Do genes influence outcome from anaesthesia?

Anaesthesia and cancer: can anaesthetic drugs modify gene expression?

Cancer remains a primary cause of morbidity and mortality worldwide, and its incidence continues to increase. The most common cause of death in cancer patients is tumour recurrence. Surgery is the gold standard in the treatment of most tumours. However, cancer surgery can lead to the release of tumour cells into the systemic circulation. Surgical stress and several perioperative factors have been suggested to boost tumour growth, thereby increasing the risk of metastatic recurrence. Preclinical and clinical studies suggest that anaesthetics and adjuvants administered during the perioperative period may impact cancer recurrence and survival. This document summarises the current evidence regarding the effects of anaesthetic drugs and analgesic techniques on the immune system, systemic inflammatory response and tumour cells, as well as their impact on cancer recurrence.

Pharmacogenomics, concepts for the future of perioperative medicine and pain management: A review

Pharmacogenomics is the study of how genetic differences between individuals affect pharmacokinetics and pharmacodynamics. These differences are apparent to clinicians when taking into account the wide range of responses to medications given in clinical practice. A review of literature involving pharmacogenomics and pain management was performed. The implementation of preoperative pharmacogenomics will allow us to better care for our patients by delivering personalized, safer medicine. This review describes the current state of pharmacogenomics as it relates to many aspects of clinical practice and how clinicians can use these tools to improve patient outcomes.

Pharmacogenetics of Anesthesia: An Integrative Review

BACKGROUND

Monitoring a patient's response to drug therapy and early identification of an adverse reaction are important responsibilities of nurses. Despite the relative safety of anesthesia practice, 1 in 20 perioperative medication administrations includes a medication error and/or adverse drug reaction. Although several factors contribute to an individual's response to medications, genetic predisposition accounts for over 50% of that response.

OBJECTIVE

The purpose of this review is to explore the evidence of genetic variability associated with response to volatile and intravenous anesthetics.

METHODS

A comprehensive search of published literature in PubMed, CINAHL, and Cochrane databases from 1960 to May 30, 2015, was performed. Iterative reading of the primary articles was performed to ensure congruence between the extracted data and the primary article and reduce the data to draw conclusions.

RESULTS

The analysis revealed that most anesthetics are metabolized by enzymes in the CYP2 and UGT1 family. CYP2B6 catalyzes propofol and ketamine metabolism. CYP2B6*6 allele is associated with decreased propofol and ketamine metabolism and increased adverse effects. Genetic variants in the UGT1A9 enzyme are associated with the need for higher induction dose and increased clearance of propofol.

DISCUSSION

Despite the significant gaps in the literature, current evidence suggests that close monitoring is required when administering anesthetics to individuals with the CYP2B6*6 allele. Future research to address identified gaps in this review may have the potential to identify underlying genetic contribution to anesthetic response and prevent significant adverse events during anesthesia delivery and perioperative nursing care.

Pharmacogenetics and anaesthetic drugs: Implications for perioperative practice

Pharmacogenetics seeks to elucidate the variations in individual's genetic sequences in order to better understand the differences seen in pharmacokinetics, drug metabolism, and efficacy between patients. This area of research is rapidly accelerating, aided by the use of novel and more economical molecular technologies. A substantial evidence base is being generated with the hopes that in the future it may be used to generate personalised treatment regimens in order to improve patient comfort and safety and reduce incidences of morbidity and mortality. Anaesthetics is an area of particular interest in this field, with previous research leading to better informed practice, specifically with regards to pseudocholinesterase deficiency and malignant hyperthermia. In this review, recent pharmacogenetic data pertaining to anaesthetic drugs will be presented and possible future applications and implications for practice will be discussed.

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Pharmacogenetic variations in anaesthetic drugs affect enzymes, transport proteins and drug receptors.

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Genotyping may provide more clues as to aetiology of conditions related to usage of anaesthetic drugs e.g. propofol infusion syndrome.

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Improved and more economical molecular technology will lead to increase in quantity of pharmacogenetic data.

