Computed Tomography

HYPAQUE-76 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, HYPAQUE-76, brand of diatrizoate meglumine and diatrizoate sodium injection, 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. The 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.

Effects of Steroid Therapy

The anti-inflammatory and antiedema effects in patients receiving steroid therapy have interfered with the expected distribution of CT tissue enhancement on the scan in certain diseases.

SEVERE ADVERSE EVENTS - INADVERTENT INTRATHECAL ADMINISTRATION

Serious adverse reactions have been reported due to the inadvertent intrathecal administration of iodinated contrast media that are not indicated for intrathecal use. These serious adverse reactions include: death, convulsions, cerebral hemorrhage, coma, paralysis, arachnoiditis, acute renal failure, cardiac arrest, seizures, rhabdomyolysis, hyperthermia, and brain edema. Special attention must be given to insure that this drug product is not administered intrathecally.

Ionic iodinated contrast media inhibit blood coagulation, in vitro, more than nonionic contrast media. Nonetheless, it is prudent to avoid prolonged contact of blood with syringes containing ionic contrast media.

Serious, rarely fatal, thromboembolic events causing myocardial infarction and stroke have been reported during angiographic procedures with both ionic and nonionic contrast media. Therefore, meticulous intravascular administration technique is necessary, particularly during angiographic procedures, to minimize thromboembolic events. Numerous factors, including length of procedure, catheter and syringe material, underlying disease state and concomitant medications may contribute to the development of thromboembolic events. For these reasons, meticulous angiographic techniques are recommended including close attention to guidewire and catheter manipulation, use of manifold systems and/or three-way stopcocks, frequent catheter flushing with heparinized saline solutions and minimizing the length of the procedure. The use of plastic syringes in place of glass syringes has been reported to decrease but not eliminate the likelihood of in vitro clotting.

Excretory urography is potentially hazardous in patients with multiple myeloma. In some of those patients, therapeutically resistant anuria resulting in progressive uremia, renal failure, and eventually death has followed this procedure. Although neither the contrast agent nor dehydration has been proved separately to be the cause of anuria in myelomatous patients, it has been speculated that the combination of both may be causative. The risk of excretory urography in myelomatous patients is not a contraindication to the procedure; however, they require special precautions. Partial dehydration in the preparation of these patients for the examination is not recommended since this may predispose to the precipitation of myeloma protein in the renal tubules. Myeloma, which occurs most commonly in persons over age 40, should be considered before instituting urographic procedures.

Contrast media may promote sickling in individuals who are homozygous for sickle cell disease when the material is injected intravenously or intra-arterially.

Administration of radiopaque materials to patients known or suspected of having pheochromocytoma should be performed with extreme caution. If, in the opinion of the physician, the possible benefits of such procedures outweigh the considered risks, the procedures may be performed; however, the amount of radiopaque medium injected should be kept to an absolute minimum. The blood pressure should be assessed throughout the procedure and measures for treatment of a hypertensive crisis should be available.

Recent reports of thyroid storm occurring following the intravascular use of iodinated radiopaque diagnostic agents in patients with hyperthyroidism or with an autonomously functioning thyroid nodule suggest that this additional risk be evaluated in such patients before use of diatrizoate salts.

Contrast media administered for cardiac catheterization and angiocardiography may cause cellular injury to circulating lymphocytes. Chromosomal damage in humans includes inhibition of mitosis, increases in the number of micronuclei, and chromosome aberrations. The damages appear to be related to the contrast medium itself rather than to the x-ray radiation. It is to be noted that those agents have not been adequately tested in animal or laboratory systems.

Urography should be performed with caution in patients with severely impaired renal function and patients with combined renal and hepatic disease.

Subcutaneous extravasation causes transitory stinging, chiefly because of hypertonic cellulitis. If the volume extravasated is small, ill effects are very unlikely. However, if the extravasation is extensive, especially in poorly vascularized areas (e.g., dorsum of the foot or hand), and especially in the presence of vascular disease, skin slough may occur. Injection of sterile water to dilute or addition of spreading agents to speed absorption have not been successful and may aggravate the condition.

