Models of schedule dependent haematological toxicity of 2'-deoxy-2'-methylidenecytidine (DMDC)

OBJECTIVE: DMDC (2'-deoxy-2'-methylidenecytidine) is-a potential antitumour deoxycytidine analogue of cytosine arabinoside. The major dose-limiting toxicity of DMDC is haematological depression, particularly neutropenia, and therefore quantitative exposure-toxicity relationships for DMDC are warranted. METHODS: Data on the survival fraction at nadir of leukocytes, neutrophils and platelets from 66 patients receiving a once-daily regimen and 85 patients receiving a twice-daily regimen of DMDC were related to DMDC concentration-time profiles using area under the plasma concentration-time curve (AUC), threshold and general models. A semiphysiological model of neutrophils versus time after DMDC administration included transient compartments to imitate the differentiation stages in the bone marrow. RESULTS: The relationship between plasma DMDC concentration-time profiles and the haematological toxicity at nadir was best described using an AUC-dependent model with separate functions for once- and twice-daily dosing, indicating schedule dependence of DMDC effects, even if differences in treatment duration had a similar explanatory value. Twice-daily dosing was associated with greater toxic effects than once-daily dosing. The AUC required for a 70% reduction in the neutrophils was 16 mg.h/l and 4.2 mg.h/l for the once- and twice-daily regimens, respectively. The semiphysiological model included nine proliferating transient compartments that were sensitive to DMDC in a schedule-dependent manner, five non-mitotic, non-sensitive compartments and one compartment for circulating neutrophils. CONCLUSIONS: The haematological toxicity of DMDC is schedule dependent. The survival fractions of leukocytes, neutrophils and platelets are predicted to be lower when given on a twice-daily regimen than on a once-daily regimen. A semiphysiological model with transient compartments successfully described the entire time course of neutropenia after DMDC administration.     

Extended-release formulations for the treatment of epilepsy

This review analyses the concept of extended-release (ER) formulations in epilepsy and evaluates ER formulations of carbamazepine, valproic acid and a modified-release (MR) formulation of oxcarbazepine. ER formulations are usually designed to reduce dose frequency and maintain relatively constant or flat plasma drug concentration. It is questionable whether flat plasma concentrations of an antiepileptic drug (AED) improve antiepileptic efficacy compared with fluctuating plasma concentrations. More certainly, they minimise concentration-related adverse effects, and the dosing flexibility and consistency of plasma concentrations may simplify the management of antiepileptic drug therapy. Neurologists would like ER formulations that can be administered once- and/or twice-daily to tailor therapy for the individual patient; however, switching dosage schedules from multiple dosages per day to once daily, although more convenient, will not generally improve therapeutic coverage (maintenance of effective drug concentration in biological fluids and tissue). Pharmacokinetically, the impact of a missed dose is greater the larger the dose and the less frequent the administration. Therefore, the risk of breakthrough seizure is higher during AED once-daily administration than twice-daily administration. Consequently, the increased compliance observed with fewer dosages per day should be weighed against the impact or forgiveness of omitted dose(s) and the shorter 'forgiveness' period associated with once-daily administration. Currently, the trend is to treat patients with epilepsy with ER formulations because of the better compliance, convenience and flat plasma concentration versus time curve. Thus, it seems that the term 'flatter is better' for AED plasma profiles has precipitated in the last 10-15 years among neurologists and epilepsy caregivers, and is being promoted by marketing forces of pharmaceutical companies. Data from the literature support the trend to treat epileptic patients with twice-daily administration of the existing ER formulations of valproic acid and carbamazepine, and oxcarbazepine-MR; however, the author of this article is not convinced that these ER formulations can guarantee a complete therapeutic coverage throughout the 24-hour dosing interval following once-daily administration.Epilepsy is a single-episode disease, and the convenience and possible better compliance associated with once-daily administration must be weighed against the shorter 'forgiveness' period and possible higher risk of breakthrough seizure due to sub-therapeutic plasma levels and/or omitted doses. Data suggest just a small difference in compliance between once- and twice-daily administration, with no significant difference in efficacy. Therefore, the increased compliance following once-daily administration may be counter-productive in minimising the occurrence of sub-therapeutic drug concentrations. Weighing up the advantages and disadvantages for once- versus twice-daily administration of ER formulations in epilepsy leads to a conclusion in favour of twice-daily administration.     

