Potential for drug interactions involving cytochromes P450 2D6 and 3A4 on general adult psychiatric and functional elderly psychiatric wards

Child and Adolescent Bariatric Surgery in an Urban Tertiary Center: Special Anesthetic Considerations for Obesity

Children and adolescents with obesity who present for weight loss surgery are a unique subset of patients. A thorough understanding of the perioperative needs of these individuals is essential to avoid deleterious complications. This review illustrates the necessity for specialized care, including the continued need of specified drug dosing and a systematic approach in the management of the pediatric bariatric patient.

Mechanistic aspects of reactive metabolite formation in clomethiazole catalyzed biotransformation by cytochrome P450 enzymes

Clomethiazole (CLM), a sedative and anticonvulsant drug, is commonly employed for the treatment of alcohol withdrawal syndrome because it suppresses cytochrome P450 (P450) activity associated with the generation of free radicals and liver damage. The catalyzed biotransformation of thiazole-containing drugs by P450 is known to afford reactive metabolites. These metabolites can alter the biological functions of macromolecules and result in toxicity and adverse drug interactions. Multitargeted molecular modeling and quantum chemical DFT calculations were performed to explore the binding modes and molecular mechanisms underlying the mechanism-based inactivation (MBI) of P450 by CLM. The mechanistic details associated with reactive metabolite formation from further metabolic processes were extensively assessed. Seven possible routes were proposed for CLM-P450 biotransformation including CLM hydroxylation, sulfoxidation, N-oxidation, CN epoxidation (oxaziridine formation), and CC epoxidation. The results revealed a degree of preference for the C-N epoxidation pathway because of the low energy requirements of its rate-determining step (8.74 and 10.07 kcal mol-1 for LS and HS states, respectively). A kinetic competition for the CLM-methyl hydroxylation pathway was detected because the H-abstraction energy barrier was relatively comparable to the thermodynamically prevailing oxaziridine formation rate-determining step (12.58 and 14.52 kcal mol-1 for quartet and doublet states, respectively). Our studies assessed the mechanisms of covalent nucleophilic epoxide adduct formation through nucleophilic addition, hydrolysis of epoxidation products, and nonenzymatic degradation. CLM was shown to display P450-inhibitory activity by forming covalent adducts rather than further metabolization to reactive metabolites. The outcomes of molecular docking allowed assessing the binding profile of CLM with three human P450 isozymes, namely, CYP2E1, CYP3A4, and CYP2D6.

Pharmacological approaches to the management of panic disorder in older patients: a systematic review

INTRODUCTION

Recommendations for treating panic disorder (PD) in older patients are scarce. The authors have systematically reviewed whether several recommended medications are superior to others and their optimal doses in this age group.

METHODS

A database search of studies involving patients with PD with/without agoraphobia aged ≥ 60 years was carried out using PubMed, PsycINFO, Embase, and Clinical Trials.gov, from their inception dates to 1 March 2023. Only four (published from 2002 to 2010) of the 1292 records screened were included. A risk of bias assessment was provided. This systematic review was performed using The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA).

RESULTS

Two studies were randomized clinical trials, whereas two were open-label, including paroxetine, citalopram, escitalopram, and sertraline; three studies reported short-term evaluations, whereas one study included a 26-week follow-up. Medications provided benefits, with good tolerability. Preliminary results suggested greater benefits of paroxetine in reducing panic attacks vs. cognitive - behavioral therapy, and an earlier decrease in PAs with escitalopram vs. citalopram. Risk of bias was considerable.

CONCLUSIONS

The pharmacological management of PD in older patients has received no attention. Findings are scant, dated, and affected by methodological flaws; thus, they do not provide significant advances.

Delirium secondary to anticholinergics

We present a case of a young man who developed sudden deterioration in his physical and mental state whilst being treated as an inpatient for substance-induced psychosis. This deterioration was manifested by sudden disorientation, change in behaviour and visual hallucinations. It was only after excluding other potential causes that this presentation was attributed to the regular administration of procyclidine that was being used to counteract the extrapyramidal side effects from antipsychotics. The patient showed a dramatic improvement on stopping procyclidine. This case highlights the importance of awareness of rare adverse drug reactions and the resultant distressing effect for the patient himself.

Impact of the CYP2D6 Genotype on Metoprolol Tolerance and Adverse Events in Elderly Chinese Patients With Cardiovascular Diseases

The latest consensus has changed CYP2D6 genotyping among Chinese population, while its impact on metoprolol tolerance and adverse events in elderly Chinese patients with cardiovascular diseases remains unclear. In this study, we prospectively included elderly patients who started metoprolol treatment for cardiovascular indications. According to the latest consensus on CYP2D6 genotype-to-phenotype translation, the patients were categorized as normal, intermediate, or poor metabolizers (NMs, IMs, or PMs, respectively) by detecting the presence of the CYP2D6*1, *2, *5, *10, and *14. Logistic regression model was used to analyze the correlation between the CYP2D6 phenotype and incidence of adverse events, which were assessed over a 12-week period. In this study, there were 651 (62.7%) NMs, 385 (37.1%) IMs, and 3 (0.3%) PMs. After 12 weeks of follow-up, compared with NMs, IMs had the lower maintenance dose [50.0 (25.0–50.0) mg/day vs. 25.0 (25.0–50.0) mg/day, p < 0.001] and lower weight-adjusted maintenance doses (0.52 ± 0.25 mg/day/kg vs. 0.42 ± 0.22 mg/day/kg, p < 0.001), and had higher incidence of postural hypotension (6.0% vs. 10.9%, p = 0.006), bradycardia (21.5% vs. 28.6%, p = 0.011), asystole (0.8% vs. 3.1%, p = 0.009) and syncope (2.0% vs. 6.2%, p = 0.001). In logistic regression model, the overall incidence of adverse events was 1.37-fold larger in IMs than in NMs (odds ratio = 1.37, 95% confidence interval = 1.05–1.79, p = 0.021). We conclude that IMs have lower tolerance and higher incidence of metoprolol-related adverse events than NMs in elderly Chinese patients with cardiovascular diseases. CYP2D6 genotyping is justifiable in elderly patients to minimize the risk of adverse events and ensure the benefits of metoprolol.

Prevalence and sort of pharmacokinetic drug-drug interactions in hospitalized psychiatric patients

Psychiatric patients are high-risk patients for the development of pharmacokinetic drug-drug interactions (DDIs), leading to highly variable (victim) drug serum concentrations. Avoiding and targeting high-risk drug combinations could reduce preventable adverse drug reactions (ADRs). Pharmacokinetic cytochrome P450 (CYP)-mediated DDIs are often predictable and, therefore, preventable. The retrospective, longitudinal analysis used informations from a large pharmacovigilance study (Optimization of pharmacological treatment in hospitalized psychiatric patients study, study number 01VSF16009, 01/2017), conducted in 10 psychiatric hospitals in Germany. Medication data were examined for the co-prescription of clinically relevant CYP inhibitors or inducers and substrates of these enzymes (victim drugs). In total, data from 27,396 patient cases (45.6% female) with a mean (mean ± standard deviation (SD)) age of 47.3 ± 18.3 years were available for analysis. CYP inhibitors or inducers were at least once prescribed in 14.4% (n = 3946) of the cases. The most frequently prescribed CYP inhibitors were melperone (n = 2504, 28.1%) and duloxetine (n = 1324, 14.9%). Overall, 51.0% of the cases taking melperone were combined with a victim drug (n = 1288). Carbamazepine was the most frequently prescribed CYP inducer (n = 733, 88.8%). Combinations with victim drugs were detected for 58% (n = 427) of cases on medication with carbamazepine. Finally, a DDI was detected in 43.6% of the cases in which a CYP inhibitor or inducer was prescribed. The frequency of CYP-mediated DDI is considerably high in the psychiatric setting. Physicians should be aware of the CYP inhibitory and inducing potential of psychotropic and internistic drugs (especially, melperone).

