The influence of ethnicity and antidepressant pharmacogenetics in the treatment of depression

Pharmacogenetics of Obsessive-Compulsive Disorder: An Evidence-Update

Pharmacogenetics has become increasingly important in the treatment of psychiatric disorders because approximately 50% of individuals who take psychotropic medications do not typically respond to them. Obsessive-compulsive disorder (OCD) is one such chronic and often debilitating mental illness with significant non-response to even the first-line medication, serotonin reuptake inhibitors. Precision medicine utilizing genetic testing panels has received significant attention based on the evidence that the variability of antidepressant response and adverse effects is partly due to the variability in an individual's genome. Thus, extensive research has investigated the role of genetic factors on antidepressant response in major depressive disorder (MDD) and their utility for guiding antidepressant treatment to significantly improving outcomes in individuals with MDD. However, limited progress remains in the pharmacogenetics of OCD. This chapter will provide an overview of the recent findings in the pharmacogenetics of OCD. Promising results with limited replications have been reported for the cytochrome P450 liver metabolism genes in addition to several serotonergic and glutamatergic system genes, which may play an important role in antidepressant response in the treatment of OCD.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

Pharmacogenetic guidelines and decision support tools for depression treatment: application to late-life

Late-life depression (LLD) is a major depressive disorder that affects someone after the age of 60 years. LLD is frequently associated with inadequate response and remission from antidepressants, in addition to polypharmacy. Pharmacogenetics offers a promising approach to improve clinical outcomes in LLD via new discoveries determining the genetic basis of response rates and side effects, as well as the development of tailored pharmacogenetic-based decision support tools. This invited review evaluates the LLD pharmacogenetic evidence base and the extent to which this was incorporated into existing commercial decision support tools and clinical pharmacogenetic guidelines.

Comparative Pharmacology and Guide to the Use of the Serotonin 5-HT3 Receptor Antagonists for Postoperative Nausea and Vomiting

Since the introduction of the serotonin 5-hydroxy tryptamine 3 (5-HT₃) receptor antagonists in the early 1990s, the incidence of postoperative nausea and vomiting (PONV) and post-discharge nausea and vomiting (PDNV) has decreased, yet continues to be a problem for the surgical patient. The clinical application of the 5-HT₃ receptor antagonists has helped define the approach and role of these antiemetics in the prevention and treatment of PONV and PDNV. Pharmacological and clinical differences exist among these medications resulting in corresponding differences in effectiveness, safety, optimal dosage, time of administration, and use as combination and rescue antiemetic therapy. The clinical application of the 5-HT₃ receptor antagonist antiemetics has improved the prevention and treatment of PONV and PDNV. The most recent consensus guidelines for PONV published in 2014 outline the use of these antiemetics. The 5-HT₃ receptor antagonists play an important role to help prevent PONV and PDNV in perioperative care pathways such as Enhanced Recovery After Surgery (ERAS). Comparisons and guidelines for use of the 5-HT₃ receptor antagonists in relation to the risk for PONV and PDNV are reviewed.

Depression Remission Rates Among Older Black and White Adults: Analyses From the IRL-GREY Trial

OBJECTIVE

This study explored whether older black and white adults with major depressive disorder differed in rates of remission or attrition during open-label treatment with venlafaxine and supportive care.

METHODS

A total of 47 black (10%) and 412 white (90%) adults age ≥60 were treated with open-label venlafaxine extended-release (≤300 mg per day) for 12-14 weeks during the initial phase of an multisite, randomized, placebo-controlled augmentation trial. Participants were help-seeking older adults with nonpsychotic major depressive disorder (single or recurrent episode) referred from specialty clinics, primary care practices, advertisements, and research programs. Remission was defined as a Montgomery-Asberg Depression Rating Scale score of ≤10 for two consecutive assessments at the end of 12 weeks. Kaplan-Meier curves displayed time to dropout and time to initial remission. Cox proportional hazards models assessed differences in attrition and remission rates.

RESULTS

Black participants had greater baseline general medical comorbidity, worse physical health-related quality of life, and poorer cognitive function than white participants. White participants were more likely to have received an adequate trial of antidepressant and psychotherapy before study entry. Baseline depression severity, depression duration, age at onset, and recurrence history did not differ between groups. The groups had similar final doses of venlafaxine and similar rates of attrition and remission. Side-effect profiles were comparable between the groups.

CONCLUSIONS

Despite greater medical comorbidity, lower cognitive function, and less adequate prior exposure to antidepressant treatment and psychotherapy, black participants were no more likely to discontinue antidepressant pharmacotherapy and experienced a rate of remission comparable to white participants.