Protection of the cardiovascular system by imidapril,a versatile angiotensin-converting enzyme inhibitor

Imidapril hydrochloride (imidapril) is a long-acting, non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor, which has been used clinically in the treatment of hypertension, chronic congestive heart failure (CHF), acute myocardial infarction (AMI), and diabetic nephropathy. It has the unique advantage over other ACE inhibitors in causing a lower incidence of dry cough. After oral administration, imidapril is rapidly converted in the liver to its active metabolite imidaprilat. The plasma levels of imidaprilat gradually increase in proportion to the dose, and decline slowly. The time to reach the maximum plasma concentration (T(max)) is 2.0 h for imidapril and 9.3 h for imidaprilat. The elimination half-lives (t(1/2)) of imidapril and imidaprilat is 1.7 and 14.8 h, respectively. Imidapril and its metabolites are excreted chiefly in the urine. As an ACE inhibitor, imidaprilat is as potent as enalaprilat, an active metabolite of enalapril, and about twice as potent as captopril. In patients with hypertension, blood pressure was still decreased at 24 h after imidapril administration. The antihypertensive effect of imidapril was dose-dependent. The maximal reduction of blood pressure and plasma ACE was achieved with imidapril, 10 mg once daily, and the additional effect was not prominent with higher doses. When administered to patients with AMI, imidapril improved left ventricular ejection fraction and reduced plasma brain natriuretic peptide (BNP) levels. In patients with mild-to-moderate CHF [New York Heart Association (NYHA) functional class II-III], imidapril increased exercise time and physical working capacity and decreased plasma atrial natriuretic peptide (ANP) and BNP levels in a dose-related manner. In patients with diabetic nephropathy, imidapril decreased urinary albumin excretion. Interestingly, imidapril improved asymptomatic dysphagia in patients with a history of stroke. In the same patients it increased serum substance P levels, while the angiotensin II receptor antagonist losartan was ineffective. These studies indicate that imidapril is a versatile ACE inhibitor. In addition to its effectiveness in the treatment of hypertension, CHF, and AMI, imidapril has beneficial effects in the treatment of diabetic nephropathy and asymptomatic dysphagia. Good tissue penetration and inhibition of tissue ACE by imidapril contributes to its effectiveness in preventing cardiovascular complications of hypertension. The major advantages of imidapril are its activity in the treatment of various cardiovascular diseases and lower incidence of cough compared with some of the older ACE inhibitors.     

Pharmacological and clinical profile of moexipril: a concise review

Angiotensin-converting enzyme (ACE) inhibitors are effective and safe antihypertensive drugs, with the exception of the rare occasion of angioedema. These drugs have demonstrated additional cardiovascular protective effects to their blood pressure lowering, and their combination with the diuretic hydrochlorothiazide potentiates their antihypertensive effectiveness. Moexipril is a long-acting ACE inhibitor suitable for once-daily administration, and like some ACE inhibitors, moexipril is a prodrug and needs to be hydrolyzed in the liver into its active carboxylic metabolite, moexiprilat, to become effective. Moexipril alone and in combination with low-dose hydrochlorothiazide has been shown in clinical trials to be effective in lowering blood pressure and be well tolerated and safe given in single daily doses. In this review, the pharmacological profile of this drug and its clinical usefulness are discussed.     

Once-daily inhaled corticosteroids in mild to moderate asthma: improving acceptance of treatment

