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Pharmacokinetics of Lofexidine Hydrochloride in Healthy Volunteers
PHARMACOKINETICS, PHARMACODYNAMICS AND DRUG METABOLISM Pharmacokinetics of Lofexidine Hydrochloride in Healthy Volunteers ABEER M. AL-GHANANEEM Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, Kentucky 40536-0082
Received 14 December 2007; accepted 29 February 2008 Published online 4 April 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jps.21401
ABSTRACT: The objective of this study was to characterize the clinical pharmacokinetic profile of lofexidine after oral delivery. A single dose, cross-over study and a multidose study using healthy volunteers were conducted for that purpose. In the single dose study the average time to maximum concentration was observed at approximately 3 h for the single doses tested (1.2 mg dose and 2.0 mg). Area under the curve from time zero to infinity (AUC01) demonstrated a degree of dose proportionality with a 1.72-fold increase as the dose increased by a factor of 1.67. Elimination rates and terminal halflives were comparable between dose levels. The average elimination rates for the 1.2 mg and the 2.0 mg doses were 0.063 and 0.065 h1, respectively. In the multidose study, the average maximum concentration observed after the first dose of 0.4 mg was 433 ng/L and ranged from 338 to 586 ng/L. This was slightly lower in proportion to the maximum concentration observed in the single dose study where Cmax was 1755 ng/L at the 1.2 mg dose (normalized to 585 ng/L for 0.4 mg dose) and for the 2.0 mg dose (normalized to 559 ng/L for 0.4 mg dose). The average time to maximum concentration (Tmax) was 3.33 h which is comparable to values observed in the single dose study. The pharmacokinetic data indicate that lofexidine has a consistent profile. Steady state seems to be reached after 2 days on lofexidine, which is consistent with the lofexidine elimination half-life of approximately 11 h. Evaluation of the Tmax, elimination rate, and terminal half-life are consistent across all dose levels studied, suggesting that changing the dose does not affect the absorption or elimination rates of lofexidine HCl. Thus, although preliminary due to the limited number of subjects, these findings are the first to document lofexidine clinical pharmacokinetic parameters in healthy volunteers using a highly sensitive liquid chromatography tandem mass spectrometric analysis. ß 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:319–326, 2009
Keywords:
lofexidine; substance abuse; pharmacokinetic; LC-MS/MS; clinical trial
INTRODUCTION
Correspondence to: Abeer M. Al-Ghananeem (Telephone: 859-257-4032; Fax: 859-257-7585; E-mail: [email protected]) Journal of Pharmaceutical Sciences, Vol. 98, 319–326 (2009) ß 2008 Wiley-Liss, Inc. and the American Pharmacists Association
Lofexidine, 2-[1-(2,6-dichlorophenoxy)ethyl]-4,5dihydro-1H-Imidazole (Fig. 1), is an a2-adrenergic receptor agonist analogue of clonidine that acts centrally to suppress opiate withdrawal symptoms.1–3 Lofexidine binds presynaptically to a2-adrenergic receptors located on the nerve
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Figure 1. Chemical structure of lofexidine hydrochloride.
endings of noradrenergic neurones and reduces the release of noradrenaline which occurs when the inhibitory effect of opiates is removed.1,4 The drug has been available for use as a nonopioid medication for opioid detoxification in the United Kingdom under the label BritLofex since 1992. Many clinical trials were published which demonstrate the drug’s effectiveness for the management of opioid withdrawal.5–10 Reports from preliminary open-label studies have suggested that lofexidine is as effective as clonidine in the management of opiate withdrawal, but without the same limitation of postural hypotension.11 Preclinical pharmacokinetic analysis gathered in the past with radiolabeled lofexidine standard given by gavage to rats showed that absorption of lofexidine is fast and almost complete from the gastrointestinal tract.12 The bioavailability following oral dosing of 0.2 mg/kg and 0.05 mg/kg in rats were about 53–54% and 54.7–55%, respectively.12,13 Furthermore, pharmacokinetic analysis of the lofexidine blood concentration-time curves after intragastric administration to rats illustrated that the time to reach the maximum blood concentration (Tmax) was 2.2–2.5 h and the terminal half-life (T1/2) was 10.5–11.8 h.13 Although the pharmacology and efficacy of lofexidine is documented in the scientific literature, there is a lack of clinical pharmacokinetic information on this compound. In a study reported by Midgley et al.14 the absorption of single oral doses of 14C-labeled lofexidine in human subjects was almost complete, with nearly the entire administered radioactivity being eliminated in the urine. It was found that peak plasma concentrations of radioactivity occurred at 2–5 h after drug administration and that 80–90% of the JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009
plasma radioactivity was protein-bound in samples collected around Tmax.14 Lofexidine was reported to be metabolized more extensively than the related anti-hypertensive agent, clonidine.15 The principal metabolite of lofexidine was 2,6-dichlorophenol, which was apparently excreted in urine as two O-glucuronic acid conjugates. The same two metabolites were also the main 14C components circulating in plasma at peak 14C concentration. Furthermore, it was reported that patterns of 3H components in the urine of rats and dogs after oral administration of 3H-lofexidine hydrochloride (0.1 mg/kg) were generally similar to those in human urine.15 Presently available pharmacokinetic data on lofexidine is scarce due to the low amount of drug administered. The previously cited data on the plasma levels of the compound and the pharmacokinetic analysis should be considered in the light of the low analytical capability. To the best of our knowledge, lofexidine absorption and pharmacokinetics in humans have never been reported using sophisticated highly sensitive analytical methodologies. This study aimed to address these deficiencies by utilizing a highly sensitive liquid chromatography tandem mass (LC-MS/MS) spectrometric analysis in collecting preliminary pharmacokinetic parameters in healthy volunteers after single and multiple oral doses of lofexidine.