Pharmacogenetics of antidepressant treatment in obsessive–compulsive disorder: an update and implications for clinicians

Obsessive–compulsive disorder (OCD) is a chronic neuropsychiatric disorder with high genetic influence. Antidepressants such as serotonin reuptake inhibitors, are widely accepted as the first-line medications for OCD; however, approximately 50% of OCD patients show poor response. Personalized medicine utilizing genetic testing has recently received much attention because the variability of antidepressant response and tolerability are partly due to an individual’s genetic variations. This has led to researchers investigating the role of specific genetic factors on antidepressant response and utility of testing in the clinical realm. Genetic test panels are showing promise for guiding antidepressant treatment to improve outcomes in depression. This article will review the most recent findings in the pharmacogenetics of OCD and its related disorders. Promising results have been reported for several serotonergic and glutamatergic system genes and the cytochrome CYP450 liver enzyme genes, which appear to play an important role in OCD and antidepressant response.

Meta-analyses of the effect of CYP1A1 and CYP2D6 polymorphisms on the risk of head and neck squamous cell carcinoma

BACKGROUND

CYP1A1 and CYP2D6 are important genes encoding enzymes involved in the metabolism of toxic chemicals and carcinogens. However, inconclusive results for the association between CYP1A1 and CYP2D6 polymorphisms and the risk of head and neck squamous cell carcinoma (HNSCC) have been reported. We conducted a meta-analysis to evaluate the association of CYP1A1 and CYP2D6 polymorphisms with the risk of HNSCC.

METHODS

A database search yielded 19 relevant studies. 3 polymorphisms were included in the meta-analysis: CYP1A1, CYP2D6*4 and CYP2D6*10. Random or fixed effect models were used in the analysis.

RESULTS

The CYP1A1 polymorphism was associated with HNSCC (for m1m1 vs. m1m2: odds ratio (OR) = 1.26, 95% confidence interval (CI) = 1.030-1.542, pheterogeneity = 0.025; for the recessive model: OR = 1.316, 95% CI = 1.065-1.625, pheterogeneity = 0.001). The analysis showed evidence for association between the CYP2D6*4 polymorphism and HNSCC in Asian populations; however, negative results were also observed in other models. A significant association was also observed between CYP2D6*10 polymorphism and HNSCC risk.

CONCLUSIONS

The current study demonstrates that the CYP1A1 and CYP2D6 polymorphisms are associated with susceptibility to both development and progression of HNSCC.

Antidepressants in elderly: metaregression of double-blind, randomized clinical trials

BACKGROUND

Depression is common in the elderly and in the last few years this led to a significant increase in antidepressant prescription rates. However, little is known about antidepressant efficacy profile in relation with socio-demographic and clinical features in this population. The aim of the present study was to define the most suitable socio-demographic and clinical profile for the use of antidepressant treatments in late-life depression.

METHODS

MEDLINE, EMBASE and PsycINFO were searched for randomized controlled trials (RCTs) focused on efficacy of antidepressants of all classes in major depressed elderly subjects (>60 years old). Reviews and meta-analyses focusing on this topic have been considered as well. Thirty-four RCTs were included and socio-demographic and clinical features were investigated via meta-regression analysis as moderators of efficacy measures (standardized mean difference based on Hamilton Depressive Rating Scale and Montgomery-Asberg Depression Rating Scale).

RESULTS

A lower rate of response to antidepressants of all classes was found in patients of male gender, of older age, and with a longer mean duration of the current episode. On the contrary, a higher rate of response was found in patients with a higher baseline severity and at their first episode of illness. Subsamples treated with selective serotonin reuptake inhibitors alone yielded similar results.

LIMITATIONS

RCTs only have been included.

CONCLUSIONS

A number of socio-demographic and clinical features have been found to moderate antidepressant efficacy in elderly population. Those variables could help clinicians for a more individualized treatment.

Frequencies of Functional Polymorphisms in Three Pharmacokinetic Genes of Clinical Interest within the Admixed Puerto Rican Population

OBJECTIVE

This cross-sectional study was aimed at determining the allele frequencies for the CYP2C19*2, CYP2C19*3, CYP2D6*10 and PON1 (rs662) polymorphisms in the Puerto Rican population. The CYP2C19, CYP2D6 and PON1 genes are known to be associated with functional changes in drug metabolism and activation. Individuals carrying the aforementioned polymorphisms are at a higher risk of suffering from drug-induced adverse events and/ or unresponsiveness from a variety of drugs that includes antidepressants, atypical antipsychotics and antiplatelet compounds. Information on the frequency of these polymorphisms is more commonly found on homogeneous populations, but is scarce in highly heterogeneous populations like Hispanics, as in the case of Puerto Ricans.

