Enalapril (10–20 μM) reduces DAD- and EAD-induced activity and shows antiarrhythmic effects in an ultrafiltered PV sleeve preparation isolated from canine heart [1]. Only when enalapril (50 μM, 24 h) is administered before treating HUVEC with Alzheimer's disease (AD) serum does it prevent patient serum-induced apoptosis [2]. The thermal stability of pure enalapril is superior to that of pure enalapril [3].

The infarct volume generated by middle cerebral artery occlusion can be reduced by enalapril (intraperitoneal injection, 0.03 mg/kg, once, 1 hour), though neither lower nor higher dosages are beneficial in male NMRI mice [4].

Apoptosis analysis [2]
Cell Types: Human umbilical vein EC (HUVEC)
Tested Concentrations: 50 μM
Incubation Duration: 24 hrs (hours)
Experimental Results: Inhibition of apoptosis induced by patient serum.

Animal/Disease Models: Male NMRI mice 20-40 g [4]
Doses: 0.03 mg/kg
Route of Administration: intraperitoneal (ip) injection; one-time
Experimental Results:0.03 mg/kg can reduce the infarct area of the middle cerebral artery in mice.

Absorption, Distribution and Excretion
Following oral administration, the peak plasma concentrations (Cmax) of enalapril is achieved within 1 hour post dosing while the Cmax of enalaprilat occurs at three to four hours post dosing. The steady-state is achieved by the fourth daily dose and there is no accumulation with repeated dosing. However, accumulation of enalaprilat may occur in patients with creatinine clearance less than 30 mL/min. Food intake is reported to have a minimal effect on drug absorption. Following oral administration, about 60% of enalapril was absorbed. Bioavailability of enalapril averaged about 40% when intravenous enalaprilat was used as a reference standard.
Enalapril is mainly eliminated through renal excretion, where approximately 94% of the total dose is excreted via urine or feces as either enalaprilat or unchanged parent compound. About 61% and 33% of the total dose can be recovered in the urine and feces, respectively. In the urine, about 40% of the recovered dose is in the form of enalaprilat.
The volume of distribution of enalapril has not been established. Enalaprilat is shown to penetrate into most tissuesm, in particular the kidneys and vascular tissuem, although penetration of the blood-brain barrier has not been demonstrated after administration at therapeutic doses. In dog studies, enalapril and enalaprilat cross the blood-brain barrier poorly. Minimal penetration occurs into breast milk but significant fetal transfer occurs. The drug crosses the placental barrier in rats and hamsters.
Following oral administration in healthy male volunteers, the renal clearance was approximately 158 ± 47 mL/min. It is reported that enalapril and enalaprilat are undetectable in the plasma by 4 hours post-dosing.
Pharmacokinetic and pharmacodynamic of IV enalapril at 0.50 mg/kg, PO placebo and PO enalapril at three different doses (0.50, 1.00 and 2.00 mg/kg) were analyzed in 7 healthy horses. Serum concentrations of enalapril and enalaprilat were determined for pharmacokinetic analysis. Angiotensin-converting enzyme (ACE) activity, serum ureic nitrogen (SUN), creatinine and electrolytes were measured, and blood pressure was monitored for pharmacodynamic analysis. The elimination half-lives of enalapril and enalaprilat were 0.67 and 2.76 hr respectively after IV enalapril. Enalapril concentrations after PO administrations were below the limit of quantification (10 ng/mL) in all horses and enalaprilat concentrations were below the limit of quantification in 4 of the 7 horses. Maximum mean ACE inhibitions from baseline were 88.38, 3.24, 21.69, 26.11 and 30.19% for IV enalapril at 0.50 mg/kg, placebo and PO enalapril at 0.50, 1.00 and 2.00 mg/kg, respectively. Blood pressures, SUN, creatinine and electrolytes remained unchanged during the experiments.
Enalapril maleate, unlike enalaprilat, is well absorbed following oral administration. Although enalaprilat is a more potent angiotensin converting enzyme inhibitor than enalapril, it is poorly absorbed from the GI tract because of its high polarity, with only about 3-12% of an orally administered dose being absorbed. Approximately 55-75% of an oral dose of enalapril maleate is rapidly absorbed from the GI tract in healthy individuals and hypertensive patients. Food does not appear to substantially affect the rate or extent of absorption of enalapril maleate. Following oral administration, enalapril maleate appears to undergo first pass metabolism principally in the liver, being hydrolyzed to enalaprilat.
The hypotensive effect of a single oral dose of enalapril maleate is usually apparent within 1 hr and maximal in 4-8 hr. The hypotensive effect of usual doses of the drug generally persists for 12-24 hr but may diminish toward the end of the dosing interval in some patients. Reduction in blood pressure may be gradual, and several weeks of therapy may be required before the full effect is achieved.
Following IV administration of enalaprilat, the hypotensive effect is usually apparent within 5-15 min with maximal effect occurring within 1-4 hr; the duration of hypotensive effect appears to be dose related, but with the recommended doses, the duration of action in most patients is approximately 6 hr. Plasma angiotensin converting enzyme inhibition and reduction in blood pressure appear to be correlated to a plasma enalaprilat concentration of 10 ng/mL, a concentration at which maximal blockade of plasma angiotensin converting enzyme is achieved. After withdrawal of enalapril or enalaprilat, blood pressure gradually returns to pretreatment levels; rebound hypertension following abrupt withdrawal of the drug has not been reported to date. /Enalaprilat/
For more Absorption, Distribution and Excretion (Complete) data for Enalapril (11 total), please visit the HSDB record page.

