Pharmacokinetics and pharmacodynamics of enalapril and its active metabolite, enalaprilat, at four different doses in healthy horses

Intrathecal enalapril reduces adhesion formation in experimentally induced digital flexor tendon sheath injuries in horses

OBJECTIVE

The objectives of the study were to describe a standing percutaneous adhesion induction model in the digital flexor tendon sheath (DFTS) of horses and to evaluate the effect of intrathecal administration of the angiotensin-converting enzyme (ACE) inhibitor enalapril on tendon healing and adhesion formation.

STUDY DESIGN

Randomized, blinded, controlled experimental study.

ANIMALS

Eight healthy horses.

METHODS

A collagenase-induced adhesion model was implemented in the deep digital flexor tendon (DDFT) of both forelimbs under standing ultrasonographic guidance. Daily intrathecal injections of 5 mg enalapril (the treatment condition) were administered to a randomly assigned forelimb for 5 days, with the contralateral limb receiving an equivalent volume of 0.9% NaCl (the control). Lameness and limb circumference were recorded weekly. Horses were euthanized after 8 weeks and evaluated for gross digital flexor tendon sheath (DFTS) adhesions. Tendons were collected for histopathologic scoring of DDFT healing. Paired data were analyzed using a one-sided alternative sign test and longitudinal regression.

RESULTS

Multiple DFTS adhesions were formed in control limbs of all horses. The median number of gross DFTS adhesions in treated limbs was less than in control limbs (p = .0039). The average reduction in limb circumference and lameness scores over time occurred faster in treated versus control limbs (p < .025). There were no differences in DDFT histopathologic scores between groups.

CONCLUSION

The standing percutaneous DFTS adhesion induction model demonstrated that intrathecal enalapril reduced DFTS adhesion formation, lameness scores, and limb circumference over time.

CLINICAL SIGNIFICANCE

Intrathecal enalapril administration may reduce morbidity in horses with naturally occurring tendon injuries.

Enalapril increases the urinary excretion of metformin in rats by inducing multidrug and toxin excretion protein 1 in the kidney

Two-thirds of patients with type 2 diabetes mellitus have hypertension, and thus the combination of two or more drugs to treat these diseases is common. It has been shown that the combination of metformin and enalapril has beneficial effects, but few studies have evaluated the interactions between these two drugs. This study investigated the effects of enalapril on the pharmacokinetics and urinary excretion of metformin in rats, with a focus on transporter-mediated drug interactions. Rats were dosed orally with metformin alone (100 mg/kg) or in combination with enalapril (4 mg/kg). The concentration of metformin was measured by high performance liquid chromatography and the level of organic cation transporters (rOCTs) and multidrug and toxin excretion protein 1 (rMATE1), which mediate the uptake and efflux of metformin, respectively, were evaluated by immunoblotting. After single and 7-day dosing, the plasma concentration of metformin in the co-administration group was significantly lower than that in the metformin-only group, and the CL/F and urinary excretion were increased in the co-administration group. Enalapril did not affect the K_p of metformin but reduced renal slice-uptake of metformin. The expression of rMATE1 was increased, whereas rOCT2 expression was decreased in rat kidney. Importantly, long-term co-administration of metformin and enalapril markedly decreased the level of lactic acid and uric acid in the blood. Enalapril increases the urinary excretion of metformin through the up-regulation of rMATE1. This reveals a new mechanism of drug interactions and provides a basis for drug dosage adjustment when these drugs are co-administered.

Preliminary investigation of orally administered benazepril in horses with left-sided valvular regurgitation

BACKGROUND

Despite the paucity of data available, orally administered angiotensin-converting enzyme (ACE) inhibitors are empirically used in horses with valvular regurgitation.

OBJECTIVE

Evaluate the echocardiographic and hormonal changes in response to oral benazepril in horses with left-sided valvular regurgitation.

STUDY DESIGN

Prospective, randomised double-blind, placebo-controlled trial.

METHODS

Horses with mitral valve (MR) and/or aortic valve regurgitation (AR) received oral benazepril (n = 6) at a dosage of 1 mg/kg q 12 h or a placebo (n = 5) for 28 days. Echocardiography was performed before drug administration and after 28 days of treatment. Plasma renin activity, serum ACE activity, angiotensin II concentration, aldosterone concentration and biochemical variables were measured before drug administration and after 7 and 28 days of treatment.

