The pharmacokinetic interaction between nasally administered naloxone and the opioid remifentanil in human volunteers

Purpose Remifentanil has been shown to increase the bioavailability of nasally administered naloxone. The aim of this study was to explore the nature of this observation. Methods We analysed samples from three pharmacokinetic studies to determine the serum concentrations of naloxone-3-glucuronide (N3G), the main metabolite of naloxone, with or without exposure to remifentanil. To enable direct comparison of the three studies, the data are presented as metabolic ratios (ratio of metabolite to mother substance, N3G/naloxone) and dose-corrected values of the area under the curve and maximum concentration (Cmax). Results Under remifentanil exposure, the time to maximum concentration (Tmax) for N3G was significantly higher for intranasal administration of 71 min compared to intramuscular administration of 40 min. The dose-corrected Cmax of N3G after intranasal administration of naloxone under remifentanil exposure was significantly lower (4.5 ng/mL) than in subjects not exposed to remifentanil (7.8–8.4 ng/mL). The metabolic ratios after intranasal administration rose quickly after 30–90 min and were 2–3 times higher at 360 min compared to intravenous and intramuscular administration. Remifentanil exposure resulted in a much slower increase of the N3G/naloxone ratio after intranasal administration compared to intranasal administration with the absence of remifentanil. After remifentanil infusion was discontinued, this effect gradually diminished. From 240 min there was no significant difference between the ratios observed after intranasal naloxone administration. Conclusion Remifentanil increases the bioavailability of naloxone after nasal administration by reducing the pre-systemic metabolism of the swallowed part of the nasal dose. Supplementary Information The online version contains supplementary material available at 10.1007/s00228-021-03190-1.


Subjects
Twelve healthy volunteers participated in each of study I and II. In study III, 22 participants participated in the study and 12 of these were randomly selected for analysis of naloxone-3glucuronide after the study had been completed. In all, 36 healthy volunteers (18 men, 18 women) contributed with samples from three separate studies. The study designs and the summary of the studies are shown in supplementary tables S1 and S2. Healthy men and women aged 18-40 were eligible for inclusion. Before screening subjects were given information about the study and signed a written informed consent.
Inclusion criteria were ASA class I (medical history, clinical examination, ECG without pathological findings and with laboratory tests including haemoglobin, creatinine, alanine aminotransferase, aspartate aminotransferase and gamma-glutamyltransferase within reference values). A body mass index within 18.5-24.9 (study I) and 18.5-26.0 kg/m2 (study II and III) was requiered. Women with childbearing potential had to use high efficacy contraception throughout the study until the last visit.
Exclusion criteria in all the studies were: -Subjects using medication on a regular basis, including regular use of nasal spray of any form -History of prior drug allergy -Hypersensitivity to naloxone or any of its excipients -Subjects having local nasal disease or nasal surgery for the last 2 months -Pregnant or breastfeeding women. A serum HCG below 3 U/L must be demonstrated in women of childbearing potential at screening visit -Current or history of drug or alcohol abuse -Have received another new medical chemical entity (defined as a compound which has not been approved for marketing) or have participated in any other clinical study that included drug treatment within 3 months of the administration of investigational product in this study (only for study III). -Investigator considers subject unlikely to comply with study procedures, restrictions and/ or other requirements.
For study I and II the following exclusion criteria were also applied as the subjects were given remifentanil: -Participants with a history of contact with police or authorities in relation to alcohol or drug offences -A history of prolonged use of opioid analgesics -Participants who had access to remifentanil or other potent opioids in their workplace -Previous participation in trials where they received opioids -Subjects who had a history of drug and/or alcohol abuse were excluded.
Potential participants had to answer the CAGE-AID questionnaire, and subjects answering yes to two or more questions were excluded. In study II they also had to pass the Allen's test of collateral circulation of the hand, and blood donation 6 weeks before and after study participation was not allowed.

Study designs
All studies were open, randomised, controlled cross-over trials, except study II that was a study with only one treatment arm. The studies were conducted during 2014 -2016 at the Clinical Research Facility, St. Olavs hospital, Trondheim University Hospital, Norway. Study III also had a study centre at Rikshospitalet, Oslo, Norway.
Each study session lasted for 6-7 hours and the sessions were separated by at least 72-hours wash-out periods, in all studies except study II having a three-hours study session only. Subjects had to abstain from all medications for 7 days before treatment. No fasting or other meal restrictions were required in study III. In study I and II the participants were exposed to a remifentanil infusion, and a pre-intervention 6-hours fasting regime was required. Naloxone was given intranasally (IN), intravenously (IV) and intramuscularly (IM) in various doses. The doses and administration routes of naloxone for the different studies are described in table S1. The order of treatment allocation was decided by randomisation. This was performed in a concealed fashion by an internet-based service.

Treatments
Naloxone was given as naloxone hydrochloride. Dose and route of naloxone administration for the different studies are shown in table S1. All medications were weighed before and after delivery for determination of the exact doses.
Nasal naloxone for study I were delivered by Department of Biopharmaceutical Production, Norwegian Institute of Public Health (FHI), Oslo, Norway. Nasal sprays for study III were manufactured by AS Den norske Eterfabrikk, Oslo, Norway. A disposable nasal spray device from Aptar Pharma (Louveciennes, France), the "Aptar Unitdose" device was used for delivering the nasal spray. The device delivered 0.1 ml per actuation. The formulation was tested with different concentrations of naloxone hydrochloride: 8 mg/ml and 14 mg/ml. The nasal formulation is previously published [4].
The Hospital Pharmacy at St Olavs hospital, Trondheim University Hospital delivered Naloxon B. Braun 0.4 mg/ml (Melsungen, Germany) for intravenous and intramuscular administration. The intravenous injections were administrated as a 1.0 -2.5 ml rapid bolus. Intramuscular injections were administered as 2.0 ml bolus in the deltoid muscle.

Pharmacodynamic study design
Study I and II were pharmacokinetic-pharmacodynamic studies. To assess the effects of naloxone it must be administered to subjects under influence of an opioid. The subjects were given an intravenous infusion of remifentanil. It was given by plasma target controlled infusion (TCI), Minto model using Alaris PK Guardrail pumps (CareFusion Cooperation, UK). Three different targets were used in study I: 1.0 (n=3), 1.3 (n=5) and 2.5 ng/ml (n=4). The same participant had the same target on both study days. In study II the plasma target was 1.3 ng/ml for all the participants. The infusion was given for 12 minutes before naloxone was administrated. The infusion was discontinued 90 minutes after naloxone administration. The total infusion time was therefore 102 minutes.
The effect of the opioid and the antagonist were measured with pupillometry, a wellrecognised measure of opioid effect in experimental studies in man. The measurements were conducted using a Neuroptics VIP 200 Pupillometer (Neuroptics, Irvine, CA, USA), and the participants were asked to focus on a distant point in the room during the measurements. The participants were kept in a room with stable ambient lighting, and a luxometer was used to ensure similar light conditions in each visit of each participant.

Blood sampling
Every study day a venous cannula for blood sampling was placed in the antecubital fossa, and participants were monitored for oxygen saturation and non-invasive blood pressure for safety. For the studies with intravenous administration of medications, a separate venous cannula was placed for this purpose. Venous blood samples were taken prior to naloxone administration and at 2, 5, 10, 15, 20, 25, 30, 35, 45, 60, 90, 120, 240, and 360 min after naloxone administration. For study II, the last sample was taken at 120 minutes.
In studies I-II serum was used to analyze naloxone and the main metabolite naloxone-3glucuronide. Plasma (K2EDTA) was used for these analyses in study III.