Is perhexiline essential for the optimal management of angina pectoris?

Optic neuropathy secondary to perhexiline and amiodarone

Bilateral optic disc swelling is an important clinical sign for potentially life-threatening and sight-threatening conditions, with the most common being raised intracranial pressure and pseudopapillitis. Perhexiline-related and amiodarone-related optic disc swellings are diagnoses of exclusion. This report describes the diagnosis of a man with perhexiline-induced and amiodarone-induced optic neuropathy after extensive investigation consisting of full ophthalmic examination, biochemical screen, temporal artery biopsy, CT, MRI, positron emission tomography and lumbar puncture. There was partial to complete resolution of optic neuropathy following cessation of the causative medication. We postulate that the underlying mechanism of perhexiline toxicity could be mitochondrial dysfunction related. Our case demonstrates that patients treated with perhexiline and amiodarone should be monitored closely for ocular side effects.

The validation of an LC-MS/MS assay for perhexiline and major hydroxy metabolites, and its application to therapeutic monitoring in patient plasma

AIM

Perhexiline (PEX), being developed to treat hypertrophic cardiomyopathy, is toxic at levels above the therapeutic range. Plasma level monitoring is therefore essential. The absence of a UV-absorbing chromophore has in the past required quantitative analysis of PEX in plasma using lengthy derivatization methods, followed by HPLC and fluorescence detection. The routine and urgent analysis of a large number of patient plasma samples necessitates faster and reliable analytical methodology.

RESULTS

An LC-MS/MS method, using two novel internal standards, has been validated for the quantitative measurement of PEX and its major hydroxy metabolites in human plasma.

CONCLUSION

The assay has been applied to therapeutic drug monitoring (TDM), where PEX and the ratio of the drug to cis-hydroxy perhexiline, were measured at designated intervals.

Drug Therapy for Hypertrophic Cardiomypathy: Physiology and Practice

HCM is the most common inherited heart condition occurring in 1:500 individuals in the general population. Left ventricular outflow obstruction at rest or after provocation occurs in 2/3 of HCM patients and is a frequent cause of limiting symptoms. Pharmacologic therapy is the first-line treatment for obstruction, and should be aggressively pursued before application of invasive therapy. Beta-blockade is given first, and up-titrated to decrease resting heart rate to between 50 and 60 beats per minute. However, beta-blockade is not expected to decrease resting gradients; its effect rests on decreasing the rise in gradient that accompanies exercise. For patients who fail beta-blockade the addition of oral disopyramide in adequate dose often will decrease resting gradients and offer meaningful relief of symptoms. Disopyramide vagolytic side effects, if they occur, can be greatly mitigated by simultaneous administration of oral pyridostigmine. This combination allows adequate dosing of disopyramide to achieve therapeutic goals. Verapamil utility in obstructive HCM with high resting gradients is limited by its vasodilating effects that can, infrequently, worsen gradient and symptoms. As such, we tend to avoid it in patients with high gradients and limiting heart failure symptoms. In a head-to-head comparison of intravenous drug administration in individual obstructive HCM patients the relative efficacy for lowering gradient was disopyramide > beta-blockade > verapamil. Severe symptoms in non-obstructive HCM are caused by fibrosis or severe myocyte disarray, and often by very small LV chamber size. Severe symptoms caused by these anatomic and histologic abnormalities, in the absence of obstruction, are less amenable to current pharmacotherapy. New pharmacotherapeutic approaches to HCM are on the horizon, that are to be evaluated in formal therapeutic trials.

Changes in the cardiac metabolome caused by perhexiline treatment in a mouse model of hypertrophic cardiomyopathy

Energy depletion has been highlighted as an important contributor to the pathology of hypertrophic cardiomyopathy (HCM), a common inherited cardiac disease. Pharmacological reversal of energy depletion appears an attractive approach and the use of perhexiline has been proposed as it is thought to shift myocardial metabolism from fatty acid to glucose utilisation, increasing ATP production and myocardial efficiency. We used the Mybpc3-targeted knock-in mouse model of HCM to investigate changes in the cardiac metabolome following perhexiline treatment. Echocardiography indicated that perhexiline induced partial improvement of some, but not all hypertrophic parameters after six weeks. Non-targeted metabolomics, applying ultra-high performance liquid chromatography-mass spectrometry, described a phenotypic modification of the cardiac metabolome with 272 unique metabolites showing a statistically significant change (p < 0.05). Changes in fatty acids and acyl carnitines indicate altered fatty acid transport into mitochondria, implying reduction in fatty acid beta-oxidation. Increased glucose utilisation is indirectly implied through changes in the glycolytic, glycerol, pentose phosphate, tricarboxylic acid and pantothenate pathways. Depleted reduced glutathione and increased production of NADPH suggest reduction in oxidative stress. These data delineate the metabolic changes occurring during improvement of the HCM phenotype and indicate the requirements for further targeted interventions.

