Antidepressant drug interactions and the cytochrome P450 system. The role of cytochrome P450 2D6

Evaluation and Management of Pruritus and Scabies in the Elderly Population

Pruritus is the most common dermatologic complaint in the geriatric population. Its growing prevalence coincides with the rapid growth of the elderly population (>65 years of age) in the United States. According to the US Census Bureau, 16.9% of the population, or more than 56 million adults 65 years and older, lived in the United States in 2022. Pruritus is a condition that accompanies a diverse array of underlying etiologic factors. The mechanism of normal itch impulse transmission has been recently elucidated. The itch sensation originates from epidermal/dermal receptors connected to unmyelinated, afferent C-fibers that transmit the impulse from the periphery.

Antidepressants and Antipsychotic Agents as Repurposable Oncological Drug Candidates

Drug repurposing, also known as drug repositioning/reprofiling, is a relatively new strategy for the identification of alternative uses of well-known therapeutics that are outside the scope of their original medical indications. Such an approach might entail a number of advantages compared to standard de novo drug development, including less time needed to introduce the drug to the market, and lower costs. The group of compounds that could be considered as promising candidates for repurposing in oncology include the central nervous system drugs, especially selected antidepressant and antipsychotic agents. In this article, we provide an overview of some antidepressants (citalopram, fluoxetine, paroxetine, sertraline) and antipsychotics (chlorpromazine, pimozide, thioridazine, trifluoperazine) that have the potential to be repurposed as novel chemotherapeutics in cancer treatment, as they have been found to exhibit preventive and/or therapeutic action in cancer patients. Nevertheless, although drug repurposing seems to be an attractive strategy to search for oncological drugs, we would like to clearly indicate that it should not replace the search for new lead structures, but only complement de novo drug development.

A Review of Antipsychotics and Priapism

INTRODUCTION

Pharmacologically induced priapism is now the most common cause of priapism, with approximately 50% of drug-related priapism being attributed to antipsychotic usage. The majority of pharmacologic priapism is believed to result in ischemic priapism (low flow), which may lead to irreversible complications, such as erectile dysfunction. It is imperative that prescribing physicians be aware of potentially inciting medications.

OBJECTIVES

To identify medications, specifically antipsychotics, associated with priapism and prolonged erections and understand the rates and treatment of these side effects.

METHODS

A PubMed search of all articles available on the database relating to priapism, prolonged erections, and antipsychotics was performed.

RESULTS

Various typical and atypical antipsychotic drugs (APDs) have been implicated in pharmacologically induced priapism. In addition to dopaminergic and serotoninergic receptors, APDs have affinities for a wide array of other receptors in the central nervous system, including histaminergic, noradrenergic, and cholinergic receptors. Although the exact mechanism is unknown, the most commonly proposed mechanism of priapism associated with APDs is α-adrenergic blockade in the corpora cavernosa of the penis. Priapism appears in only a small fraction of men using medications with α1-receptor-blocking properties, indicating differential sensitivities to the α-blocking effect among men, and/or additional risk factors that may contribute to the development of priapism. The best predictor for the subsequent development of priapism is a past history of having prolonged and painless erections. The acute management algorithm of APD-induced priapism is the same as for other causes of low-flow priapism.

CONCLUSION

Clinicians should educate patients treated with antipsychotics about the potential for priapism and its sequelae including permanent erectile dysfunction. Appropriate patient education will raise awareness, encourage early reporting, and help reduce the long-term consequences associated with priapism through early intervention. Hwang T, Shah T,Sadeghi-NejadH. A Review of Antipsychotics and Priapism. Sex Med Rev 2021;9:464-471.

Treatment of Depression in Women

Women are more likely than men to experience depression throughout the life span. Sex differences in neurochemistry and brain structure, as well as societal factors may contribute to women's increased likelihood of depression. Pharmacological research targeting depression has historically excluded women, leading to a knowledge gap regarding effective antidepressant treatment in women. Antidepressant pharmacokinetics and pharmacodynamics are clearly different in men and women, necessitating a thoughtful approach to their prescription and management. Hormone changes associated with the menstrual cycle, pregnancy, and menopause also contribute to differences in depression and effective antidepressant use in women. Finally, it is important to consider potential interactions between antidepressant drugs and medications specifically used by women (oral contraceptives, tamoxifen, and estrogen).

Impact of CYP2D6 Functional Allelic Variations on Phenoconversion and Drug-Drug Interactions

We investigated whether CYP2D6 extensive metabolizers carrying a nonfunctional allele are at higher risk of phenoconversion to poor metabolizers in the presence of CYP2D6 inhibitors. Seventeen homozygous carriers of two fully-functional alleles and 17 heterozygous carriers of one fully-functional and one nonfunctional allele participated in this trial. Dextromethorphan 5 mg and tramadol 10 mg were given at each of the three study sessions. CYP2D6 was inhibited by duloxetine 60 mg (session 2) and paroxetine 20 mg (session 3). A higher rate of phenoconversion to intermediate metabolizers with duloxetine (71% vs. 25%, P = 0.009) and to poor metabolizers with paroxetine (94% vs. 56%, P = 0.011) was observed in heterozygous than homozygous extensive metabolizers. The magnitude of drug-drug interaction between dextromethorphan and paroxetine was higher in homozygous than in heterozygous subjects (14.6 vs. 8.5, P < 0.028). Our study suggests that genetic extensive metabolizers may not represent a homogenous population and that available genetic data should be considered when addressing drug-drug interactions in clinical practice.

