Pharmacokinetics of milnacipran in renal impairment

Milnacipran for the Treatment of Fibromyalgia

Purpose of review

This is a comprehensive review of the literature regarding the use of milnacipran in treating fibromyalgia. A chronic pain disorder with other system disturbances, fibromyalgia is often resistant to many therapeutic approaches. This review presents the background, evidence, and indications for using milnacipran as a treatment option for this condition.

Recent Findings

The definition of fibromyalgia has evolved over many years as it is a relatively tricky syndrome to measure objectively. Today, it is characterized by chronic, widespread pain accompanied by alterations in sleep, mood, and other behavioral aspects. A variety of therapeutic regimens currently used to treat the syndrome as a singular approach are rarely effective.Milnacipran is one of three drugs currently approved by the FDA for the treatment of fibromyalgia. It acts as a serotonin and norepinephrine reuptake inhibitor, which results in decreased pain transmission. Milnacipran remains an effective treatment option for fibromyalgia in adults and needs to be further evaluated with existing therapeutic approaches.

Summary

Fibromyalgia is a broad-spectrum disorder primarily characterized by chronic pain coupled with disturbances in cognitive functioning and sleep. The progression of this syndrome is often debilitating and significantly affects the quality of life. Milnacipran is one of three FDA-approved drugs used to alleviate the symptom burden and is comparatively more therapeutic in specific domains of fibromyalgia. A more holistic approach is needed to treat fibromyalgia effectively and further research, including direct comparison studies, should be conducted to fully evaluate the usefulness of this drug.

Pharmacotherapeutic Management of Neuropathic Pain in End-Stage Renal Disease

Background

Chronic noncancer pain is pervasive throughout the general patient population, transcending all chronic disease states. Patients with end-stage renal disease (ESRD) present a complicated population for which medication management requires careful consideration of the pathogenesis of ESRD and intimate knowledge of pharmacology. The origin of pain must also guide treatment options. As such, the presentation of neuropathic pain in ESRD can present a challenging case. The authors aim to provide a review of available classes of medications and considerations for the treatment of neuropathic pain in ESRD.

Summary

In this narrative review, the authors discuss important strategies and considerations for the treatment of neuropathic pain in ESRD, including the pathogenesis of neuropathic pain, physiological changes for consideration in ESRD patients, and disease-specific consideration for medication selection. Pharmacotherapeutic classes discussed include: anticonvulsants, antiarrhythmics, antidepressants, topicals, and opioids.

Key Message

Pain management in ESRD patients requires careful assessment of drug-specific properties, accumulation, metabolism (presence of active/toxic metabolites), extraction by dialysis, and presence of drug - drug interactions. In the absence of pharmacokinetic data in ESRD patients, therapeutic window and potential risks should be factored in the decision making along with continued monitoring throughout therapy.

