Therapeutic drug monitoring for drugs used in the treatment of substance-related disorders: literature review using a therapeutic drug monitoring appropriateness rating scale

Levomethadone Therapeutic Drug Monitoring to Aid Opioid Withdrawal Therapy: A Short Communication

BACKGROUND

Therapeutic drug monitoring (TDM) is recommended for opioid maintenance therapy with levomethadone. However, TDM has not yet been applied to monitor opioid withdrawal therapy clinically, although tools to improve it are required.

METHODS

In this observational cohort study, repeated TDM with levomethadone was performed according to a prospective opioid withdrawal study protocol. Objective and subjective opioid withdrawal symptoms were measured using validated rating scales and correlated to levomethadone plasma concentrations. Plasma levels were measured using high-pressure liquid chromatography with column switching and spectroscopic detection of methadone and its major metabolite.

RESULTS

This study included 31 opioid-dependent patients who participated in standardized opioid withdrawal therapy. The serum levels of levomethadone were found to be highly variable and below the recommended therapeutic reference range of 250 ng/mL for maintenance therapy. These serum levels were positively correlated with dosage (r = 0.632; P < 0.001) and inversely correlated with subjective (r = -0.29; P = 0.011) and objective (r = -0.28; P = 0.014) withdrawal symptoms.

CONCLUSIONS

The evidence provided sheds light on how to improve levomethadone withdrawal therapy in patients with opioid dependence. It seems likely that higher initial doses at the beginning and lower dose reductions would have been advantageous. TDM can enhance the safety of opioid withdrawal therapies, minimize withdrawal symptoms, and reduce dropout rates.

Pharmacological Treatments and Therapeutic Drug Monitoring in Patients with Chronic Pain

Pain is an unpleasant sensory and emotional experience that affects every aspect of a patient's life and which may be treated through different pharmacological and non-pharmacological approaches. Analgesics are the drugs most commonly used to treat pain, and in specific situations, the use of opioids may be considered with caution. These drugs, in fact, do not always induce optimal analgesia in patients, and several problems are associated with their use. The purpose of this narrative review is to describe the pharmacological approaches currently used for the management of chronic pain. We review several aspects, from the pain-scale-based methods currently available to assess the type and intensity of pain, to the most frequently administered drugs (non-narcotic analgesics and narcotic analgesics), whose pharmacological characteristics are briefly reported. Overall, we attempt to provide an overview of different pharmacological treatments while also illustrating the relevant guidelines and indications. We then report the strategies that may be used to reduce problems related to opioid use. Specifically, we focus our attention on therapeutic drug monitoring (TDM), a tool that could help clinicians select the most suitable drug and dose to be used for each patient. The actual potential of using TDM to optimize and personalize opioid-based pain treatments is finally discussed based on recent scientific reports.

Development and validation of a rapid liquid chromatography/tandem mass spectrometry method to quantitate gabapentin and buprenorphine in human serum

RATIONALE

Gabapentin has shown initial promise as an opioid-sparing medication in pain patients as well as a treatment for opioid withdrawal and liquid chriomatography/tandem mass spectrometry (LC/MS/MS) is often used for clinical monitoring. Despite reports of validated tandem mass spectrometric methods for the determination of gabapentin and buprenorphine, mechanisms for the collision-induced fragmentation have not been adequetely described.

METHODS

A rapid analytical method has been developed to determine gabapentinoid, gabapentin, and the partial opioid agonist, buprenorphine, in 20 μL of human serum using LC/MS/MS with a chromatographic run time of 2 min. A simplified sample cleanup procedure using methanol precipitation of serum proteins/lipids followed by evaporation and reconstitution in mobile phase was demonstrated. Gabapentin and buprenorphine were detected following positive ion electrospray ionization using multiple-reaction monitoring. The internal standard approach was used for quantitation with labeled gabapentin-D10 and buprenorphine-D4 serving as internal standards. Using organic reaction principals and stable isotope labels, collision-induced fragmentation mechanisms for both gabapentin and buprenorphine are proposed. The method was validated according to the FDA Guidance for Industry - Bioanalytical Method Validation.

