Tinzaparin sodium is a low molecular weight heparin with antithrombotic properties. Tinzaparin sodium inhibits reactions that lead to the clotting of blood including the formation of fibrin clots, both in vitro and in vivo. It acts as a potent co-inhibitor of several activated coagulation factors, especially Factors Xa and IIa (thrombin). The primary inhibitory activity is mediated through the plasma protease inhibitor, antithrombin.
Bleeding time is usually unaffected by tinzaparin sodium. Activated partial thromboplastin time (aPTT) is prolonged by therapeutic doses of tinzaparin sodium used in the treatment of deep vein thrombosis (DVT). Prothrombin time (PT) may be slightly prolonged with tinzaparin sodium treatment but usually remains within the normal range. Neither aPTT nor PT can be used for therapeutic monitoring of tinzaparin sodium.
Neither unfractionated heparin nor tinzaparin sodium have intrinsic fibrinolytic activity; therefore, they do not lyse existing clots. Tinzaparin sodium induces release of tissue factor pathway inhibitor, which may contribute to the antithrombotic effect. Heparin is also known to have a variety of actions that are independent of its anticoagulant effects. These include interactions with endothelial cell growth factors, inhibition of smooth muscle cell proliferation, activation of lipoprotein lipase, suppression of aldosterone secretion, and induction of platelet aggregation.
Anti-Xa and anti-IIa activities are the primary biomarkers for assessing tinzaparin sodium exposure because plasma concentrations of low molecular weight heparins cannot be measured directly. Because of analytical assay limitations, anti-Xa activity is the more widely used biomarker. The measurements of anti-Xa and anti-IIa activities in plasma serve as surrogates for the concentrations of molecules which contain the high-affinity binding site for antithrombin (anti-Xa and anti-IIa activities). Monitoring patients based on anti-Xa activity is generally not advised. The data are provided in Figure 1 and Table 2. below.
Studies with tinzaparin sodium in healthy volunteers and patients have been conducted with both fixed- and weight-adjusted dose administration. Recommended therapy with tinzaparin sodium is based on weight-adjusted dosing (see DOSAGE AND ADMINISTRATION).
Figure 1. Mean and Standard Deviation of Anti-Xa Activity Following SC Administration of a Single 4,500 IU* dose and Once Daily Multiple SC Dose of 175 IU/kg Tinzaparin Sodium to Healthy Volunteers
Table 2 Summary of Pharmacokinetic Parameters (Mean and Standard Deviation) Based on Anti-Xa Activity Following Single and Once Daily Multiple Dose SC Administration of Tinzaparin Sodium to Healthy Volunteers
| Parameter (Units) || Single Dose (N=23) || Multiple Dose (N=14) |
| Day 1 |
| Day 5 |
*Dosing based on single dose of 4,500 IU. Mean dose administered was 64.3 IU/kg.
|Cmax (IU/mL)||0.25 (0.05)||0.87 (0.15)||0.93 (0.15)|
|Tmax (hr)||3.7 (0.9)||4.4 (0.7)||4.6 (1.0)|
|AUC0‑∞(IU*hr/mL)||2.0 (0.5)||9.0 (1.1)||9.7 (1.4)|
|Half-life (hr)||3.4 (1.7)||3.3 (0.8)||3.5 (0.6)|
Plasma levels of anti-Xa activity increase in the first 2 to 3 hours following SC injection of tinzaparin sodium and reach a maximum within 4 to 5 hours. Maximum concentrations (Cmax) of 0.25 and 0.87 IU/mL are achieved following a single SC fixed dose of 4,500 IU (approximately 64.3 IU/kg) and weight-adjusted dose of 175 IU/kg of tinzaparin sodium, respectively. Based on the extent of absorption (AUC0‑∞), a comparison of 4,500 IU and 12,250 IU single doses indicates that increases in anti-Xa activity are greater than dose proportional relative to the increase in dose. Following a single SC injection of tinzaparin sodium, the mean anti-Xa to anti-IIa activity ratio, based on the area under the anti-Xa and anti-IIa time profiles, is 2.8 and is higher than that of unfractionated heparin (approximately 1.2). The absolute bioavailability (following 4,500 IU SC and intravenous [IV] administrations) is 86.7% based on anti-Xa activity.
The volume of distribution of tinzaparin sodium ranges from 3.1 L to 5.0 L. These values are similar in magnitude to blood volume, suggesting that the distribution of anti-Xa activity is limited to the central compartment.
Low molecular weight heparins are partially metabolized by desulphation and depolymerization.
In healthy volunteers, the elimination half-life following SC administration of 4,500 IU or 175 IU/kg tinzaparin sodium is approximately 3-4 hours based on anti-Xa activity. Clearance following IV administration of 4,500 IU tinzaparin sodium is approximately 1.7 L/hr. The primary route of elimination is renal. Anti-Xa activity did not accumulate with once daily dosing of 175 IU/kg for five days in healthy volunteers. (See Figure 1 and Table 2.)