Despite the established efficacy of inhaled corticosteroids in improving lung function in asthma, there has not been a corresponding improvement in morbidity and mortality associated with the disease, which, in part, may result from non-compliance with the prescribed regimen. The reasons for this are many and varied, but an important measure in improving the level of compliance in asthma patients is simplification of the treatment regimen, which may be achieved by reducing the dose frequency and improving the ease of administration. In clinical trials designed to determine whether a reduction in dose frequency to once daily is associated with similar efficacy to that with more frequent administration, a number of studies have shown that once-daily administration of inhaled corticosteroids in both adults and children is as effective in controlling asthma as twice-daily administration of the same dosage, both when given as initial therapy in corticosteroid-na?ve patients and in patients already receiving an inhaled corticosteroid. The drug for which most evidence to support a dosage change from twice-daily to once-daily therapy currently exists is budesonide, though limited evidence with other inhaled corticosteroids such as beclomethasone dipropionate, fluticasone propionate and flunisolide also supports once-daily use. Despite the larger single dosage with once-daily budesonide therapy, there has been no evidence in clinical trials of a greater incidence of local adverse effects such as hoarseness, throat irritation or oropharyngeal candidosis, and no evidence of adrenal suppression or growth retardation. Since compliance is an important factor that can affect the success or failure of asthma therapy, a reduction in the frequency of administration to once daily offers the potential advantage of improved compliance with treatment and hence better control of asthma. In the short term clinical trials conducted to date, patient preferences have favoured the once-daily regimen over twice-daily administration. When combined with other (e.g. educational) measures to improve patient compliance, a switch from twice-daily (or more frequent) administration to once-daily inhaled corticosteroid therapy seems likely to be beneficial in improving the long term outcome of treatment.     

Ocular carteolol: a review of its use in the management of glaucoma and ocular hypertension

Ocular carteolol (Mikelan), Teoptic, Ocupress) is a nonselective beta-adrenoceptor antagonist with intrinsic sympathomimetic activity (ISA). Ocular carteolol effectively reduces intraocular pressure (IOP) in patients with open-angle glaucoma (OAG) or ocular hypertension (OH). Twice-daily administration of standard carteolol has generally similar IOP-lowering efficacy to other ocular beta-adrenoceptor antagonists such as timolol, betaxolol and metipranolol in patients with OAG or OH. In addition, long-term treatment with carteolol has similar efficacy to timolol and betaxolol in terms of reducing IOP and maintaining visual fields in patients with newly diagnosed primary OAG (POAG). The new long-acting formulation of once-daily carteolol has equivalent efficacy to the standard formulation of carteolol administered twice daily in patients with OAG or OH. Both the standard and long-acting formulations of ocular carteolol are generally well tolerated in terms of topical adverse effects involving the eyes or systemic adverse effects involving the cardiovascular system. Thus, twice-daily carteolol is a well established option in the treatment of glaucoma and OH, and the new once-daily formulation of long-acting carteolol offers similar efficacy and tolerability with a potential for improved patient adherence.     

EPILIM® CHRONO: A MULTIDOSE,CROSSOVER COMPARISON OF TWO FORMULATIONS OF VALPROATE IN HEALTHY VOLUNTEERS

The pharmacokinetic properties and relative bioequivalence of two formulations of the antiepileptic Epilim® were compared in a three-period, repeat dose, randomized crossover study in 18 male volunteers. A daily dose of 1000 mg of antiepileptic was given either as twice-daily enteric-coated sodium valproate tablets or as twice- or once-daily controlled release tablets (Epilim® Chrono, sodium valproate/valproic acid mixture). All regimens were bioequivalent with respect to area under the curve and elimination half-life. The twice-daily controlled release formulation showed reduced mean peak plasma valproate levels and raised mean trough levels compared with the enteric coated tablets. The once-daily controlled release regimen gave reduced mean peak levels but similar mean trough levels to the twice-daily enteric-coated regimen. No major differences between regimens were observed in the time at which peak concentration was observed. Both formulations were well tolerated. The most frequently reported adverse event was mild diarrhoea (all on Chrono treatment) which is probably related to the lack of enteric coating on this formulation. The reduced mean peak--trough variation in plasma valproate levels observed with the twice-daily controlled release regimen is likely to reduce further the low incidence of concentration-related side-effects with sodium valproate and permit more reliable plasma level monitoring. This study also indicates that once-daily treatment with Epilim® controlled release would be a suitable replacement for twice-daily dosing with either formulation. Once-daily treatment is likely to give considerable benefits both in convenience and in better patient compliance.     

Determination of the pharmacokinetics of glycopyrronium in the lung using a population pharmacokinetic modelling approach

Aims

Glycopyrronium bromide (NVA237) is a once-daily long-acting muscarinic antagonist recently approved for the treatment of chronic obstructive pulmonary disease. In this study, we used population pharmacokinetic (PK) modelling to provide insights into the impact of the lung PK of glycopyrronium on its systemic PK profile and, in turn, to understand the impact of lung bioavailability and residence time on the choice of dosage regimen.

