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Magnevist (Gadopentetate Dimeglumine) - Description and Clinical Pharmacology

 
 



DESCRIPTION

Magnevist® (brand of gadopentetate dimeglumine) injection is the N-methylglucamine salt of the gadolinium complex of diethylenetriamine pentaacetic acid, and is an injectable contrast medium for magnetic resonance imaging (MRI). Magnevist Injection is provided as a sterile, clear, colorless to slightly yellow aqueous solution for intravenous injection.

Magnevist Injection is a 0.5-mol/L solution of 1-deoxy-1-(methylamino)-D-glucitol dihydrogen [N,N-bis[2-[bis(carboxymethyl)amino]ethyl] glycinato (5-) ]gadolinate(2-)(2:1) with a molecular weight of 938, an empirical formula of C28H54GdN5O20, and has the following structural formula:

Each mL of Magnevist injection contains 469.01 mg gadopentetate dimeglumine, 0.99 mg meglumine, 0.40 mg diethylenetriamine pentaacetic acid, and water for injection. Magnevist injection contains no antimicrobial preservative.

Magnevist Injection has a pH of 6.5 to 8.0. Pertinent physicochemical data are noted below:

PARAMETER

Osmolality (mOsmol/kg) water)

at 37° C

1,960

Viscosity (CP)

at 20° C

4.9

at 37° C

2.9

Density (g/mL)

at 25° C

1.195

Specific Gravity

at 25° C

1.208

Octanol: H2O Coefficient

at 25° C, pH7 log Pow = - 5.4

Magnevist injection has an osmolality 6.9 times that of plasma, which has an osmolality of 285 mOsmol/kg water. Magnevist injection is hypertonic under conditions of use.

CLINICAL PHARMACOLOGY

Mechanism of Action

Gadopentetate dimeglumine is a paramagnetic agent and, as such, it 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.

Pharmacodynamics

In magnetic resonance imaging (MRI), visualization of normal and pathological brain tissue depends in part on variations in the radiofrequency signal intensity that occur with 1) changes in proton density; 2) alteration of the spin-lattice or longitudinal relaxation time (T1); and 3) variation of the spin-spin or transverse relaxation time (T2). When placed in a magnetic field, gadopentetate dimeglumine decreases the T1 and T2 relaxation time in tissues where it accumulates. At usual doses, the effect is primarily on the T1 relaxation time.

Gadopentetate dimeglumine does not cross the intact blood-brain barrier and, therefore, does not accumulate in normal brain or in lesions that do not have an abnormal blood-brain barrier, e.g., cysts, mature post-operative scars, etc. However, disruption of the blood-brain barrier or abnormal vascularity allows accumulation of gadopentetate dimeglumine in lesions such as neoplasms, abscesses, and subacute infarcts. The pharmacokinetic parameters of Magnevist in various lesions are not known.

Pharmacokinetics

The pharmacokinetics of intravenously administered gadopentetate dimeglumine in normal subjects conforms to a two compartment open-model with mean distribution and elimination half-lives (reported as mean ± SD) of about 0.2 ± 0.13 hours and 1.6 ± 0.13 hours, respectively.

Upon injection, the meglumine salt is completely dissociated from the gadopentetate dimeglumine complex. Gadopentetate is exclusively eliminated in the urine with 83 ± 14% (mean ± SD) of the dose excreted within 6 hours and 91 ± 13% (mean ± SD) by 24 hours, post-injection. There was no detectable biotransformation or decomposition of gadopentetate dimeglumine.

The renal and plasma clearance rates (1.76 ± 0.39 mL/min/kg and 1.94 ± 0.28 mL/min/kg, respectively) of gadopentetate 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 (266 ± 43 mL/kg) is equal to that of extracellular water and clearance is similar to that of substances which are subject to glomerular filtration.

In vitro laboratory results indicate that gadopentetate does not bind to human plasma protein. In vivo protein binding studies have not been done.

Renal Impairment

Gadopentetate dimeglumine is excreted via the kidneys, even in patients with impaired renal function. In patients with impaired renal function, the serum half-life of gadopentetate dimeglumine is prolonged. Mean serum elimination half-lives of a single intravenous dose of gadopentetate dimeglumine (0.1 mmol/kg) were 2.6 ± 1.2 h, 4.2 ± 2.0 h and 10.8 ± 6.9 h, for mildly (creatinine clearance, CLCR = 60 to < 90 mL/min), moderately (CLCR = 30 to < 60 mL/min) and severely (CLCR = < 30 mL/min) impaired patients, respectively, as compared with 1.6 ± 0.1 h in healthy subjects.