METHOD

Genotyping was carried out in 100 genomic DNA samples from dried blood spots supplied by the Puerto Rican Newborn Screening program using Taqman® Genotyping Assays.

RESULTS

The Minor Allele Frequencies (MAF) obtained were 9% for CYP2C19*2 and CYP2D6*10, 50% for PON1 (rs662), while the CYP2C19*3 variant was not detected in our study. Furthermore, Hardy Weinberg equilibrium analysis was assessed as well as a comparison between Puerto Rico and other reference populations using a Z-test for proportions.

CONCLUSION

The observed allele and genotype frequencies on these relevant pharmacogenes in Puerto Ricans were more closely related to those early reported in two other reference populations of Americans (Mexicans and Colombians).

Frequency of certain single-nucleotide polymorphisms and duplication of CYP2D6 in the Jordanian population

The CYP2D6 isozymes are responsible for metabolism of 7-10% of clinically available drugs. Genetic polymorphism in CYP2D6 may have an impact on drug efficacy and toxicity. The aim of this study was to determine the allelic frequency of CYP2D6*4, *10, and *17 and CYP2D6*2×N duplication allele in 192 healthy unrelated male and female Jordanian volunteers. Polymerase chain reaction (PCR)-restriction fragment length polymorphism-based methods were used to identify the CYP2D6*4, *10, and *17 genotypes; and allele-specific long PCR was used to determine the CYP2D6*2×N allelic frequency. The CYP2D6*10 allele was the most frequent mutant allele in Jordanians (14.8%) followed by CYP2D6*4 and *17 at 12.8%, and 8.3%, respectively. The duplication allele was found in 13.5% of the studied sample. The CYP2D6*4 G-A heterozygote genotype frequency was 20.3%, and the homozygous mutant genotype was 2.6%. In case of CYP2D6*10 C-T and CYP2D6*17 G-C heterozygote genotypes, the frequencies were 21.4% and 12.5%, respectively, while the homozygous mutant genotype frequencies of T-T and C-C were 4.2% and 2.1%, respectively. In conclusion, the allelic distributions of the CYP2D6 gene among Jordanians are different from other Mediterranean groups, especially the *10 and *17 single-nucleotide polymorphisms, and more importantly the CYP2D6*2×N duplication allele, which seems to follow a gradient reduction in prevalence from Ethiopia to Northern Europe.

Specificity profile of paroxetine in major depressive disorder: meta-regression of double-blind, randomized clinical trials

BACKGROUND

Meta-analyses and reviews are powerful tools to inform clinicians on overall effects of their therapeutic choices, but do not provide practically useful clinical profiles for each drug optimal efficacy. Therefore clinicians in everyday practice have to rely mainly on personal or anecdotic experience. The aim of present study was to define the most suitable sociodemographic and disease-related profile for the use of paroxetine as an antidepressant treatment.

METHODS

MEDLINE, EMBASE, CINAHL, and PsycINFO were searched for randomized controlled trials (RCT) in English focused on "paroxetine" and "depressive disorder" or "major depression". We also considered reviews and meta-analyses focusing on paroxetine. Fifty-five total unique RCTs were included and sociodemographic and clinical data as moderator of efficacy measures (standardized mean difference based on Hamilton Depressive Rating Scale and Montgomery-Asberg Depression Rating Scale) were investigated via meta-regression analysis.

RESULTS

Paroxetine was significantly characterized by better response in females and in Caucasians, whilst for patients who have been ill for a longer time before treatment, the smaller was the antidepressant effect. Other disease-related variables were not found to be significant moderators in clinical outcome.

LIMITATIONS

Meta-regression may lack sufficient sensibility to detect specific subtle features, so a failure to find significant effect is not definitive evidence of a lack of effect.

CONCLUSIONS

Our results, though significant, were generally observed with small estimate values, their clinical relevance is subtle since each feature is expected to influence marginally the whole outcome, and probably a more pronounced effect could result only by analyzing very large samples.

