Kevin John Smith

Low absolute bioavailability of oral naloxone in healthy subjects.

OBJECTIVE To determine the absolute bioavailability of naloxone from oral doses ranging from 5 mg to 120 mg. MATERIALS AND METHODS In this open-label study, 28 healthy subjects received naloxone 1 mg (0.4 mg/ml) as an intravenous infusion (reference treatment), and the following oral doses as prolonged release (PR) naloxone tablets: 5 mg, 20 mg, 40 mg, 80 mg and 120 mg. The pharmacokinetic characteristics of 40 mg administered per rectum were also investigated. Each subject received five of the seven treatments as single doses with a 7 day washout between doses. Pharmacokinetic blood sampling and safety monitoring were performed for 24 h after the intravenous dose, and 72 h after the oral and rectal doses. RESULTS The mean absolute bioavailability of naloxone from the orally administered PR tablets was very low, ranging from 0.9% for the 5 mg dose to 2% for the 40, 80 and 120 mg doses, based on AUC(t) values. The pharmacokinetics of naloxone were linear across the range of oral doses. Where AUC(inf) values were calculated, these confirmed the results based on AUC(t) values (mean absolute bioavailability ranging from 1.9% to 2.2% for the 20 mg to 120 mg oral doses). The absolute bioavailability of naloxone was higher following rectal administration compared with oral administration, but was still low at 15%. CONCLUSIONS The mean oral absolute bioavailability of naloxone in this study was ≤ 2% at doses ranging from 5 mg to 120 mg.

Single- and multiple-dose pharmacokinetic evaluation of oxycodone and naloxone in an opioid agonist/antagonist prolonged-release combination in healthy adult volunteers

BACKGROUND There is an increasing body of evidence supporting the need for prophylactic management of the adverse events (AEs) associated with long-term opioid use in patients with chronic pain. Symptoms of bowel dysfunction, such as constipation, may have a significant impact on a patients quality of life and willingness to continue opioid therapy, and therefore should be managed proactively to ensure that the patient can continue effective pain management. The fixed-dose combination (FDC) prolonged-release (PR) oxycodone/naloxone (OXN) may be an effective therapeutic approach to delivering analgesia, with a reduced risk for opioid-induced constipation. OBJECTIVE The aim of this paper was to report the pharmacokinetic results from a single-dose study and a multiple-dose bioequivalence study of OXN versus separate formulations of oxycodone PR and naloxone PR administered concurrently in healthy subjects. METHODS Both studies were open-label, randomized crossover studies in healthy adult male and female subjects. In the single-dose study, subjects were randomly assigned to 1 of 4 treatment groups: OXN FDC (44 x 10/55-mg, 2 x 20/110-mg, or 1 x 40/20-mg dose strength [each given at a total combined dose of 40/220 mg]) or oxycodone PR 40 mg + naloxone PR 20 mg given in separate formulations. In the multiple-dose study, 34 subjects were randomly assigned to 1 of 3 treatment groups: OXN FDC 40/20 mg, oxycodone PR 40 mg, or naloxone PR 20 mg. Treatments were considered bioequivalent if the 90% CIs for relative bioavailability calculations fell within a predetermined range of 80% to 125%. AEs were assessed by the investigator at each study visit. RESULTS The single-dose study included 28 subjects (22 men, 6 women; mean [SD] age, 32.3 [5.44] years; weight, 75.5 [9.3] kg; and body mass index [BMI], 24.2 [2.5] kg/mm(2)). The mean plasma oxycodone concentration-time curves for OXN and oxycodone PR + naloxone PR were similar. With oxycodone, the mean (SD) AUC(t) values with OXN 10/5, 20/10, and 40/20 mg and oxycodone PR + naloxone PR were 473.49 (72.16), 491.22 (82.18), 488.89 (91.04), and 502.28 (84.13) ng . h/mL, respectively; mean C(max) values were 34.91 (4.36), 35.73 (4.93), 34.46 (5.03), and 40.45 (4.71) ng/mL. For naloxone-3-glucuronide (the primary analyte of naloxone), the mean (SD) AUC(t) values with OXN 10/5, 20/10, and 40/20 mg and oxycodone PR + naloxone PR were 539.93 (142.24), 522.45 (128.57), 520.10 (133.18), and 523.37 (119.75) ng . h/mL, respectively; mean C(max) values were 62.01 (15.96), 63.62 (19.51), 61.95 (18.37), and 63.55 (16.75) ng/mL. There were no statistically significant differences between the treatments, and each of the treatment comparisons resulted in 90% CIs within the range for bioequivalence. The multiple-dose steady-state bioequivalence study included 34 subjects (28 men, 6 women; mean [SD] age, 36 [9.4] years; weight,78.9 [11.7] kg; and BMI, 24.6 [1.9] kg/m(2)). No significant differences were observed between the treatments, with the exception of naloxone-3-glucuronide C(min,ss) values. Mean C(min,ss) values of 22.6 and 24.0 ng/mL were obtained for the OXN combination and naloxone PR tablet, respectively. In the multiple-dose study, the most frequently reported AEs with OXN,oxycodone PR, and naloxone PR were headache (7%, 26%, and 17%, respectively), anorexia (10%, 16%, and 13%), and nausea (10%, 13%, and 7%). CONCLUSIONS The results from the single-dose study were consistent with the regulatory definition of bioequivalence of the FDCs and single components across the range of doses administered. The pharmacokinetic properties of the OXN FDC were similar to those of oxycodone PR + naloxone PR given as separate formulations, based on the regulatory definition. These findings were consistent with the results of the multiple-dose steady-state bioequivalence study. In this population of healthy volunteers, the pharmacokinetic properties of oxycodone apparently were not significantly influenced by administering oxycodone in a combination product, and the availability of naloxone-3-glucuronide from OXN was similar to that from the naloxone PR tablet. These findings suggest that the coadministration of oxycodone PR and naloxone PR in an FDC would not significantly affect the bioavailability of either of its constituents in these subjects.

