Pharmacokinetics of cilazapril in patients with renal failure

Simultaneously Predicting the Pharmacokinetics of CES1-Metabolized Drugs and Their Metabolites Using Physiologically Based Pharmacokinetic Model in Cirrhosis Subjects

Hepatic carboxylesterase 1 (CES1) metabolizes numerous prodrugs into active ingredients or direct-acting drugs into inactive metabolites. We aimed to develop a semi-physiologically based pharmacokinetic (semi-PBPK) model to simultaneously predict the pharmacokinetics of CES1 substrates and their active metabolites in liver cirrhosis (LC) patients. Six prodrugs (enalapril, benazepril, cilazapril, temocapril, perindopril and oseltamivir) and three direct-acting drugs (flumazenil, pethidine and remimazolam) were selected. Parameters such as organ blood flows, plasma-binding protein concentrations, functional liver volume, hepatic enzymatic activity, glomerular filtration rate (GFR) and gastrointestinal transit rate were integrated into the simulation. The pharmacokinetic profiles of these drugs and their active metabolites were simulated for 1000 virtual individuals. The developed semi-PBPK model, after validation in healthy individuals, was extrapolated to LC patients. Most of the observations fell within the 5th and 95th percentiles of simulations from 1000 virtual patients. The estimated AUC and Cmax were within 0.5-2-fold of the observed values. The sensitivity analysis showed that the decreased plasma exposure of active metabolites due to the decreased CES1 was partly attenuated by the decreased GFR. Conclusion: The developed PBPK model successfully predicted the pharmacokinetics of CES1 substrates and their metabolites in healthy individuals and LC patients, facilitating tailored dosing of CES1 substrates in LC patients.

Impact of Disease States on the Pharmacokinetics and Pharmacodynamics of Angiotensin-Converting Enzyme Inhibitors

The pharmacokinetics and pharmacodynamics of angiotensin-converting enzyme inhibitors (ACE) in elderly patients and patients with renal and hepatic impairment were examined, and a role for an AUC/EC50 ratio to guide dosing was evaluated. A Medline and International Pharmaceutical Abstracts search was used to identify human studies and abstracts. Relevant data were evaluated and summarized. Dosing regimens were compared using an AUC/EC50 ratio. Most studies evaluating ACE inhibitors in renal impairment report a strong linear correlation between creatine clearance and drug elimination. AUC and EC50 values for these drugs in elderly subjects appear similar to younger and hypertensive patients. There is increased AUC in some patients with hepatic impairment. Pharmacodynamic data are conflicting. Prolonged ACE inhibition is evident in renal impairment but not necessarily other disease states. ACE inhibitor dosing for hypertension is reasonable based on pharmacokinetics and EC50 values. Further individualization of therapy may improve outcomes, and using the threshold AUC/EC50 ratio may help guide appropriate dosing.

Evaluation of a novel method to estimate absolute bioavailability of drugs from oral data

The goal of this investigation was to evaluate the performance of a novel method allowing estimation of absolute bioavailability from oral data only. In contrast to the traditional method, which compares areas under the drug concentration time curves after oral and intravenous administration in subjects with normal renal function, the novel method uses total and renal clearance values following oral administration from subjects with varying renal functions to estimate bioavailability. The novel method can also provide estimates for nonrenal clearance.Published data on total clearance and renal clearance of drugs obtained from subjects with variable renal functions were collected, the novel method applied, estimates of bioavailability and nonrenal clearance obtained and compared with reported estimates by the traditional methods. In addition computations were performed to assess various factors that could possibly affect the reliability of the novel method. The results indicated that the novel method provides accurate estimates for bioavailability of drugs meeting the prerequisites: linear kinetics, predominant renal excretion in normals, absence of metabolic polymorphism and independence of bioavailability and nonrenal clearance from renal function. The average (standard deviation) of the prediction error and bias of the bioavailability estimates by the novel method was 7.8 (6.0) and -1.4 (9.8)%, respectively. The estimates for nonrenal clearance by the novel method were less accurate. The computations confirmed that the estimates by the novel method are sensitive to renal-function dependent changes in nonrenal clearance and bioavailability and also depend on the extent of renal excretion of a drug. In conclusion, the novel method's main use is to diagnose absence or presence of changes in bioavailability and non-renal clearance of drugs in populations with varying renal function.