METHODS Materials Lofexidine HCl tablets were obtained from Britannia Pharmaceuticals Ltd (Surrey, UK), 4 D-lofexidine HCl internal standard (IS) was obtained from National Institute on Drug Abuse, NIDA (Bethesda, MD). Cyclohexane, methylene chloride, methyl-butyl-ether, ammonium acetate, acetic acid, potassium chloride (KCl) and HPLC grade methanol for the LC-MS/MS analysis was obtained from Fisher Scientific (Pittsburgh, PA). Water for HPLC use was passed through a reverse osmosis system (Milli-Q1 Reagent Water System) before use. Siliconized microcentrifuge tubes, vials, and tips were purchased from Fisher Scientific (Somerville, NJ). Saline (0.9%, injectable) and heparin sodium (10000 USP U/mL) were purchased from Baxter Healthcare Corporation (Deerfield, IL). Heparinized caraway capillary tubes were purchased from Baxter Healthcare Corporation. DOI 10.1002/jps
LOFEXIDINE HYDROCHLORIDE IN HEALTHY VOLUNTEERS
Study Design and Subjects Healthy male volunteers aged 19–40 years were eligible to participate in the study. All subjects underwent a baseline evaluation, which included a medical history, physical examination, and clinical laboratory testing. After baseline screening, subjects were randomly assigned to the studies. Gateway Medical Research Institutional Review Board approved the study protocol. All subjects provided written informed consent prior to participation. These pilot pharmacokinetic studies were conducted by Gateway Medical Research (St. Charles, MI). The dose for lofexidine required to control withdrawal symptoms varies for each opiate addict depending on the treatment, frequency and duration of opioid used. In the UK, lofexidine clinical treatment is initiated at 0.2 mg twice daily and increase up to a final dose of 2.4 mg/day. The dosage and the dosing strategies in the current study were chosen to be in agreement with early phase clinical trials. The first study used a randomized, single-dose, twoway crossover design. The objective of this pilot protocol was to evaluate the single dose pharmacokinetics of Lofexidine HCl tablets in a test population of four normal healthy adult male volunteers under fasting conditions. Four healthy male volunteers randomly received two separate oral drug administrations during two study periods separated by a washout period of at least 7 days. Drug administration ‘‘A’’ consisted of an oral 1.2 mg dose, taken on study day 1 of either Period I or Period II. Drug administration ‘‘B’’ consisted of an oral 2.0 mg dose, taken on the alternate period. A second study was designed to assess the pharmacokinetic profile of lofexidine HCl tablets when administered to normal healthy volunteers in multiple doses over a maximum of 8 days. Although this study is on healthy volunteers, however, the study protocol was designed to mimic lofexidine clinical trials in addicts which usually had three phases. Phase one (opioid agonist stabilization phase), phase two (treatment phase), and phase three (post detoxification phase). The study used an open-label, randomized design. Three healthy male volunteers received multiple doses of lofexidine between study days 9 and 16. On study days 1–8 the subjects did not receive any medications and this period was used to mimic phase one in lofexidine clinical trials in addicts. On the first day of dosing (study day 9) the subjects received 0.4 mg lofexidine twice DOI 10.1002/jps
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daily (BID). From days 10 to 15 of the study they received 0.8 mg BID. The dosing schedule ended on day 16 of the study, when the subjects received a 0.6 mg dose BID. LC-MS/MS Analysis A Hitachi LC-MS/MS system (Tokyo, Japan) consisting of a Gilson 232 autosampler, two Hitachi L-6000 pumps, and a Quattro II triple quadrupole tandem mass spectrometer (Fisons Instruments, Altrincham, UK) equipped with an electrospray ionization source was used in connection with Hitachi MS workstation software for data acquisition and processing. Chromatography was performed on a Spherisorb CN C18 (4.6 mm 50 mm, 5 mm) HPLC column with mobile phase A consisting of water mixed with 0.50 g ammonium acetate and 2.0 mL acetic acid per liter and mobile phase B consisting of Methanol. Before use, the mobile phase was filtered through a 0.45 mm membrane filter. The flow-rate was set at 0.25 mL/min and the injection volume was 25 mL and a gradient elution program was run for 6 min per sample as follow: solvent A, 50% at 0.00 min ! 40% at 2.00 min ! 50% at 3.00 min ! 50% at 6.00 min. The ESI-MS spectrometer was operated in the positive ion mode. The electrospray capillary potential was set to 3 kV and the cone voltage was 35 V. The source block and desolvation temperatures were 1008C and 3008C, respectively. Nitrogen was used as the nebulization and drying gas at flow rates of 40 and 400 L/h, respectively. Protonated analyte molecules were subjected to collision induced dissociation using argon as the collision gas to yield product ions for each analyte. The collision energy was 10 eV for lofexidine and the I.S. Detection was achieved by MS/MS with electrospray ionization in positive ion mode and multiple reactions monitoring of the ion transitions m/z 259 ! 98 for lofexidine and m/z 263 ! 102 for the internal standard (IS). MS control and spectral processing were performed using MassLynxTM software, version 3.5. Pharmacokinetics Lofexidine tablets were orally administered to the healthy volunteers per the dosing regimen described above. The actual time of dosing was recorded using 24 h clock notation. Blood was sampled from a cubital vein by venipuncture immediately before the administration (t0) and JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009
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post dose at 0.5, 1, 2, 3, 4, 6, 8, 12, 16, 24, and 30 h. A total of 12 blood samples were collected per subject during each study period. There were no missing blood samples. For the multidose study, blood samples were drawn per predetermined sampling periods on days 9, 10 and 15. Each sampling period consisted of a predose (hour 0) sample, followed by sample collections at 0.5, 1, 2, 3, 4, 6, 8, and 12 h post dose. Blood samples were drawn predose and at 12 h postdose on study 11, and only predose on study day 16. Blood was sampled into heparin-coated tubes, and after 30 min, centrifuged at 3000g for 5 min. The resulting plasma was transferred to glass tubes and submitted to liquid–liquid extraction as follow: 0.5 mL plasma was spiked with 25 mL IS working solution (50 ng/mL) and added to 4.5 mL extraction solution consisted of cyclohexane, methylene chloride, and methyl-butyl-ether (1:1:1) mixed with 150 mL 0.1 M KCl solution in 10 mL polypropylene test tubes. The samples were vortexed for 10 min and centrifuged at 2000 rpm for 7 min. An aliquot part (4 mL) of the resulting organic layer was evaporated to dryness with nitrogen gas at ambient temperature, and then reconstituted with 75 mL methanol. The plasma samples were analyzed for lofexidine using the LC-MS/MS procedure described above.
Plasma lofexidine concentrations versus time data were evaluated by noncompartmental methods (WinNonlin Professional, version 4.0.1, Pharsight Corporation, Mountain view, CA). The highest observed plasma concentration during a dosing interval and the corresponding time were defined as Cmax and Tmax, respectively. The firstorder terminal elimination rate constant (Ke) was estimated by linear regression from the points describing the elimination phase in a log-linear plot, and the half-life (t1/2) was derived from this rate constant. The area under the curve from time zero to infinity (AUC01) was estimated using this software.
RESULTS The assay of lofexidine in plasma samples was performed using a validated, highly sensitive liquid chromatography tandem mass spectrometric method which afforded a 50 pg/mL limit of quantification. The assay was validated for accuracy and precision for inter- and intra-assay analysis. The linearity of this procedure was evaluated by analyzing eight calibration standards over the nominal concentration range of 50–10000 ng/L (QC samples concentrations were
Figure 2. Representative mass ion LC-MS/MS chromatogram of lofexidine sample (m/z 259 ! 98) and lofexidine internal standard (m/z 263 ! 102). JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009
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Figure 4. Plasma lofexidine concentration time profile in the three subjects at day 9 (first day of 0.4 mg BID dosing). Data reported is mean SD (n ¼ 3).
