Potentially significant drug interactions of class III antiarrhythmic drugs

Arrhythmias in oncological patients: a compact overview for the clinician

Chemotherapy is the cornerstone of antineoplastic treatment in patients with malignancies. The cardiotoxic effect of antineoplastic therapy has been known for many decades. Part of chemotherapy-induced cardiotoxicity is the development of heart rhythm disturbances. This short review aims to provide a compact overview for the clinical cardiologist of the dysrhythmic potential created by antineoplastic agents in cancer survivors.

Mechanism-based inactivation of cytochromes P450: implications in drug interactions and pharmacotherapy

Cytochrome P40 (CYP) enzymes dominate the metabolism of numerous endogenous and xenobiotic substances. While it is commonly believed that CYP-catalysed reactions result in the detoxication of foreign substances, these reactions can also yield reactive intermediates that can bind to cellular macromolecules to cause cytotoxicity or irreversibly inactivate CYPs that create them.Mechanism-based inactivation (MBI) produces either irreversible or quasi-irreversible inactivation and is commonly caused by CYP metabolic bioactivation to an electrophilic reactive intermediate. Many drugs that have been known to cause MBI in CYPs have been discovered as perpetrators in drug-drug interactions throughout the last 20-30 years.This review will highlight the key findings from the recent literature about the mechanisms of CYP enzyme inhibition, with a focus on the broad mechanistic elements of MBI for widely used drugs linked to the phenomenon. There will also be a brief discussion of the clinical or pharmacokinetic consequences of CYP inactivation with regard to drug interaction and toxicity risk.Gaining knowledge about the selective inactivation of CYPs by common therapeutic drugs helps with the assessment of factors that affect the systemic clearance of co-administered drugs and improves comprehension of anticipated interactions with other drugs or xenobiotics.

Spontaneous Hemorrhagic Pericardial Effusion as a Consequence of Apixaban Utilization for New-Onset Atrial Fibrillation

Although anticoagulation stands as a standardized therapeutic approach for mitigating thrombotic risks in atrial fibrillation, the potential for bleeding associated with direct oral anticoagulants (DOACs) is consistently weighed in the risk/benefit analysis prior to initiating therapy for non-valvular atrial fibrillation. While the typical bleeding risks from DOACs predominantly affect the gastrointestinal system, occurrences of spontaneous hemorrhagic pericardial effusions are rare. This case presentation illustrates a patient developing spontaneous hemorrhagic pericardial effusion four days after commencing apixaban therapy and subsequent management.

MATE1 Deficiency Exacerbates Dofetilide-Induced Proarrhythmia

Dofetilide is a rapid delayed rectifier potassium current inhibitor widely used to prevent the recurrence of atrial fibrillation and flutter. The clinical use of this drug is associated with increases in QTc interval, which predispose patients to ventricular cardiac arrhythmias. The mechanisms involved in the disposition of dofetilide, including its movement in and out of cardiomyocytes, remain unknown. Using a xenobiotic transporter screen, we identified MATE1 (SLC47A1) as a transporter of dofetilide and found that genetic knockout or pharmacological inhibition of MATE1 in mice was associated with enhanced retention of dofetilide in cardiomyocytes and increased QTc prolongation. The urinary excretion of dofetilide was also dependent on the MATE1 genotype, and we found that this transport mechanism provides a mechanistic basis for previously recorded drug-drug interactions of dofetilide with various contraindicated drugs, including bictegravir, cimetidine, ketoconazole, and verapamil. The translational significance of these observations was examined with a physiologically-based pharmacokinetic model that adequately predicted the drug-drug interaction liabilities in humans. These findings support the thesis that MATE1 serves a conserved cardioprotective role by restricting excessive cellular accumulation and warrant caution against the concurrent administration of potent MATE1 inhibitors and cardiotoxic substrates with a narrow therapeutic window.

CLInical Profile and Side Effects of chronic use of oral Amiodarone in cardiology outpatients department (CLIPSE-A Study)- A prospective observational study

Background

Amiodarone belongs to Class-III anti-arrhythmic drugs. It is one of the most effective anti-arrhythmic drugs used to treat or prevent several types of arrhythmias including atrial fibrillation, atrial flutter, ventricular tachycardia, and wide complex tachycardia, but unfortunately carries a high toxicity profile. Also, side effects of amiodarone involving various organs can be life-threatening.

Materials & methods

This was an observational study carried out for six months i.e from April to September. The study included patients who are on amiodarone for greater than or equal to six months. The required data was collected in-person from the case sheets, treatment charts, and by interviewing the patients. The data for 67 patients was documented in suitable data collection form for analysis.

Results

From our study data, it was noted that amiodarone was used for 3 different indications-atrial fibrillation, atrial flutter, and ventricular tachycardia. Among 67 patients enrolled, 38 had no side-effects. Side-effects data in the rest grouped basing on the organ system affected: 9 patients had renal effects, 6 patients had ophthalmic effects, 4 patients had endocrine effects, and 5 patients had hepatic effects.

Conclusion

From our study, it is concluded that amiodarone is a safe and effective anti-arrhythmic drug at lower doses i.e. 200-1100 mg/week. When treated in lower doses of 1400–2800 mg/week, many side effects have been incident. Although these effects are mild and develop only after prolonged usage of the drug, it should be used judiciously.

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Amiodarone has an unusual spectrum of side effects with a prevalence of 15% in the first year, increasing up to 50% during long-term use.

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Our study demonstrated amiodarone does not produce significant side-effects when used in doses of 200–1100 mg/week.

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Few side-effects are observed when amiodarone is used in higher doses of 1200–2800 mg/week.

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When a side-effect is observed, mere reducing the dose or withdrawal of drug might help.

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In most of the cases of atrial fibrillation, amiodarone is discontinued or altered in first year of treatment basing on risk/benefit ratio.

