Anticoagulation in children: Making the most of little patients and little evidence

Thrombotic complications are increasing at a steady and significant rate in children resulting in the more widespread use of anticoagulation in this population. Anticoagulant drugs in children can be divided into the standard agents (heparin, low molecular weight heparin, and vitamin K antagonists) and alternative agents (argatroban, bivalirudin, and fondaparinux). This review will compare and contrast the standard and alternative anticoagulants and suggest situations in which it may be appropriate to use argatroban, bivalirudin, and fondaparinux. Clearly, the standard anticoagulants all have significant shortcomings including variable pharmacokinetics, issues with therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects. The alternative anticoagulants have properties which overcome these shortcomings and prospective clinical trial data are presented supporting the current and future use of these agents in place of the standard anticoagulants.

[Experimental study of dicholine succinate pharmacokinetics]

We have conducted for the first time an experimental study of pharmacokinetics of dicholine succinate (DCS) for different ways of its administration in rats The quantitative evaluation of DCS and its metabolites was performed by the radioactive isotope technique. Various parameters of DCS pharmacokinetics were estimated, including the dose dependence of drug content in the blood plasma, total bioavailability, distribution kinetics, and the main ways of DCS excretion.

[Argatroban: pharmacological properties and anaesthesiological aspects]

Argatroban is a direct, selective and reversible active site thrombin inhibitor derived from L-arginine. It is a representative of a new class of antithrombotic drugs which offer inhibition of clot-bound as well as fluid-phase thrombin. Argatroban is characterised by favourable pharmacokinetics (beta-elimination half-time approximately 40-50 min) undergoing hepatic metabolism and mainly biliary excretion. Renal impairment will not result in altered or delayed elimination. For many years, argatroban has been used in Japan and in the United States and is approved by the FDA for anticoagulation in patients with heparin-induced thrombocytopenia (HIT type II). The ease of monitoring with the activated partial thromboplastin time, lack of induction of antibodies and adequate safety in renal failure patients, make this drug a favourable mode therapy in comparison with other anticoagulants such as lepirudin or heparinoids. Since June 2005 argatroban has been approved in Germany for the treatment of patients with HIT type II. The main characteristics of the drug with special considerations for anaesthesiologists and intensive care physicians are presented in this review.

Prolonged half-life of argatroban in patients with renal dysfunction and antiphospholipid antibody syndrome being treated for heparin-induced thrombocytopenia

Argatroban is a direct thrombin inhibitor approved for the treatment of heparin-induced thrombocytopenia (HIT) type II. Argatroban is predominantly metabolized in the liver. It is widely believed that no dosage adjustment is required in patients with renal insufficiency, making it a preferred agent in patients on renal replacement therapy (Reddy and Grossman, Ann Pharm 2005;39:1601-1605). The elimination half-life of argatroban is approximately 50 min. Lupus anticoagulants can cause baseline elevation of the PTT and hence it is difficult to monitor the effects of anticoagulants such as heparin, lepirudin, or argatroban in patients with antiphospholipid antibody syndrome. Heparin levels may be used as an alternative for heparin monitoring but plasma levels of argatroban are not commercially available. A chromogenic antifactor IIa assay could be useful for monitoring argatroban in the presence of a lupus anticoagulant, but it is not widely available at present. We report a patient with end-stage renal disease, maintained on peritoneal dialysis with HIT, who demonstrated a markedly prolonged half-life when treated with argatroban despite the discontinuation of therapy. This case also demonstrates the lack of guidelines for the monitoring of argatroban therapy in the presence of an underlying lupus anticoagulant.

Effect of renal function on argatroban therapy in heparin-induced thrombocytopenia

BACKGROUND

Argatroban is considered to be an alternative anticoagulant of choice in patients with heparin-induced thrombocytopenia (HIT) and renal impairment. The recommended initial dose in HIT is 2 microg/kg/min (0.5 microg/kg/min in hepatic impairment), adjusted to achieve activated partial thromboplastin times (aPTTs) 1.5-3 times baseline. Although argatroban is predominantly hepatically metabolized with minimal renal clearance, recent limited data have suggested that a patient's renal function should also be considered when initiating argatroban therapy for HIT. We retrospectively evaluated the effect of renal function on argatroban therapy in HIT patients with normal hepatic function, with the goal of refining dosing guidance, if needed.

