Clinical Pharmacology for Xenoview
Mechanism Of Action
When hyperpolarized xenon Xe 129 gas is inhaled, a multi-nuclear capable MRI scanner can be used to image the hyperpolarized xenon Xe 129 distribution throughout the ventilated lung. Hyperpolarized xenon Xe 129 nuclei are directly detected by a Xe 129 MRI coil.
Pharmacodynamics
The MRI signal of hyperpolarized xenon Xe 129 is dependent on the volume of gas inhaled, degree of xenon Xe 129 isotopic enrichment, and degree of hyperpolarization [see DOSAGE AND ADMINISTRATION].
Pharmacokinetics
The pharmacokinetics of hyperpolarized xenon Xe 129 are similar to those of non-polarized xenon.
Distribution
Xenon is a readily diffusible gas. Inhalation of xenon results in dispersion in the ventilated areas of the lung with uptake of a small amount of xenon into the pulmonary vessels followed by distribution to more distal organs. The solubility of xenon is higher in fatty tissues than in aqueous tissues and body compartments such as plasma.
Elimination
Following a single breath hold, xenon is eliminated through exhalation with an elimination half-life of 14.5 seconds for a 75% Xe/25% N2 gas mixture and 14.3 seconds for a 25% Xe/75% N2 gas mixture.
Clinical Studies
The safety and efficacy of XENOVIEW were evaluated in two prospective, multi-center, randomized, open-label, cross-over clinical trials that compared XENOVIEW MRI to xenon Xe 133 scintigraphy in adult patients with pulmonary disorders: Study 1 (NCT03417687) and Study 2 (NCT03418090). The mean XENOVIEW dose used in these trials was 99 mL DE of hyperpolarized xenon Xe 129 at the time of measurement within 5 minutes of administration.
Study 1
Study 1 compared XENOVIEW and xenon Xe 133 imaging in patients being evaluated for possible lung resection surgery with respiratory disorders including: pulmonary mass (44%), COPD (35%), cough (15%), sleep apnea syndrome (12%), and asthma (12%). A total of 32 patients, with a mean age of 62 years (range 25 to 77 years) of whom 78% were White and 69% were male, completed both scans.
On each XENOVIEW and xenon Xe 133 scan, the fraction of total signal in the lungs was calculated in each of six zones consisting of upper, middle, and lower regions in each lung. These values were used to estimate the post-operative percentage of lung ventilation predicted to remain after planned resection of a pre-specified lung area.
One of the 32 patients who completed both scans was excluded from the primary analysis because no planned resection area was recorded. In the remaining 31 patients, the mean within-patient difference in the predicted post-operative percentage of remaining lung ventilation between XENOVIEW and xenon Xe 133 imaging was within a pre-specified equivalence interval with an observed estimate of 1.4% (95% confidence interval: -0.8%, 3.6%). In an exploratory analysis that standardized the within-patient difference of the predicted remaining lung ventilation between XENOVIEW and xenon Xe 133 imaging to each patient’s xenon Xe 133 results, the percentage of patients who had standardized differences within ± 10%, ± 15%, and ± 20% were 81% (25/31), 94% (29/31), and 94% (29/31), respectively.
Study 2
Study 2 compared XENOVIEW and xenon Xe 133 imaging in patients being evaluated for possible lung transplant surgery with respiratory disorders including: interstitial lung disease (49%), idiopathic pulmonary fibrosis (29%), COPD (22%), sleep apnea syndrome (16%), other pulmonary fibrosis (14%), allergic rhinitis (12%), and cough (10%). A total of 49 patients, with a mean age of 62 years (range 19 to 77 years), of whom 94% were White and 69% were male, completed both scans.
On each XENOVIEW and xenon Xe 133 scan, right lung signal and total signal in the lungs were calculated and used to estimate the percentage of overall lung ventilation contributed by the right lung.
In the primary analysis of the 49 patients who completed both scans, the mean within-patient difference in the percentage of overall lung ventilation contributed by the right lung between XENOVIEW and xenon Xe 133 imaging was within a pre-specified equivalence interval with an observed estimate of 1.6% (95% confidence interval: -3.7%, 0.5%). In an exploratory analysis that standardized the within-patient difference of right lung ventilation between XENOVIEW and xenon Xe 133 imaging to that of each patient’s xenon Xe 133 results, the percentage of patients who had standardized differences of ± 10%, ± 15%, and ± 20% were 65% (32/49), 80% (39/49), and 96% (47/49), respectively.