Single and Multiple Dose Pharmacokinetics of Ticlopidine in Young and Elderly Subjects

Br. J. clin. Pharmac. (1991), 32, 761-764

Single and multiple dose pharmacokinetics of ticlopidine in young and elderly subjects

J. SHAH', P. TEITELBAUM', B. MOLONY', T. GABUZDA2 & I. MASSEY' 'Syntex Research, A3-BMR, Palo Alto, CA 94304 and 2Division of Hematology-Oncology, The Lankenau Hospital and Medical Research Center, Philadelphia, PA 19151, USA

The pharmacokinetics of orally administered ticlopidine hydrochloride, a novel inhibitor of platelet aggregation, were determined both after a single dose and after 21 days of twice daily dosing in 12 young (mean 28.6 years) and 13 elderly (mean 69.5 years) subjects. Concentrations of unchanged ticlopidine in plasma were measured by g.l.c. After a single 250 mg dose of ticlopidine, the mean area under the curve, AUC (0-12 h) was 1.11 ,ug ml-1 h in young subjects and 2.04 ,ug ml-1 h in old subjects (P = 0.002). Mean values of t½/2,z in young and elderly subjects were 7.9 h and 12.6 h, respectively (P = 0.01). Steady state plasma drug concentrations were attained after 14 days of dosing with ticlopidine. After the final dose on day 21, AUC values in elderly subjects were 2-3 times those in young subjects (P < 0.001). The plasma t½/2,z averaged 4.0 days for young subjects and 3.8 days for elderly subjects (P = 0.7). The longer t/2,z and higher AUC values after multiple dosing probably reflect an increase in bioavailability of ticlopidine after repeated dosing, saturation of metabolism or insufficient analytical sensitivity to characterize the terminal elimination phase after single dose.