Figure 3. Plasma lofexidine concentration time profile in the four subjects after 1.2 and 2.0 mg single dose of lofexidine. Data reported is mean SD (n ¼ 4).
50, 100, 250, 500, 1000, 2000, 4000, 6000, 8000, and 10000 ng/L) with correlation coefficients higher than 0.995. In the present study, intraassay and inter-assay accuracy range was 6.7– 10.5% and 11.3–1.9%, respectively, of the nominal concentrations of lofexidine. The interassay and intra-assay variation did not exceed 7%. Figure 2 illustrated the mass ion chromatograms for lofexidine transition (m/z 259 ! 98) and lofexidine internal standard (m/z 263 ! 102). All plasma sample concentrations that were below sensitivity (0.05 ng/L), were set to zero. Pharmacokinetic parameters following administration of a single oral dose of lofexidine tablets to four healthy subjects after a 10 h overnight fast are presented in Figure 3 and Table 1. Following a single oral dose of 1.2 mg of lofexidine tablets the average maximum concentration (Cmax) observed was 1755 306 ng/L at a time (Tmax) of 3.00 0.8 h. Following a single oral dose of 2.0 mg of lofexidine the Cmax observed value was 2795 593 ng/L at Tmax of 3.25 1.7 h. The areas under the plasma concentrationtime profiles from time zero to infinity, AUC(0– 1), were 31652 5356 ng/L/h and 54321 11592 ng/L/h after oral dosing of 1.2 mg and 2.0 mg, respectively. The mean plasma lofexidine concentration-time profiles for day 9 (first day of dosing) and day 10
(second day of dosing) in the multidose studies are presented in Figures 4 and 5. The concentrationtime profiles were analyzed by a noncompartmental method, and pharmacokinetic parameters were determined. Table 2 illustrates the main pharmacokinetic parameters calculated for the three subjects on day 9 which is the first day of dosing, at 0.4 mg BID. The Cmax observed was 433 134 ng/L at Tmax of 3.33 0.58 h. Table 3 illustrates the pharmacokinetic parameters measured on the second day of dosing. The noncompartmental WinNonlin analysis of the pharmacokinetic parameters on the second day of dosing resulted in an average half-life and an average elimination rate of 10.97 h and 0.06 h1, respectively. The Tmax and Cmax were 3 h and 1450 ng/L, respectively. Only one subject completed all dosing and blood draws through study day 16, while the other two subjects dropped on study day 11. The data analysis for study day 15 (n ¼ 1) is not reported here.
DISCUSSION Recently, the number of studies using liquid chromatography tandem mass spectrometric analysis technology in the field of pharmacokinetics and clinical studies has increased significantly.16–18
Table 1. Pharmacokinetic Parameters for Lofexidine in Healthy Volunteers (n ¼ 4, Mean SD) Dose (mg) 1.2 2.0 DOI 10.1002/jps
AUC(0–1) (ng/L/h)
Cmax (ng/L)
Tmax (h)
t1/2 (h)
Ke (h1)
31652 5356 54321 11592
1755 306 2795 593
3.00 0.8 3.25 1.7
11.16 1.7 11.44 4.1
0.063 0.065
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Figure 5. Plasma lofexidine concentration time profile in the three subjects at day 10 (second day of dosing, dose ¼ 0.8 mg BID). Data reported is mean SD (n ¼ 3).
Such sensitive analytical techniques are suitable for the analysis and quantitation of low levels of analytes in biological fluids with high accuracy and precision. In the current study an LC–MS/MS method with high sensitivity limits was used to support preliminary clinical pharmacokinetic studies of lofexidine which represents a vast improvement over the assay methodologies listed in earlier lofexidine pharmacokinetic studies. The lofexidine pharmacokinetic parameters calculated following the single dose studies in the healthy volunteers illustrated a 1.59-fold increase in maximum plasma concentration associated with the 1.67-fold increase in dosage, suggesting dose proportionality. These data are in general agreement with the literature reported lofexidine pharmacokinetic parameters after intragastric administration to the rat, which illustrated that the time to reach the maximum blood concentration (Tmax) was 2.2–2.5 h, and terminal half-life (t1/2) was 10.5–11.8 h (13). Both parameters were not statistically significant ( p > 0.05)
when compared with the values from the current healthy human subject study. The areas under the plasma concentration-time profiles from time zero to infinity, AUC(0–1), were 31652 5356 ng/L/h 54321 11592 ng/L/h after oral dosing of 1.2 and 2.0 mg, respectively. Elimination rates and terminal half-lives were comparable between dose levels. The average elimination rate for the 1.2 mg dose was 0.063/h and for the 2.0 mg dose was 0.065/h. Terminal half-life was calculated and found to be 11.16 1.7 h for the 1.2 mg dose and 11.44 4.1 h for the 2.0 mg dose. Clinically, lofexidine is designed to be prescribed flexibly so that dosage administration can be titrated against withdrawal symptoms and side effects. The elimination half-life supports a twice daily dose. In the United Kingdom, lofexidine clinical treatment is initiated at 0.2 mg twice daily and increase up to a final dose of 2.4 mg/day. All subjects reached maximum concentration between 2 and 4 h except for subject 3, who reached the maximum concentration at 6 h after dosing with 2.0 mg. Area under the curve for both AUC(0t) and AUC(0–1) also demonstrated a degree of dose proportionality with a 1.67-fold increase in the AUC(0t) and a 1.72-fold increase in AUC[0–1] as the dose increased by a factor of 1.67. In the multidose study it was found that the average maximum concentration observed after a dose of 0.4 mg was 433 ng/L with a range of 338–586 ng/L. This was slightly lower in proportion to the maximum concentration observed in the single dose studies where Cmax was 1755 ng/L at the 1.2 mg dose (normalized to 585 ng/L for 0.4 mg dose) and for the 2.0 mg dose (normalized to 559 ng/L for 0.4 mg dose). Table 2 illustrates the main pharmacokinetic parameters calculated for the three subjects on
Table 2. Pharmacokinetic Parameters for Lofexidine Plasma Samples Collected on Day 9 (First Day of 0.4 mg BID Dosing), (n ¼ 3) PK Parameter t1/2 (h) Ke (h1) Tmax (h) Cmax (ng/L) AUC(0–12) (h ng/L) AUC(0–1) (h ng/L) Vz/F (L) Cl/F (L/h)
Subject #1
Subject #2
Subject #3
Average
SD
9.79 0.07 4 338 3092 5778 977.6 69.2
11.63 0.06 3 374 3155 6621 1013.8 60.4
13.10 0.05 3 586 5155 12383 609.0 32.3
11.51 0.06 3.33 433 3801 8261 867.0 54.0
1.66 0.42 0.58 134 1173 3595 224.0 19.3
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Table 3. Pharmacokinetic Parameters for Lofexidine Plasma Samples Collected on Day 10 (Second Day of Dosing), (n ¼ 3) PK Parameter t1/2 (h) Ke (h1) Tmax (h) Cmax (ng/L) AUC(0–12) (h ng/L) AUC(0–1) (h ng/L) Vz/F (L) Cl/F (L/h)
