Pharmacokinetics of intravenously and orally administered eprosartan in healthy males: absolute bioavailability and effect of food

Protective and therapeutic role of mango pulp and eprosartan drug and their anti-synergistic effects against thioacetamide-induced hepatotoxicity in male rats

The present study was done to evaluate the protective and therapeutic role of mango pulp (M), eprosartan drug (E), and their co-administration (EM) against hepatotoxicity induced by thioacetamide (T). Seven groups of rats were prepared as follows: the control (C) group (normal rats), T group (the rats were injected with T), T-M group (the rats were injected with T, and then treated with M), T-E group (the rats were injected with T, and then treated with E), T-EM group (the rats were injected with T, and then treated with E and M), M-TM-M group (the rats were administered with M before, during, and after T injection), and M group (the healthy rats were administered with M only). Firstly, the characterizations of M were determined. Also, the markers of hepatic oxidative stress [malondialdehyde (MDA) and glutathione (GSH) levels and the activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GSR)], inflammation and fibrosis [(tumor necrosis factor-α (TNF-α) and platelet-derived growth factor-BB (PDGF-BB) levels and gene expression of transforming growth factor-beta1(TGF-β1)], and liver functions and microscopic examination were evaluated. The present results revealed that M contains 419 ± 1.04 μg total phenolics as gallic acid equivalent and 6.8 ± 0.05 μg total flavonoids as quercetin equivalent. The analysis of phenolics and flavonoids showed the presence of chlorogenic, caffeic, 2,5-dihydroxy benzoic, 3,5-dicaffeoylquinic, 4,5-dicaffeoylquinic, tannic, cinnamic acidS, and catechin, phloridzin, and quercetin with different concentrations. Also, M contains various minerals with different concentrations involving potassium, calcium, magnesium, sodium, iron, copper, zinc, and manganese. The current results showed that the total antioxidant capacity of 1 g of M was 117.2 ± 1.16 as μg ascorbic acid equivalent. Our biochemical studies showed that all treatments significantly reduced T-induced hepatotoxicity and liver injuries, as the oxidative stress and inflammatory and fibrotic markers were diminished where MDA level and the activities of GST, GSSG, and GR were decreased when compared with T group. In contrast, GSH level and the activities of SOD and GPx and GSH/GSSG ratio were increased. In addition, TNF-α and PDGF-BB levels were reduced, and the gene expression of TGF-β1 was down-regulated. Consequently, the liver functions were significantly improved. In conclusion, each E, M, and EM has a therapeutic effect against T-induced hepatotoxicity via the reduction of the OS, inflammation, and fibrosis. Unfortunately, treatment with M and E simultaneously revealed the less effectiveness than the treatment with M or E demonstrates the presence of anti-synergistic effect between them. Additionally, M-TM-M treatment showed a better effect than T-M treatment against T-induced hepatotoxicity revealing the prophylactic role of M. The administration of healthy rats with M for 12 weeks has no side effect.

Formulation and characterization of eprosartan mesylate and β-cyclodextrin inclusion complex prepared by microwave technology

The goal of this work was to improve the aqueous solubility and dissolution rate of eprosartan mesylate by preparing inclusion complex of drug with β-cyclodextrin (β-CD) by microwave technique. In order to determine the solubility of eprosartan, phase solubility was determined and dissolution study was also conducted. Further, analytical techniques for instance, particle size distribution, differential scanning calorimetry, powder X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy were used for the characterization of inclusion complex. In addition, the binding pattern of eprosartan with the β-CD was investigated by molecular modeling study. Phase solubility study revealed that approximately 4.48 folds improvement in the solubility of drug was noted with β-CD (10 mM). The estimated stability constant (K_c) values for eprosartan:β-CD binary mixture was found to be 280.78 M^–1. The prepared inclusion complex of drug with β-CD presented better drug release profile (62.96 ± 2.01% in 1 h) as compared to their physical mixture (41.41 ± 1.77% in 1 h) or drug per se (29.97 ± 3.13%). The inclusion complex demonstrated different features and properties from pure drug, and we inferred that this could be due to the inclusion of drug into cyclodextrin cavity that confirmed by different analytical method. Molecular modeling study demonstrated a good affinity of eprosartan to entangle to β-CD. The outcomes have shown that guest molecule has many significant interactions with the host molecule. These observations are very interesting and may be a valuable approach to improve the solubility and in turn the bioavailability of eprosartan.