Pharmacokinetics of antidepressants in patients with hepatic impairment

Appropriate use of antidepressant in patients with hepatic impairment requires careful consideration of how the hepatic illness may affect pharmacokinetics. This review aims to analyze pharmacokinetic profile, plasma level variations so as the metabolism of several antidepressants relating to their use in patients with an hepatic impairment. Due to the lack of data regarding hepatic impairment itself, the review is focused mainly on studies investigating pharmacokinetics in hepatic cirrhosis or alcohol-related conditions. More data on reduced hepatic metabolism can be extrapolated by drug studies conducted in elderly populations. Dose adjustment of antidepressants in these patients is important as most of these drugs are predominantly metabolized by the liver and many of them are associated with dose-dependent adverse reactions. As no surrogate parameter is available to predict hepatic metabolism of drugs, dose adjustment according to pharmacokinetic properties of the drugs is proposed. There is a need for a more balanced assessment of the benefits and risks associated with antidepressants use in patients with hepatic impairment, particularly considering pharmacokinetic profile of the drugs to ensure that patients, who would truly benefit from these agents, are not denied appropriate treatment. In conclusion, kinetic studies for centrally acting drugs including antidepressants with predominant hepatic metabolism should be carried out in patients with liver disease to allow precise dose recommendations for enhanced patient safety.

Brain serotonin content regulates the manifestation of tramadol-induced seizures in rats: disparity between tramadol-induced seizure and serotonin syndrome

BACKGROUND

Tramadol-induced seizures might be pathologically associated with serotonin syndrome. Here, the authors investigated the relationship between serotonin and the seizure-inducing potential of tramadol.

METHODS

Two groups of rats received pretreatment to modulate brain levels of serotonin and one group was treated as a sham control (n = 6 per group). Serotonin modulation groups received either para-chlorophenylalanine or benserazide + 5-hydroxytryptophan. Serotonin, dopamine, and histamine levels in the posterior hypothalamus were then measured by microdialysis, while simultaneously infusing tramadol until seizure onset. In another experiment, seizure threshold with tramadol was investigated in rats intracerebroventricularly administered with either a serotonin receptor antagonist (methysergide) or saline (n = 6).

RESULTS

Pretreatment significantly affected seizure threshold and serotonin fluctuations. The threshold was lowered in para-chlorophenylalanine group and raised in benserazide + 5-hydroxytryptophan group (The mean ± SEM amount of tramadol needed to induce seizures; sham: 43.1 ± 4.2 mg/kg, para-chlorophenylalanine: 23.2 ± 2.8 mg/kg, benserazide + 5-hydroxytryptophan: 59.4 ± 16.5 mg/kg). Levels of serotonin at baseline, and their augmentation with tramadol infusion, were less in the para-chlorophenylalanine group and greater in the benserazide + 5-hydroxytryptophan group. Furthermore, seizure thresholds were negatively correlated with serotonin levels (correlation coefficient; 0.71, P < 0.01), while intracerebroventricular methysergide lowered the seizure threshold (P < 0.05 vs. saline).

CONCLUSIONS

The authors determined that serotonin-reduced rats were predisposed to tramadol-induced seizures, and that serotonin concentrations were negatively associated with seizure thresholds. Moreover, serotonin receptor antagonism precipitated seizure manifestation, indicating that tramadol-induced seizures are distinct from serotonin syndrome.

Priapism associated with iloperidone: a case report

Priapism is a known side effect of antipsychotics. The causal mechanism seems to be mediated through α1-adrenergic receptor blockade which many antipsychotics are known to possess. We present the first detailed case of iloperidone-induced priapism in a patient with bipolar disorder with psychotic features. His case highlights some of the important risk factors clinicians should consider when using iloperidone, as it may be the highest-risk antipsychotic for causing priapism given it is a very potent blocker of the alpha-adrenergic receptor.

Evaluation of the pharmacokinetics, safety and clinical efficacy of sertraline used to treat social anxiety

INTRODUCTION

Social anxiety disorder (SAD) is an emerging, often invalidating, syndrome with deep personal, social and psychological implications. While multiple treatment strategies exist, presently none of them can be considered superior to all others.

AREAS COVERED

The aim of this review is to provide the latest information on sertraline (SRT), one of the most important selective serotonin reuptake inhibitors (SSRIs) currently used for the pharmacological therapy of SAD. A literature search was carried out with the keywords 'sertraline', 'social anxiety', 'social phobia' and 'clinical trials'. In this process, particular attention is paid to the pharmacokinetic characteristics of the drug and its safety in clinical use.