Serotonin and Norepinephrine Reuptake Inhibitors

This chapter covers antidepressants that fall into the class of serotonin (5-HT) and norepinephrine (NE) reuptake inhibitors. That is, they bind to the 5-HT and NE transporters with varying levels of potency and binding affinity ratios. Unlike the selective serotonin (5-HT) reuptake inhibitors (SSRIs), most of these antidepressants have an ascending rather than a flat dose-response curve. The chapter provides a brief review of the chemistry, pharmacology, metabolism, safety and adverse effects, clinical use, and therapeutic indications of each antidepressant. Venlafaxine, a phenylethylamine, is a relatively weak 5-HT and weaker NE uptake inhibitor with a 30-fold difference in binding of the two transporters. Therefore, the drug has a clear dose progression, with low doses predominantly binding to the 5-HT transporter and more binding of the NE transporter as the dose ascends. Venlafaxine is metabolized to the active metabolite O-desmethylvenlafaxine (ODV; desvenlafaxine) by CYP2D6, and it therefore is subject to significant inter-individual variation in blood levels and response dependent on variations in CYP2D6 metabolism. The half-life of venlafaxine is short at about 5 h, with the ODV metabolite being 12 h. Both parent compound and metabolite have low protein binding and neither inhibit CYP enzymes. Therefore, both venlafaxine and desvenlafaxine are potential options if drug-drug interactions are a concern, although venlafaxine may be subject to drug-drug interactions with CYP2D6 inhibitors. At low doses, the adverse effect profile is similar to an SSRI with nausea, diarrhea, fatigue or somnolence, and sexual side effects, while venlafaxine at higher doses can produce mild increases in blood pressure, diaphoresis, tachycardia, tremors, and anxiety. A disadvantage of venlafaxine relative to the SSRIs is the potential for dose-dependent blood pressure elevation, most likely due to the NE reuptake inhibition caused by higher doses; however, this adverse effect is infrequently observed at doses below 225 mg per day. Venlafaxine also has a number of potential advantages over the SSRIs, including an ascending dose-antidepressant response curve, with possibly greater overall efficacy at higher doses. Venlafaxine is approved for MDD as well as generalized anxiety disorder, social anxiety disorder, and panic disorder. Desvenlafaxine is the primary metabolite of venlafaxine, and it is also a relatively low-potency 5-HT and NE uptake inhibitor. Like venlafaxine it has a favorable drug-drug interaction profile. It is subject to CYP3A4 metabolism, and it is therefore vulnerable to enzyme inhibition or induction. However, the primary metabolic pathway is direct conjugation. It is approved in the narrow dose range of 50-100 mg per day. Duloxetine is a more potent 5-HT and NE reuptake inhibitor with a more balanced profile of binding at about 10:1 for 5HT and NE transporter binding. It is also a moderate inhibitor of CYP2D6, so that modest dose reductions and careful monitoring will be needed when prescribing duloxetine in combination with drugs that are preferentially metabolized by CYP2D6. The most common side effects identified in clinical trials are nausea, dry mouth, dizziness, constipation, insomnia, asthenia, and hypertension, consistent with its mechanisms of action. Clinical trials to date have demonstrated rates of response and remission in patients with major depression that are comparable to other marketed antidepressants reviewed in this book. In addition to approval for MDD, duloxetine is approved for diabetic peripheral neuropathic pain, fibromyalgia, and musculoskeletal pain. Milnacipran is marketed as an antidepressant in some countries, but not in the USA. It is approved in the USA and some other countries as a treatment for fibromyalgia. It has few pharmacokinetic and pharmacodynamic interactions with other drugs. Milnacipran has a half-life of about 10 h and therefore needs to be administered twice per day. It is metabolized by CYP3A4, but the major pathway for clearance is direct conjugation and renal elimination. As with other drugs in this class, dysuria is a common, troublesome, and dose-dependent adverse effect (occurring in up to 7% of patients). High-dose milnacipran has been reported to cause blood pressure and pulse elevations. Levomilnacipran is the levorotary enantiomer of milnacipran, and it is pharmacologically very similar to the racemic compound, although the side effects may be milder within the approved dosing range. As with other NE uptake inhibitors, it may increase blood pressure and pulse, although it appears to do so less than some other medications. All medications in the class can cause serotonin syndrome when combined with MAOIs.

Bioanalytical method development and validation of milnacipran in rat plasma by LC-MS/MS detection and its application to a pharmacokinetic study

A simple, sensitive and specific liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for the quantification of milnacipran (MC) in rat plasma by using the liquid–liquid extraction method. Milnacipran-d10 (MCD10) was used as an internal standard (IS). Chromatographic separation was achieved on Zorbax SB-CN (4.6 mm×75 mm, 3.5 µm) column with an isocratic mobile phase composed of 10 mM ammonium acetate (pH 4.0) and methanol in the ratio of 25:75(v/v), at a flow-rate of 0.7 mL/min. MC and MCD10 were detected with proton adducts at m/z 247.2→230.3 and m/z 257.2→240.4 in multiple reaction monitoring (MRM) positive mode respectively. The method was validated over a linear concentration range of 1.00–400.00 ng/mL with a correlation coefficient (r²)≥0.9850. This method demonstrated intra- and inter-day precision within 5.40–10.85% and 4.40–8.29% and accuracy within 97.00–104.20% and 101.64–106.23%. MC was found to be stable throughout three freeze–thaw cycles, bench top and postoperative stability studies. This method was successfully applied to a pharmacokinetic study of rats through i.v. administration.

Milnacipran: a selective serotonin and norepinephrine dual reuptake inhibitor for the management of fibromyalgia

Milnacipran, a serotonin and norepinephrfrine reuptake inhibitor with preferential inhibition of norepinephrine reuptake over serotonin, is approved in the United States for the management of fibromyalgia. Owing to its effects on norepinephrine and serotonin, as well as its lack of activity at other receptor systems, it was hypothesized that milnacipran would provide improvements in pain and other fibromyalgia symptoms without some of the unpleasant side effects associated with other medications historically used for treating fibromyalgia. The clinical safety and efficacy of milnacipran 100 and 200 mg/day in individuals with fibromyalgia has been investigated in four large, randomized, double-blind, placebo-controlled studies and three long-term extension studies. The clinical studies used composite responder analyses to identify the proportion of individual patients reporting simultaneous and clinically significant improvements in pain, global status, and physical function, in addition to assessing improvement in various symptom domains such as fatigue and dyscognition. In the clinical studies, patients receiving milnacipran reported significant improvements in pain and other symptoms for up to 15 months of treatment. Most adverse events were mild to moderate in severity and were related to the intrinsic pharmacologic properties of the drug. Long-term exposure to milnacipran did not result in any new safety concerns. As with other serotonin and norepinephrine reuptake inhibitors, increases in heart rate and blood pressure have been observed in some patients with milnacipran treatment.