Pharmacokinetic drug interactions between oral contraceptives and second-generation anticonvulsants

Drug interactions between oral contraceptives (OCs) and traditional anticonvulsants have been well described. However, in the past decade, a number of new anticonvulsants have been developed, as well as modifications made in the composition of the OC preparations themselves. Additionally, anticonvulsants are increasingly employed in the therapy of nonseizure-related disorders, placing more women at risk of potential drug interactions that may lead to contraceptive failure. Second-generation anticonvulsants include felbamate, gabapentin, lamotrigine, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide. Most have been approved for adjunctive management of seizures refractory to therapy with traditional anticonvulsants. On the basis of available study data in women receiving concomitant OC preparations, gabapentin, lamotrigine, tiagabine and vigabatrin may be administered without significant pharmacokinetic interactions that potentially diminish contraceptive efficacy. However, additional or alternative contraceptive measures, including using OCs with higher estrogen content, are recommended when using felbamate, oxcarbazepine and topiramate, as these agents have demonstrated enzyme-inducing activity leading to reduced plasma steroid concentrations. The effects of zonisamide in women receiving OCs have yet to be reported. It is important to characterise the properties [e.g. substrate and enzyme activity (particularly cytochrome P450 3A4 induction)] of new anticonvulsants and recognise their potential to interfere with OCs. However, a pharmacokinetic interaction does not in itself indicate loss of OC efficacy. Contraceptive failure should be measured by changes in ovarian hormone concentrations, maturation of ovarian follicle(s) or ovulation.

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.

Pharmacokinetics and haemodynamic effects of the angiotensin converting enzyme inhibitor cilazapril in hypertensive patients with normal and impaired renal function

1. The pharmacokinetic and pharmacodynamic properties of the angiotensin converting enzyme (ACE) inhibitor cilazapril were studied in 30 hypertensive patients with various degrees of renal function. 2. After a single oral dose, apparent cilazaprilat clearance was dependent on renal function being 16.0 +/- 3.0, 11.1 +/- 3.0, 8.7 +/- 3.7 and 6.7 +/- 2.1 l h-1 (means +/- s.d.) in patients with creatinine clearances (CLcr) of > 100, 41-100, 21-40, and 8-20 ml min-1, respectively. .3 During 11 weeks of treatment with cilazapril, doses were adjusted to the CLcr and varied from 0.5 to 5.0 mg once daily. At 24 h after drug administration a clear antihypertensive response was seen only in the low clearance groups (CLcr < 40 ml min-1). In contrast, and despite higher once daily dosages, the decline of mean arterial pressure was small and cilazaprilat concentrations after 24 h were lower in the high clearance groups. 4. This study demonstrates that chronic once daily treatment with cilazapril is effective in patients with impaired renal function at dosages adjusted to creatinine clearance. No accumulation was seen. Since cilazaprilat clearance was high in the high creatinine clearance groups, a clear antihypertensive response in these groups was only seen at 3 h after drug administration.

ACE inhibitors. Differential use in elderly patients with hypertension

High blood pressure (BP) in the elderly must not be ignored as a normal consequence of aging. The criteria for the diagnosis of hypertension and the necessity to treat it are the same in elderly and younger patients. The aim of treatment of elderly hypertensive patients is to decrease BP safely and to reduce risk factors associated with cerebrovascular, cardiovascular and renal morbidity and mortality. The treatment of elderly hypertensive patients should be adjusted according to the needs of the individual, based upon age, race, severity of hypertension, co-existing medical problems, other cardiovascular risk factors, target-organ damage, risk-benefit considerations and costs. In addition to the elevated BP, other cardiovascular risk factors include smoking, glucose intolerance, hyperinsulinaemia, dyslipidaemia, hypercreatininaemia, peripheral vascular disease, left ventricular hypertrophy, and microalbuminuria (or albuminuria). Thus, the choice of initial antihypertensive therapy in elderly hypertensive patients should be based not only on the expected response, but also on the effects of therapy on lipid, potassium, glucose and uric acid levels, and left ventricular anatomy and function. Co-existing medical conditions (such as asthma, diabetes mellitus, heart failure, renal failure, gout, coronary artery disease, hyperlipidaemia and peripheral vascular disease) are major determinants for the selection of antihypertensive medications. With previous therapies (diuretics, beta-blockers, etc.), good BP control in the elderly was associated with clear and statistically significant reductions in stroke-related morbidity and mortality, but the overall effects on cardiovascular and renal complications of hypertension was either more variable or less obvious. Angiotensin converting enzyme (ACE) inhibitors are not only efficacious antihypertensive agents in the elderly, but also appear promising in counteracting some of the cardiovascular and renal consequences of hypertension. They are well tolerated and have a relatively low incidence of adverse effects. ACE inhibitors possess ancillary characteristics that are potentially beneficial for many elderly patients, including reduction of left ventricular mass, lack of metabolic and lipid disturbances, no adverse CNS effects, no risk of induction of heart failure, and a low risk of orthostatic hypotension. Since ACE inhibitors may improve perfusion to the heart, kidney and brain, they are well worth considering for the treatment of elderly patients with hypertensive target organ damage, especially in patients with heart failure, and diabetic patients with early nephropathy.