METHODS

From case records of previous prospective studies of argatroban in clinically diagnosed HIT, we identified patients who had baseline laboratory data on liver and renal function. Individuals with abnormal hepatic function (serum total bilirubin > 1.5 mg/dl or ALT or AST > 100 U/l) were excluded. Patients were stratified according to their estimated creatinine clearance (CL(cr)): normal or mild impairment (CL(cr) > 60 ml/min), moderate impairment (CL(cr) 30-60 ml/min), or severe impairment (CL(cr) < 30 ml/min). Argatroban doses, aPTTs, and clinical outcomes were summarized overall and by group. By-patient relationships between CL(cr) and dose or aPTT during therapy were explored using regression analyses.

RESULTS

The analysis population included 260 patients with normal to mild (n = 144), moderate (n = 80), or severe (n = 36) renal impairment. Argatroban was initiated at a mean infusion dose of 1.8 +/- 0.7 microg/kg/min (overall), titrated to achieve aPTTs 1.5-3 times baseline. Among renal function groups, no significant differences occurred in argatroban dose during therapy (overall value, 1.9 +/- 1.1 microg/kg/min), duration of therapy (7 +/- 6 days), or aPTTs (63 +/- 17 s). Regression analyses showed a 0.1 microg/kg/min increase in dose (r2 = 0.02) for each 30 ml/min increase in CL(cr). Within a 37 day follow-up, 46 (17.7%) patients died, most often when severe renal impairment was present. New thrombosis (11.5% overall) and major bleeding (5.0%) did not differ among groups.

CONCLUSIONS

In this large cohort of HIT patients with normal hepatic function and varying levels of renal function, argatroban administered in accordance with current recommendations provided adequate levels of anticoagulation and was well tolerated. Altered renal function did not clinically significantly affect argatroban doses, aPTT responses, or rates of thrombosis or bleeding. These findings further support argatroban as an alternative anticoagulant of choice, without need for initial dose adjustment, in most patients with HIT and renal impairment.

CONDENSED ABSTRACT

We retrospectively evaluated the effect of renal function on argatroban therapy in HIT patients with normal hepatic function, with the goal of refining current dosing guidance, if needed. From previous prospective studies of argatroban in HIT, we identified 260 patients with clinically diagnosed HIT, normal hepatic function, and varying degrees of renal function. Among patients whose renal function was normal or mildly impaired (estimated creatinine clearance, CL(cr) > 60 ml/min); moderately impaired (CL(cr) 30-60 ml/min), or severely impaired (CL(cr) < 30 ml/min), no significant differences occurred in the argatroban dose, aPTT response, duration of therapy, or rates of thrombosis or major bleeding. By regression analysis, there was a clinically insignificant 0.1 microg/kg/min increase in dose for each 30 ml/min increase in CL(cr). Overall, argatroban administered in accordance with current recommendations provided adequate levels of anticoagulation and was well tolerated, supporting its use as an alternative anticoagulant of choice, without need for initial dose adjustment, in most patients with HIT and renal impairment.