Mitochondrial dysfunction caused by saturated fatty acid loading induces myocardial insulin-resistance in differentiated H9c2 myocytes: a novel ex vivo myocardial insulin-resistance model

Heart failure (HF) is often accompanied with metabolic disorders and insufficient energy production. Some previous studies have suggested an elevated serum free fatty acid (FA) due to chronic adrenergic stimulation induces myocardial insulin-resistance, which further impairs myocardial energy production. Because little is known about the pathogenesis of FA-induced cardiac insulin-resistance, we established an ex vivo cardiac insulin-resistant model and investigated the relationship between insulin-resistance and mitochondrial dysfunction. The ex vivo insulin-resistant myocytes, which was produced by treating differentiated H9c2 myocytes with palmitate (saturated FA; 0.2mM) for 24h, exhibited insulin-signaling deficiency and attenuated 2-deoxy-d-glucose (2-DG) uptake. When myocytes were pretreated with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride (TMPyP, a ROS scavenger; 200 μM), the insulin-signaling deficiency by palmitate was restored, whereas the attenuated 2-DG uptake was remained. In contrast to TMPyP, the pretreatment with perhexiline (a mitochondrial FA uptake inhibitor; 2 μM) restored the insulin-signaling deficiency and the attenuated 2-DG uptake by palmitate. Perhexiline restored the depolarized mitochondrial membrane potential (ΔΨm) and the reduced intracellular ATP by palmitate, and thereby improved the impaired GLUT4 recruitment to plasma membrane after insulin, whereas TMPyP failed to do so. These results suggested that the mitochondrial dysfunction by saturated FA loading and consequent intracellular energy shortage induced myocardial insulin-resistance in our ex vivo insulin-resistant model.

Perhexiline

Perhexiline, 2-(2,2-dicyclohexylethyl)piperidine, was originally developed as an anti-anginal drug in the 1970s. Despite its success, its use diminished due to the occurrence of poorly understood side effects including neurotoxicity and hepatotoxicity in a small proportion of patients. Recently, perhexiline's mechanism of action and the molecular basis of its toxicity have been elucidated. Perhexiline reduces fatty acid metabolism through the inhibition of carnitine palmitoyltransferase, the enzyme responsible for mitochondrial uptake of long-chain fatty acids. The corresponding shift to greater carbohydrate utilization increases myocardial efficiency (work done per unit oxygen consumption) and this oxygen-sparing effect explains its antianginal efficacy. Perhexiline's side effects are attributable to high plasma concentrations occurring with standard doses in patients with impaired metabolism due to CYP2D6 mutations. Accordingly, dose modification in these poorly metabolizing patients identified through therapeutic plasma monitoring can eliminate any significant side effects. Herein we detail perhexiline's pharmacology with particular emphasis on its mechanism of action and its side effects. We discuss how therapeutic plasma monitoring has led to perhexiline's safe reintroduction into clinical practice and how recent clinical data attesting to its safety and remarkable efficacy led to a renaissance in its use in both refractory angina and chronic heart failure. Finally, we discuss the application of pharmacogenetics in combination with therapeutic plasma monitoring to potentially broaden perhexiline's use in heart failure, aortic stenosis, and other cardiac conditions.

Can pharmacogenetics help rescue drugs withdrawn from the market?

