Pharmacokinetics, metabolism and biliary and urinary excretion of oral ramipril in man

Population pharmacokinetics of ramipril in patients with chronic heart failure: A real-world longitudinal study

In patients with chronic heart failure (CHF), the use of angiotensin-converting enzyme inhibitors, including ramipril, is recommended to reduce the risk of heart failure worsening, hospitalisation, and death. Our aim was to investigate the influence of body composition on the pharmacokinetics of ramipril and its active metabolite ramiprilat and to evaluate the changes in pharmacokinetics after prolonged therapy. Twenty-three patients with CHF who were on regular therapy with ramipril participated at the first study visit ( median age 77 years, 65 % male, and 70 % New York Heart Association Class II); 19 patients attended the second study visit and the median time between the two visits was 8 months. Pharmacokinetics were assessed using a nonlinear mixed-effects parent-metabolite model comprising two compartments for ramipril and one compartment for ramiprilat. The influence of body size and composition was best described by an allometric relationship with fat-free mass. In addition, ramipril clearance was related to patient age and daily ramipril dose, while clearance of ramiprilat was influenced by glome rular filtration rate and daily ramipril dose. There were no clinically relevant changes in the pharmacokinetics of ramipril and ramiprilat between the study visits. Due to the relatively stable pharmacokinetics of ramipril, regular outpatient visits at 6-month intervals seem appropriate to evaluate ramipril therapy.

How to Treat Hypertension in Venlafaxine-Medicated Patients-Pharmacokinetic Considerations in Prescribing Amlodipine and Ramipril

BACKGROUND

Amlodipine (AMLO) and ramipril (RAMI) belong to the most prescribed drugs in patients with hypertension, a condition also encountered in depression. Venlafaxine may worsen hypertension because of noradrenergic properties. Although of special clinical relevance, data on pharmacokinetic interactions between AMLO, RAMI, and venlafaxine (VEN) are lacking.

METHODS

Two TDM databases consisting of plasma concentrations of VEN and its active metabolite O-desmethylvenlafaxine (ODVEN) were analyzed. We considered a group of patients comedicated with AMLO, VAMLO (n = 22); a group comedicated with RAMI, VRAMI (n = 20); and a 4:1 control group age matched to the VAMLO group receiving VEN without confounding medications, V0 (n = 88). Plasma concentrations of VEN, ODVEN, and active moiety, AM (VEN + ODVEN); metabolic ratio (ODVEN/VEN); and dose-adjusted plasma concentrations (C/D) were compared using nonparametric tests.

RESULTS

Groups did not differ in daily VEN dose, age, or sex. The metabolic ratio (ODVEN/VEN) was lower in the AMLO group (P = 0.029), whereas the RAMI group showed lower values for ODVEN (P = 0.029). All other parameters showed no significant differences.

CONCLUSIONS

Significantly lower values for the metabolic ratio in the AMLO group are unlikely to be explained by cytochrome P450 (CYP) 3A4 and weak CYP2D6 inhibition by AMLO. Other factors such as differences in CYP2D6 polymorphisms and metabolizer status may better explain the findings. Ramipril showed modest effects with changes in ODVEN concentrations that did not remain significant after dose-adjusted comparisons.

Predicted environmental concentration and fate of the top 10 most dispensed Australian prescription pharmaceuticals

A basic environmental risk assessment was carried out for the top 10 dispensed pharmaceuticals in Melbourne, Australia, in contrast to the more commonly assessed measure of the most used drugs by physical mass. This allowed for the evaluation of compounds that had not previously been the subject of risk assessment. Estimations of the possible fate and behaviour of the target pharmaceuticals in sewage treatment plants were also made. The predicted removal rates of most drugs within standard sewage treatment were expected to be low, with the exception of the statins, which had high removal rates. Each pharmaceutical was predicted to be present in Melbourne wastewater at the nanogram per litre range or lower. All compounds were predicted to be of low toxicity risk, although it was not possible to model mixture effects. Atorvastatin and Irbesartan were also found to possess the potential to possibly bioaccumulate in the aquatic food chain but not to the extent that would require regulation or labelling.