EXPERT OPINION

SRT is an effective drug in the treatment of SAD, especially when used in combination with some form of psychological support. While it does not seem to be significantly more effective than other SSRIs, SRT could offer some peculiar advantages: for example, it has a long half-life, allowing a single daily administration, and seems to be particularly indicated for the control of specific symptoms of SAD.

Effects of single or repeated silymarin administration on pharmacokinetics of risperidone and its major metabolite, 9-hydroxyrisperidone in rats

1. The interactions between herbal dietary supplements and therapeutic drugs have emerged as an important issue and P-glycoprotein (P-gp) has been reported as one of the significant factors of these interactions. 2. The objective of this article is to examine the effects of single and repeated administrations of silymarin on pharmacokinetics of a P-gp substrate, risperidone, and its major metabolite, 9-hydroxyrisperidone, in rats. 3. To determine the plasma levels of risperidone and 9-hydroxyrisperidone in rats, a HPLC method was developed using a liquid-liquid acid back extraction. When risperidone (6 mg/kg) was co-administered with silymarin (40 mg/kg) to rats orally, the C(max) of 9-hydroxyrisperidone was significantly increased to1.3-fold (p < 0.05), while the other pharmacokinetic parameters did not show any significant differences. Expanding the experiment where rats were repeatedly administered with silymarin for 5 days prior to giving risperidone, the C(max) of risperidone and 9-hydroxyrisperidone were significantly increased to 2.4-fold (p < 0.001) and 1.7-fold (p < 0.001), respectively, and the AUC(0-t), as well to 1.7-fold (p < 0.05) and 2.1-fold (p < 0.01), respectively. 4. The repeated exposures of silymarin, compared to single administration of silymarin, increased oral bioavailability and affected the pharmacokinetics of risperidone and 9-hydroxyrisperidone, by inhibiting P-gp.

Clinically significant psychotropic drug-drug interactions in the primary care setting

In recent years, the growing numbers of patients seeking care for a wide range of psychiatric illnesses in the primary care setting has resulted in an increase in the number of psychotropic medications prescribed. Along with the increased utilization of psychotropic medications, considerable variability is noted in the prescribing patterns of primary care providers and psychiatrists. Because psychiatric patients also suffer from a number of additional medical comorbidities, the increased utilization of psychotropic medications presents an elevated risk of clinically significant drug interactions in these patients. While life-threatening drug interactions are rare, clinically significant drug interactions impacting drug response or appearance of serious adverse drug reactions have been documented and can impact long-term outcomes. Additionally, the impact of genetic variability on the psychotropic drug's pharmacodynamics and/or pharmacokinetics may further complicate drug therapy. Increased awareness of clinically relevant psychotropic drug interactions can aid clinicians to achieve optimal therapeutic outcomes in patients in the primary care setting.

What are the clinical implications of new onset or worsening anxiety during the first two weeks of SSRI treatment for depression?

OBJECTIVE

To evaluate the prevalence of new onset or worsening of anxiety symptoms, as well as their clinical implications, during the first 2 weeks of Selective Serotonin Reuptake Inhibitor (SSRI) pharmacotherapy for depression.

METHOD

Adult outpatients with nonpsychotic major depressive disorder were enrolled in an 8-week acute phase SSRI treatment trial at 15 clinical sites across the United States. Worsening anxiety was defined as a greater than 2-point increase on the Beck Anxiety Inventory (BAI) between baseline and Week 2. New onset of anxiety symptoms was ascribed when the BAI baseline rating was 0 and the Week 2 value was greater or equal to 2 points on the BAI.

RESULTS

Overall, after 2 weeks of treatment, 48.8% (98 of 201 participants) reported improvement in anxiety symptoms, 36.3% (73 of 201) reported minimal symptom change, and 14.9% (30 of 201) reported worsening of anxiety symptoms. No association was found between change in anxiety symptoms within the first 2 weeks and change in depressive symptoms or remission at the end of 8 weeks of treatment. For participants with clinically meaningful anxiety symptoms at baseline, however, worsening of anxiety during the first 2 weeks of treatment was associated with worsening depressive symptoms by 8 weeks (P = .054).

CONCLUSIONS

The trajectory of anxiety symptom change early in SSRI treatment is an important indicator of eventual outcome for outpatients with major depression and baseline anxiety symptoms.

The importance of drug-drug interactions as a cause of adverse drug reactions: a pharmacovigilance study of serotoninergic reuptake inhibitors in France

PURPOSE

To quantify the importance of drug-drug interactions (DDIs) in the occurrence of adverse drug reactions (ADRs) reported with serotoninergic reuptake inhibitors in a pharmacovigilance database.

METHODS

All spontaneous reports of ADRs registered in 2008 by the Midi-Pyrénées PharmacoVigilance Centre that contained mention of one of the serotoninergic reuptake inhibitor (SRI) antidepressants marketed in France were reviewed. DDIs were identified according to the French National Drug Formulary (Vidal) and the interaction supplement of the French independent drug bulletin La Revue Prescrire. ADRs explained by DDIs were characterised.