Cytochrome P450 (CYP450) Interactions Involving Atypical Antipsychotics are Common in Community-Dwelling Older Adults Treated for Behavioral and Psychological Symptoms of Dementia

Treatment of behavioral and psychological symptoms of dementia (BPSD) and comorbidities often necessitates the concomitant use of antipsychotics and non-antipsychotic drugs, thereby potentiating the risk for drug–drug interactions (DDIs). The primary objective of our study was to identify potentially clinically relevant cytochrome P450 (CYP)-mediated DDIs involving antipsychotics among participants enrolled in the Program of All-Inclusive Care for the Elderly (PACE) with BPSD. Additionally, we wanted to determine the prevalence of antipsychotic use in this population. The study included 10,001 PACE participants. The practice setting used a proprietary clinical decision support system (CDSS) to analyze simultaneous multidrug interactions. A retrospective analysis of pharmacy claims data was conducted to identify DDIs involving antipsychotics prescribed for BPSD, using snapshots of medication profiles paired with the CDSS. Of the participants who met inclusion criteria, 1190 (11.9%) were prescribed an antipsychotic; of those, 1071 (90.0%) were prescribed an atypical antipsychotic. Aripiprazole commonly caused (being a perpetrator drug 94.6% of the time) potential DDIs with antidepressants (e.g., duloxetine, venlafaxine, mirtazapine), opioids (e.g., hydrocodone, oxycodone, tramadol) and metoprolol via the CYP2D6 isoform. Risperidone commonly caused (85.7%) potential DDIs with donepezil, lamotrigine and trazodone via the CYP3A4 isoform. Quetiapine exclusively suffered (100%) from potential DDIs with amlodipine, buspirone, omeprazole or topiramate via the CYP3A4 isoform. Antipsychotics are commonly prescribed to PACE participants for BPSD treatment and they may interact with other drugs used to treat comorbidities. A thorough review of concomitant medications will help mitigate the likelihood of potentially dangerous CYP-mediated DDIs involving antipsychotics.

City-wide electronic health records reveal gender and age biases in administration of known drug-drug interactions

The occurrence of drug-drug-interactions (DDI) from multiple drug dispensations is a serious problem, both for individuals and health-care systems, since patients with complications due to DDI are likely to reenter the system at a costlier level. We present a large-scale longitudinal study (18 months) of the DDI phenomenon at the primary- and secondary-care level using electronic health records (EHR) from the city of Blumenau in Southern Brazil (pop. ≈340,000). We found that 181 distinct drug pairs known to interact were dispensed concomitantly to 12% of the patients in the city's public health-care system. Further, 4% of the patients were dispensed drug pairs that are likely to result in major adverse drug reactions (ADR)-with costs estimated to be much larger than previously reported in smaller studies. The large-scale analysis reveals that women have a 60% increased risk of DDI as compared to men; the increase becomes 90% when considering only DDI known to lead to major ADR. Furthermore, DDI risk increases substantially with age; patients aged 70-79 years have a 34% risk of DDI when they are dispensed two or more drugs concomitantly. Interestingly, a statistical null model demonstrates that age- and female-specific risks from increased polypharmacy fail by far to explain the observed DDI risks in those populations, suggesting unknown social or biological causes. We also provide a network visualization of drugs and demographic factors that characterize the DDI phenomenon and demonstrate that accurate DDI prediction can be included in health care and public-health management, to reduce DDI-related ADR and costs.

Drug-drug interactions involving CYP3A4 and p-glycoprotein in hospitalized elderly patients

Polypharmacy is very common in older patients and may be associated with drug-drug interactions. Hepatic cytochrome P450 (notably 3A4 subtype, CYP3A4) is a key enzyme which metabolizes most drugs; P-glycoprotein (P-gp) is a transporter which significantly influences distribution and bioavailability of many drugs. In this study, we assess the prevalence and patterns of potential interactions observed in an hospitalized older cohort (Registro Politerapia Società Italiana di Medicina Interna) exposed to at least two interacting drugs involving CYP3A4 and P-gp at admission, during hospitalization and at discharge. Individuals aged 65 and older (N-4039; mean age 79.2; male 48.1%), hospitalized between 2010 and 2016, were selected. The most common combinations of interacting drugs (relative frequency > 5%) and socio-demographic and clinical factors associated with the interactions were reported. The prevalence of interactions for CYP3A4 was 7.9% on admission, 10.3% during the stay and 10.7% at discharge; the corresponding figures for P-gp interactions were 2.2%, 3.8% and 3.8%. The most frequent interactions were amiodarone-statin for CYP3A4 and atorvastatin-verapamil-diltiazem for P-gp. The prevalence of some interactions, mainly those involving cardiovascular drugs, decreased at discharge, whereas that of others, e.g. those involving neuropsychiatric drugs, increased. The strongest factor associated with interactions was polypharmacy (OR 6.7, 95% CI 5.0-9.2). In conclusion, hospital admission is associated with an increased prevalence, but also a changing pattern of interactions concerning CYP3A4 and P-gp in elderly. Educational strategies and appropriate use of dedicated software seem desirable to limit drug interactions and the inherent risk of adverse events in older patients.

Drug-drug Interactions in Psychiatric Practice, Part 1: Reasons, Importance, and Strategies to Avoid and Recognize Them

This column begins a series exploring drug-drug interactions (DDIs) with a special emphasis on psychiatric medications. As explained in this column, this topic is important for multiple reasons. First, a large percentage of the population is receiving psychiatric medications. Second, these patients are likely to be on multiple medications which means that they are at risk for an adverse DDI. Third, DDIs may occur but not be recognized even though they have significant health care consequences for the patient. Fourth, these consequences can range from a catastrophic outcome to more everyday clinical problems involving a myriad of presentations as enumerated in this column. Also discussed in this column is the fact that all drugs, including psychiatric medications, interact on the basis of their pharmacodynamics and pharmacokinetics rather than their therapeutic use. Therefore, psychiatric medications may interact with medications prescribed for nonpsychiatric reasons as well as with other psychiatric medications. Tables are included that explain reasons for multiple medication use and principles to follow to minimize the risk of adverse DDIs.

Sequential drug treatment algorithm for agitation and aggression in Alzheimer's and mixed dementia

INTRODUCTION

Behavioural and psychological symptoms of dementia (BPSD) include agitation and aggression in people with dementia. BPSD is common on inpatient psychogeriatric units and may prevent individuals from living at home or in residential/nursing home settings. Several drugs and non-pharmacological treatments have been shown to be effective in reducing behavioural and psychological symptoms of dementia. Algorithmic treatment may address the challenge of synthesizing this evidence-based knowledge.

METHODS

A multidisciplinary team created evidence-based algorithms for the treatment of behavioural and psychological symptoms of dementia. We present drug treatment algorithms for agitation and aggression associated with Alzheimer's and mixed Alzheimer's/vascular dementia. Drugs were appraised by psychiatrists based on strength of evidence of efficacy, time to onset of clinical effect, tolerability, ease of use, and efficacy for indications other than behavioural and psychological symptoms of dementia.