Subject #1
Subject #2
Subject #3
Average
SD
9.30 0.07 4 1053 9270 17180 624.5 46.6
11.39 0.06 2 1348 10450 20232 650 39.5
12.23 0.06 3 1949 17274 37585 375.7 21.3
10.97 0.06 3 1450 12331 24999 550.1 35.8
1.51 0.01 1 457 4321 11006 151.5 13.0
day 9 which is the first day of dosing, at 0.4 mg BID. The Cmax observed was 433 134 ng/L at Tmax of 3.33 0.58 h. The latter is in agreement with the literature reported range for Tmax of 2–5 h after single oral doses of 14C-labeled lofexidine in human subjects.14 The average area under the curve AUC [0t] and AUC [01] were 3801 and 8261 ng/L, respectively. The extrapolated portion of AUC [01] was high as a result of having plasma samples collected for only 12 h postdose, which was near the estimated half-life of lofexidine HCl. The average time to maximum concentration was 3.33 h, comparable to Tmax observed in the previous single lofexidine dose study. Furthermore, the average elimination rate was 0.06/h and the average terminal half-life was 11.51 h, which are also comparable to those observed in the single dose study. Lofexidine is effective as a nonsubstitute detoxification method. Many studies demonstrated the effectiveness of lofexidine and clonidine in alleviating opiate withdrawal symptoms.5,8,11 Both compounds are widely used in practice, including sometimes in services which positively wish to avoid prescribing opioid drugs. Clonidine has adverse effects of sedation and hypotension and often clinicians will use this only in inpatient settings, whereas lofexidine lacks these effects and is entirely safe for community treatment. Minor side-effects were reported and were found to follow the time course of the plasma concentration of lofexidine. The side-effect could be anticipated from its mode of action as an alpha adrenoceptor agonist.
CONCLUSION Although preliminary, these findings are the first to document lofexidine clinical pharmacokinetic parameters in healthy volunteers utilizing a DOI 10.1002/jps
highly sensitive liquid chromatography tandem mass spectrometric analysis. The data from the single dose study indicates that plasma lofexidine levels were dose proportional at the study doses of 1.2 and 2.0 mg. Also the study showed that there was no dose-dependency in Tmax, elimination rate and terminal elimination half-life pharmacokinetic parameters with a 1.67-fold increase in dose. The pharmacokinetic data, from the multidose study indicates that lofexidine has a consistent profile; steady state seems to be reached after 2 days on lofexidine, which is consistent with the half-life of approximately 11 h. The Tmax, elimination rate, and terminal halflife pharmacokinetic parameters were consistent across dose levels studied, suggesting that change in dose does not affect the absorption or elimination rates of lofexidine HCl.
ACKNOWLEDGMENTS The clinical studies were sponsored by Britannia Pharm. Ltd. (London, UK). The Wisconsin Analytical Research Services a division of PPDPharmaco, International was involved in the development and validation of the LC-MS/MS analytical method.
REFERENCES 1. Gold MS, Pottash ALC. 1981. Endorphins, locus ceruleus, clonidine, and lofexidine: A mechanism for opiate withdrawal and new nonopiate treatments. Adv Alcohol Subst Abuse 1:33–52. 2. Washton AM, Resnick RB, Geyer G. 1983. Opiate withdrawal using lofexidine, a clonidine analogue with fewer side effects. J Clin Psychiatry 44:335– 337. JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009
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3. Bearn J, Gossop M, Strang J. 1996. Randomized double-blind comparison of lofexidine and methadone in the in-patient treatment of opiate withdrawal. Drug Alcohol Depend 43:87–91. 4. Akhurst JS. 1999. The use of lofexidine by drug dependency units in the United Kingdom. Eur Addict Res 5:43–49. 5. Gowing LR, Farrell M, Ali RL, White JM. 2002. Alpha2-adrenergic agonists in opioid withdrawal. Addiction (Abingdon, England) 97:49–58. 6. Gold MS, Pottash AC, Sweeney DR, Exstein I, Annitto WJ. 1981. Opiate detoxification with lofexidine. Drug Alcohol Depend 8:307–315. 7. Washton AM, Resnick RB. 1982. Lofexidine in abrupt methadone withdrawal. Psychopharmacol Bull 18:220–221. 8. Carnwath T, Hardman J. 1998. Randomized double-blind comparison of lofexidine and clonidine in the out-patient treatment of opiate withdrawal. Drug Alcohol Depend 50:251–254. 9. Strang J, Bearn J, Gossop M. 1999. Lofexidine for opiate detoxification: Review of recent randomised and open controlled trials. Am J Addict 8:337– 348. 10. Bearn J, Gossop M, Strang J. 1996. Randomized double blind comparison of lofexidine and methadone in the in-patient treatment of opiate withdrawal. Drug Alcohol Depend 43:87–89. 11. Lin SK, Strang J, Su LW, Tsai CJ, Hu WH. 1997. Double-blind randomized controlled trial of lofexidine versus clonidine in the treatment of heroin withdrawal. Drug Alcohol Depend 48:127– 133.
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12. Lu C, Li H, Yang S, Du X. 2000. Absolute bioavailability of [3H]-lofexidine hydrochloride in rats. Zhongguo Yaolixue Tongbao 16:97–98. 13. Lu CY, Wang HY, Xu WM, Xie XL, Wu T. 2006. Pharmacokinetics of [3H] lofexidine-hydrochloride in rats. Xiandai Shipin Yu Yaopin Zazhi 16:55–57. 14. Midgley I, Chasseaud LF, Taylor T, Darragh A. 1982. The absorption and excretion of 14C-lofexidine hydrochloride in man. Arzneimittelforschung 32:972–975. 15. Midgley I, Fowkes AG, Chasseaud LF, Hawkins DR, Girkin R, Kesselring K. 1983. Biotransformation of lofexidine in humans. Xenobiotica 13:87–95. 16. Alexander MS, Kiser MM, Culley T, Kern JR, Dolan JW, McChesney JD, Zygmunt J, Bannister SJ. 2003. Measurement of paclitaxel in biological matrices: High-throughput liquid chromatographictandem mass spectrometric quantification of paclitaxel and metabolites in human and dog plasma. J Chromatogr B Analyt Technol Biomed Life Sci 2: 253–261. 17. Al-Ghananeem AM, Albayati ZF, Malkawi A, Sonar VN, Freeman ML, Crooks PA. 2007. A pharmacokinetic study on Z-(R/)-2-(1-benzylindole-3-yl-methylene)azabicyclo[2.2.2]octane-3-ol; a novel radiosensitization agent. Cancer Chemother Pharmacol 60:915–919. 18. Ramakrishna NVS, Vishwottam KN, Koteshwara M, Manoj S, Santosh M, Varma DP. 2005. Rapid quantification of nebivolol in human plasma by liquid chromatography coupled with electrospray ionization tandem mass spectrometry. J Pharm biomed Anal 5:1006–1013.