New antiepileptic drugs for children: felbamate, gabapentin, lamotrigine, and vigabatrin

After a 15-year hiatus, several new antiepileptic drugs have been approved or are under Food and Drug Administration investigation for use in the United States. This article reviews four of these new drugs--felbamate, gabapentin, lamotrigine, and vigabatrin. Although these drugs have been primarily developed for use in adults with partial seizures, they will also likely be used in children with partial epilepsy. Pediatric experience with several of these drugs has demonstrated safety and efficacy in other seizure types and epilepsy syndromes. These drugs will be an important addition to the therapeutic armamentarium for pediatric epilepsy. Additional studies are needed to fully explore the safety and efficacy of these drugs in a variety of pediatric epilepsies and to compare them to existing antiepileptic drugs.

The pharmacokinetics and pharmacodynamics of fosinopril in haemodialysis patients

The pharmacokinetics and pharmacodynamics of fosinoprilat, the diacid of fosinopril sodium (a new angiotensin-converting enzyme (ACE) inhibitor), were investigated in six haemodialysis patients. Intravenous 14C-fosinoprilat (7.5 mg), oral 14C-fosinopril sodium (10 mg) and oral fosinopril sodium (10 mg) were administered in an open-label, randomized study. Mean maximum concentration (Cmax), clearance (CL), volume of distribution at steady-state (Vss), mean residence time (MRTiv), and t1/2 values after IV administration of 14C-fosinoprilat were 2,042 micrograms.ml-1, 11.3 ml.min-1, 11.0 l, 16.3 h and 28.3 h, respectively. Following oral administration of 14C-fosinopril, mean Cmax, time to maximum plasma concentration (tmax), and fosinoprilat bioavailability values were 197 ng.ml-1, 5.2 h and 29.2%. Para-hydroxy fosinoprilat and fosinoprilat glucuronide comprised approximately 15% and 2% of radioactivity recovered in faeces. Four hours of haemodialysis only cleared approximately 1.5% of the administered dose. The maximum effect (Emax) model was fitted to the percentage inhibition of serum ACE activity vs. fosinoprilat concentration data in three patients. Emax ranged from 95.3 to 102.5%, and IC50 (the fosinoprilat concentration required to produce 50% of Emax) ranged from 2.6 to 4.2 ng.ml-1. Pharmacokinetic variables of the patients were similar to those in patients with moderate to severe renal dysfunction. Dosage modifications or supplemental dosing following dialysis are unnecessary.

Clinical pharmacokinetics of angiotensin converting enzyme (ACE) inhibitors in renal failure

