Pharmacokinetic & Pharmacodynamic Interaction of Lofexidine and Buprenorphine in Buprenorphine Maintained Patients

Overview

The primary objective of this study is to assess lofexidine related effects on QTc (an interval of the heart rhythm) in subjects receiving buprenorphine maintenance. The secondary objectives of the study are to evaluate the safety and tolerability of lofexidine by evaluating and monitoring pharmacokinetics (amounts of drug in the blood), vital signs (heart rate and blood pressure) and adverse events (side effects) when co-administered with buprenorphine; to describe effects on opiate withdrawal when lofexidine is introduced following a 50% buprenorphine dose reduction, as required to elicit a withdrawal response; and to evaluate QTc interaction effects of lofexidine compared with placebo. The Investigators hypothesize that while lofexidine is known to prolong the QTc interval, the combination of the drugs will not create an additive effect which creates a significant safety concern. The Investigators further hypothesize that subjects will be able to tolerate the therapeutic dose of lofexidine (0.8 mg four times daily) when the buprenorphine maintenance dose is lowered to elicit withdrawal.

This will be a randomized, double-blind, placebo-controlled multiple ascending dose study to assess the safety, tolerability, and electrocardiographic effects of lofexidine in 30 buprenorphine-maintained adult subjects. The study will include a Screening Visit, an Inpatient Treatment Visit, and a Follow-Up Visit. Subjects will be randomized in 4:1 ratio to receive up to 4 tablets of lofexidine (0.2 mg/tablet) QID or 4 tablets matching placebo QID. Subjects who are on a stable dose of total daily sublingual buprenorphine 16-24 mg/day with or without naloxone (Suboxone® or Subutex®, respectively), 16 - 24 mg/day, and who satisfy inclusion and exclusion criteria will be eligible for the study. Subjects who are eligible for the study will be encouraged to begin shifting their medication dose to a total daily dose at 2 PM in anticipation of the study dosing schedule during the Inpatient Treatment Visit. Subjects who are receiving Suboxone tablets or Subutex at study enrollment will be converted to Suboxone film at the inpatient check-in and will receive Suboxone sublingual film throughout the study. Within 21 days of the Screening Visit, subjects will report to the inpatient study facility to begin the Inpatient Treatment Visit which will last between approximately 11 to 21 days. This visit will include an inpatient check-in (1 day), Buprenorphine Baseline (1 day), Initial Lofexidine Titration (3 to 5 days), 1 or 2 Lofexidine Plateaus (2 to 4 days), Buprenorphine Reduction (2 to 6 days) and Buprenorphine Re-Titration and Discharge (2 to 4 days). The order of steps subjects will proceed through during the Inpatient Treatment Visit will vary depending on whether subjects are able to titrate to the highest dose of lofexidine or placebo during the Initial Lofexidine Titration. The highest dose of lofexidine (or placebo) will be 4 tablets QID (0.2 mg lofexidine per tablet or placebo) for a total daily lofexidine dose of 16 tablets (3.2 mg or placebo). During the Buprenorphine Baseline phase subjects will take a single daily dose of buprenorphine at 2 PM. Buprenorphine Baseline Day study assessments will begin at approximately 7 AM and include electrocardiogram (ECG) monitoring, blood collection for buprenorphine pharmacokinetics, and opiate withdrawal assessments (Clinical Opiate Withdrawal Scale, COWS and Short Opiate Withdrawal Scale, SOWS). The next day subjects will proceed to the Initial Lofexidine Titration phase. Subjects will continue using their baseline buprenorphine dose. Lofexidine will be initiated at 2 tablets (0.4 mg or placebo) QID and titrated in daily increments of a single tablet (0.2 mg or placebo) QID to a total daily dose of 0.8 mg QID (or placebo), if tolerated by the subject. Lofexidine doses will escalate daily unless at any point the subject meets protocol-defined dose hold criteria (described below), which will trigger a reduction in dose to the previous highest tolerated dose (or to the 1 tablet dose, 0.2 mg or placebo, if subjects cannot tolerate the initial 2 tablets, 0.4 mg or placebo). Once subjects have titrated to the highest dose (ie, 4 tablets QID) or once the highest tolerated dose has been determined, they will proceed to a 2-day Lofexidine Plateau phase during which they will continue to receive their buprenorphine maintenance dose. If the subject is unable to titrate up to 4 tablets QID (0.8 mg or placebo), the subject will continue to receive their highest tolerated dose in equal increments (eg, 2 or 3 tablets QID at 8AM, 1PM, 6PM, 11PM) for both days of the plateau. Subjects who tolerate 4 tablets QID (0.8 mg or placebo) on the first day will receive the 4 tablets QID (0.8 mg or placebo) according to the normal dosing schedule. On the second day, the lofexidine dosing schedule will be modified with subjects receiving a 1-tablet increase (ie, 0.2 mg or placebo) of the 1 PM lofexidine dose (5 tablets: 1 mg or placebo) and a 1-tablet reduction (0.2 mg or placebo) in the subsequent lofexidine dose (3 tablets: 0.6 mg or placebo) with the other 2 doses of 4 tablets (0.8 mg or placebo) for a total daily dose of 16 tablets (3.2 mg/day or placebo). On the second day of the Lofexidine Plateau phase, subjects will undergo ECG monitoring and blood collection for buprenorphine and lofexidine pharmacokinetics. COWS and SOWS assessments will be performed on both days of the Lofexidine Plateau. Subjects who are titrated