DOI 10.1002/jps
Received 14 December 2007; accepted 29 February 2008 Published online 4 April 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jps.21401
ABSTRACT: The objective of this study was to characterize the clinical pharmacokinetic profile of lofexidine after oral delivery. A single dose, cross-over study and a multidose study using healthy volunteers were conducted for that purpose. In the single dose study the average time to maximum concentration was observed at approximately 3 h for the single doses tested (1.2 mg dose and 2.0 mg). Area under the curve from time zero to infinity (AUC01) demonstrated a degree of dose proportionality with a 1.72-fold increase as the dose increased by a factor of 1.67. Elimination rates and terminal halflives were comparable between dose levels. The average elimination rates for the 1.2 mg and the 2.0 mg doses were 0.063 and 0.065 h1, respectively. In the multidose study, the average maximum concentration observed after the first dose of 0.4 mg was 433 ng/L and ranged from 338 to 586 ng/L. This was slightly lower in proportion to the maximum concentration observed in the single dose study where Cmax was 1755 ng/L at the 1.2 mg dose (normalized to 585 ng/L for 0.4 mg dose) and for the 2.0 mg dose (normalized to 559 ng/L for 0.4 mg dose). The average time to maximum concentration (Tmax) was 3.33 h which is comparable to values observed in the single dose study. The pharmacokinetic data indicate that lofexidine has a consistent profile. Steady state seems to be reached after 2 days on lofexidine, which is consistent with the lofexidine elimination half-life of approximately 11 h. Evaluation of the Tmax, elimination rate, and terminal half-life are consistent across all dose levels studied, suggesting that changing the dose does not affect the absorption or elimination rates of lofexidine HCl. Thus, although preliminary due to the limited number of subjects, these findings are the first to document lofexidine clinical pharmacokinetic parameters in healthy volunteers using a highly sensitive liquid chromatography tandem mass spectrometric analysis. ß 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:319–326, 2009
Keywords:
lofexidine; substance abuse; pharmacokinetic; LC-MS/MS; clinical trial
INTRODUCTION
Correspondence to: Abeer M. Al-Ghananeem (Telephone: 859-257-4032; Fax: 859-257-7585; E-mail: [email protected]) Journal of Pharmaceutical Sciences, Vol. 98, 319–326 (2009) ß 2008 Wiley-Liss, Inc. and the American Pharmacists Association
Lofexidine, 2-[1-(2,6-dichlorophenoxy)ethyl]-4,5dihydro-1H-Imidazole (Fig. 1), is an a2-adrenergic receptor agonist analogue of clonidine that acts centrally to suppress opiate withdrawal symptoms.1–3 Lofexidine binds presynaptically to a2-adrenergic receptors located on the nerve
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Figure 1. Chemical structure of lofexidine hydrochloride.
endings of noradrenergic neurones and reduces the release of noradrenaline which occurs when the inhibitory effect of opiates is removed.1,4 The drug has been available for use as a nonopioid medication for opioid detoxification in the United Kingdom under the label BritLofex since 1992. Many clinical trials were published which demonstrate the drug’s effectiveness for the management of opioid withdrawal.5–10 Reports from preliminary open-label studies have suggested that lofexidine is as effective as clonidine in the management of opiate withdrawal, but without the same limitation of postural hypotension.11 Preclinical pharmacokinetic analysis gathered in the past with radiolabeled lofexidine standard given by gavage to rats showed that absorption of lofexidine is fast and almost complete from the gastrointestinal tract.12 The bioavailability following oral dosing of 0.2 mg/kg and 0.05 mg/kg in rats were about 53–54% and 54.7–55%, respectively.12,13 Furthermore, pharmacokinetic analysis of the lofexidine blood concentration-time curves after intragastric administration to rats illustrated that the time to reach the maximum blood concentration (Tmax) was 2.2–2.5 h and the terminal half-life (T1/2) was 10.5–11.8 h.13 Although the pharmacology and efficacy of lofexidine is documented in the scientific literature, there is a lack of clinical pharmacokinetic information on this compound. In a study reported by Midgley et al.14 the absorption of single oral doses of 14C-labeled lofexidine in human subjects was almost complete, with nearly the entire administered radioactivity being eliminated in the urine. It was found that peak plasma concentrations of radioactivity occurred at 2–5 h after drug administration and that 80–90% of the JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009
plasma radioactivity was protein-bound in samples collected around Tmax.14 Lofexidine was reported to be metabolized more extensively than the related anti-hypertensive agent, clonidine.15 The principal metabolite of lofexidine was 2,6-dichlorophenol, which was apparently excreted in urine as two O-glucuronic acid conjugates. The same two metabolites were also the main 14C components circulating in plasma at peak 14C concentration. Furthermore, it was reported that patterns of 3H components in the urine of rats and dogs after oral administration of 3H-lofexidine hydrochloride (0.1 mg/kg) were generally similar to those in human urine.15 Presently available pharmacokinetic data on lofexidine is scarce due to the low amount of drug administered. The previously cited data on the plasma levels of the compound and the pharmacokinetic analysis should be considered in the light of the low analytical capability. To the best of our knowledge, lofexidine absorption and pharmacokinetics in humans have never been reported using sophisticated highly sensitive analytical methodologies. This study aimed to address these deficiencies by utilizing a highly sensitive liquid chromatography tandem mass (LC-MS/MS) spectrometric analysis in collecting preliminary pharmacokinetic parameters in healthy volunteers after single and multiple oral doses of lofexidine.