Prophylaxis of postoperative nausea and vomiting: controversies in the use of serotonin 5-hydroxytryptamine subtype 3 receptor antagonists

Postoperative nausea and vomiting (PONV) continues to be a "big little problem" despite recent advances in anesthesia. Because of an increased interest in, and the abundant publications on this topic, guidelines for the management of PONV were published in 2003. Several key but controversial issues regarding PONV prophylaxis were left unaddressed, however. These included whether clinical differences exist between the 5-hydroxytryptamine subtype 3 (5-HT3) receptor antagonists, concern over optimal dosage and timing of administration, optimal 5-HT3 receptor antagonist combination therapy, and whether rescue therapy is effective after prior administration of the same or a different 5-HT3 receptor antagonist. The application of these antiemetics in clinical practice has raised questions regarding the role of the 5-HT3 receptor antagonists in the treatment of postdischarge nausea and vomiting and opioid-induced nausea and vomiting. A brief overview of the incidence, risk factors and current management recommendations for PONV and current controversies with special emphasis on the 5-HT3 receptor antagonists, is discussed.

Interethnic differences in genetic polymorphisms of CYP2D6 in the U.S. population: clinical implications

DNA polymorphisms have been identified in the genes encoding a number of the cytochrome P450 (CYP) enzymes, leading to wide interindividual variation in drug clearance. CYP2D6 metabolizes a significant number of clinically used medications, and genetic variants of the CYP2D6 isozyme that result in varying levels of metabolic activity are of clinical importance in some settings. The exact nature of the clinical effect caused by polymorphisms of the gene depends on the drug in question and the specific variant alleles expressed, as individual variants result in differing phenotypes with a range of levels of enzymatic activity. Compromised drug efficacy due to CYP2D6 variation has been documented with a variety of agents, and this review considers a number of examples, including the 5-HT(3)-receptor antagonists, which are used in oncology supportive care for the prophylaxis of nausea and vomiting. CYP2D6 is involved in the metabolism of all of the most commonly available agents, except granisetron, and their efficacy and side effects may therefore be affected by the CYP2D6 polymorphism. Significant interethnic differences in CYP2D6 allele frequencies have been demonstrated from studies across many countries. However, incidences of polymorphisms in the U.S. population have been challenging to characterize because of the country's wide ethnic diversity. The CYP2D6 polymorphism may become more important as robust clinical tests become widely available and as the use of multiple medications and the attendant risk for drug-drug interactions increases.

5-hydroxytryptamine type-3 receptor antagonists for chemotherapy-induced and radiotherapy-induced nausea and emesis: can we safely reduce the dose of administered agents?

BACKGROUND

Nausea and emesis as a consequence of chemotherapy or radiotherapy can have an adverse effect on patients' quality of life during cancer treatment and may last for > 5 days after administration. Guidelines suggest that, used at appropriate doses, the 5-hydroxytryptamine type-3 (5-HT3) receptor antagonists--which are considered the antiemetic "gold standard" when they are administered in combination with corticosteroids--demonstrate equivalent efficacy and safety. However, due to financial considerations, these agents often are used at lower doses than recommended.

METHODS

A literature review of relevant publications pertaining to the control of chemotherapy-induced nausea and emesis and dosing issues of the 5-HT3 receptor antagonists was undertaken to provide a comprehensive review of dosing issues relevant to the 5-HT3 receptor antagonists.

RESULTS

The issue of "down dosing" was particularly pertinent because of the nature of the 5-HT3 receptor antagonist dose-response curve: A steep dose-response profile within a narrow dose range suggests that antiemetic control will be lost suddenly after dose deescalation. However, the array of predisposing and confounding patient factors indicates that it is unlikely that a loss of antiemetic control will be apparent across a population; rather, individuals will experience loss of control as the dose is reduced below threshold. Of the 4 5-HT3 receptor antagonists currently licensed in the United States (granisetron, ondansetron, dolasetron, and palonosetron), ondansetron is used sometimes at lower than optimal doses, and there is evidence to suggest that even the approved oral dose of dolasetron may be suboptimal.

CONCLUSIONS

Suboptimal dosing not only will be detrimental to patients' quality of life but, ultimately, will prove counterproductive in terms of hospital resources, and it will add to the already significant socioeconomic burden associated with cancer therapy. Therefore, the dose of antiemetic agent administered should be sufficiently high to ensure good emesis control across the whole patient population.

Is there a pharmacological basis for differences in 5-HT3-receptor antagonist efficacy in refractory patients?