Pharmacokinetics of cycloalliin, an organosulfur compound found in garlic and onion, in rats

Cycloalliin, an organosulfur compound found in garlic and onion, has been reported to exert several biological activities and also to remain stable during storage and processing. In this study, we investigated the pharmacokinetics of cycloalliin in rats after intravenous or oral administration. Cycloalliin and its metabolite, (3R,5S)-5-methyl-1,4-thiazane-3-carboxylic acid, in plasma, urine, feces, and organs was determined by a validated liquid chromatography-mass spectrometry method. When administered intravenously at 50 mg/kg, cycloalliin was rapidly eliminated from blood and excreted into urine, and its total recovery in urine was 97.8% +/- 1.3% in 48 h. After oral administration, cycloalliin appeared rapidly in plasma, with a tmax of 0.47 +/- 0.03 h at 25 mg/kg and 0.67 +/- 0.14 h at 50 mg/kg. Orally administered cycloalliin was distributed in heart, lung, liver, spleen, and especially kidney. The Cmax and AUC0-inf values of cycloalliin at 50 mg/kg were approximately 5 times those at 25 mg/kg. When administered orally at 50 mg/kg, cycloalliin was excreted into urine (17.6% +/- 4.2%) but not feces. However, the total fecal excretion of (3R,5S)-5-methyl-1,4-thiazane-3-carboxylic acid was 67.3% +/- 5.9% (value corrected for cycloalliin equivalents). In addition, no (3R,5S)-5-methyl-1,4-thiazane-3-carboxylic acid was detected in plasma (<0.1 microg/mL), and negligible amounts (1.0% +/- 0.3%) were excreted into urine. In in vitro experiments, cycloalliin was reduced to (3R,5S)-5-methyl-1,4-thiazane-3-carboxylic acid during anaerobic incubation with cecal contents of rats. These data indicated that the low bioavailability (3.73% and 9.65% at 25 and 50 mg/kg, respectively) of cycloalliin was due mainly to reduction to (3R,5S)-5-methyl-1,4-thiazane-3-carboxylic acid by the intestinal flora and also poor absorption in the upper gastrointestinal tract. These findings are helpful for understanding the biological effects of cycloalliin.

Assessing nonlinearity in compartment models via the relative curvature measure

In pharmacokinetics, compartment models often play an important role in the description of the concentration of the drug in the blood over time after its administration to an individual. Statistical inference in these models can be conducted based on a linear approximation with respect to the parameter related to pharmacokinetic indices, in the same way that the usual nonlinear regression models are dealt with. Therefore, it is necessary to assess the degree of nonlinearity in a compartment model and to evaluate its effect on the linear approximation. The relative curvature measure that enables us to assess the intrinsic and parameter-effects (PE) nonlinearity can be used, but in practice it has not been applied to compartment models in pharmacokinetics. One reason may be that the relative curvature measure cannot be directly applied to blood drug concentration data that exhibit heteroscedasticity. Therefore, the relative curvature measure including the heteroscedastic variance function was utilized to assess the nonlinearity in the compartment models, and in particular, the influences of some of the reparameterizations that are empirically used in fitting the compartment models were examined. Several examples showed that the reparameterized compartment model had less PE nonlinearity than the original compartment model, but that several reparameterizations could increase the PE nonlinearity. In addition, by means of a simulation experiment with heteroscedastic blood drug concentration data, the accuracy, and precision of the relative curvature measure with the heteroscedastic variance function were evaluated and compared with those of the original relative curvature measure. The results showed that the relative curvature measure with the variance function was not affected by heteroscedastic blood drug concentration data and could be utilized for the assessment of the nonlinearity in compartment models.

Cardiac surgery in a patient with heparin-induced thrombocytopenia--cautions with use of the direct thrombin inhibitor, argatroban

Heparin-induced thrombocytopenia (HIT) is being recognized in an increasing number of patients referred for cardiac surgery, as a result of previous exposure to heparin. We present a case of a patient with HIT scheduled for aortic valve replacement and coronary bypass graft surgery, who was managed with the direct thrombin inhibitor, argatroban for anticoagulation during cardiopulmonary bypass (CPB). The patient sustained continued bleeding in excess of the acknowledged half-life of the drug and required a substantial number of blood products to restore coagulation following CPB. Pertinent reports using argatroban for cardiac surgery with CPB are reviewed in the context of the present case report. The pharmacologic basis, cost analysis and resource utilization of heparin substitutes are discussed for the patient with HIT requiring CPB.