The Evaluation of Angiotensin-Converting Enzyme Inhibitors in Renal Elimination with Selected Molecular Descriptors

Angiotensin-converting enzyme (ACE) inhibitors modulate the function of the renin-angiotensin-aldosterone system, and they are commonly prescribed antihypertensive drugs especially in patients with renal failure. In this study, the relationships between several molecular properties of eight ACE inhibitors (enalapril, quinapril, fosinopril, ramipril, benazepril, perindopril, moexipril, trandolapril) and their renal elimination data, from relevant literature, were investigated. The ’molecular descriptors of the ACE inhibitors, which included aqueous solubility data (logS); an electronic descriptor, polar surface area (PSA);, a constitutional parameter, molecular mass (Mr); and a geometric descriptor, volume value (Vol), as well as lipophilicity descriptors (logP values), were calculated using different software packages. Simple linear regression analysis showed the best correlation between renal elimination data and lipophilicity descriptor AClogP values (R2 = 0.5742). In the next stage of the study, multiple linear regression was applied to assess a higher correlation between the ACE inhibitors’ renal elimination data and lipophilicity, AClogP, with one additional descriptor as an independent variable. Good correlations were established between renal elimination data from the literature and the AClogP lipophilicity descriptor using the constitutional parameter (molecular mass (R2 = 0.7425)) or the geometric descriptor (volume value (R2 = 0.7224)) as an independent variable. The application of computed molecular descriptors in evaluating drug elimination is of great importance in drug research.

Human Health Relevance of Pharmaceutically Active Compounds in Drinking Water

In Canada, as many as 20 pharmaceutically active compounds (PhACs) have been detected in samples of treated drinking water. The presence of these PhACs in drinking water raises important questions as to the human health risk posed by their potential appearance in drinking water supplies and the extent to which they indicate that other PhACs are present but have not been detected using current analytical methods. Therefore, the goal of the current investigation was to conduct a screening-level assessment of the human health risks posed by the aquatic release of an evaluation set of 335 selected PhACs. Predicted and measured concentrations were used to estimate the exposure of Canadians to each PhAC in the evaluation set. Risk evaluations based on measurements could only be performed for 17 PhACs and, of these, all were found to pose a negligible risk to human health when considered individually. The same approach to risk evaluation, but based on predicted rather than measured environmental concentrations, suggested that 322 PhACs of the evaluation set, when considered individually, are expected to pose a negligible risk to human health due to their potential presence in drinking waters. However, the following 14 PhACs should be prioritized for further study: triiodothyronine, thyroxine, ramipril and its metabolite ramiprilat, candesartan, lisinopril, atorvastatin, lorazepam, fentanyl, atenolol, metformin, enalaprilat, morphine, and irbesartan. Finally, the currently available monitoring data for PhACs in Canadian surface and drinking waters was found to be lacking, irrespective of whether their suitability was assessed based on risk posed, predicted exposure concentrations, or potency.

Effect of Contrasted Sodium Diets on the Pharmacokinetics and Pharmacodynamic Effects of Renin–Angiotensin System Blockers

Dietary sodium, the main determinant of the pharmacodynamic response to renin–angiotensin system blockade, influences the pharmacokinetics of various cardiovascular drugs. We compared the effect of contrasted sodium diets on the pharmacokinetics of single oral doses of 8 mg candesartan cilexetil, 160 mg valsartan, 10 mg ramipril, and 50 mg atenolol administered to 64 (16 per group) normotensive male subjects randomly assigned to sodium depletion (SD) or sodium repletion (SR) in a crossover study. Pharmacodynamic response was assessed as the increase in plasma renin concentration for renin–angiotensin system blockers and electrocardiographic changes in PR interval duration for atenolol. The area under the curve (AUC) for plasma candesartan and atenolol concentrations was significantly lower for SR than for SD (respective ratios of AUC 0–∞ : 0.74; [90% CI, 0.66–0.82] and 0.69 [90% CI, 0.54–0.88], respectively), indicating a lack of bioequivalence between SR and SD. SR did not affect the pharmacokinetics of valsartan or ramipril. The increase in plasma renin concentration with the 3 renin–angiotensin system blockers was 10 times lower during the SR than the SD period. In the multiple regression analysis, the AUC 0–24 of plasma drug concentration explained <1% and 21% of the variance of the AUC 0–24 of delta plasma renin concentration for candesartan ( P =0.8882/ P =0.0368) during the SR and SD periods, respectively. The atenolol-induced lengthening of PR interval was fully reversed by SR. Thus, sodium balance modulates the pharmacokinetics of candesartan cilexetil and atenolol, with measurable effects on the selected pharmacodynamic end points.

Methods to evaluate biliary excretion of drugs in humans: an updated review

Determining the biliary clearance of drugs in humans is very challenging because bile is not readily accessible due to the anatomy of the hepatobiliary tract. The collection of bile usually is limited to postsurgical patients with underlying hepatobiliary disease. In healthy subjects, feces typically are used as a surrogate to quantify the amount of drug excreted via nonurinary pathways. Nevertheless, it is very important to characterize hepatobiliary elimination because this is a potential site of drug interactions that might result in significant alterations in systemic or hepatic exposure. In addition to the determination of in vivo biliary clearance values of drugs, the availability of in vitro models that can predict the extent of biliary excretion of drugs in humans may be a powerful tool in the preclinical stages of drug development. In this review, recent advances in the most commonly used in vivo methods to estimate biliary excretion of drugs in humans are outlined. Additionally, in vitro models that can be employed to investigate the molecular processes involved in biliary excretion are discussed to present an updated picture of the new tools and techniques that are available to study the complex processes involved in hepatic drug transport.