5-HT3-receptor antagonists are the current antiemetic 'gold standard' for chemotherapy- and radiotherapy-induced nausea and vomiting. Interestingly, studies have shown that patients experiencing poor control of acute chemotherapy-induced nausea and vomiting with one antiemetic therapy may respond well to another agent, including a drug of the same class. This review examines pharmacological differences between the 5-HT3-receptor antagonists in order to determine potential reasons for their differing efficacy, particularly in relation to refractory emesis. Differences in drug metabolism by the cytochrome P450 system, inadequate dosing of the respective agents, differences in onset and duration of action, and effects on serotonin release and reuptake are discussed.

Comparison of mirtazapine and fluoxetine in the treatment of major depressive disorder: a double-blind, randomized trial

BACKGROUND

Depression is an international public health problem. The aim of this study was to compare the efficacy and tolerability of mirtazapine and fluoxetine treatment in a sample population consisting of Iranian patients suffering major depressive disorder.

METHODS

Thirty-six inpatients and outpatients with a diagnosis of major depressive disorder (Diagnostic and Statistical Manual of Mental Disorders-IV) and a score > or = 18 on the 17-item Hamilton Rating Scale for Depression (HAM-D-17) were randomly assigned to 6 weeks of treatment with mirtazapine (30 mg/day) or fluoxetine (20 mg/day). Efficacy was assessed by HAM-D-17. Information about adverse events was obtained by questioning of participants and/or their examination. Assessments were performed at weeks 0, 1, 2, 3, 4 and 6.

RESULTS

Sixteen of mirtazapine-treated patients and fifteen of fluoxetine-treated patients completed the 6-week study period. Both treatment groups were well matched at baseline with respect to demographic and disease characteristics. Both drugs showed a significant improvement over the 6 weeks of treatment (P < 0.001). There was no statistically significant difference between the mean +/- SEM HAM-D scores of two groups at weeks 1, 2, 3, 4, and at the end point. There were no significant differences between two groups in terms of response to treatment (> or = 50% decrease from baseline in HAM-D-17 total score) and remission (HAM-D-17 score of < or = 7). None of the differences in reported adverse events was statistically significant.

CONCLUSION

In this study, mirtazapine and fluoxetine were equally effective and well tolerated after 6 weeks of treatment in patients with major depressive disorder.

Angiotensin Converting Enzyme Genotype Influences the Response to the Angiotensin II Receptor Antagonist Losartan in Patients with Hypertension

To examine whether the response to the angiotensin II receptor antagonist losartan varies depending on the angiotensin converting enzyme (ACE) genotype, we prospectively studied the effect of losartan in 42 hypertensive patients (20 men, 22 women; mean age: 60.4 years). After a 4-week observation period, losartan was administered at 50 mg/day and blood pressure was measured every 2 to 4 weeks for 12 weeks. Among the 42 patients, 19, 11, and 12, respectively, had the II, ID, and DD ACE genotypes. The baseline plasma ACE activity in patients with the ID or DD genotype was significantly higher than that in patients with the II genotype (13.8 +/- 4.2 vs. 9.6 +/- 2.3 IU/l; p = 0.0002). However, age, gender, baseline systolic and diastolic blood pressure (SBP/DBP), and body mass index (BMI) were not different among the groups. After 12 weeks of treatment with losartan alone, DBP in the ID+DD group was significantly higher than that in the II group (85.0 +/- 9.0 vs. 77.8 +/- 9.6 mmHg, p = 0.018), while the percent reduction in DBP in the ID+DD group was significantly smaller than that in the II group (7.9 +/- 8.8 vs. 14.3 +/- 10.1%, p = 0.035). Multiple regression analysis showed that the significant predictors of the DBP at 12 weeks were age (p = 0.030), ACE genotype (p = 0.029) and baseline DBP (p = 0.0001). The ACE genotype may be a determinant of the response to losartan in hypertensive patients.

5-HT3-receptor antagonists and the cytochrome P450 system: clinical implications

Many patients with cancer receive multiple chemotherapy agents as well as other medications for coexisting medical conditions. Despite the introduction of 5-HT3 receptor antagonists, the management of nausea and vomiting following cancer treatment and after cancer surgery remains complex, particularly when patients are receiving multiple prescription medications. As a drug class, the 5-HT3 receptor antagonists have good antiemetic efficacy and an improved safety profile over conventional antiemetics. Nevertheless, pharmacologic differences exist between these agents, such as their interaction with the metabolic cytochrome P450 system. This review examines the major metabolic differences between the most frequently prescribed 5-HT3 receptor antagonists, dolasetron, granisetron, ondansetron, and tropisetron. The potential drug interactions that these differences may precipitate and key genetic interindividual variations in drug metabolism are also considered. To avoid or minimize potential drug interactions, the 5-HT3 receptor antagonist with the lowest risk of these interactions should be considered as first choice.