RESULTS

Accuracy was demonstrated by error values ≤15% for buprenorphine and ≤6% for gabapentin. The inter-day precision was ≤4.88% and 15.59% for gabapentin and buprenorphine and the intra-day precision was ≤5.20% and 11.65% for gabapentin and buprenorphine. The lower limit of quantitation corresponded to 10 ng/mL for gabapentin and 1 ng/mL for buprenorphine in serum. Recoveries were 104 ± 2.55% and 85 ± 2.03% for gabapentin and buprenorphine, respectively.

CONCLUSIONS

Concentrations of gabapentin and buprenorphine were determined for five authentic human serum samples to further validate the utility of the method and applicable to therapeutic drug monitoring beyond its use as a drug screening assay. Furthermore, new mechanisms for the collision-induced dissociation of gabapentin and buprenorphine have been proposed.

Buprenorphine-cannabis interaction in patients undergoing opioid maintenance therapy

Buprenorphine is a partial μ-opioid agonist widely used for opioid maintenance therapy (OMT). It is mainly metabolized to pharmacologically active norbuprenorphine by the cytochrome P450 (CYP) isozyme 3A4. This may give rise to drug-drug interactions under combinations with inhibitors or inducers of CYP3A4. Cannabis is a potential inhibitor of CYP3A4, and there is a large degree of concomitant cannabis use among OMT patients. We performed a retrospective analysis on liver healthy OMT patients substituted with buprenorphine, either with (n = 15) or without (n = 17) concomitant use of cannabis. Patients with additional illicit drugs or medications affecting CYP3A were excluded. Measured blood concentrations of buprenorphine and norbuprenorphine were compared between the two groups. Cannabis users and non-users received similar doses, but users had 2.7-fold higher concentrations of buprenorphine (p < 0.01) and 1.4-fold for norbuprenorphine (1.4-fold, p = 0.07). Moreover, the metabolite-to-parent drug ratio was 0.98 in non-users and 0.38 in users (p = 0.02). Female gender did not produce significant effects. These findings indicate that cannabis use decreases the formation of norbuprenorphine and elevates buprenorphine and norbuprenorphine concentrations in blood most probably by inhibition of CYP3A4. The pharmacokinetic interaction may give rise to enhanced or altered opioid activity and risk of intoxications. Physicians should inform patients about this risk and supervise cannabis users by regular control of buprenorphine blood levels, i.e., by therapeutic drug monitoring.

Determination of acamprosate in human plasma by UPLC-MS/MS: Application to therapeutic drug monitoring

Acamprosate is a medication used to treat alcohol dependence. Therapeutic drug monitoring is important in drugs for the treatment of substance-related disorders. Therefore, in this study, a new selective, very simple and rapid ultra-performance liquid chromatography-tandem mass spectrometer method was developed for the therapeutic drug monitoring of acamprosate. The developed method allows the determination of acamprosate in human plasma. The method was validated in terms of selectivity and linearity, which was in the range of 100-1,200 ng/ml for acamprosate. Intra-assay and inter-assay accuracy and precision were within the acceptable limits of the Eueopean Medicines Agency guideline. The lower limit of quantitation was 100 ng/ml for acamprosate. The developed method was successfully applied for therapeutic drug monitoring in patient plasma samples.