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Metabolism / Metabolites
About 60% of the absorbed dose is extensively hydrolyzed to enalaprilat via de-esterification mediated by hepatic esterases. In humans, metabolism beyond bioactivation to enalaprilat is not observed.
About 60% of an absorbed dose of enalapril is extensively hydrolyzed to enalaprilat, principally in the liver via esterases. About 20% appears to be hydrolyzed on first pass through the liver; this hydrolysis does not appear to occur in plasma in humans. Enalaprilat is a more potent angiotensin converting enzyme inhibitor than enalapril. There is no evidence of other metabolites of enalapril in humans, rats, or dogs. However, a despropyl metabolite of enalaprilat was identified in urine in rhesus monkeys, accounting for 13% of an oral dose of enalapril maleate. Hydrolysis of enalapril to enalaprilat may be delayed and/or impaired in patients with severe hepatic impairment, but the pharmacodynamic effects of the drug do not appear to be significantly altered.

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Biological Half-Life
The average terminal half life of enalaprilat is 35-38 hours. The effective half life following multiple doses is 11-14 hours. The prolonged terminal half-life is due to the binding of enalaprilat to ACE.
Following oral admin, the half-life of unchanged enalapril appears to be <2 hr in healthy individuals and in patients with normal hepatic and renal functions, but may be increased in patients with congestive heart failure. Following oral admin of a single 5 or 10 mg dose of enalapril maleate in patients with congestive heart failure, the half-life of enalapril was 3.4 or 5.8 hr, respectively.
Elimination of enalaprilat may also be prolonged in patients with congestive heart failure or impaired hepatic function compared with healthy individuals and patients with hypertension observations of serum concns of enalaprilat over long periods following oral or iv admin suggest that enalaprilat has an avg terminal half-life of about 35-38 hr (range: 30-87 hr). ...The effective half-life for accumulation of enalaprilat (determined from urinary recovery) has been reported to average about 11 hr in healthy individuals with normal renal function.

Hepatotoxicity
Enalapril, like other ACE inhibitors, has been associated with a low rate of serum aminotransferase elevations (
Likelihood score: B (likely but rare cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Because of the low levels of enalapril in breastmilk, amounts ingested by the infant are small and would not be expected to cause any adverse effects in breastfed infants.
◉ Effects in Breastfed Infants
None reported in 4 breastfed infants whose mothers were taking oral enalapril 5 to 10 mg daily.
◉ Effects on Lactation and Breastmilk
In 15 postmenopausal hypertensive women (prior lactation status not stated), serum prolactin levels were decreased by 22% compared to placebo after enalapril 20 mg once daily for 15 days. The maternal prolactin level in a mother with established lactation may not affect her ability to breastfeed.
A woman with pre-eclampsia was treated was started at term with oral enalapril 10 mg daily. Her milk came in on day 3 postpartum and she had no difficulties with nursing during 5 weeks of observation.

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Protein Binding
It is reported that less than 50% of enalaprilat is bound to human plasma proteins, based on limited data from binding studies of enalaprilat in human plasma both by equilibrium dialysis and by ultrafiltration.