RESULTS

After baseline assessment and discontinuation of potentially exacerbating medications, sequential trials are recommended with risperidone, aripiprazole or quetiapine, carbamazepine, citalopram, gabapentin, and prazosin. Titration schedules are proposed, with adjustments for frailty. Additional guidance is given on use of electroconvulsive therapy, optimization of existing cholinesterase inhibitors/memantine, and use of pro re nata medications.

CONCLUSION

This algorithm-based approach for drug treatment of agitation/aggression in Alzheimer's/mixed dementia has been implemented in several Canadian Hospital Inpatient Units. Impact should be assessed in future research.

Discontinuation and dose adjustment of metoprolol after metoprolol-paroxetine/fluoxetine co-prescription in Dutch elderly

Purpose

Co‐prescription of paroxetine/fluoxetine (a strong CYP2D6 inhibitor) in metoprolol (a CYP2D6 substrate) users is common, but data on the clinical consequences of this drug‐drug interaction are limited and inconclusive. Therefore, we assessed the effect of paroxetine/fluoxetine initiation on the existing treatment with metoprolol on the discontinuation and dose adjustment of metoprolol among elderly.

Methods

We performed a cohort study using the University of Groningen IADB.nl prescription database (www.IADB.nl). We selected all elderly (≥60 years) who had ever been prescribed metoprolol and had a first co‐prescription of paroxetine/fluoxetine, citalopram (weak CYP2D6 inhibitor), or mirtazapine (negative control) from 1994 to 2015. The exposure group was metoprolol and paroxetine/fluoxetine co‐prescription, and the other groups acted as controls. The outcomes were early discontinuation and dose adjustment of metoprolol. Logistic regression was applied to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI).

Results

Combinations of metoprolol‐paroxetine/fluoxetine, metoprolol‐citalopram, and metoprolol‐mirtazapine were started in 528, 673, and 625 patients, respectively. Compared with metoprolol‐citalopram, metoprolol‐paroxetine/fluoxetine was not significantly associated with the early discontinuation and dose adjustment of metoprolol (OR = 1.07, 95% CI:0.77‐1.48; OR = 0.87, 95% CI:0.57‐1.33, respectively). In comparison with metoprolol‐mirtazapine, metoprolol‐paroxetine/fluoxetine was associated with a significant 43% relative increase in early discontinuation of metoprolol (OR = 1.43, 95% CI:1.01‐2.02) but no difference in the risk of dose adjustment. Stratified analysis by gender showed that women have a significantly high risk of metoprolol early discontinuation (OR = 1.62, 95% CI:1.03‐2.53).

Conclusion

Paroxetine/fluoxetine initiation in metoprolol prescriptions, especially for female older patients, is associated with the risk of early discontinuation of metoprolol.

Potential drug-drug interactions and polypharmacy in institutionalized elderly patients in a public hospital in Brazil

WHAT IS KNOWN ON THE SUBJECT?: Older individuals constitute an increasing proportion of the population, and therefore, are the major consumers of drugs. The elderly, especially those with mental disabilities, frequently develop chronic diseases and start using numerous drugs. Drug-drug interactions (DDIs) are a major clinical problem in the elderly population, and previous studies have focused only on antidepressants and others types of drugs used to treat mental health conditions. WHAT THIS ARTICLE ADDS TO EXISTING KNOWLEDGE?: This study shows that in hospitalized elderly patients with mental disorders (aged 60-69 years), polypharmacy (≥5 drugs) and the use of drugs that act on the cardiovascular, respiratory and nervous systems can lead to potential drug-drug interactions. Moreover, it was reported that the prevalence of drug-drug interactions in elderly patients with mental disorders was high during their hospitalization in a public hospital in Brazil. WHAT ARE THE IMPLICATIONS FOR PRACTICE?: Nurses should know the factors associated with drug-drug interactions in hospitalized elderly patients with mental disorders to choose appropriate strategies for avoiding treatment failure and adverse events in patients.

ABSTRACT

Introduction Despite the impact on patient safety and the fact that prevalence is higher in older patients, previous research did not analyse drug-drug interactions (DDIs) in view of nursing care of elderly psychiatric patients. Aim To identify potential drug-drug interactions and polypharmacy in prescriptions of aged inpatients with psychiatric disorders and analyse associated factors. Methods In this retrospective cross-sectional study, we analysed the medical records of institutionalized patients diagnosed with psychiatric disorders (n = 94), aged >60 years, and prescribed multiple medications. Drug prescriptions were checked at admission, midway through and the last prescription. Factors associated with DDI occurrence were assessed using multivariable logistic regression analysis. Results A DDI prevalence potential of 67.0%, 74.5% and 80.8% occurred in patients at admission, midway through hospitalization and the last prescription, respectively. Most of the prescribed drugs were nervous system agents. A high percentage of serious and contraindicated potential DDIs occurred. Age between 60 and 69 years, use of cardiovascular and respiratory system drugs, and the number of medications contributed significantly to DDI. Implications for mental health nursing Knowledge on the factors associated with DDIs in patients with mental disorders can contribute to the improvement of effectiveness and safety of nursing care.

Prescribing safely in elderly psychiatric wards: survey of possible drug interactions

Aims and Method

A cross-sectional survey of patient drug prescriptions on two elderly psychiatric wards was carried out to estimate the potential of drug–drug interactions. Two standardised databases, British National Formulary (BNF; British Medical Association & Royal Pharmaceutical Society of Great Britain, 2007) and Upto Date (www.uptodate.com/), were employed.

Results

A majority (96%) of drug prescriptions in our study could potentially cause drug–drug interactions. Most patients were on multiple drugs (on average eight drugs per patient). There was poor concordance between the two databases: BNF picked up fewer cases of potential drug–drug interactions than Upto Date (43 v. 152 instances) and they also estimated the potential for hazardousness differently.

Clinical Implications

Polypharmacy is common in elderly psychiatric patients and this increases the possibility of a drug–drug interaction. Estimating the risk of interactions depends on a sound knowledge in therapeutics and/or referring to a standardised source of information. the results of this study question the concordance of two well-referenced databases.

Interações medicamentosas potenciais entre medicamentos psicotrópicos dispensados

RESUMO Objetivo Estimar a frequência e caracterizar as interações medicamentosas potenciais entre fármacos psicotrópicos sujeitos a controle especial pela portaria 344/98 da Agência Nacional de Vigilância Sanitária (Anvisa), os quais foram prescritos e dispensados em uma farmácia pública do Município de Cascavel, Paraná. Métodos Estudo retrospectivo com desenho seccional foi realizado em uma Farmácia Pública Municipal. A amostra foi composta por prescrições de medicamentos sujeitos a controle especial, dispensados entre primeiro de julho a 31 de agosto de 2010. As prescrições retidas na farmácia foram analisadas retrospectivamente e as informações, coletadas. As interações medicamentosas potenciais foram identificadas em 824 prescrições. Resultados As prescrições eram na maioria para pacientes do sexo feminino e com idade entre 19 e 59 anos. Em relação à especialidade do prescritor, 30,6% foram prescritas por psiquiatra. Em 77,9% das prescrições identificou-se pelo menos uma interação medicamentosa potencial. Foram descritas 54 diferentes interações medicamentosas potenciais, sendo 34 graves e 20 moderadas. Encontrou-se uma correlação linear entre medicamentos prescritos e interações medicamentosas potenciais (p valor < 0,001). Conclusão O presente estudo identificou uma alta frequência de interações medicamentosas potenciais envolvendo fármacos de controle especial e uma associação positiva entre o número de fármacos prescritos com a maior frequência dessas interações.

