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Reno-60 (Diatrizoate Meglumine) - Description and Clinical Pharmacology

 
 



RENO-60®
Diatrizoate Meglumine
Injection USP 60%

DESCRIPTION

Reno-60 is a radiopaque contrast agent supplied as a sterile, aqueous solution for parenteral use. Each mL provides 600 mg diatrizoate meglumine; at manufacture, 3.2 mg sodium citrate buffer and 0.4 mg edetate disodium sequestering agent are added per mL. The pH has been adjusted between 6.0 and 7.7 with meglumine and diatrizoic acid. Each mL of solution also contains approximately 0.91 mg (0.04 mEq) sodium and 282 mg organically bound iodine. At the time of manufacture, the air in the container is replaced by nitrogen.

CLINICAL PHARMACOLOGY

Following intravascular injection, Reno-60 is rapidly transported through the bloodstream to the kidneys and is excreted unchanged in the urine by glomerular filtration. When urinary tract obstruction is severe enough to block glomerular filtration, the agent appears to be excreted by the tubular epithelium.

Certain applications of the contrast agent make use of the natural physiologic mechanism of excretion. Thus the intravenous injection of the agent permits visualization of the kidneys and urinary passages.

Renal accumulation is sufficiently rapid that the period of maximal opacification of the renal passages may begin as early as five minutes after injection. In infants and small children excretion takes place somewhat more promptly than in adults, so that maximal opacification occurs more rapidly and is less sustained. The normal kidney eliminates the contrast medium almost immediately. In nephropathic conditions, particularly when excretory capacity has been altered, the rate of excretion varies unpredictably, and opacification may be delayed for 30 minutes or more after injection; with severe impairment opacification may not occur. Generally, however, the medium is concentrated in sufficient amounts and promptly enough to permit a thorough evaluation of the anatomy and physiology of the urinary tract. After intramuscular injection, the contrast agent is promptly absorbed and normally reaches the renal passages within 20 to 60 minutes.

Intravascular injection of diatrizoate meglumine also opacifies those vessels in the path of flow of the medium, permitting visualization until the circulating blood dilutes the concentration of the medium. Thus selective angiography may be performed following injection directly into veins or arteries such as the carotid, the vertebral, or the vessels of the extremities.

Under certain circumstances, specific parts of the body which do not concentrate the contrast agent physiologically may be visualized by injecting the agent directly into the region to be studied. The biliary tract is one organ system which may be visualized in this manner. In operative cholangiography, injection of the radiopaque medium into the cystic duct or choledochal lumen, at laparotomy, opacifies the intra- and extrahepatic biliary ductal system, revealing the nature and location of obstructions such as stones or strictures. Injection of the medium through an in-place T-tube, immediately after exploration of the common duct, permits the visualization of retained stones. A repetition of “T-tube cholangiography,” performed as part of the postoperative follow-up, insures the patency of the ductal system before removal of the T-tube. The biliary ductal system may also be opacified by the percutaneous transhepatic route. In relatively long-standing biliary obstruction, the biliary ducts are usually enlarged sufficiently to be located promptly by percutaneous transhepatic probing, permitting injection of the contrast agent directly into the biliary ductal system.

If the contrast agent is injected directly into the splenic pulp, significant opacification of the splenic and portal veins is obtained. Because of gravity, the dependent portions of the portal system are better opacified than the superior portions. The agent is carried from the portal vein into the hepatic veins, and a diffuse opacification of the liver results. In patients with portal hypertension, collateral pathways caused by the change in portal blood flow may be visualized and esophageal varices are often delineated. The procedure may reveal the site of portal obstruction.

Injection of Reno-60 directly into a joint space provides visual information about joint derangements.

A small amount of the radiopaque agent injected into a normal cervical or lumbar disk will, under optimal conditions, concentrate within the nucleus pulposus. In the presence of disk pathology the injected agent may reveal significant bulging or disruption of the annulus beyond its normal confines and may identify disk degeneration, retropulsion, or rupture.

Computed Tomography

Reno-60 (Diatrizoate Meglumine Injection USP 60%) enhances computed tomographic brain scanning through augmentation of radiographic efficiency. The degree of enhancement of visualization of tissue density is directly related to the iodine content in an administered dose; peak iodine blood levels occur immediately following rapid injection of the dose. These levels fall rapidly within five to ten minutes.This can be accounted for by the dilution in the vascular and extracellular fluid compartments which causes an initial sharp fall in plasma concentration. Equilibration with the extracellular compartments is reached in about ten minutes; thereafter, the fall becomes exponential. Maximum contrast enhancement frequently occurs after peak blood iodine levels are reached. The delay in maximum contrast enhancement can range from five to forty minutes, depending on the peak iodine levels achieved and the cell type of the lesion. This lag suggests that radiographic contrast enhancement is at least in part dependent on the accumulation of iodine within the lesion and outside the blood pool, although the mechanism by which this occurs is not clear. The radiographic enhancement of nontumoral lesions, such as arteriovenous malformations and aneurysms is probably dependent on the iodine content of the circulating blood pool.

In brain scanning, Reno-60 does not accumulate in normal brain tissue due to the presence of the “blood-brain” barrier. The increase in X-ray absorption in normal brain is due to the presence of contrast agent within the blood pool. A break in the blood-brain barrier such as occurs in malignant tumors of the brain allows the accumulation of the contrast medium within the interstitial tumor tissue. Adjacent normal brain tissue does not contain the contrast medium.

In nonneural tissues (during computed tomography of the body), diatrizoate diffuses rapidly from the vascular into the extravascular space. Increase in X-ray absorption is related to blood flow, concentration of the contrast medium, and extraction of the contrast medium by interstitial tumor tissue since no barrier exists. Contrast enhancement is thus due to the relative differences in extravascular diffusion between normal and abnormal tissue, quite different from that in the brain.

The pharmacokinetics of diatrizoate in both normal and abnormal tissue have been shown to be variable. Contrast enhancement appears to be greatest soon after administration of the contrast medium, and following intra-arterial rather than intravenous administration. Thus, greatest enhancement can be detected by a series of consecutive two- to three-second scans performed just after injection (within 30 to 90 seconds), i.e., dynamic computed tomographic scanning.

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