Observations over the later half of the last century have suggested that genetic factors may be the prime determinant of drug response, at least for some drugs. Retrospectively gathered data have provided further support to the notion that genotype-based prescribing will improve the overall efficacy rates and minimize adverse drug reactions (ADRs), making personalized medicine a reality. During the last 16 years, 38 drugs have been withdrawn from major markets due to safety concerns. Inevitably, a question arises as to whether it might be possible to 'rescue' some of these drugs by promoting genotype-based prescribing. However, ironically pharmacogenetics has not perceptibly improved the risk/benefit of a large number of genetically susceptible drugs that are already in wide clinical use and are associated with serious ADRs. Drug-induced hepatotoxicity and QT interval prolongation (with or without torsade de pointes) account for 24 (63%) of these 38 drug withdrawals. In terms of the number of drugs implicated, both these toxicities are on the increase. Many others have had to be withdrawn due to their inappropriate use. This paper discusses the criteria that a drug would need to fulfill, and summarizes the likely regulatory requirements, before its pharmacogenetic rescue can be considered to be realistic. One drug that fulfils these criteria is perhexiline (withdrawn worldwide in 1988) and is discussed in some detail. For the majority of these 38 drugs there are, at present, no candidates for genetic traits to which the toxicity that led to their withdrawal may be linked. For a few other drugs where a potential candidate for a genetic trait might explain the toxicity of concern, the majority of patients who experienced the index toxicity had easily managed nongenetic risk factors. It may be possible to rescue these drugs simply by careful attention to their dose, interaction potential and prescribing patterns, but without the need for any pharmacogenetic test. In addition, the pharmacogenetic rescue of drugs might not be as effective as anticipated as hardly any pharmacogenetic test is known to have the required test efficiency to promote individualized therapy. Multiple pathways of drug elimination, contribution to toxicity by metabolites as well as the parent drug, gene-gene interactions, multiple mechanisms of toxicity and inadequate characterization of phenotype account for this lack of highly predictive tests. The clinical use of tests that lack the required efficiency carries the risks of over- or under-dosing some patients, denying the drug to others and decreasing physician vigilance of patients. Above all, at present, prescribing physicians lack an adequate understanding of pharmacogenetics and its limitations. It is also questionable whether their prescribing will comply with the requirements for pretreatment pharmacogenetic tests to make pharmacogenetic rescue a realistic goal.

Metabolic therapeutics in angina pectoris: history revisited with perhexiline

The ever-increasing burden of ischaemic heart disease and its common manifestation chronic angina pectoris calls for the exploration of other treatment options for those patients who despite the maximum conventional pharmacological and surgical interventions continue to suffer. Such exploration has led to the increasing use of new metabolically acting antianginal agents and the re-emergence of an old and somewhat forgotten pharmacological agent, perhexiline maleate. This review aims to update the cardiac nurse with knowledge to manage the care a patient receiving perhexiline maleate treatment and provide a brief review of three new metabolic agents: trimetazidine, ranolazine and etomoxir.

Concentration-time profile for perhexiline and hydroxyperhexiline in patients at steady state

AIM

To define inter- and intraday variability in plasma perhexiline concentrations, time-to-maximum plasma perhexiline concentration and variability in the ratio of hydroxyperhexiline to parent perhexiline concentrations over the course of the day in patients at steady state.

METHODS

Eight blood samples were taken over a 24-h period from 12 adult patients already taking perhexiline for the treatment of angina pectoris. These patients were assumed to be at steady state, having taken the same dose of perhexiline for more than 4 weeks and having no changes made to other drug therapy that might have affected plasma perhexiline concentrations (especially drugs that interfere with CYP2D6). Perhexiline was assayed by HPLC/FL. The percentage increase over baseline concentration was determined for each patient for both perhexiline and hydroxyperhexiline.

RESULTS

Trough plasma perhexiline concentrations from two patients were below the limit of quantification of the assay (0.05 mg l-1) and thus were excluded from the analysis. The greatest mean percentage increase in plasma perhexiline concentration over the day was 21% (95%CI 9%, 33%, range -19% to 45%) which occurred 6 h postdose. The greatest mean percentage increase in plasma hydroxyperhexiline concentration was 10.8% (95%CI -5.3%, 26.9%, range -13% to 60%) which occurred 4 h postdose. However individual patients demonstrated > 60% intraday variability in perhexiline concentrations which was not related to the concomitant use of drugs that affect CYP2D6 activity. Changes in random plasma perhexiline concentration which are attributed to changes in concomitant drug therapy should be supported by additional kinetic data. Inter-day variability in plasma perhexiline concentration as determined by the ratio of C24 : C0 was small (mean 0.90, 95%CI 0.77, 1.03) which supports C0 as the best sampling time for perhexiline concentration monitoring. The variability in C24 : C0 for hydroxyperhexiline concentrations was smaller (mean 0.96, 95%CI 0.81, 1.11). Variability in the ratio of plasma concentrations of hydroxyperhexiline to perhexiline over the day was also small. The ratio of plasma hydroxyperhexiline to perhexiline concentration over the day fell within a narrow range for all subjects with 95% confidence intervals being < 15% for eight patients and < 25% for the remaining patient. This suggests that formation of the metabolite occurs rapidly and may be presystemic. It also supports the calculation of the hydroxyperhexiline : perhexiline ratio (in patients at steady state) on blood samples taken at any time during the dosing interval.