METHODS Materials Lofexidine HCl tablets were obtained from Britannia Pharmaceuticals Ltd (Surrey, UK), 4 D-lofexidine HCl internal standard (IS) was obtained from National Institute on Drug Abuse, NIDA (Bethesda, MD). Cyclohexane, methylene chloride, methyl-butyl-ether, ammonium acetate, acetic acid, potassium chloride (KCl) and HPLC grade methanol for the LC-MS/MS analysis was obtained from Fisher Scientific (Pittsburgh, PA). Water for HPLC use was passed through a reverse osmosis system (Milli-Q1 Reagent Water System) before use. Siliconized microcentrifuge tubes, vials, and tips were purchased from Fisher Scientific (Somerville, NJ). Saline (0.9%, injectable) and heparin sodium (10000 USP U/mL) were purchased from Baxter Healthcare Corporation (Deerfield, IL). Heparinized caraway capillary tubes were purchased from Baxter Healthcare Corporation. DOI 10.1002/jps
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Study Design and Subjects Healthy male volunteers aged 19–40 years were eligible to participate in the study. All subjects underwent a baseline evaluation, which included a medical history, physical examination, and clinical laboratory testing. After baseline screening, subjects were randomly assigned to the studies. Gateway Medical Research Institutional Review Board approved the study protocol. All subjects provided written informed consent prior to participation. These pilot pharmacokinetic studies were conducted by Gateway Medical Research (St. Charles, MI). The dose for lofexidine required to control withdrawal symptoms varies for each opiate addict depending on the treatment, frequency and duration of opioid used. In the UK, lofexidine clinical treatment is initiated at 0.2 mg twice daily and increase up to a final dose of 2.4 mg/day. The dosage and the dosing strategies in the current study were chosen to be in agreement with early phase clinical trials. The first study used a randomized, single-dose, twoway crossover design. The objective of this pilot protocol was to evaluate the single dose pharmacokinetics of Lofexidine HCl tablets in a test population of four normal healthy adult male volunteers under fasting conditions. Four healthy male volunteers randomly received two separate oral drug administrations during two study periods separated by a washout period of at least 7 days. Drug administration ‘‘A’’ consisted of an oral 1.2 mg dose, taken on study day 1 of either Period I or Period II. Drug administration ‘‘B’’ consisted of an oral 2.0 mg dose, taken on the alternate period. A second study was designed to assess the pharmacokinetic profile of lofexidine HCl tablets when administered to normal healthy volunteers in multiple doses over a maximum of 8 days. Although this study is on healthy volunteers, however, the study protocol was designed to mimic lofexidine clinical trials in addicts which usually had three phases. Phase one (opioid agonist stabilization phase), phase two (treatment phase), and phase three (post detoxification phase). The study used an open-label, randomized design. Three healthy male volunteers received multiple doses of lofexidine between study days 9 and 16. On study days 1–8 the subjects did not receive any medications and this period was used to mimic phase one in lofexidine clinical trials in addicts. On the first day of dosing (study day 9) the subjects received 0.4 mg lofexidine twice DOI 10.1002/jps
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daily (BID). From days 10 to 15 of the study they received 0.8 mg BID. The dosing schedule ended on day 16 of the study, when the subjects received a 0.6 mg dose BID. LC-MS/MS Analysis A Hitachi LC-MS/MS system (Tokyo, Japan) consisting of a Gilson 232 autosampler, two Hitachi L-6000 pumps, and a Quattro II triple quadrupole tandem mass spectrometer (Fisons Instruments, Altrincham, UK) equipped with an electrospray ionization source was used in connection with Hitachi MS workstation software for data acquisition and processing. Chromatography was performed on a Spherisorb CN C18 (4.6 mm 50 mm, 5 mm) HPLC column with mobile phase A consisting of water mixed with 0.50 g ammonium acetate and 2.0 mL acetic acid per liter and mobile phase B consisting of Methanol. Before use, the mobile phase was filtered through a 0.45 mm membrane filter. The flow-rate was set at 0.25 mL/min and the injection volume was 25 mL and a gradient elution program was run for 6 min per sample as follow: solvent A, 50% at 0.00 min ! 40% at 2.00 min ! 50% at 3.00 min ! 50% at 6.00 min. The ESI-MS spectrometer was operated in the positive ion mode. The electrospray capillary potential was set to 3 kV and the cone voltage was 35 V. The source block and desolvation temperatures were 1008C and 3008C, respectively. Nitrogen was used as the nebulization and drying gas at flow rates of 40 and 400 L/h, respectively. Protonated analyte molecules were subjected to collision induced dissociation using argon as the collision gas to yield product ions for each analyte. The collision energy was 10 eV for lofexidine and the I.S. Detection was achieved by MS/MS with electrospray ionization in positive ion mode and multiple reactions monitoring of the ion transitions m/z 259 ! 98 for lofexidine and m/z 263 ! 102 for the internal standard (IS). MS control and spectral processing were performed using MassLynxTM software, version 3.5. Pharmacokinetics Lofexidine tablets were orally administered to the healthy volunteers per the dosing regimen described above. The actual time of dosing was recorded using 24 h clock notation. Blood was sampled from a cubital vein by venipuncture immediately before the administration (t0) and JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009
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post dose at 0.5, 1, 2, 3, 4, 6, 8, 12, 16, 24, and 30 h. A total of 12 blood samples were collected per subject during each study period. There were no missing blood samples. For the multidose study, blood samples were drawn per predetermined sampling periods on days 9, 10 and 15. Each sampling period consisted of a predose (hour 0) sample, followed by sample collections at 0.5, 1, 2, 3, 4, 6, 8, and 12 h post dose. Blood samples were drawn predose and at 12 h postdose on study 11, and only predose on study day 16. Blood was sampled into heparin-coated tubes, and after 30 min, centrifuged at 3000g for 5 min. The resulting plasma was transferred to glass tubes and submitted to liquid–liquid extraction as follow: 0.5 mL plasma was spiked with 25 mL IS working solution (50 ng/mL) and added to 4.5 mL extraction solution consisted of cyclohexane, methylene chloride, and methyl-butyl-ether (1:1:1) mixed with 150 mL 0.1 M KCl solution in 10 mL polypropylene test tubes. The samples were vortexed for 10 min and centrifuged at 2000 rpm for 7 min. An aliquot part (4 mL) of the resulting organic layer was evaporated to dryness with nitrogen gas at ambient temperature, and then reconstituted with 75 mL methanol. The plasma samples were analyzed for lofexidine using the LC-MS/MS procedure described above.
Plasma lofexidine concentrations versus time data were evaluated by noncompartmental methods (WinNonlin Professional, version 4.0.1, Pharsight Corporation, Mountain view, CA). The highest observed plasma concentration during a dosing interval and the corresponding time were defined as Cmax and Tmax, respectively. The firstorder terminal elimination rate constant (Ke) was estimated by linear regression from the points describing the elimination phase in a log-linear plot, and the half-life (t1/2) was derived from this rate constant. The area under the curve from time zero to infinity (AUC01) was estimated using this software.
RESULTS The assay of lofexidine in plasma samples was performed using a validated, highly sensitive liquid chromatography tandem mass spectrometric method which afforded a 50 pg/mL limit of quantification. The assay was validated for accuracy and precision for inter- and intra-assay analysis. The linearity of this procedure was evaluated by analyzing eight calibration standards over the nominal concentration range of 50–10000 ng/L (QC samples concentrations were
Figure 2. Representative mass ion LC-MS/MS chromatogram of lofexidine sample (m/z 259 ! 98) and lofexidine internal standard (m/z 263 ! 102). JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 98, NO. 1, JANUARY 2009
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Figure 4. Plasma lofexidine concentration time profile in the three subjects at day 9 (first day of 0.4 mg BID dosing). Data reported is mean SD (n ¼ 3).