Arterial hypertension occurs frequently in patients with chronic renal failure. Antihypertensive treatment of arterial hypertension with angiotensin converting enzyme (ACE) inhibitors has been shown to be effective with a low incidence of adverse effects compared with other drug classes. Furthermore, treatment with ACE inhibitors may slow the progression of renal function impairment in certain groups of patients, such as those with diabetes. Most ACE inhibitors are prodrugs which are converted by hepatic esterolysis to an active diacid metabolite. Only captopril and lisinopril have sufficient oral bioavailability and are given as active drugs. ACE inhibitors can be subdivided into 3 classes with regard to the active group: the majority of ACE inhibitors are carboxyl-containing drugs, a new class of ACE inhibitors possess a phosphoryl-group and captopril and related compounds are sulfhydryl-containing drugs. The predominant elimination pathway of ACE inhibitors is excretion via the kidneys. Therefore, renal insufficiency is associated with reduced elimination of most ACE inhibitors and, thus, altered pharmacokinetic properties. This is most evident in chronic renal failure when glomerular filtration rates (GFR) are < 30 to 40 ml/min (1.8 to 2.4 L/h). As renal clearance decreases, the peak plasma concentration and area under the plasma concentration-time curve of the active drugs or diacids are increased and time to peak concentrations and half-life are prolonged. However, there are large between-drug differences in the changes in pharmacokinetic parameters, resulting in different degrees of drug accumulation after consecutive administration. This leads, for example, to high accumulation rates for drugs such as lisinopril, or cilazaprilat. In contrast, fosinopril, which is also excreted to a large extent by the hepatobiliary pathway, does not seem to accumulate in renal failure. In general, pharmacokinetics and conversion of prodrugs seem to be slightly affected in chronic renal failure; however, these changes do not appear to be clinically relevant. Efficiency of clearance for prodrugs or active drugs and their respective metabolites by haemodialysis or peritoneal dialysis varies considerably. For some ACE inhibitors, such as captopril or enalapril, the high elimination fraction by haemodialysis necessitates a supplemental dose after dialysis. Other ACE inhibitors, such as quinapril or cilazapril, are only poorly eliminated by haemodialysis or peritoneal dialysis. Dosage recommendations for treatment with ACE inhibitors in chronic renal failure depend on the specific pharmacokinetic properties of the various agents. For most ACE inhibitors, dosage adjustment is recommended in moderate and severe impairment of renal function, with resultant dosages being 25 to 50% of those recommended for patients with normal renal function.

Effect of renal function on the pharmacokinetics and pharmacodynamics of trandolapril

1. The pharmacokinetics and pharmacodynamics of a single dose of trandolapril, an angiotensin converting enzyme (ACE) inhibitor with an active metabolite, trandolaprilat, which is in part further metabolised prior to renal elimination, were evaluated in 31 subjects with a wide range of renal function (creatinine clearance 4-112 ml min-1 1.73 m-2). 2. The pharmacokinetics of trandolapril were unaffected by differences in renal function. 3. In contrast, there was a close correlation between the renal clearance (0-96 h) of trandolaprilat and creatinine clearance (r = 0.95, P = 0.0001). The maximum plasma concentration of trandolaprilat, and the area under the concentration curve (0-96 h) correlated inversely with creatinine clearance (r = -0.59, P < 0.001; and r = -0.61, P < 0.001 respectively). 4. Significant changes in plasma trandolaprilat concentrations were seen only in patients with creatinine clearances of 30 ml min-1 1.73 m-2 or less, suggesting that a dose reduction in trandolapril might be advisable in severe renal impairment. 5. However, the majority of parameters of ACE inhibition were unrelated to creatinine clearance, although area under the curve for ACE inhibition (0-336 h) showed a weak negative correlation (r = -0.49, P < 0.01). Similarly, weighted mean changes in blood pressure were not influenced by renal function. 6. Therefore, while the pharmacokinetic parameters of trandolaprilat correlated with creatinine clearance, pharmacodynamic measurements (ACE inhibition and blood pressure changes) in general showed no such relationship, indicating that dose adjustment of ACE inhibitors in renal impairment should be based on pharmacokinetic results only in conjunction with pharmacodynamic data.

The effect of renal failure on hepatic drug clearance

It is known that loss of renal function decreases the hepatic clearance of some drugs, but the mechanisms by which this occurs are unclear. Knowledge of which drugs display reduced hepatic metabolism may be important for appropriate dosing of these drugs in uremic patients. Although no firm conclusions can be made regarding common pharmacokinetic and metabolic characteristics of drugs that display decreased hepatic metabolism in renal failure, certain observations deserve consideration. It appears that drugs metabolized by oxidation, conjugation, or both may be predisposed to decreased hepatic clearance in renal failure. Drugs that undergo oxidation by the P-450IID6 isozyme may be more likely to exhibit inhibition whereas those metabolized by the P-450IIIA4 isozyme may be spared. Future studies designed to clarify the mechanisms of decreased hepatic clearance in renal failure should take into account the multiplicity of P-450 enzymes for drugs that are oxidatively metabolized. The phenomenon of reduced hepatic drug clearance in uremia should be considered when evaluating the influence of renal failure on drug disposition.