RESULTS

Among the 2,101 spontaneous reports recorded, 177 involved at least one SRI antidepressant. Among the 156 ADRs with at least one theoretical DDI, 41% (95% confidence interval 34-49%) could be explained by a DDI. The most frequent antidepressant involved in DDIs was escitalopram, followed by fluoxetine and citalopram. Among the 65 ADRs related to DDIs, 37 (52.9%) were "serious", mainly bleedings, confusion and falls, hyponatremia and serotoninergic syndromes. The most frequent drug interactions occurred with psychotropics (antipsychotics, benzodiazepines, among others), followed by antithrombotic agents (antagonists of vitamin K, antiplatelets), diuretics and angiotensin II antagonists. The group with ADRs related to DDIs was older than the group with ADRs not related to DDIs. ADRs were threefold more "serious" in the case of DDIs.

CONCLUSION

Around 40% of ADRs reported with SRIs were related to DDIs. Most of these occurred after association with psychotropics, antithrombotics, or diuretics, especially in the elderly.

Pharmacogenetics and gender association with psychotic episodes on nortriptyline lower doses: patient cases

The variation in individual responses to psychotropic drug treatment remains a critical problem in the management of psychotic disorders. Although most patients will experience remission, some patients may develop drug-induced adverse effects that may range from troublesome to life threatening. Antidepressants are freely prescribed by general practitioners, and there should be constant awareness in the medical community about possible serious side effects. We describe two cases of adverse drug reactions on low dosage treatment that led to extreme psychotic episodes as examples of the potential for dangerous side effects. The patients developed adverse reactions on the normal recommended dosage of nortriptyline, a tricyclics antidepressant (TCA). Both were females, with no history of antidepressant treatment, unsocial behaviour, nor any family history of psychosis, but both experienced severe psychiatric symptoms. Pharmacogenetic tests can easily be performed and interpreted according to the likelihood of adverse reactions and should be included in toxicity interpretation.

Drug interactions of clinical importance among the opioids, methadone and buprenorphine, and other frequently prescribed medications: a review

Drug interactions are a leading cause of morbidity and mortality. Methadone and buprenorphine are frequently prescribed for the treatment of opioid addiction. Patients needing treatment with these medications often have co-occurring medical and mental illnesses that require medication treatment. The abuse of illicit substances is also common in opioid-addicted individuals. These clinical realities place patients being treated with methadone and buprenorphine at risk for potentially toxic drug interactions. A substantial literature has accumulated on drug interactions between either methadone or buprenorphine with other medications when ingested concomitantly by humans. This review summarizes current literature in this area.

Role of cytochrome P450 in drug interactions

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues. Many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Pravastatin-induced colitis

We report an unusual case of pravastatin-induced colitis in an 80-year old lady. Onset of symptoms was noted within 48 h of starting the medication. Colonoscopy revealed diffuse ulceration throughout the colon with relative sparing of the rectum, with the biopsies showing ulceration and inflammation. The patient received a short course of steroid therapy and 5 months after stopping pravastatin, there was complete macroscopic and microscopic resolution of the colonic lesions. Drug interaction of pravastatin with amitryptiline could have resulted in this uncommon complication.

Paroxetine

BACKGROUND

Paroxetine is a widely used antidepressant that has received attention regarding suicide risk in younger patients.

OBJECTIVE

The purpose of this paper is to review the pharmacology, efficacy and safety of paroxetine in the affective disorders.

METHODS

The authors performed a PubMed search for all literature in English crossing the words 'paroxetine' and 'Paxil' against the words 'serotonin transporter,' 'clinical trials,' 'depression' and 'SSRI'. A search for paroxetine-related information at the FDA website and under the clinical trial register of the GSK website were also performed.

RESULTS/CONCLUSION

Paroxetine is a serotonin re-uptake inhibitor with good selectivity and no significant active metabolites. Paroxetine is approved (ages >or= 18 years) for the treatment of major depressive disorder, panic disorder, obsessive-compulsive disorder, social anxiety disorder (social phobia), post-traumatic stress disorder, and generalized anxiety disorders. Drug - drug interactions involving the CYP enzyme system have been documented, as well as concern for increased suicidality risk in younger adults and recent FDA alerts regarding teratogenicity, serotonin syndrome and persistent pulmonary hypertension.

Perspectives on pain and intellectual disability

Historically, individuals with intellectual disability (ID) have been excluded from pain research and assumed to be insensitive or indifferent to pain. The weight of the evidence suggests that individuals with ID have been subject to practices and procedures with little regard for their ability to experience or express pain. A number of issues central to improving understanding of pain in ID will be introduced and current research related to the definition of pain and its social context, underlying sensory and metabolic systems and factors influencing judgments about the ability to experience pain will be reviewed. Accumulating evidence from interdisciplinary research designed to improve assessment, understand individual differences, and evaluate bias and beliefs about pain suggests that new perspectives are emerging and beginning to shape an innovative frontier of research that will ultimately pay tremendous dividends for improving the quality of life of individuals with ID.

