnitude of the effect and the high consistency of the reported outcome-indicate that future research efforts are warranted.

Therapeutic targeting of TRPV1 by resiniferatoxin, from preclinical studies to clinical trials

In primary sensory neurons, the capsaicin receptor TRPV1 functions as a molecular integrator for a broad range of seemingly unrelated chemical and physical noxious stimuli, including heat and altered pH. Indeed, TRPV1 is thought to be a major transducer of the thermal hyperalgesia that follows inflammation and tissue injury as this response is impaired in TRPV1-deficient mice. Following the molecular cloning of TRPV1 in 1997, over a dozen companies embarked on efforts to find clinically useful TRPV1 antagonists, but side-effects and limited efficacy have thus far prevented any compounds from progressing beyond phase II. This has rekindled interest in desensitization of nociceptive neurons to TRPV1 agonists (e.g. capsaicin and its ultrapotent analog resiniferatoxin) as an alternative pharmacological approach to block pain in the periphery where it is generated. The clinical value of capsaicin is, however, limited by its unfavorable irritancy to desensitization ratio. In animal experiments, resiniferatoxin treatment is a powerful approach to achieve long-lasting analgesia. In patients with overactive bladder, intravesical resiniferatoxin improves bladder function (or even restores continence) without significant irritancy and/or toxicity. In this review, we argue that resiniferatoxin is an attractive alternative to capsaicin in that it achieves lasting desensitization without the side effects that complicate capsaicin therapy.

The development of new analgesics over the past 50 years: a lack of real breakthrough drugs

Fifty-nine drugs identified as analgesics were introduced from 1960 to 2009 and remain in use. Seven can be regarded as having novel molecular targets; however, only one, sumatriptan, was sufficiently effective to motivate the introduction of many similar drugs acting at the same target (triptans). Publication productivity in the area of pain grew exponentially during this period. Pain-related publications on morphine were dominant among other analgesics. Very intensive research efforts directed at diverse molecular targets related to pain mechanisms produced thousands of publications, but those efforts have not yet yielded new analgesics with sufficient effectiveness to change the share of publications on opioids or nonsteroidal antiinflammatory drugs. Morphine and aspirin, introduced for the treatment of pain more than a century ago, continue to dominate biomedical publications despite their limited effectiveness in many areas (e.g., neuropathic pain) and multiple serious adverse effects. The present assessment reveals the lack of real breakthroughs in analgesic drug development despite intense research efforts. Possible factors contributing to the apparent drought of novel analgesics are discussed.

Preemptive analgesia: problems with assessment of clinical significance

The results of clinical studies on the value of preemptive analgesia are far from being unanimous. There are a number of potential problems related to preemptive analgesia that could lead to controversy regarding its clinical significance. The following potential problems are analyzed: (1) terminology, (2) approach to reveal the effect of preemptive analgesia, (3) verification of the direct pharmacological effect of a treatment, (4) partial preemptive effect in control, (5) intensity of noxious stimuli, (6) difference in a drug concentration between study groups during postoperative period, and (7) outcome measures.

Vanilloid-induced conduction analgesia: selective, dose-dependent, long-lasting, with a low level of potential neurotoxicity

Vanilloid agonists (capsaicin, resiniferatoxin, [RTX]) applied to the peripheral nerves provide conduction blockade. In contrast to the analgesic component of conduction anesthesia produced by local anesthetics, vanilloid agonists provide conduction analgesia not associated with suppression of motor or sensory functions not related to pain. Vanilloid agonists provide conduction analgesia selectively because their effect on the nerve trunks is limited to C- and ADelta-fibers. RTX is much more potent than capsaicin and has a wider therapeutic window. In rat experiments, perineural RTX produced a long-lasting thermal and mechanical hypoalgesia with a very wide separation between effective concentrations (from 0.00003% to 0.001%) providing an effect lasting from several hours to several weeks. A nerve block with RTX prevented the development of thermal and mechanical hyperalgesia as well as pain behavior in a model of incisional pain. RTX-induced conduction blockade has an inherent drawback of TRPV1 agonists, the initial excitation (pain); therefore, a local anesthetic should be injected to prevent it. When RTX was applied to the rat's sciatic nerve in doses necessary to provide conduction analgesia, the frequency of unmyelinated fiber degeneration was more than an order of magnitude lower than that with the therapeutic concentration of lidocaine. These promising results should be confirmed by experiments in species other than rodents (pigs, sheep). Taken together, the data indicate possible clinical applicability of vanilloid-induced conduction analgesia.

Persistent changes in spinal cord gene expression after recovery from inflammatory hyperalgesia: a preliminary study on pain memory

BACKGROUND

Previous studies found that rats subjected to carrageenan injection develop hyperalgesia, and despite complete recovery in several days, they continue to have an enhanced hyperalgesic response to a new noxious challenge for more than 28d. The study's aim was to identify candidate genes that have a role in the formation of the long-term hyperalgesia-related imprint in the spinal cord. This objective was undertaken with the understanding that the long-lasting imprint of acute pain in the central nervous system may contribute to the transition of acute pain to chronicity.