Methods

We developed and validated a population PK model to characterize the lung absorption of glycopyrronium using plasma PK data derived from studies in which this drug was administered by different routes to healthy volunteers. The model was also used to carry out simulations of once-daily and twice-daily regimens and to characterize amounts of glycopyrronium in systemic compartments and lungs.

Results

The model-derived PK parameters were comparable to those obtained with noncompartmental analysis, confirming the usefulness of our model. The model suggested that the lung absorption of glycopyrronium was dominated by slow-phase absorption with a half-life of about 3.5 days, which accounted for 79% of drug absorbed through the lungs into the bloodstream, from where glycopyrronium was quickly eliminated. Simulations of once-daily and twice-daily administration generated similar PK profiles in the lung compartments.

Conclusions

The slow absorption from the lungs, together with the rapid elimination from the systemic circulation, could explain how once-daily glycopyrronium provides sustained bronchodilatation with a low incidence of adverse effects in patients with chronic obstructive pulmonary disease. Its extended intrapulmonary residence time also provides pharmacokinetic evidence that glycopyrronium has the profile of a once-daily drug.     

Estimation of the comparative therapeutic superiority of QD and BID dosing regimens, based on integrated analysis of dosing history data and pharmacokinetics

Once-daily dosing almost invariably shows a slightly higher percentage of prescribed doses taken than does twice-daily dosing. Many pharmaceutical scientists, regulators, and prescribers have considered this finding to signify the therapeutic superiority of once-daily dosing. The therapeutically more relevant question, however, is not the percentage of prescribed doses taken but the comparative impact of missed doses on the pharmacologic effects of a drug under the two dosing regimens. A key point in this regard is that the pharmacokinetic equivalent of a single missed once-daily dose is 2–3 sequentially omitted twice-daily doses. Thus, an important parameter in comparing the two regimens is the probability of two or three twice-daily doses being sequentially omitted, versus the probability of missing a single once-daily dose. Our data indicate that the probability of sequential omission of 2–3 twice daily doses is half the probability of omission of a single once-daily dose. For that reason, a twice-daily regimen could prove to be superior to a once-daily regimen in maintaining drug concentrations within a therapeutically desirable range. A more important consideration, however, is to maintain not just the concentration of drug in plasma, but the drug’s therapeutic action. The duration of therapeutic drug action following a last-taken dose is not only drug-specific, but also, for some drug, dependent on the pharmacodynamic properties. Judging the comparative superiority of one dosing regimen over another requires knowledge of the drug’s duration action after a last-taken dose, plus knowledge of the comparative probabilities of the various patterns of dose omission. When applied to HIV protease inhibitors, a twice-daily regimen appears to be better than an once-daily regimen in maintaining therapeutically effective drug actions.     

Imidapril in heart failure.

Angiotensin-converting enzyme (ACE) inhibitors improve the prognosis in mild, moderate and severe heart failure, as well as preventing the onset of heart failure in patients with chronic asymptomatic left-ventricular dysfunction and in those with reduced ejection fraction after myocardial infarction (MI). Imidapril is a long-acting ACE inhibitor that is rapidly converted in the liver to its active metabolite, imidaprilat. Maximum plasma concentrations of imidapril and imidaprilat are achieved after 2 and 5-6 hours, respectively, with corresponding elimination half-lives of 1.1-2.5 and 10-19 hours. Imidapril is used in the treatment of hypertension, chronic heart failure, acute MI and diabetic nephropathy. In patients with mild-to-moderate chronic heart failure, imidapril 10 mg once-daily increased exercise time and physical working capacity, decreased plasma atrial natriuretic peptide and brain natriuretic peptide levels and reduced blood pressure. It also improved left ventricular ejection fraction, being significantly more effective than bisoprolol, in patients with acute MI. Imidapril is well tolerated and preliminary studies suggest it has an advantage over captopril and enalapril in terms of a lower incidence of cough. In conclusion, imidapril is a well-investigated versatile ACE inhibitor for the treatment of a range of cardiovascular diseases.     

