CLARISCAN (Page 4 of 7)

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Gadoterate is a paramagnetic molecule that develops a magnetic moment when placed in a magnetic field. The magnetic moment enhances the relaxation rates of water protons in its vicinity, leading to an increase in signal intensity (brightness) of tissues.

In magnetic resonance imaging (MRI), visualization of normal and pathological tissue depends in part on variations in the radiofrequency signal intensity that occurs with:

1)
differences in proton density
2)
differences of the spin-lattice or longitudinal relaxation times (T1)
3)
differences in the spin-spin or transverse relaxation time (T2)

When placed in a magnetic field, gadoterate shortens the T1 and T2 relaxation times in target tissues. At recommended doses, the effect is observed with greatest sensitivity in the T1-weighted sequences.

12.2 Pharmacodynamics

Gadoterate affects proton relaxation times and consequently the MR signal, and the contrast obtained is characterized by the relaxivity of the gadoterate molecule. The relaxivity values for gadoterate are similar across the spectrum of magnetic field strengths used in clinical MRI (0.2-1.5 T).

Disruption of the blood-brain barrier or abnormal vascularity allows distribution of gadoterate in lesions such as neoplasms, abscesses, and infarcts.

12.3 Pharmacokinetics

The pharmacokinetics of total gadolinium assessed up to 48 hours following an intravenously administered 0.1 mmol/kg dose of gadoterate meglumine in healthy adult subjects demonstrated a mean elimination half-life (reported as mean ± SD) of about 1.4 ± 0.2 hours and 2.0 ± 0.7 hours in female and male subjects, respectively. Similar pharmacokinetic profile and elimination half-life values were observed after intravenous injection of 0.1 mmol/kg of gadoterate meglumine followed 20 minutes later by a second injection of 0.2 mmol/kg (1.7 ± 0.3 hours and 1.9 ± 0.2 hours in female and male subjects, respectively).

Distribution

The volume of distribution at steady state of total gadolinium in healthy subjects is 179 ± 26 and 211 ± 35 mL/kg in female and male subjects respectively, roughly equivalent to that of extracellular water. Gadoterate does not undergo protein binding in vitro. The extent of blood cell partitioning of gadoterate is not known.

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

Metabolism

Gadoterate is not known to be metabolized.

Elimination

Following a 0.1 mmol/kg dose of gadoterate meglumine, total gadolinium is excreted primarily in the urine with 72.9 ± 17.0% and 85.4 ± 9.7% (mean ± SD) eliminated within 48 hours, in female and male subjects, respectively. Similar values were achieved after a cumulative dose of 0.3 mmol/kg (0.1 + 0.2 mmol/kg, 20 minutes later), with 85.5 ± 13.2% and 92.0 ± 12.0% recovered in urine within 48 hours in female and male subjects, respectively.

In healthy subjects, the renal and total clearance rates of total gadolinium are comparable (1.27 ± 0.32 and 1.74 ± 0.12 mL/min/kg in females; and 1.40 ± 0.31 and 1.64 ± 0.35 mL/min/kg in males, respectively) indicating that the drug is primarily cleared through the kidneys. Within the studied dose range (0.1 to 0.3 mmol/kg), the kinetics of total gadolinium appear to be linear.

Specific Populations

Renal Impairment

A single intravenous dose of 0.1 mmol/kg of gadoterate meglumine was administered to 8 patients (5 men and 3 women) with impaired renal function (mean serum creatinine of 498 ± 98 µmol/L in the 10-30 mL/min creatinine clearance group and 192 ± 62 µmol/L in the 30-60 mL/min creatinine clearance group). Renal impairment delayed the elimination of total gadolinium. Total clearance decreased as a function of the degree of renal impairment. The distribution volume was unaffected by the severity of renal impairment (Table 5). No changes in renal function test parameters were observed after gadoterate meglumine injection. The mean cumulative urinary excretion of total gadolinium was approximately 76.9 ± 4.5% in 48 hours in patients with moderate renal impairment, 68.4 ± 3.5% in 72 hours in patients with severe renal impairment and 93.3 ± 4.7% in 24 hours for subjects with normal renal function.