Biliary Excretion-Mediated Food Effects and Prediction

Many orally administered drugs with negative food effects (i.e., lower exposure under fed conditions) are often primarily or partially eliminated by biliary excretion. The aim of this study is to assess the potential correlation between a negative food effect and biliary excretion. Correlation analysis was conducted using a training dataset containing 27 drugs which met the following criteria: (1) immediate-release formulations, (2) shows a negative food effect, (3) > 10% biliary clearance, and (4) does not undergo extensive metabolism. A correlation between fed-state biliary clearance (CL_b,fed) and fasted-state biliary clearance (CL_b,fast) (y = 1.81*x, R² = 0.68) was observed. The 1.8-fold increase in biliary clearance was then used as a correction factor to improve physiologically based pharmacokinetic (PBPK) prediction of food effects for 12 test drugs. The mean deviations of predicted fed/fasting AUC ratio and C_max ratio from clinically observed values were reduced from 32.4 to 17.2% and from 63.3 to 54.3%, respectively. In contrast to the positive food effects on most biopharmaceutics classification system (BCS) class II drugs for which food-stimulated bile flow increases drug solubility and absorption, our results suggest that the elimination of biliary excreted drugs is increased by food-stimulated bile flow, resulting in negative food effects.

Physicochemical properties of dietary phytochemicals can predict their passive absorption in the human small intestine

A diet high in phytochemical-rich plant foods is associated with reducing the risk of chronic diseases such as cardiovascular and neurodegenerative diseases, obesity, diabetes and cancer. Oxidative stress and inflammation (OSI) is the common component underlying these chronic diseases. Whilst the positive health effects of phytochemicals and their metabolites have been demonstrated to regulate OSI, the timing and absorption for best effect is not well understood. We developed a model to predict the time to achieve maximal plasma concentration (Tmax) of phytochemicals in fruits and vegetables. We used a training dataset containing 67 dietary phytochemicals from 31 clinical studies to develop the model and validated the model using three independent datasets comprising a total of 108 dietary phytochemicals and 98 pharmaceutical compounds. The developed model based on dietary intake forms and the physicochemical properties lipophilicity and molecular mass accurately predicts Tmax of dietary phytochemicals and pharmaceutical compounds over a broad range of chemical classes. This is the first direct model to predict Tmax of dietary phytochemicals in the human body. The model informs the clinical dosing frequency for optimising uptake and sustained presence of dietary phytochemicals in circulation, to maximise their bio-efficacy for positively affect human health and managing OSI in chronic diseases.

Fimasartan: A New Angiotensin Receptor Blocker

Fimasartan is the ninth, and most recent, angiotensin II receptor antagonist approved as an antihypertensive agent. Fimasartan, a pyrimidin-4(3H)-one derivative of losartan with the imidazole ring replaced, which enables higher potency and longer duration than losartan. Fecal elimination and biliary excretion are the predominant elimination pathways of fimasartan and the urinary excretion was found to be less than 3 % 24 h after administration. Fimasartan is primarily catabolized by cytochrome P450 isoform 3A and no significant drug interaction was observed when used in combination with hydrochlorothiazide, amlodipine, warfarin, or digoxin. Fimasartan at a dosage range of 60-120 mg once daily showed an antihypertensive effect over 24 h. In a large, population-based observational study, fimasartan showed an excellent safety profile. Anti-inflammatory and organ-protecting effects of fimasartan have been shown in various preclinical studies, including aortic balloon injury, myocardial infarct ischemia/reperfusion, doxorubicin cardiotoxicity, and ischemic stroke models.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

In situ artificial membrane permeation assay under hydrodynamic control: correlation between drug in vitro permeability and fraction absorbed in humans

The purpose of this study was to develop an in vitro permeation model that will predict the fraction of drugs absorbed in humans. A rotating-diffusion cell with two aqueous compartments, separated by a lipid-impregnated artificial membrane, was used to determine the permeability of drugs under conditions of controlled hydrodynamics. The measured effective permeability coefficient was modified to include the paracellular transport derived from a previously reported colorectal adenocarcinoma epithelial cell line (Caco-2) permeability study and the effects of unstirred water layer anticipated in vivo. Permeability data were collected for 31 different marketed drugs with known absolute oral bioavailability and human hepatic clearance data. Literature bioavailability values were corrected for the first pass hepatic clearance thus obtaining the fraction absorbed from intestinal lumen (fraction absorbed), F(a), while assuming that the fraction escaping intestinal extraction, F(g), was approximately ~1. Permeability obtained under conditions of controlled hydrodynamics was compared with the permeability measured under unstirred conditions. It is shown that the optimized effective permeability correlates with the fraction absorbed. In contrast, permeability data obtained under unstirred conditions does not show a good correlation. The in vitro permeation model developed in this study predicts the fraction absorbed of the selected drugs in humans within experimental uncertainty. It has been demonstrated that the correlation with the fraction absorbed is greatly improved using the permeability data obtained under controlled hydrodynamics with paracellular transport included in the model.