New and emerging therapeutic agents for the treatment of fibromyalgia: an update

Fibromyalgia (FM) is a chronic widespread pain condition that is estimated to affect 5 million US adults. Several molecular pathophysiologies are thought to contribute to the symptoms of FM, complicating the development of effective clinical management techniques. It is now known that abnormalities in both nociceptive and central pain processing systems are necessary (but perhaps not sufficient) to condition the onset and maintenance of FM, producing associated neuropsychologic symptoms such as pronounced fatigue, sleep abnormalities, cognitive difficulties, stress sensitivity, anxiety, and depression. Current treatment strategies are focused primarily on correcting the pathophysiologic mechanisms underlying these nervous system abnormalities. Clinical studies demonstrate the safety and efficacy of three drugs recently approved for the treatment of FM: pregabalin (an alpha-2-delta ligand), and duloxetine and milnacipran (serotonin/norepinephrine reuptake inhibitors). This review describes these pharmaceuticals in detail and discusses their current roles in FM management.

Role and rationale for the use of milnacipran in the management of fibromyalgia

Fibromyalgia (FM) is a complex syndrome characterized by chronic widespread musculoskeletal pain which is often accompanied by multiple other symptoms, including fatigue, sleep disturbances, decreased physical functioning, and dyscognition. Due to these multiple symptoms, as well as high rates of comorbidity with other related disorders, patients with FM often report a reduced quality of life. Although the pathophysiology of FM is not completely understood, patients with FM experience pain differently from the general population, most likely due to dysfunctional pain processing in the central nervous system leading to both hyperalgesia and allodynia. In many patients with FM, this aberrant pain processing, or central sensitization, appears to involve decreased pain inhibition within the spinal tract, which is mediated by descending pathways that utilize serotonin, norepinephrine, and other neurotransmitters. The reduced serotonin and norepinephrine levels observed in patients with FM suggest that medications which increase the levels of these neurotransmitters, such as serotonin and norepinephrine reuptake inhibitors (SNRIs), may have clinically beneficial effects in FM and other chronic pain conditions. Milnacipran is an SNRI that has been approved for the management of FM. In clinical trials, treatment with milnacipran for up to 1 year has been found to improve the pain and other symptoms of FM. Because FM is characterized by multiple symptoms that all contribute to the decreased quality of life and ability to function, the milnacipran pivotal trials implemented responder analyses. These utilized a single composite endpoint to identify the proportion of patients who reported simultaneous and clinically significant improvements in pain, global disease status, and physical function. Other domains assessed during the milnacipran trials include fatigue, multidimensional functioning, mood, sleep quality, and patient-reported dyscognition. This review article provides information intended to help clinicians make informed decisions about the use of milnacipran in the clinical management of patients with FM. It draws primarily on results from 2 of the pivotal clinical trials that formed the basis of approval of milnacipran in the United States by the Food and Drug Administration.

Milnacipran for the management of fibromyalgia syndrome

Fibromyalgia syndrome (FMS) is a widespread pain condition associated with fatigue, cognitive dysfunction, sleep disturbance, depression, anxiety, and stiffness. Milnacipran is one of three medications currently approved by the Food and Drug Administration in the United States for the management of adult FMS patients. This review is the second in a three-part series reviewing each of the approved FMS drugs and serves as a primer on the use of milnacipran in FMS treatment including information on pharmacology, pharmacokinetics, safety and tolerability. Milnacipran is a mixed serotonin and norepinephrine reuptake inhibitor thought to improve FMS symptoms by increasing neurotransmitter levels in descending central nervous system inhibitory pathways. Milnacipran has proven efficacy in managing global FMS symptoms and pain as well as improving symptoms of fatigue and cognitive dysfunction without affecting sleep. Due to its antidepressant activity, milnacipran can also be beneficial to FMS patients with coexisting depression. However, side effects can limit milnacipran tolerability in FMS patients due to its association with headache, nausea, tachycardia, hyper- and hypotension, and increased risk for bleeding and suicidality in at-risk patients. Tolerability can be maximized by starting at low dose and slowly up-titrating if needed. As with all medications used in FMS management, milnacipran works best when used as part of an individualized treatment regimen that includes resistance and aerobic exercise, patient education and behavioral therapies.