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility

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

A comprehensive battery of in vitro and in vivo studies in bacterial and mammalian systems suggest that gadopentetate dimeglumine is not mutagenic or clastogenic and does not induce unscheduled DNA repair in rat hepatocytes or cause cellular transformation of mouse embryo fibroblasts. However, the drug did show some evidence of mutagenic potential in vivo in the mouse dominant lethal assay at doses of 6 mmol/kg, but did not show any such potential in the mouse and dog micronucleus tests at intravenous doses of 9 mmol/kg and 2.5 mmol/kg, respectively.

When administered intra-peritoneally to male and female rats daily prior to mating, during mating, and during embryonic development for up to 74 days (males) or 35 days (females), gadopentetate caused a decrease in number of corpora lutea at the 0.1 mmol/kg dose level. After daily dosing with 2.5 mmol/kg suppression of food consumption and body weight gain (males and females) and a decrease in the weights of testes and epididymis were observed.

In a separate experiment in rats, daily injections of gadopentetate dimeglumine over 16 days caused spermatogenic cell atrophy at a dose level of 5 mmol/kg but not at a dose level of 2.5 mmol/kg. This atrophy was not reversed within a 16-day observation period following the discontinuation of the drug.

CLINICAL STUDIES

Magnevist injection was administered to 1272 patients in open label controlled clinical studies. The mean age of these patients was 46.4 years (range 2 to 93 years). Of these patients, 55% (700) were male and 45% (572) were female. Of the 1271 patients who received Magnevist injection and for whom race was reported, 82.1% (1043) were Caucasian, 9.7% (123) were Black, 5.3% (67) were Hispanic, 2.1% (27) were Oriental/Asian, and 0.9% (11) were other. Of the 1272 patients, 550 patients were evaluated in blinded reader studies. These evaluated the use of contrast enhancement in magnetic resonance imaging of lesions in the head and neck, brain, spine and associated tissues, and body (excluding the heart). Of the 550 patients, all patients had a reason for an MRI and efficacy assessments were based on pre-and post- Magnevist injection film quality, film contrast, lesion configuration (border, size, and location), and the number of lesions. The protocols did not include systematic verification of specific diseases or histopathologic confirmation of findings.

Of the above 550 patients, 97 patients received 0.1 mmol/kg Magnevist injection IV in two clinical trials of Magnevist MRI contrast enhancement for body imaging. Of these 97, 68 had MRIs of the internal organs/structures of the abdomen or thorax (excluding the heart); 8 had breast images and 22 had images of appendages. The results of MRIs before and after Magnevist use were compared blindly. Overall additional lesions were identified in 22/97 (23%) of the patients after Magnevist injection. The mean number of lesions identified before (1.49/patient) and after Magnevist (1.75/patient) were similar. Seven (8%) of the patients had lesions seen before Magnevist that were not seen after Magnevist. Overall, after Magnevist injection, 41% of the images had a higher contrast score than before injection; and 18% of the images had a higher contrast score before Magnevist injection than after Magnevist injection. Magnevist MRI of the 8 patients with breast images were not systematically compared to the results to mammography, breast biopsy or other modalities. In the 22 patients with appendage images (e.g., muscle, bone and intraarticular structures), Magnevist MRI was not systematically evaluated to determine the effects of contrast biodistribution in these different areas.

Of the above 550 patients, 66 patients received Magnevist 0.1 mmol/kg IV in clinical trials of Magnevist MRl contrast enhancement of lesions in the head and neck. A total of 66 MRI images were evaluated blindly by comparing each pair of MRI images, before and after Magnevist injection. In these paired images, 56/66 (85%) had greater enhancement after Magnevist and 40/66 (61%) had better lesion configuration or border delineation after Magnevist. Overall, there was better contrast after Magnevist in 55% of the images, comparable enhancement in 44 (36%) before and after Magnevist, and better enhancement in 9% without Magnevist.

In the studies of the brain and spinal cord, Magnevist 0.1 mmol/kg IV provided contrast enhancement in lesions with an abnormal blood brain barrier.

In two studies, a total of 108 patients were evaluated to compare the dose response effects of 0.1 mmol/kg and 0.3 mmol/kg of Magnevist in CNS MRI. Both dosing regimens had similar imaging and general safety profiles; however, the 0.3 mmol/kg dose did not provide additional benefit to the final diagnosis (defined as number of lesions, location, and characterization).

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