[1]. Antiarrhythmic effects of losartan and enalapril in canine pulmonary vein sleeve preparations. J Cardiovasc Electrophysiol. 2011 Jun;22(6):698-705.

[2]. Enalapril protects endothelial cells against induced apoptosis in Alzheimer's disease. J Res Med Sci. 2013 Mar;18(Suppl 1):S1-5.

[3]. Effect of stearic acid on enalapril stability and dissolution from multiparticulate solid dosage forms. AAPS PharmSciTech. 2013 Sep;14(3):1150-7.

[4]. Enalapril and moexipril protect from free radical-induced neuronal damage in vitro and reduce ischemic brain injury in mice and rats. Eur J Pharmacol. 1999 May 28;373(1):21-33.

Enalapril is a dicarboxylic acid monoester that is ethyl 4-phenylbutanoate in which a hydrogen alpha to the carboxy group is substituted by the amino group of L-alanyl-L-proline (S-configuration). It has a role as a prodrug, an EC 3.4.15.1 (peptidyl-dipeptidase A) inhibitor, an antihypertensive agent and a geroprotector. It is a dicarboxylic acid monoester and a dipeptide. It is functionally related to an enalaprilat (anhydrous).
Enalapril is a prodrug belonging to the angiotensin-converting enzyme (ACE) inhibitor drug class that works on the renin-angiotensin-aldosterone system, which is responsible for the regulation of blood pressure and fluid and electrolyte homeostasis. Enalapril is an orally-active and long-acting nonsulphydryl antihypertensive agent that suppresses the renin-angiotensin-aldosterone system to lower blood pressure. It was developed from a targeted research programmed using molecular modelling. Being a prodrug, enalapril is rapidly biotransformed into its active metabolite, [enalaprilat], which is responsible for the pharmacological actions of enalapril. The active metabolite of enalapril competitively inhibits the ACE to hinder the production of angiotensin II, a key component of the renin-angiotensin-aldosterone system that promotes vasoconstriction and renal reabsorption of sodium ions in the kidneys. Ultimately, enalaprilat works to reduce blood pressure and blood fluid volume. Commonly marketed under the trade name Vasotec, enalapril was first approved by the FDA in 1985 for the management of hypertension, heart failure, and asymptomatic left ventricular dysfunction. It is also found in a combination product containing [hydrochlorothiazide] that is used for the management of hypertension. The active metabolite enalaprilat is also available in oral tablets and intravenous formulations for injection.
Enalapril is an Angiotensin Converting Enzyme Inhibitor. The mechanism of action of enalapril is as an Angiotensin-converting Enzyme Inhibitor. The physiologic effect of enalapril is by means of Decreased Blood Pressure.
Enalapril is an angiotensin-converting enzyme (ACE) inhibitor widely used in the therapy of hypertension and heart failure. Enalapril is associated with a low rate of transient serum aminotransferase elevations and has been linked to rare instances of acute liver injury.
Enalapril is a dicarbocyl-containing peptide and angiotensin-converting enzyme (ACE) inhibitor with antihypertensive activity. As a prodrug, enalapril is converted by de-esterification into its active form enalaprilat. Enalaprilat competitively binds to and inhibits ACE, thereby blocking the conversion of angiotensin I to angiotensin II. This prevents the potent vasoconstrictive actions of angiotensin II and results in vasodilation. Enalapril also decreases angiotensin II-induced aldosterone secretion by the adrenal cortex, which leads to an increase in sodium excretion and subsequently increases water outflow.
An angiotensin-converting enzyme inhibitor that is used to treat HYPERTENSION and HEART FAILURE.
See also: Enalaprilat (annotation moved to).

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Drug Indication
Indicated for the management of essential or renovascular hypertension as monotherapy or in combination with other antihypertensive agents, such as thiazide diuretics, for an additive effect. Indicated for the treatment of symptomatic congestive heart failure, usually in combination with diuretics and digitalis. Indicated for the management of asymptomatic left ventricular dysfunction in patients with an ejection fraction of ≤ to 35 percent to decrease the rate of development of overt heart failure and the incidence of hospitalization for heart failure.
FDA Label

