Enalkiren

Summary

Enalkiren is a synthetic dipeptide that directly inhibits renin, the enzyme that initiates the renin‑angiotensin‑aldosterone system. Developed as a research‑only agent, it has been investigated intravenously in healthy volunteers, hypertensive patients, and those with congestive heart failure. The compound lowers plasma renin activity and angiotensin II, producing dose‑dependent reductions in systolic and diastolic blood pressure that persist for many hours after infusion.

Mechanism of Action

Enalkiren mimics the transition state of angiotensinogen, the natural substrate of renin, binding to the active site of human renin and preventing cleavage of angiotensinogen to angiotensin I. By blocking this first step, the drug suppresses downstream formation of angiotensin II and aldosterone, leading to vasodilation and reduced renal vascular resistance. The inhibition is achieved at the enzyme level, distinct from ACE inhibitors that act later in the cascade.

What the Research Shows

Early human studies compared enalkiren with the ACE inhibitor captopril, showing similar suppression of plasma angiotensin II and comparable increases in renal plasma flow. Dose‑ranging trials in congestive heart failure linked plasma concentrations (EC50 ≈ 3,500 ng/ml) to modest blood‑pressure reductions, though individual responses varied. In essential hypertension, repeated intravenous dosing (0.1–1.2 mg/kg every six hours) produced sustained suppression of plasma renin activity for ≥24 hours and significant systolic/diastolic blood‑pressure drops lasting 12 hours or more, without tachyphylaxis. Small sample sizes and short treatment periods characterize the available data.

Reported Benefits

Clinical investigations report that enalkiren can lower systolic and diastolic blood pressure in hypertensive subjects, with effects persisting beyond the drug’s short plasma half‑life. The agent also reduces plasma renin activity and angiotensin II levels, potentially offering a more specific blockade of the renin‑angiotensin system than ACE inhibitors. In heart‑failure patients, measurable hemodynamic changes were observed, suggesting possible utility in conditions driven by renin excess.

Limitations of the Evidence

Evidence derives from limited, short‑term studies involving small numbers of participants, and all administrations were intravenous (or subcutaneous), reflecting poor oral bioavailability (<2%). The relationship between renin suppression and blood‑pressure response showed unexplained dissociation, and individual sensitivity varied widely. No large‑scale or long‑term safety or efficacy trials have been reported, and the compound has not achieved regulatory approval.

Safety Considerations

Across the reported trials, enalkiren was generally well tolerated, with no significant changes in pulse rate and no evidence of tachyphylaxis after one week of dosing. Specific adverse events were not detailed in the abstracts, and the short half‑life (≈1.6 h) did not translate into overt toxicity in the studied populations. Nonetheless, safety conclusions are limited by the small sample sizes and brief exposure periods.

How It Is Administered

Enalkiren has been administered intravenously, typically as weight‑based infusions ranging from 0.1 mg/kg to 1.2 mg/kg given every six hours for up to one week. Subcutaneous delivery has been explored in research settings. The drug’s plasma half‑life is around 1.6 hours, yet pharmacologic effects on blood pressure and renin activity persist for many hours after dosing.

Routes of Administration

Goals & Uses

• Antihypertensive effectCardiovascularModerate
• Heart failure managementCardiovascularLow
• RAAS suppressionCardiovascular/EndocrineModerate

Contraindications

• Hypersensitivity to enalkiren or excipientsImmunologicHigh
• PregnancyPopulationHighPotential fetal risk or insufficient safety data
• Bilateral renal artery stenosisVascular/RenalHigh

Adverse Effects

• Injection site reactionsLocalCommon
• HypotensionCardiovascularCommonLow blood pressure
• Renal function impairmentRenalUncommon
• HyperkalemiaElectrolyte ImbalanceUncommon

Drug Interactions

• Potassium-sparing diuretics / potassium supplementsModerate
• ACE inhibitors / ARBsHigh
• NSAIDsModerateMay increase renal risk in susceptible patients

Population Constraints

• Patients with renal impairmentOrgan ImpairmentRelative
• Pregnant womenReproductiveAbsolute
• Volume-depleted patientsCardiovascularRelative

Regulatory Status

• European UnionUnapprovedNo regulatory submission or approval; remained a research compound.
• United StatesUnapprovedInvestigated in Phase II clinical trials; never submitted for or received FDA approval.
• United KingdomUnapprovedNo approval; used only in clinical research settings.

Never received regulatory approval in any jurisdiction. Remained a research/investigational compound. Development was discontinued in favor of orally bioavailable renin inhibitors.

Evidence & Sources

• Responses to converting enzyme and renin inhibition. Role of angiotensin II in humans
  Journal ArticleModerateFisher ND, et al.1994-01-01T00:00:00.000000Z
• Simultaneous modeling of the pharmacokinetic and pharmacodynamic properties of enalkiren (Abbott-64662, a renin inhibitor). II: A dose-ranging study in patients with congestive heart failure
  Journal ArticleModerateGupta SK, et al.1993-01-01T00:00:00.000000Z
• Renin inhibitors in hypertension
  Journal ArticleModerateLuther RR, Glassman HN, Boger RS1991-01-01T00:00:00.000000Z
• Aliskiren, the first direct renin inhibitor for treatment of hypertension: the path of its development
  Journal ArticleModerateJadhav M, et al.2012-01-01T00:00:00.000000Z
• Clinical pharmacology of enalkiren, a novel, dipeptide renin inhibitor
  Journal ArticleModerateGlassman HN, et al.1990-01-01T00:00:00.000000Z
• Prolonged duration of blood pressure response to enalkiren, the novel dipeptide renin inhibitor, in essential hypertension
  Journal ArticleModerateBoger RS, et al.1990-01-01T00:00:00.000000Z

Frequently Asked Questions