The pharmacokinetics and dose proportionality of cilazapril

Transcription

1 Br. J. clin. Pharmac. (1989), 27, 199S-204S The pharmacokinetics and dose proportionality of cilazapril J. MASSARELLA, T. DEFEO, A. LIN, R. LIMJUCO & A. BROWN Departments of Drug Metabolism and Clinical Research, Hoffmann-La Roche Inc., Nutley, USA 1 The pharmacokinetics and dose proportionality of cilazapril, an orally active angiotensin-converting enzyme (ACE) inhibitor, were investigated in a four-way randomized crossover study in 24 volunteers, over the 0.5 to 5 mg dose range intended for therapeutic use. 2 Plasma concentrations of cilazapril and of the active metabolite cilazaprilat together with plasma ACE activity were determined by radio-enzymatic assay. 3 Plasma concentrations of both cilazapril and cilazaprilat increased in proportion to dose over the range studied. All doses produced substantial inhibition of ACE. Higher doses were associated with earlier onset and longer duration of maximal effect. Keywords cilazapril pharmacokinetics volunteers ACE inhibition Introduction Cilazapril is an orally active angiotensinconverting enzyme (ACE) inhibitor currently under investigation for use in patients with hypertension and congestive heart failure. Studies conducted in hypertensive animals (Hefti et al., 1986) and man (Fasanella d'amore et al., 1987) have suggested that the pharmacological effect of cilazapril may be more potent than either captopril or enalapril. Pharmacokinetic studies conducted thus far indicate that cilazapril is rapidly converted to its active metabolite, cilazaprilat, following oral dosing (Francis et al., 1987). Maximum plasma concentrations of cilazaprilat are attained within 2 h followed by a decrease in plasma concentrations with an initial half-life of 1-2 h and a subsequent prolonged elimination phase with a terminal half-life of h. Preliminary studies have suggested that plasma concentrations of cilazapril increase linearly with dose over the range of 1.25 to 10 mg (Francis, 1984; Kler et al., 1985, data on file, Hoffmann- La Roche). Presented herein are the results of a definitive study conducted to assess the dose proportionality of cilazapril over the 0.5 to 5 mg dose range intended for therapeutic use. Methods Twenty-four healthy volunteers ranging in age from 20 to 47 years (mean 29 years) and in body weight from 50 to 93 kg (mean 74 kg) completed the study. Each subject's good general health was established by baseline history, physical examination (including ECG) and a laboratory examination consisting of blood chemistry, full blood count with differential and urinalysis. The subjects were within ±15% of their ideal body weight, were not receiving and did not anticipate receiving any medication for the duration of the study. The protocol was approved by the Newark Beth Medical Center Institutional Review Board and all subjects gave written informed consent to participate in the study. Twelve hours prior to the start of each study interval, all volunteers were confined to the study area. Ten hours prior to dosing, volunteers were served a light snack after which an absolute fast except for water was maintained until the 4 h blood sample was obtained. In the morning the volunteers received a single 0.5, 1.0, 2.5 or 5 mg dose of cilazapril with 240 ml water. The treatments were administered in a four-way randomised crossover fashion with a 1 week washout period. No food was ingested until the 4 h blood Correspondence: Dr Joseph Massarella, Hoffmann-La Roche 86/8, Nutley, New Jersey 07110, USA 199S