Ramipril in the treatment of vascular diseases

Ramipril is an angiotensin-converting enzyme inhibitor that has been extensively studied in randomised, controlled clinical trials in patients with cardiovascular diseases. Therapy with ramipril in patients with various cardiovascular disorders has demonstrated significant and clinically important reductions in cardiovascular death, myocardial infarction, stroke, congestive heart failure, progressive renal impairment and onset of diabetes. Ramipril is usually dosed at 2.5-10 mg/day. Beneficial effects of ramipril are observed in the treatment of hypertension and congestive heart failure, prevention of cardiovascular events in high-risk patients, prevention of congestive heart failure, diabetes and other vascular events.

Interference from a glucuronide metabolite in the determination of ramipril and ramiprilat in human plasma and urine by gas chromatography–mass spectrometry

In the course of development and validation of a gas chromatography-mass spectrometry (GC-MS) method for ramipril and its biologically active metabolite ramiprilat, evidence was found for an unknown interfering metabolite. Sample treatment included isolation from plasma or urine by solid-phase extraction, methylation with trimethylsilyldiazomethane and acylation with trifluoroacetic anhydride (TFAA). When liquid chromatography was used to fractionate plasma extracts prior to derivatization, the alkyl, acyl-derivative of ramipril was obtained from two separate LC fractions. Electrospray ionization mass spectral data, together with circumstances for the derivatization, were consistent with the presence of an N-glucuronide of ramipril. Interference from the metabolite was eliminated by including a wash step after extraction/alkylation, prior to acylation. The final assay had a lower limit of quantification at 1.0 nmol/L and a linear range of 1-300 nmol/L. Intra- and inter-batch precision for ramipril and ramiprilat in plasma or urine were better than 10 and 5% at 2 and 80 nmol/L, respectively.

Human physiologically based pharmacokinetic model for ACE inhibitors: ramipril and ramiprilat

Background

The angiotensin-converting enzyme (ACE) inhibitors have complicated and poorly characterized pharmacokinetics. There are two binding sites per ACE (high affinity "C", lower affinity "N") that have sub-nanomolar affinities and dissociation rates of hours. Most inhibitors are given orally in a prodrug form that is systemically converted to the active form. This paper describes the first human physiologically based pharmacokinetic (PBPK) model of this drug class.

Methods

The model was applied to the experimental data of van Griensven et. al for the pharmacokinetics of ramiprilat and its prodrug ramipril. It describes the time course of the inhibition of the N and C ACE sites in plasma and the different tissues. The model includes: 1) two independent ACE binding sites; 2) non-equilibrium time dependent binding; 3) liver and kidney ramipril intracellular uptake, conversion to ramiprilat and extrusion from the cell; 4) intestinal ramipril absorption. The experimental in vitro ramiprilat/ACE binding kinetics at 4°C and 300 mM NaCl were assumed for most of the PBPK calculations. The model was incorporated into the freely distributed PBPK program PKQuest.

Results

The PBPK model provides an accurate description of the individual variation of the plasma ramipril and ramiprilat and the ramiprilat renal clearance following IV ramiprilat and IV and oral ramipril. Summary of model features: Less than 2% of total body ACE is in plasma; 35% of the oral dose is absorbed; 75% of the ramipril metabolism is hepatic and 25% of this is converted to systemic ramiprilat; 100% of renal ramipril metabolism is converted to systemic ramiprilat. The inhibition was long lasting, with 80% of the C site and 33% of the N site inhibited 24 hours following a 2.5 mg oral ramipril dose. The plasma ACE inhibition determined by the standard assay is significantly less than the true in vivo inhibition because of assay dilution.

Conclusion

If the in vitro plasma binding kinetics of the ACE inhibitor for the two binding sites are known, a unique PBPK model description of the Griensven et. al. experimental data can be obtained.

Effects of ACE inhibition and bradykinin antagonism on cardiovascular changes in uremic rats

BACKGROUND

Cardiovascular death continues to be a major problem in renal failure. Structural abnormalities of the heart and the vasculature contribute to the increased cardiovascular risk. They are ameliorated by angiotensin-converting enzyme (ACE) inhibitors, but because of the nonspecifity of ACE inhibition, it is uncertain whether the beneficial effect is mediated by interfering with angiotensin II (Ang II) or by modulating other effector systems, for example, bradykinin.