Eprosartan: a review of its use in hypertension

Eprosartan is an angiotensin II receptor antagonist (angiotensin II receptor blocker [ARB]) used in the treatment of hypertension. In large, randomized trials, eprosartan (with or without hydrochlorothiazide [HCTZ]) demonstrated superior antihypertensive efficacy to that of placebo and, when administered at comparable dosage regimens, had similar blood pressure-lowering effects to enalapril. Eprosartan was generally well tolerated in clinical trials and had a lower incidence of persistent dry cough than enalapril. Eprosartan has a neutral effect on metabolic parameters, such as serum lipid levels and glucose homeostasis, and a low propensity for pharmacokinetic drug interactions. The use of eprosartan or other ARBs in combination with HCTZ tends to reverse the potassium loss associated with thiazide diuretics. Independent of its antihypertensive effects, eprosartan was associated with improved clinical outcomes (primary composite endpoint of all causes of mortality and all cardiovascular and cerebrovascular events, including all recurrent events) compared with nitrendipine in a randomized, secondary prevention trial in hypertensive patients with previous cerebrovascular events (MOSES trial). Eprosartan also reduced blood pressure and was associated with a modest improvement in cognitive function in a large observational study in patients > or =50 years of age with newly diagnosed hypertension (OSCAR study). In both of these trials, additional antihypertensive therapy, such as HCTZ, was permitted. Therefore, eprosartan is a useful treatment option in the management of a broad range of patients with hypertension, and its use with HCTZ provides a rational combination regimen.

Significance of protein binding in pharmacokinetics and pharmacodynamics

The significance of plasma protein binding on drug efficacy and, subsequently, the clinical relevance of changes in protein binding has been controversially discussed for decades. The uncertainty concerning the impact of plasma protein binding on a drug's pharmacological activity is, in part, related to the approach used when investigating and interpreting protein binding effects in vitro and in vivo. Frequently, a generalized one-size-fits-all approach, such as "protein binding does matter/does not matter," may not be applicable. An appropriate analysis requires careful consideration of both pharmacokinetic and pharmacodynamic processes, as they both contribute to the safety and efficacy of drugs. Therefore, the aim of this article is to provide a concise review of the theoretical concepts of protein binding, and to discuss relevant examples where applicable.

Clinical pharmacokinetics of losartan

Losartan is the first orally available angiotensin-receptor antagonist without agonist properties. Following oral administration, losartan is rapidly absorbed, reaching maximum concentrations 1-2 hours post-administration. After oral administration approximately 14% of a losartan dose is converted to the pharmacologically active E 3174 metabolite. E 3174 is 10- to 40-fold more potent than its parent compound and its estimated terminal half-life ranges from 6 to 9 hours. The pharmacokinetics of losartan and E 3174 are linear, dose-proportional and do not substantially change with repetitive administration. The recommended dosage of losartan 50 mg/day can be administered without regard to food. There are no clinically significant effects of age, sex or race on the pharmacokinetics of losartan, and no dosage adjustment is necessary in patients with mild hepatic impairment or various degrees of renal insufficiency. Losartan, or its E 3174 metabolite, is not removed during haemodialysis. The major metabolic pathway for losartan is by the cytochrome P450 (CYP) 3A4, 2C9 and 2C10 isoenzymes. Overall, losartan has a favorable drug-drug interaction profile, as evidenced by the lack of clinically relevant interactions between this drug and a range of inhibitors and stimulators of the CYP450 system. Losartan does not have a drug-drug interaction with hydrochlorothiazide, warfarin or digoxin. Losartan should be avoided in pregnancy, as is the case with all other angiotensin-receptor antagonists. When given in the second and third trimester of pregnancy, losartan is often associated with serious fetal toxicity. Losartan is a competitive antagonist that causes a parallel rightward shift of the concentration-contractile response curve to angiotensin-II, while E 3174 is a noncompetitive "insurmountable" antagonist of angiotensin-II. The maximum recommended daily dose of losartan is 100mg, which can be given as a once-daily dose or by splitting the same total daily dose into two doses. Losartan reduces blood pressure comparably to other angiotensin-receptor antagonists. Losartan has been extensively studied relative to end-organ protection, with studies having been conducted in diabetic nephropathy, heart failure, post-myocardial infarction and hypertensive patients with left ventricular hypertrophy. The results of these studies have been sufficiently positive to support a more widespread use of angiotensin-receptor antagonists in the setting of various end-organ diseases. Losartan, like other angiotensin-receptor antagonists, is devoid of significant adverse effects.