The burden and management of cytochrome P450 2D6 (CYP2D6)-mediated drug-drug interaction (DDI): co-medication of metoprolol and paroxetine or fluoxetine in the elderly

PURPOSE

Metoprolol and paroxetine/fluoxetine are inevitably co-prescribed because cardiovascular disorders and depression often coexist in the elderly. This leads to CYP2D6-mediated drug-drug interactions (DDI). Because systematic evaluations are lacking, we assessed the burden of metoprolol-paroxetine/fluoxetine interaction in the elderly and how these interactions are managed in Dutch community pharmacies.

METHOD

Dispensing data were collected from the University of Groningen pharmacy database (IADB.nl, 1999-2014) for elderly patients (≥60 years) starting beta-blockers and/or antidepressants. Based on the two main DDI alert systems (G-Standard and Pharmabase), incidences were divided between signalled (metoprolol-fluoxetine/paroxetine) and not-signalled (metoprolol-alternative antidepressants and alternative beta-blockers-paroxetine/fluoxetine) combinations. Incident users were defined as patients starting at least one signalled or a non-signalled combination. G-Standard signalled throughout the study period, whereas Pharmabase stopped after 2005.

RESULTS

A total of 1763 patients had 2039 metoprolol-paroxetine/fluoxetine co-prescriptions, despite DDI alert systems, and about 57.3% were signalled. The number of metoprolol-alternative antidepressant combinations (incidences = 3150) was higher than alternative beta-blocker-paroxetine/fluoxetine combinations (incidences = 1872). Metoprolol users are more likely to be co-medicated with an alternative antidepressant (incidences = 2320) than paroxetine/fluoxetine users (incidences = 1232) are. The number of paroxetine/fluoxetine users co-prescribed with alternative beta-blockers was comparable to those co-medicated with metoprolol (about 50%). Less than 5% of patients received a substitute therapy after using metoprolol-paroxetine/fluoxetine. Most of the metoprolol users (90%) received a low dose (mean DDD = 0.47) regardless whether they were prescribed paroxetine/fluoxetine.

CONCLUSION

Despite the signalling software, metoprolol-paroxetine/fluoxetine combinations are still observed in the elderly population. The clinical impact of these interactions needs further investigation. Copyright © 2017 John Wiley & Sons, Ltd.

Prevalence of Patients Using Drugs Metabolized by Cytochrome P450 2D6 in Different Populations: a Cross-Sectional Study

Background:

Despito a large number of studies investigating the potential clinical relevance of CYP2D6 genotyping in preventing treatment failure (eg, insufficient efficacy and/or unacceptable adverse effects), the prevalence of patients using drugs metabolized by that isoenzyme is relatively unknown.

Objective:

To investigate the prevalence of patients in different populations using drugs metabolized by CYP2D6.

Methods:

In this cross-sectional study. 6 different patient populations were investigated: general, general hospital, geriatric, psychogoriatric, psychiatric, and mentally retarded. From every population, 150 adults using at least one drug were randomly selected. Primary outcome was the prevalence of patients using at least one drug metabolized by CYP2D6. The prevalence of patients using at least one CYP2D6 substrate in different populations was compared with the general population using χ2 statistics. Data were expressed as a relative risk with a 95% confidence interval.

Results:

Patients from the general hospital (RR 1.81; 95% CI 1.26 to 2.62), geriatric patients (RR 2.16; 95% CI 1.26 to 2.62), psychogeriatric patients (RR 2.31; 95% CI 1.63 to 3.27), and psychiatric patients (RR 2.44; 95% CI 1.73 to 3.44) were treated more frequently with at least one drug metabolized by CYP2D6 compared with patients in the general population. Approximately 50% of psychiatric (52%), psychogeriatric (49%), and geriatric (46%) patients used at least one drug metabolized by CYP2D6. In total, 416 drugs metabolized by CYP2D6 were prescribed, with 257 (62%) of these classified as an antidepressant (Anatomical and Therapeutic Chemical [ATC] category N06A) or antipsychotic (ATC N05A).

Conclusions:

Several patient populations (eg, psychiatric, psychogeriatric, geriatric) have a high prevalence of patients treated with at least one drug metabolized by CYP2D6. This study does not provide evidence regarding the clinical evidence of CYP2D6 genotyping, but shows that, if CYP2D6 genotyping is relevant for patient care, the highest probability of cost-effectiveness will, most likely, be in specific populations.

Frequency and clinical relevance of potential cytochrome P450 drug interactions in a psychiatric patient population - an analysis based on German insurance claims data

BACKGROUND

Numerous drugs used in the treatment of psychiatric disorders are substrates of cytochrome P450 enzymes and are potential candidates for drug-drug interactions (DDIs).

METHODS

Claims data of a German statutory health insurance company from severely mentally ill patients who registered in an integrated care contract from August 2004 to December 2009 were analysed. We measured time periods of concomitant prescription of drugs that have been reported to interact via cytochrome P450, with a focus on drugs acting as strong inhibitors. Such drug-drug exposure (DDE) is an incontrovertible precursor of DDIs. We assessed whether potential DDIs were considered clinically relevant based on the prescribing information of the respective drugs.

RESULTS

Among all 1221 patients, 186 patients (15.2 %; Clopper-Pearson 95 % confidence interval (CI): 13.3-17.4 %) had at least one DDE prescription, and 58 patients (4.8 %; 95 % CI 3.6-6.1) had at least one DDE prescription involving a strong cytochrome P450 inhibitor. In 59 patients, (4.8 %; 95 % CI: 3.7-6.2 %) five or more DDEs were identified, and five or more DDEs with a strong inhibitor were identified in 18 patients (1.5 %; 95 % CI: 0.9-2.3). The rates of DDEs were 0.27 (Garwood 95%CI: 0.25-0.28) per person-year and 0.07 (95 % CI: 0.07-0.08) for strong-inhibitor DDEs. Four of the ten most frequent DDEs were identified as clinically relevant, and seven of the eight most frequent DDEs involving a strong inhibitor were clinically relevant.

CONCLUSIONS

The number of patients with DDEs was not alarmingly high in our sample. Nevertheless, prescription information showed that some prescribed drug combinations could result in serious adverse consequences that are known to weaken or strengthen the effect of the drugs and should therefore be avoided.

Evaluation of Potential Drug-Drug Interactions with Antidepressants in Two Tertiary Care Hospitals

BACKGROUND

Limited resources of healthcare system and high use of antidepressants have raised some serious concerns regarding proper surveillance system of prescribed medicines. Not much literature is available from Pakistan regarding the potential drug-drug interactions (pDDIs) associated with antidepressants.

OBJECTIVE

The objective of this study was to assess the frequency of pDDIs associated with antidepressants, their severity, significance and their association with patient characteristics.

MATERIALS AND METHODS

A prospective, observational study was conducted in two major hospitals of Karachi for the period of three months. Patient profiles, medication charts, and physician notes were thoroughly reviewed to gather all the relevant information. Inclusion and exclusion criteria were set prior to data collection. The collected data was then analysed using Micromedex Drug-REAX System. Descriptive and binomial logistic regression analysis was used to express results.