The ontogeny of drug metabolism enzymes and implications for adverse drug events

Profound changes in drug metabolizing enzyme (DME) expression occurs during development that impacts the risk of adverse drug events in the fetus and child. A review of our current knowledge suggests individual hepatic DME ontogeny can be categorized into one of three groups. Some enzymes, e.g., CYP3A7, are expressed at their highest level during the first trimester and either remain at high concentrations or decrease during gestation, but are silenced or expressed at low levels within one to two years after birth. SULT1A1 is an example of the second group of DME. These enzymes are expressed at relatively constant levels throughout gestation and minimal changes are observed postnatally. ADH1C is typical of the third DME group that are not expressed or are expressed at low levels in the fetus, usually during the second or third trimester. Substantial increases in enzyme levels are observed within the first one to two years after birth. Combined with our knowledge of other physiological factors during early life stages, knowledge regarding DME ontogeny has permitted the development of robust physiological based pharmacokinetic models and an improved capability to predict drug disposition in pediatric patients. This review will provide an overview of DME developmental expression patterns and discuss some implications of the data with regards to drug therapy. Common themes emerging from our current knowledge also will be discussed. Finally, the review will highlight gaps in knowledge that will be important to advance this field.

Priapism associated with atypical antipsychotic medications: a review

Priapism defined as persistent, painful and prolonged penile erection, was previously thought to be associated only with the use of the older, conventional first generation or typical antipsychotic medications as well as some other medications, notably, trazodone. The mechanism of priapism associated with antipsychotics is not clear but is thought to be related to alpha-adrenergic blockage that is mediated by the alpha receptors in the corpora cavernosa of the penis. Atypical antipsychotics, also known as second-generation antipsychotics, owing to their favorable side effect profile, are being prescribed with increasing frequency and are not as frequently considered to cause priapism. Some case reports reporting this side effect with their use, however, are found. Pubmed and Ovid databases were searched to obtain all articles and case reports of antipsychotic drug-induced priapism. Key search words included 'priapism', 'antipsychotics' and 'drug-induced priapism'. References of all identified studies were also reviewed. A total of 50 publications were obtained. Most of the atypical antipsychotics have been reported to cause priapism. These cases have occurred in patients shortly after having been started on the antipsychotic medications as well as in those who have been on them for an extended period of time without modification in dosage, and have also occurred sometimes, with the addition of another antipsychotic, lithium or serotonin-specific reuptake inhibitor. Priapism has been documented with nearly all the atypical antipsychotic medications. It is, however, a rarely reported side effect and therefore, underappreciated. Priapism can cause irreversible erectile dysfunction and is a urologic emergency. Clinicians should monitor patients on these medications for this rare, yet significant side effect. Furthermore, caution must be used when adding new drugs to the regimen and patients should be closely monitored for this side effect. Educating patients about the risk of developing priapism would help increase awareness of the side effect and promote early reporting thereby, decreasing long-term morbidity.

Potential genetic causes of heterogeneity of treatment effects

Nongenetic biologic and lifestyle-related factors, including age, sex, hepatic/renal function, diet/exercise practices, illness severity, smoking, and alcohol consumption habits can account for the heterogeneity of treatment effects (HTE). However, even when these factors are taken into account, considerable variation remains unexplained and could potentially be attributable to genetic differences between patients. Drug response may be dictated by variation in genes involved in both pharmacokinetic (PK) (absorption, distribution, metabolism, excretion [ADME]) and pharmacodynamic (PD) (receptors, ion channels, enzymes, immune system) pathways. Functional variants of the ADME genes can result in patients being poor, intermediate, efficient, or ultrarapid metabolizers of specific agents, thereby affecting efficacy and/or susceptibility to adverse drug reaction and necessitating individualized dosing. A well-documented example of ADME gene variation is the debrisoquine polymorphism, which is characterized by markedly different metabolism of numerous commonly prescribed drugs based on variants of the cytochrome P450 2D6 gene. Variants of genes regulating PD pathways cause altering of drug target pathways, which may affect efficacy in a more pronounced manner. Examples of gene variants affecting PD pathways include those coding for dopamine metabolism, synthesis, and transport. These gene variants may act independently, in combination with each other, and/or in combination with PK genes to affect drug response, for example to antipsychotic medications. Increased understanding of a patient's genotype and its corresponding effect on drug response would be useful to the practicing clinician in choosing an effective drug and in optimizing the dose in a timely manner.

N-Benzyl-N-(tetrahydro-2H-pyran-4-yl)pyrrolidin-3-amines as selective dual serotonin/noradrenaline reuptake inhibitors

A series of N-benzyl-N-(tetrahydro-2H-pyran-4-yl)pyrrolidin-3-amine monoamine reuptake inhibitors are described. Selective dual 5-HT and NA reuptake inhibition was achieved, and analogues with weak CYP2D6 inhibition, good human in vitro metabolic stability and wide ligand selectivity, such as 12b, were identified.

