Iothalamates

Some of the ionic iodinated substances used in CAT scans include amidotrizoates (salts of diatrizoic acid) and iothalamates (salts of iothalamic acid)J l The typical cations are sodium ion or meglumine (A-methyl-Z)-glucamine) ion (Fig. 10.1.1),... 

Iothalamate Sodium, Conray-400, Mallinckrodt Material Safety Data Sheet, http //imaging.mallinckrodt.com/ Attachments/MSDS/connr.htm... 

Most contrast agents elicit nephrotoxicity because they are primarily excreted by the kidneys. However, when administered in small doses, they constitute a rich source of GFR markers. The two major classes of contrast agents that are finding clinical utility as GFR markers are iodinated aromatic compounds and metal complexes. lodinated aromatics such as iohexol and iothalamate (Fig. 13) are commonly used as contrast agents for computed tomography (GT). They also have pharmacokinetics similar to inulin and hence are useful indicators of renal status [215]. The iodinated molecules used for GFR measurements consist of a triiodo-benzene core and hydrophilic groups to enhance solubility in aqueous medium. 

Labeling of iodinated aromatics with radioactive or has proved to be a valuable approach to measure GFR in nuclear medicine. Prominent among these is sodium iothalamate, which is specifically marketed in the US for GFR measurement by the name Glofil . Studies have shown that the clearance of this marker by the glomeruli is reproducible, simple, reliable and accurate, especially in children and those with advanced renal diseases [234]. This marker can also be administered by subcutaneous infusion to obtain GFR values without the need for urine collection [235]. Since very low doses (nanomolar scale) of radioactive aromatics are administered, monitoring of renal function may be achieved without disruption of normal physiologic functions. Concerns over radioactivity and associated handling costs may prevent the use of these compounds for routine GFR measurements. 

The first modern hydrophilic nonspecific iodinated CA was diatrizoic acid, which, formulated as a sodium and/or meglumine salt, is still used. This agent was first synthesized in 1953 [1]. Osmolality for this compound, at concentrations compatible with imaging (ie. 300-370 mgl mL" ), is about 5-7 times that of plasma (1500-2100 mOsm kg H2O). Other HOCA such as iothalamate, metrizoate and ioxithalamate, were synthesized and marketed over the next few years. In an attempt to reduce the osmolality of the injected solution and thus reduce pain and haemodynamic disturbances, metrizamide, a compound resulting from the condensation of metrizoic acid and glucosamine, was synthesized. It was the first nonionic CA. 

Because of their low molecular weight (<2000 Da), the standard NS-CA are extravasated to a massive extent on first pass in noncerebral areas. Thus, Canty et al. reported that first-pass extraction of a conventional nonionic CA averaged 33 % in normally perfused myocardial areas and 50% in stenotic areas (where coronary blood flow was reduced by 50%) [15]. These data may even have underestimated first-pass myocardial extraction of CA because of back diffusion of the molecule. In another model, approximately 80% of the myocardial content of I-iothalamate was found in the extravascular space 1 minute after intravenous injection in rats [16]. 

Many radiocontrast media contain iodine. These include iodixonal, iohexol, iomeprole, iopamidole, iopanoic acid, iopitridole, iopromide, iothalamate, iotrolan, ioversol, and ioxaglate. 

Common Name Iothalamate sodium Jodtalaminatrium Sodium isothalamate... 

Angio-Conray Iothalamate Sodium Vasco ray Vasco ray... 

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