Pharmacokinetic Interaction of the Direct Renin Inhibitor Aliskiren with Furosemide and Extended-Release Isosorbide-5-Mononitrate in Healthy Subjects

Contribution of Uptake and Efflux Transporters to Oral Pharmacokinetics of Furosemide

Furosemide is a widely used diuretic for treating excessive fluid accumulation caused by disease conditions like heart failure and liver cirrhosis. Furosemide tablet formulation exhibits variable pharmacokinetics (PK) with bioavailability ranging from 10 to almost 100%. To explain the variable absorption, we integrated the physicochemical, in vitro dissolution, permeability, distribution, and the elimination parameters of furosemide in a physiologically-based pharmacokinetic (PBPK) model. Although the intravenous PBPK model reasonably described the observed in vivo PK data, the reported low passive permeability failed to capture the observed data after oral administration. To mechanistically justify this discrepancy, we hypothesized that transporter-mediated uptake contributes to the oral absorption of furosemide in conjunction with passive permeability. Our in vitro results confirmed that furosemide is a substrate of intestinal breast cancer resistance protein (BCRP), multidrug resistance-associated protein 4 (MRP4), and organic anion transporting polypeptide 2B1 (OATP2B1), but it is not a substrate of P-glycoprotein (P-gp) and MRP2. We then estimated the net transporter-mediated intestinal uptake and integrated it into the PBPK model under both fasting and fed conditions. Our in vitro data and PBPK model suggest that the absorption of furosemide is permeability-limited, and OATP2B1 and MRP4 are important for its permeability across intestinal membrane. Further, as furosemide has been proposed as a probe substrate of renal organic anion transporters (OATs) for assessing clinical drug-drug interactions (DDIs) during drug development, the confounding effects of intestinal transporters identified in this study on furosemide PK should be considered in the clinical transporter DDI studies.

Screening of cardiovascular agents in plasma with LC-MS/MS: A valuable tool for objective drug adherence assessment

Adherence to cardiovascular preventive agents is important to prevent short and long term cardiovascular events. Recently, qualitatively compound screening using liquid chromatography-tandem mass spectrometry (LC-MS/MS) has gained interest for drug adherence assessment in patients at high risk of cardiovascular events. Therefore, we developed and tested an assay including 52 compounds and metabolites, covering over 95% of the antihypertensive and antithrombotic agents available worldwide. Trichloroacetic acid was used as simple and fast method for protein precipitation. The assay was validated for lower limit of quantification (LLOQ), linearity, stability for freeze/thaw, room temperature, autosampler and matrix effects. The LLOQ for each compound was targeted under the population trough concentration (PTC) as reported in literature to assure high sensitivity for adherence detection. This was accomplished for 50 of 52 compounds with a LLOQ equal or lower compared to the PTC. Linearity was confirmed for all compounds (r² > 0.995), except for acetylsalicylic acid (r² = 0.991). For room temperature stability, 12 compounds showed degradation over 20% after 20 h. 3 compounds suffer from matrix effect with recoveries < 50%. After analytical validation, blood samples from 91 patients with difficult-to-treat hypertension were analyzed. Patients were unaware of adherence assessment. Adherence varied largely per agent and per concentration ratio (CR) (ratio of the detected concentration with LC-MS/MS and the PTC) cut-off value. Additionally, stratification by adherence group showed that the percentage of patients classified as non-adherent increased from 6.6% for qualitative analysis (pos/neg) to 19.8% for a CR cut-off of 0.5. The data imply that using the CR cut off values has a significant and relevant effect on patient adherence classification.

Aliskiren as a novel therapeutic agent for hypertension and cardio-renal diseases

Objectives

High blood pressure (BP) is a major risk factor for cardiovascular and renal complications. A majority of treated hypertensive patients still complain of high BP. The renin-angiotensin aldosterone system (RAAS) has been a centre-stage target for all the cardiovascular and cardio-renal complications. Aliskiren, is the first direct renin inhibitor (DRI) to be approved by the US FDA. Renin controls the rate-limiting step in the RAAS cascade and hence is the most favorable target for RAAS suppression.

Key findings

This review article strives to summarize the pharmacokinetic, preclinical and clinical studies done so far pertaining to the efficacy of aliskiren. Further, the pharmacology of aliskiren has been comprehensively dealt with to enhance understanding so as to further research in this unfathomed area in the multitude of cardiovascular disorders and renal diseases.

Summary

Aliskiren has been shown to have comparable BP-lowering effects to other RAAS inhibitors. Recent clinical trials have indicated that it might contribute significantly in combination with other agents for the protection of end-organ diseases.

Long-term safety and efficacy of aliskiren and valsartan combination with or without the addition of HCT in patients with hypertension

OBJECTIVE

To assess the long-term safety and antihypertensive efficacy of aliskiren/valsartan 300/320 mg combination.