Figure 3. Plasma lofexidine concentration time profile in the four subjects after 1.2 and 2.0 mg single dose of lofexidine. Data reported is mean SD (n ¼ 4).
50, 100, 250, 500, 1000, 2000, 4000, 6000, 8000, and 10000 ng/L) with correlation coefficients higher than 0.995. In the present study, intraassay and inter-assay accuracy range was 6.7– 10.5% and 11.3–1.9%, respectively, of the nominal concentrations of lofexidine. The interassay and intra-assay variation did not exceed 7%. Figure 2 illustrated the mass ion chromatograms for lofexidine transition (m/z 259 ! 98) and lofexidine internal standard (m/z 263 ! 102). All plasma sample concentrations that were below sensitivity (0.05 ng/L), were set to zero. Pharmacokinetic parameters following administration of a single oral dose of lofexidine tablets to four healthy subjects after a 10 h overnight fast are presented in Figure 3 and Table 1. Following a single oral dose of 1.2 mg of lofexidine tablets the average maximum concentration (Cmax) observed was 1755 306 ng/L at a time (Tmax) of 3.00 0.8 h. Following a single oral dose of 2.0 mg of lofexidine the Cmax observed value was 2795 593 ng/L at Tmax of 3.25 1.7 h. The areas under the plasma concentrationtime profiles from time zero to infinity, AUC(0– 1), were 31652 5356 ng/L/h and 54321 11592 ng/L/h after oral dosing of 1.2 mg and 2.0 mg, respectively. The mean plasma lofexidine concentration-time profiles for day 9 (first day of dosing) and day 10
(second day of dosing) in the multidose studies are presented in Figures 4 and 5. The concentrationtime profiles were analyzed by a noncompartmental method, and pharmacokinetic parameters were determined. Table 2 illustrates the main pharmacokinetic parameters calculated for the three subjects on day 9 which is the first day of dosing, at 0.4 mg BID. The Cmax observed was 433 134 ng/L at Tmax of 3.33 0.58 h. Table 3 illustrates the pharmacokinetic parameters measured on the second day of dosing. The noncompartmental WinNonlin analysis of the pharmacokinetic parameters on the second day of dosing resulted in an average half-life and an average elimination rate of 10.97 h and 0.06 h1, respectively. The Tmax and Cmax were 3 h and 1450 ng/L, respectively. Only one subject completed all dosing and blood draws through study day 16, while the other two subjects dropped on study day 11. The data analysis for study day 15 (n ¼ 1) is not reported here.
DISCUSSION Recently, the number of studies using liquid chromatography tandem mass spectrometric analysis technology in the field of pharmacokinetics and clinical studies has increased significantly.16–18
Table 1. Pharmacokinetic Parameters for Lofexidine in Healthy Volunteers (n ¼ 4, Mean SD) Dose (mg) 1.2 2.0 DOI 10.1002/jps
AUC(0–1) (ng/L/h)
Cmax (ng/L)
Tmax (h)
t1/2 (h)
Ke (h1)
31652 5356 54321 11592
1755 306 2795 593
3.00 0.8 3.25 1.7
11.16 1.7 11.44 4.1
0.063 0.065
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Figure 5. Plasma lofexidine concentration time profile in the three subjects at day 10 (second day of dosing, dose ¼ 0.8 mg BID). Data reported is mean SD (n ¼ 3).
Such sensitive analytical techniques are suitable for the analysis and quantitation of low levels of analytes in biological fluids with high accuracy and precision. In the current study an LC–MS/MS method with high sensitivity limits was used to support preliminary clinical pharmacokinetic studies of lofexidine which represents a vast improvement over the assay methodologies listed in earlier lofexidine pharmacokinetic studies. The lofexidine pharmacokinetic parameters calculated following the single dose studies in the healthy volunteers illustrated a 1.59-fold increase in maximum plasma concentration associated with the 1.67-fold increase in dosage, suggesting dose proportionality. These data are in general agreement with the literature reported lofexidine pharmacokinetic parameters after intragastric administration to the rat, which illustrated that the time to reach the maximum blood concentration (Tmax) was 2.2–2.5 h, and terminal half-life (t1/2) was 10.5–11.8 h (13). Both parameters were not statistically significant ( p > 0.05)
when compared with the values from the current healthy human subject study. The areas under the plasma concentration-time profiles from time zero to infinity, AUC(0–1), were 31652 5356 ng/L/h 54321 11592 ng/L/h after oral dosing of 1.2 and 2.0 mg, respectively. Elimination rates and terminal half-lives were comparable between dose levels. The average elimination rate for the 1.2 mg dose was 0.063/h and for the 2.0 mg dose was 0.065/h. Terminal half-life was calculated and found to be 11.16 1.7 h for the 1.2 mg dose and 11.44 4.1 h for the 2.0 mg dose. Clinically, lofexidine is designed to be prescribed flexibly so that dosage administration can be titrated against withdrawal symptoms and side effects. The elimination half-life supports a twice daily dose. In the United Kingdom, lofexidine clinical treatment is initiated at 0.2 mg twice daily and increase up to a final dose of 2.4 mg/day. All subjects reached maximum concentration between 2 and 4 h except for subject 3, who reached the maximum concentration at 6 h after dosing with 2.0 mg. Area under the curve for both AUC(0t) and AUC(0–1) also demonstrated a degree of dose proportionality with a 1.67-fold increase in the AUC(0t) and a 1.72-fold increase in AUC[0–1] as the dose increased by a factor of 1.67. In the multidose study it was found that the average maximum concentration observed after a dose of 0.4 mg was 433 ng/L with a range of 338–586 ng/L. This was slightly lower in proportion to the maximum concentration observed in the single dose studies where Cmax was 1755 ng/L at the 1.2 mg dose (normalized to 585 ng/L for 0.4 mg dose) and for the 2.0 mg dose (normalized to 559 ng/L for 0.4 mg dose). Table 2 illustrates the main pharmacokinetic parameters calculated for the three subjects on
Table 2. Pharmacokinetic Parameters for Lofexidine Plasma Samples Collected on Day 9 (First Day of 0.4 mg BID Dosing), (n ¼ 3) PK Parameter t1/2 (h) Ke (h1) Tmax (h) Cmax (ng/L) AUC(0–12) (h ng/L) AUC(0–1) (h ng/L) Vz/F (L) Cl/F (L/h)
Subject #1
Subject #2
Subject #3
Average
SD
9.79 0.07 4 338 3092 5778 977.6 69.2
11.63 0.06 3 374 3155 6621 1013.8 60.4
13.10 0.05 3 586 5155 12383 609.0 32.3
11.51 0.06 3.33 433 3801 8261 867.0 54.0