Pharmacokinetics of newer drugs in patients with renal impairment (Part II)

Cardiovascular diseases occur frequently in patients with renal failure. Any pharmacokinetic impairment in these diseases should be considered when individualizing drug therapy. The pharmacokinetics of new cardiovascular drugs in uraemic patients are reviewed: alpha- and beta-blocking agents, ACE inhibitors, centrally acting antihypertensive agents, calcium antagonists, antiarrhythmic agents and inotropic agents. Guidelines are proposed for adjustment of dosage regimens as a function of renal impairment. Renal or extrarenal elimination of drugs and their metabolites, and the activity of the latter, are taken into account. The disposition of new drugs such as flestolol, alacepril, delapril, propafenone, milrinone or enoximone, is not well documented in patients with renal failure. Further characterizations of the elimination of these compounds are needed and the potential therapeutic or toxic effects of the metabolites require evaluation to determine whether the dosage needs to be adjusted. Until such investigations are performed, those drugs should not be used in uraemic patients; if no therapeutic alternative is available, clinical controls are necessary at regular intervals. Relationships between pharmacological or therapeutic effects and drug plasma concentrations should be evaluated for such long term use drugs. The knowledge of a plasma concentration therapeutic window is important to provide information which will be useful in determining appropriate drug dosage in renal failure.

Clinical pharmacology of cilazapril

In clinical pharmacology studies, cilazapril, after its bioactivation to cilazaprilat, was characterised as a potent, reversible angiotensin converting enzyme (ACE) inhibitor with a terminal half-life of 30 to 50 hours, which is consistent with saturable binding to ACE. Despite the arterial vasodilatation, only slight increases in heart rate occurred during cilazapril administration. Cilazapril had no acute effect on cardiovascular reflexes, and increased effective renal plasma flow slightly. Glomerular filtration rate remained unaltered. A close positive correlation was found between the cilazaprilat plasma concentration and degree of ACE inhibition. The potency of cilazaprit, defined as the concentration of cilazaprilat causing 50% inhibition of ACE, was approximately 1 microgram/L plasma. In short term studies in patients with hypertension, it appeared that more than 90% inhibition of plasma ACE was needed to obtain blood pressure reduction. Results of various dose-response studies established the indirect relationship between dose, the plasma concentration of the drug, and the blood pressure response, and identified the dose producing the maximal effect to be 5mg. Cilazapril inhibited ACE for a relatively long period which was extended in patients with severe chronic renal impairment or hepatic failure. In these patients a reduction of the dose and/or less frequent administration is recommended. There was no clinically relevant interaction of cilazapril with food, furosemide (frusemide), digoxin or coumarins. The effects of hydrochlorothiazide on sodium and chloride excretion were potentiated by cilazapril, and an additive effect of propranolol and nitrendipine on the blood pressure response to cilazapril was observed. An interaction with indomethacin and cilazapril might occur, potentially reducing the blood pressure-lowering effect of cilazapril. In general, cilazapril was well tolerated.

The pharmacokinetics and pharmacodynamics of quinapril and quinaprilat in renal impairment

1. The pharmacokinetics and pharmacodynamics of quinapril and its active metabolite quinaprilat were studied in 20 subjects with renal function varying from normal to severe renal failure, during the approach to and at steady-state, and for 72 h after cessation of quinapril 20 mg orally for 7 days. 2. The apparent oral plasma clearance of quinaprilat (dose of quinapril equivalent/AUC of quinaprilat) was directly related to creatinine clearance (CLCr). The predicted apparent oral clearance of quinaprilat was zero when CLCr was zero, suggesting minimal extrarenal elimination. 3. Peak and trough concentrations of quinaprilat, and its apparent elimination half-life, varied inversely with CLCr. 4. Trough concentrations of quinaprilat showed no accumulation between 2 and 7 days, even in severe renal impairment. 5. There was a weak relationship between the oral plasma clearance of quinapril and CLCr. 6. ACE inhibition was marked and prolonged in all subjects, with 50% inhibition at 2.7 +/- 1.9% ng ml-1 of quinaprilat. The time for which ACE inhibition was greater than 90% was related inversely to CLCr. 7. Aldosterone concentrations and plasma renin activity responded in a predictable way, but with no clear relationship To CLCr. 8. Atrial natriuretic peptide concentrations were not affected by quinapril administration. 9. Glomerular filtration rate, as measured by Tc99mDTPA clearance, was not affected by quinapril administration. 10. Blood pressure at steady-state decreased significantly in the subjects with hypertension. The changes in blood pressure were not related to renal function. 11. These results suggest that the dosage rate of quinapril may have to be altered in renal impairment.(ABSTRACT TRUNCATED AT 250 WORDS)