Argatroban, a direct thrombin inhibitor for heparin-induced thrombocytopaenia: present and future perspectives

Heparin remains the most commonly used anticoagulant in the treatment of patients with acute vascular syndromes, including myocardial infarction, unstable angina and ischaemic stroke. However, heparin therapy is not always associated with a significant improvement of clinical outcomes, is linked with enhanced bleeding risk and can occasionally provoke the development of heparin-induced thrombocytopaenia, the most devastating complication of conventional therapy with unfractioned heparin. Understanding the key role of thrombin in clot formation and platelet activation has stimulated the development of a new class of drugs - direct thrombin inhibitors. The direct thrombin inhibitor argatroban has been known for decades. Similar to the unfractioned heparin, argatroban requires intravenous administration and activated partial prothrombin time-dependent dose adjustment; however, this pharmacological agent has a relatively short half-life that broadens its safety margins, as well as its low antigenic potential due to the small molecular weight of the compound. The efficacy of argatroban has been demonstrated among patients with acute coronary syndromes and stroke. However, this drug is currently approved by the FDA only for the treatment of patients with heparin-induced thrombocytopaenia. Indeed, in such patients, argatroban significantly improves clinical outcomes, and is associated with reduced mortality. Further clinical studies are needed to present more clinical evidence necessary to broad the indication spectrum of this agent.

Argatroban and Lepirudin Requirements in a 6-Year-Old Patient with Heparin-Induced Thrombocytopenia

A 6-year-old girl required argatroban at dosages up to 18 mug/kg/minute for treatment of heparin-induced thrombocytopenia (HIT) type 2; however, her activated partial thromboplastin time (aPTT) values remained subtherapeutic. Treatment was converted to lepirudin, which resulted in therapeutic aPTT values, and later to long-term warfarin therapy; no further thromboembolic incidents occurred. The reporting of cases of HIT in prepubertal patients has generally been scarce. Argatroban and lepirudin dosing and pharmacokinetics have not yet been established for young children. The argatroban dosage for this patient exceeded the upper limit of the dose range for adults. Several possible explanations for why argatroban did not illustrate typical first-order pharmacokinetics in this patient are discussed, and the pharmacokinetics and pharmacodynamics of argatroban are compared with those of lepirudin, with special consideration given to the pediatric population.

Discovery of 3-OH-3-methylpipecolic hydroxamates: Potent orally active inhibitors of aggrecanase and MMP-13

A series of 3-hydroxy-3-methylpipecolic hydroxamate inhibitors of MMP-13 and aggrecanase was designed based on the observation of increased aggrecanase activity with substitution at the 3-position of the piperidine ring. Potency versus aggrecanase was optimized by modification of the benzyloxyarylsulfonamide group that binds in the S1' pocket. These compounds also possess markedly improved bioavailability and lower metabolic clearance compared to analogous 3,3-dimethyl-5-hydroxypipecolic hydroxamates. These improvements are attributed to lowered lipophilicity proximal to the metabolically labile hydroxamic acid. Synthesis, structure activity relationships, and in vivo efficacy data are described.

Carotid tissue levels of argatroban after direct local delivery during carotid endarterectomy to prevent perioperative cerebral embolism

OBJECTIVE

Argatroban is a synthetic direct thrombin inhibitor. We applied argatroban locally during carotid endarterectomy to prevent local mural thrombus formation. Although local delivery of argatroban is expected to be effective for inhibition of mural clot formation, there is no report of the evaluation of its clinical effectiveness or local drug concentration in humans.

METHODS

Five mg of argatroban (0.5 mg/ml) was applied twice intraoperatively just after arteriotomy for measurement of intraplaque level of argatroban and during closure of the arteriotomy for preventing thrombus formation. After exposure of the carotid plaque to argatroban for a specified duration (0, 3, 5, or 10 min), argatroban was sufficiently washed with saline and the carotid plaque was removed for measurement of tissue concentration of argatroban. Intraplaque level of argatroban was determined by high-performance liquid chromatography. A second application was performed during closure of the arteriotomy. Argatroban was applied for 10 minutes, followed by washing with saline. Postoperative embolic cerebrovascular complications and carotid restenosis also were investigated to verify the efficacy of direct local application of argatroban.