Candidate Proficiency Test Chemicals to Address Industrial Chemical Applicability Domains for in vitro Human Cytochrome P450 Enzyme Induction

Cytochrome P450 (CYP) enzymes play a key role in the metabolism of both xenobiotics and endogenous chemicals, and the activity of some CYP isoforms are susceptible to induction and/or inhibition by certain chemicals. As CYP induction/inhibition can bring about significant alterations in the level of in vivo exposure to CYP substrates and metabolites, CYP induction/inhibition data is needed for regulatory chemical toxicity hazard assessment. On the basis of available human in vivo pharmaceutical data, a draft Organisation for Economic Co-operation and Development Test Guideline (TG) for an in vitro CYP HepaRG test method that is capable of detecting the induction of four human CYPs (CYP1A1/1A2, 2B6, and 3A4), has been developed and validated for a set of pharmaceutical proficiency chemicals. However to support TG adoption, further validation data was requested to demonstrate the ability of the test method to also accurately detect CYP induction mediated by industrial and pesticidal chemicals, together with an indication on regulatory uses of the test method. As part of "GOLIATH", a European Union Horizon-2020 funded research project on metabolic disrupting chemical testing approaches, work is underway to generate supplemental validated data for an additional set of chemicals with sufficient diversity to allow for the approval of the guideline. Here we report on the process of proficiency chemical selection based on a targeted literature review, the selection criteria and considerations required for acceptance of proficiency chemical selection for OECD TG development (i.e. structural diversity, range of activity, relevant chemical sectors, global restrictions etc). The following 13 proposed proficiency chemicals were reviewed and selected as a suitable set for use in the additional validation experiments: tebuconazole, benfuracarb, atrazine, cypermethrin, chlorpyrifos, perfluorooctanoic acid, bisphenol A, N,N-diethyl-m-toluamide, benzo-[a]-pyrene, fludioxonil, malathion, triclosan, and caffeine. Illustrations of applications of the test method in relation to endocrine disruption and non-genotoxic carcinogenicity are provided.

Arrhythmic Complications Associated with Cancer Therapies

Over the last several decades, advancements in cancer screening and treatment have significantly improved cancer mortality and overall quality of life. Unfortunately, non-cancer-related side effects, including cardiovascular toxicities can impact the continued delivery of these treatments. Arrhythmias are an increasingly recognized class of cardiotoxicity that can occur as a direct consequence of the treatment or secondary to another type of toxicity such as heart failure, myocarditis, or ischemia. Atrial arrhythmias, particularly atrial fibrillation (AF) are most commonly encountered, however, ventricular- and bradyarrhythmias can also occur, albeit at lower rates. Treatment strategies tailored to patients with cancer are essential to allow for the safe delivery of the cancer treatment without affecting short- or long-term oncologic or cardiovascular outcomes.

Prevalence of potentially harmful multidrug interactions on medication lists of elderly ambulatory patients

Background

It has been hypothesized that polypharmacy may increase the frequency of multidrug interactions (MDIs) where one drug interacts with two or more other drugs, amplifying the risk of associated adverse drug events (ADEs). The main objective of this study was to determine the prevalence of MDIs in medication lists of elderly ambulatory patients and to identify the medications most commonly involved in MDIs that amplify the risk of ADEs.

Methods

Medication lists stored in the electronic health record (EHR) of 6,545 outpatients ≥60 years old were extracted from the enterprise data warehouse. Network analysis identified patients with three or more interacting medications from their medication lists. Potentially harmful interactions were identified from the enterprise drug-drug interaction alerting system. MDIs were considered to amplify the risk if interactions could increase the probability of ADEs.

Results

MDIs were identified in 1.3 % of the medication lists, the majority of which involved three interacting drugs (75.6 %) while the remainder involved four (15.6 %) or five or more (8.9 %) interacting drugs. The average number of medications on the lists was 3.1 ± 2.3 in patients with no drug interactions and 8.6 ± 3.4 in patients with MDIs. The prevalence of MDIs on medication lists was greater than 10 % in patients prescribed bupropion, tramadol, trazodone, cyclobenzaprine, fluoxetine, ondansetron, or quetiapine and greater than 20 % in patients prescribed amiodarone or methotrexate. All MDIs were potentially risk-amplifying due to pharmacodynamic interactions, where three or more medications were associated with the same ADE, or pharmacokinetic, where two or more drugs reduced the metabolism of a third drug. The most common drugs involved in MDIs were psychotropic, comprising 35.1 % of all drugs involved. The most common serious potential ADEs associated with the interactions were serotonin syndrome, seizures, prolonged QT interval and bleeding.

Conclusions

An identifiable number of medications, the majority of which are psychotropic, may be involved in MDIs in elderly ambulatory patients which may amplify the risk of serious ADEs. To mitigate the risk, providers will need to pay special attention to the overlapping drug-drug interactions which result in MDIs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-021-02594-z.

Icotinib Induces Mechanism-Based Inactivation of Recombinant Human CYP3A4/5 Possibly via Heme Destruction by Ketene Intermediate

Icotinib (ICT) is an antitumor drug approved by China National Medical Products Administration and is found to be effective against non-small cell lung cancer. The present study aimed at the interaction of ICT with CYP3A. ICT exhibited time-, concentration-, and NADPH-dependent inhibitory effect on recombinant human CYP3A4/5. About 60% of CYP3A activity was suppressed by ICT at 50 μM after 30 minutes. The observed enzyme inhibition could not be recovered by dialysis. Nifedipine protected CYP3A from the inactivation by ICT. The inhibitory effects of ICT on CYP3A were influenced neither by glutathione/N-acetyl lysine nor by superoxide dismutase/catalase. Incubation of ICT with human hepatic microsomes produced a ketene reactive intermediate trapped by 4-bromobenzylamine. CYP3A4 dominated the metabolic activation of ICT to the ketene intermediate. Ethyl and vinyl analogs of ICT did not induce inactivation of recombinant human CYP3A4/5, which indicates that acetylenic bioactivation of ICT contributed to the enzyme inactivation. Moreover, the metabolic activation of ICT resulted in heme destruction. In conclusion, this study demonstrated that ICT was a mechanism-based inactivator of recombinant human CYP3A4/5, and heme destruction by the ketene metabolite may be responsible for the observed CYP3A inactivation. SIGNIFICANCE STATEMENT: Cytochrome P450 enzymes play an important role in drug-drug interactions. The present study demonstrated that icotinib, an inhibitor of epidermal growth factor receptor used to treat non-small cell lung cancer, is a mechanism-based inactivator of recombinant human CYP3A4/5. The study provided solid evidence for the involvement of acetylene moiety in the metabolic activation as well as the inactivation of the enzyme. Furthermore, the resulting ketene intermediate was found to destroy heme, which is possibly responsible for the observed enzyme inactivation.

