Effect of ranitidine on the pharmacokinetics of orally administered eprosartan, an angiotensin II antagonist, in healthy male volunteers

The Model for End-stage Liver Disease score is potentially a useful predictor of hyperkalemia occurrence among hospitalized angiotensin receptor blocker users

WHAT IS KNOWN AND OBJECTIVE

Angiotensin receptor blockers (ARBs) are medications commonly used for treating conditions such as hypertension. However, ARBs are frequently associated with hyperkalemia, a potentially critical adverse event, in high-risk patients. Although both the liver and the kidney are major elimination routes of ARBs, the relationship between hepatorenal function and ARB-related hyperkalemia has not yet been investigated. The purpose of this study was to evaluate the risk of hyperkalemia, in terms of various hepatorenal functions, for hospitalized patients newly initiated on ARB treatment.

METHODS

We evaluated ARB-related hyperkalemia in a cohort of 5530 hospitalized patients, who had not previously used ARBs, between 12 April 2004 and 31 May 2012. Hepatorenal function was assessed by the Model for End-stage Liver Disease (MELD) score. Hyperkalemia risk was assessed by hepatorenal function, risks were categorized into the four MELD scoring groups, and the groups were compared with one another.

RESULTS AND DISCUSSION

The MELD score was significantly different between the hyperkalemic and non-hyperkalemic groups (independent t-test, P < 0.001). The MELD score 10-14, 15-19 and ≥ 20 groups showed higher risks of hyperkalemia than the lowest MELD score group {log-rank test, P < 0.001; multiple Cox proportional hazard model, hazard ratios 1.478 (P = 0.003), 2.285 (P < 0.001) and 3.024 (P < 0.001), respectively}.

WHAT IS NEW AND CONCLUSION

The MELD score showed a stronger predictive performance for hyperkalemia than either serum creatinine or estimated glomerular filtration rate alone. Furthermore, the MELD score showed good predictive performance for ARB-related hyperkalemia among hospitalized patients. The clinical implications and reasons for these findings merit future investigation.

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.

Drug interactions with angiotensin receptor blockers

Many patients with high blood pressure receive multiple medications for hypertension and other conditions, placing them at risk for adverse drug interactions. Additionally, as the prevalence of hypertension increases with age, factors like greater frailty, comorbidity of the elderly requiring polypharmacy, and reduced hepatic and renal clearance rates for the elimination of drugs increase the likelihood of drug interactions. Angiotensin receptor blockers (ARBs) are the most recent class of agents for the treatment of hypertension. Due to a favourable side effect profile, this class of drugs deserves increased attention. This article reviews drug interactions of ARBs and suggests measures for reducing the risk of adverse events when drugs are co-administered. MEDLINE, EMBASE, Cochrane library, and CINAHL were searched. Reported and likely clinical relevant interactions of ARBs with concomitantly given drugs are summarised in Table 2 and 3. Compared to other classes of antihypertensive agents, the ARBs appear to have a low potential for drug interactions; however, interactions with this class occur and variations within the class have been detected, mainly due to different affinities for cytochrome P450 isoenzymes.

Eprosartan for the treatment of hypertension

Antihypertensive agents are proven to reduce the cardiovascular risk of stroke, coronary heart disease and cardiac failure. The ideal antihypertensive agent should control all grades of hypertension and have a placebo-like side effect profile. Angiotensin II (AII) receptor antagonists are a relatively new class of antihypertensive agent that block AII Type 1 (AT(1)) receptors, and reduce the pressor effects of AII in the vasculature. By this mechanism, they induce similar pharmacological effects compared with angiotensin-converting enzyme (ACE) inhibitors, resulting in a lowering of blood pressure. However, AII receptor blockers differ from ACE inhibitors with respect to side effects, and induce less cough, a side effect which may be related to bradykinin or other mediators such as substance P. Within the class of AII blockers, eprosartan differs from other currently available agents in terms of chemical structure, as it is a non-biphenyl, non-tetrazole, non-peptide antagonist with a dual pharmacological mode of action. Eprosartan acts at vascular AT(1) receptors (postsynaptically) and at presynaptic AT(1) receptors, where it inhibits sympathetically stimulated noradrenaline release. Its lack of metabolism by cytochrome P450 enzymes confers a low potential for metabolic drug interactions and may be of importance when treating elderly patients and those on multiple drugs. In clinical trials, eprosartan has been demonstrated to be at least as effective in reducing blood pressure as the ACE inhibitor enalapril, and has significantly lower side effects. Eprosartan is safe, effective and well-tolerated in long-term treatment, either as a monotherapy or in combination with other antihypertensive drugs such as hydrochlorothiazide.

Eprosartan: an angiotensin-II receptor antagonist for the management of hypertension

Eprosartan is a competitive angiotensin-II receptor antagonist with a high affinity for the angiotensin-II subtype 1 receptor. The drug has an elimination half-life of approximately 5 to 9 hours and duration of antihypertensive effect of up to 24 hours. The antihypertensive efficacy of eprosartan has been examined in a number of placebo-controlled, dose-finding, and comparative trials. Results of these clinical trials have consistently shown statistically significant differences in antihypertensive efficacy favoring eprosartan doses of 400 mg or greater per day over placebo. Eprosartan was also shown to be at least as effective as enalapril at lowering blood pressure in patients with mild to severe hypertension. The frequency of adverse events observed with eprosartan has been similar to that seen with placebo. In addition, there are no clinically significant drug interactions associated with eprosartan. Given the excellent tolerability and drug-interaction profiles of eprosartan, the use of this agent may help to improve patient compliance to a drug regimen. In addition, eprosartan may be particularly advantageous when used as a part of combination therapy for the management of hypertension.

A review of eprosartan pharmacokinetic and pharmacodynamic drug interaction studies

A series of clinical pharmacology studies was conducted to characterize potential interactions between eprosartan and other commonly prescribed drugs. Separate studies assessed the effect of eprosartan on the pharmacokinetics of digoxin and hydrochlorothiazide (HCTZ) and the pharmacodynamics of warfarin and glyburide (glibenclamide), as well as the effects of ranitidine, HCTZ, fluconazole, and ketoconazole on eprosartan pharmacokinetics. Eprosartan had no significant effect on the pharmacokinetics of digoxin and HCTZ and the pharmacodynamics of warfarin and glyburide. Thus, no dosing adjustments are necessary during concomitant therapy with these agents. Ranitidine, HCTZ, ketoconazole, and fluconazole had no effect on eprosartan pharmacokinetics. Single or multiple oral doses of eprosartan were safe and well tolerated when coadministered with these agents.

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.