2 200S J. Massarella et al. sample was collected, after which an institutional meal was served. Dinner was served 10 h following the dose after which food could be consumed ad libitum. All volunteers were confined to the study site until the 24 h blood sample was obtained and returned to the study site for withdrawal of the remaining blood samples. Blood samples (7 ml) were collected prior to drug administration and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 12, 18, 24, 36, 48, 60 and 72 h after drug administration. All blood samples were drawn into heparinized Vacutainer tubes through an indwelling catheter placed in the arm or by venipuncture. After centrifugation, the plasma was transferred to 20 ml glass scintillation vials and promptly frozen at -20 C or below. Plasma concentrations of cilazapril, the active metabolite cilazaprilat and plasma angiotensinconverting enzyme activity were determined by radio-enzymatic assay (Francis et al., 1987). The mean inter-assay precision over the 0.17 to 676 ng ml- 1 concentration range for cilazaprilat was 5.2%. Plasma concentrations of cilazapril and cilazaprilat were used to calculate various pharmacokinetic and biopharmaceutic parameters. The maximum plasma concentration (Cmax) and time of maximum plasma concentration (tmax) following drug administration were read directly from the individual concentrationtime data. The elimination rate constant (Xz) was calculated by fitting the individual data from the terminal phase of the concentration-time data to a log-linear regression equation using the method of least squares. The terminal elimination half-life (t½12) was calculated by dividing by Xz. The area under the plasma concentrationtime curve from time zero to infinity (AUC 0-oo) was determined by conventional trapezoidal and extrapolation techniques. Previous studies (Francis et al., 1987) have shown that plasma concentrations beyond 24 h after ingestion of ACE inhibitors are not proportional to dose and represent binding to constant plasma levels of ACE. Therefore, the area under the curve to 24 h (AUC -24) was also determined. Similar parameters were determined from the ACE inhibition-time data to assess the effect of dose on inhibition of ACE. Emax is defined as the maximal percent inhibition, Etmax is the time to achieve maximal effect and EAUC is the area under the percent inhibition-time curve. Each pharmacokinetic parameter was analyzed separately. Using a model taken from Hedayat and Afsarinejad (Hedayat & Afsarinejad, 1978), an analysis of variance of the raw data was performed, accounting for the effects of subjects, time periods, treatments and possible carryover effects from the preceding treatments. Sequence effects were not included because only two subjects had the same sequence of treatment administration. The Cmax and AUC data were dose-normalized before the statistical analysis. Results Mean plasma concentration-time profiles for cilazapril and cilazaprilat following four dosage strengths are shown in Figure 1. Mean ACE inhibition time profiles are depicted in Figure 2. Pharmacokinetic parameters derived from the cilazapril and cilazaprilat data are summarized in Tables 1 and 2 respectively. Pharmacodynamic parameters determined from the ACE-inhibition data are given in Table 3. The relationship between the parameters Cmax and AUC(0,24) and the administered dose is shown for cilazapril and cilazaprilat in Figure 3. Cilazapril Mean (± % CV) maximum concentrations of cilazapril after 0.5, 1, 2.5 and 5 mg doses were 17.0 (42), 33.9 (44), 82.7 (40) and 182 (31) w ejd%n. 5O. l1oo lbm*4ih) Figure 1 Mean cilazapril and cilazaprilat plasma concentration-time profiles following single 0.5 (0), 1 (O), 2.5 (l) and 5 (O) mg doses of cilazapril to healthy subjects. 7.2.

3 Pharmacokinetics of cilazapril 201S 100' 75 c C: Lu25 0 I IL Time (h) Figure 2 Mean angiotensin-converting enzyme (ACE) inhibition-time profiles following single 0.5 (0), 1 (0), 2.5 (O) and 5 (U) mg doses of cilazapril to healthy subjects. 250 a ~ 0 E~~~~~~~~~ 100 D x (m '~125-8 b Figure 3 Relationship of cilazapril (a) and cilazaprilat (b) Cmax and AUC(0,24) with the administered dose. The filled circles represent mean data. The solid lines represent the regression of all data.

