CLINICAL PHARMACOLOGY
Mechanism of Action: When taken orally, ticlopidine hydrochloride
causes a time- and dose-dependent inhibition of both platelet aggregation and
release of platelet granule constituents, as well as a prolongation of bleeding
time. The intact drug has no significant in vitro activity at the concentrations
attained in vivo; and, although analysis of urine and plasma indicates at least
20 metabolites, no metabolite which accounts for the activity of ticlopidine
has been isolated.
Ticlopidine hydrochloride, after oral ingestion, interferes with platelet membrane
function by inhibiting ADP-induced platelet-fibrinogen binding and subsequent
platelet-platelet interactions. The effect on platelet function is irreversible
for the life of the platelet, as shown both by persistent inhibition of fibrinogen
binding after washing platelets ex vivo and by inhibition of platelet aggregation
after resuspension of platelets in buffered medium.
Pharmacokinetics and Metabolism: After oral administration of
a single 250-mg dose, ticlopidine hydrochloride is rapidly absorbed with peak
plasma levels occurring at approximately 2 hours after dosing and is extensively
metabolized. Absorption is greater than 80%. Administration after meals results
in a 20% increase in the AUC of ticlopidine.
Ticlopidine hydrochloride displays nonlinear pharmacokinetics and clearance
decreases markedly on repeated dosing. In older volunteers the apparent half-life
of ticlopidine after a single 250-mg dose is about 12.6 hours; with repeat dosing
at 250 mg bid, the terminal elimination half-life rises to 4 to 5 days and steady-state
levels of ticlopidine hydrochloride in plasma are obtained after approximately
14 to 21 days.
Ticlopidine hydrochloride binds reversibly (98%) to plasma proteins, mainly
to serum albumin and lipoproteins. The binding to albumin and lipoproteins is
nonsaturable over a wide concentration range. Ticlopidine also binds to alpha-1
acid glycoprotein. At concentrations attained with the recommended dose, only
15% or less ticlopidine in plasma is bound to this protein.
Ticlopidine hydrochloride is metabolized extensively by the liver; only trace
amounts of intact drug are detected in the urine. Following an oral dose of
radioactive ticlopidine hydrochloride administered in solution, 60% of the radioactivity
is recovered in the urine and 23% in the feces. Approximately 1/3 of the dose
excreted in the feces is intact ticlopidine hydrochloride, possibly excreted
in the bile. Ticlopidine hydrochloride is a minor component in plasma (5%) after
a single dose, but at steady-state is the major component (15%). Approximately
40% to 50% of the radioactive metabolites circulating in plasma are covalently
bound to plasma proteins, probably by acylation.
Clearance of ticlopidine decreases with age. Steady-state trough values in
elderly patients (mean age 70 years) are about twice those in younger volunteer
populations.
Hepatically Impaired Patients: The effect of decreased hepatic
function on the pharmacokinetics of TICLID (ticlopidine hcl) was studied in 17 patients with advanced
cirrhosis. The average plasma concentration of ticlopidine in these subjects
was slightly higher than that seen in older subjects in a separate trial (see
CONTRAINDICATIONS).
Renally Impaired Patients: Patients with mildly (Ccr 50 to 80
mL/min) or moderately (Ccr 20 to 50 mL/min) impaired renal function were compared
to normal subjects (Ccr 80 to 150 mL/min) in a study of the pharmacokinetic
and platelet pharmacodynamic effects of TICLID (ticlopidine hcl) (250 mg bid) for 11 days. Concentrations
of unchanged TICLID (ticlopidine hcl) were measured after a single 250-mg dose and after the final
250-mg dose on Day 11.
AUC values of ticlopidine increased by 28% and 60% in mild and moderately impaired
patients, respectively, and plasma clearance decreased by 37% and 52%, respectively,
but there were no statistically significant differences in ADP-induced platelet
aggregation. In this small study (26 patients), bleeding times showed significant
prolongation only in the moderately impaired patients.
Pharmacodynamics: In healthy volunteers over the age of 50, substantial
inhibition (over 50%) of ADP-induced platelet aggregation is detected within
4 days after administration of ticlopidine hydrochloride 250 mg bid, and maximum
platelet aggregation inhibition (60% to 70%) is achieved after 8 to 11 days.
Lower doses cause less, and more delayed, platelet aggregation inhibition, while
doses above 250 mg bid give little additional effect on platelet aggregation
but an increased rate of adverse effects. The dose of 250 mg bid is the only
dose that has been evaluated in controlled clinical trials.
After discontinuation of ticlopidine hydrochloride, bleeding time and other
platelet function tests return to normal within 2 weeks, in the majority of
patients.
At the recommended therapeutic dose (250 mg bid), ticlopidine hydrochloride
has no known significant pharmacological actions in man other than inhibition
of platelet function and prolongation of the bleeding time.
Clinical Trials
Stroke Patients: The effect of ticlopidine on the risk of stroke
and cardiovascular events was studied in two multicenter, randomized, double-blind
trials.
