Individualized Hydrocodone Therapy Based on Phenotype, Pharmacogenetics, and Pharmacokinetic Dosing

Pharmacogenomics of Opioid Treatment for Pain Management

Pain affects approximately 100 million Americans. Pain harms quality of life and costs patients billions of dollars per year. Clinically, nonpharmacologic and pharmacologic therapies can alleviate acute and chronic pain suffering. Opioids are one type of medication used to manage pain. However, opioids can potentially create dependence and substance abuse, and the effects are not consistent in all patients. Pharmacogenomics is the study of the genome to understand the effects of drugs on individual patients based on their genetic information. Through pharmacogenomics, researchers can investigate genetic polymorphisms related to pain that maximize individual patient drug responses and minimize toxicity. This chapter discusses the pharmacogenomics of opioids to treat pain, including individual genetic differences to opioid treatments, opioid pharmacokinetics and pharmacodynamics, and the genetic polymorphisms associated with individual opioid medications.

Human variability in polymorphic CYP2D6 metabolism: Implications for the risk assessment of chemicals in food and emerging designer drugs

The major human cytochrome P450 CYP2D6 isoform enzyme plays important roles in the liver and in the brain with regards to xenobiotic metabolism. Xenobiotics as CYP2D6 substrates include a whole range of pharmaceuticals, pesticides and plant alkaloids to cite but a few. In addition, a number of endogenous compounds have been shown to be substrates of CYP2D6 including trace amines in the brain such as tyramine and 5-methoxytryptamine as well as anandamide and progesterone. Because of the polymorphic nature of CYP2D6, considerable inter-phenotypic and inter-ethnic differences in the pharmaco/toxicokinetics (PK/TK) and metabolism of CYP2D6 substrates exist with potential consequences on the pharmacology and toxicity of chemicals. Here, large extensive literature searches have been performed to collect PK data from published human studies for a wide range of pharmaceutical probe substrates and investigate human variability in CYP2D6 metabolism. The computed kinetic parameters resulted in the largest open source database, quantifying inter-phenotypic differences for the kinetics of CYP2D6 probe substrates in Caucasian and Asian populations, to date. The database is available in supplementary material (CYPD6 DB) and EFSA knowledge junction (DOI to added). Subsequently, meta-analyses using a hierarchical Bayesian model for markers of chronic oral exposure (oral clearance, area under the plasma concentration time curve) and acute oral exposure (maximum plasma concentration (Cmax) provided estimates of inter-phenotypic differences and CYP2D6-related uncertainty factors (UFs) for chemical risk assessment in Caucasian and Asian populations classified as ultra-rapid (UM), extensive (EMs), intermediate (IMs) and poor metabolisers (PMs). The model allowed the integration of inter-individual (i.e. inter-phenotypic and inter-ethnic), inter-compound and inter-study variability together with uncertainty in each PK parameter. Key findings include 1. Higher frequencies of PMs in Caucasian populations compared to Asian populations (>8% vs 1-2%) for which EM and IM were the most frequent phenotype. 2. Large inter-phenotypic differences in PK parameters for Caucasian EMs (coefficients of variation (CV) > 50%) compared with Caucasian PMs and Asian EMs and IMs (i.e CV < 40%). 3. Inter-phenotypic PK differences between EMs and PMs in Caucasian populations increase with the quantitative contribution of CYP2D6 for the metabolism (fm) for a range of substrates (fm_CYP2D6 range: 20-95% of dose) (range: 1-54) to a much larger extent than those for Asian populations (range: 1-4). 4. Exponential meta-regressions between Fm_CYP2D6 in EMs and inter-phenotypic differences were also shown to differ between Caucasian and Asian populations as well as CYP2D6-related UFs. Finally, implications of these results for the risk assessment of food chemicals and emerging designer drugs of public health concern, as CYP2D6 substrates, are highlighted and include the integration of in vitro metabolism data and CYP2D6-variability distributions for the development of quantitative in vitro in vivo extrapolation models.

Impact of CYP2D6 Pharmacogenomic Status on Pain Control Among Opioid-Treated Oncology Patients

BACKGROUND

Several opioids have pharmacogenomic associations impacting analgesic efficacy. However, germline pharmacogenomic testing is not routinely incorporated into supportive oncology. We hypothesized that CYP2D6 profiling would correlate with opioid prescribing and hospitalizations.

MATERIALS AND METHODS

We analyzed 61,572 adult oncology patients from 2012 to 2018 for opioid exposures. CYP2D6 metabolizer phenotype (ultra-rapid [UM], normal metabolizer [NM], intermediate [IM], or poor [PM]), the latter two of which may cause inefficacy of codeine, tramadol, and standard-dose hydrocodone, was determined for patients genotyped for reasons unrelated to pain. The primary endpoint was number of opioid medications received during longitudinal care (IM/PMs vs. NMs). Secondary endpoint was likelihood of pain-related hospital encounters.