Milnacipran: beyond a role of antidepressant

Milnacipran is a serotonin and norepinephrine reuptake inhibitor (SNRI) with negligible effects on any presynaptic or postsynaptic receptors. Milnacipran has unique pharmacokinetic and pharmacodynamic characteristics that distinguish it from the other marketed serotonin and norepinephrine reuptake inhibitors, venlafaxine, desvenlafaxine, and duloxetine such as equipotent serotonin and norepinephrine reuptake inhibition and a linear dose-concentration trend at therapeutic doses. The half-life of milnacipran is approximately 8 hours. In addition, milnacipran does not inhibit the cytochrome P 450 system, indicating minimal propensity for drug-drug interactions. The antidepressant efficacy of milnacipran has been clearly established in a number of randomized, double-blind, placebo-controlled clinical trials, and it has been widely used for treating major depressive disorder. Moreover, evidence suggests that milnacipran is effective and tolerable in the treatment of fibromyalgia and may have usefulness for fatigue and anxiety symptoms. The current paper reviews researches conducted to date that is relevant to the efficacy, tolerability, and mechanism of action of milnacipran in the treatment of depression, fibromyalgia, and other psychiatric syndromes. Future directions of research are also identified.

Effects of milnacipran on cardiac repolarization in healthy participants

Milnacipran is approved for management of fibromyalgia in the United States. In this double-blind, placebo- and active drug-controlled study (N = 100), effects of supratherapeutic doses of milnacipran on cardiac repolarization were evaluated in healthy volunteers. The primary outcome was the largest mean difference between milnacipran and placebo in time-matched baseline-adjusted QT interval corrected for heart rate using an individual correction formula (QTcNi). In addition, data were analyzed using the Fridericia formula (QTcF) and a post hoc piecewise QTcNi analysis based on a dichotomous cut of RR interval data at 800 ms. Moxifloxacin (400 mg single dose) was used to establish assay sensitivity. Using the QTcNi method, the largest difference in baseline-adjusted QTcNi between milnacipran 300 mg bid and placebo was -4.7 ms (90% confidence interval [CI]: -9.4 to -0.1), indicating no QT prolongation. Analysis using the Fridericia formula (QTcF) showed a maximum adjusted mean change of +7.7 ms, but QTcF versus RR interval plots indicated overcorrection with this method. The piecewise QTcNi correction method demonstrated a more accurate correction for drug-induced heart rate increase; mean baseline-adjusted between-group difference was +0.9 ms (90% CI: -6.6 to 8.3). The results suggest that milnacipran would not significantly affect cardiac repolarization at clinically relevant therapeutic and supratherapeutic concentrations.

Serotonin norepinephrine reuptake inhibitors (SNRIs) in anxiety disorders: a comprehensive review of their clinical efficacy

Anxiety disorders are common psychiatric conditions that typically require long-term treatment. This review summarizes current knowledge of the pharmacological treatment of anxiety disorders with serotonin norepinephrine reuptake inhibitors (SNRIs) with specific emphasis on the findings of recent randomized clinical trials and relevant neurobiological investigations. It is now well established that gabaergic, noradrenergic and serotonergic systems play a critical role in the pathophysiology of anxiety disorders, abnormalities in these systems being related to structural and functional alterations in specific brain areas such as the amygdala, prefrontal cortex, locus coeruleus and hippocampus, as repeatedly shown by neuroimaging studies. SNRIs selectively inhibit norepinephrine and serotonin reuptake and have shown to be efficacious and generally well tolerated treatments in patients with anxiety disorders, with some potential clinical advantages over selective serotonin reuptake inhibitors (SSRIs), which are considered by many to represent first-line pharmacological treatments in patients with anxiety disorders. Anxiety disorders are characterized by a typically chronic course, high rates of comorbidity and frequent partial response to standard treatments, and the increasing use of SNRIs reflects currently unmet clinical need, in terms of overall response, remission rates and treatment tolerability.