Salmeterol/fluticasone propionate via Diskus once daily versus fluticasone propionate twice daily in patients with mild asthma not previously receiving maintenance corticosteroids

BACKGROUND and objective: The efficacy and safety of twice-daily inhaled salmeterol/fluticasone propionate combination (SFC) therapy have been well established in the treatment of adults and adolescents with asthma. Once-daily administration of SFC could also be appropriate in patients with mild persistent asthma. This study aimed to investigate whether once-daily SFC 50 microg/100 microg was at least as effective as fluticasone propionate (FP) 100 microg twice daily, and more effective than twice-daily placebo, over 52 weeks as initial maintenance therapy in patients with mild persistent asthma. METHODS: This was a randomized, double-blind, double-dummy, placebo-controlled, multicentre, parallel-group study carried out in primary and secondary care. Patients aged between 12 and 79 years with a documented clinical history of asthma for > or =6 months who were currently receiving inhaled short-acting beta(2)-adrenoceptor agonists only were enrolled. Patients were randomized to receive either once-daily inhaled SFC 50 microg/100 microg, twice-daily inhaled FP 100 microg (i.e. twice the dose of FP compared with SFC) or placebo for 52 weeks. The primary efficacy endpoints were mean morning peak expiratory flow (PEF), as recorded by patients prior to the use of bronchodilator or study medication, and the rate of investigator-recorded asthma exacerbations. RESULTS: Patients receiving twice-daily FP and once-daily SFC showed greater improvements in mean morning PEF compared with those receiving placebo (FP, difference in means 20.1 L/min; 95% CI 14.7, 25.5; p < 0.001; SFC, difference in means 14.8 L/min; 95% CI 9.4, 20.2; p < 0.001). The difference in adjusted mean PEF between once-daily SFC and twice-daily FP was -5.3 L/min (95% CI -9.1, -1.6). PEF results showed that once-daily SFC was non-inferior to twice-daily FP. Over 52 weeks, there was a 35% reduction in exacerbation rates with once-daily SFC, which in this respect demonstrated superiority over placebo (p < 0.001). Non-inferiority between once-daily SFC and twice-daily FP with respect to exacerbation rates was not shown. Once-daily SFC significantly improved clinic forced expiratory flow between 25% and 75% of forced vital capacity (difference in means 0.129 L/s; p < 0.001) and clinic PEF (difference in means 10.8 L/min; p < 0.001) compared with twice-daily FP. Both treatments were well tolerated and the safety profile of each was similar to that seen with placebo. CONCLUSION: In patients with mild persistent asthma not previously receiving maintenance therapy, once-daily SFC 50 microg/100 microg is an effective treatment compared with placebo, and was non-inferior to twice-daily FP 100 microg with respect to mean morning PEF. However, in this study, once-daily SFC was not as efficacious as twice-daily FP in reducing asthma exacerbation rates. This study confirms the benefits of regular maintenance treatment in patients with mild persistent asthma.     

Does Aspirin Interfere with the Therapeutic Efficacy of Angiotensin-converting Enzyme Inhibitors in Hypertension or Congestive Heart Failure?

We conducted a MEDLINE search of published literature from 1966 to January 1998 regarding the impact of aspirin (ASA) on the therapeutic effect of angiotensin-converting enzyme (ACE) inhibitors in hypertension and congestive heart failure. Selected references from these articles and results of recent clinical trials were also included. By inhibiting cyclooxygenase, ASA may interfere with the prostaglandin-mediated hemodynamic effects of ACE inhibitors. Although other nonsteroidal antiinflammatory drugs may increase blood pressure in hypertensive patients taking an ACE inhibitor, low-dosage (≤ 100 mg/day) ASA does not. However, higher dosages of ASA may attenuate the benefits of ACE inhibitors in patients with hypertension and/or congestive heart failure (CHF). Low-dosage ASA appears to interact little with ACE inhibitors, whereas higher dosages may produce a more significant interaction. Patients with CHF may also be more susceptible to this interaction because of underlying disease.     

Is once-daily mesalazine equivalent to the currently used twice-daily regimen? A study performed in 30 healthy volunteers

A randomized, 2-way, crossover study was conducted in 30 volunteers to compare the pharmacokinetic profile of a new once-daily dosing regimen of mesalazine (1 x 4 g/d) with the current twice-daily dosage (2 x 2 g/d) used in many European countries. The 2 dosages were administrated orally for 8 days, separated by a 2-week washout. Plasma concentrations of mesalazine and N-acetyl-mesalazine were determined on days 1 and 8 by a validated high-performance liquid chromatography method and C(max), t(max), and AUCs calculated. The bioequivalence was obtained for a 90% confidence interval of the AUC(0-24h) ratio (test/reference) for mesalazine and N-acetyl-mesalazine on days 1 and 8, within the range of 0.80 to 1.25. The bioequivalence was demonstrated on day 1 for mesalazine and N-acetyl-mesalazine and on day 8 for mesalazine. As it is desirable to offer patients a preparation with a less frequent administration to enhance compliance, this once-daily regimen may be an attractive dosing option.     