Table 5: Pharmacokinetic Profile of Total Gadolinium in Normal and Renally Impaired Patients
Population Elimination Half-life(hr) Plasma Clearance(L/h/kg) Distribution Volume(L/kg)
Healthy volunteers 1.6 ± 0.2 0.10 ± 0.01 0.246 ± 0.03
Patients with moderate renal impairment 5.1 ± 1.0 0.036 ± 0.007 0.236 ± 0.01
Patients with severe renal impairment 13.9 ± 1.2 0.012 ± 0.001 0.234 ± 0.01

Gadoterate was shown to be dialyzable after an IV injection of gadoterate meglumine in 10 patients with end-stage renal failure who required hemodialysis treatment. Gd serum concentration decreased over time by 88%, 93% and 97% at 0.5 hours, 1.5 hours, and 4 hours after start of dialysis, respectively. A second and third hemodialysis session further removed Gd. After the third dialysis, Gd serum concentration decreased by 99.7%.

Pediatric Population

The pharmacokinetics of gadoterate in pediatric patients receiving gadoterate meglumine aged birth (term neonates) to 23 months, was investigated in an open label, multicenter study, using a population pharmacokinetics approach. A total of 45 subjects (22 males, 23 females) received a single intravenous dose of gadoterate meglumine 0.1 mmol/kg (0.2 mL/kg). The age ranged from less than one week to 23.8 months (mean 9.9 months) and body weight ranged from 3 to 15 kg (mean 8.1 kg). Individual level of renal maturity in the study population, as expressed by eGFR ranged between 52 and 281 mL/min/1.73 m2 and 11 patients had an eGFR below 100 mL/min/1.73 m2 (range 52 to 95 mL/min/1.73 m2).

Gadoterate concentrations obtained up to 8 hours after gadoterate meglumine administration were best fitted using a biphasic model with linear elimination from the intravascular space. The mean clearance adjusted to body weight was estimated at 0.16 ± 0.07 L/h/kg and increased with eGFR. The estimated mean elimination half-life was 1.47 ± 0.45 hours.

The body weight adjusted clearance of gadoterate after single intravenous injection of 0.1 mmol/kg of gadoterate meglumine in pediatric subjects aged less than 2 years was similar to that observed in healthy adults.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term animal studies have not been performed to evaluate the carcinogenic potential of gadoterate meglumine.

Gadoterate meglumine did not demonstrate mutagenic potential in in vitro bacterial reverse mutation assays (Ames test) using Salmonella typhimurium, in an in vitro chromosome aberration assay in Chinese hamster ovary cells, in an in vitro gene mutation assay in Chinese hamster lung cells, nor in an in vivo mouse micronucleus assay.

No impairment of male or female fertility and reproductive performance was observed in rats after intravenous administration of gadoterate meglumine at the maximum tested dose of 10 mmol/kg/day (16 times the maximum human dose based on surface area), given during more than 9 weeks in males and more than 4 weeks in females. Sperm counts and sperm motility were not adversely affected by treatment with the drug.

13.2 Animal Toxicology and/or Pharmacology

Local intolerance reactions, including moderate irritation associated with infiltration of inflammatory cells were observed after perivenous injection in rabbits suggesting the possibility of local irritation if the contrast medium leaks around the veins in a clinical setting [see Warnings and Precautions (5.5)].

Toxicity of gadoterate meglumine was evaluated in neonatal and juvenile (pre- and post-weaning) rats following a single or repeated intravenous administration at doses 1, 2, and 4 times the MHD based on BSA. Gadoterate meglumine was well tolerated at all dose levels tested and had no effect on growth, pre-weaning development, behavior and sexual maturation.

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