Naloxone as part of a prolonged release oxycodone/naloxone combination reduces oxycodone-induced slowing of gastrointestinal transit in healthy volunteers

Objectives: This exploratory study in healthy volunteers investigated the effect of single doses of oxycodone on gastrointestinal (GI) transit time and the degree to which a single dose of naloxone reverses the oxycodone-induced effect. Methods: Fifteen healthy male volunteers received: oxycodone 10 and 20 mg, oxycodone/naloxone 10/5 and 20/10 mg (all as prolonged release tablets) and placebo. Each dose was radiolabelled and administered with a capsule containing radiolabelled resin (surrogate for GI contents). Results: Scintigraphic analysis showed that 20 mg oxycodone significantly increased colon arrival time (mean 7.19 vs 5.15 h for placebo, p = 0.0159). Mean colon arrival time for oxycodone/naloxone 20/10 mg (5.16 h) was similar to placebo, although the difference between oxycodone/naloxone 20/10 mg versus oxycodone 20 mg was not significant (p = 0.0653). Colonic geometric centre analysis showed a significant increase in mean time for the resin to reach the colon following oxycodone 10 and 20 mg compared with placebo (increases of 5.3 and 8.8 h). There was no significant effect of naloxone at the lower dose; however, oxycodone/naloxone 20/10 mg significantly reduced mean colonic transit time by 2.1 h (p = 0.0376). Conclusion: A single dose of oxycodone 20 mg significantly prolonged GI transit time but this effect was reduced by co-administration of naloxone.