Keywords ticlopidine pharmacokinetics age steady state platelet aggregation

Introduction Ticlopidine hydrochloride [(chloro-2 benzyl)-5 tetrahydro week and returns to baseline approximately 1-2 weeks 4, 5, 6 thieno (3, 2-c) pyridine] is a novel inhibitor of after therapy is discontinued. The metabolism of ticlo- platelet function that differs in its structure and mech- pidine is complex; at least four metabolites have been anism of action from aspirin and other NSAIDs (Bruno isolated in man and 13 metabolites have been isolated & Molony, 1983; Knudsen & Gormsen, 1979; Panak et in rats (Panak et al., 1983; Picard-Fraire, 1984). The al., 1983). Ticlopidine acts primarily by inhibiting the main quantitative metabolic routes in man are N- adenosine diphosphate (ADP) pathway of platelet dealkylation and oxidation of the thiophene ring (Bruno aggregation (Feliste et al., 1987). Although the exact & Molony, 1983). Hepatic clearance accounts for most mechanism of action of ticlopidine has not been fully of the total body clearance of ticlopidine, as only trace elucidated, it is thought that the drug may interfere with amounts of ticlopidine are eliminated unchanged via the the membrane functions of the thrombocyte by inhibit- kidney. The duration of inhibition of platelet function ing platelet-fibrinogen binding, platelet-platelet inter- corresponds to the normal life-span of the platelet (Panak actions, and binding of ADP to membrane receptors. et al., 1983). Approximately 98% of ticlopidine in plasma Ticlopidine does not inhibit cyclic-AMP phosphodi- is reversibly bound to plasma proteins, mainly to serum esterase or the cyclooxygenase pathway, and it does not albumin and lipoproteins. Ticlopidine also binds to cxl- block production of thromboxane by platelets or of acid glycoprotein (Glasson et al., 1982) but at concentra- prostacyclin by endothelial cells (Bruno, 1983). tions associated with therapeutic doses 15% or less of In humans, ticlopidine is absorbed rapidly and exten- ticlopidine is bound to this protein. sively, and causes a time- and dose dependent inhibition Two large multicentre trials have recently established of ADP-induced platelet aggregation. At the recom- the efficacy of ticlopidine for the prevention of threatened mended therapeutic dose of 500 mg day-', inhibition of and recurrent stroke. The Ticlopidine-Aspirin Stroke platelet aggregation is maximal after approximately 1 Study (TASS) demonstrated that ticlopidine was more Correspondence: Dr J. Shah, Syntex Research, A3-BMR, Palo Alto, CA 94304, USA 761 762 J. Shah et al. effective than aspirin for the prevention of stroke in Analysis of ticlopidine in plasma patients who have suffered from transient cerebrovascular ischaemic events and who are consequently at increased A methanolic solution (100 pLI, 2 jig mlF-1) ofthe dichloro risk of stroke (Hass et al., 1989). The results of the analogue of ticlopidine was added to 1 ml of plasma as Canadian-American Ticlopidine Study (CATS) indicated an internal standard. After addition of 66 mm phosphate that ticlopidine was superior to placebo for the preven- buffer (pH 8; 1 ml), the plasma was extracted with 10 tion of recurrent strokes in patients who had already ml hexane. The hexane layer was removed and then experienced a stroke (Gent et al., 1988). Ticlopidine extracted with 0.2N HCl (2 ml). Potassium hydroxide treatment is associated with a variety of mild gastro- solution (2N; 0.3 ml) was added to the acidic extract, and intestinal side effects and skin rashes. About 1-2% of the aqueous phase was extracted with hexane: pentyl patients experience drug induced neutropenia usually acetate (1:1; 50 ,ul). The lower aqueous layer was re- within the first 3 months of treatment with ticlopidine. moved using a Pasteur pipet. A portion (3-5 ,lI) of the The average age of the subjects in TASS and CATS pentyl acetate extract was injected into a gas chromato- were 63 and 66 years, respectively. A growing awareness graphic column. A 5880A Hewlett Packard gas chroma- of the potential for altered drug disposition in the elderly tograph equipped with a nitrogen-phosphorous detector has prompted examination of the pharmacokinetics of and a level-four integrating terminal was used. The many drugs in elderly subjects. The effect of ageing on injection port and the detector temperatures were main- drug absorption, distribution, metabolism, and tained at 2500 C and 3000 C, respectively. The accuracy elimination is variable and often unpredictable. The and reproducibility of this method was assessed by the present study was undertaken to compare the pharmaco- analysis of samples of plasma fortified with ticlopidine kinetics of ticlopidine in young and elderly subjects and at concentrations of0-150 ng ml-1. Drug recovery ranged to determine the pharmacokinetics of ticlopidine after from 98.7-102.2% and the CV of the assay was < 4% at multiple dosing. all concentrations. The lower limit of reliable measure- ment was 10 ng ml-1, which was the lowest point on the calibration curve. Data adjustments Methods The concentration of ticlopidine in the plasma at 12 h Study design after dosing on day 1 was calculated by linear regression of the data for the elimination phase following the single Following approval of the study protocol and the consent dose. The concentration of ticlopidine in the plasma form by the Institutional Review Board of the Lankenau 12 h after dosing on day 21 was assumed to be the same Medical Research Center, 12 young subjects (seven men as that at time zero on day 21. Data from two subjects in and five women), and 13 elderly subjects (eight men and the elderly group were not used in the pharmacokinetic five women) were recruited. The mean age and weight of analysis for day 21. One of these subjects did not take young and elderly subjects were 28.6 and 69.5 years and any medication after day 8; the other had an unusually 87.4 and 76.5 kg, respectively. Females participating in long half-life (510 h). the study were either surgically sterile or postmeno- pausal. Subjects were judged to be healthy on the basis Analysis of data of medical histories, normal physical examination, were calculated routine blood chemistries, normal blood counts, Pharmacokinetic parameters using normal chest and creatinine compartment model-independent methods. The elimi- urinalysis, ECG, X-ray nation half-life (tl,,Z) of ticlopidine was calculated by clearance. All concomitant medications, including non- least squares regression analysis of the terminal log- prescription drugs, were discontinued; alcohol was the linear portion of the plasma drug concentration-time prohibited for 24 h prior to and during study period. The area under the concen- After receiving an explanation of the risks and incon- curve. total plasma drug be all of the tration-time curve (AUC) was determined by the linear veniences that could reasonably expected, trapezoidal rule with extrapolation to infinity by adding subjects signed an informed consent form. concen- a tablet of the ratio of the last measurable plasma drug In the first part of the study, single 250 mg tration divided the terminal elimination rate constant was administered with a light breakfast and by ticlopidine (C(last)/z). Values of AUC and t½l,,z were calculated for 10 ounces of water. Samples of blood were collected for the oral dose and on analysis of concentrations of ticlopidine at intervals of 0 each subject following single day 24 and 48 h after dosing. 21 following repeated oral dosing. Peak plasma drug (pre-dose), 1, 2, 3, 4, 6, 8, concentration, Cmax (,ug ml-l), and time to peak plasma Following a 1 week washout period, the second part of indivi- The at a concentration, tmax (h), were obtained from the the study began. subjects received ticlopidine dual curves. The average steady-state plasma drug con- dose of 250 mg twice a day for 3 weeks. Samples of blood was calculated from: (10 ml) were collected at time 0 (pre-dose) and 2 h after centration (Cav) the morning dose on days 1, 2, 3, 7 and 14 of the dosing Cav = AUC(T) (1) regimen. On day 21 samples of blood were collected at T 0, 1, 2, 3, 4, 6, 8, 24, 48, 72 and 96 h after the last dose. Samples of blood were collected in heparinized where AUC(T) is the AUC within the dosing interval Vacutainer® (Becton Dickinson) tubes. The plasma was at steady state and separated, frozen and stored until analysis. T is the dosing interval (12 h). Short report 763

