Prevalence and Factors Associated with Analgesic Prescribing in Poly-Medicated Elderly Patients.

BACKGROUND: Pain is common in older patients and management guidelines rarely consider the effect of multiple comorbidities and concurrent medications on analgesic selection. OBJECTIVES: The objectives of this study were to identify the prevalence and pattern of analgesic prescribing and associated factors in older patients with polypharmacy. METHODS: Older patients (aged ≥ 75 years) admitted to the Royal Adelaide Hospital between September 2015 and August 2016 and with polypharmacy were included and their comorbidities and medications prescribed at discharge were recorded. Drug Burden Index and Charlson Comorbidity Index were calculated. The number of medications that increased the risk of orthostatic hypotension were recorded. Logistic regression was used to compute the association between analgesic use and participant characteristics, and results were presented as odds ratios and 95% confidence intervals, adjusted for age, sex, Charlson Comorbidity Index, Drug Burden Index and orthostatic hypotension. RESULTS: Over 15,000 admissions were identified, of which 1192 patients were included, 824 (69%) of whom were prescribed an analgesic medication. Paracetamol (used by 89% of analgesic users), opioids (34%) and adjuvants (17%) were used more frequently than non-steroidal anti-inflammatory drugs (8%). Analgesic users had a higher Drug Burden Index, were prescribed more medications and were less likely to be male compared with non-users. Charlson Comorbidity Index across the cohort was high (7.3 ± 1.9) but there was no difference between analgesic users and non-users, but analgesic users were more likely to have a documented diagnosis of osteoarthritis, osteoporosis and falls. Opioid use was associated with the Drug Burden Index, while adjuvant use was associated with orthostatic hypotension. Opioid use was associated with having a diagnosis of osteoporosis and falls. CONCLUSIONS: In our cohort of poly-medicated elderly patients, prescription of analgesic medications was common, and these patients are likely to have an increased rate of adverse drug reactions and falls compared with those who were not prescribed analgesic medications.

Challenges and innovations of drug delivery in older age.

Both drug delivery performance and various age-related physical, mental and physiological changes can affect drug effectiveness and safety in elderly patients. The many drug delivery systems developed over the years include recent novel transdermal, nasal, pulmonary and orally disintegrating tablets that provide consistent, precise, timely and more targeted drug delivery. Certain drug delivery systems may be associated with suboptimal outcomes in the elderly because of the nature of drug present, a lack of appreciation of the impact of age-related changes in drug absorption, distribution and clearance, the limited availability of pharmacokinetic, safety and clinical data. Polypharmacy, patient morbidity and poor adherence can also contribute to sub-optimal drug delivery systems outcomes in the elderly. The development of drug delivery systems for the elderly is a poorly realised opportunity, with each system having specific advantages and limitations. A key challenge is to provide the innovation that best meets the specific physiological, psychological and multiple drug requirements of individual elderly patients.

Impact of CYP2C8*3 polymorphism on in vitro metabolism of imatinib to N-desmethyl imatinib.

1. Imatinib is metabolized to N-desmethyl imatinib by CYPs 3A4 and 2C8. The effect of CYP2C8*3 genotype on N-desmethyl imatinib formation was unknown. 2. We examined imatinib N-demethylation in human liver microsomes (HLMs) genotyped for CYP2C8*3, in CYP2C8*3/*3 pooled HLMs and in recombinant CYP2C8 and CYP3A4 enzymes. Effects of CYP-selective inhibitors on N-demethylation were also determined. 3. A single-enzyme Michaelis-Menten model with autoinhibition best fitted CYP2C8*1/*1 HLM (n = 5) and recombinant CYP2C8 kinetic data (median ± SD Ki = 139 ± 61 µM and 149 µM, respectively). Recombinant CYP3A4 showed two-site enzyme kinetics with no autoinhibition. Three of four CYP2C8*1/*3 HLMs showed single-enzyme kinetics with no autoinhibition. Binding affinity was higher in CYP2C8*1/*3 than CYP2C8*1/*1 HLM (median ± SD Km = 6 ± 2 versus 11 ± 2 µM, P=0.04). CYP2C8*3/*3 (pooled HLM) also showed high binding affinity (Km = 4 µM) and single-enzyme weak autoinhibition (Ki = 449 µM) kinetics. CYP2C8 inhibitors reduced HLM N-demethylation by 47-75%, compared to 0-30% for CYP3A4 inhibitors. 4. In conclusion, CYP2C8*3 is a gain-of-function polymorphism for imatinib N-demethylation, which appears to be mainly mediated by CYP2C8 and not CYP3A4 in vitro in HLM.