4 202S J. Massarella et al. Table 1 Mean (+ %CV) pharmacokinetic parameters for cilazapril following single oral doses of cilazapril to 24 healthy subjects Parameter Crnax (ng ml 1) 17.0 (42) 33.9 (44) 82.7 (40) 182 (31) tmax (h) 1.1 (29) 1.1 (38) 1.1 (35) 1.0 (29) AUC(0,24) (ng ml-1 h) 52.6 (56) 99.8 (61) 256 (57) 496 (62) AUC(0,cx) (ng ml-1 h) 61.7 (47) 111 (56) 272 (54) 519 (62) X7 (h-1) (62) (43) (124) (74) t, (h)* * Harmonic mean. Table 2 Mean (+ % CV) pharmacokinetic parameters for cilazaprilat following single oral doses of cilazapril to 24 healthy subjects Parameter Cmax(ng ml ) 5.4 (22) 12.4 (31) 37.7 (34) 94.2 (21) tmax (h) 1.8 (30) 1.8 (36) 1.9 (20) 1.6 (28) AUC(0,24) (ng ml-1 h) 42.1 (16) 79.1 (17) 175 (18) 342 (18) AUC(0,x) (ng ml-1 h) 115 (37) 151 (28) 251 (18) 427 (17) X7 (h-') (29) (28) (21) (22) t,x2 (h)* * Harmonic mean. Table 3 Mean (± %CV) parameters for ACE inhibition following single oral doses of cilazapril to 24 healthy subjects Parameter Emax (%) 78.6 (8) 91.0 (5) 97.3 (2) 99.1 (1) Etmax (h) 2.8 (44) 2.6 (45) 2.3 (58) 1.7 (32) EAUC (% h) 2987 (14) 3620 (14) 3917 (14) 4260 (11) Ego-onset (h) (34) 1.2 (63) 0.8 (34) Ego-duration (h) (46) 4.6 (29) 7.0 (22) ng ml-', respectively and were reached within 2 h at all four dose levels. Mean AUC(0,24) values were 52.6 (56), 99.8 (61), 256 (57) and 496 (62) ng ml-1 h over the 0.5 to 5 mg dosage range, respectively. Mean AUC(0,oo) values also increased with increasing dose. Harmonic mean half-lives were h. Results from the ANOVA showed that both Cmax and AUC(0,24) were dose proportional from 0.5 to 5 mg. The dose-normalized AUC(0,oo) at 0.5 mg was significantly larger than at the other three doses, indicating that AUC(0,oo) was dose proportional from 1 to 5 mg, but not at the 0.5 mg dose. Cilazaprilat Mean (± %CV) maximum concentrations of cilazaprilat after 0.5 to 5 mg cilazapril were 5.4 (22), 12.4 (31), 37.7 (34) and 94.2 (21) ng ml- 1, respectively, and were achieved within h at all four dose levels. Mean AUC(0,24) increased with dose over this dosage range. Harmonic mean half-lives were 48.9, 39.8, 38.5 and 35.8 h for 0.5, 1, 2.5 and 5 mg doses, respectively. Results from the ANOVA showed that Cmax (after adjusting for dose) significantly increased with dose, indicating that greater than proportional increases in this parameter were

5 observed over the dose range studied. AUC(0,24) was dose proportional from 2.5 to 5 mg. However, dose-normalized AUC(0,24) at the 0.5 and 1 mg doses were larger than those at higher doses. The terminal rate constant (Xz) significantly increased as the dose was increased; the greatest increase was from 0.5 to 1 mg, with a more gradual increase from 1 to 5 mg. ACE inhibition After doses of 1 to 5 mg of cilazapril, inhibition of ACE greater than 90% was attained in most subjects. Inhibition of ACE was less than 90% in all subjects after the 0.5 mg dose. Maximal inhibition was attained within 4 h in all subjects after 1 to 5 mg cilazapril, with a mean (± %CV) onset of 90% inhibition of 1.6 (34), 1.2 (63) and 0.8 (34) h, respectively. The duration of 90% ACE inhibition increased with increasing doses of 1 to 5 mg, with mean (± %CV) values of 2.1 (46), 4.6 (29) and 7.0 (22) h, respectively. Discussion Following administration of cilazapril in doses ranging from 0.5 to 5 mg, the pharmacokinetic profile of both cilazapril and cilazaprilat were characterized by a rapid increase in plasma concentrations. Maximum plasma concentrations were achieved within 2 h in most subjects, followed by a biphasic decline thereafter. During the absorption and first declining phases of the pharmacokinetic profile (up to approximately 8 h), plasma concentrations of both cilazapril and cilazaprilat were generally proportional to dose. Subsequently, plasma concentrations converged at all doses and beyond 24 to 36 h plasma concentrations were indistinguishable. It has been suggested that the convergence phenomenon followed by a prolonged terminal elimination phase represents dissociation of ACE-bound drug or degradation of ACE-drug complex and its subsequent elimination (Francis et al., 1987). This phenomenon provides a plausible explanation for any observed differences in the dose-normalized pharmacokinetic parameters. Following administration of cilazapril, the drug is rapidly absorbed from the GI tract, undergoes fractional biotransformation to the active metabolite and enters the systemic circulation. Cilazaprilat quickly binds to circulating ACE, saturating this system at therapeutic doses. Therefore, plasma concentration profiles represent both ACE-bound drug and non-acebound drug. The amount of drug bound to ACE under saturable conditions is constant but rela- Pharmacokinetics of cilazapril 203S tively low compared with total drug concentration over the first 8-24 h such that the plasma concentration profiles largely represent non-acebound drug. Later, after most non-ace-bound drug has been eliminated (24 to 36 h after a single dose), the dissociation of ACE-bound drug or degradation of the ACE-drug complex (and its subsequent elimination) controls the rate of decline in plasma levels and these concentrations are in the same range at all doses. For this reason, the assessment of dose proportionality was made using only data up to 24 h. Comparison of the dose-normalized pharmacokinetic profiles over the first 24 h post-dose showed several significant differences, generally occurring at the lowest dose. These differences are also explainable in terms of binding of cilazaprilat to converting enzyme. At high doses the portion of the AUC representing non-acebound drug is much greater than that representing ACE-bound drug resulting in dose-proportional plasma concentrations. As the dose is decreased however, the constant area corresponding to ACE-bound drug represents an increasing fraction of the total AUC. At smaller doses, the observed AUC may be larger than that predicted by extrapolation of data from higher doses. Similar results have been shown for enalapril (Todd & Heel, 1986). It should be noted that, although statistical analysis indicates a degree of non-proportionality at the 0.5 mg dose, a review of the data suggests that the degree is small, readily explainable and probably not of clinical consequence. The overall proportionality seen during the absorption phase and initial declining phase of cilazapril and cilazaprilat indicates that the drug is absorbed from the GI tract, undergoes fractional biotransformation to the active metabolite and enters the systemic circulation in a dose-related fashion. The results of this study are in agreement with those reported previously for cilazapril in healthy subjects over a 1.25 to 10 mg (Kler et al., 1985) and 1 to 160 mg (Francis, 1984) dose range. These data indicate that the pharmacokinetics of cilazapril are consistent and predictable over the therapeutic dosage range. Furthermore, the dissolution profiles were similar among these strengths of cilazapril tablets indicating consistent performance of the dosage forms used in the study. In addition to plasma concentrations of cilazapril and cilazaprilat, activity of ACE was determined in this study. At the 0.5 and 1 mg doses, plasma ACE-inhibition was observed within 1 h of dosing, whereas at the 2.5 and 5 mg doses, inhibition was observed within 30 min. After 1 to 5 mg of cilazapril, most subjects