A comparison of characteristics of depressed patients and efficacy of sertraline and amitriptyline between Japan and the West

BACKGROUND

This study was conducted to investigate the differences and similarities of the profile of depressed patients and the efficacy of the antidepressants, sertraline and amitriptyline, between Japan and the West (United States, Europe), using the Hamilton Depression Rating Scale (HAM-D) score of the individual patients.

METHODS

Using common selection criteria, 680 patients from three regional clinical studies were chosen for this investigation. Factor analysis of the HAM-D scores for each regional group was carried out to compare the profile of depressed patients. Analysis of covariance was used to compare the efficacy of sertraline and amitriptyline between the regions.

RESULTS

Factor analyses clearly showed three main factors (major depressive symptoms, anxiety and sleep disturbance) to be common across all three geographic regions. Higher HAM-D component scores of "Work and interests" and "Retardation" and lower ones of "Depressed mood" and "Feeling of guilt" were observed for the Japanese patients compared to the Western patients. Improvement of anxiety symptoms was marked for the Japanese amitriptyline treated patients.

LIMITATIONS

Although the patient data used in these analyses were restricted by using identical selection criteria, there still remains some methodological shortcomings due to the original study design differences.

CONCLUSIONS

Overall, the three main factors of depression and their magnitudes were similar between Japan and the West. The presentation of major depressive symptoms in Japanese patients differed from Western patients; this could be related to social, cultural and religious differences. Marked sedative effect for Japanese patients appeared to be due to the factor of anxiety being the strongest of the three main factors in Japanese depressed patients.

Pharmacogenetics in diverse ethnic populations--implications for drug discovery and development

It is widely acknowledged that the vast quantities of data now publicly available as a result of the human genome initiative have the potential to revolutionize the pharmaceutical industry. More tangibly to the drug development business, the dawn of the pharmacogenetics era has the potential to impact not only the discovery of new medicines but also the safety and efficacy of pharmaceutical agents. Coincident with these scientific advances is the emergence of new markets for pharmaceutical agents. Japan, which represents the world's second biggest market, is a good example. With the ICH E5 agreement in 1998 and a rapid change in the drug registration process in Japan, there are increasing opportunities to improve access to more medicines in all parts of the world. However, it is increasingly clear that significant genetic variation still exists between populations, with a host of data on interethnic variation in drug metabolizing enzyme and drug transporter activity. Evidence suggesting that this genetic variation may play an important role in defining some of the interethnic variation in drug response to currently marketed compounds is reviewed here, and future possibilities of using such information to better streamline the drug development process are discussed.

Drug interactions with patient-controlled analgesia

Patient-controlled analgesia (PCA) has become standard procedure in the clinical treatment of pain. Its widespread use in patients with all kinds of diseases opens a variety of possible interactions between analgesics used for PCA and other drugs that might be administered concomitantly to the patient. Many of these drug interactions are of little clinical importance. However, some drug interactions have been reported to result in serious clinical problems. Drug interactions can either predominantly affect the pharmacokinetics or pharmacodynamics of the drug. Most important pharmacokinetic drug interactions occur at the level of drug metabolism or protein binding. Acceleration of methadone metabolism caused by cytochrome P450 (CYP) 3A4 induction by antiretroviral drugs or rifampicin (rifampin) has caused methadone withdrawal symptoms. Lack of morphine formation from codeine as a result of CYP2D6 inhibition by quinidine results in an almost complete loss of the analgesic effects of codeine. Alterations of methadone protein binding caused by an inhibition of alpha1-acid glycoprotein synthesis by alkylating substances are another possibility for predominantly pharmacokinetically based drug interactions during PCA. Furthermore, inhibition of P-glycoprotein by anticancer drugs could result in altered transmembrane transport of morphine, methadone or fentanyl, although this has not been shown to be of clinical relevance. Synergistic effects of systemically administered opioids with spinally or topically delivered opioids or anaesthetics have been reported frequently. The same is true for the opioid-sparing effects of coadministered non-opioid analgesics. Antidepressants, anticonvulsants or alpha2-adrenoreceptor agonists have also been shown to exert additive analgesic effects when administered together with an opioid. Inconsistent findings, however, are reported regarding the treatment of patients with opioid-induced nausea and sedation, since coadministration of antiemetics either increased or decreased the respective adverse effects or revealed additional unwanted drug effects.