Milnacipran

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Advances in the enantioseparation of second-generation antidepressant drugs by electrodriven methods

Stereochemistry is steadily increasing in importance in the development of new drugs, and the availability of pure enantiomer drugs can make therapy safer and more efficacious. In particular, almost all second-generation antidepressant drugs possess one or more chiral centres; however, only some of them are administered as single enantiomers. A fundamental part of the quality control of pharmaceutical formulations is the determination of enantiomeric excess and enantiomeric purity; this is also important for the therapeutic drug monitoring of depressed patients. For this purpose, efficient and reliable analytical methods are needed and electrodriven techniques (most of all CE, CEC and MEKC) are very efficient and inexpensive candidates for the role. In this review, the enantioselective electrodriven methods available for the analysis of second-generation antidepressant are presented and discussed. In particular, the following pharmacological classes of antidepressants will be considered: selective serotonin reuptake inhibitors (fluoxetine, citalopram, paroxetine, sertraline); norepinephrine reuptake inhibitors (reboxetine); serotonin and norepinephrine reuptake inhibitors (venlafaxine, milnacipran, duloxetine); and noradrenergic and specific serotonergic antidepressants (mirtazapine).

Lack of Interaction of Milnacipran with the Cytochrome P450 Isoenzymes Frequently Involved in the Metabolism of Antidepressants

OBJECTIVE

To compare the pharmacokinetics of milnacipran in extensive metabolisers (EMs) and poor metabolisers (PMs) of sparteine and mephenytoin, and to assess the influence of multiple administrations of milnacipran on the activity of cytochrome P450 (CYP) isoenzymes through its own metabolism and through various probes, namely CYP2D6 (sparteine/dextromethorphan), CYP2C19 (mephenytoin), CYP1A2 (caffeine) and CYP3A4 (endogenous 6-beta-hydroxy-cortisol excretion).

METHODS

Twenty-five healthy subjects, 12 EMs for both sparteine/dextromethorphan and mephenytoin, nine EMs for mephenytoin and PMs for sparteine/dextromethorphan (PM(2D6)) and four PMs for mephenytoin and EMs for sparteine/dextromethorphan (PM(2C19)) were administered milnacipran as a single 50 mg capsule on day 1 followed by a 50 mg capsule twice daily for 7 days. The pharmacokinetics of milnacipran and its oxidative metabolites were assessed after the first dose (day 1) and after multiple administration (day 8), and were compared for differences between CYP2D6 and CYP2C19 PMs and EMs. Metabolic tests were performed before (day -2), during (days 1 and 8) and after (day 20) milnacipran administration.

RESULTS

Milnacipran steady state was rapidly achieved. Metabolism was limited: approximately 50% unchanged drug, 30% as glucuronide and 20% as oxidative metabolite (mainly F2800 the N-dealkyl metabolite). Milnacipran administration to PM2D6 and PM2C19 subjects did not increase parent drug exposure or decrease metabolite exposure. Milnacipran oxidative metabolism is not mediated through CYP2D6 or CYP2C19 polymorphic pathways nor does it significantly interact with CYP1A2, CYP2C19, CYP2D6 or CYP3A4 activities.

CONCLUSION

Limited reciprocal pharmacokinetic interaction between milnacipran and CYP isoenzymes would confer flexibility in the therapeutic use of the drug when combined with antidepressants. Drug-drug interaction risk would be low, even if the combined treatments were likely to inhibit CYP2D6 and CYP2C19 isoenzyme activities.

Pharmacokinetics of milnacipran in liver impairment

The pharmacokinetics of single 50 mg oral and intravenous doses of milnacipran, a new non tricyclic antidepressant drug, were compared in 11 chronic liver impaired (LI) subjects and in 6 control subjects. Hepatic impairments, classified according to the PUGH scale were moderate (1 grade A), intermediate (6 grade B) and severe (4 grade C). Concentrations of unchanged drug and its conjugated form (its main metabolite) were measured in plasma and urines. In control subjects, milnacipran present high absolute bioavailability (mean value of 90%). Around 50% of the dose are excreted in urines as unchanged, while around 14% are excreted as glucuroconjugate. The remaining is composed of free and conjugated phase I inactive metabolites. Administration of milnacipran in LI subjects results in non significant changes in its pharmacokinetics, although its variability is increased. Unchanged drug exposure is not modified in LI subjects, while plasma levels of the conjugate are slightly decreased compared to the control group. This could either be due to a slight reduction in the conjugation process, or to a change in the distribution of the drug as urine excretion of both unchanged and conjugated forms are not modified compared to the control group. A few LI subjects present supra-bioavailability resulting in higher drug exposure after oral administration than after intravenous infusion. These modifications are not clinically relevant as drug exposure of the parent drug is not modified. As the unchanged drug is the only compound responsible for the activity of milnacipran, no dosage adjustment is needed in patients presenting liver impairment.