RESULTS

Of 245 prescriptions reviewed, 141 prescriptions had at least one pDDI (57.5%). A total of 181 pDDIs were identified in prescription containing antidepressant. The ratio of pDDI per prescriptions was 0.78. 42.5% interactions were moderate in severity, 30% of interactions were rapid in onset, and 43% were considered as significant interactions. Polypharmacy (OR=3.41, p< 0.001) and presence of chronic problems (OR=2.14, p=0.002) were significantly associated with the occurrence of pDDIs. Citalopram and diclofenac (11.6%) was commonly prescribed interacting pair in this study.

CONCLUSION

The findings of this study recorded high frequency of antidepressants associated pDDIs. Our results confirm the significant association of polypharmacy with the occurrence of pDDIs with antidepressants. Future studies are warranted to establish these results by including hospitals in different parts of the country.

Understanding and preventing drug-drug and drug-gene interactions

Concomitant administration of multiple drugs can lead to unanticipated drug interactions and resultant adverse drug events with their associated costs. A more thorough understanding of the different cytochrome P450 isoenzymes and drug transporters has led to new methods to try to predict and prevent clinically relevant drug interactions. There is also an increased recognition of the need to identify the impact of pharmacogenetic polymorphisms on drug interactions. More stringent regulatory requirements have evolved for industry to classify cytochrome inhibitors and inducers, test the effect of drug interactions in the presence of polymorphic enzymes, and evaluate multiple potentially interacting drugs simultaneously. In clinical practice, drug alert software programs have been developed. This review discusses drug interaction mechanisms and strategies for screening and minimizing exposure to drug interactions. We also provide future perspectives for reducing the risk of clinically significant drug interactions.

Extent of poly-pharmacy, occurrence and associated factors of drug-drug interaction and potential adverse drug reactions in Gondar Teaching Referral Hospital, North West Ethiopia

The aim of this study was to assess the extent of poly-pharmacy, occurrence, and associated factors for the occurrence of drug-drug interaction (DDI) and potential adverse drug reaction (ADR) in Gondar University Teaching Referral Hospital. Institutional-based retrospective cross-sectional study. This study was conducted on prescriptions of both in and out-patients for a period of 3 months at Gondar University Hospital. Both bivariate analysis and multivariate logistic regression were used to identify risk factors for the occurrence of DDI and possible ADRs. All the statistical calculations were performed using SPSS(®) software. A total of 12,334 prescriptions were dispensed during the study period of which, 2,180 prescriptions were containing two or more drugs per prescription. A total of 21,210 drugs were prescribed and the average number of drugs per prescription was 1.72. Occurrences of DDI of all categories (Major, Moderate, and Minor) were analyzed and DDI were detected in 711 (32.6%) prescriptions. Sex was not found to be a risk factor for the occurrence of DDI and ADR, while age and number of medications per prescription were found to be significant risk factors for the occurrence of DDI and ADR. The mean number of drugs per prescription was 1.72 and hence with regard to the WHO limit of drugs per prescription, Gondar hospital was able to maintain the limit and prescriptions containing multiple drugs supposed to be taken systemically. Numbers of drugs per prescription as well as older age were found to be predisposing factors for the occurrence of DDI and potential ADRs while sex was not a risk factor.

Prevalence and risk of potential cytochrome P450-mediated drug-drug interactions in older hospitalized patients with polypharmacy

BACKGROUND

As rates of polypharmacy rise and medication regimens become more complex, the risk of potential cytochrome P450 (CYP)-mediated drug-drug interactions (DDIs) is a growing clinical concern for older adults.

OBJECTIVE

To determine the prevalence of potential CYP-mediated DDIs in older hospitalized adults with polypharmacy and analyze the relationship between the number of drugs dispensed and the probability of these interactions in this high-risk population.

METHODS

A prospective 16-week cohort study was conducted among consecutive new patients aged 65 years and older with polypharmacy (>5 drugs) admitted to a community hospital. The medication profiles of these patients were analyzed with a new multidrug cytochrome-specific software program. The prevalence of potential CYP-mediated DDIs was determined, with the probability calculated as a function of the number of medications dispensed using multivariate Poisson regression adjusted for age and sex. Comparative performance of the software program and a standard 2-drug alert program for detecting these DDIs was evaluated using the Wilcoxon-Mann-Whitney rank-sum test. Pharmacists' decisions to recommend medication adjustment based on the probability of CYP-mediated DDIs were recorded.

RESULTS

The prevalence of potential CYP-mediated DDIs detected among 275 older adults with polypharmacy was 80%. The probability of at least 1 CYP-mediated DDI was 50% for persons taking 5-9 drugs, 81% with 10-14 drugs, 92% with 15-19 drugs, and 100% with 20 or more drugs. Addition of each medication to a 5-drug regimen conferred a 12% increased risk of a potential CYP-mediated DDI after adjustment for age and sex (OR 1.12; 95% CI 1.09-1.14). The multidrug software identified a median increase of 3 (95% CI 2.5-3.5) potential CYP-mediated DDIs per patient, compared to use of the standard 2-drug alert software. Pharmacists targeted patients for medication adjustment or close clinical monitoring in 23% of cases.

CONCLUSIONS

The prevalence of potential CYP-mediated DDIs is high in geriatric patients with polypharmacy. The risk of DDIs increases as a function of the number of medications dispensed. Pharmacists' decision to intervene for potential CYP-mediated DDIs depends on clinical judgment in addition to the output from drug alert software programs, but may be facilitated by a single multicomponent, multidrug potential CYP-mediated DDI assessment.

Prevalence of drug interactions in hospital healthcare

AIM OF THE REVIEW

To study the prevalence of drug interactions in hospital healthcare by reviewing literature.

METHOD

A review was carried out of studies written in Spanish and English on the prevalence of drug interactions in hospital care published in Pubmed between January 1990 and September 2008. The search strategy combined free text and MeSH terms, using the following keywords: "Drug interaction", "prevalence" and "hospital". For each article, we classified independent variables (pathology, age of population, whether patients were hospitalized or not, geographical location, etc.) and dependent variables (number of interactions per 100 patients studied, prevalence of patients with interactions, most common drug interactions, and others).

RESULTS

The search generated 436 articles. Finally, 47 articles were selected for the study, 3 provided results about drug interactions with real clinical consequences, 42 about potential interactions, and 2 described both. The prevalence of patients with interactions was between 15 and 45 % and the number of interactions per 100 patients was between 37 and 106, depending on the group of studies analyzed. There was a considerable increase in these rates in patients with heart diseases and elderly persons.

CONCLUSION

There is a large number of studies on the prevalence of drug interactions in hospitals but they report widely varying results. The prevalence is higher in patients with heart diseases and elderly people.

Dose-response relationship between selective serotonin re-uptake inhibitors and injurious falls: a study in nursing home residents with dementia

AIM

The contribution of selective serotonin re-uptake inhibitors (SSRIs) to injurious fall risk in patients with dementia has not been quantified precisely until now. Our objective was to determine whether a dose-response relationship exists for the use of SSRIs and injurious falls in a population of nursing home residents with dementia.

METHODS

Daily drug use and daily falls were recorded in 248 nursing home residents with dementia from 1 January 2006 until 1 January 2008. For each resident and for each day of the study period, data on drug use were abstracted from the prescription database, and information on falls and subsequent injuries was retrieved from a standardized incident report system, resulting in a dataset of 85,074 person-days.

RESULTS

We found a significant dose-response relationship between injurious falls and the use of SSRIs. The risk of an injurious fall increased significantly with 31% at 0.25 of the Defined Daily Dose (DDD) of a SSRI, 73% at 0.50 DDD, and 198% at 1.00 DDD (Hazard ratio = 2.98; 95% confidence interval 1.94, 4.57). The risk increased further in combination with a hypnotic or sedative.

