General: GastroMARK is an oral aqueous suspension of a superparamagnetic magnetic resonance imaging (MRI) contrast agent. After oral administration of GastroMARK, the agent fills the stomach and small intestine by 30 to 45 minutes after ingestion. The imaging agent passes distally to the large intestine by 4 to 7 hours after ingestion. GastroMARK is primarily eliminated in the feces.
Absorption: Following the administration of 600 mL of GastroMARK containing 10μCi of 59Fe (105 mg of iron) to 3 healthy, male volunteers and the same GastroMARK dose containing 9.5μCi of 59Fe (105 mg of iron) to 3 male patients with inflammatory bowel diseases, the blood concentration of 59Fe in all subjects/patients for Days 1, 3, 7, and 14 after dosing were low (respectively, 0-0.024, 0-0.015, 0- 0.058 and 0-0.044 nCi/mL). When normalized to a 70 kg man with 5000 mL of blood for Days 1, 3, 7, and 14 after dosing, these concentrations amount to 1.3%, 0.8%, 3.0% and 2.3% of the doses of59Fe administered. This study is too small to reliably predict differences in absorption between healthy people and patients with inflammatory bowel disease. Absorption of GastroMARK has not been studied in women.
Generally, the extent of absorption of iron from the gastrointestinal tract is expected to depend upon the existing body stores of iron. The lower the body iron stores, the more iron may be absorbed from GastroMARK.
Distribution and Metabolism: Iron absorbed from GastroMARK enters the hematopoietic pathway and is incorporated into the hemoglobin of the red blood cells or into ferritin for storage. The extent to which silicone is absorbed or metabolized in humans is not known.
Elimination: Unabsorbed iron in GastroMARK is eliminated in feces. Based upon literature information, iron absorbed into the blood is highly conserved. In healthy normal adult men, about 10% of the body’s iron store is lost per year (1 mg per day). Iron is excreted from the gastrointestinal tract in extravasated red cells, in bile and in exfoliated mucosal cells. Small amounts of iron are lost in the urine and in desquamated skin. Additional iron loss occurs in menstrual flow in women.
Food Effect: GastroMARK is intended for administration under fasting conditions. The effect of food on the disposition of GastroMARK has not been studied.
Special Populations: Studies have not been conducted to evaluate the disposition of GastroMARK in special populations such as patients with hepatic and renal diseases, or patients with hemochromatosis, hemosiderosis and other blood disorders.
The amount of iron absorbed in patients with active inflammatory bowel disease has not been studied adequately.
Drug-Drug Interactions: Drug interaction studies have not been conducted with GastroMARK. The effect of iron supplements or drugs that increase or decrease gastrointestinal transit time on imaging with GastroMARK has not been studied.