Impact of Pharmacological Treatments for Opioid Use Disorder on Mortality

The use of pharmacological treatments for opioid use disorders, including methadone, buprenorphine and naltrexone has been associated with a reduction in mortality compared with illicit opioid use. However, these treatments can also contribute significantly to the risk of death. The opioid agonists methadone and buprenorphine achieve clinical efficacy in patients with an opioid use disorder through suppressing craving and diminishing the effectiveness of illicit opioid doses, while the antagonist naltrexone blocks the action of opioids. Pharmacological differences between opioid pharmacotherapies then create different temporal patterns of protection and mortality risk, different risks of relapse to illicit opioid use, and variations in direct and indirect toxicity, which are revealed in clinical and epidemiological studies. Induction onto methadone and the cessation of oral naltrexone treatment are associated with an elevated risk of opioid poisoning, which is not apparent in patients treated with buprenorphine or sustained-release naltrexone. Beyond drug-related mortality, these pharmacotherapies can impact a participant's risk of death. Buprenorphine may also have some advantages over methadone in patients with depressive disorders or cardiovascular abnormalities. Naltrexone, which is also commonly prescribed to manage problem alcohol use, may reduce deaths in chronic co-alcohol users. Understanding these pharmacologically driven patterns then guides the judicious choice of drug and dosing schedule and the proactive risk management that is crucial to minimising the risk of death in treatment.

Urine Assay to Measure Tenofovir Concentrations in Patients Taking Tenofovir Alafenamide

Background: HIV pre-exposure prophylaxis (PrEP) with tenofovir/emtricitabine is effective when taken daily. Previously, we developed a urine assay capable of detecting the prodrug tenofovir (TFV) in patients taking tenofovir disoproxil fumarate (TDF)-based PrEP. However, tenofovir alafenamide (TAF) has replaced TDF due to its different safety profile for HIV treatment and was recently approved as PrEP. Given the need to ensure the aforementioned assay remains available for the purpose of objective adherence monitoring, it is critical to ensure its accuracy for detecting TFV in patients taking TAF. Methods: Blood and urine samples were collected from 3 cohorts of patients: (1) 10 participants living with HIV (PLWH) with suppressed virus on a TAF-based regimen, (2) 10 HIV-participants administered 1 dose of TAF/FTC followed by urine and plasma sampling for 7 days starting 1-3 h post-dose, and (3) 10 HIV-participants administered 7 doses of TAF/FTC followed by urine and plasma sampling for 10 days starting 1-3 h after the last dose. Samples were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with high sensitivity and specificity for TFV. HIV-samples were compared to a historical cohort administered one dose of TDF/FTC. Results: PLWH were 90% male, 40% African American, and 10% Hispanic (mean age = 57 y; SD 8.88 y). HIV-participants were 55% male and 70% Caucasian (mean age = 31.6 y; SD 7.70 y). Samples from PLWH demonstrated TFV concentrations 2 logs higher in urine than plasma (1,000 ng/mL vs ±10 ng/mL) at the time of collection. Urine samples following a single dose of TAF in HIV-participants yielded TFV concentrations ranging from 100 to 1,000 ng/mL 1-3 h post-dose and remained >100 ng/mL for 6 days in 8 of 10 participants. Urine samples collected after 7 consecutive doses of TAF yielded TFV concentrations >1,000 ng/mL 1-3 h after dosing discontinuation, with TFV concentrations >1,00 ng/mL 7 days post discontinuation in 8 of 10 participants. Urine TFV concentrations following TAF administration were comparable to those from a historical cohort administered TDF/FTC. Plasma TFV concentrations were low(±10 ng/mL) in both HIV-cohorts at all time points. Conclusions: TFV persists in urine at detectable concentrations in participants taking TAF/FTC for at least 7 days despite largely undetectable plasma concentrations, with urine TFV concentrations comparable to patients taking TDF/FTC. This study demonstrates the ability of a urine TFV assay to measure recent TAF adherence.