CONCLUSIONS

Even at low doses, SSRIs are associated with increased risk of an injurious fall in nursing home residents with dementia. Higher doses increase the risk further with a three-fold risk at 1.00 DDD. New treatment protocols might be needed that take into account the dose-response relationship between SSRIs and injurious falls.

Modeling chemical interaction profiles: II. Molecular docking, spectral data-activity relationship, and structure-activity relationship models for potent and weak inhibitors of cytochrome P450 CYP3A4 isozyme

Polypharmacy increasingly has become a topic of public health concern, particularly as the U.S. population ages. Drug labels often contain insufficient information to enable the clinician to safely use multiple drugs. Because many of the drugs are bio-transformed by cytochrome P450 (CYP) enzymes, inhibition of CYP activity has long been associated with potentially adverse health effects. In an attempt to reduce the uncertainty pertaining to CYP-mediated drug-drug/chemical interactions, an interagency collaborative group developed a consensus approach to prioritizing information concerning CYP inhibition. The consensus involved computational molecular docking, spectral data-activity relationship (SDAR), and structure-activity relationship (SAR) models that addressed the clinical potency of CYP inhibition. The models were built upon chemicals that were categorized as either potent or weak inhibitors of the CYP3A4 isozyme. The categorization was carried out using information from clinical trials because currently available in vitro high-throughput screening data were not fully representative of the in vivo potency of inhibition. During categorization it was found that compounds, which break the Lipinski rule of five by molecular weight, were about twice more likely to be inhibitors of CYP3A4 compared to those, which obey the rule. Similarly, among inhibitors that break the rule, potent inhibitors were 2–3 times more frequent. The molecular docking classification relied on logistic regression, by which the docking scores from different docking algorithms, CYP3A4 three-dimensional structures, and binding sites on them were combined in a unified probabilistic model. The SDAR models employed a multiple linear regression approach applied to binned 1D ¹³C-NMR and 1D ¹⁵N-NMR spectral descriptors. Structure-based and physical-chemical descriptors were used as the basis for developing SAR models by the decision forest method. Thirty-three potent inhibitors and 88 weak inhibitors of CYP3A4 were used to train the models. Using these models, a synthetic majority rules consensus classifier was implemented, while the confidence of estimation was assigned following the percent agreement strategy. The classifier was applied to a testing set of 120 inhibitors not included in the development of the models. Five compounds of the test set, including known strong inhibitors dalfopristin and tioconazole, were classified as probable potent inhibitors of CYP3A4. Other known strong inhibitors, such as lopinavir, oltipraz, quercetin, raloxifene, and troglitazone, were among 18 compounds classified as plausible potent inhibitors of CYP3A4. The consensus estimation of inhibition potency is expected to aid in the nomination of pharmaceuticals, dietary supplements, environmental pollutants, and occupational and other chemicals for in-depth evaluation of the CYP3A4 inhibitory activity. It may serve also as an estimate of chemical interactions via CYP3A4 metabolic pharmacokinetic pathways occurring through polypharmacy and nutritional and environmental exposures to chemical mixtures.

Modeling chemical interaction profiles: I. Spectral data-activity relationship and structure-activity relationship models for inhibitors and non-inhibitors of cytochrome P450 CYP3A4 and CYP2D6 isozymes

An interagency collaboration was established to model chemical interactions that may cause adverse health effects when an exposure to a mixture of chemicals occurs. Many of these chemicals—drugs, pesticides, and environmental pollutant—interact at the level of metabolic biotransformations mediated by cytochrome P450 (CYP) enzymes. In the present work, spectral data-activity relationship (SDAR) and structure-activity relationship (SAR) approaches were used to develop machine-learning classifiers of inhibitors and non-inhibitors of the CYP3A4 and CYP2D6 isozymes. The models were built upon 602 reference pharmaceutical compounds whose interactions have been deduced from clinical data, and 100 additional chemicals that were used to evaluate model performance in an external validation (EV) test. SDAR is an innovative modeling approach that relies on discriminant analysis applied to binned nuclear magnetic resonance (NMR) spectral descriptors. In the present work, both 1D ¹³C and 1D ¹⁵N-NMR spectra were used together in a novel implementation of the SDAR technique. It was found that increasing the binning size of 1D ¹³C-NMR and ¹⁵N-NMR spectra caused an increase in the tenfold cross-validation (CV) performance in terms of both the rate of correct classification and sensitivity. The results of SDAR modeling were verified using SAR. For SAR modeling, a decision forest approach involving from 6 to 17 Mold² descriptors in a tree was used. Average rates of correct classification of SDAR and SAR models in a hundred CV tests were 60% and 61% for CYP3A4, and 62% and 70% for CYP2D6, respectively. The rates of correct classification of SDAR and SAR models in the EV test were 73% and 86% for CYP3A4, and 76% and 90% for CYP2D6, respectively. Thus, both SDAR and SAR methods demonstrated a comparable performance in modeling a large set of structurally diverse data. Based on unique NMR structural descriptors, the new SDAR modeling method complements the existing SAR techniques, providing an independent estimator that can increase confidence in a structure-activity assessment. When modeling was applied to hazardous environmental chemicals, it was found that up to 20% of them may be substrates and up to 10% of them may be inhibitors of the CYP3A4 and CYP2D6 isoforms. The developed models provide a rare opportunity for the environmental health branch of the public health service to extrapolate to hazardous chemicals directly from human clinical data. Therefore, the pharmacological and environmental health branches are both expected to benefit from these reported models.

Detection and prevention of drug-drug interactions in the hospitalized elderly: utility of new cytochrome p450-based software

BACKGROUND

Polypharmacy increases the risk of cytochrome P450-based drug-drug interactions (CYP450-DDIs), leading to decreased therapeutic efficacy or increased drug toxicity.

OBJECTIVE

The aims of this study were to investigate the utility of a new CYP450-DDI software, InterMED-Rx, in aiding pharmacists in detecting CYP450-DDIs in hospitalized elderly patients and to ascertain pharmacists' agreement on how to intervene for each CYP450-DDI.

METHODS

A consensus panel of geriatric pharmacists first established guidelines for managing clinically relevant pharmacokinetic CYP450-DDIs. A prospective study was then conducted of patients newly admitted to a geriatric hospital whose pharmaceutical profile underwent analysis with InterMED-Rx. Rates and types of interventions were recorded.

RESULTS

Pharmacists' interrater agreement on how to manage CYP450-DDIs was initially only moderate (Cohen's κ, 0.51; 95% CI, 0.39-0.62), but improved subsequent to deliberation (Cohen's κ, 0.79; 95% CI, 0.70-0.88). Persistent disagreement involved interactions between 2 drugs with similar affinities for the same cytochrome. One hundred patients with polypharmacy (≥5 medications) aged 82.3 years (range, 65-96), with a mean (SD) of 12.2 (4.1) drugs (range, 5-27) were recruited for the prospective study. Eighty percent of patients had at least 1 CYP450 DDI detected with InterMED-Rx. A total of 238 CYP450-DDIs were identified involving CYP3A4 (70.2%), CYP2D6 (22.7%), and CYP2C9 (3.4%) substrates or inhibitors. Nineteen percent of patients received immediate medication adjustment, and 39% required follow-up of clinical signs, symptoms, and laboratory tests to determine whether future modification was needed. More than one half (56%) of all patients who required clinical follow-up had further medication adjustment prior to discharge.