Treatment of depression with selective serotonin inhibitors: the role of fluvoxamine

The advent of the selective serotonin reuptake inhibitors (SSRIs) is generally considered to have improved the treatment of depression. Head-to-head trials comparing SSRIs to each other have shown little difference in efficacy among agents. The main differences between the SSRIs relate to safety and tolerability profiles, reflecting the fact that the SSRIs possess significant and variable secondary pharmacological properties. This heterogeneity contributes to clinically relevant differences that clinicians are increasingly using to select antidepressant treatment more closely appropriate to specific patient populations and circumstances. This review assesses the place of fluvoxamine amongst the SSRIs in the context of current issues and concerns with drug therapy. Fluvoxamine has a proven efficacy and safety profile in treating elderly patients with depression. The beneficial effects of fluvoxamine in obsessive-compulsive disorder (OCD) are also well documented. On the other hand, its σ1-receptor binding profile may account for the observed high level of efficacy in psychotic depression and may explain the benefit of fluvoxamine in treating depression comorbid with anxiety/stress. There is no definitive evidence that suicide risk is higher with SSRIs than with other antidepressants or nonpharmacological treatments and postmarketing surveillance indicates that fluvoxamine is not associated with a higher level of suicidality.

Risk and predictability of drug interactions in the elderly

The issue of drug-drug interactions is particularly relevant for geriatric patients with epilepsy because they are often treated with multiple medications for concurrent diseases such as cardiovascular disease and psychiatric disorders (e.g., dementia and depression). The antidepressants with the least potential for altering antiepileptic drug (AED) metabolism are citalopram, escitalopram, venlafaxine, duloxetine, and mirtazapine. The use of established AEDs with enzyme-inducing properties, such as carbamazepine, phenytoin, and phenobarbital, may be associated with reductions in the levels of drugs such as donepezil, galantamine, and particularly warfarin. Carbamazepine, phenytoin, and phenobarbital have been reported to decrease prothrombin time in patients taking oral anticoagulants, although with phenytoin, an increase in prothrombin time has also been reported. Drugs associated with increased risk of bleeding in patients taking oral anticoagulants include selective serotonin reuptake inhibitors (especially fluoxetine), gemfibrozil, fluvastatin, and lovastatin. Other drugs affected by enzyme inducers include cytochrome P450 3A4 substrates, such as calcium channel blockers (e.g., nimodipine, nilvadipine, nisoldipine, and felodipine) and the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors atorvastatin, lovastatin, and simvastatin. Although there have been no reports of AEDs altering ticlopidine metabolism, ticlopidine coadministration can result in carbamazepine and phenytoin toxicity. Also, there is a significant risk of elevated levels of carbamazepine when diltiazem and verapamil are administered. In addition, there are case reports of phenytoin toxicity when administered with diltiazem. Drugs with a lower potential for metabolic drug interactions include (1) cholinesterase inhibitors (although the theoretical possibility of a reduction in donepezil and galantamine levels by enzyme-inducing AEDs should be considered) and the N-methyl-D-aspartate receptor antagonist memantine and (2) antihypertensives such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, hydrophilic beta-blockers, and thiazide diuretics. There is a moderate risk that enzyme-inducing AEDs will decrease levels of lipophilic beta-blockers. Newer AEDs have a lower potential for drug interactions. In particular, levetiracetam and gabapentin have not been reported to alter enzyme activity. In summary, there is a significant potential for drug interactions between AEDs and drugs commonly prescribed in geriatric patients with epilepsy.

Cytochrome P450 and xenobiotic receptor humanized mice

Most xenobiotics that enter the body are subjected to metabolism that functions primarily to facilitate their elimination. Metabolism of certain xenobiotics can also result in the production of electrophilic derivatives that can cause cell toxicity and transformation. Many xenobiotics can also activate receptors that in turn induce the expression of genes encoding xenobiotic-metabolizing enzymes and xenobiotic transporters. However, there are marked species differences in the way mammals respond to xenobiotics, which are due in large part to molecular differences in receptors and xenobiotic-metabolizing enzymes. This presents a problem in extrapolating data obtained with rodent model systems to humans. There are also polymorphisms in xenobiotic-metabolizing enzymes that can impact drug therapy and cancer susceptibility. In an effort to generate more reliable in vivo systems to study and predict human response to xenobiotics, humanized mice are under development.