CONCLUSIONS

The within-day variability in plasma perhexiline concentrations was small. While C0 is probably the best time for therapeutic drug monitoring purposes, it is not unreasonable to use samples drawn at any time during the dosing interval. The therapeutic range used in this hospital (0.15-0.6 mg l-1) was devised from earlier work using 4 h postdose blood sampling which is close to the 'peak' concentration and a mean of 16% higher than C0 in this study. This increase is probably clinically insignificant and a different C0 range is therefore not warranted.

Population pharmacokinetics of perhexiline from very sparse, routine monitoring data

Using NONMEM, the population pharmacokinetics of perhexiline were studied in 88 patients (34 F, 54 M) who were being treated for refractory angina. Their mean +/- SD (range) age was 75 +/- 9.9 years (46-92), and the length of perhexiline treatment was 56 +/- 77 weeks (0.3-416). The sampling time after a dose was 14.1 +/- 21.4 hours (0.5-200), and the perhexiline plasma concentrations were 0.39 +/- 0.32 mg/L (0.03-1.56). A one-compartment model with first-order absorption was fitted to the data using the first-order (FO) approximation. The best model contained 2 subpopulations (obtained via the $MIXTURE subroutine) of 77 subjects (subgroup A) and 11 subjects (subgroup B) that had typical values for clearance (CL/F) of 21.8 L/h and 2.06 L/h, respectively. The volumes of distribution (V/F) were 1470 L and 260 L, respectively, which suggested a reduction in presystemic metabolism in subgroup B. The interindividual variability (CV%) was modeled logarithmically and for CL/F ranged from 69.1% (subgroup A) to 86.3% (subgroup B). The interindividual variability in V/F was 111%. The residual variability unexplained by the population model was 28.2%. These results confirm and extend the existing pharmacokinetic data on perhexiline, especially the bimodal distribution of CL/F manifested via an inherited deficiency in hepatic and extrahepatic CYP2D6 activity.

Systematic review of the efficacy and safety of perhexiline in the treatment of ischemic heart disease

Perhexiline was introduced about 30 years ago and rapidly gained a reputation for efficacy in the management of angina pectoris. However, hepatic and neurological adverse effects associated with perhexiline administration led to a marked decline in its use. The drug was originally classified as a coronary vasodilator, and later as a calcium channel antagonist, but recent data suggests that it acts as a cardiac metabolic agent, through inhibition of the enzyme, carnitine palmitoyltransferase-1 (CPT-1). Given the drug's unique anti-ischemic action and favorable hemodynamic profile, together with an improved understanding of the mechanisms underlying the adverse effects of the drug and the clear clinical need for additional therapies in refractory patients, perhexiline is currently being re-appraised as a potentially useful agent in the management of severe myocardial ischemia. Perhexiline is being considered for registration or re-registration in a number of countries and is being evaluated in a large-scale clinical trial in elderly patients with aortic stenosis and myocardial ischemia. This systematic review examines the evidence from available published literature in relation to the efficacy and tolerability of perhexiline in the treatment of cardiac disease. While there is a lack of well designed controlled trials using objective end-points to determine efficacy (almost all trials used a crossover design, included small numbers of patients and had limited statistical analysis of results), there is consistency in the data available that perhexiline is considerably more effective than placebo when used as monotherapy. Furthermore, it affords additional symptom relief in those already receiving maximal conventional anti-anginal therapy. However, there is a paucity of trials demonstrating the efficacy of low dosages of perhexiline (100 to 200 mg/day) in patients with refractory angina pectoris. Available evidence also suggests that the incidence of adverse events can be minimised, and the efficacy maintained, by keeping plasma perhexiline concentrations within a therapeutic range (150 to 600 micro g/L)

Inhibition of HERG channels stably expressed in a mammalian cell line by the antianginal agent perhexiline maleate

Perhexiline has been used as an anti-anginal agent for over 25 years, and is known to cause QT prolongation and torsades de pointes. We hypothesized that the cellular basis for these effects was blockade of I(Kr). A stable transfection of HERG into a CHO-K1 cell line produced a delayed rectifier, potassium channel with similar properties to those reported for transient expression in Xenopus oocytes. Perhexiline caused voltage- and frequency-dependent block of HERG (IC50 7.8 microM). The rate of inactivation was increased and there was a 10 mV hyperpolarizing shift in the voltage-dependence of steady-state inactivation, suggestive of binding to the inactivated state. In conclusion, perhexiline potently inhibits transfected HERG channels and this is the probable mechanism for QT prolongation and torsades de pointes. Channel blockade shows greatest affinity for the inactivated state.