CONCLUSIONS

Use of the InterMED-Rx software identified elderly patients at risk for pharmacokinetic interactions and facilitated interventions aimed at reducing adverse drug events. Although consensus can be reached among pharmacists on how to intervene for many CYP450-DDI scenarios, certain situations allow for multiple intervention strategies.

Characterisation of zuclopenthixol metabolism by in vitro and therapeutic drug monitoring studies

OBJECTIVE

Zuclopenthixol pharmacokinetics is incompletely characterised. We investigated potential interactions mediated through cytochrome P450 enzymes.

METHOD

In vitro, we examined the impact of CYP2D6 and CYP3A4 inhibitors on zuclopenthixol metabolism in microsomes from six human livers. Subsequently, we compared dose-corrected serum zuclopenthixol concentrations in 923 samples from a therapeutic drug monitoring database from patients prescribed oral (n = 490) or injected (n = 423) zuclopenthixol alone or with fluoxetine, paroxetine, levomepromazine or carbamazepine.

RESULTS

In vitro fluoxetine, paroxetine, ketoconazole and quinidine all significantly inhibited zuclopenthixol metabolism. Ketoconazole and quinidine together abolished zuclopenthixol disappearance. Clinically, dose-corrected oral zuclopenthixol serum concentrations increased significantly, after adjustment, by 93%, 78% and 46% during co-treatment with fluoxetine, paroxetine and levomepromazine and decreased 67% with carbamazepine. Carbamazepine caused dose-dependent reductions in the oral zuclopenthixol concentration-dose ratio (P < 0.001), fluoxetine (P < 0.001) and paroxetine (P = 0.011) dose-dependent increases and levomepromazine an increase related to its serum concentration (P < 0.001). Results for injected zuclopenthixol were similar but not all reached statistical significance.

CONCLUSION

The In vitro study suggests zuclopenthixol is metabolised primarily by CYP2D6 and CYP3A4. The clinical study supports this, demonstrating the impact of co-prescribed inhibitors or inducers. Guidelines should incorporate these interactions noting the potential for zuclopenthixol-related toxicity or treatment failure.

Drug-drug interactions in general hospital and psychiatric hospital in-patients prescribed psychotropic medications

Abstract Objectives. Drug-drug interactions (DDIs) present a serious, ever increasing clinical problem. Previous studies identified DDIs among psychiatric inpatients prescribed psychotropics, but none have focused on psychotropics prescribed to General Hospital inpatients. This study aimed to identify: putative drug-drug interactions; mechanisms; potential seriousness among patients prescribed psychotropes in both psychiatric and general hospital inpatients settings. We hypothesised that potential interactions per person would be greater in General Hospital inpatients on psychotropics, due to polypharmacy. Method. We surveyed psychotropic prescribing in hospital wards in a public sector mental health organisation and a 500-bed general hospital. Ward pharmacists collected drug prescription data. A computer based protocol evaluated DDIs. Results. A total of 7.4% of General Hospital inpatients and 100% of Psychiatric Unit inpatients surveyed were prescribed psychotropic medication. The General Hospital group had significantly more potential interactions per person (3.0) than Psychiatric inpatients (1.3) (P<0.05). There were significantly more potentially serious interactions in the general hospital group (P<0.025). Conclusions. DDIs affect those prescribed psychotropics in both General and Psychiatric Hospitals. The General Hospital patients had a higher number per person and more serious potential interactions, yet are often poorly served by psychiatric services, suggesting that liaison psychiatrists have a role in physician education and DDI assessment.

Nationwide drug-dispensing data reveal important differences in adherence to drug label recommendations on CYP2D6-dependent drug interactions

AIMS

The study aimed to investigate the clinical adherence to drug label recommendations on important drug-drug interactions (DDIs). Dispensing data on drug combinations involving selective serotonin reuptake inhibitor (SSRI) antidepressants could help to identify areas for intensified medical education.

METHODS

This was a retrospective, cross-sectional analysis of individual dispensing data regarding all individuals > or =15 years old in Sweden. The study analysed the prescribing and dispensing of CYP2D6 drugs (metoprolol, donepezil, galantamine, codeine, tamoxifen) together with CYP2D6-blocking SSRIs (paroxetine/fluoxetine) or SSRIs without significant CYP2D6 inhibition (citalopram/escitalopram/sertraline), and the related prescribing of CYP2D6-independent comparator drugs (atenolol, rivastigmine, propoxyphene, anastrozole). Odds were calculated between each CYP2D6 drug and the corresponding comparator drug in patients on fluoxetine/paroxetine and citalopram/escitalopram/sertraline, respectively. The odds ratio (OR) was calculated by dividing the obtained odds in patients on fluoxetine/paroxetine by the corresponding odds in patients on citalopram/escitalopram/sertraline.

RESULTS

Compared with patients that were dispensed citalopram/escitalopram/sertraline, patients dispensed fluoxetine/paroxetine had lower prescribing rates of metoprolol (adjusted OR 0.80; 95% confidence interval 0.76, 0.85), donepezil (0.65; 0.49, 0.86) and galantamine (0.58; 0.41, 0.81). In contrast, the use of prodrugs codeine (compared woth propoxyphene) or tamoxifen (compared with anastrozole) was similar among patients on fluoxetine/paroxetine and citalopram/escitalopram/sertraline (adjusted OR 1.03; 0.94, 1.12 and 1.29; 0.96, 1.73, respectively).

CONCLUSIONS

Clinically important DDIs that are associated with impaired bioactivation of prodrugs might be more easily neglected in clinical practice compared with DDIs that cause drug accumulation and symptomatic adverse drug reactions.

Pharmacogenetic testing and therapeutic drug monitoring are complementary tools for optimal individualization of drug therapy

Genetic factors contribute to the phenotype of drug response, but the translation of pharmacogenetic outcomes into drug discovery, drug development or clinical practice has proved to be surprisingly disappointing. Despite significant progress in pharmacogenetic research, only a few drugs, such as cetuximab, dasatinib, maraviroc and trastuzumab, require a pharmacogenetic test before being prescribed. There are several gaps that limit the application of pharmacogenetics based upon the complex nature of the drug response itself. First, pharmacogenetic tests could be more clinically applicable if they included a comprehensive survey of variation in the human genome and took into account the multigenic nature of many phenotypes of drug disposition and response. Unfortunately, much of the existing research in this area has been hampered by limitations in study designs and the nonoptimal selection of gene variants. Secondly, although responses to drugs can be influenced by the environment, only fragmentary information is currently available on how the interplay between genetics and environment affects drug response. Third, the use of a pharmacogenetic test as a standard of care for drug therapy has to overcome significant scientific, economic, commercial, political and educational barriers, among others, in order for clinically useful information to be effectively communicated to practitioners and patients. Meanwhile, the lack of efficacy is in this process is quite as costly as drug toxicity, especially for very expensive drugs, and there is a widespread need for clinically and commercially robust pharmacogenetic testing to be applied. In this complex scenario, therapeutic drug monitoring of parent drugs and/or metabolites, alone or combined with available pharmacogenetic tests, may be an alternative or complementary approach when attempts are made to individualize dosing regimen, maximize drug efficacy and enhance drug safety with certain drugs and populations (e.g. antidepressants in older people).