Pharmacophore, Drug Metabolism, and Pharmacokinetics Models on Non-Peptide AT1, AT2, and AT1/AT2Angiotensin II Receptor Antagonists

About 20 non-peptide angiotensin II receptor antagonists are in various stages of clinical development. Different modeling approaches were used to predict the pharmacophoric requirements for AT(1) (angiotensin II receptor subtype 1) affinity. However, to our knowledge, none was used to predict both the selectivity toward AT(1) and AT(2) (angiotensin II receptor subtype 2) receptor subtypes. In this paper, partial least squares discriminant analysis is applied to derive the chemical features guiding AT(1) and AT(2) selectivity or mixed AT(1)/AT(2) receptor binding. The method can be used to modulate AT(1) versus AT(2) selectivity. Concerns that unopposed stimulation of the AT(2) receptor might produce adverse effects initiated a search for new balanced antagonists. Moreover, it can serve as a fast filtering procedure in database searches. Finally, some relevant pharmacokinetics and metabolic properties of the database of 53 compounds are calculated using the VolSurf and MetaSite software to allow the simultaneous characterization of pharmacodynamic and pharmacokinetics properties of the chemical space of angiotensin II receptor antagonists.

Effects of telmisartan compared with eprosartan on blood pressure control, glucose metabolism and lipid profile in hypertensive, type 2 diabetic patients: a randomized, double-blind, placebo-controlled 12-month study

We evaluated the antihypertensive activity, glucose homeostasis and plasma lipid profile in patients with mild hypertension and type 2 diabetes mellitus treated by diet and exercise, and not in receipt of oral hyperglycemics, following 12-month treatment with either telmisartan or eprosartan. In this double-blind, placebo-controlled trial, 119 patients with mild essential hypertension (diastolic blood pressure [DBP] 91-104 mmHg) and type 2 diabetes were divided into three groups and randomized to receive once-daily telmisartan 40 mg, eprosartan 600 mg, or placebo for 12 months. At enrollment, patients were advised on diet (1,400-1,600 kcal/day) and exercise (physical aerobics on a bicycle for at least 30 min on 4 days each week). Compared with baseline, a significant reduction (p<0.01) in seated trough systolic blood pressure (SBP) was detected after 12-month treatment with either telmisartan or eprosartan. Seated trough DBP was also reduced by telmisartan (p<0.01) and eprosartan (p<0.05); the antihypertensive effect of telmisartan was significantly superior (p<0.05). No change in body mass index or glucose metabolism was observed with either active treatment, or with placebo. Telmisartan, but not eprosartan, significantly improved plasma total cholesterol (p<0.01), low-density lipoprotein cholesterol (p<0.01) and triglycerides (p<0.05) compared with eprosartan. In conclusion, 12-month telmisartan treatment produced a significantly greater reduction in DBP than eprosartan and significantly improved plasma lipids. The improvement could be due to varying pharmacokinetic/pharmacodynamic properties of telmisartan compared with eprosartan, even if it is not clear about the relationship between angiotensin-II receptor blockade and 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibition.

Eprosartan

The angiotensin II receptor antagonist eprosartan is approved for the treatment of essential hypertension and may be administered using a convenient once-daily regimen. The drug is a well tolerated and effective antihypertensive agent with benefit in the secondary prevention of cerebrovascular events, independent of blood pressure (BP)-lowering effects. Eprosartan has a low potential for serious adverse events and has not been associated with clinically significant drug interactions, establishing it as a promising agent for combination antihypertensive strategies. Unlike ACE inhibitors such as enalapril, eprosartan does not have a tendency to cause persistent nonproductive cough. Accordingly, eprosartan represents a useful therapeutic option in the management of patients with hypertension, including those who have had a stroke and those with co-morbid type 2 diabetes mellitus.