Determination of hydroxybupropion in human serum for routine therapeutic drug monitoring in psychiatry: A tool for dose-individualization in treatment with bupropion

Therapeutic drug monitoring (TDM) has become a clinical routine in psychiatry. Nevertheless, for bupropion there is only one method available that is suitable for routine use. However, it involves a complex sample clean-up. Owing to the instability of bupropion in serum, the main and active metabolite hydroxybupropion was chosen as the target substance. Therefore, a simple and robust high-performance liquid chromatography method for the quantification of hydroxybupropion in serum was developed and validated. A volume of 30 μL serum was used for easy sample clean-up, based on protein precipitation with acetonitrile followed by online solid-phase extraction. As hydroxybupropion was present in high serum concentrations, UV detection was possible. Owing to the commonly available instrumentation, the method could easily be integrated in routine TDM. The newly developed method was validated following the guidelines for bioanalytical method validation of the European Medicines Agency and US Food and Drug Administration. The lower limit of quantification was 100 ng/mL (0.391 μm) and linearity was shown between 100 and 2500 ng/mL. Intraday and interday precision ranged from 1.17 to 6.79% and from 6.07 to 9.41%, respectively. Intraday and interday accuracy ranged from 89.97 to 110.86% and from 95.05 to 101.2%. The method was shown to be selective, accurate and precise. Additionally, the method was successfully implemented in the therapeutic drug monitoring laboratory of the Department of Psychiatry, Psychosomatics and Psychotherapy at the University Hospital of Würzburg, Germany. Six months of routine analysis showed a rather low correlation between applied dose and serum concentration and therefore the necessity of TDM for dose-individualization in the treatment with bupropion.

Therapeutic Drug Monitoring of Naltrexone and 6β-Naltrexol During Anti-craving Treatment in Alcohol Dependence: Reference Ranges

Aims

Aim of this study was to associate concentration of naltrexone and its major active metabolite 6β-naltrexol in blood with therapeutic outcome during treatment with naltrexone in subjects with alcohol dependence. Treatment with the μ-opiate receptor antagonist naltrexone has been shown to reduce craving for alcohol and alcohol intake in patients suffering from alcohol dependence.

Short summary

This article shows the use of therapeutic drug monitoring in alcohol dependent patients, who are treated with naltrexone. The plasma concentrations of naltrexone and 6β-naltrexol showed high inter-individual variability. They were predictive for treatment response, as they correlated significantly with the reduction of alcohol craving.

Methods

Naltrexone and 6β-naltrexol were analysed by high performance liquid chromatography with column switching and spectrophotometric detection. Alcohol craving was assessed with the Obsessive-Compulsive Drinking Scale (OCDS).

Results and conclusions

The study included 43 patients who were treated with naltrexone with a dose of 50 mg/day. Blood was taken for drug analysis 8 h after the last dose of the day at Week 4, 8 and 12. The plasma concentrations of naltrexone and 6β-naltrexol showed high inter-individual variability. They were predictive for treatment response, as they correlated significantly with the reduction of alcohol craving. Defining patients with OCDS reduction of 70% or higher as responders, the mean±SD concentration of naltrexone plus naltrexol was 22 ± 13 ng/ml compared to 15 ± 8 ng/ml in patients with score reductions of 1-69%. Further analyses indicated that concentrations of 17-50 ng/ml at 8 h and 7-20 ng/ml at 24 h after drug intake were required for treatment response.

Conclusions

Since plasma concentration of naltrexone plus 6β-naltrexol was found to be predictive for reduction of alcohol craving, it is concluded that therapeutic drug monitoring has the potential to enhance naltrexone's moderate therapeutic efficiency in patients with alcohol dependence.

Methadone Dose Adjustments, Plasma R-Methadone Levels and Therapeutic Outcome of Heroin Users: A Randomized Clinical Trial

AIMS

We aimed to improve the retention in treatment and therapeutic outcome of methadone maintenance treatment (MMT) patients by adjusting the oral methadone dose in order to reach a "target" plasma R-methadone level (80-250 ng/mL).

METHODS

A multicenter randomized controlled trial was organized.