Recognition, Prevention, and Management of Arrhythmias and Autonomic Disorders in Cardio-Oncology: A Scientific Statement From the American Heart Association

With the advent of novel cancer therapeutics and improved screening, more patients are surviving a cancer diagnosis or living longer with advanced disease. Many of these treatments have associated cardiovascular toxicities that can manifest in both an acute and a delayed fashion. Arrhythmias are an increasingly identified complication with unique management challenges in the cancer population. The purpose of this scientific statement is to summarize the current state of knowledge regarding arrhythmia identification and treatment in patients with cancer. Atrial tachyarrhythmias, particularly atrial fibrillation, are most common, but ventricular arrhythmias, including those related to treatment-induced QT prolongation, and bradyarrhythmias can also occur. Despite increased recognition, dedicated prospective studies evaluating true incidence are lacking. Moreover, few studies have addressed appropriate prevention and treatment strategies. As such, this scientific statement serves to mobilize the cardio-oncology, electrophysiology, and oncology communities to develop clinical and scientific collaborations that will improve the care of patients with cancer who have arrhythmias.

Comparable risk of recurrent ventricular tachyarrhythmias in implantable cardioverter-defibrillator recipients treated with single beta-blocker or combined amiodarone

This study sought to assess the prognostic impact of treatment with single beta-blocker (BB) compared to combined therapy with BB plus amiodarone (BB-AMIO) on recurrences of ventricular tachyarrhythmias in implantable cardioverter-defibrillator (ICD) recipients. A large retrospective registry was used including consecutive ICD recipients with index episodes of ventricular tachyarrhythmias from 2002 to 2016. Patients treated with BB were compared to patients treated with BB-AMIO. Kaplan-Meier and Cox regression analyses were applied for the evaluation of the primary end-point defined as first recurrences of ventricular tachyarrhythmias at five years. Secondary end-points comprised first appropriate ICD therapies, first cardiac rehospitalization and all-cause mortality at five years. Among 512 ICD recipients, 81% were treated with BB and 19% with BB-AMIO. BB and BB-AMIO were associated with comparable risk of first recurrences of ventricular tachyarrhythmias (46% vs. 43%; log rank P = .941; HR = 1.013; 95% CI 0.725-1.415; P = .941) and appropriate ICD therapies (35% vs. 37%; log rank P = .389; HR = 0.852; 95% CI 0.591-1.228; P = .390). BB was associated with decreased long-term all-cause mortality within an univariable analysis only (20% vs. 28%; log rank p = 0.023). In conclusion, BB and BB-AMIO were associated with comparable risks regarding recurrences of ventricular tachyarrhythmias at five years.

Validation of in vitro methods for human cytochrome P450 enzyme induction: Outcome of a multi-laboratory study

CYP enzyme induction is a sensitive biomarker for phenotypic metabolic competence of in vitro test systems; it is a key event associated with thyroid disruption, and a biomarker for toxicologically relevant nuclear receptor-mediated pathways. This paper summarises the results of a multi-laboratory validation study of two in vitro methods that assess the potential of chemicals to induce cytochrome P450 (CYP) enzyme activity, in particular CYP1A2, CYP2B6, and CYP3A4. The methods are based on the use of cryopreserved primary human hepatocytes (PHH) and human HepaRG cells. The validation study was coordinated by the European Union Reference Laboratory for Alternatives to Animal Testing of the European Commission's Joint Research Centre and involved a ring trial among six laboratories. The reproducibility was assessed within and between laboratories using a validation set of 13 selected chemicals (known human inducers and non-inducers) tested under blind conditions. The ability of the two methods to predict human CYP induction potential was assessed. Chemical space analysis confirmed that the selected chemicals are broadly representative of a diverse range of chemicals. The two methods were found to be reliable and relevant in vitro tools for the assessment of human CYP induction, with the HepaRG method being better suited for routine testing. Recommendations for the practical application of the two methods are proposed.

[Amiodarone-induced optic neuropathy: A rare side effect]

INTRODUCTION

The diagnosis of bilateral papilledema implies emergency medical care to look for intracranial hypertension and arteritic ischemic neuropathy. However, other causes must also be mentioned, including drugs. Too often underrated because of their usual benignity, drug side ophthalmological effects can be severe and are typically bilateral.

CASE REPORT

An 80-year-old woman was hospitalized for bilateral papilledema, predominantly in the left eye, with lowered visual acuity. After ruling out intracranial hypertension, arteritic ischemic optic neuropathy, non-arteritic, and inflammatory bilateral papilledema, the diagnosis was toxic optic neuropathy.

CONCLUSION

Bilateral edematous optic neuropathy is a known side effect of amiodarone, uncommon but to be known because of the large number of patients benefiting from this treatment.

Colchicine in Pericardial Disease: from the Underlying Biology and Clinical Benefits to the Drug-Drug Interactions in Cardiovascular Medicine

PURPOSE OF REVIEW

This is an in-depth review on the mechanism of action, clinical utility, and drug-drug interactions of colchicine in the management of pericardial disease.

RECENT FINDINGS

Recent evidence about therapeutic targets on pericarditis has demonstrated that NALP3 inflammasome blockade is the cornerstone in the clinical benefits of colchicine. Such benefits extend from acute and recurrent pericarditis to transient constriction and post-pericardiotomy syndrome. Despite the increased utilization of colchicine in cardiovascular medicine, safety concerns remains unsolved regarding the long-term use of colchicine in the cardiac patient. Moreover, recent evidence has demonstrated that numerous cardiovascular medications, ranging from antihypertensive medication to antiarrhythmics, are known to interact with the CYP3A4 and/or P-gp system increasing the toxicity potential of colchicine. The use of adjunctive colchicine in the management of inflammatory pericardial diseases is standard of care in current practice. It is advised that a careful medication reconciliation with emphasis on pharmacokinetic is completed before prescribing colchicine in order to avoid harmful interaction by finding an alternative regimen or adjusting colchicine dosing.

Comparison of posttransplant outcomes in patients with no, acute, or chronic amiodarone use before heart transplantation

Background

Major concerns about the safety of pretransplant amiodarone use have been raised. As a result of its long half-life, the cardiac allograft is exposed to amiodarone posing potential risks such as bradycardia, requirement for pacemaker implantation, or increased mortality after heart transplantation (HTX).

Objective

The aim of this study is to investigate the posttransplant outcomes of patients with no, acute, or chronic amiodarone use before HTX.

