ARGATROBAN (Page 4 of 6)

8.6 Hepatic Impairment

Dose reduction and careful titration are required when administering argatroban to patients with hepatic impairment. Reversal of anticoagulation effect may be prolonged in this population [see Dosage and Administration (2.4), Warnings and Precautions (5.2), Clinical Pharmacology (12.3)] .

10 OVERDOSAGE

Excessive anticoagulation, with or without bleeding, may be controlled by discontinuing argatroban or by decreasing the argatroban dose. In clinical studies, anticoagulation parameters generally returned from therapeutic levels to baseline within 2 to 4 hours after discontinuation of the drug. Reversal of anticoagulant effect may take longer in patients with hepatic impairment.

No specific antidote to argatroban is available; if life- threatening bleeding occurs and excessive plasma levels of argatroban are suspected, discontinue argatroban immediately and measure aPTT and other coagulation parameters. When argatroban was administered as a continuous infusion (2 mcg/kg/min) prior to and during a 4-hour hemodialysis session, approximately 20% of argatroban was cleared through dialysis.

Single intravenous doses of argatroban at 200, 124, 150, and 200 mg/kg were lethal to mice, rats, rabbits, and dogs, respectively. The symptoms of acute toxicity were loss of righting reflex, tremors, clonic convulsions, paralysis of hind limbs, and coma.

11 DESCRIPTION

Argatroban is a synthetic direct thrombin inhibitor. The chemical name is 1-[(2S)-5-[(aminoimino-methyl)amino]-1-oxo-2-[[(1,2,3,4-tetrahydro-3-methyl-8-quinolinyl)sulfonyl]amino]pentyl]-4-methyl-,(2R,4R)- 2-Piperidinecarboxylic acid. Argatroban has 4 asymmetric carbons. One of the asymmetric carbons has an R configuration (stereoisomer Type I) and an S configuration (stereoisomer Type II). Argatroban consists of a mixture of R and S stereoisomers at a ratio of approximately 65:35.

The molecular formula of argatroban is C ₂₃ H ₃₆ N ₆ O ₅ S. Its molecular weight is 508.63 g/mol. The structural formula is:

Argatroban in Sodium Chloride Injection is a sterile, non-pyrogenic, clear, colorless to pale yellow isotonic solution. It is supplied in a single-dose clear glass vial containing 50 mg of argatroban in 50 mL sodium chloride solution. Each mL contains 1 mg argatroban, 9 mg sodium chloride, USP and 3 mg sorbitol, NF in water for injection, USP. The pH of the solution is between 3.2 to 7.5.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Argatroban is a direct thrombin inhibitor that reversibly binds to the thrombin active site. Argatroban does not require the co-factor antithrombin III for antithrombotic activity. Argatroban exerts its anticoagulant effects by inhibiting thrombin-catalyzed or –induced reactions, including fibrin formation; activation of coagulation factors V, VIII, and XIII; activation of protein C; and platelet aggregation.

Argatroban inhibits thrombin with an inhibition constant (K _i ) of 0.04 μM. At therapeutic concentrations, argatroban has little or no effect on related serine proteases (trypsin, factor Xa, plasmin, and kallikrein).

Argatroban is capable of inhibiting the action of both free and clot-associated thrombin.

12.2 Pharmacodynamics

When argatroban is administered by continuous infusion, anticoagulant effects and plasma concentrations of argatroban follow similar, predictable temporal response profiles, with low intersubject variability. Immediately upon initiation of argatroban infusion, anticoagulant effects are produced as plasma argatroban concentrations begin to rise. Steady-state levels of both drug and anticoagulant effect are typically attained within 1 to 3 hours and are maintained until the infusion is discontinued or the dosage adjusted. Steady-state plasma argatroban concentrations increase proportionally with dose (for infusion doses up to 40 mcg/kg/min in healthy subjects) and are well correlated with steady-state anticoagulant effects. For infusion doses up to 40 mcg/kg/min, argatroban increases in a dose-dependent fashion, the activated partial thromboplastin time (aPTT), the activated clotting time (ACT), the prothrombin time (PT), the International Normalized Ratio (INR), and the thrombin time (TT) in healthy volunteers and cardiac patients. Representative steady-state plasma argatroban concentrations and anticoagulant effects are shown below for argatroban infusion doses up to 10 mcg/kg/min (see Figure 1).

Figure 1.
Relationship at Steady State Between Argatroban Dose, Plasma Argatroban
Concentration and Anticoagulant Effect

Effect on International Normalized Ratio (INR): Because argatroban is a direct thrombin inhibitor, co-administration of argatroban and warfarin produces a combined effect on the laboratory measurement of the INR. However, concurrent therapy, compared to warfarin monotherapy, exerts no additional effect on vitamin K-dependent factor Xa activity.

The relationship between INR on co-therapy and warfarin alone is dependent on both the dose of argatroban and the thromboplastin reagent used. This relationship is influenced by the International Sensitivity Index (ISI) of the thromboplastin. Data for 2 commonly utilized thromboplastins with ISI values of 0.88 (Innovin, Dade) and 1.78 (Thromboplastin C Plus, Dade) are presented in Figure 2 for an argatroban dose of 2 mcg/kg/min. Thromboplastins with higher ISI values than shown result in higher INRs on combined therapy of warfarin and argatroban. These data are based on results obtained in normal individuals [see Dosage and Administration (2.5) , Warnings and Precautions (5.3)] .

Figure 2.
INR Relationship of Argatroban Plus Warfarin Versus Warfarin Alone

Figure 2 demonstrates the relationship between INR for warfarin alone and INR for warfarin co-administered with argatroban at a dose of 2 mcg/kg/min. To calculate INR for warfarin alone (INR _W ), based on INR for co-therapy of warfarin and argatroban (INR _WA ), when the argatroban dose is 2 mcg/kg/min, use the equation next to the appropriate curve. Example: At a dose of 2 mcg/kg/min and an INR performed with Thromboplastin A, the equation 0.19 + 0.57 (INR _WA ) = INR _W would allow a prediction of the INR on warfarin alone (INR _W ). Thus, using an INR _WA value of 4 obtained on combined therapy: INR _W = 0.19 + 0.57 (4) = 2.47 as the value for INR on warfarin alone. The error (confidence interval) associated with a prediction is ± 0.4 units. Similar linear relationships and prediction errors exist for argatroban at a dose of 1 mcg/kg/min. Thus, for argatroban doses of 1 or 2 mcg/kg/min, INR _W can be predicted from INR _WA . For argatroban doses greater than 2 mcg/kg/min, the error associated with predicting INR _W from INR _WA is ± 1. Thus, INR _W cannot be reliably predicted from INR _WA at doses greater than 2 mcg/kg/min.