RESULTS

Tissue levels of argatroban in the carotid plaque after 3, 5, and 10 minutes of direct application were 24.0 +/- 13.7, 31.6 +/- 20.0, and 44.0 +/- 15.1 mug/g, respectively. The concentrations at all time points were significantly elevated compared with the control, and a significant difference in concentration was observed between 3 minutes and 10 minutes. In the present study, concentration at 3 minutes was much higher than the effective tissue levels of argatroban reported in experimental studies. No patient developed postoperative cerebrovascular complications.

CONCLUSION

The results suggest that direct local application of argatroban during carotid endarterectomy for at least 3 minutes may deliver high local tissue levels. Argatroban may be effective for prevention of perioperative embolic cerebral complications during carotid endarterectomy.

A prospective comparison of three argatroban treatment regimens during hemodialysis in end-stage renal disease

BACKGROUND

We prospectively evaluated 3 treatment regimens of argatroban, a direct thrombin inhibitor, for providing adequate, safe anticoagulation in patients with end-stage renal disease (ESRD) during hemodialysis.

METHODS

In this randomized, 3-way crossover study, ESRD patients underwent hemodialysis sessions of 3- or 4-hour duration using high-flux membranes and each of 3 argatroban treatment regimens (A: 250-microg/kg bolus, with an additional 250-microg/kg bolus allowed; B: 250-microg/kg bolus followed by 2-microg/kg/min infusion; C: steady-state, 2-microg/kg/min infusion initiated 4 hours before dialysis). Pharmacodynamic effects including activated clotting times (ACTs); hemodialysis efficacy including single-pool Kt/V, urea reduction ratio (URR), and circuit flow; and safety through a 3-day follow-up were monitored. Argatroban pharmacokinetic parameters including dialytic clearance were evaluated during regimen C.

RESULTS

Thirteen patients completed 38 hemodialysis sessions (1 patient withdrew consent after 2 sessions). Mean +/- SD ACTs increased from 131 +/- 14 seconds at baseline to 153 +/- 24, 200 +/- 30, and 197 +/- 33 seconds, respectively, after 60 minutes of hemodialysis using regimens A, B, and C. Across regimens, mean Kt/Vs (1.5-1.6) and URRs (70%-73%) were comparable. No dialyzer was changed; 1 session was shortened 15 minutes because of circuit clot formation. Systemic argatroban clearance increased approximately 20% during hemodialysis, without clinically significantly affecting ACTs. Upon argatroban discontinuation, ACTs and plasma argatroban decreased concurrently (elimination half-life, 35 +/- 6 min). No thrombosis, bleeding, serious adverse events, or clinically significant changes in vital signs or routine laboratory measures occurred.

CONCLUSION

Argatroban, administered by each treatment regimen, provides safe, adequate anticoagulation to enable successful hemodialysis in ESRD patients. Argatroban dialytic clearance by high-flux membranes is clinically insignificant.

Anticoagulant use in patients with chronic renal impairment

Patients with renal failure have an increased risk of both thrombotic and bleeding complications. A number of antithrombotic drugs undergo renal clearance. Therefore, estimation of renal function is necessary when prescribing these drugs to patients with renal dysfunction. Pharmacokinetic and clinical data in patients with chronic renal impairment are limited for several anticoagulants, and adequate administration information is often absent. Dose adjustment of anticoagulants may be indicated when the creatinine clearance falls below 30 mL/min. Unfractionated heparin, argatroban, and vitamin K antagonists generally do not require dose adjustment with renal dysfunction. However, smaller doses of warfarin may be required to achieve a particular target international normalized ratio. Close monitoring of anticoagulation is recommended when argatroban or high doses of unfractionated heparin are administered in patients with severe chronic renal impairment. Low-molecular weight heparins, danaparoid sodium, hirudins, and bivalirudin all undergo renal clearance. Lower doses and closer anticoagulation monitoring may be advisable when these agents are used in patients with chronic renal failure. We recommend that fondaparinux sodium and ximelagatran (not yet licensed) be avoided in the presence of severe renal impairment and be used with caution in patients with moderate renal dysfunction. While acknowledging the lack of pharmacokinetic data, this review provides specific recommendations for the use of anticoagulants in patients with chronic renal impairment.

