1887

Radiographic contrast agents

Barium and iodinated contrast media

See .

MRI contrast media

Several gadolinium chelates are used for magnetic resonance imaging (MRI) contrast studies. None of them is authorized for veterinary use and all are POM.

Action

Gadolinium is a paramagnetic agent and exerts its effects due to seven unpaired electrons, which cause a shortening of T1 and T2 relaxation times of adjacent tissues. This results in increased signal intensity on T1-weighted MR images. Unbound gadolinium is highly toxic and so is chelated to reduce toxicity. Gadolinium chelates do not cross the normal blood–brain barrier due to their large molecular size.

Use

During MRI examination to identify areas of abnormal vascularization or increased interstitial fluid, delineate masses, demonstrate disruption of the blood–brain barrier and areas of inflammation. Gadodiamide, gadobutrol, gadoteric acid and gadobenic acid are also used for contrast-enhanced magnetic resonance angiography (MRA). The low concentration form of gadopentetic acid (2 mmol/l) is authorized for intra-articular use for MR arthrography in humans. Gadobenic acid and gadoxetic acid are also transported across hepatocyte cell membranes (gadoxetic acid via organic anionic-acid transporting peptide 1) and are used in the characterization of liver lesions.

Safety and handling

Contact with skin and eyes may cause mild irritation.

Contraindications

Use with caution in cardiac disease, pre-existing renal disease and neonates. Contraindicated in severe renal impairment.

Adverse reactions

Nephrogenic systemic fibrosis (most commonly associated with gadodiamide but also gadopentetic acid and gadoversetamide) reported in humans but not in animals. Increase in QT interval and other arrhythmias have also been reported, and cardiac monitoring is recommended in the event of accidental overdosage. Many are hyper-osmolar and irritant if extravasation occurs, therefore should be given through an intravenous catheter. Anaphylaxis occurs rarely. May cause a transient increase in serum bilirubin if there is pre-existing hepatic disease. In experimental studies may cause fetal abnormalities in rabbits.

Drug interactions

May have interactions with Class 1a and 3 antiarrhythmics. Gadobenic acid may compete for cannalicular multispecific organic anionic transporter sites. Caution should be used if administering anthracyclines, vinca alkyloids and other drugs using this transporter. Anionic drugs excreted in bile (e.g. rifampicin) may reduce hepatic uptake of gadoxetic acid, reducing contrast enhancement. May affect some laboratory results, e.g. serum iron determination using complexometric methods, transient increase in liver enzymes, false reduction in serum calcium measurement.

Doses and further advice on use

Should be used routinely for MRI examinations of the brain. Use for MRI of other body regions if suspect abnormal vascularization, inflammation, neoplasia, for postsurgical evaluation or if MRI study is normal despite significant clinical signs. Post-contrast images should ideally be obtained within 30 minutes of contrast administration. Total doses should not exceed 0.3 mmol/kg (varies with product).

Generic name Trade name Manufacturer Authorized indications in humans Excretion Properties Protein binding Dose Formulations
Gadopentetic acid Magnevist Bayer CNS; whole body (excluding heart); arthrography Renal Linear Ionic 1960 mOsm/kg 0 0.1–0.3 mmol/kg

469 mg/ml, 2 mmol/l

5, 10, 15, 20 ml vials; 10, 15, 20 ml pre-filled syringes; 50, 100 ml pharmacy bulk package

Gadoteric acid Dotarem Guerbet Laboratories Ltd CNS; whole body; MRA Renal Cyclic Ionic 1350 mOsm/kg 0 0.1–0.3 mmol/kg

279.3 mg/ml

5, 10, 15, 20 ml vials; 15, 20 ml pre-filled syringes

Gadoteridol Prohance Bracco CNS; whole body Renal Cyclic Non-ionic 630 mOsm/kg 0 0.1 mmol/kg

279.3 mg/ml

5, 10, 15, 20 ml vials; 5, 10, 15, 17 ml pre-filled syringes

Gadodiamide Omniscan Nycomed Amersham CNS; whole body Renal Linear Non-ionic 789 mOsm/kg 0 0.1–0.3 mmol/kg

287 mg/ml

5, 10, 15, 20, 40, 50 ml vials; 10, 15, 20 ml pre-filled syringes

Gadobutrol Gadovist Bayer CNS Renal Cyclic Non-ionic 1603 mOsm/kg 0 0.1 mmol/kg

604.72 mg/ml

7.5, 10, 15 ml vials; 7.5, 10, 15 ml pre-filled syringes; 30, 65 ml bulk packages

Gadoxetic acid Primovist Bayer Liver 50% renal, 50% biliary Linear Ionic 688 mOsm/kg <15% 0.025 mmol/kg

181.43 mg/ml

10 ml pre-filled syringes

Gadobenic acid MultiHance Bracco CNS; liver; MRA; breast Renal (biliary up to 4%) Linear Ionic 1970 mOsm/kg <5% CNS: 0.1 mmol/kg; liver: 0.05 mmol/kg

334 mg/ml

5, 10, 15, 20 ml vials

Gadoversetamide Optimark Covidien CNS; liver Renal Linear Non-ionic 1110 mOsm/kg 0 0.1 mmol/kg

330 mg/ml

10, 15, 20, 30 ml pre- filled syringes

  • Dogs 0.1 mmol/kg i.v. (all except gadoxetic acid). Give as bolus if performing MRA, dynamic contrast or liver studies; 0.025 mmol/kg i.v. bolus of gadoxetic acid for liver studies; 0.05 mmol/kg of gadobenic acid for liver studies. Repeat doses (not gadoxetic acid) of up to 0.3 mmol/kg total dose may be helpful in some cases if poor contrast enhancement with standard dose or for detection of metastases and if using low-field scanner. Enhancement visible up to 45–60 minutes post-administration.
Composition of intravenous fluids

Fluid Na (mmol/l) K (mmol/l) Ca (mmol/l) Cl (mmol/l) HCO Dext. (g/l) Osmol. (mosm/l)
0.45% NaCl 77 77 155
0.9% NaCl 154 154 308
5% NaCl 856 856 1722
Ringer’s 147 4 2 155 310
Lactated Ringer’s (Hartmann’s) 131 5 2 111 29 280
Darrow’s 121 35 103 53 312
0.9% NaCl +
5.5% Dext. 154 154 50 560
0.18% NaCl +
4% Dext. 31 31 40 264
Duphalyte 2.6 1.0 3.6 454 unknown

Dext. = dextrose; Osmol. = osmolality.

*Bicarbonate is present as lactate.

**Also contains a mixture of vitamins and small quantities of amino acids and 1.2 mmol/l of MgSO

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