1.66 0.42 0.58 134 1173 3595 224.0 19.3
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Table 3. Pharmacokinetic Parameters for Lofexidine Plasma Samples Collected on Day 10 (Second Day of Dosing), (n ¼ 3) PK Parameter t1/2 (h) Ke (h1) Tmax (h) Cmax (ng/L) AUC(0–12) (h ng/L) AUC(0–1) (h ng/L) Vz/F (L) Cl/F (L/h)
Subject #1
Subject #2
Subject #3
Average
SD
9.30 0.07 4 1053 9270 17180 624.5 46.6
11.39 0.06 2 1348 10450 20232 650 39.5
12.23 0.06 3 1949 17274 37585 375.7 21.3
10.97 0.06 3 1450 12331 24999 550.1 35.8
1.51 0.01 1 457 4321 11006 151.5 13.0
day 9 which is the first day of dosing, at 0.4 mg BID. The Cmax observed was 433 134 ng/L at Tmax of 3.33 0.58 h. The latter is in agreement with the literature reported range for Tmax of 2–5 h after single oral doses of 14C-labeled lofexidine in human subjects.14 The average area under the curve AUC [0t] and AUC [01] were 3801 and 8261 ng/L, respectively. The extrapolated portion of AUC [01] was high as a result of having plasma samples collected for only 12 h postdose, which was near the estimated half-life of lofexidine HCl. The average time to maximum concentration was 3.33 h, comparable to Tmax observed in the previous single lofexidine dose study. Furthermore, the average elimination rate was 0.06/h and the average terminal half-life was 11.51 h, which are also comparable to those observed in the single dose study. Lofexidine is effective as a nonsubstitute detoxification method. Many studies demonstrated the effectiveness of lofexidine and clonidine in alleviating opiate withdrawal symptoms.5,8,11 Both compounds are widely used in practice, including sometimes in services which positively wish to avoid prescribing opioid drugs. Clonidine has adverse effects of sedation and hypotension and often clinicians will use this only in inpatient settings, whereas lofexidine lacks these effects and is entirely safe for community treatment. Minor side-effects were reported and were found to follow the time course of the plasma concentration of lofexidine. The side-effect could be anticipated from its mode of action as an alpha adrenoceptor agonist.
CONCLUSION Although preliminary, these findings are the first to document lofexidine clinical pharmacokinetic parameters in healthy volunteers utilizing a DOI 10.1002/jps
highly sensitive liquid chromatography tandem mass spectrometric analysis. The data from the single dose study indicates that plasma lofexidine levels were dose proportional at the study doses of 1.2 and 2.0 mg. Also the study showed that there was no dose-dependency in Tmax, elimination rate and terminal elimination half-life pharmacokinetic parameters with a 1.67-fold increase in dose. The pharmacokinetic data, from the multidose study indicates that lofexidine has a consistent profile; steady state seems to be reached after 2 days on lofexidine, which is consistent with the half-life of approximately 11 h. The Tmax, elimination rate, and terminal halflife pharmacokinetic parameters were consistent across dose levels studied, suggesting that change in dose does not affect the absorption or elimination rates of lofexidine HCl.
ACKNOWLEDGMENTS The clinical studies were sponsored by Britannia Pharm. Ltd. (London, UK). The Wisconsin Analytical Research Services a division of PPDPharmaco, International was involved in the development and validation of the LC-MS/MS analytical method.
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3. Bearn J, Gossop M, Strang J. 1996. Randomized double-blind comparison of lofexidine and methadone in the in-patient treatment of opiate withdrawal. Drug Alcohol Depend 43:87–91. 4. Akhurst JS. 1999. The use of lofexidine by drug dependency units in the United Kingdom. Eur Addict Res 5:43–49. 5. Gowing LR, Farrell M, Ali RL, White JM. 2002. Alpha2-adrenergic agonists in opioid withdrawal. Addiction (Abingdon, England) 97:49–58. 6. Gold MS, Pottash AC, Sweeney DR, Exstein I, Annitto WJ. 1981. Opiate detoxification with lofexidine. Drug Alcohol Depend 8:307–315. 7. Washton AM, Resnick RB. 1982. Lofexidine in abrupt methadone withdrawal. Psychopharmacol Bull 18:220–221. 8. Carnwath T, Hardman J. 1998. Randomized double-blind comparison of lofexidine and clonidine in the out-patient treatment of opiate withdrawal. Drug Alcohol Depend 50:251–254. 9. Strang J, Bearn J, Gossop M. 1999. Lofexidine for opiate detoxification: Review of recent randomised and open controlled trials. Am J Addict 8:337– 348. 10. Bearn J, Gossop M, Strang J. 1996. Randomized double blind comparison of lofexidine and methadone in the in-patient treatment of opiate withdrawal. Drug Alcohol Depend 43:87–89. 11. Lin SK, Strang J, Su LW, Tsai CJ, Hu WH. 1997. Double-blind randomized controlled trial of lofexidine versus clonidine in the treatment of heroin withdrawal. Drug Alcohol Depend 48:127– 133.
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12. Lu C, Li H, Yang S, Du X. 2000. Absolute bioavailability of [3H]-lofexidine hydrochloride in rats. Zhongguo Yaolixue Tongbao 16:97–98. 13. Lu CY, Wang HY, Xu WM, Xie XL, Wu T. 2006. Pharmacokinetics of [3H] lofexidine-hydrochloride in rats. Xiandai Shipin Yu Yaopin Zazhi 16:55–57. 14. Midgley I, Chasseaud LF, Taylor T, Darragh A. 1982. The absorption and excretion of 14C-lofexidine hydrochloride in man. Arzneimittelforschung 32:972–975. 15. Midgley I, Fowkes AG, Chasseaud LF, Hawkins DR, Girkin R, Kesselring K. 1983. Biotransformation of lofexidine in humans. Xenobiotica 13:87–95. 16. Alexander MS, Kiser MM, Culley T, Kern JR, Dolan JW, McChesney JD, Zygmunt J, Bannister SJ. 2003. Measurement of paclitaxel in biological matrices: High-throughput liquid chromatographictandem mass spectrometric quantification of paclitaxel and metabolites in human and dog plasma. J Chromatogr B Analyt Technol Biomed Life Sci 2: 253–261. 17. Al-Ghananeem AM, Albayati ZF, Malkawi A, Sonar VN, Freeman ML, Crooks PA. 2007. A pharmacokinetic study on Z-(R/)-2-(1-benzylindole-3-yl-methylene)azabicyclo[2.2.2]octane-3-ol; a novel radiosensitization agent. Cancer Chemother Pharmacol 60:915–919. 18. Ramakrishna NVS, Vishwottam KN, Koteshwara M, Manoj S, Santosh M, Varma DP. 2005. Rapid quantification of nebivolol in human plasma by liquid chromatography coupled with electrospray ionization tandem mass spectrometry. J Pharm biomed Anal 5:1006–1013.
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