RESULTS

The intention-to-treat statistical analysis showed that repeated dose adjustments performed in order to obtain therapeutic plasma R-methadone levels did not improve retention in treatment of heroin-dependent patients. However, patients having plasma methadone levels in the "target range" at the beginning of the study had a better retention in treatment than controls. Furthermore, patients succeeding in keeping plasma R-methadone target levels (per protocol analysis) remained in treatment and improved their social scores better than controls. -Conclusion: Although the primary endpoint of this study was not demonstrated, a post hoc and a per protocol analysis suggested that patients in MMT with plasma R-methadone concentrations in the target range have a better therapeutic outcome than controls.

Urine assay for tenofovir to monitor adherence in real time to tenofovir disoproxil fumarate/emtricitabine as pre-exposure prophylaxis

OBJECTIVES

Tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) is approved for pre-exposure prophylaxis (PrEP) against HIV infection. Adherence is critical for the success of PrEP, but current adherence measurements are inadequate for real-time adherence monitoring. We developed and validated a urine assay to measure tenofovir (TFV) to objectively monitor adherence to PrEP.

METHODS

We developed a urine assay using high-performance liquid chromatography coupled to tandem mass spectrometry with high sensitivity/specificity for TFV that allowed us to determine TFV concentrations in log₁₀ categories between 0 and 10 000 ng/mL. We validated the assay in three cohorts: (1) HIV-positive subjects with undetectable viral loads on a TDF/FTC-based regimen, (2) healthy HIV-negative subjects who received a single dose of TDF/FTC, and (3) HIV-negative subjects receiving daily TDF/FTC as PrEP for 24 weeks.

RESULTS

The urine assay detected TFV with greater sensitivity than plasma-based measures and with a window of measurements within 7 days of the last TDF/FTC dose. Based on the urine log-linear clearance after the last dose and its concordance with all detectable plasma levels, a urine TFV concentration > 1000 ng/mL was identified as highly predictive of the presence of TFV in plasma at > 10 ng/mL. The urine assay was able to distinguish high and low adherence patterns within the last 48 h (> 1000 ng/mL versus 10-1000 ng/mL), as well as nonadherence (< 10 ng/mL) extended over at least 1 week prior to measurement.

CONCLUSIONS

We provide proof of concept that a semiquantitative urine assay measuring levels of TFV could be further developed into a point-of-care test and be a useful tool to monitor adherence to PrEP.

Serum concentrations of hydroxybupropion for dose optimization of depressed patients treated with bupropion

BACKGROUND

Bupropion is a dopamine and norepinephrine reuptake inhibitor approved for the treatment of depression and smoking cessation. According to the recently published reviews, it is a candidate for therapeutic drug monitoring (TDM) to improve therapeutic outcomes and reduce risks of intolerability or intoxication. In practice, however, the use of TDM is limited due to the chemical instability of bupropion. This investigation sought to determine if the major, active, and chemically stable metabolite 4-hydroxybupropion is a suitable measure to guide antidepressant drug therapy with bupropion.

METHODS

4-Hydroxybupropion serum levels were measured using a newly developed and validated high-performance liquid chromatography assay with ultraviolet detection. They correlated with therapeutic effects measured by the clinical global impression scale for improvement.

RESULTS

The study included 52 patients (50% women). Patients who were markedly improved according to the clinical global impression scale score had significantly (P = 0.042) higher 4-hydroxybupropion serum levels than those with moderate or minimal improvement (mean ± SD, 1113 ± 576, 825 ± 398, and 475 ± 331 ng/mL, respectively). Analysis of receiver operating characteristics revealed significant predictive properties of 4-hydroxybupropion serum levels (P = 0.002) for marked improvement with a lower threshold level of 858 ng/mL. Under similar mean doses (265 ± 107 versus 239 ± 100 mg, respectively), women attained significantly higher serum levels than men (1050 ± 524 versus 589 ± 352 ng/mL, respectively) and exhibited a better therapeutic effect (P = 0.018).