to a daily dose of 4 tablets (0.8 mg or placebo) QID while receiving their full dose of buprenorphine will undergo a 4-day buprenorphine dose reduction of 50% while continuing to take lofexidine or placebo at a daily dose of 16 tablets to evaluate the effects of lofexidine on buprenorphine withdrawal signs and symptoms. These subjects who complete the initial Lofexidine Plateau at a dose of 0.8 mg lofexidine (or placebo) QID and who reach a COWS of 5 or greater prior to the fourth day of the reduced buprenorphine dose administration may proceed early to Buprenorphine Re-titration and Discharge at the Investigator's discretion. If the COWS score does not reach 5 within 4 days, the subject will proceed to Buprenorphine Re-titration and Discharge. Subjects who are unable to titrate to the highest lofexidine dose (4 tablets: 0.8 mg or placebo QID) while receiving their full dose of buprenorphine will undergo a buprenorphine dose reduction of 50% for up to 6 days while continuing to receive their highest tolerated dose of lofexidine from the initial titration. On the fourth day (or earlier at the investigator's discretion based on withdrawal response), lofexidine titration will resume by adding an incremental 1 tablet (0.2 mg or placebo) QID to the previously established tolerated dose up to the maximum 4 tablet (0.8 mg or placebo) QID dose. During these subsequent titration attempts lofexidine (or placebo) doses will escalate daily beginning on the fourth day of the reduction (or earlier based on discretion of the investigator) unless in any event a subject meets protocol defined dose-hold criteria (described below), which will trigger a reduction in dose to the previous highest tolerated dose and will require the Lofexidine Plateau procedures described above to be repeated while maintaining the subject on their newly reduced buprenorphine dose (eg, 50% of their maintenance dose). Subjects who are unable to titrate to a higher lofexidine dose during the 50% Buprenorphine Reduction than the dose they titrated to during the Initial Lofexidine Titration will not repeat the Lofexidine Plateau procedures. During Buprenorphine Reduction, COWS and SOWS assessments of opiate withdrawal will be performed. On days when the lofexidine dose is increased, holter monitoring and pharmacokinetic (PK) sampling will be done for those subjects who did not titrate all the way up to the maximum dose of lofexidine during the initial titration period. Following completion of the Lofexidine Plateau (repeated as necessary) and Buprenorphine Reduction, subjects will begin the Buprenorphine Re-Titration and Discharge phase during which lofexidine or placebo will be discontinued and buprenorphine will be re-titrated to the starting dose (or to a higher or lower dose relative to baseline as medically indicated at the discretion of the investigator). Lofexidine may be used to treat withdrawal symptoms, if necessary. Following successful buprenorphine titration and completion of study assessments, subjects will be discharged from the inpatient study clinic. Subjects will return to the study clinic for a follow-up visit 7 days (±2 days) following clinic discharge for safety follow-up and adverse event collection. Subjects will be discharged from the study at this time unless they are medically unstable on their dose of buprenorphine. Subject may be medically followed at a regular interval, as determined by the investigator, until the subject is considered sufficiently stable for study discharge. Subjects who withdraw consent or meet any one of the following study termination criteria prior to completion of the study will be withdrawn. Study termination criteria will apply only to pre-dose sitting vital signs and the daily safety ECG readings (excluding HR). Baseline values for vital signs and ECG readings refer to values obtained at the time subjects are admitted to the clinic. 1.Cardiovascular events including the following\*: a. Systolic blood pressure (SBP) \<70 mmHg and \>20% below baseline value, b. Diastolic blood pressure (DBP) \<40 mmHg and \>20% below baseline value (if subject is asymptomatic, DBP termination criteria \<30 mmHg), c. Heart rate \<40 bpm and \>20% below baseline value (if subject is asymptomatic, HR termination criteria \<30 bpm), d. Changes in QTcF that meet any of the following criteria: i.QTcF \>500 ms in females or QTcF\>480 ms in males, ii. QTcF \>25% above baseline value for both males and females, iii. QTcF\<500 ms in females or QTcF \<480 ms in males with a persistent (ie, greater than 24 hours) increase in QTcF value \>60 ms from baseline accompanied by abnormal electrolytes (ie, potassium and sodium), e. Absolute QRS\>120 ms along with a 25% increase from baseline, f. Absolute PR\>240 ms along with a 25% increase from baseline, g. Syncope h. Clinically significant arrhythmia (including telemetry indication of ventricular tachycardia, ventricular fibrillation, Torsade de Pointes, 2nd degree AV block) \*ECGs and vital signs may be repeated as appropriate to confirm values and rule out extraneous results. 2.Serious medical problems thought to be related or unrelated to the study medications. 3.Intercurrent illness or medical complications that, in the opinion of the site investigator, preclude safe administration of study medications. At the time of termination from the study, subjects will be discontinued from lofexidine or placebo; however, they may remain inpatient for usually up to 4 days, with extension allowed as deemed necessary per Investigator, while their buprenorphine maintenance dose is re-titrated to their pre-study maintenance dose.