RESULTS

Relative to baseline, horses treated with benazepril had statistically significant reduction in left ventricular internal diameter in systole (mean difference between groups = -0.97 cm; 95% CI = -1.5 to -0.43 cm), aortic sinus diameter (-0.31 cm; -0.54 to -0.07 cm), and percentage of the aortic annulus diameter occupied by the base of the AR jet (-17.05%; -31.17 to -2.93%) compared with horses receiving a placebo. In addition, horses treated with benazepril had a significantly greater increase in cardiac output (11.95 L/min; 1.17-22.73 L/min) and fractional shortening (7.59%; 3.3-11.88%) compared with horses receiving a placebo. Despite profound serum ACE inhibition, renin activity and concentrations of angiotensin II and aldosterone were not significantly different between treatment groups or among time points.

MAIN LIMITATIONS

Very small sample size and short treatment period.

CONCLUSIONS

Treatment with oral benazepril resulted in statistically significant echocardiographic changes that might indicate reduced cardiac afterload in horses with left-sided valvular regurgitation. Additional studies with a larger sample size will be necessary to determine if administration of benazepril is beneficial in horses with valvular regurgitation. The Summary is available in Spanish - see Supporting Information.

Pharmacokinetic/pharmacodynamic modeling of benazepril and benazeprilat after administration of intravenous and oral doses of benazepril in healthy horses

Pharmacokinetic and pharmacodynamic (PK/PD) properties of the angiotensin-converting enzyme inhibitor (ACEI) benazeprilat have not been evaluated in horses. This study was designed to establish PK profiles for benazepril and benazeprilat after intravenous (IV) and oral (PO) administration of benazepril using a PK/PD model. This study also aims to determine the effects of benazeprilat on serum angiotensin converting enzyme (ACE), selecting the most appropriate dose that suppresses ACE activity. Six healthy horses in a crossover design received IV benazepril at 0.50mg/kg and PO at doses 0 (placebo), 0.25, 0.50 and 1.00mg/kg. Blood pressures (BP) were measured and blood samples were obtained at different times in order to measure serum drug concentrations and serum ACE activity, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and spectrophotometry, respectively. Systemic bioavailability of benazeprilat after PO benazepril was 3-4%. Maximum ACE inhibitions from baseline were 99.63% (IV benazepril), 6.77% (placebo) and 78.91%, 85.74% and 89.51% (for the three PO benazepril doses). Significant differences in BP were not found. Although oral availability was low, benazeprilat 1.00mg/kg, reached sufficient serum concentrations to induce long lasting serum ACE inhibitions (between 88 and 50%) for the first 48h. Additional research on benazepril administration in equine patients is indicated.

Pharmacokinetics and pharmacodynamics of ramipril and ramiprilat after intravenous and oral doses of ramipril in healthy horses

The pharmacokinetics and pharmacodynamics (PK/PD) of the angiotensin-converting enzyme inhibitor (ACEI) ramiprilat after intravenous (IV) and oral (PO) administration of ramipril have not been evaluated in horses. This study was designed to establish PK profiles for ramipril and ramiprilat as well as to determine the effects of ramiprilat on serum angiotensin converting enzyme (ACE) and to select the most appropriate ramipril dose that suppresses ACE activity. Six healthy horses in a cross-over design received IV ramipril 0.050 mg/kg, PO at a dose of 0 (placebo), and 0.050, 0.10, 0.20, 0.40 and 0.80 mg/kg ramipril. Blood pressures were measured and blood samples obtained at different times. Serum ramipril and ramiprilat concentrations and serum ACE activity were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and spectrophotometry, respectively. Systemic bioavailability of ramiprilat after PO ramipril was 6-9%. Percentages of maximum ACE inhibitions from baseline were 98.88 (IV ramipril), 5.31 (placebo) and 27.68, 39.27, 46.67, 76.13 and 84.27 (the five doses of PO ramipril). Blood pressure did not change during the experiments. Although oral availability of ramiprilat was low, ramipril has sufficient enteral absorption and bioconversion to ramiprilat to induce serum ACE inhibitions of almost 85% after a dose of 0.80 mg/kg ramipril. Additional research on ramipril administration in equine patients is indicated.