Mechanism of Action
Gadobenate dimeglumine is a paramagnetic agent and, as such, develops a magnetic moment when placed in a magnetic field. The large magnetic moment produced by the paramagnetic agent results in a large local magnetic field, which can enhance the relaxation rates of water protons in its vicinity leading to an increase of signal intensity (brightness) of tissue.
In magnetic resonance imaging (MRI), visualization of normal and pathological 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, gadobenate dimeglumine decreases the T1 and T2 relaxation time in target tissues. At recommended doses, the effect is observed with greatest sensitivity in the T1-weighted sequences.
Unlike other tested paramagnetic contrast agents (See Table 2), MultiHance demonstrates weak and transient interactions with serum proteins that causes slowing in the molecular tumbling dynamics, resulting in strong increases in relaxivity in solutions containing serum proteins. The improved relaxation effect can contribute to increased contrast-to-noise ratio and lesion-to-brain ratio, which may improve visualization.
TABLE 2: RELAXIVITY (mM-1s-1) OF GADOLINIUM CHELATES
|r1 and r2 relaxivities indicate the
efficiency in shortening T1 and T2 relaxation times, respectively.
1 In heparinized human plasma, at 39°C.
2 In citrated human plasma, at 37°C.
--- Not available
MultiHance injection does not cross the intact blood-brain barrier and, therefore, does not enhance normal brain or lesions that have a normal blood-brain barrier, e.g., cysts, mature postoperative scars. However, disruption of the blood-brain barrier or abnormal vascularity allows enhancement by MultiHance of lesions such as neoplasms, abscesses, and infarcts. Uptake of MultiHance into hepatocytes has been demonstrated.
Three single-dose intravenous studies were conducted in 32 healthy male subjects to assess the pharmacokinetics of gadobenate dimeglumine. The doses administered in these studies ranged from 0.005 to 0.4 mmol/kg. Upon injection, the meglumine salt is completely dissociated from the gadobenate dimeglumine complex. Thus, the pharmacokinetics is based on the assay of gadobenate ion, the MRI contrast effective ion in gadobenate dimeglumine. Data for plasma concentration and area under the curve demonstrated linear dependence on the administered dose. The pharmacokinetics of gadobenate ion following intravenous administration can be best described using a two-compartment model.
Gadobenate ion has a rapid distribution half-life (reported as mean ± SD) of 0.084 ± 0.012 to 0.605 ± 0.072 hours. Volume of distribution of the central compartment ranged from 0.074 ± 0.017 to 0.158 ± 0.038 L/kg, and estimates of volume of distribution by area ranged from 0.170 ± 0.016 to 0.282 ± 0.079 L/kg. These latter estimates are approximately equivalent to the average volume of extracellular body water in man. In vitro studies showed no appreciable binding of gadobenate ion to human serum proteins.
Gadobenate ion is eliminated predominately via the kidneys, with 78% to 96% of an administered dose recovered in the urine. Total plasma clearance and renal clearance estimates of gadobenate ion were similar, ranging from 0.093 ± 0.010 to 0.133 ± 0.270 L/hr/kg and 0.082 ± 0.007 to 0.104 ± 0.039 L/hr/kg, respectively. The clearance is similar to that of substances that are subject to glomerular filtration. The mean elimination half-life ranged from 1.17 ± 0.26 to 2.02 ± 0.60 hours. A small percentage of the administered dose (0.6% to 4%) is eliminated via the biliary route and recovered in feces.
There was no detectable biotransformation of gadobenate ion. Dissociation of gadobenate ion in vivo has been shown to be minimal, with less than 1% of the free chelating agent being recovered alone in feces.
Pharmacokinetics in Special Populations
Renal Impairment: A single intravenous dose of 0.2 mmol/kg of MultiHance was administered to 20 subjects with impaired renal function (6 men and 3 women with moderate renal impairment [urine creatinine clearance >30 to <60 mL/min] and 5 men and 6 women with severe renal impairment [urine creatinine clearance >10 to <30 mL/min]). Mean estimates of the elimination half-life were 6.1 ± 3.0 and 9.5 ± 3.1 hours for the moderate and severe renal impairment groups, respectively as compared with 1.0 to 2.0 hours in healthy volunteers.