METHODS

To assess a potential role of bradykinin, subtotally nephrectomized Sprague-Dawley rats (SNX) received either the ACE inhibitor Ramipril (Rami, 0.2 mg/kg body weight p.o.), the specific B2 bradykinin receptor antagonist Hoe140 (0.2 mg/kg body weight, s.c.), or a combination of both, and were compared to sham-operated controls. To separately assess the effect of Ramipril on development and reversal of structural abnormalities, animals were either treated from the third day after SNX or from the fourth week after SNX onward (0.01 mg/kg body weight, p.o.).

RESULTS

Heart and aorta were evaluated by morphometric and stereologic techniques. The weight of the perfused left ventricle, as an index of cardiac hypertrophy, was significantly higher in untreated SNX. While it was significantly lower in animals with early and late Ramipril treatment, the beneficial effect was completely antagonized by Hoe140. The wall-to-lumen ratio of intramyocardial arterioles was significantly higher in untreated SNX compared with controls, but failed to be modified by administration of either Ramipril or Hoe140. In the heart, the intercapillary distance was significantly higher in SNX, but it was not lowered by either early or late Ramipril or Hoe140 treatment. Treatment of SNX with Hoe140 alone, however, resulted in a marked further increase in intercapillary distance. The wall thickness of the aorta was significantly higher in SNX than in controls; early and late Ramipril treatment prevented such increase, and this effect was antagonized by Hoe140.

CONCLUSION

These findings illustrate that bradykinin plays an important role for the beneficial effect of Ramipril in preventing (and potentially reversing) abnormal cardiovascular structure in uremic hypertensive rats.

Clinical pharmacokinetics of vasodilators. Part I

Understanding the mechanism of action and the pharmacokinetic properties of vasodilatory drugs facilitates optimal use in clinical practice. It should be kept in mind that a drug belongs to a class but is a distinct entity, sometimes derived from a prototype to achieve a specific effect. The most common pharmacokinetic drug improvement is the development of a drug with a half-life sufficiently long to allow an adequate once-daily dosage. Developing a controlled release preparation can increase the apparent half-life of a drug. Altering the molecular structure may also increase the half-life of a prototype drug. Another desirable improvement is increasing the specificity of a drug, which may result in fewer adverse effects, or more efficacy at the target site. This is especially important for vasodilatory drugs which may be administered over decades for the treatment of hypertension, which usually does not interfere with subjective well-being. Compliance is greatly increased with once-daily dosing. Vasodilatory agents cause relaxation by either a decrease in cytoplasmic calcium, an increase in nitric oxide (NO) or by inhibiting myosin light chain kinase. They are divided into 9 classes: calcium antagonists, potassium channel openers, ACE inhibitors, angiotensin-II receptor antagonists, alpha-adrenergic and imidazole receptor antagonists, beta 1-adrenergic agonist, phosphodiesterase inhibitors, eicosanoids and NO donors. Despite chemical differences, the pharmacokinetic properties of calcium antagonists are similar. Absorption from the gastrointestinal tract is high, with all substances undergoing considerable first-pass metabolism by the liver, resulting in low bioavailability and pronounced individual variation in pharmacokinetics. Renal impairment has little effect on pharmacokinetics since renal elimination of these agents is minimal. Except for the newer drugs of the dihydropyridine type, amlodipine, felodipine, isradipine, nilvadipine, nisoldipine and nitrendipine, the half-life of calcium antagonists is short. Maintaining an effective drug concentration for the remainder of these agents requires multiple daily dosing, in some cases even with controlled release formulations. However, a coat-core preparation of nifedipine has been developed to allow once-daily administration. Adverse effects are directly correlated to the potency of the individual calcium antagonists. Treatment with the potassium channel opener minoxidil is reserved for patients with moderately severe to severe hypertension which is refractory to other treatment. Diazoxide and hydralazine are chiefly used to treat severe hypertensive emergencies, primary pulmonary and malignant hypertension and in severe preeclampsia. ACE inhibitors prevent conversion of angiotensin-I to angiotensin-II and are most effective when renin production is increased. Since ACE is identical to kininase-II, which inactivates the potent endogenous vasodilator bradykinin, ACE inhibition causes a reduction in bradykinin degradation. ACE inhibitors exert cardioprotective and cardioreparative effects by preventing and reversing cardiac fibrosis and ventricular hypertrophy in animal models. The predominant elimination pathway of most ACE inhibitors is via renal excretion. Therefore, renal impairment is associated with reduced elimination and a dosage reduction of 25 to 50% is recommended in patients with moderate to severe renal impairment. Separating angiotensin-II inhibition from bradykinin potentiation has been the goal in developing angiotensin-II receptor antagonists. The incidence of adverse effects of such an agent, losartan, is comparable to that encountered with placebo treatment, and the troublesome cough associated with ACE inhibitors is absent.