Vasopressin (antidiuretic hormone) is a polypeptide hormone secreted by the hypothalamus and stored in the posterior pituitary. Its pharmacology is discussed in Chapters 17 and 37. Although its primary physiologic role is to maintain serum osmolality, it is also a potent arterial vasoconstrictor. When administered intravenously by continuous infusion, vasopressin causes splanchnic arterial vasoconstriction that leads to reduced splanchnic perfusion and lowered portal venous pressures. Before the advent of octreotide, vasopressin was commonly used to treat acute variceal hemorrhage. However, because of its high adverse-effect profile, it is no longer used for this purpose. In contrast, for patients with acute gastrointestinal bleeding from small bowel or large bowel vascular ectasias or diverticulosis, vasopressin may be infused—to promote vasospasm—into one of the branches of the superior or inferior mesenteric artery through an angiographically placed catheter. Adverse effects with systemic vasopressin are common. Systemic and peripheral vasoconstriction can lead to hypertension, myocardial ischemia or infarction, or mesenteric infarction. These effects may be reduced by coadministration of nitroglycerin, which may further reduce portal venous pressures (by reducing portohepatic vascular resistance) and may also reduce the coronary and peripheral vascular vasospasm caused by vasopressin. Other common adverse effects are nausea, abdominal cramps, and diarrhea (due to intestinal hyperactivity). Furthermore, the antidiuretic effects of vasopressin promote retention of free water, which can lead to hyponatremia, fluid retention, and pulmonary edema.
Terlipressin is a vasopressin analog that appears to have similar efficacy to vasopressin with fewer adverse effects. Although this agent is available in other countries, it has never been approved for use in the USA.
The pharmacology of β-receptor-blocking agents is discussed in Chapter 10. Beta-receptor antagonists reduce portal venous pressures via a decrease in portal venous inflow. This decrease is due to a decrease in cardiac output (β1 blockade) and to splanchnic vasoconstriction (β2 blockade) caused by the unopposed effect of systemic catecholamines on α receptors. Thus, nonselective β blockers such as propranolol and nadolol are more effective than selective β1 blockers in reducing portal pressures. Among patients with cirrhosis and esophageal varices who have not previously had an episode of variceal hemorrhage, the incidence of bleeding among patients treated with nonselective β blockers is 15% compared with 25% in control groups. Among patients with a history of variceal hemorrhage, the likelihood of recurrent hemorrhage is 80% within 2 years. Nonselective β blockers significantly reduce the rate of recurrent bleeding, although a reduction in mortality is unproved.
H2-receptor blockers, eg, cimetidine: Effective reduction of nocturnal acid but less effective against stimulated secretion; very safe, available over the counter (OTC). Cimetidine, but not other H2 blockers, is a weak antiandrogenic agent and a potent CYP enzyme inhibitor
Sucralfate: Polymerizes at site of tissue damage (ulcer bed) and protects against further damage; very insoluble with no systemic effects; must be given four times daily
Antacids: Popular OTC medication for symptomatic relief of heartburn; not as useful as PPI and H2 blockers in peptic diseases
Domperidone: Like metoclopramide, but less CNS effect; not available in USA
Cholinomimetics: Neostigmine often used for colonic pseudo-obstruction in hospitalized patients
Macrolides: Erythromycin useful in diabetic gastroparesis but tolerance develops