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Mechanism of Action
The renin-angiotensin-aldosterone system (RAAS) is a signaling pathway that works in synergism with the sympathetic system to regulate blood pressure and fluid and electrolyte homeostasis. Activation of this system upon stimulation by different factors, such as low blood pressure and nerve impulses, leads to increased release of norepinephrine (NE) from sympathetic nerve terminals and effects on the vascular growth, vasoconstriction, and salt retention in the kidneys. Renin is released from Renin acts on the precursor prottein angiotensinogen, which is a plasma globulin synthesized from the liver, to produce cleaved peptide hormone angiotensin I. Angiotensin I then can be further cleaved by ACE to produce angiotensin II, a vasoconstrictive peptide hormone. Present in different isoforms, angiotensin converting enzyme (ACE) is peptidyl dipeptidase enzyme expressed in various tissues, including the vascular tissues, such as the heart, brain, and kidneys. ACE also plays a role in inactivation of bradykinin, a potent vasodepressor peptide. Angiotensin II mediates various actions on the body by working on its G-protein coupled receptors, AT1 and AT2. It causes direct vasoconstriction of precapillary arterioles and postcapillary venules, inhibits the reuptake of NE thereby increasing available levels, stimulates the release of catecholamines from the adrenal medulla, reduces urinary excretion of sodium ions and water by promoting proximal tubular reabsorption, stimulates synthesis and release of aldosterone from the adrenal cortex, and stimulates hypertrophy of both vascular smooth muscle cells and cardiac myocytes. Enalapril is a pharmacologically inactive prodrug that requires hepatic biotransformation to form [enalaprilat], its active metabolite that works on the RAAS to inhibit ACE. Biotransformation is critial for the therapeutic actions of the drug, as enalapril itself is only a weak inhibitor of ACE. ACE inhibition results in reduced production and plasma levels of angiotensin II, increased plasma renin activity due to the loss of feedback inhibition by angiotensin II, and decreased aldosterone secretion. However, plasma aldosterone levels usually return to normal during long-term administration of enalapril. Decreased levels of angiotensin II subsequently leads to the dilatation of peripheral vessles and reduced vascular resistance which in turn lower blood pressure. While inhibition of ACE leading to suppression of RAAS is thought to be the primary mechanism of action of enalapril, the drug was shown to still exert antihypertensive effects on individuals with low-renin hypertension. It is suggested that enalapril may mediate its pharmacological actions via other modes of action that are not fully understood. As ACE is structurally similar to kininase I, which is a carboxypeptidase that degrades bradykinin, whether increased levels of bradykinin play a role in the therapeutic effects of enalapril remains to be elucidated.
Enalapril maleate is a prodrug of enalaprilat and has little pharmacologic activity until hydrolyzed in vivo to enalaprilat. ... Enalapril prevents the conversion of angiotensin I to angiotensin II (a potent vasoconstrictor) through inhibition of angiotensin-converting enzyme (ACE). The drug competes with physiologic substrate (angiotensin I) for the active site of ACE; the affinity of enalaprilat for ACE is approximately 200,000 times greater than that of angiotensin I. In vitro on a molar basis, the affinity of enalaprilat for ACE is 300-1000 or 2-17 times that of enalapril or captopril, respectively. However, in vitro on a molar basis, the ACE-inhibitory effect of enalapril was shown to be similar to that of enalaprilat in rat plasma and kidneys, because these tissues extensively hydrolyze enalapril to form enalaprilat. The drug apparently does not inhibit brain ACE in animals.

C20H28N2O5

376.45

376.199

75847-73-3

Enalapril maleate;76095-16-4;Enalapril-d5 maleate;349554-02-5;Enalapril sodium;149404-21-7

5388962

White to off-white solid powder

1.2±0.1 g/cm3

582.3±50.0 °C at 760 mmHg

143-144.5ºC

306.0±30.1 °C

0.0±1.7 mmHg at 25°C

1.550

2.43

2

6

10

27

519

3

O=C(O)[C@H]1N(C([C@H](C)N[C@H](C(OCC)=O)CCC2=CC=CC=C2)=O)CCC1

GBXSMTUPTTWBMN-XIRDDKMYSA-N

InChI=1S/C20H28N2O5/c1-3-27-20(26)16(12-11-15-8-5-4-6-9-15)21-14(2)18(23)22-13-7-10-17(22)19(24)25/h4-6,8-9,14,16-17,21H,3,7,10-13H2,1-2H3,(H,24,25)/t14-,16-,17-/m0/s1

((S)-1-ethoxy-1-oxo-4-phenylbutan-2-yl)-L-alanyl-L-proline

Kinfil Bonuten Enalapril Gadopril

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)