Methods

This retrospective single-center study included 530 adult patients who received HTX between 06/1989 and 12/2012. Patients were stratified by their amiodarone therapy before HTX: no continuous amiodarone use (≤90 days before HTX), acute amiodarone use (≤90 days before HTX), and chronic amiodarone use (>90 days before HTX). Differences between the 3 groups in demographics, posttransplant medication, echocardiographic features, heart rates including occurrences of bradycardia, permanent pacemaker implantation, atrial fibrillation (AF), and survival were analyzed.

Results

A total of 412 patients (77.7%) were in the “no amiodarone” group, 23 patients (4.4%) in the “acute amiodarone” group, and 95 patients (17.9%) in the “chronic amiodarone” group. Left ventricular ejection fraction (P=0.5819), heart rates including occurrence of bradycardia during posttransplant week 1 (P=0.0979 and P=0.2695), week 2 (P=0.1214 and P=0.8644), week 3 (P=0.1033 and P=0.8894), and week 4 (P=0.2892 and P=0.8644), permanent pacemaker implantation within 30-day (P=0.8644), or overall follow-up after HTX (P=0.8664) were not significant between groups. Patients with chronic pretransplant amiodarone therapy had the lowest rate of early posttransplant AF (P=0.0065). There was no statistically significant difference between groups in 30-day (P=0.8656), 1-year (P=1.0000), 2-year (P=0.8763), 5-year (P=0.5174), or overall posttransplant follow-up mortality (P=0.1936).

Conclusion

Administration of acute or chronic pretransplant amiodarone was not related to an increased occurrence of bradycardia, requirement for permanent pacemaker implantation, or mortality after HTX. Importantly, chronic amiodarone use effectively reduced early AF after HTX, whereas acute amiodarone use showed no such effect.

NXY-059: Review of Neuroprotective Potential for Acute Stroke

Objective:

To review available literature on the pharmacology, pharmacokinetics, efficacy, and tolerability of NXY-059, an Investigational agent with a potential role in the treatment of acute stroke.

Data Sources:

Information was obtained from a MEDLINE search (1966–February 2006) of English-language literature utilizing the following search terms: NXY-059, cerovive, nitrones, neuroprotection, free radical trapper, and secondary neurologic injury.

Study Selection and Data Extraction:

Data from animal and human trials were evaluated to summarize the mechanism of action, efficacy, and safety of NXY-059. All published and unpublished trials and abstracts citing NXY-059 were selected.

Data Synthesis:

NXY-059 is an intravenous, nitrone-based, free radical trapping agent in Phase III trials for treatment of acute stroke. In various animal models, NXY-059 has shown reductions in infarct volume and neurologic deficits. Pharmacokinetic studies indicate that NXY-059 displays a predictable pharmacokinetic profile and primarily undergoes renal elimination. Results from 2 Phase II clinical trials showed favorable results for the safety and tolerability of the drug. A recent analysis of one of the Phase III trials showed a statistically significant reduction in the primary outcome of disability after acute stroke in patients who received NXY-059 compared with placebo.

Conclusions:

NXY-059 is a novel agent undergoing worldwide Phase III trials. Initial safety and efficacy data have not revealed any serious adverse events requiring special monitoring and/or precautions, with the exception of drug accumulation in patients with renal insufficiency. The potential benefit of this agent can change the current management algorithm for acute stroke and may represent significant advancement for the care of these patients.

Effects of continuous renal replacement therapy on linezolid pharmacokinetic/pharmacodynamics: a systematic review

Background

Major alterations in linezolid pharmacokinetic/pharmacodynamic (PK/PD) parameters might be expected in critically ill septic patients with acute kidney injury (AKI) who are undergoing continuous renal replacement therapy (CRRT). The present review is aimed at describing extracorporeal removal of linezolid and the main PK-PD parameter changes observed in critically ill septic patients with AKI, who are on CRRT.

Method

Citations published on PubMed up to January 2016 were systematically reviewed according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement. All authors assessed the methodological quality of the studies and consensus was used to ensure studies met inclusion criteria. In-vivo studies in adult patients with AKI treated with linezolid and on CRRT were considered eligible for the analysis only if operational settings of the CRRT machine, membrane type, linezolid blood concentrations and main PK-PD parameters were all clearly reported.

Results

Among 68 potentially relevant articles, only 9 were considered eligible for the analysis. Across these, 53 treatments were identified among the 49 patients included (46 treated with high-flux and 3 with high cut-off membranes). Continuous veno-venous hemofiltration (CVVH) was the most frequent treatment performed amongst the studies. The extracorporeal clearance values of linezolid across the different modalities were 1.2–2.3 L/h for CVVH, 0.9–2.2 L/h for hemodiafiltration and 2.3 L/h for hemodialysis, and large variability in PK/PD parameters was reported. The optimal area under the curve/minimum inhibitory concentration (AUC/MIC) ratio was reached for pathogens with an MIC of 4 mg/L in one study only.

Conclusions

Wide variability in linezolid PK/PD parameters has been observed across critically ill septic patients with AKI treated with CRRT. Particular attention should be paid to linezolid therapy in order to avoid antibiotic failure in these patients. Strategies to improve the effectiveness of this antimicrobial therapy (such as routine use of target drug monitoring, increased posology or extended infusion) should be carefully evaluated, both in clinical and research settings.

P450-Based Drug-Drug Interactions of Amiodarone and its Metabolites: Diversity of Inhibitory Mechanisms

In this study, IC50 shift and time-dependent inhibition (TDI) experiments were carried out to measure the ability of amiodarone (AMIO), and its circulating human metabolites, to reversibly and irreversibly inhibit CYP1A2, CYP2C9, CYP2D6, and CYP3A4 activities in human liver microsomes. The [I]u/Ki,u values were calculated and used to predict in vivo AMIO drug-drug interactions (DDIs) for pharmaceuticals metabolized by these four enzymes. Based on these values, the minor metabolite N,N-didesethylamiodarone (DDEA) is predicted to be the major cause of DDIs with xenobiotics primarily metabolized by CYP1A2, CYP2C9, or CYP3A4, while AMIO and its N-monodesethylamiodarone (MDEA) derivative are the most likely cause of interactions involving inhibition of CYP2D6 metabolism. AMIO drug interactions predicted from the reversible inhibition of the four P450 activities were found to be in good agreement with the magnitude of reported clinical DDIs with lidocaine, warfarin, metoprolol, and simvastatin. The TDI experiments showed DDEA to be a potent inactivator of CYP1A2 (KI = 0.46 μM, kinact = 0.030 minute(-1)), while MDEA was a moderate inactivator of both CYP2D6 (KI = 2.7 μM, kinact = 0.018 minute(-1)) and CYP3A4 (KI = 2.6 μM, kinact = 0.016 minute(-1)). For DDEA and MDEA, mechanism-based inactivation appears to occur through formation of a metabolic intermediate complex. Additional metabolic studies strongly suggest that CYP3A4 is the primary microsomal enzyme involved in the metabolism of AMIO to both MDEA and DDEA. In summary, these studies demonstrate both the diversity of inhibitory mechanisms with AMIO and the need to consider metabolites as the culprit in inhibitory P450-based DDIs.

