Introduction
Figure 1. The structural formula of ornipressin
Ornipressin is a synthetic analogue of vasopressin, which is replaced by Ornipressin at residue 8 of the cyclic nonapeptide. As an effective vasoconstrictor, ornipressin plasma volume expansion to improve the effective arterial blood volume by albumin. And it originates deep vasoconstriction by contracting smooth-muscle cells in the vascular bed, particularly in capillaries, small arterioles, and venules. Ornipressin is most commonly used for the treatment of hemorrhagic esophageal varices.
Pharmacologic action
Ornipressin functions as hemostatic agent by arresting the blood flow. Hemostatics are absorbable, which can provide a mechanical substrate form an artificial clot to arrest bleeding, and then promote clotting when applied directly to the bleeding surface. These agents play a better role in the capillary but cannot block arterial or venous bleeding effectively under any significant intravascular pressure. On the other side, ornipressin mainly has a vasoconstriction effect on the volumetric blood vessels, leading to pale appearance at the injection site. When it comes to the local vasoconstrictor action, ornipressin is similar to adrenaline. Therefore, in order to reduce blood loss and construct a bloodless surgical area, ornipressin is used for generating local hemostasis.
Function
From the perspective of local vasoconstrictor property, ornipressin is almost equivalent to epinephrine. Regardless of whether the anesthetic is used, ornipressin agents have been used for controlling bleeding in burn treatment, gynecologic procedures, scalp infiltration for neurosurgery procedures, and prostatic surgery. Esophageal varices are also treated with intravenous ornipressin. For hemostasis, solutions containing up to 5 U of ornipressin in 20 to 60 mL of 0.9% sodium chloride are penetrated into the area involved. In most cases, the appropriate amount of ornipressin is 0.01 IU/mL. However, this value has a wide variation practically. It's worth noting that the maximum total dose of ornipressin is 5 IU, above which ornipressin may cause vasodilation.
Pharmacokinetics and metabolism
Ornipressin is a synthetic derivative of vasopressin (arginine-8-vasopressin) in which ornithine is substituted for arginine at the 8 position. The pressor and anti-diuretic effect of ornipressin depend on the alkalinity of the amino-acid residue at position 8 of the molecule. With tissue infiltration, the onset of ornipressin activity occurs within three minutes. Topical application of ornipressin to debrided areas produces hemostasis within 20 seconds. The duration of ornipressin action continues about 45 to 120 minutes. Ultimately, it is metabolized in the liver and kidneys.
References:
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3. Kam, P. C. A., Tay, T. M., The pharmacology of ornipressin (POR-8): a local vasoconstrictor used in surgery. European Journal of Anaesthesiology, 1998, 15(2): 133-139.
4. Clodius, L., Smahel, J., POR 8, a new vasoconstrictor substitute for adrenaline in plastic surgery. British Journal of Plastic Surgery, 1970, 23(1): 73-76.
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