CONCLUSIONS

Despite multiple limitations of this naturalistic study, evidence could be given that the measurement of 4-hydroxybupropion in serum is suitable to perform TDM for bupropion. Blood levels should be above 860 ng/mL to attain therapeutic improvement. Potential sex differences in bupropion pharmacokinetics, probably due to differential activities of CYP2B6, should be taken into account when the drug is prescribed.

Population pharmacokinetic/pharmacodynamic model of clozapine for characterizing the relationship between accumulated exposure and PANSS scores in patients with schizophrenia

BACKGROUND

The aim of this study was to characterize the relationship between accumulated exposure of clozapine and changes in Positive and Negative Syndrome Scale (PANSS) score in Chinese patients with schizophrenia by pharmacokinetic/pharmacodynamic (PK/PD) modeling.

METHODS

Sparse clozapine PK data and PANSS scores were collected from 2 clinical studies of Chinese inpatients with schizophrenia. Two other rich PK data sets were included for more accurate assessment of clozapine PK characteristics. The relationship between clozapine-accumulated exposure and PANSS score was investigated using linear, log-linear, E(max), and sigmoid models, and each model was evaluated using visual predictive condition and normalized prediction distribution error methods. Simulations based on the final PK/PD model were preformed to investigate the effect of clozapine on PANSS scores under different dose regimens.

RESULTS

A total of 1391 blood clozapine concentrations from 198 subjects (180 patients and 18 healthy volunteers) and 576 PANSS scores from 137 patients were included for PK and PK/PD analysis. A first-order 2-compartment PK model with covariates gender and smoking status influencing systemic clearance adequately described the PK profile of clozapine. The decrease in total PANSS score during treatment was best characterized using cumulated clozapine area under the curve (AUC) data in the E(max) model. The maximum decrease in PANSS during clozapine treatment (Emax) was 55.4%, and the cumulated AUC(50) (cAUC(50)) required to attain half of E(max) was 296 mg·L(-1)·h(-1)·d(-1). The simulations demonstrated that the accelerated dose titration and constant dose regimens achieved a similar maximum drug response but with a slower relief of symptoms in dose titration regimen.

CONCLUSIONS

The PK/PD model can describe the clinical response as measured by decreasing PANSS score during treatment and may be useful for optimizing the dose regimen for individual patients.

Pharmacological maintenance treatments of opiate addiction

For people seeking treatment, the course of heroin addiction tends to be chronic and relapsing, and longer duration of treatment is associated with better outcomes. Heroin addiction is strongly associated with deviant behaviour and crime, and the objectives in treating heroin addiction have been a blend of humane support, rehabilitation, public health intervention and crime control. Reduction in street heroin use is the foundation on which all these outcomes are based. The pharmacological basis of maintenance treatment of dependent individuals is to minimize withdrawal symptoms and attenuate the reinforcing effects of street heroin, leading to reduction or cessation of street heroin use. Opioid maintenance treatment can be moderately effective in suppressing heroin use, although deviations from evidence-based approaches, particularly the use of suboptimal doses, have meant that treatment as delivered in practice may have resulted in poorer outcomes than predicted by research. Methadone treatment has been 'programmatic', with a one-size-fits-all approach that in part reflects the perceived need to impose discipline on deviant individuals. However, differences in pharmacokinetics and in side-effects mean that many patients do not respond optimally to methadone. Injectable diamorphine (heroin) provides a more reinforcing medication for some 'nonresponders' and can be a valuable option in the rehabilitation of demoralized, socially excluded individuals. Buprenorphine, a partial agonist, is a less reinforcing medication with different side-effects and less risk of overdose. Not only is it a different medication, but also it can be used in a different paradigm of treatment, office-based opioid treatment, with less structure and offering greater patient autonomy.