Selective spinal arteriography or arteriography of trunks providing spinal branches can cause mild to severe muscle spasm. However, serious neurologic sequelae, including permanent paralysis, could occur with even small doses of the 76 percent concentration.

In patients with subarachnoid hemorrhage, a rare association between contrast administration and clinical deterioration, including convulsions and death, has been reported. Therefore, administration of intravascular iodinated ionic contrast media in these patients should be undertaken with caution.

Information for Patients

Patients receiving injectable radiopaque diagnostic agents should be instructed to:

1. Inform the physician if they are pregnant (see CLINICAL PHARMACOLOGY).
2. Inform the physician if they are diabetic or if they have multiple myeloma, pheochromocytoma, homozygous sickle cell disease or known thyroid disorder (see WARNINGS—General).
3. Inform the physician if they are allergic to any drugs, food, or if they have had any reactions to previous injections of dyes used for x-ray procedures (see PRECAUTIONS—General).
4. Inform the physician about any other medications they are currently taking, including nonprescription drugs, before they are administered this drug.

Drug Interactions

Renal toxicity has been reported in a few patients with liver dysfunction who were given oral cholecystographic agents followed by urographic agents. Administration of intravascular urographic agents should therefore be postponed in any patient with a known or suspected hepatic or biliary disorder who has recently received a cholecystographic contrast agent.

Addition of an inotropic agent to contrast agents may produce a paradoxical depressant response which can be deleterious to the ischemic myocardium.

Diphenhydramine hydrochloride may cause precipitation when mixed in the same syringe with HYPAQUE-76.

Under certain circumstances (pH, temperature, concentrations, time), diatrizoate solutions are incompatible with promethazine hydrochloride, diphenhydramine hydrochloride, brompheniramine maleate, or papavarine hydrochloride solutions.

Do not prefill plastic syringes with HYPAQUE-76 for prolonged periods (i.e., for several hours or longer) before use.

Drug/Laboratory Test Interactions

If any of these studies, which might be affected by contrast media, are indicated, it is recommended that they be performed prior to administration of the contrast medium or two or more days afterwards.

Diatrizoate salts interfere with several laboratory urine and blood tests.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term studies in animals have not been performed in order to evaluate carcinogenic potential, mutagenesis, or whether HYPAQUE-76 can affect fertility in males or females.

Pregnancy Category C

Animal reproduction studies have not been conducted with HYPAQUE-76. It is also not known whether HYPAQUE-76 can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. HYPAQUE-76 should be given to a pregnant woman only if clearly needed.

Labor and Delivery

It is not known whether use of these contrast agents during labor or delivery has immediate or delayed adverse effects on the fetus, prolongs the duration of labor or increases the likelihood that forceps delivery or other obstetrical intervention or resuscitation of the newborn will be necessary.

Nursing Mothers

Diatrizoate salts are excreted unchanged in human milk. Because of the potential adverse reactions, although it has not been established that serious adverse reactions occur in nursing infants, caution should be exercised when these contrast media are administered to a nursing woman.

Pediatric Use

Infants and small children should not have any fluid restriction prior to excretory urography or any other procedures (see PRECAUTIONS—General). Guidelines for pediatric dosages are presented in DOSAGE AND ADMINISTRATION—General.

Greater Than 1 in 100 Patients

Body as a Whole: Reported incidences of death range from 6.6 per 1 million (0.00066 percent) to 1 in 10,000 patients (0.01 percent). Most deaths occur during injection or 5 to 10 minutes later, the main feature being cardiac arrest with cardiovascular disease as the main aggravating factor.

Isolated reports of hypotensive collapse and shock following urography are found in the literature. The incidence of shock is estimated to occur in 1 out of 20,000 (0.005 percent) patients.

Cardiovascular System: The most frequent adverse reaction to diatrizoate salts is vasodilation (feeling of warmth). The estimated incidence is 49 percent.

Digestive System: Nausea 6 percent, vomiting 3 percent.

Nervous System: Paresthesia 6 percent, dizziness 5 percent.

Respiratory System: Rhinitis 1 percent, increased cough 2 percent.