Population pharmacokinetics and optimization of the dosing regimen of digoxin in adult patients

Background

This study aimed to evaluate the population pharmacokinetics of digoxin in Japanese patients and establish a dosage regimen based on the pharmacokinetic data.

Methods

We analyzed 287 serum digoxin samples from 192 individuals by using the nonlinear mixed effects model. We used simulations to optimize the dosage regimen of digoxin to achieve a high likelihood of the target concentration (0.5–0.8 ng/mL).

Results

The total body clearance (CL/F ([L/h]) was calculated using the following formula: CL/F = (1.21 + 0.0532 × CLcr [(mL/min]) × (1 + 0.787 × AMD), where CLcr is the creatinine clearance and AMD is 0 in the case of concomitant administration of amiodarone and 1 otherwise. To achieve the target concentration (0.5–0.8 ng/mL), the dosage of digoxin was 0.0625 mg/day (CLcr < 35 mL/min and AMD = 0); 0.125 mg/day (CLcr, 35–65 mL/min and AMD = 0); 0.1875 mg/day (CLcr, 65–100 mL/min and AMD = 0); 0.0625 mg/every other day (CLcr < 30 mL/min and AMD = 1); and 0.0625 mg/day (CLcr, 30–85 mL/min and AMD = 1).

Conclusions

Our findings suggest that population parameters are useful for evaluating digoxin pharmacokinetics.

Investigation of the antifibrillatory drug interactions between Amiodarone and Ibutilide in isolated, perfused Rabbit hearts

In view of the reliability of the serial-shock method of measuring ventricular fibrillation threshold (VFT) in quantitatively assessing the antifibrillatory potency of many anti-arrhythmic drugs and the alarming reports of the proarrhythmic effects of several anti-arrhythmic agents, it was decided to use the above technique to study the possible interactions that may occur when anti-arrhythmic drugs from different classes are combined. Hearts isolated from New Zealand white rabbits of either sex weighing 1.5-2 kg were perfused by the Langendorff method with McEwen's solution. In six hearts, measurement of VFT was made in the absence of any drug throughout the experiments. Perfusion with either amiodarone or ibutilide produced significant, dose-dependent increase in VFT. In addition, there was no significant difference in the increase in VFT produced by the combined infusion of 1 μmol of amiodarone and 0.01 μmol of ibutilide and the summation of the increases produced by the separate infusion of these two concentrations. This is in contrast to a significant synergistic antifibrillatory effect of the combined use of lidocaine and propranolol that was reported previously. The lack of antifibrillatory interactions between amiodarone and Ibutilide may suggest the safety of combining the two drugs in the treatment of cardiac arrhythmias. However, further studies are required to establish this in the clinical setup.

Personalized medicine: importance of clinical interpretative skills for real-world patient care

Sequencing of the human genome led to great hopes and expectations for a 'genomics revolution' where disease diagnosis as well as therapies would be based on an individual's genetic makeup. Although significant progress has been made, a number of challenging hurdles must be overcome prior to the broader adoption and implementation of pharmacogenomics and personalized medicine as a part of standard patient care. One aspect of pharmacogenomics-based personalized medicine that has not garnered as much attention, a key focus of this perspective, is the importance of interpreting pharmacogenomic test results in a patient-specific clinical context, and expert physicians and other allied health care providers with the requisite expertise in clinical pharmacology and genomics who are able to provide such services.

A model predicting fluindione dose requirement in elderly inpatients including genotypes, body weight, and amiodarone

Indandione VKAs have been widely used for decades, especially in Eastern Europe and France. Contrary to coumarin VKAs, the relative contribution of individual factors to the indandione-VKA response is poorly known. In the present multicentre study, we sought to develop and validate a model including genetic and non-genetic factors to predict the daily fluindione dose requirement in elderly patients in whom VKA dosing is challenging. We prospectively recorded clinical and therapeutic data in 230 Caucasian inpatients mean aged 85 ± 6 years, who had reached international normalized ratio stabilisation (range 2.0-3.0) on fluindione. In the derivation cohort (n=156), we analysed 13 polymorphisms in seven genes potentially involved in the pharmacological effect or vitamin-K cycle (VKORC1, CYP4F2, EPHX1) and fluindione metabolism/transport (CYP2C9, CYP2C19, CYP3A5, ABCB1). We built a regression model incorporating non-genetic and genetic data and evaluated the model performances in a separate cohort (n=74).Body-weight, amiodarone intake, VKORC1, CYP4F2, ABCB1 genotypes were retained in the final model, accounting for 31.5% of dose variability. None influence of CYP2C9 was observed. Our final model showed good performances: in 83.3% of the validation cohort patients, the dose was accurately predicted within 5 mg, i.e.the usual step used for adjusting fluindione dosage. In conclusion, in addition to body-weight and amiodarone-intake, pharmacogenetic factors (VKORC1, CYP4F2, ABCB1) related to the pharmacodynamic effect and transport of fluindione significantly influenced the dose requirement in elderly patients while CYP2C9 did not. Studies are required to know whether fluindione could be an alternative VKA in carriers of polymorphic CYP2C9 alleles, hypersensitive to coumarins.