Pharmacogenetics, plasma concentrations, clinical signs and EEG during propofol treatment.

A variety of techniques have been developed to monitor the depth of anaesthesia. Propofol's pharmacokinetics and response vary greatly, which might be explained by genetic polymorphisms. We investigated the impact of genetic variations on dosage, anaesthetic depth and recovery after total intravenous anaesthesia with propofol. A total of 101 patients were enrolled in the study. The plasma concentration of propofol during anaesthesia was measured using high-performance liquid chromatography. EEG was monitored during the surgical procedure as a measure of anaesthetic depth. Pyrosequencing was used to determine genetic polymorphisms in CYP2B6, CYP2C9, the UGTIA9-promotor and the GABRE gene. The correlation between genotype and to plasma concentration at the time of loss of consciousness (LOC), the total induction dose, the time to anaesthesia, eye opening and clearance were investigated. EEG monitoring showed that the majority of the patients had not reached a sufficient level of anaesthetic depth (subdelta) at the time of loss of consciousness despite a high induction dose of propofol. Patients with UGT1A9-331C/T had a higher propofol clearance than those without (p = 0.03) and required a higher induction dose (p = 0.03). The patients with UGT1A9-1818T/C required a longer time to LOC (p = 0.03). The patients with CYP2C9*2 had a higher concentration of propofol at the time of LOC (p = 0.02). The polymorphisms in the metabolizing enzymes and the receptor could not explain the large variation seen in the pharmacokinetics of propofol and the clinical response seen. At LOC, the patients showed a large difference in EEG pattern.

Identification of candidate SNPs for drug induced toxicity from differentially expressed genes in associated tissues.

The growing collection of publicly available high-throughput data provides an invaluable resource for generating preliminary in silico data in support of novel hypotheses. In this study we used a cross-dataset meta-analysis strategy to identify novel candidate genes and genetic variations relevant to paclitaxel/carboplatin-induced myelosuppression and neuropathy. We identified genes affected by drug exposure and present in tissues associated with toxicity. From ten top-ranked genes 42 non-synonymous single nucleotide polymorphisms (SNPs) were identified in silico and genotyped in 94 cancer patients treated with carboplatin/paclitaxel. We observed variations in 11 SNPs, of which seven were present in a sufficient frequency for statistical evaluation. Of these seven SNPs, three were present in ABCA1 and ATM, and showed significant or borderline significant association with either myelosuppression or neuropathy. The strikingly high number of associations between genotype and clinically observed toxicity provides support for our data-driven computations strategy to identify biomarkers for drug toxicity.

Impact of CYP3A5*3 and CYP2C8-HapC on paclitaxel/carboplatin-induced myelosuppression in patients with ovarian cancer.

The influence of genetic variants on paclitaxel-induced toxicity is of considerable interest for reducing adverse drug reactions. Recently, the genetic variants CYP2C8*3, CYP2C8-HapC, and CYP3A5*3 were associated with paclitaxel-induced neurotoxicity. We, therefore, investigated the impact of CYP2C8-HapC and CYP3A5*3 on paclitaxel/carboplatin-induced myelosuppression and neurotoxicity. Thirty-three patients from a prospective pharmacokinetics study were genotyped using pyrosequencing. Patients with variant alleles of CYP2C8-HapC were found to have significantly lower nadir values of both leukocytes and neutrophils (p < 0.05) than patients with the wild-type genotype. CYP3A5*3/*1 patients were shown to have borderline, significantly lower nadir values of leukocytes (p = 0.07) than *3/*3 patients. Combining the two genotypes resulted in a significant correlation with both leukopenia and neutropenia (p = 0.01). No effect of these genetic variants on neurotoxicity could be shown in this rather small study, but their importance for paclitaxel-induced toxicity could be confirmed.