Skin and Appendages: Urticaria 1 percent.

Pain at the injection site is estimated to occur in about 12 percent of the patients undergoing urography. Pain is usually due to extravasation.

Painful hot erythematous swelling above the venipuncture site was estimated to occur in more than one percent of the patients undergoing phlebography.

Special Senses: Perversion of taste 11 percent.

Urogenital System: Osmotic nephrosis of the proximal tubular cells is estimated to occur in 23 percent of patients following excretory urography.

Less Than 1 in 100 Patients

Other infrequently reported reactions without accompanying incidence rates are listed below, grouped by organ system.

Body as a Whole: Malaria relapse, uremia, high creatinine and BUN (see PRECAUTIONS—General, Drug/Laboratory Test Interactions), thrombocytopenia, leukopenia, and anemia.

Cardiovascular System: Cerebral hematomas, hemodynamic disturbances, sinus bradycardia, transient electrocardiographic abnormalities, ventricular fibrillation, petechiae, chest pain, and cardiac arrest.

Digestive System: Severe unilateral or bilateral swelling of the parotid and submaxillary glands.

Nervous System: Convulsions, paralysis, and coma. (See PRECAUTIONS—General.)

Respiratory System: Asthma, dyspnea, laryngeal edema, pulmonary edema, and bronchospasm.

Skin and Appendages: Extravasation necrosis, urticaria with or without pruritus, mucocutaneous edema, and angioneurotic edema.

Special Senses: Bilateral ocular irritation, lacrimation, itching, conjunctival chemosis, infection, and conjunctivitis.

Urogenital: Renal failure, pain.

Pediatric Dosage

Pediatric doses of injectable radiopaque diagnostic agents are generally determined on a weight basis and should be calculated for each patient individually. (See INDIVIDUAL INDICATIONS AND USAGE section.)

Drug Incompatibilities

Diatrizoate salts are incompatible in vitro with some antihistamines and many other drugs. It is believed that one of the chief causes of in vitro incompatibility is an alteration of pH. Turbidity of solutions of intravascular contrast medium occurs between pH 2.5 and 4.1. Another cause is chemical interaction; therefore, other pharmaceuticals should not be mixed with contrast agents in the same syringe.

EXCRETORY UROGRAPHY

Diatrizoate salts are used in small, medium, and large dose urography. Visualization of the urinary tract can be achieved by either direct intravenous bolus injection, intravenous drip infusion, or incidentally following intra-arterial procedures. Visualization of the urinary tract is delayed in infants less than 1 month old, and in patients with urinary tract obstruction (see CLINICAL PHARMACOLOGY).

ANGIOGRAPHY—General

Diatrizoate salts are used for radiographic studies throughout the cardiovascular system.

Intravascular radiopaque diagnostic agents of high concentration are not recommended for cerebral or spinal angiography (see CONTRAINDICATIONS—General), and contrast agents with the lowest compatible viscosity and higher concentration of iodine (310 mg/mL to 480 mg/mL of bound iodine) must be used for angiocardiography. Contrast media approaching serum ionic content and osmolality have less potential for deleterious effects on the myocardium (see PRECAUTIONS—General, Drug Interactions).

Addition of chelating agents may contribute to toxicity in coronary angiography, and the sodium content of angiographic agents used in coronary arteriography is of crucial importance.

AORTOGRAPHY

HYPAQUE-76 solution may be injected by commonly accepted techniques, such as translumbar, retrograde catheter, retrograde pressure injection (by cannula) or antegrade (brachial) catheter, for examination of the aorta and its major branches.

ANGIOCARDIOGRAPHY

PERIPHERAL ANGIOGRAPHY

The use of HYPAQUE-76 is sometimes preferred over less concentrated media in selected cases for femoral and brachio-axillary arteriography in adults.