In addition, the following ratios were calculated for each Table 1 Pharmacokinetic parameters (mean ± s.d) of subject and averaged for each group. ticlopidine in young and elderly subjects R (a measure of linearity) = AUC(T) day 21 (2) Parameters Young Elderly P-value AUC day 1 Day 1 n 12 13 and Rac (a measure of accumulation) = Cmax (,ug ml-') 0.41 (0.24) 0.70 (0.52) 0.035* AUC(T) day 21 (3) # tmax (h) 2.0 (1.0-3.0) 2.0 (1.0-4.0) ns t,12 z (h) 7.9 (3.0) 12.7 (0.9) 0.013* AUC (0-12) day 1 AUC(jxgml 'h) 1.4 (0.8) 2.8 (1.2) 0.002* For statistical analysis, an analysis of variance model Day 21 appropriate for the 2 x 2 factorial design was used, with n 12 11 P c 0.05 as the level of significance. The model incor- Cmax (p.g ml-') 0.89 (0.37) 1.42 (0.75) 0.015* porated effects due to sex, age, and an age-by-sex # tmaX (h) 1.0 (1.0-3.0) 2.0 (1.0-4.0) ns t½/2z (h) 98 (64) 91 (33) ns interaction term. AUC(p.gml-lh) 3.6 (1.7) 8.3 (3.2) 0.001* Cav(Rg mI-1) 0.30 (0.14) 0.69 (0.27) 0.003* R 3.1 (1.6) 3.2 (0.8) Rac 3.5 (5.5) 4.2 (3.0) Results *Significantly different (P c 0.05). #Median value and the upper and lower range. Single dose study

The mean concentrations of ticlopidine in plasma Multiple dose study following administration to young and elderly subjects are shown in Figure 1. The mean concentration of in Administration of 250 mg ticlopidine twice daily to the ticlopidine plasma at 1 h was 0.28 and 0.52 ,ug ml-' young subjects resulted in mean trough plasma concen- for the young and the elderly subjects, respectively. 1 From trations of 0.103, 0.187 and 0.146 pug ml- on days 7, 14, 2-8 h, the concentrations of ticlopidine in plasma and 21, respectively. At all time points, the trough for elderly subjects were significantly greater than those concentrations for the in young subjects. The average plasma elimination half- elderly subjects were higher. life Trough levels on weeks 2 and 3 ofdosing were respectively (t½.2Z) of ticlopidine in elderly subjects (12.7 h) was 0.441 and 0.397 ,ug ml-' for elderly subjects. Steady- significantly longer than that for young subjects (7.9 h, state trough concentrations (Css,min) were reached by P = 0.013) (Table 1). Likewise, values for Cmax and 14 days. AUC were significantly higher for elderly subjects than for Figure 1 shows plasma concentrations of ticlopidine young subjects. in young and elderly subjects following the last dose of ticlopidine on day 21. Values of tmax were 1.4 and 2.1 h for the young and the elderly subjects, respectively (Table 1). Values of Cmax were 0.89 and 1.42 ,ug ml-', ¶s.DAYI respectively. The plasma elimination half-life (t,/2Z) averaged 98 and 91 h for young and elderly subjects P.+k (P = 0.652). Mean Cay was greater for elderly than for younger subjects (P = 0.003). The mean R and Rac E.. values were 3.1 and 3.5, respectively, for young subjects and 3.2 and 4.2 for elderly subjects, respectively. There ~0.031_ was no significant effect of gender on the pharmacokinetics of ticlopidine after multiple doses.