Hemodialysis: A single intravenous dose of 0.2 mmol/kg of MultiHance was administered to 11 subjects (5 males and 6 females) with end-stage renal disease requiring hemodialysis to determine the pharmacokinetics and dialyzability of gadobenate. Approximately 72% of the dose was recovered by hemodialysis over a 4-hour period. The mean elimination half-life on dialysis was 1.21 ± 0.29 hours as compared with 42.4 ± 24.4 hours when off dialysis.
Hepatic Impairment: A single intravenous dose of 0.1 mmol/kg of MultiHance was administered to 11 subjects (8 males and 3 females) with impaired liver function (Class B or C modified Child-Pugh Classification). Hepatic impairment had little effect on the pharmacokinetics of MultiHance with the parameters being similar to those calculated for healthy subjects.
Gender, Age, Race: A multiple regression analysis performed using pooled data from several pharmacokinetic studies found no significant effect of sex upon the pharmacokinetics of gadobenate. Clearance appeared to decrease slightly with increasing age. Since variations due to age appeared marginal, dosage adjustment for geriatric population is not recommended. Pharmacokinetic differences due to race have not been systematically studied.
Pediatric: A population pharmacokinetic analysis incorporated data from 25 healthy subjects (14 males and 11 females) and 15 subjects undergoing MR imaging of the central nervous system (7 males and 8 females) between ages of 2 and 16 years. The subjects received a single intravenous dose of 0.1 mmol/kg of MultiHance. The geometric mean Cmax was 62.3 μg/mL (n=16) in children 2 to 5 years of age, and 64.2 μg/mL (n=24) in children older than 5 years. The geometric mean AUC0-∞ was 77.9 μg-h/mL in children 2-5 years of age (n=16) and 82.6 μg-h/Ml in children older than 5 years (n=24). The geometric mean half-life was 1.2 hours in children 2 to 5 years of age and 0.93 hours in children older than 5 years. There was no significant gender-related difference in the pharmacokinetic parameters in the pediatric patients. Over 80% of the dose was recovered in urine after 24 hours.
MultiHance was evaluated in 426 adult patients in 2 controlled clinical trials of the central nervous system (Study A and Study B), enrolling 217 men and 209 women with a mean age of 52 years (range 18 to 88 years). The racial and ethnic representations were 88% Caucasian, 6% Black, 4% Hispanic, 1% Asian, and 1% other racial or ethnic groups. These trials were designed to compare MultiHance contrast MRI to non-contrast MRI alone. In Study A, patients highly suspected of having a lesion(s) of the CNS based on nuclear medicine imaging, computed tomography (CT), contrast CT, MRI, contrast- MRI, or angiography were randomized to receive two MRI evaluations with 0.05 mmol/kg (n=140) or 0.1 mmol/kg (n=136) of MultiHance. In Study B, patients with known metastatic disease to the CNS were randomized to receive two MRI evaluations with 0.05 mmol/kg (n=74) or 0.1 mmol/kg (n=76) of MultiHance. MRI scans were performed pre-contrast and within 5 minutes after each injection. The studies were designed to evaluate the effect of MultiHance MRI compared to the non-contrast MRI on a lesion level. Pre-contrast, post-contrast, and pre-plus-post contrast images (paired images) were independently evaluated by three blinded readers. The images were evaluated for the following endpoints using a scale from 0 to 4: the degree of lesion border delineation, the degree of visualization of lesion internal morphology, and the degree of lesion contrast enhancement. Lesion counting was also performed for the pre-contrast and paired image sets.
The 0.1 mmol/kg dose of MultiHance demonstrated consistently better visualization for all readers for all visualization endpoints. However, the 0.05 mmol/kg dose of MultiHance provided inconsistent visualization results between readers.