Pharmacokinetics of concentrated naloxone nasal spray for opioid overdose reversal: Phase I healthy volunteer study

Abstract Background and Aims Take‐home naloxone can prevent death from heroin/opioid overdose, but pre‐provision is difficult because naloxone is usually given by injection. Non‐injectable alternatives, including naloxone nasal sprays, are currently being developed. To be effective, the intranasal (i.n.) spray dose must be adequate but not excessive, and early absorption must be comparable to intramuscular (i.m.) injection. We report on the pharmacokinetics (PK) of a specially produced concentrated novel nasal spray. The specific aims were to: (1) estimate PK profiles of i.n. naloxone, (2) compare early systemic exposure with i.n. versus i.m. naloxone and (3) estimate i.n. bioavailability. Design Open‐label, randomized, five‐way cross‐over PK study. Setting Clinical trials facility (Croydon, UK). Participants Thirty‐eight healthy volunteers (age 20–54 years; 11 female). Intervention and comparator Three doses of i.n. (1 mg/0.1 ml, 2 mg/0.1 ml, 4 mg/0.2 ml) versus 0.4 mg i.m. (reference) and 0.4 mg intravenous (i.v.) naloxone. Measurements Regular blood samples were taken, with high‐frequency sampling during the first 15 minutes to capture early systemic exposure. PK parameters were determined from plasma naloxone concentrations. Exploratory analyses involved simulation of repeat administration. Findings Mean peak concentration (Cmax) values for 1 mg (1.51 ng/ml), 2 mg (2.87 ng/ml) and 4 mg (6.02 ng/ml) i.n. exceeded 0.4 mg i.m. (1.27 ng/ml) naloxone. All three i.n. doses rapidly achieved plasma levels > 50% of peak concentrations (T50%) by 10 minutes, peaking at 15–30 minutes (Tmax). For comparison, the i.m. reference reached Tmax at 10 minutes. Mean bioavailability was 47–51% for i.n. relative to i.m. naloxone. Simulation of repeat dosing (2 × 2 mg i.n. versus 5 × 0.4 mg i.m. doses) at 3‐minute intervals showed that comparable plasma naloxone concentrations would be anticipated. Conclusions Concentrated 2 mg intranasal naloxone is well‐absorbed and provides early exposure comparable to 0.4 mg intramuscular naloxone, following the 0.4 mg intramuscular curve closely in the first 10 minutes post‐dosing and maintaining blood levels above twice the intramuscular reference for the next 2 hours.

Validated in vitro/in vivo correlation of prolonged-release oxycodone/naloxone with differing dissolution rates in relation to gastrointestinal transit times

Objectives: To formally establish the relationship between oxycodone dissolution, in vitro, from a prolonged-release, oral, combination of oxycodone and naloxone (OXN PR) tablets with in vivo absorption, by developing a validated Level A in vitro/in vivo correlation (IVIVC) and subsequently ascertaining the temporal absorption of oxycodone during gastrointestinal transit. Methods: In vitro dissolution data from formulations of OXN PR (20/10 mg) tablets with slow, medium and fast dissolution rates were generated using United States Pharmacopeia I apparatus 2 (paddle at 50 rpm) in simulated gastric fluid, pH 1.2. These batches were administered to healthy volunteers and plasma concentration data were collected during a randomised, open-label, cross-over study. A Level A correlation was established for oxycodone through the determination of in vivo absorption profiles obtained by deconvolution of plasma concentrations with in vitro dissolution data. The IVIVC model was validated using the internal predictability assessment. Results: A Level A correlation between the in vitro and in vivo release data was established. The polynomial function describing the IVIVC produced a goodness of fit (R2) of 0.99. Conclusions: The rate of absorption of oxycodone from OXN PR tablets correlated well with the in vitro release rates, demonstrating that a Level A IVIVC with internal predictability has been successfully developed for OXN PR tablets. In conjunction with a previous gastrointestinal transit study, this report demonstrates that the majority of oxycodone enters the circulation before reaching the colon, thus it is important that naloxone counteracts opioid-induced bowel dysfunction throughout the entire gut.