Cytochrome P450-2D6 Genotype Definition May Improve Therapy for Paroxysmal Atrial Fibrillation A Case of Syncope Following "Pill-in-the-Pocket" Quinidine plus Propafenone

Classes 1A, 1C and III anti-arrhythmics may be ineffective or induce adverse events including potentially fatal arrhythmias when administered in recommended doses. Serum levels of these medications vary widely during conventional dosing due in large part to variations in cytochrome P450-2D6 isoenzyme activity which metabolizes most antiarrhythmics in addition to over 25% of other commonly prescribed medications. 2D6 activity is also profoundly inhibited by some antiarrhythmics and other commonly used medications and varies widely between the individuals of all populations, a pattern which has resulted in separation of subjects into 4 phenotypes and genotypes consisting of poor metabolizers (PM), intermediate metabolizers (IM), efficient metabolizers (EM), and ultra-rapid metabolizers (UM). Patients with a phenotype PM classification almost universally are also genotype PM due to the possession of two inactive 2D6 alleles, with this PM pattern often inducing supratherapeutic and toxic antiarrhythmic blood levels during conventional antiarrhythmic therapy. UM individuals have supranormal levels of 2D6 activity often created by the presence of 3 or more active alleles which often induce subtherapeutic and ineffective drug levels during antiarrhythmic administration in conventional doses. We searched for evidence relating Cytochrome P450-2D6 phenotypes or genotypes to antiarrhythmic metabolism in order to judge whether this analysis might contribute to improved safety and effectiveness of antiarrhythmic medications commonly utilized in the treatment of atrial fibrillation. The available evidence strongly supported these possibilities. We also describe a patient in whom knowledge of his IM/PM CYP2D6 genotype might have prevented the only episode of syncope and myocardial stunning which developed during his 28 years of "Pill-in-a-Pocket" therapy.

Current treatment options for atrial flutter and results with cryocatheter ablation

Rhythm disturbances arising in the upper chambers of the heart are not uncommon. They are associated with a heavy burden of illness for the affected individual, as well as society in general. Atrial flutter, a re-entrant atrial tachycardia, is one such rhythm disturbance. The objective of this review article is twofold: first, to provide a brief insight into atrial flutter and the typical treatments for this arrhythmia in clinical practice; and second, to give an in-depth account of cryocatheter ablation as a relatively new treatment option for this potentially debilitating condition. The many recent clinical studies documenting the use of cryocatheter ablation for treatment of atrial flutter are presented, and their results briefly discussed. Overall, as cryocatheter ablation embeds itself among the arsenal of treatments for atrial flutter, the promising results from clinical studies appear destined to elevate cryocatheter ablation to a premier position among the treatment options for atrial flutter.

Herb-drug interaction of Fucus vesiculosus extract and amiodarone in rats: a potential risk for reduced bioavailability of amiodarone in clinical practice

Fucus vesiculosus is a seaweed claimed to be useful for obesity management. Therefore, considering the relationship between obesity and cardiovascular diseases, this work aimed to assess the potential for an herb-drug interaction among a standardized F. vesiculosus extract (GMP certificate) and amiodarone (a narrow therapeutic index drug) in rats. In a first pharmacokinetic study, rats were simultaneously co-administered with a single-dose of F. vesiculosus (575 mg/kg, p.o.) and amiodarone (50 mg/kg, p.o.); in a second study, rats were pre-treated during 14 days with F. vesiculosus (575 mg/kg/day, p.o.) and received amiodarone (50 mg/kg, p.o.) on the 15th day. Rats of the control groups received the corresponding volume of vehicle. After analysis of the pharmacokinetic data it deserves to be highlighted the significant decrease in the peak plasma concentration of amiodarone (55.4%) as well as the reduction of systemic exposure to the parent drug (~30%) following the simultaneous co-administration of F. vesiculosus extract and amiodarone. This paper reports, for the first time, the herb-drug interaction between F. vesiculosus and amiodarone, which determined a considerable decrease on amiodarone bioavailability in rats. Therefore, the therapeutic efficacy of amiodarone may be compromised by the concurrent administration of herbal slimming medicines/dietary supplements containing F. vesiculosus.

Amiodarone-associated optic neuropathy: a critical review

Although amiodarone is the most commonly prescribed anti-arrhythmic drug, its use is limited by serious toxicities, including optic neuropathy. Current reports of amiodarone-associated optic neuropathy identified from the Food and Drug Administration's Adverse Event Reporting System and published case reports were reviewed. A total of 296 reports were identified: 214 from the Adverse Event Reporting System, 59 from published case reports, and 23 from adverse events reports for patients enrolled in clinical trials. Mean duration of amiodarone therapy before vision loss was 9 months (range 1-84 months). Insidious onset of amiodarone-associated optic neuropathy (44%) was the most common presentation, and nearly one third were asymptomatic. Optic disk edema was present in 85% of cases. Following drug cessation, 58% had improved visual acuity, 21% were unchanged, and 21% had further decreased visual acuity. Legal blindness (<20/200) was noted in at least one eye in 20% of cases. Close ophthalmologic surveillance of patients during the tenure of amiodarone administration is warranted.

[Specific considerations on the prescription and therapeutic interchange of statins]

OBJECTIVE

The pharmaceutical industry currently offers six different statins in Spain and there is one more soon to be available. Choosing the most appropriate drug and dose is determined by the therapeutic target (reduction in LDL-C levels). Statin doses that decrease LDL-C at the same percentage are considered equivalent. Evaluating the pharmacokinetic characteristics of each statin can be useful when setting selection criteria, helping to determine which statin may be more appropriate for a patient based on their individual characteristics and on the other co-administered drugs.

METHODS

We reviewed the pharmacokinetics properties of each statin and its possible involvement in drug interactions.

RESULTS

CYP3A4 was responsible for the metabolism of lovastatin, simvastatin and atorvastatin; fluvastatin depends on CYP2C9; P-glycoprotein is responsible for decreased atorvastatin, pravastatin, simvastatin and lovastatin concentrations. The OATPA1B1 transporter involved in all statins' access to the hepatocyte, except for fluvastatin, is essential for rosuvastatin and pravastatin. These circumstances cause those drugs inhibiting or inducing isoenzymes or transporters' activity not to have the same effect on the different statins.

CONCLUSION

The pharmacokinetics is important when choosing the best statin and could be a limitation in the use of interchange therapeutic programmes when other drugs are present.

Cytochrome P450-mediated cardiovascular drug interactions

INTRODUCTION

There are numerous drug-drug interactions (DDIs) related to cardiovascular medications and many of these are mediated via the cytochrome P450 (CYP) system. Some of these may lead to serious adverse events and it is, therefore, essential that clinicians are aware of the important interactions that occur.

