ProHance (Page 4 of 5)

12  CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Gadoteridol is a paramagnetic agent and, as such, develops a magnetic moment when placed in a magnetic field. The relatively large magnetic moment produced by the paramagnetic agent results in a relatively large local magnetic field, which can enhance the relaxation rates of water protons in the vicinity of the paramagnetic agent.

In MRI, visualization of normal and pathologic brain tissue depends, in part, on variations in the radiofrequency signal intensity that occur with: 1) differences in proton density; 2) differences of the spin-lattice or longitudinal relaxation times (T1); and 3) differences in the spin-spin or transverse relaxation time (T2). When placed in a magnetic field, gadoteridol decreases T1 relaxation times in the target tissues. At recommended doses, the effect is observed with greatest sensitivity in the T1-weighted sequences.

12.2 Pharmacodynamics

Gadoteridol affects proton relaxation times and consequently the MR signal. Signal intensity is affected by the dose and relaxivity of the gadoteridol molecule. Consistently, for all gadolinium based contrast agents, the relaxivity of gadoteridol decreases with the increase of the magnetic field strength used in clinical MRI (0.2 – 3.0T).

Disruption of the blood-brain barrier or abnormal vascularity allows accumulation of gadoteridol in lesions such as neoplasms, abscesses, and subacute infarcts. The pharmacokinetics of gadoteridol in various lesions is not known.

12.3 Pharmacokinetics

The pharmacokinetics of intravenously administered gadoteridol in normal subjects conforms to a two-compartment open model.

Distribution
After intravenous administration, gadoteridol is rapidly distributed in the extracellular space. The plasma distribution volume (mean ± SD) for the non-renally impaired adults was 0.205 ± 0.025 L/kg. It is unknown if protein binding of gadoteridol occurs in vivo.

Following GBCA administration, gadolinium is present for months or years in brain, bone, skin, and other organs [see Warnings and Precautions (5.3)].

Metabolism
It is unknown if biotransformation or decomposition of gadoteridol occur in vivo.

Elimination
Gadoteridol is eliminated unchanged via the kidneys. The elimination half-life (mean ± SD) is about 1.57 ± 0.08 hours. Within 24 hours post-injection, 94.4 ± 4.8% of the dose is excreted in the urine. The renal and plasma clearance rates (1.41 ± 0.33 mL/ min/kg and 1.50 ± 0.35 mL/ min/kg, respectively) of gadoteridol are essentially identical, indicating no alteration in elimination kinetics on passage through the kidneys and that the drug is essentially cleared through the kidney. The volume of distribution (204 ± 58 mL/kg) is equal to that of extracellular water, and clearance is similar to that of substances which are subject to glomerular filtration.

Specific Populations
Gender
Gender has no clinically relevant effect on the pharmacokinetics of gadoteridol.

Geriatric
There were 7 elderly subjects receiving 0.1 (n = 3) and 0.3 mmol/kg (n = 4) dose of ProHance. The clearance was slightly lower in elderly subjects as compared to non-elderly subjects. [see Use in Specific Populations (8.5)].

Pediatric
A population pharmacokinetic analysis incorporated data from 79 subjects, 45 males and 34 females. Among 79 subjects, 41 were healthy subjects including 28 pediatric subjects between 5 years and 15 years of age. The pediatric subjects received a single intravenous dose of 0.1 mmol/kg of ProHance. From population PK model, the mean Cmax was 0.66 ± 0.21 mmol/L in pediatric subjects 2 years to 6 years of age, 0.58 ± 0.06 mmol/L in pediatric subjects 6 years to 12 years of age, and 0.68 ± 0.12 mmol/L in adolescent subjects older than 12 years. The mean AUC 0-∞ was 0.74 ± 0.20 mmol/L⋅h in pediatric subjects 2 years to 6 years of age, 0.74 ± 0.09 mmol/L⋅h in pediatric subjects 6 years to 12 years of age, and 0.98 ± 0.09 mmol/L⋅h in adolescent subjects older than 12 years of age. The mean distribution half- life (t1/2,alpha ) was 0.14 ± 0.04 hours in pediatric subjects 2 years to 6 years of age, 0.18 ± 0.07 hours in pediatric subjects 6 years to 12 years of age, and 0.20 ± 0.07 hours in adolescent subjects older than 12 years of age. The mean elimination half-life (t1/2,beta ) was 1.32 ± 0.006 hours in pediatric subjects 2 years to 6 years, 1.32 ± 0.07 hours in pediatric subjects 6 years to 12 years of age, and 1.61 ± 0.19 hours in adolescent subjects older than 12 years of age. There was no significant gender-related difference in the pharmacokinetic parameters in the pediatric patients. Over 80% of the dose was recovered in urine for pediatric subjects after 10 hours. Pharmacokinetic simulations indicate similar half-life, AUC, and Cmax values for ProHance in pediatric subjects less than 2 years of age when compared to those reported for adults; no age-based dose adjustment is necessary for this pediatric population.