RESULTS

To analyze changes in gene expression when carrageenan-induced hyperalgesia has disappeared but propensity for the enhanced hyperalgesic response is still present, we determined the gene expression profile using oligo microarray in the lumbar part of the spinal cord in three groups of rats: 28d after carrageenan injection, 24h after injection (the peak of inflammation), and with no injection (control group). Out of 17,000 annotated genes, 356 were found to be differentially expressed compared with the control group at 28d, and 329 at 24h after carrageenan injection (both groups at p < 0.01). Among differentially expressed genes, 67 (39 in 28d group) were identified as being part of pain-related pathways, altered in different models of pain, or interacting with proteins involved in pain-related pathways. Using gene ontology (GO) classification, we have identified 3 functional classes deserving attention for possible association with pain memory: They are related to cell-to-cell interaction, synaptogenesis, and neurogenesis.

CONCLUSION

Despite recovery from inflammatory hyperalgesia, persistent changes in spinal cord gene expression may underlie the propensity for the enhanced hyperalgesic response. We suggest that lasting changes in expression of genes involved in the formation of new synapses and neurogenesis may contribute to the transition of acute pain to chronicity.

Sciatic nerve block with resiniferatoxin: an electron microscopic study of unmyelinated fibers in the rat

BACKGROUND

Perineural administration of the naturally occurring vanilloids (capsaicin, resiniferatoxin [RTX]) produces selective nociceptive blockade. Studies using perineural vanilloids in high concentrations suggest that they can cause a degeneration of unmyelinated fibers. However, electron microscopic studies of local vanilloid toxicity produced conflicting outcomes. In the present study, we sought to determine whether RTX-induced reversible sciatic nerve block results in the degenerative changes of unmyelinated fibers.

METHODS

In rat experiments, RTX was administered percutaneously at the sciatic nerve. The effect of RTX was monitored by measuring the rat's response to noxious heat. The sciatic nerves were removed 48 h after the blockade initiation. Quantitative electron microscopic evaluation of the unmyelinated fibers was performed in three groups of animals: RTX 0.0001% (0.1 microg), RTX 0.001% (1 microg), and control (RTX vehicle, 0.1 mL).

RESULTS

Cross-sections of the sciatic nerve 48 h after the initiation of RTX-induced reversible nerve blockade appeared essentially normal. One rarely observed finding was the irregularly compacted membranous deposits in the unmyelinated axons. The frequency of this finding was approximately one per thousand fibers with both concentrations of RTX.

CONCLUSIONS

The results of the study suggest that a selective and long-lasting sciatic nerve block (up to 2 wk) can be provided by RTX without any significant damage to the unmyelinated nerve fibers.

Perineural resiniferatoxin prevents the development of hyperalgesia produced by loose ligation of the sciatic nerve in rats

BACKGROUND

The vanilloid receptors (TRPV1) are found in peripheral nerve fibers; their stimulation by capsaicin leads to release of calcitonin gene-related peptide and other neuropeptides participating in neuroinflammation. On the other hand, various inflammatory mediators, released after nerve damage, can activate or sensitize the TRPV1 receptors. These findings together suggest a protective effect of TRPV1 receptor blockade in neuropathy. In the present study, we tested the hypothesis that perineural resiniferatoxin (RTX) can prevent the development of hyperalgesia caused by placing loosely constrictive ligatures around the sciatic nerve.

METHODS

Male Sprague-Dawley rats received a single percutaneous injection of RTX (0.0005%, 0.1 mL) or vehicle at the sciatic nerve, and underwent surgery 3 h later to place four loose ligatures around the nerve on the side of drug administration. Responses to noxious heat (withdrawal latency, paw-lift duration), repetitive stimulation with von Frey filaments, and changes in hindpaw posture (toe spread, ventroflexion, and foot exorotation) were assessed.

RESULTS

Perineural RTX administered before surgery completely prevented ligation-induced reduction in withdrawal latency, increase in paw lift duration and increase in withdrawal frequency to von Frey filaments. The preventive effect of RTX on the development of deficits in hindpaw posture was pronounced but not complete, e.g., on day 7 after surgery, the cumulative paw-posture score (0-6) was 1.69 +/- 0.92 with RTX and 4.06 +/- 1.68 with vehicle (P < 0.005). The effect of RTX used against the background of already developed neuropathy was limited to thermal hypoalgesia lasting for a relatively short period.

CONCLUSION

Perineural RTX prevents the development of neuropathy caused by placing loosely constrictive ligatures on the sciatic nerve. Perioperative use of drugs acting via the TRPV1 receptors may hold the promise for preventing neuropathic pain after surgery on peripheral nerves.