AREAS COVERED

An extensive literature search was performed to analyze the CYP-mediated cardiovascular DDIs that lead to a loss of efficacy or potential toxicity. Cardiovascular drugs may be victims or act as perpetrators of DDIs. The paper analyzes CYP-mediated drug interactions concerning anticoagulants, antiplatelet agents, antiarrhythmics, β-blockers, calcium antagonists, antihypertensive medications, lipid-lowering drugs and oral antidiabetic agents.

EXPERT OPINION

Cardiovascular DDIs involving the CYP system are numerous. Additionally, the spectrum of drugs prescribed is constantly changing, particularly with cardiovascular diseases and it is not necessarily the case that drugs that had shown safety earlier will always show safety. Clinicians are encouraged to develop their knowledge of CYP-mediated DDIs so that they can choose safe drug combination regimens, adjust drug dosages appropriately and conduct therapeutic drug monitoring for drugs with narrow therapeutic indices.

Extrapyramidal symptoms with concomitant use of amitriptyline and amiodarone in an elderly patient

BACKGROUND

Amitriptyline is a tricyclic antidepressant useful for the treatment of depression. Amiodarone is a class III antiarrhythmic agent used for the treatment of cardiac dysrhythmias.

OBJECTIVE

The objective of the current report is to describe the case of a previously asymptomatic patient receiving amitriptyline who developed extrapyramidal symptoms within 1 month of initiating concomitant treatment with amiodarone for atrial fibrillation.

CASE SUMMARY

An 82-year-old, right-handed, white woman was brought to the medical center's emergency department with speech difficulty suggesting stroke. She was noted to have continuous orobuccal dyskinesias, upper and lower extremity shaking, and dry mouth. Once it was determined that no other focal neurologic findings indicated stroke, her medications were reviewed. The patient had been taking amitriptyline 50 mg/d for the past year for insomnia without any adverse events. However, 1 month before presentation, she also initiated treatment with amiodarone 200 mg/d for atrial fibrillation and had developed the symptoms of concern shortly thereafter. The patient's amitriptyline treatment was discontinued and she received benzotropine for extrapyramidal symptoms from amitriptyline toxicity. She experienced complete resolution of dysarthric speech and limb shaking within 2 days. A total score of 7 was achieved using Naranjo's adverse drug reaction causality algorithm, suggesting amitriptyline was a probable cause of these adverse events.

CONCLUSION

This was a probable case of extrapyramidal symptoms in an elderly woman who began using amiodarone while also taking amitriptyline.

Amiodarone for the emergency care of children

Amiodarone is a class 3 antiarrhythmic agent used for a broad range of arrhythmias including adenosine-resistant supraventricular tachycardia, junctional ectopic tachycardia, and ventricular tachycardia. Compared with adults, there are few data on its use in children with arrhythmias resistant to conventional therapy. National and international guidelines for cardiopulmonary resuscitation and emergency cardiovascular care recommend its use for a variety of arrhythmias based on case reports, cohort studies, and extrapolation from adult data. This article will review the historical development, chemical properties, metabolism, indications and contraindications, and adverse effects of amiodarone in infants and children. After completing this CME activity, the reader should be able to utilize amiodarone in the pediatric population for arrhythmias and identify complications associated with its use.

Up-regulation of renal Mdr1 and Mrp2 transporters during amiodarone pretreatment in rats

Although amiodarone (AMD) is known to produce drug-drug interactions through inhibition of transporter-mediated excretion of drugs, its impact on these mechanisms during chronic treatment has not been described yet. Therefore, the aim of this study was to investigate the influence of AMD pretreatment on the main multidrug transporting proteins, Mdr1 and Mrp2, in the liver and kidney. The expression of the transporters and pharmacokinetics of their substrates, rhodamine-123 (Rho123) and endogenous conjugated bilirubin (CB), were evaluated in rats after either AMD oral pretreatments (4-14 days) or single intravenous bolus. AMD pretreatment of all durations up-regulated renal Mdr1 and Mrp2 protein expression to 155-190% and 152-223% of the control values, respectively. In agreement, we observed a corresponding increase in renal clearance of both substrates. Hepatic expression was increased only for Mdr1 to 234-270% of controls, which was associated with increased biliary elimination of amiodarone without change in Rho123 biliary clearance. Interestingly, hepatic expression of another Mdr transporter, Mdr2, was progressively decreased by amiodarone administration. Acute administration of AMD reduced Rho123 biliary clearance by 64%. Our results indicate that repeated administration of AMD to rats is associated with significant increase in hepatic and renal expression of Mdr1 and Mrp2 transporters, which may contribute to variability in pharmacokinetics of AMD and simultaneously applied drugs.

Simvastatin and Amiodarone: Emergence of a Potentially Toxic Interaction

This continuing feature updates readers on recent developments in cardiovascular pharmacotherapy. Cardiovascular disease remains the number 1 killer in the United States, and more clinical outcome trials have been conducted in cardiology than in any other field of medicine. Given this rapidly expanding knowledge base, if pharmacists stay current with developments in drug therapy, they can have a significant impact on prevention and treatment.

Gender-related Differences in Drug-induced Prolongation of Cardiac Repolarization in Prepubertal Guinea Pigs

Underlying mechanisms of drug-induced long QT syndrome are not fully understood. Our objective was to evaluate gender-related differences for block of the rapid (IKr ) or/and the slow (IKs) components of the delayed rectifier potassium current in prepubertal male and female guinea pigs (n = 120) treated with or without verapamil. Indapamide (IKs blocker) prolonged the monophasic action potential duration at 90% repolarisation (MAPD 90) in females more than in males (15.1 + 0.5 vs 9.7 + 1.3 msec; P < .05) in verapamil treated animals. In contrast, MAPD90 prolongation induced by domperidone or dofetilide (IKr blockers) was not different between genders. Verapamil treatment augmented prolongation of MAPD 90 caused by dofetilide or domperidone (P < .01). In conclusion, 1) females exhibited greater prolongation of MAPD90 when exposed to indapamide, 2) no gender-related differences were observed for I Kr blockers, and 3) verapamil treatment did not uncover gender-related differences in IKr or IKs block, although it augmented prolongation of cardiac repolarization by IKr blockers.