RESULTS

Most patients with cancer (n = 34,675, 56%) received multiple opioids (average 2.8 ± 1.6/patient). Hydrocodone was most commonly prescribed (62%), followed by tramadol, oxycodone, and codeine. In the CYP2D6 genotyped cohort (n = 105), IM/PMs received a similar number of opioids (3.4 ± 1.4) as NMs (3.3 ± 1.9). However, IM/PMs were significantly more likely to experience pain-related hospital encounters compared with NMs, independent of other variables (odds ratio [OR] = 5.4; 95% confidence interval [CI], 1.2-23.6; p = .03). IM/PMs were also more likely to be treated with later-line opioids that do not require CYP2D6 metabolism, such as morphine and hydromorphone (OR = 3.3; 95% CI, 1.1-9.8; p = .03).

CONCLUSION

CYP2D6 genotype may identify patients with cancer at increased risk for inadequate analgesia when treated with typical first-line opioids like codeine, tramadol, or standard-dose hydrocodone. Palliative care considerations are an integral part of optimal oncology care, and these findings justify prospective evaluation of preemptive genotyping as a strategy to improve oncology pain management.

IMPLICATIONS FOR PRACTICE

Genomic variation in metabolic enzymes can predispose individuals to inefficacy when receiving opioid pain medications. Patients with intermediate and/or poor CYP2D6 metabolizer status do not adequately convert codeine, tramadol, and hydrocodone into active compounds, with resulting increased risk of inadequate analgesia. This study showed that patients with cancer frequently receive CYP2D6-dependent opioids. However, patients with CYP2D6 intermediate and poor metabolizer status had increased numbers of pain-related hospitalizations and more frequently required the potent non-CYP2D6 opioids morphine and hydromorphone. This may reflect inadequate initial analgesia with the common "first-line" CYP2D6-metabolized opioids. Preemptive genotyping to guide opioid prescribing during cancer care may improve pain-related patient outcomes.

Nephrotoxicity in a Patient With Inadequate Pain Control: Potential Role of Pharmacogenetic Testing for Cytochrome P450 2D6 and Apolipoprotein L1

A case is presented which demonstrates the perils of opioid inefficacy and how pharmacogenomic testing may have prevented nonsteroidal anti-inflammatory drug (NSAID)-induced nephrotoxicity and progression to chronic kidney disease (CKD). A 62 year-old female with back pain was treated with tramadol and hydrocodone; however, neither proved effective. Consequently, to control her pain, she resorted to cocaine, marijuana, and high dose nonsteroidal anti-inflammatory drugs (NSAIDs). She eventually developed CKD. To identify CKD contributors, she underwent genotyping for Apolipoprotein L1 (APOL1), a known risk factor of CKD, as well as relevant pharmacogenomic genes. Her APOL1 genotype was *G1(GM)/*G1(GM), placing her at increased risk of CKD progression. Her CYP2D6 genotype was *5/*17, consistent with intermediate metabolism, making opioid drugs reliant on CYP2D6 activation, such as tramadol and hydrocodone, relatively ineffective in this patient. Thus, this patient was at genetic risk for CKD and reduced opioid efficacy. We conclude that this genetic combination likely contributed to opioid inefficacy and the eventual progression to CKD.

Update on the pharmacogenomics of pain management

Pharmacogenomics is the study of genetic variants that impact drug effects through changes in a drug’s pharmacokinetics and pharmacodynamics. Pharmacogenomics is being integrated into clinical pain management practice because variants in individual genes can be predictive of how a patient may respond to a drug treatment. Pain is subjective and is considered challenging to treat. Furthermore, pain patients do not respond to treatments in the same way, which makes it hard to issue a consistent treatment regimen for all pain conditions. Pharmacogenomics would bring consistency to the subjective nature of pain and could revolutionize the field of pain management by providing personalized medical care tailored to each patient based on their gene variants. Additionally, pharmacogenomics offers a solution to the opioid crisis by identifying potentially opioid-vulnerable patients who could be recommended a nonopioid treatment for their pain condition. The integration of pharmacogenomics into clinical practice creates better and safer healthcare practices for patients. In this article, we provide a comprehensive history of pharmacogenomics and pain management, and focus on up to date information on the pharmacogenomics of pain management, describing genes involved in pain, genes that may reduce or guard against pain and discuss specific pain management drugs and their genetic correlations.

Clinical application of pharmacogenetics in pain management

There is growing experience translating genomic data into clinical practice, as seen with the Implementing GeNomics In pracTicE (IGNITE) network. A primary example is the influence of CYP2D6 genotype on the beneficial and adverse effects of some opioids. Clinical recommendations exist to guide drug therapy based on CYP2D6 genotype for codeine, tramadol, oxycodone and hydrocodone, although the level of supporting evidence differs by drug. Limited evidence also supports the use of genetic data to guide other medications in chronic pain therapy, including tricyclic antidepressants and celecoxib. Pragmatic clinical trial data are needed in this area to better understand the impact of diverse populations, therapeutic interventions and clinical care environments on genotype-guided drug therapy for chronic pain.