Corrected QT interval during treatment with methadone and buprenorphine--relation to doses and serum concentrations

BACKGROUND

Methadone and buprenorphine are widely used in the treatment of opioid addiction. Some study results suggest that methadone can be associated with QT interval prolongation and torsades de pointes ventricular arrhythmias, whereas no such risk has been observed for buprenorphine. The aim of this study is to determine the risk of corrected QT interval (QTc) increase among patients treated with these medications in an opioid maintenance treatment (OMT) programme, and to study possible associations between QTc changes and serum concentrations of methadone or buprenorphine.

METHODS

Eighty patients enrolled in the OMT programme were followed after start of treatment with methadone (n=45) or buprenorphine (n=35). QTc interval was assessed by electrocardiography (ECG) at baseline and after 1 month (n=79) and 6 months (n=66) in the OMT programme. Blood samples were obtained for the analysis of serum concentrations of buprenorphine, (R)-methadone, (S)-methadone and total methadone.

RESULTS

No patients had QTc prolongation (defined as a QTc value above 450 ms) at baseline or after 1 or 6 months. When analysed in a linear mixed effects model, QTc was not associated with the serum concentrations of buprenorphine or methadone. However, low serum potassium levels increased QTc significantly.

CONCLUSIONS

These results support and extend previous findings that treatment with methadone in modest doses (i.e. below 100mg/d) is not associated with clinically significant QTc increases, and that buprenorphine in commonly used doses is a suitable alternative to methadone with regard to the risk of QTc prolongation.

On enzyme-based anticancer molecular dietary manipulations

Evidence from both epidemiological and experimental observations has fuelled the belief that the high consumption of fruits and vegetables rich in nutrients and phytochemicals may help prevent cancer and heart disease in humans. This concept has been drastically simplified from the dietary approaches to the use of single bioactive components both as a single supplement or in functional foods to manipulate xenobiotic metabolism. These procedures, which aim to induce mutagen/carcinogen detoxification or inhibit their bioactivation, fail to take into account the multiple and paradoxical biological outcomes of enzyme modulators that make their effects unpredictable. Here, we show that the idea that the physiological roles of specific catalysts may be easily manipulated by regular long-term administration of isolated nutrients and other chemicals derived from food plants is not viable. In contrast, we claim that the consumption of healthy diets is most likely to reduce mutagenesis and cancer risk, and that both research endeavours and dietary recommendations should be redirected away from single molecules to dietary patterns as a main strategy for public health policy.

Analysis of naltrexone and its metabolite 6-beta-naltrexol in serum with high-performance liquid chromatography

BACKGROUND

Naltrexone has been proven to be an effective treatment option for the treatment of alcohol dependency. In this article we introduce a reliable and simple method developed for the simultaneous determination of naltrexone and 6-β-naltrexol in human serum by using high-performance liquid chromatography (HPLC).

FINDINGS

Liquid-liquid extraction with butyl acetate from basic solutions (pH 9) was chosen for extraction with nalorphine as an internal standard (IS). Analytes were back-extracted from organic solvent into perchloric acid. The acid extract was chromatographed by HPLC with a reverse-phase ODS-column and electrochemical detector. The mobile phase was a NaH(2)PO(4)-solution with acetonitrile as an organic modifier and octanesulphonic acid and tetraethylammonium hydrogen sulphate as ion-pair reagents. The recovery of the extraction method was 48% for naltrexone and 75% for 6-β-naltrexol. The limit of quantification was 5.0 ng/ml for naltrexone and 1.0 ng/ml for 6-β-naltrexol. The analysed concentrations of naltrexone differed from the theoretic concentrations by 0.7 to 2.3% and those of 6-β-naltrexol by 2.6%. The relative standard deviation of within-day assay was from 0.9 to 5.7% for naltrexone and from 0.8 to 4.2% for 6-β-naltrexol; for the between-day assay it was 5.7% and 4.2%, respectively.

CONCLUSIONS

Our results indicate that the developed method is suitable for determination of naltrexone and 6-β-naltrexol in human serum.