The effects of perhexiline on the rat coronary vasculature

The predominant site and mechanism(s) of perhexiline-induced coronary vasodilatation were investigated in the rat heart. Perhexiline was more potent in the Langendorff perfused heart than in the left anterior descending coronary artery (EC50; 0.27 microM, confidence limits 0.19-0.39: 2.7 microM, 2.0-3.4, respectively). Selective endothelial inactivation with Triton X-100 in the perfused heart, reduced the response to perhexiline 1 microM (76+8% to 30+3% of control). 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) 3 microM, Nomega-nitro-L-arginine 100 microM, or a combination of the latter with indomethacin 10 microM, had no significant effect on responses to perhexiline in the perfused heart. Unlike bradykinin-induced vasodilatation, responses to perhexiline were not inhibited by tetrabutylammonium 1 mM, or charybdotoxin 20 nM. SKF525A 5 microM inhibited both perhexiline and bradykinin responses, while apamin 1 microM and glibenclamide 3 microM inhibited neither. Perhexiline exerts partially endothelium-dependent coronary vasodilator effects in the rat, predominantly on small coronary arteries, which appear to be independent of nitric oxide (NO), prostacyclin and the endothelium-derived hyperpolarising factor (EDHF) released by bradykinin.

Method for the analysis of perhexiline and its hydroxy metabolite in plasma using high-performance liquid chromatography with precolumn derivatization

A high-performance liquid chromatographic method for the analysis of perhexiline and its monohydroxy metabolite in plasma has been developed. After a simple extraction procedure, the analytes are derivatized over a 30-min period with trans-4-nitrocinnamoyl chloride. The derivatized products are monitored at 340 nm following separation on a 5-micron phenyl reversed-phase column under isocratic conditions. The limits of detection for perhexiline and its hydroxy metabolite are 0.03 and 0.02 mg/l, respectively. The between-day and within-day assay coefficients of variation for perhexiline and its hydroxy metabolite at concentrations of 0.2 and 1.0 mg/I were less than 10%. The method has proved robust and suitable for the routine monitoring of perhexiline and hydroxyperhexiline.

Interaction of serotonin re-uptake inhibitors with perhexiline

OBJECTIVE

To report two cases of perhexiline toxicity associated with selective serotonin re-uptake inhibitor (SSRI) treatment.

CLINICAL PICTURE

Serum perhexiline concentrations progressively increased after a 69-year-old man was concurrently prescribed paroxetine for the treatment of depression. An 84-year-old woman was admitted to hospital with severe, symptomatic perhexiline toxicity associated with fluoxetine treatment.

TREATMENT

In both cases, perhexiline therapy was suspended and treatment with SSRIs was withdrawn.

OUTCOME

Serum perhexiline concentrations declined following the withdrawal of paroxetine in one case, but in the case of the second patient perhexiline concentrations were extremely slow to decrease, resulting in referral to a rehabilitative care unit for convalescence.

CONCLUSIONS

Serum perhexiline concentrations may be elevated during concurrent treatment with SSRIs, potentially resulting in severe toxicity.

Relationship between plasma perhexiline concentration and symptomatic status during short-term perhexiline therapy

We tested the hypothesis that resolution versus persistence of symptomatic ischaemia and/or development of nausea/dizziness on the third day of loading with perhexiline maleate (PM), is correlated with perhexiline plasma concentrations after the standard loading phase in patients with acute coronary syndromes. Forty consecutive patients with either unstable angina pectoris or non-Q-wave myocardial infarction with persistent angina pectoris, despite maximal pharmacological therapy (other than PM), were studied. All patients received PM 400 mg/day for 3 days and 200 mg/day thereafter. On days 2 and 3 observers blinded to the 72-96 h plasma perhexiline concentration assessed the patient regarding episodes of angina and/or nausea/dizziness. On the third day of loading with PM, 12 patients experienced angina and 11 patients had nausea and/or dizziness. Plasma perhexiline concentrations at 72-96 h varied widely: mean 0.46 +/- 0.26 (range 0.11-1.77) microgram/ml. There was a relationship of borderline statistical significance between resolution of anginal symptoms and plasma perhexiline concentration > 0.15 microgram/ml (p = 0.055). There was a close relationship between emergence of nausea/dizziness with plasma perhexiline concentration > 0.06 microgram/ml (p < 0.01). We conclude that this study (a) suggests that PM exerts incremental antianginal effects over those of other antiischaemic agents in patients with acute coronary syndromes and (b) establishes that the development of nausea and/or dizziness in such patients is strongly predictive of accumulation of perhexiline beyond the therapeutic range of the drug.