Tolerability and safety of fluvoxamine and other antidepressants

Selective serotonin [5-hydroxytryptamine (5-HT)] reuptake inhibitors (SSRIs) and the 5-HT noradrenaline reuptake inhibitor, venlafaxine, are mainstays in treatment for depression. The highly specific actions of SSRIs of enhancing serotonergic neurotransmission appears to explain their benefit, while lack of direct actions on other neurotransmitter systems is responsible for their superior safety profile compared with tricyclic antidepressants. Although SSRIs (and venlafaxine) have similar adverse effects, certain differences are emerging. Fluvoxamine may have fewer effects on sexual dysfunction and sleep pattern. SSRIs have a cardiovascular safety profile superior to that of tricyclic antidepressants for patients with cardiovascular disease; fluvoxamine is safe in patients with cardiovascular disease and in the elderly. A discontinuation syndrome may develop upon abrupt SSRI cessation. SSRIs are more tolerable than tricyclic antidepressants in overdose, and there is no conclusive evidence to suggest that they are associated with an increased risk of suicide. Although the literature suggests that there are no clinically significant differences in efficacy amongst SSRIs, treatment decisions need to be based on considerations such as patient acceptability, response history and toxicity.

Liver enzyme induction and inhibition: implications for anaesthesia

Recent breakthroughs in molecular biology have enabled a reclassification of drug metabolising enzymes based on their amino acid sequence. This has led to a better understanding of drug metabolism and drug interactions. The majority of these drug metabolising enzymes may be either induced or inhibited by drugs or by extraneous substances including foodstuffs, cigarette smoke and environmental pollutants. Virtually all drugs used in anaesthesia are metabolised by either hepatic phase 1 or phase II enzymes. This review considers the classification of drug metabolising enzymes, explains the mechanisms of enzyme induction and inhibition, and also considers how the action of drugs commonly used by anaesthetists, including opioids and neuromuscular blocking drugs, may be altered by this mechanism.

Role of efflux pumps and metabolising enzymes in drug delivery

The impact of efflux pumps and metabolic enzymes on the therapeutic activity of various drugs has been well established. The presence of efflux pumps on various tissues and tumours has been shown to regulate the intracellular concentration needed to achieve therapeutic activity. The notable members of efflux proteins include P-glycoprotein, multi-drug resistance protein and breast cancer resistance protein. These efflux pumps play a pivotal role not only in extruding xenobiotics but also in maintaining the body's homeostasis by their ubiquitous presence and ability to coordinate among themselves. In this review, the role of efflux pumps in drug delivery and the importance of their tissue distribution is discussed in detail. To improve pharmacokinetic parameters of substrates, various strategies that modulate the activity of efflux proteins are also described. Drug metabolising enzymes mainly include the cytochrome P450 family of enzymes. Extensive drug metabolism due to the this family of enzymes is the leading cause of therapeutic inactivity. Therefore, the role of metabolising enzymes in drug delivery and disposition is extensively discussed in this review. The synergistic relationship between metabolising enzymes and efflux proteins is also described in detail. In summary, this review emphasises the urgent need to make changes in drug discovery and drug delivery as efflux pumps and metabolising enzymes play an important role in drug delivery and disposition.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.

Effects of venlafaxine treatment on clozapine plasma levels in schizophrenic patients

Depressive symptoms are found at any stage of schizophrenia, and antidepressant medication may be beneficial. Selective serotonin reuptake inhibitor antidepressants have been considered safe in schizophrenia but in combination with clozapine, that is widely used in chronic treatment-resistant schizophrenia, remarkable pharmacokinetic interactions can occur causing an elevation in clozapine plasma levels. To investigate this further, the plasma levels of clozapine were measured in 11 schizophrenic male patients with depressive symptoms who were administered both clozapine and venlafaxine. Low to moderate doses of venlafaxine did not seem to have any significant effect on clozapine plasma levels.

Pharmacology of palliative medicine

OBJECTIVE

To describe the concepts of both pharmacokinetics and pharmacodynamics and how it applies to palliative medicine.

DATA SOURCES

Research and review articles and textbooks.

CONCLUSION

Most patients who have an illness that requires palliation are elderly, have co-morbid conditions, and are on many medications. Both age and disease can alter the way drugs are handled by the body (pharmacokinetics) and how they affect the body (pharmacodynamics).

IMPLICATIONS FOR NURSING PRACTICE

The oncology nurse, armed with the correct knowledge about medications, can have an important inmpact on improving the patient's care, safety, and quality of life.

Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates

Cytochrome P450 2D6 (CYP2D6) is the first well-characterized polymorphic phase I drug-metabolizing enzyme, and more than 80 allelic variants have been identified for the CYP2D6 gene, located on human chromosome 22q13.1. Human debrisoquine and sparteine metabolism is subdivided into two principal phenotypes--extensive metabolizer and poor metabolizer--that arise from variant CYP2D6 genotypes. It has been estimated that CYP2D6 is involved in the metabolism and disposition of more than 20% of prescribed drugs, and most of them act in the central nervous system or on the heart. These drug substrates are characterized as organic bases containing one nitrogen atom with a distance about 5, 7, or 10 A from the oxidation site. Aspartic acid 301 and glutamic acid 216 were determined as the key acidic residues for substrate-enzyme binding through electrostatic interactions. CYP2D6 transgenic mice, generated using a lambda phage clone containing the complete wild-type CYP2D6 gene, exhibits enhanced metabolism and disposition of debrisoquine. This transgenic mouse line and its wild-type control are models for human extensive metabolizers and poor metabolizers, respectively, and would have broad application in the study of CYP2D6 polymorphism in drug discovery and development, and in clinical practice toward individualized drug therapy. Endogenous 5-methoxyindole- thylamines derived from 5-hydroxytryptamine were identified as high-affinity substrates of CYP2D6 that catalyzes their O-demethylations with high enzymatic capacity and specificity. Thus, polymorphic CYP2D6 may play an important role in the interconversions of these psychoactive tryptamines, including a crucial step in a serotonin-melatonin cycle.