Pharmacokinetics and pharmacodynamics of argatroban in combination with a platelet glycoprotein IIB/IIIA receptor antagonist in patients undergoing percutaneous coronary intervention

The pharmacokinetic-pharmacodynamic (PK-PD) relationship of argatroban, administered in combination with a platelet glycoprotein IIb/IIIa receptor antagonist, was characterized in patients undergoing percutaneous coronary intervention (PCI). Plasma argatroban and activated clotting times (ACTs) were assessed periprocedurally in 152 patients administered argatroban (250- or 300-microg/kg bolus, then 15-microg/kg/min infusion) in combination with abciximab or eptifibatide during PCI. The PK and PK-PD models were developed utilizing a sequential population approach in NONMEM. Population PK estimates for clearance, central volume, and peripheral volume were 22.0 L/h, 11.0 L, and 13.0 L, respectively (coefficients of variation [CVs] </= 10%). By covariate analysis, clearance increased linearly with body weight. Plasma argatroban and ACT effect were well described using a sigmoidal E(max) model. For argatroban in combination with platelet glycoprotein IIb/IIIa receptor blockade in patients undergoing PCI, population PK parameters are consistent with values reported for argatroban in healthy subjects. A predictable relationship exists between argatroban concentration and effect in this setting.

Practical issues in the development of argatroban: a perspective

Argatroban was the very first antithrombin agent that was approved for clinical use. It represents a synthetic arginomimetic drug with multiple pharmacologic properties. Unlike other antithrombin drugs, argatroban is a reversible antithrombin agent. Furthermore, it modulates endothelial cell function and downregulates various inflammatory and thrombotic cytokines. Argatroban is an effective anticoagulant agent, which at equivalent anticoagulant levels (activated clotting time; ACT) produces a stronger anticoagulant effect in comparison to heparins and hirudins. At a comparable ACT (300 s), argatroban produces much stronger inhibition of thrombin generation as measured by F(1.2) and thrombin-antithrombin complex generation. Argatroban does not generate any neutralizing or non-neutralizing antibodies and, therefore, it does not require any dosage adjustment during the course of therapy as other thrombin inhibitors require. The pharmacological profile of argatroban is unique as this antithrombin drug not only inhibits thrombogenesis but also modulates cellular functions. Because of its broad spectral actions, argatroban will have more expanded indications.

An overview of the direct thrombin inhibitor argatroban

Argatroban is a small molecule direct thrombin inhibitor. The main attributes of this synthetic drug are its rapid onset of anti-thrombin action, rapid reversibility of its anticoagulant effect, potent inhibition of clot-bound thrombin, absence of antibody formation and no need for initial dosage adjustment in patients with renal impairment. It is eliminated by hepatic metabolism. These properties make argatroban a predictable anticoagulant with intravenous use in a routine clinical setting. Argatroban is approved in the US and Canada for both prophylaxis and treatment of thrombosis in patients with heparin-induced thrombocytopenia (HIT); and it is approved in Japan and Korea for treatment of various thrombotic disorders. Argatroban has been shown in limited trials to provide reliable anticoagulation during percutaneous coronary interventions on HIT and non-HIT patients. Preliminary reports document the feasibility of using argatroban for anticoagulation during peripheral vascular interventions, hemodialysis and as adjunct to thrombolysis for treatment of myocardial infarction. Current recommendations for argatroban monitoring are to use the activated partial thromboplastin time for low doses and the activated clotting time for high doses. The ease of monitoring argatroban, its 'turn-on/turn-off' characteristic and its consistent safety profile provide the rationale to continue studies of argatroban as an anticoagulant in clinical settings.