Eprosartan: a review of its use in the management of hypertension

Eprosartan is a potent and selective angiotensin II subtype 1 receptor antagonist. Results of large (n > 100) randomised double-blind studies in patients with mild, moderate or severe hypertension demonstrated that the antihypertensive efficacy of eprosartan (usually 400 to 800 mg/day as a single daily dose or in 2 divided doses) is significantly greater than that of placebo and at least as good as that of enalapril. In placebo-controlled trials, eprosartan achieved mean reductions from baseline in trough sitting systolic blood pressure of 6.3 to 15 mm Hg and in diastolic blood pressure of 4.1 to 9.7 mm Hg. Response rates associated with once daily administration of eprosartan 400 to 800 mg were approximately double those with placebo. Overall, eprosartan was well tolerated with a similar tolerability profile to that of placebo. In comparative trials, in which the incidence of persistent dry cough was evaluated as the primary end-point, enalapril was several-fold more likely to induce this adverse event than eprosartan (the difference being statistically significant regardless of study population and definition of cough). In conclusion, the angiotensin II receptor antagonist eprosartan is a well tolerated and effective antihypertensive agent that is administered once or twice daily without regard to meals. Eprosartan has a low potential for serious adverse events, and the drug has not been associated with clinically significant drug interactions. Unlike ACE inhibitors such as enalapril, eprosartan does not have a high propensity to cause persistent nonproductive cough. Thus, eprosartan represents a useful therapeutic option in the management of patients with hypertension.

Pharmacokinetics of eprosartan in healthy subjects, patients with hypertension, and special populations

After oral administration of eprosartan to healthy volunteers, bioavailability is approximately 13%, with peak plasma concentrations occurring 1-2 hours after an oral dose in the fasted state. Food slows the rate of absorption and changes the overall extent by less than 25%, which is unlikely to be of clinical consequence. Plasma concentrations increase in a slightly less than dose-proportional manner from 100-800 mg. There is no evidence of significant accumulation of eprosartan with long-term therapy. The drug's terminal elimination half-life is typically 5-9 hours after oral administration. The agent is highly protein bound (approximately 98%), with low plasma clearance (approximately 130 ml/minute) and small volume of distribution (approximately 13 L). It is primarily unmetabolized by the liver, with less than 2% of an oral dose recovered in the urine as a glucuronide. Biliary (primary) and renal excretion contribute to its elimination. No dosage adjustment is required in patients with mild to moderate renal impairment. Although an increase in systemic exposure to eprosartan was observed in the elderly, in patients with hepatic impairment, and in those with severe renal disease, this finding is unlikely to be of clinical consequence, based on the drug's excellent safety and tolerability profile (doses up to 1200 mg) in phase III clinical trials in hypertensive patients. Eprosartan can be safely administered to these special populations without an initial dosage adjustment, with subsequent dosing individualized based on tolerability and response.

Effect of age and gender on the pharmacokinetics of eprosartan

AIMS

To compare the pharmacokinetics of eprosartan between young (18-45 years) and elderly (65 years) men and between young men and young, premenopausal women (18-45 years).

METHODS

Twenty-four subjects (eight subjects/group) received a single 200 mg eprosartan oral dose followed by serial blood sampling over 24 h.

RESULTS

Eprosartan was safe and well tolerated. There were no apparent differences in the pharmacokinetics of eprosartan between young females and young males or in the plasma protein binding of eprosartan (98%) for the three groups. On average, AUC (0,infinity) and Cmax values were approximately 2-fold higher in elderly men than young men [AUC (0,infinity) 95% CI: 1.22, 4.34; Cmax 95% CI: 0.98, 4.001. Similarly, unbound AUC (0,infinity) and Cmax values were, on average, approximately 2-fold higher in elderly men than young men [unbound AUC (0,infinity) 95% CI: 1.29, 4.44; unbound Cmax 95% CI: 1.02, 4.12]. tmax was delayed in the elderly men compared with young men, with a median difference of 2.5 h (95% CI: 1.00, 3.01 h).

CONCLUSIONS

No gender differences were observed in the pharmacokinetics of eprosartan. There were approximately two fold higher AUC and Cmax values for eprosartan observed in elderly men as compared with young men, most likely due to increased bioavailability of eprosartan in the elderly. Based on the excellent safety profile in the elderly in Phase III clinical trials (doses up to 1200 mg eprosartan) eprosartan can be safely administered to elderly hypertensive patients without an initial dose adjustment. Subsequently, the dose of eprosartan, as for other antihypertensive agents, may be individualized based on tolerability/response.

Eprosartan

Eprosartan is a nonpeptide angiotensin II receptor antagonist which has a high affinity for the AT1 receptor subtype. When administered at dosages of 400 to 800 mg/day (once or twice daily) for 13 weeks to patients with mild to moderate essential hypertension, eprosartan significantly reduced blood pressure compared with placebo. Eprosartan was at least as effective as enalapril 10 to 40 mg/day in a dose-titration study in patients with severe hypertension. Eprosartan is generally well tolerated; clinical trials have shown the drug to have a tolerability profile similar to that of placebo. As with other angiotensin II receptor antagonists, it does not cause cough. Eprosartan is not metabolised by the cytochrome P450 system and therefore has a low potential for drug interactions.