Anti-Xa concentrations from approximately 180 patients receiving SC tinzaparin sodium once daily (175 IU/kg body weight) as the treatment of proximal DVT and approximately 240 patients undergoing elective hip replacement surgery receiving SC tinzaparin sodium once daily (~65 IU/kg body weight) were analyzed by population pharmacokinetic methods. The results indicate that neither age nor gender significantly alter tinzaparin sodium clearance based on anti-Xa activity (see PRECAUTIONS, General). However, a reduction in tinzaparin sodium clearance was observed in patients with impaired renal function (reduced calculated creatinine clearance) (see Special Populations, Renal Impairment ). Weight is also an important factor for the prediction of tinzaparin sodium clearance, consistent with the recommendation that INNOHEP® therapy be based on weight-adjusted dosing (see DOSAGE AND ADMINISTRATION).
In patients being treated with tinzaparin sodium (175 IU/kg) for DVT, a population pharmacokinetic (PK) analysis determined that tinzaparin sodium clearance based on anti-Xa activity was related to creatinine clearance calculated by the Cockroft Gault equation. In this PK analysis, a reduction in tinzaparin sodium clearance in moderate (30-50 mL/min) and severe (<30 mL/min) renal impairment was observed. Patients with severe renal impairment exhibited a 24% reduction in tinzaparin sodium clearance relative to patients with normal renal function (>80 mL/min).
In a study of 12 chronic renal failure patients undergoing hemodialysis, anti-Xa clearance was reduced 28%, consistent with estimates from the population PK analyses. In another study of 6 patients undergoing hemodialysis, the half-life of anti-Xa activity following a single IV dose of 75 IU/kg of tinzaparin sodium on an off-dialysis day was prolonged relative to that for healthy volunteers (5.2 versus 1.6 hours).
Patients with severe renal impairment should be dosed with caution (see PRECAUTIONS). Patients aged 90 years or older with creatinine clearance ≤ 60 mL/min should not be treated with INNOHEP® (see CONTRAINDICATIONS).
No prospective studies have assessed tinzaparin sodium pharmacokinetics or pharmacodynamics in hepatically-impaired patients. However, the hepatic route is not a major route of elimination of low molecular weight heparins (see WARNINGS, Hemorrhage).
Since renal function declines with age, elimination of tinzaparin sodium may be reduced in elderly patients. In a prospective study of 30 elderly patients [6 men, 24 women; aged 87.0 ± 5.9 years; mean body weight 62.7 ± 14.6 kg; creatinine clearance 40.6 ± 15.3 mL/min (range 20-72)] treated with tinzaparin sodium 175 IU/kg once daily for ten days for acute venous thromboembolism, there was no accumulation of anti-Xa activity based on peak anti-Xa activity levels.
A phase III/IV clinical study (IRIS; INNOHEP® in Renal Insufficiency Study) compared INNOHEP® (175 IU/kg once daily) and unfractionated heparin (UFH) in the initial treatment of deep vein thrombosis (DVT) and/or pulmonary embolism (PE) in elderly patients with renal insufficiency (i.e., patients aged 70 years or older with estimated creatinine clearance of ≤ 30 mL/min calculated by the Cockcroft Gault formula or patients aged 75 years or older with estimated creatinine clearance of ≤ 60 mL/min). Oral anticoagulants were co-administered beginning on Days 1-3 and study treatment was continued for at least 5 days until INR was between 2-3 on 2 successive days; oral anticoagulants were then continued alone and patients were followed until 90 days after treatment start. An interim analysis of this ongoing study with INNOHEP® indicates that patients aged 90 years or older with renal insufficiency have an increased mortality. Based on this finding, patients aged 90 years or older with creatinine clearance ≤ 60 mL/min should not be treated with INNOHEP® (see CONTRAINDICATIONS).
Based on the results of a prospective clinical study and the population PK analyses, weight-based dosing is appropriate for heavy/obese patients. Tinzaparin sodium PK parameters based on anti-Xa activity are independent of body weight and body mass index (BMI) when tinzaparin sodium is dosed on a weight basis at 175 IU/kg or 75 IU/kg. In a prospective study of heavy/obese subjects (101 to 165 kg; BMI 26‑61 kg/m2), anti-Xa activity time profiles were similar to those in normal-weight volunteer studies. Data at the 175 IU/kg dose are shown in Figure 2. Clinical trial experience is limited in patients with a BMI >40 kg/m2.
Figure 2 Mean and Standard Deviation of Anti-Xa Activity Following a Single SC Administration of 175 IU/kg Tinzaparin Sodium to Obese Subjects and Normal-Weight Volunteers
The disposition of INNOHEP® was studied in 54 pregnant patients in any trimester. In this open-label, prospective, dose finding study, those treated with an INNOHEP® dose of 175 IU/kg had similar 24-hour anti-Xa curves at 28 (n=17) and 36 (n=20) weeks gestation. The 175 IU/kg dose resulted in a mean anti-Xa level of 0.3 to 1.0 IU/mL 4 hours after administration. Mean anti-Xa levels 4 hours post dose suggest that as pregnancy advances there is no clinically significant decrease in anti-Xa levels. Pregnancy has little or no influence on the pharmacokinetics of INNOHEP® and no dosing adjustment is needed for pregnancy. (See Dosage And Administration.)