The challenge of managing drug interactions in elderly people

Drug therapy is essential when caring for elderly patients, but clearly it is a double-edged sword. Elderly patients are at high risk of having drug interactions, but the prevalence of these interactions is not well documented. Several types of interactions exist: drug-drug, drug-disease, drug-food, drug-alcohol, drug-herbal products, and drug-nutritional status. Factors such as age-related changes in pharmacokinetics and pharmacodynamics, frailty, interindividual variability, reduced homoeostatic mechanisms, and psychosocial issues need to be considered when drug interactions are assessed. Software can help clinicians to detect drug interactions, but many programmes have not been updated with the evolving knowledge of these interactions, and do not take into consideration important factors needed to optimise drug treatment in elderly patients. Any generated recommendations have to be tempered by a holistic, geriatric, multiprofessional approach that is team-based. This second paper in a series of two on prescribing in elderly people proposes an approach to categorise drug interactions, along with strategies to assist in their detection, management, and prevention.

PRN prescribing in psychiatric inpatients: potential for pharmacokinetic drug interactions

Medications are commonly prescribed to psychiatric inpatients on a PRN (pro re nata/as required) basis, allowing drugs to be administered on patient request or at nurses' discretion for psychiatric symptoms, treatment side effects or physical complaints. However, there has been no formal study of the pharmacokinetic implications of PRN prescribing. The objective of the study was to determine the prevalence of PRN drug prescription and administration, and to assess the potential for interactions involving CYP2D6 and CYP3A4 between drugs prescribed and administered to inpatients on psychiatry wards.A cross-sectional survey of prescriptions on general adult and functional elderly psychiatric wards in one city was carried out. Data were recorded from prescription charts of 323 inpatients (236 on general adult and 87 on functional elderly wards). Of 2089 prescriptions, 997 (48%) of prescriptions were on a PRN basis (most commonly benzodiazepines and other hypnotic agents, antipsychotics, analgesics and anticholinergic agents), but only 143 (14%) of these had been administered in the previous 24 hours. One fifth of patients were prescribed drug combinations interacting with CYP2D6 or CYP3A4 of potential clinical importance which included one or more drugs prescribed on a PRN basis.PRN prescribing is common among inpatients in psychiatry, and may lead to cytochrome P450 mediated interactions. Prescribers should be aware of the potential for unpredictability in plasma concentrations, side effects and efficacy which PRN prescribing may cause through these interactions, particularly in old age psychiatry and in treatment of acute psychosis.

Antidepressant-drug interactions are potentially but rarely clinically significant

The salient pharmacologic features of the selective serotonin reuptake inhibitors (SSRIs) discovered in the late 1980s included an in vitro ability to inhibit various cytochrome P450 enzymes (CYPs). Differences in potency among the SSRIs for CYP inhibition formed the basis of a marketing focus based largely on predictions of in vivo pharmacokinetic drug interactions from in vitro data, conclusions derived from case reports, and the extrapolation of the results of pharmacokinetic studies conducted in healthy volunteers to patients. Subsequently introduced antidepressants have undergone a similar post hoc scrutiny for potential drug-drug interactions. Concern for the untoward consequences of drug interactions led the FDA to publish guidance for the pharmaceutical industry in 1997 recommending that in vitro metabolic studies be conducted early in the drug development process to evaluate inhibitory properties toward the major CYPs. However, the prevalence of clinically significant enzyme inhibition interactions occurring during antidepressant treatment remains poorly defined despite millions of exposures. Although lack of evidence does not equate to evidence of absence, sparse epidemiological and post-marketing surveillance data do not substantiate a conclusion that widespread morbidity results from antidepressant-induced drug interactions. This commentary discusses points of uncertainty and controversy in the field of drug interactions, notes areas where inadequate data exist, and suggests explanations for a low prevalence of serious interactions. The conclusion is drawn that drug interactions from CYP inhibition caused by the newer antidepressants are potentially, but rarely, clinically significant.

Pharmacogenomics, informatics, and individual drug therapy in psychiatry: past, present and future

The modern era of psychopharmacology began in the 10 year period from the late 1940s to the late 1950s. During this period, the first antidepressants, antipsychotics, anxiolytics and mood stabilizers were all discovered. In the 1960s, the pharmacology of these drugs was elucidated and theories about the mechanisms of action proposed. In the 1970s and 1980s, new, more selective compounds were developed based on improved structure-activity relationships derived from in vitro receptor binding studies and animal models. These compounds entered clinical testing in the 1980s and began to be marketed in the late 1980s and 1990s. All of these agents were approved to treat psychiatric syndromes which are conditions defined by a cluster of signs and symptoms. None of these agents was developed based on an understanding of the pathophysiology of the illnesses being treated. None of these agents are curative and virtually all have limited clinical efficacy. In the earliest days of the modern era, there were few drugs available to combine and many had such broad actions that they were often marginally tolerated or unsafe when used in combination (tricyclic antidepressants and monoamine oxidase inhibitors). With the advent of more medications, the frequency and extent of polypharmacy has exploded. In addition to simply having more drugs from which to select with different pharmacological profiles, many newer medications are also more selective in their pharmacological actions and thus are often better tolerated and safer when used in combination. In addition, there is the concern that the trade-off for more selective pharmacology may have been better tolerability at the expense of reduced efficacy, which clinicians then compensate for by using more medications in combination. For all of the above reasons, polypsychopharmacology has been present from the beginning of the modern era of psychopharmacotherapy and continues to be the rule rather than the exception. In fact, the frequency and the complexity of such polypsychopharmacology are both enormous and increasing. The percentage of patients being discharged from the Biological Branch of the National Institute of Mental Health on more than three psychiatric medications increased more than ten times between 1974-79, and 1990-95. The majority of patients seen in the Veterans Administration Medical System in the United States are on unique combinations of medications and the frequency and complexity of such polypharmacotherapy is increased in patients on psychiatric medications. Throughout the modern era, there have been attempts to determine whether there are populations of patients selectively responsible to specific agents (e.g. serotonin versus norepinephrine reuptake inhibitors). However, no compelling data have so far emerged. Instead, clinicians generally resort to combining drugs on the basis of symptoms such as psychosis and depression or anxiety and depression. Science has primarily informed the clinician about safety concerns rather than efficacy concerns when using such combinations. That will change in the future with a better understanding of the pathophysiology of psychiatric illnesses which in turn will lead to improved therapies and the potential for more rationally derived combination treatments.

Potential for drug interactions involving cytochrome P450 in patients attending palliative day care centres: a multicentre audit

AIM

To determine the potential for drug interactions involving cytochrome P450 (CYP) in patients receiving palliative day care.

METHODS

Drugs used by patients attending four specialist palliative day care centres were reviewed to identify combinations that could result in a pharmacokinetic interaction via any of the five main human forms of CYP.

RESULTS

Of 160 patients, 145 (91%) were prescribed at least one drug that was a substrate, inhibitor or inducer of one of the five main CYP isoforms. Twenty-four drug combinations, involving 34 patients, could have given rise to a clinically important interaction.

CONCLUSIONS

Prescribers should be aware that in this group of patients, one in five are at risk of a clinically important CYP-mediated drug interaction.

Program to improve cognitive functioning in patients with schizophrenia: reflections

Cognitive dysfunction in patients who suffer from schizophrenia is a major clinical problem. For such patients, the neurobiological cause(s) for the cognition deficits are not clear. Treatments with high doses of compounds that work at the coagonist site of the NMDA receptor have demonstrated that some degree of improvement can be elicited in patients. Thus, the NIMH effort to delineate the clinical responses that would allow new drugs to be registered for this use is very timely. Significant credit is due Dr. Steven Hyman and his colleagues for stimulating this bold initiative. Many problems remain to be solved to accomplish the goal. This article articulates a few such problems.