The association of CYP2D6 genotype and postoperative nausea and vomiting in orthopedic trauma patients

The CYP2D6 gene encodes for an enzyme that is involved in the metabolism of more than 25% of all medications, including many opioids and antiemetics. It may contribute to the risk of postoperative nausea and vomiting (PONV), a common surgical complication. However, little research has been conducted in this area. The purpose of this study was to explore the association of CYP2D6 genotypes with PONV in adult surgical trauma patients. Data from 112 patients (28% female) with single extremity fractures, aged 18-70 years, were analyzed. PONV was defined as present if patients reported nausea, were observed vomiting, or received medication for PONV. Saliva samples collected for DNA extraction and Taqman(®) allele discrimination and quantitative real time polymerase chain reaction (qRT-PCR) were used to collect genotype data that were then used to assign CYP2D6 phenotype classification. The incidence of PONV was 38% in the postanesthesia care unit and increased to 50% when assessed at 48 hr. CYP2D6 classification results were 7 (6%) poor metabolizers, 34 (30%) intermediate metabolizers, and 71 (63%) extensive metabolizers. No ultrarapid metabolizers were identified. Patients who were classified as poor metabolizers had less PONV and higher pain scores. Gender and history of PONV, but not smoking, were also significant risk factors. Findings suggest variability in CYP2D6 impacts susceptibility to PONV.

The role of fMRI in drug discovery

Pharmacological functional (phMRI) studies are making a significant contribution to our understanding of drug-effects on brain systems. Pharmacological fMRI has an additional contribution to make in the translation of disease models and candidate compounds from preclinical to clinical investigation and in the early clinical stages of drug development. Here it can demonstrate a proof-of-concept of drug action in a small human cohort and thus contribute substantially to decision-making in drug development. We review the methods underlying pharmacological fMRI studies and the links that can be made between animal and human investigations. We discuss the potential fMRI markers of drug effect, experimental designs and caveats in interpreting hemodynamic fMRI data as reflective of changes in neuronal activity. Although there are no current published examples of fMRI applied to novel compounds, we illustrate the potential of fMRI across a range of applications and with specific reference to processing of pain in the human brain and pharmacological analgesia. Pharmacological fMRI is developing to meet the neuroscientific challenges. Electrophysiological methods can be used to corroborate the drug effects measured hemodynamically with fMRI. In future, pharmacological fMRI is likely to extend to examinations of the spinal cord and into pharmacogenetics to relate genetic polymorphisms to differential responses of the brain to drugs.

Pharmacogenetics and anesthesiologists

Genetic variation contributes to an individual’s sensitivity and response to a variety of drugs important to anesthetic practice. Early insights into the clinical impact of pharmacogenetics were provided by anesthesiology – investigations into prolonged apnea after succinylcholine administration, thiopental-induced porphyria and malignant hyperthermia contributed to the novel science of pharmacogenetics in the early 1960s. Genetic polymorphisms involved in pharmacokinetics (absorption, distribution, metabolism, and excretion of drugs) and pharmacodynamics (receptors, ion channels and enzymes) can affect an individual’s response to the drugs used in anesthetic practice. In addition, genetic variation in proteins directly unrelated to drug action or metabolism can influence responses to environmental changes that occur during anesthesia. This review will summarize the current knowledge of genetic variation in response to drugs relevant to anesthesia, and how this impacts upon clinical practice.

Watson and Crick 50 years on. From double helix to pharmacogenomics

The second half of the 20th century has seen quantum leaps in our understanding of molecular biology. The technological advances, which facilitated the recent successful completion of the Human Genome Project, have provided the tools for deciphering the complexity of the human condition. At present, the function of only 50% of genes is known. However, as understanding of the human genome improves, a plethora of gene targets for treating disease will be uncovered - leading to therapies which will be considered revolutionary. Genome related science has begun to impact almost every facet of medicine including anaesthesia and intensive care. Better understanding of interindividual differences will enable better prediction of illness susceptibility as well as response to treatment. These insights will permit therapies to be tailored to individuals or racial groups. At present, there is only rudimentary knowledge of factors controlling gene regulation, but in the future, better understanding of gene-environment interactions and gene expression will enable pharmaceutical companies to develop new therapies and permit clinicians to optimise their effects, without recourse to current laborious testing regimens. As genomic science progresses, new ethical, legal, social and philosophical dilemmas will also continue to emerge.