Benzofuran derivatives and the thyroid

Amiodarone and dronedarone are two clinically important benzofuran derivatives. Amiodarone has been used widely for treating resistant tachyarrhythmias in the past three decades. However amiodarone and its main metabolically active metabolite desethylamiodarone can adversely affect many organs, including the thyroid gland. Amiodarone-induced thyroid disorders are common and often present as a management challenge for endocrinologists. The pathogenesis of amiodarone-induced thyroid dysfunction is complex but the inherent effects of the drug itself as well as its high iodine content appear to play a central role. The non-iodinated dronedarone also exhibits anti-arrhythmic properties but appears to be less toxic to the thyroid. This review describes the biochemistry of benzofuran derivatives, including their pharmacology and the physiology necessary for understanding the cellular mechanisms involved in their actions. The known effects of these compounds on thyroid action are described. Recommendations for management of amiodarone-induced hypothyroidism and thyrotoxicosis are suggested. Dronedarone appears to be an alternative but less-effective anti-arrhythmic agent and it does not have adverse effects on thyroid function. It may have a future role as an alternative agent in patients being considered for amiodarone therapy especially those at high risk of developing thyroid dysfunction but not in severe heart failure.

Clinical relevance of pharmacokinetics and pharmacodynamics in cardiac critical care patients

Pharmacokinetics is a discipline aimed at predicting the best dosage and dosing regimen for each single drug in order to ensure and maintain therapeutically effective concentrations at the action sites. In cardiac critical care patients, various pathophysiological conditions may significantly alter the pharmacokinetic behaviour of drugs. Gastrointestinal drug absorption may be erratic and unpredictable in the early postoperative period, and so patients may be unresponsive to oral therapy; thus the intravenous route should be preferred for life-saving drugs whenever feasible. Variations in the extracellular fluid content as a response to the trauma of surgery and the fluid load or significant drug loss through thoracic drainages may significantly lower plasma concentrations of extracellularly distributed hydrophilic antimicrobials (beta-lactams, aminoglycosides and glycopeptides). Drug metabolism may be altered by the systemic inflammatory response and/or multiple organ failure and/or drug-drug pharmacokinetic interactions that can potentially occur during polytherapy, especially in immunosuppressed cardiac transplant patients. Instability of renal function may promote significant changes in body fluid concentrations of renally eliminated drugs, even in a brief period of hours. Finally, the application of extracorporeal circulation by means of cardiopulmonary bypass may significantly alter the disposition of several drugs during the operation because of acute haemodilution, hypoalbuminaemia, hypothermia and/or adsorption to the bypass equipment. Accordingly, to avoid either overexposure and the consequent increased risk of toxicity or underexposure and the consequent risk of therapeutic failure in critically ill cardiac patients, the dosing regimens of several drugs are expected to be significantly different from those suggested for clinically stable patients. Additionally, therapeutic drug monitoring may be helpful in the management of drug therapy and should be routinely used to guide individualized dose adjustments for (i) immunosuppressants whenever cytochrome P450 3A4 isoenzyme inhibitors (e.g. macrolide antibacterials, azole antifungals) or inducers (e.g. rifampicin [rifampin]) are added to or withdrawn from the regimen; and (ii) glycopeptide and aminoglycoside antibacterials whenever haemodynamically active agents (such as dopamine, dobutamine and furosemide [frusemide]) are added to or withdrawn from the regimen, and also whenever significant changes of haemodynamics and/or of renal function occur.

Hepatotoxicity after intravenous amiodarone

Amiodarone is a class III antiarrhythmic agent with a long half-life which is used to control atrial and ventricular arrhythmias, including atrial flutter and fibrillation. We describe here the case of an elderly woman (77 years of age) who was hospitalized for acute atrial fibrillation, abdominal pain, and dyspnea. In the Emergency Department, treatment with intravenous amiodarone was begun. The following day, the patient developed acute liver damage; improved liver function occurred following the withdrawal of amiodarone. Complete recovery of liver function was documented after three weeks. Unfortunately, the patient died from a severe infectious disease, with multiple organ failure.

Amiodarone modulates pharmacokinetics of low-dose methotrexate in rats

Clinical studies of low-dose methotrexate (LDMTX) pharmacokinetics document increased plasma concentrations of MTX after co-administration of the drug with amiodarone or macrolide antibiotics. As drug-drug interactions may increase the toxicity of LDMTX, a rat model was used to follow renal and biliary elimination of MTX during its constant-rate i.v. infusion and concomitant single bolus i.v. injections of amiodarone or azithromycin. The mean steady-state plasma concentration of 1.7+/-0.1 micromol/l was reached and the total clearance achieved 17.7+/-1.0 ml/min/kg. Administration of amiodarone decreased the biliary clearance of MTX to 73% of the control values (p<0.05). Correspondingly, the total clearance decreased to 72% and plasma MTX concentrations were augmented to 2.5+/-0.4 micromol/l (p<0.05). Amiodarone-treated rats exhibited a 3.3-fold decrease in the renal clearance (p<0.05) of conjugated bilirubin, which was associated with its increased plasma concentration. In contrast, azithromycin did not alter any of the MTX pharmacokinetic parameters. In conclusion, this is the first report describing the impairment of MTX hepatic elimination during co-administration with amiodarone. This study also provides new insight into acute amiodarone-induced hyperbilirubinaemia, where increased bilirubin production and decreased renal clearance may contribute to this effect. Importantly, azithromycin seems to be a safe co-medication during LDMTX therapy.

A survey of the use of herbs among patients attending secondary-level health care facilities in southwestern Nigeria

This study was carried out to evaluate the herb usage among patients attending secondary health facilities in Southwestern Nigeria. Data including allergies to drug and herbs, use of social drugs, and herbs and their perceived efficacy to herbs was collected from 265 patients (inpatients n = 65; outpatients n = 200) using structured questionnaire and patients' drug charts. A total of 15.4% of inpatients were found to be using herbs that may be potentially harmful due to drug-drug/drug-herb interactions. Nine percent experienced adverse effects with the use of herbs, whereas 2% experienced adverse reactions on coadministration with prescribed drugs. A high percent of outpatients, 38%, were using alcoholic beverages for extracting the plant materials themselves. The study showed that the use of herbs with drugs is widely practiced among patients attending secondary health care facilities in Nigeria, usually without the doctor or pharmacist's knowledge.