Pharmacokinetic Interactions Between Buprenorphine and Kaletra (Lopinavir/Ritonavir)

Inclusion Criteria: * Chronic BUP users enrolled in BUP program, receiving BUP for at least 3 months and on a stable BUP dose for at least 3 weeks. * Acceptable medical history, physical examination, 12 lead electrocardiogram, and clinical laboratory evaluations consistent with BUP maintenance * Subjects who meet the criteria of opiate dependence, are enrolled in long-term BUP maintenance therapy, and have been on a stable dose of BUP for at least 3 weeks. * Body weight \>60 kg for males and \>40 kg for females * Body Mass Index (BMI) of 18 to 30 kg/m2, inclusive. BMI = weight (kg)/ \[height (m)\]2. * Male or females, ages 18 to 65 years. * Women of childbearing potential (WOCBP) must not be nursing, pregnant and on adequate non-hormonal contraception to avoid pregnancy. WOCBP must have a negative serum or urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of HCG) within 24 hours prior to the start of Study Day 1. Exclusion Criteria: Sex and Reproductive Status Exceptions * WOCBP who are unwilling or unable to use an acceptable method to avoid pregnancy for the entire study period and for up to 4 weeks before and after the study. * WOCBP using a prohibited contraceptive method (oral, injectable, or implantable hormonal agents) * Women who are pregnant or breastfeeding * Women with a positive pregnancy test on enrollment or prior to study drug administration. Medical History and Concurrent Diseases * History or current evidence of any significant acute or chronic medical illness that, within the investigator's discretion, would interfere with the conduct or interpretation of the study. * History of nephrolithiasis * History of acute or chronic pancreatitis. * History of uncontrolled chronic medical illness which could adversely affect the subject's adherence to study protocol or affect patient safety in the opinion of the investigator * Use of any medication thought to significantly alter the metabolism of Kaletra, Buprenorphine or naloxone. * History of any hemolytic disorders (including drug-induced hemolysis). * Proven or suspected acute hepatitis at the time of study entry. * Current or recent (within 3 months) gastrointestinal disease which would interfere with the conduct or interpretation of the study. * Any major surgery within 4 weeks of enrollment. Minor surgical procedures requiring local anesthesia are exceptions. * Any gastrointestinal surgery that could impact upon the absorption of study drug. * Donation of blood or plasma to a blood bank or in a clinical study (except a screening visit) within 4 weeks of enrollment. * Blood transfusion within 4 weeks of enrollment. * Inability to tolerate oral medication. * Inability to tolerate venipuncture and/or absence of secure venous access. * Inability to refrain from smoking during in-patient period * Known or suspected HIV infection (subjects who are found to be positive upon screen for HIV will be excluded). * Known active drug or alcohol abuse, which in the opinion of the investigator makes study participation to completion unlikely. * Any other sound medical, psychiatric and/or social reason as determined by the Investigator. Physical and Laboratory Test Findings * Evidence of organ dysfunction or any clinically relevant deviations from the norms observed in a buprenorphine treated population in physical examination, vital signs, ECG or clinical laboratory determinations. * Ingestion of alcohol within 24 hours prior to the dose of study medication * Positive breathalyzer alcohol test, or positive urine screen for barbiturates, benzodiazepines, amphetamines or opiates other than buprenorphine. * Positive blood screen for HIV antibody. * QTc interval \>450 msec for males or \>470 msec for females. * Second or third-degree AV block. * Creatinine clearance(as estimated by method of Cockcroft and Gault) less than 80 mL/min. * CLcr=0.85(females only)x(140-age)x weight(kg) * serum creatinine(mg/dL)x 72 * Subjects with bilirubin \>2 mg/dL, serum albumin \<2.5 g/dL and ascites, AST and ALT \>3 times ULN, hemoglobin \<9 g/dL, and platelet count \<75,000/mm3. * Positive serum or urine for HCG.