Comparison of pre-contrast versus post-contrast (0.1 mmol/kg) images showed that the mean score differences were significant and favored contrast for subjects in Study B (all subjects with known metastatic lesions) and for subjects with known tumors in Study A. However, the mean score differences between the pre-contrast and post-contrast images were not significant for non-tumor patients in Study A. These negative results may be attributed to a lack of lesion enhancement in non-tumor CNS disease.
Table 3 shows a comparison of paired images (pre-and post-contrast) versus pre-contrast images with respect to the difference in the mean score and with respect to the proportion of lesions read as better, worse, or the same as the pre-contrast MRI images. Table 3 shows that based on a lesion-level analysis 0.1 mmol/kg MultiHance provided a statistically significant improvement for the three structural parameters evaluated. Also, more lesions were seen in the paired images than in the pre-contrast images alone.
TABLE 3: LESION LEVEL RESULTS OF MRI CENTRAL NERVOUS
SYSTEM ADULT STUDIES WITH 0.1 MMOL/KG MULTIHANCE
|Endpoints||Study A||Study B|
|Reader 1||Reader 2||Reader 3||Reader 1||Reader 2||Reader 3|
|N = 395||N = 384||N = 299||N = 245||N = 275||N = 254|
|Border Delineation: Difference of Means a||0.8*||0.6*||0.8*||1.8*||1.5*||1.9*|
|Worseb||44 (11 %)||61 (16%)||57 (19%)||13(5%)||24 (9%)||15 (6%)|
|Same||146(37%)||168(44%)||89 (30%)||11 (5%)||19(7%)||18 (7%)|
|Better||205 (52%)||155(40%)||153(51%)||221 (90%)||232 (84%)||221 (87%)|
|Internal Morphology: Difference of Means||0.8*||0.6*||0.7*||1.7*||1.4*||2.1*|
|Worse||37 (10%)||63 (17%)||62(21%)||13(5%)||26 (10%)||14 (5%)|
|Same||147(37%)||151 (39%)||84 (28%)||16(7%)||22 (8%)||22 (9%)|
|Better||211 (53%)||170(44%)||153(51%)||216(88%)||227 (82%)||218(86%)|
|Contrast Enhancement: Difference of Means||0.7*||0.5*||0.8*||1.9*||1.3*||1.9*|
|Worse||75 (19%)||74 (19%)||50 (17%)||13(5%)||32 (12%)||17 (7%)|
|Same||148(37%)||152(40%)||109(36%)||11 (5%)||21 (7%)||14 (5%)|
|Better||172(44%)||158(41%)||140(47%)||221 (90%)||222(81%)||223 (88%)|
|a Difference of means = (paired mean) - (pre
b Worse = paired score is less than the pre score
Same = paired score is the same as the pre score
Better = paired score is greater than the pre score
* Statistically significant for the mean (paired t test)
The efficacy and safety of MultiHance were evaluated in 92 pediatric patients with known or highly suspected disease of the central nervous system. MRI scans were performed pre-contrast and within 3 to 10 minutes following the administration of MultiHance 0.1 mmol/kg. Pre-contrast, post-contrast, and pre-plus-post contrast images (paired images) were independently evaluated by three blinded readers on a lesion level. The images were evaluated for the same endpoints as in the adult central nervous system trials using a scale from 0 to 4: the degree of lesion border delineation, the degree of visualization of lesion internal morphology, and the degree of lesion contrast enhancement. Lesion counting was also performed for the pre-contrast and paired image sets. The pre-contrast versus the paired image set was the primary comparison. Fortynine percent of study subjects were male and the overall mean age was 10.6 years (range 2 to 17 years). The racial and ethnic representations were 77% Caucasian, 13% Asian, 5% Black, and 4% other racial or ethnic groups. MultiHance increased lesion border delineation, lesion internal morphology, and lesion contrast enhancement relative to non-contrast and these results were comparable to those seen in adults.
Last reviewed on RxList: 7/12/2012
This monograph has been modified to include the generic and brand name in many instances.
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