Fosinopril. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in essential hypertension.

Fosinopril is a phosphinic acid prodrug which, after oral administration, undergoes rapid hydrolysis to its active diacid, the angiotensin converting enzyme (ACE) inhibitor fosinoprilat. Unlike other ACE inhibitors, fosinoprilat has a compensatory dual route of elimination and is cleared by the liver and kidneys. Thus, in patients with diminished renal function increased hepatic clearance of fosinoprilat is noted and, similarly, in patients with diminished hepatic function increased renal clearance seems to occur. Because of this compensatory elimination, fosinopril therapy for all patients can begin with the same recommended dosage. Fosinopril 10 to 40mg administered once daily is an effective antihypertensive regimen that has shown efficacy similar to that of enalapril 5 to 10 mg/day, propranolol 80 to 160 mg/day, hydrochlorothiazide 25 to 50 mg/day and sustained release nifedipine 40 mg/day in preliminary clinical trials. Generally, fosinopril is well tolerated and adverse events associated with the drug are usually mild and similar to those associated with other ACE inhibitors. Thus, fosinopril appears to be a useful alternative to certain 'established' agents used for treating patients with essential hypertension.     

Perindopril: in congestive heart failure

Perindopril is a long-acting ACE inhibitor, acting through its only active metabolite perindoprilat. It inhibits the renin-angiotensin system by preventing both the conversion of angiotensin I to angiotensin II and the degradation of bradykinin, thereby reducing the vasoconstriction and left ventricular remodelling characteristic of heart failure. Perindopril 4mg significantly improved a range of haemodynamic parameters in single-dose and long-term (8 weeks and 3 months) studies involving patients with congestive heart failure (CHF), with little or no effect on blood pressure or heart rate. In randomised, double-blind, placebo-controlled clinical trials conducted over 3 months and a large noncomparative study (up to 30 months), perindopril 4mg once daily significantly increased exercise tolerance and reduced symptoms of heart failure in patients with mild to moderate CHF. Perindopril 4mg once daily is generally well tolerated in patients with mild to moderate CHF. In a large noncomparative study the most commonly reported adverse clinical event was cough, which led to 2.8% of patients discontinuing treatment. In short-term comparative trials there was a significantly lower incidence of first-dose hypotension following the recommended starting dose of perindopril 2mg than after the equivalent starting doses of captopril, enalapril and lisinopril.     

The effect of captopril on pharmacokinetics of digoxin in patients with mild congestive heart failure.

The effect of captopril on steady-state pharmacokinetics of digoxin was studied in 12 patients with mild congestive heart failure (CHF; New York Heart Association functional class 1 or 2). Serum and urine digoxin concentrations were determined before and after a repeated administration of captopril in the patients on chronic digoxin therapy. The patients were taking digoxin, 0.25-0.375 mg/day, once daily, and were concurrently administered captopril, 37.5 mg/day, three times daily, for seven days. Peak serum concentration of digoxin (SCD) before and after captopril was 2.1 +/- 0.2, mean +/- SEM, and 2.0 +/- 0.1 ng/ml; the time to peak was 1.1 +/- 0.2 and 1.8 +/- 0.3 h; the terminal half-life (t1/2 alpha) was 10.9 +/- 1.0 and 8.7 +/- 0.9 h, and the area under the concentration-time curve to 24 h was 26.9 +/- 2.4 and 27.6 +/- 2.0 ng.h/ml. There was no significant difference between patients without and with captopril in SCD and its pharmacokinetic parameters. Renal digoxin clearance and creatinine clearance also showed no significant difference. After an administration of captopril, angiotensin-converting-enzyme (ACE) activity was well suppressed. These results suggest that captopril does not increase SCD in patients with CHF, and effectively suppresses ACE activity. Thus, modification in the dosage regimen of digoxin may be unnecessary in the case of coadministration with captopril.