Renal Impairment
In patients with impaired renal function, the serum half-life of gadoteridol is prolonged. After intravenous injection of 0.1 mmol/kg, the elimination half-life of gadoteridol was 10.65 ± 0.60 hours in mild to moderately impaired patients (creatinine clearance 30 to 60 mL/min) and 9.10±0.26 hours in severely impaired patients not on dialysis (creatinine clearance 10 to 30 mL/min). The mean serum clearance of gadoteridol in patients with normal renal function was 116.14 ± 26.77 mL/min, compared to 37.2 ± 16.4 mL/min in patients with mild to moderate renal impairment and 16.0 ± 3.0 mL/min in patients with severe renal impairment.

In patients with moderately and severely impaired renal function about 97% and 76% of the administered dose was recovered in the urine within 7 days and 14 days, respectively.

For patients receiving hemodialysis, physicians may consider the prompt initiation of hemodialysis following the administration of ProHance in order to enhance the contrast agent’s elimination. Seventy- two percent (72%) of gadoteridol is removed from the body after the first dialysis, 91% after the second dialysis, and 98% after the third dialysis session. [See Warnings and Precautions (5.1) and Use in Specific Populations (8.6).]

13  NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

No animal studies have been performed to evaluate the carcinogenic potential of gadoteridol.

No changes in reproductive performance and outcome of pregnancy were caused in rats and rabbits by daily intravenous administration of ProHance to parent animals before and during gestation up to 1.5 mmol/kg/day (15 times the recommended human dose).

Gadoteridol did not demonstrate genotoxic activity in: bacterial reverse mutation assays using Salmonella typhimurium and Escherichia coli ; a mouse lymphoma forward mutation assay; an in vitro cytogenetic assay measuring chromosomal aberration frequencies in Chinese hamster ovary cells; and an in vivo mouse micronucleus assay at intravenous doses up to 5.0 mmol/kg.

14  CLINICAL STUDIES

14.1 MRI of the CNS

ProHance was evaluated in two multicenter trials of 310 evaluable patients suspected of having neurological pathology. After the administration of ProHance 0.1 mmol/kg IV, the results were similar to those described below [see Clinical Studies (14.2)].

In another multicenter study of 49 evaluable adult patients with known intracranial tumor with high suspicion of having cerebral metastases, two doses of ProHance were administered. First ProHance 0.1 mmol/kg was injected followed 30 minutes later with 0.2 mmol/kg. In comparison to the 0.1 mmol/kg dose alone, the addition of the 0.2 mmol/kg dose improved visualization in 67% and improved border definition in 56% of patients. In comparison to non-contrast MRI, the number of lesions after 0.1 mmol/kg increased in 34% of patients. After ProHance 0.2 mmol/kg, this increased to 44%.

Pediatric Patients
ProHance was evaluated in a multicenter study of 103 patients undergoing brain or spine MRI. Among these patients, the age range was 2 to 20 years; 54 were between 2 and 12 years of age; 74% were Caucasian, 11% Black, 12% Hispanic, 2% Asian, and 2% other. ProHance was given in one single 0.1 mmol/kg dose. Repeat dosing was not studied. The results of the non-contrast and ProHance MRI scans were compared. In this database, MRI enhancement was noted in approximately 60% of the scans and additional diagnostic information in 30 to 95% of the scans.

A prospectively planned study of 125 pediatric patients younger than 2 years of age retrospectively selected was performed. These patients (70 boys and 55 girls) had an age range of 1 day to 24 months old; 17 were less than 1 month of age, 40 were between 1 month and 6 months of age, 29 were between 6 months and 12 months of age, and 39 were between 12 months and 24 months of age; 56% were Caucasian, 25% Black, 5% Asian, and 14% other. ProHance was given in one single 0.1 mmol/kg dose. Repeat dosing was not studied. Three independent, blinded readers evaluated pre-contrast MRI image sets and paired pre-plus-post-contrast MRI image sets using ProHance and rated the images according to three co-primary visualization endpoints: lesion border delineation, visualization of lesion internal morphology, and lesion contrast enhancement. All three blinded readers reported improvement in the paired image sets for each of the three co-primary endpoints.

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