METHODS

This was a 54-week, multicenter, open-label study (core phase), followed by a 26-week extension phase. Efficacy variables were change in msDBP and msSBP from baseline to endpoint (54-week and 80-week). Safety was assessed by monitoring and recording adverse events (AEs). ClinicalTrials.gov Identifier: NCT00386607 RESULTS: A total of 601 patients (msDBP ≥ 90 and <110 mmHg) entered the 54-week core study. Optional add-on HCT was allowed at week 10 onwards if BP was ≥ 140/90 mmHg at two consecutive visits. Of the 486 patients completed the core study, 180 patients entered the extension phase and received aliskiren/valsartan and add-on HCT (12.5 or 25 mg). Overall the combination of aliskiren/valsartan was well-tolerated and the majority of AEs were mild-to-moderate in severity. The incidence of SAEs was low (core phase: n = 22 [3.7%]; extension phase: n = 4 [2.2%]). Elevated serum potassium (>5.5 mmol/L at any time during the study) was observed in 21 (3.6%) patients. The majority of these elevations were transient and returned to normal in subsequent visits, and the discontinuation rate due to elevated serum potassium was low (0.3% [n = 2]). Decreased serum potassium levels (<3.5 mmol/L at any time during the study) was observed in 26 (4.4%) patients, mainly in patients receiving aliskiren/valsartan/HCT (n = 22; 7.1%). At the 54-week endpoint, a mean BP reduction of 20.5/13.4 mmHg from baseline (baseline BP: 152.9/97.0 mmHg) was observed and 66.9% (n = 398/595) of patients achieved BP control with aliskiren/valsartan with or without HCT. At the end of the extension phase (80-week endpoint), additional reduction in BP was obtained (overall, 28.8/18.3 mmHg) and 86.6% (n = 155/179) of patients achieved BP control with aliskiren/valsartan/HCT. A limitation is the absence of an active comparator group.

CONCLUSION

Long-term treatment with the combination of aliskiren/valsartan with or without HCT provided clinically meaningful BP reductions and high rates of BP control and was well-tolerated.

Direct renin inhibitors as antihypertensive agents

Hypertension, a serious disease affecting almost a billion people (25% of adults) worldwide, is a major modifiable risk factor for cardiovascular (CV) and renal disease. Despite numerous advances in the pharmacologic treatment of high blood pressure (BP) and availability of several antihypertensive drugs to treat hypertension, a significant proportion of treated hypertensive patients still have uncontrolled high BP, and thus, face serious morbidity and mortality. Furthermore, it is not sufficient to aim for optimum BP control, but to treat all CV risk factors, protect end-organ damage, prevent progression of disease, and prevent long-range adverse effects of the drugs. Therefore, new therapeutic modalities have to be developed to achieve the above objectives. Some years ago, investigators identified renin inhibition as the preferred pharmacologic approach to blockade of the renin-angiotensin system. Renin is a monospecific enzyme that catalyzes the rate-limiting step in the synthesis of angiotensin II. Amplified enzymatic activity and additional physiologic effects occur when renin and prorenin bind to the (pro)renin receptor. Until very recently, development of clinically effective renin inhibitors remained elusive but molecular modeling was used to develop aliskiren and other renin inhibitors that produce sustained suppression of plasma renin activity after oral administration with a dose-dependent BP. Additional studies will ultimately determine the place of renin inhibition in the treatment of hypertension and related CV disorders.

Influence of body weight and gender on the pharmacokinetics, pharmacodynamics, and antihypertensive efficacy of aliskiren

Gender and body weight influence the pharmacokinetics and pharmacodynamics of many drugs. This pooled analysis of 17 clinical studies evaluated the effect of gender, body mass index (BMI), body weight, and lean body weight (LBW) on the pharmacokinetics of the direct renin inhibitor aliskiren in healthy volunteers (n = 392). A separate pooled analysis of 5 clinical studies in patients with hypertension (n = 2327) assessed the influence of gender and BMI on the effects of aliskiren on plasma renin activity and blood pressure. Area under the aliskiren plasma concentration-time curve (AUC(τ)) was 22% lower and the peak aliskiren plasma concentration (C(max)) was 24% lower in men than women (P < .05). BMI was not significantly correlated with AUC(τ) (r = 0.005; P = .917); AUC(τ) was negatively correlated with body weight (r = -0.235; P < .0001) and LBW (r = -0.295; P < .0001). Results were similar for C(max). Adjusting individual aliskiren AUC(τ) and C(max) values for overall mean body weight or LBW abolished gender differences. Based on r(2) values, LBW variation accounted for 8.9% of aliskiren AUC(τ) variation. In patients with hypertension, gender and BMI did not significantly influence the effects of aliskiren on plasma renin activity or blood pressure. It was concluded that lower systemic exposure to aliskiren in men versus women relates to differences in body weight; neither gender nor body weight has clinically relevant effects on the pharmacokinetics or pharmacodynamics of aliskiren.

The biochemical pharmacology of renin inhibitors: implications for translational medicine in hypertension, diabetic nephropathy and heart failure: expectations and reality

The renin-angiotensin-aldosterone system (RAAS) plays a dominant role in the pathophysiology of hypertension, Diabetes mellitus (DM), chronic kidney disease (CKD) and chronic heart failure (CHF). Therefore, drugs that block key components of the RAAS such as ACE inhibitors (ACEi) and angiotensin receptor blockers (ARBs) have gained wide clinical use for these indications. Despite progress, the morbidity and mortality of patients treated with ACEi or ARBs remain high. Small molecules that directly inhibit renin (DRI) and are orally active have also been developed and one such drug, aliskiren, was introduced into clinical use for treatment of hypertension in 2007. Further clinical trials aimed to expand the therapeutic use of aliskiren are in progress for CKD-DM and CHF. In this review we analyze and review the translational medicine prospects of aliskiren in respect to the biochemical pharmacology of the RAAS, the marketed RAAS modulators and the new emerging science regarding the role of prorenin, renin and renin receptors in cardiovascular biology and disease. The information already gained with aliskiren, raises questions regarding the advantages of DRIs as monotherapy compared to marketed ACEis and ARBs, their potential added value in combination with other RAAS modulators and other unproven benefits in relation to prorenin and renin receptor biology. This review will also indicate basic and clinical research needs that are critical to determine whether DRIs can provide meaningful added medical benefits over contemporary medicines that regulate the RAAS, and the need to identify patients that are more likely to benefit from DRIs and any possible long term adverse effects.