Iatrogenic addiction in patients treated for acute or subacute pain: a systematic review

We conducted a systematic review of the literature on the evidence for iatrogenic addiction in patients treated for acute and subacute pain. Literature searches yielded 1,943 articles, 53 of which were reviewed in detail, and 41 of which met criteria for inclusion in the review of iatrogenic addiction. Two authors independently reviewed and summarized the findings of each article. Discrepancies of ratings were resolved by discussion. We identified no randomized trials or comparative longitudinal studies. The results of nine studies of low methodological quality suggest conflicting findings. This manuscript discusses some possible mechanisms of iatrogenic addiction and concludes with suggestions for methodologically stronger studies to provide more definitive data regarding the evidence for or against iatrogenic addiction in patients treated for acute and subacute pain. The systematic review of the literature could not adequately answer the study questions; thus, it is not known whether the risk for iatrogenic addiction among patients treated with opioids for acute or subacute pain is relatively high (> 10 percent) or low (< 0.1 percent).

Memory of pain: the effect of perineural resiniferatoxin

The long-lasting imprint of acute pain in the central nervous system may contribute to the transition of acute pain to chronicity. The long-term potentiation (which is proposed as a mechanism of memory) and central sensitization were each reported as a form of synaptic plasticity, and both can be initiated by stimulation of C fibers. In the current study, we assessed nociceptive memory regarding hyperalgesia by measuring distant hyperalgesia after repeated carrageenan-induced inflammation. This approach was used to determine whether selective blockade of C fibers can prevent the development of a long-lasting imprint of hyperalgesia. In rat experiments, resiniferatoxin was administered percutaneously at the sciatic and saphenous nerves, and two crossover intraplantar injections of carrageenan into the hindpaws were performed 2 wk apart. Responses to noxious pressure and heat and changes in paw volumes were measured at various intervals during two carrageenan-induced inflammations. The experiments demonstrated that after recovery of hyperalgesia induced by the initial inflammation, repeated inflammation led to the development of a distant hyperalgesia that was absent during the initial inflammation. The maximum of distant hyperalgesia (decrease of noxious pressure threshold in the contralateral hindpaw from 141 +/- 23 g to 96 +/- 19 g; P < 0.0001) was reached 24 h after the second injection of carrageenan. The development of distant hyperalgesia during the repeated inflammation was completely prevented (P < 0.0002) by perineural resiniferatoxin (0.001%) administered before the initial injection of carrageenan. These results indicate that selective blockade of nociceptive fibers prevents formation of long-term hyperalgesia-related imprint in the central nervous system. Thus, pain memory can be preempted by selective and prolonged blockade of C-fibers.

The effects of intraarticular resiniferatoxin in experimental knee-joint arthritis

In this study we sought to determine whether an intraarticular administration of a vanilloid agonist resiniferatoxin (RTX) produces an analgesic effect in experimental arthritis. Knee joint inflammation was induced in rats by intraarticular carrageenan (2%, 30 microL). Pain score and left/right hind leg weight distribution ratio were used to assess pain behavior. Changes in knee dimensions were evaluated by measuring external circumference and intraarticular area (ultrasound scanning). The intraarticular administration of RTX (0.0003% or 0.003%, 30 microL) provided a significant analgesic effect. Twenty-four hours after RTX administration, the pain score was reduced from 15.1 +/- 4.7 to 6.9 +/- 4.4 (P < 0.01) with 0.0003% and was abolished (P < 0.0001) with 0.003%. The improvement in weight distribution ratio lasted for several days after the RTX administration. Reduction in knee circumference demonstrated that intraarticular RTX suppressed the carrageenan-induced edema by at least one third. Ultrasound scanning revealed no RTX-induced decrease of the intraarticular area. The experiments demonstrated that intraarticular RTX inhibits pain behavior in knee-joint arthritis and that this effect is dose-dependent. These results suggest a new direction for peripheral analgesia.

Perineural resiniferatoxin prevents hyperalgesia in a rat model of postoperative pain

Resiniferatoxin (RTX) is a vanilloid agonist with a unique spectrum of activities. Vanilloids bind to the transient receptor potential ion channel subtype 1, a nonselective cation ionophore important in the integration of different noxious signals. Vanilloid agonists selectively decrease sensitivity to noxious stimuli. In this study, we sought to determine whether perineural RTX prevents hyperalgesia in a model of incisional pain. In a rat model, RTX was administered percutaneously to the sciatic and saphenous nerves before the plantar incision. The withdrawal response to von Frey filaments, the struggle response to pressure on the paw, and pain scoring based on weight bearing were measured before RTX and at various intervals for 8 days after RTX. A percutaneous injection of RTX (0.0003%) to the sciatic (0.1 mL) and saphenous (0.05 mL) nerves completely prevented incisional hyperalgesia. Two hours after incision, the withdrawal threshold was 51 mN without and 456 mN with RTX (P < 0.0001). RTX also prevented the incision-induced decrease in struggle threshold and abolished the pain behavior associated with weight bearing. We conclude that RTX provides a type of neural blockade when postoperative pain is abolished and that nonpainful sensations and motor functions are preserved.