General study design The design of the study is randomized, placebo-controlled crossover. Each subject will be studied twice, on one occasion he or she will receive THC and a placebo opioid capsule, and on the other occasion THC and an oxycodone capsule. The visits to the lab will be randomized, the washout period between the two occasions is at least 10 days. Subjects will be evaluated by a physician at screening and only healthy volunteers, aged 18-45 years, with a body mass index \< 30 kg.m-2, are eligible to participate in the study.
Upon arrival in the laboratory (K5-120), the investigators will perform a urinary drug test and breath alcohol test. When these tests are positive, the subject is excluded from further participation. A venous and an arterial line will be placed. The venous line is used for fluid administration (NaCl/Glucose 50-100 ml/h), the arterial line is for blood sample drawing.
Next, the first hypercapnic ventilatory responses (HCVR) will be obtained (t = -30 min). This is the pre-drug baseline measurement. At t = 0, the subjects will receive 20 mg oxycodone immediate release or placebo. Next, the investigators will obtain HCVRs at 1-hour intervals until 6 hours after oxycodone/placebo intake. At t = 1.5 h and at t = 4.5 h the subject will inhale 100 mg Bedrocan. Breathing will be measured using the "dynamic end-tidal forcing" (DEF) system. At specific time points the investigators will draw 10 mL blood for measurement of drug concentrations. After 8 hours of measurement, we will assess whether the HCVR is still depressed. If so, the investigators will take another measurement at t = 9 h and reassess the HCVR. If still depressed, a last response will be obtained at t = 10 h. If necessary, the subject will stay overnight in the hospital. This will be decided by the physician-investigator. For example, the subject may still be sedated.
The hypercapnic ventilatory response To obtain the HCVR curve, the subject will rebreathe a gas mixture from a 6 L rebreathing balloon bag containing 7% carbon dioxide in 93% oxygen. The slope of the response and ventilation at 55 mmHg will be used in the analysis.
Oxycodone intake:
At t = 0, the subject will ingest 1 oxycodone 20 mg immediate release or a placebo capsule with 100 mL water. Both drugs will be obtained from the LUMC pharmacy.
Cannabis inhalation: Bedrocan is vaporized using the CE-marked Volcano Medic vaporizer (Storz \& Bickel GmbH \& Co, Tuttlingen, Germany), a safe and reliable method of intrapulmonary administration of cannabinoids. The Volcano heats the homogenized plant material to 210 °C to allow for conversion of the THC acid and CBD acid into THC and CBD vapor for inhalation. The complete 100 mg from the glass vial will be entered into the vaporizing chamber of the Volcano Medic. The vapor will be collected in a 6-L plastic balloon that, after inflation, is detached from the vaporizer and subsequently equipped with a mouthpiece for inhalation. It is our experience that the full content of the balloon is inhaled without any problems within 3-5 min.
The Bedrocan cannabis variety contains 22% THC (220 mg per gram) and less than 1%CBD. It is developed in the Netherlands out of a requirement by the Dutch Health Ministry to have a "high THC" variety available to patients. We will administer 100 mg Bedrocan that contains 22.4-mg THC and less than 1-mg CBD, twice. Bedrocan will be obtained via the Bureau voor Medicinale Cannabis (BMO), a governmental organization (VWS) that obtains cannabis from Bedrocan Int. BV in Veenendaal, The Netherlands.
Blood sampling Ten mL blood samples will be obtained on 14 occasions on each visit (total volume = 112 mL per visit) at t = 30 and 60 min after oxycodone intake and at t = 5, 20, 40, 60, 120, 180, 185, 200, 220, 240, 300 and 360 min after the first THC inhalation. From these sample, the following drugs will be measured: oxycodone, THC, THC's metabolite 11-OH-THC and cannabidiol (CBD). CBD is measured as it is expected that some minor quantities of CBD are present in Bedrocan.
Arterial blood will be collected in EDTA tubes. After blood collection the tubes will preferably be put in ice water in aluminum foiled containers, will be centrifuged within one hour for 10 minutes at 2000 G at 4 °C. The handling of samples will be done with the lights switched off. The plasma will be equally divided in 2 tubes (Brown Sarstedt) (primary and back-up sample). Plasma samples will be stored at a temperature of -80 °C and blood samples will be sent to Analytical Biochemical Laboratory (ABL) B.V., Assen, The Netherlands on dry-ice. Pharmacokinetic analysis will be performed using a validated assay. Determination of drug concentrations will be performed using liquid chromatography with tandem-mass spectrometer detection (LC-MS/MS). Analysis of the samples and acceptance criteria are indicated in ABL Standard Operating Procedure (SOP) 0251.