6 204S J. Massarella et al. achieved 90% ACE-inhibition and this usually occurred within h. Maximum percent inhibition of ACE after the 0.5 mg dose was somewhat lower, but generally achieving 70-80%. The mean time to attain 90% inhibition decreased ( h) with increasing dose (1 to 5 mg), and the mean duration of this inhibition increased ( h) with increasing dose. At the higher doses, 90% inhibition was generally observed until 6 to 8 h post-dose. At 48 h post-dose, mean ACE-inhibition ranged from % (1 to 5 mg) which is similar to results of a previous study (Kler et al., 1985) where mean values of 43-55% were observed at doses of 1.25 to 10 mg. These results suggest that, although all doses produced substantial inhibition of ACE, higher doses were associated with an earlier onset and longer duration of maximal effect. In conclusion plasma concentrations of both cilazapril and cilazaprilat increased in proportion to dose over the 0.5 to 5 mg range studied. All doses produced substantial inhibition of ACE; higher doses were associated with earlier onset and longer duration of maximal effect. References Fasanella d'amore, T., Bussien, J. P., Nussberger, J., Waeber, B., Turini, G. A., Brunner, H. R., Kler, L. & Francis R. J. (1987). Effects of single dose of converting enzyme inhibitor cilazapril in normal volunteers. J. cardiovasc. Pharmac., 9, Francis, R. J. (1984). Ro : Single oral dose pharmacokinetics in healthy male volunteers for the dose range mg (ISN 10197). Data onfile- Hoffman-La Roche. Francis, R. J., Brown, A. N., Kler, L., Fasanella d'amore, T., Nussberger, J., Waeber, B. & Brunner, H. R. (1987). Pharmacokinetics of the converting enzyme inhibitor cilazapril in normal volunteers and the relationship to enzyme inhibition, development of a mathematical model. J. cardiovasc. Pharmac., 9, Hedayat, A. & Afsarinejad, K. (1978). Repeated measurements design, II. The Annual of Statistics, 6, Hefti, F., Fischli, W. & Gerold, M. (1986). Cilazapril prevents hypertension in spontaneously hypertensive rats. J. cardiovasc. Pharmac., 8, Kler, L., Francis, R. J., Cleur, K. A., Matheison, J., Brown, A. N. & Gandecha, R. (1985). A randomized double-blind, single dose study of cilazapril (Ro ) at four different dosages in volunteers (ISN 10335). Data on file - Hoffmann-La Roche. Todd, P. A. & Heel, R. C. (1986). Enalapril: a review of its pharmacodynamic and pharmacokinetic properties and therapeutic use in hypertension and congestive heart failure. Drugs, 31,