Codeine use among children in the United States: a nationally representative study from 1996 to 2013

BACKGROUND

Concerns regarding the safety of codeine have been raised. Cases of life-threatening respiratory depression and death in children have been attributed to codeine's polymorphic metabolic pathway. International health agencies recommend restricted use of codeine in children. Despite these recommendations, the epidemiology of codeine use among children remains unknown.

AIMS

Our objective was to examine patterns of codeine use in the US among children.

METHODS

A cross-sectional analysis of children of age 0-17 years from 1996 to 2013 in the US was performed. Data were extracted from MEPS, a nationally representative set of health care surveys. Prevalence rates of codeine use between 1996 and 2013 were examined. Multivariable logistic regression examined relationships between codeine use and patient demographics.

RESULTS

Codeine use remained largely unchanged from 1996 to 2013 (1.08 vs 1.03 million children, respectively). Odds of codeine use was higher in ages 12-17 (OR, 1.40; [1.21-1.61]), outside of the Northeastern US, and among those with poor physical health status (OR, 3.29 [1.79-6.03]). Codeine use was lower in children whose ethnicity was not white and those uninsured (OR, 0.47 [0.34-0.63]). Codeine was most frequently prescribed by emergency physicians (18%) and dentists (14%). The most common condition associated with codeine use was trauma-related pain.

CONCLUSIONS

Pediatric codeine use has declined since 1996; however, more than 1 million children still used codeine in 2013. Health care providers must be made aware of guidelines advising against the use of codeine in children. Codeine is potentially hazardous and safer alternatives to treat children's pain are available.

Dental opioid prescribing and multiple opioid prescriptions among dental patients: Administrative data from the South Carolina prescription drug monitoring program

BACKGROUND

Despite increased attention to dentists' roles in curbing opioid misuse, abuse, and diversion, information regarding prescribing practices and the frequency of multiple concurrent opioid prescriptions among dental patients is limited.

METHODS

The authors reviewed South Carolina prescription drug monitoring program data representing dispensed medication for patients prescribed at least 1 opioid by a dentist during the most recently available 2-year time frame (2012-2013). The authors used descriptive analyses to examine the types and frequency of dental opioid prescriptions and the frequency of existing multiple concurrent opioid prescriptions among dental patients.

RESULTS

Nearly all dispensed dental opioid prescriptions (99.9%; n = 653,650) were for immediate-release opioids and were initial prescription fills (96.2%). Hydrocodone (76.1%) and oxycodone (12.2%) combination products were the most frequently dispensed opioids prescribed by dentists. People younger than 21 years received 11.2% of dentist-prescribed opioids dispensed. Patients with multiple concurrent opioid prescriptions were identified within 30-day (n = 113,818), 90-day (n = 166,124), and 180-day (n = 205,576) time frames.

CONCLUSIONS

Dentists prescribed a high volume of the immediate-release opioids dispensed in South Carolina. A notable minority of dental patients had incidents of multiple preexisting opioid prescriptions, a factor implicated in patient misuse, abuse, overdose, and diversion.

PRACTICAL IMPLICATIONS

Use of a prescription drug monitoring program before prescribing provides a record of controlled substances dispensed to a patient and may inform prescribing, coordination of care, and addiction screening or referral. Patients should receive information regarding misuse behaviors and their risks, as well as the importance of secure storage and disposal of leftover opioid medications.

Iranian-Islamic traditional medicine: An ancient comprehensive personalized medicine

Personalized medicine (PM) is a novel term used for a medical model in which all diagnostic, prognostic, and therapeutic aspects of a disease are individualized for a patient using specific molecular testing. In Iranian-Islamic traditional medicine (IITM) an ancient paradigm for PM has been described which has been introduced in this paper. We reviewed the ancient resources of IITM and many valid recent studies on personalized medicine and described an ancient feature of personalized medicine in comparison with new ones. According to IITM scholars, every person has an individual temperament which is concluded of four basic humors combination. The individual temper is influenced by internal and external factors such as age, gender, ethnicity, season, and environment. This variability leads to different physical and mental behaviors toward a particular condition; so if we could identify the patient's temper, we would predict his/her health-related behaviors rather than predisposition and prognosis to different diseases, and select the best treatment. This holistic viewpoint of IITM to the human health and disease justifies the variable phenotypes among similar illnesses; the fact around which more advanced high-tech researches are being developed to explore all specific molecular pathways. IITM offers an ancient comprehensive PM (APM) which is more available and inexpensive compared to the modern PM (MPM). Moreover, APM focuses more on fitness than illness in comparison to MPM. It seems more attention to APM introduced by IITM could help us to promote health community. Design studies using high-tech MPM techniques would likely lead to clarification of most molecular aspects of APM.