.'I s-0.001 _ I ------| -- Discussion .1 0 OU.. Therapeutic use of ticlopidine will be mainly in older individuals. The present investigation was carried out to investigate the relative pharmacokinetics of ticlopidine in young and elderly normal volunteers. 0.1 The increased AUC of ticlopidine observed in the elderly subjects could result from an increased extent of absorption from the gut or a decreased metabolic clearance. Any lowering of plasma albumin in old age (Shand, 1982; Vestal, 1978) is likely to mask an even greater difference in intrinsic clearance based upon unbound Time in hours drug concentration. The degree of accumulation of Figure 1 Mean (± s.e. mean) plasma ticlopidine ticlopidine in plasma on multiple dosing was similar in concentrations in young (n = 12) (o) and elderly (n = 13) (V) the young and elderly subjects. Values of R were greater subjects - a) day 1, b) day 21. *Significantly different P _ 0.05. than unity in both groups, t½l,z values were greater after 764 J. Shah et al. multiple than single dosing and an increase was seen in Recent studies in elderly subjects failed to demonstrate Rac values. Possible explanations for these findings in- any differences in the effects of ticlopidine in elderly and clude an increase in bioavailability after repeated young subjects (Molony, unpublished data). Thus the administrations of ticlopidine, saturation of the metab- differences in the pharmacokinetics of ticlopidine olism of ticlopidine or failure to detect the slow elimina- between young and elderly subjects identified in this tion phase after the single dose because of the sensitivity study should not contribute to any unexpected pharma- limit of the analytical method. cological or adverse effects.

References

Bruno, J. J. (1983). The mechanisms of action of ticlopidine. aspirin for the prevention of stroke in high-risk patients. Thrombosis Res., Suppl. IV, 59-87. New Engi. J. Med., 321, 501-507. Bruno, J. J. & Molony, B. A. (1983). Cardiovascular drugs. Knudsen, J. B. & Gormsen, J. (1979). The effect of ticlopidine In New Drugs Annual, ed. Scriabine, A., volume 1, pp. 295- on platelet function in normal volunteers and in patients 316. New York: Raven Press. with platelet hyperaggregability in vitro. Thrombosis Res., Feliste, R., Delebassee, D. & Simon, M. F. (1987). Broad 16, 663-671. spectrum anti-platelet activity of ticlopidine and PCR 4099 Panak, E., Maffrand, J. P., Picard-Fraire, C., Vallee, E. & involves the suppression of the effects of released ADP. Blanchard, J. (1983). Ticlopidine: a promise for the preven- Thrombosis Res., 48, 403-415. tion and treatment of thrombosis. Hemostasis, 13, Suppl. Gent, M., Blakely, J. A., Easton, J. D., Ellis, D. J., Hachinski, 1, 1-54. V. C., Harbison, J. W., Panak, E., Roberts, R. S., Sicurella, Picard-Fraire, C. (1984). Pharmacokinetics and metabolic J. & Turpie, A. G. (1988). The Canadian American ticlo- characteristics of ticlopidine in relation to its inhibitory pidine study in thromboembolic stroke. Stroke, 19, 1203- properties on platelet function: Agents and Actions 1210. Supplements. Ticlopidine: Quo Vadis?, 15, (Suppl.) 68-75. Glasson, S., Zim, R. & Tillement, J. P. (1982). Multiple Shand, D. G. (1982). Biological determinants of altered human serum binding of two thienopyridine derivatives, pharmacokinetics in the elderly. Gerontology, 28, Suppl. ticlopidine and PCR 2362 and their distribution between 8-17. HSA, a-acid glycopritein and lipo-proteins. Biochem. Vestal, R. E. (1978). Drug use in the elderly: a review of Pharmac., 31, 831-835. problems and special considerations. Drugs, 16, 358-382. Hass, W. K., Easton, J. D., Adams, H. P., Pryse-Phillips, W., Molony, B. A., Anderson, S. & Kamm, B. (1989). A (Received 4 September 1990, randomized trial comparing ticlopidine hydrochloride with accepted 7 August 1991)