VENOGRAPHY

SELECTIVE RENAL ARTERIOGRAPHY

SELECTIVE VISCERAL ARTERIOGRAPHY

INTRAVENOUS DIGITAL ARTERIOGRAPHY

Arteriograms of diagnostic quality can be obtained following the intravenous administration of HYPAQUE-76 employing digital subtraction and computer imaging enhancement equipment. The intravenous route of administration using these techniques has the advantage of being less invasive than the corresponding selective catheter placement of the medium. The dose is administered into a peripheral vein usually by mechanical injection although sometimes by rapid manual injection. The technique has been used most frequently to visualize the ventricles, the aorta and most of its larger branches including carotid, cerebral, vertebral, renal, celiac, mesenterics, and the major peripheral vessels of the limbs.

CONTRAST ENHANCEMENT OF COMPUTED TOMOGRAPHIC HEAD IMAGING

Injectable radiopaque contrast media may be used to refine diagnostic precision in areas of the brain which may not otherwise have been satisfactorily visualized.

Tumors: Radiopaque diagnostic agents may be useful to investigate the presence and extent of certain malignancies such as: gliomas including malignant gliomas, glioblastomas, astrocytomas, oligodendrogliomas and gangliomas, ependymomas, medulloblastomas, meningiomas, neuromas, pinealomas, pituitary adenomas, craniopharyngiomas, germinomas, and metastatic lesions. The usefulness of contrast enhancement for the investigation of the retrobulbar space and in cases of low grade or infiltrative glioma has not been demonstrated.

In calcified lesions, there is less likelihood of enhancement. Following therapy, tumors may show decreased or no enhancement.

Nonneoplastic Conditions of the Brain: The use of HYPAQUE-76 may be beneficial in the enhancement of images of lesions not due to neoplasms. Cerebral infarctions of recent onset may be better visualized with the contrast enhancement, while some infarctions are obscured if a contrast medium is used. The use of HYPAQUE-76 improved the contrast enhancement in approximately 60 percent of cerebral infarctions studied from one week to four weeks from the onset of symptoms.

Sites of active infection also will produce contrast enhancement following contrast medium administration.

Arteriovenous malformations and aneurysms will show contrast enhancement. In the case of these vascular lesions, the enhancement is probably dependent on the iodine content of the circulating blood pool.

Hematomas and intraparenchymal bleeders seldom demonstrate any contrast enhancement. However, in cases of intraparenchymal clot, for which there is no obvious clinical explanation, contrast medium administration may be helpful in ruling out the possibility of associated arteriovenous malformation.

The opacification of the inferior vermis following contrast medium administration has resulted in false-positive diagnoses in a number of normal studies.

CONTRAST ENHANCEMENT OF COMPUTED TOMOGRAPHIC BODY IMAGING

HYPAQUE-76, brand of diatrizoate meglumine and diatrizoate sodium injection, may be used for enhancement of computed tomographic scans performed for detection and evaluation of lesions in the liver, pancreas, kidneys, aorta, mediastinum, abdominal cavity, pelvis, and retroperitoneal space.

Enhancement of computed tomography with HYPAQUE-76 may be of benefit in establishing diagnoses of certain lesions in these sites with greater assurance than is possible with CT alone, and in supplying additional features of the lesions (e.g., hepatic abscess delineation prior to percutaneous drainage). In other cases, the contrast agent may allow visualization of lesions not seen with CT alone (e.g., tumor extension), or may help to define suspicious lesions seen with unenhanced CT (e.g., pancreatic cyst).

Contrast enhancement appears to be greatest within 60 to 90 seconds after bolus administration of the contrast agent. Therefore, utilization of a continuous scanning technique (dynamic CT scanning) may improve enhancement and diagnostic assessment of tumor and other lesions such as an abscess, occasionally revealing unsuspected or more extensive disease. For example, a cyst may be distinguished from a vascularized solid lesion when precontrast and enhanced scans are compared; the nonperfused mass shows unchanged x-ray absorption (CT number). A vascularized lesion is characterized by an increase in CT number in the few minutes after a bolus of intravascular contrast agent; it may be malignant, benign or normal tissue, but would probably not be a cyst, hematoma, or other nonvascular lesion.

Because unenhanced scanning may provide adequate diagnostic information in the individual patient, the decision to employ contrast enhancement, which may be associated with risk and increased radiation exposure, should be based upon a careful evaluation of clinical, other radiological and unenhanced CT findings.