1. Study in Patients Experiencing Stroke Precursors: In a trial
comparing ticlopidine and aspirin (The Ticlopidine Aspirin Stroke Study or TASS),
3069 patients (1987 men, 1082 women) who had experienced such stroke precursors
as transient ischemic attack (TIA), transient monocular blindness (amaurosis
fugax), reversible ischemic neurological deficit or minor stroke, were randomized
to ticlopidine 250 mg bid or aspirin 650 mg bid. The study was designed to follow
patients for at least 2 years and up to 5 years.
Over the duration of the study, TICLID (ticlopidine hcl) significantly reduced the risk of fatal
and nonfatal stroke by 24% (p = .011) from 18.1 to 13.8 per 100 patients followed
for 5 years, compared to aspirin. During the first year, when the risk of stroke
is greatest, the reduction in risk of stroke (fatal and nonfatal) compared to
aspirin was 48%; the reduction was similar in men and women.
2. Study in Patients Who Had a Completed Atherothrombotic Stroke:
In a trial comparing ticlopidine with placebo (The Canadian American Ticlopidine
Study or CATS) 1073 patients who had experienced a previous atherothrombotic
stroke were treated with TICLID (ticlopidine hcl) 250 mg bid or placebo for up to 3 years.
TICLID (ticlopidine hcl) significantly reduced the overall risk of stroke by 24% (p = .017) from
24.6 to 18.6 per 100 patients followed for 3 years, compared to placebo. During
the first year the reduction in risk of fatal and nonfatal stroke over placebo
was 33%.
 |
Stent Patients: The ability of TICLID (ticlopidine hcl) to reduce the rate of thrombotic
events after the placement of coronary artery stents has been studied in five
randomized trials, one of substantial size (Stent Anticoagulation Restenosis
Study or STARS) described below, and four smaller studies. In these trials,
ticlopidine 250 mg bid with ASA (dose range from 100 mg bid to 325 mg qd) was
compared to aspirin alone or to anticoagulant therapy plus aspirin. The trials
enrolled patients undergoing both planned (elective) and unplanned coronary
stent placement. The types of stents used, the use of intravascular ultrasound,
and the use of high-pressure stent deployment varied among the trials, although
all patients in STARS received a Palmaz-Schatz stent. The primary efficacy endpoints
of the trials were similar, and included death, myocardial infarction and the
need for repeat coronary angioplasty or CABG. All trials followed patients for
at least 30 days.
In STARS, patients were randomized to receive one of three regimens for 4 weeks:
aspirin alone, aspirin plus coumadin, or aspirin plus ticlopidine. Therapy was
initiated following successful coronary stent placement. The primary endpoint
was the incidence of stent thrombosis, defined as death, Q-Wave MI, or angiographic
thrombus within the stented vessel demonstrated at the time of documented ischemia
requiring emergent revascularization. The incidence rates for the primary endpoint
and its components at 30 days are shown in the table below.
STARS |
TICLID + Aspirin
N=546 |
Aspirin
N=557 |
Coumadin +Aspirin
N=550 |
Odds Ratio
(95% C.I.)* |
p-Value* |
Primary Endpoint |
3
(0.5%) |
20
(3.6%) |
15
(2.7%) |
0.15
(0.03, 0.51) |
< 0.001 |
Deaths |
0
(0%) |
1
(0.2%) |
0
(0%) |
- |
- |
Q-Wave MI (Recurrent and Procedure Related) |
1
(0.2%) |
12
(2.2%) |
8
(1.5%) |
0.08
(0.002, 0.57) |
0.004 |
Angiographically Evident Thrombosis |
3
(0.5%) |
16
(2.9%) |
15
(2.7%) |
0.19
(0.03, 0.66) |
0.005 |
* Comparison of TICLID plus aspirin to aspirin
alone. |
The use of ticlopidine plus aspirin did not affect the rate of non-Q-wave MIs
when compared with aspirin alone or aspirin plus anticoagulants in STARS.
The use of ticlopidine plus aspirin was associated with a lower rate of recurrent
cardiovascular events when compared with aspirin alone or aspirin plus anticoagulants
in the other four randomized trials.
The rate of serious bleeding complications and neutropenia in STARS are shown
in the table below. There were no cases of thrombotic thrombocytopenic purpura
(TTP) or aplastic anemia reported in 1346 patients who received ticlopidine
plus aspirin in the five randomized trials.
STARS |
TICLID + Aspirin
N=546 |
Aspirin
N=557 |
Coumadin + Aspirin
N=550 |
Hemorrhagic Complications |
30 (5.5%) |
10 (1.8%) |
34 (6.2%) |
Cerebrovascular Accident |
0 (0%) |
2 (0.4%) |
1 (0.2%) |
Neutropenia ( ≤ 1200/mm³) |
3 (0.5%) |
0 (0%) |
1 (0.2%) |