Drug Groups

approved

Description

Fosinopril is a phosphinic acid-containing ester prodrug that belongs to the angiotensin-converting enzyme (ACE) inhibitor class of medications. It is rapidly hydrolyzed to fosinoprilat, its principle active metabolite. Fosinoprilat inhibits ACE, the enzyme responsible for the conversion of angiotensin I (ATI) to angiotensin II (ATII). ATII regulates blood pressure and is a key component of the renin-angiotensin-aldosterone system (RAAS). Fosinopril may be used to treat mild to moderate hypertension, as an adjunct in the treatment of congestive heart failure, and to slow the rate of progression of renal disease in hypertensive individuals with diabetes mellitus and microalbuminuria or overt nephropathy.

Indication

For treating mild to moderate hypertension, use as an adjunct in treating congestive heart failure, and may be used to slow the rate of progression of renal disease in hypertensive individuals with diabetes mellitus and microalbuminuria or overt nephropathy.

Pharmacology

Following oral administration, fosinopril is rapidly and completely hydrolyzed to its principle active metabolite, fosinoprilat. Hydrolysis is thought to occur in the gastrointestinal mucosa and liver. Fosinoprilat is a competitive inhibitor of ACE, a peptidyl dipeptidase that is part of the RAAS. The RAAS is a homeostatic mechanism for regulating hemodynamics, water and electrolyte balance. During sympathetic stimulation or when renal blood pressure or blood flow is reduced, renin is released from the granular cells of the juxtaglomerular apparatus in the kidneys. In the blood stream, renin cleaves circulating angiotensinogen to ATI, which is subsequently cleaved to ATII by ACE. ATII increases blood pressure using a number of mechanisms. First, it stimulates the secretion of aldosterone from the adrenal cortex. Aldosterone travels to the distal convoluted tubule (DCT) and collecting tubule of nephrons where it increases sodium and water reabsorption by increasing the number of sodium channels and sodium-potassium ATPases on cell membranes. Second, ATII stimulates the secretion of vasopressin (also known as antidiuretic hormone or ADH) from the posterior pituitary gland. ADH stimulates further water reabsorption from the kidneys via insertion of aquaporin-2 channels on the apical surface of cells of the DCT and collecting tubules. Third, ATII increases blood pressure through direct arterial vasoconstriction. Stimulation of the Type 1 ATII receptor on vascular smooth muscle cells leads to a cascade of events resulting in myocyte contraction and vasoconstriction. In addition to these major effects, ATII induces the thirst response via stimulation of hypothalamic neurons. ACE inhibitors inhibit the rapid conversion of ATI to ATII and antagonize RAAS-induced increases in blood pressure. ACE (also known as kininase II) is also involved in the enzymatic deactivation of bradykinin, a vasodilator. Inhibiting the deactivation of bradykinin increases bradykinin levels and may further sustain the effects of fosinoprilat by causing increased vasodilation and decreased blood pressure.

Toxicity

Human overdoses of fosinopril have not been reported, but the most common manifestation of human fosinopril overdosage is likely to be hypotension. Oral doses of fosinopril at 2600 mg/kg in rats were associated with significant lethality. The most common adverse effects include dizzines, cough, fatigue, and headache.

Affected Organisms

Biotransformation

Since fosinoprilat is not biotransformed after intravenous administration, fosinopril, not fosinoprilat, appears to be the precursor for the glucuronide and p-hydroxy metabolites.

Absorption

Average absolute absorption is 36%. The primary site of absorption is the proximal small intestine (duodenum/jejunum). Food slows the rate of absorption with no effect on the extent of absorption.

Half Life

12 hours

Protein Binding

Fosinoprilat is ≥95% protein bound

Elimination

After oral administration of radiolabeled fosinopril, approximately half of the absorbed dose is excreted in the urine and the remainder is excreted in the feces.

Clearance

* 26 - 39 mL/min [healthy]

References

External Links