Medication use in a rural gynecologic population: prescription, over-the-counter, and herbal medicines

OBJECTIVE

The purpose of this study was to document current medication use by a rural female population.

STUDY DESIGN

Over a 42-month period, nonpregnant women were interviewed about medication use. When applicable, interviews on subsequent visits provided a longitudinal study of medication usage and discontinuation, and data were analyzed according to the number of drugs used, age, and payment status.

RESULTS

Five hundred sixty-seven participants had 776 interviews. Ninety-two percent of the participants took prescription medications, 96.5% of the participants self-medicated with over-the-counter medications, and 59.1% of the participants used herbal medications. Usage of prescription medications increased with age and, in some instances, varied with payment status. A database query for potential interacting drugs found several instances of coadministration, including herbal medicines that were not prescribed by the physician.

CONCLUSION

Medication usage (all types) by rural women is substantial, and the frequency of usage varies on the basis of both age and payment status. Patients should also be queried concerning medications that are not prescribed by the physician for an assessment of potential drug interactions.

Which concentration of the inhibitor should be used to predict in vivo drug interactions from in vitro data?

When the metabolism of a drug is competitively or noncompetitively inhibited by another drug, the degree of in vivo interaction can be evaluated from the [I]u/Ki ratio, where [I]u is the unbound concentration around the enzyme and Ki is the inhibition constant of the inhibitor. In the present study, we evaluated the metabolic inhibition potential of drugs known to be inhibitors or substrates of cytochrome P450 by estimating their [I]u/Ki ratio using literature data. The maximum concentration of the inhibitor in the circulating blood ([I]max), its maximum unbound concentration in the circulating blood ([I]max,u), and its maximum unbound concentration at the inlet to the liver ([I]in,max,u) were used as [I]u, and the results were compared with each other. In order to calculate the [I]u/Ki ratios, the pharmacokinetic parameters of each drug were obtained from the literature, together with their reported Ki values determined in in vitro studies using human liver microsomes. For most of the drugs with a calculated [I]in,max,u/Ki ratio less than 0.25, which applied to about half of the drugs investigated, no in vivo interactions had been reported or "no interaction" was reported in clinical studies. In contrast, the [I]max,u/Ki and [I]max/Ki ratio was calculated to be less than 0.25 for about 90% and 65% of the drugs, respectively, and more than a 1.25-fold increase was reported in the area under the concentration-time curve of the co-administered drug for about 30% of such drugs. These findings indicate that the possibility of underestimation of in vivo interactions (possibility of false-negative prediction) is greater when [I]max,u or [I]max values are used compared with using [I]in,max,u values.

Inhibitory effects of tricyclic antidepressants (TCAs) on human cytochrome P450 enzymes in vitro: mechanism of drug interaction between TCAs and phenytoin

The ability of tricyclic antidepressants (TCAs) to inhibit phenytoin p-hydroxylation was evaluated in vitro by incubation studies of human liver microsomes and cDNA-expressed cytochrome p450s (p450s). The TCAs tested were amitriptyline, imipramine, nortriptyline, and desipramine. Amitriptyline and imipramine strongly and competitively inhibited phenytoin p-hydroxylation in microsomal incubations (estimated K(i) values of 5.2 and 15.5 micro M, respectively). In contrast, nortriptyline and desipramine produced only weak inhibition. In the incubation study using cDNA-expressed P450s, both CYP2C9 and CYP2C19 catalyzed phenytoin p-hydroxylation, whereas TCAs inhibited only the CYP2C19 pathway. All of the TCAs tested inhibited CYP2D6-catalyzed dextromethorphan-O-demethylation competitively, with estimated K(i) values of 31.0, 28.6, 7.9, and 12.5 micro M, respectively. The tertiary amine TCAs, amitriptyline and imipramine, also inhibited CYP2C19-catalyzed S-mephenytoin 4'-hydroxylation (estimated K(i) of 37.7 and 56.8 micro M, respectively). The secondary amine TCAs, nortriptyline and desipramine, however, showed minimal inhibition of CYP2C19 (estimated IC(50) of 600 and 685 micro M, respectively). None of the TCAs tested produced remarkable inhibition of any other p450 isoforms. These results suggest that TCAs inhibit both CYP2D6 and CYP2C19 and that the interaction between TCAs and phenytoin involves inhibition of CYP2C19-catalyzed phenytoin p-hydroxylation.