Effect of Renal Function on the Pharmacodynamics of Argatroban

BACKGROUND:

Argatroban is a direct thrombin inhibitor used to treat heparin-induced thrombocytopenia (HIT). Argatroban is primarily cleared by hepatic mechanisms, with only small amounts of unchanged drug cleared by the kidneys.

OBJECTIVE:

To assess the effects of renal function on argatroban dose and activated partial thromboplastin time (aPTT).

METHODS:

Patients treated with argatroban were identified and prospectively screened. Patients with liver dysfunction were excluded from the analysis. Charts and laboratory data were reviewed daily until a therapeutic aPTT was reached or argatroban was discontinued. Data points collected included age, weight, gender, admitting diagnosis, past medical history, indication for anticoagulation, indication for argatroban, initial dose, goal aPTT, titration instructions, liver function tests, serum creatinine (Scr), blood urea nitrogen, and estimated creatinine clearance (Clcr).

RESULTS:

A total of 66 patients were evaluated and 44 met criteria for inclusion. Baseline Scr was elevated at 1.5 mg/dL (0.9, 2.3; median 25th, 75th percentile), with an estimated Clcr 40 mL/min/1.73 m2 (26, 74). The median dose of argatroban to reach the predefined therapeutic range was 1 μg/kg/min (0.68, 2), with a corresponding aPTT of 60 seconds (54, 66). After univariate analysis, Clcr significantly predicted the therapeutic dose (coefficient b ± SE 0.019 ± 0.004; r2 0.35; p < 0.001). Covariates that predicted dose were the presence of HIT (coefficient b ± SE −0.61 ± 0.3; p = 0.045), history of myocardial infarction (coefficient b ± SE −0.74 ± 0.3; p = 0.02), and an indication for anticoagulation of deep-vein thrombosis/pulmonary embolism (coefficient b ± SE 0.69 ± 0.3; p = 0.03).

CONCLUSIONS:

Estimated Clcr significantly predicted the dose of argatroban needed to reach a therapeutic aPTT.

Decreased argatroban clearance unaffected by hemodialysis in anasarca

OBJECTIVE

To report the case of a patient with acute renal failure and anasarca undergoing hemodialysis who demonstrated a prolonged effect of argatroban despite having no hepatic dysfunction.

CASE SUMMARY

A 54-year-old white woman with a past medical history of St. Jude's prosthetic mitral valve placement was admitted for anasarca secondary to acute renal failure of unknown origin. In order to prevent valve thrombosis and stroke, argatroban was initiated. Despite having no hepatic dysfunction, the patient demonstrated an elevated activated partial thromboplastin time (aPTT) for a prolonged period of time, requiring a significant dose reduction. This suggested reduced clearance of argatroban. Furthermore, this prolonged effect persisted despite hemodialysis.

DISCUSSION

Patients with severe renal dysfunction eliminate argatroban at a rate similar to that in healthy volunteers, while those with hepatic disease have a marked decrease in argatroban elimination. Our patient apparently had a reduction in argatroban elimination similar to that in patients with hepatic dysfunction. The few published reports regarding the use of argatroban in patients undergoing hemodialysis generally lack any information regarding variations in plasma concentrations of argatroban, the aPTT, or the type of dialyzer used. The available data, as well as our report, suggest that dosing adjustment during hemodialysis may not be necessary in patients without associated hepatic dysfunction.

CONCLUSIONS

This report suggests that in patients who are fluid-overloaded, the anticoagulant effects of argatroban may be prolonged to a degree similar to that observed in patients with hepatic disease. Our report supports the previously published data that hemodialysis has little, if any, role in increasing argatroban elimination.

Excessive argatroban anticoagulation for heparin-induced thrombocytopenia

OBJECTIVE

To report 4 patients who became excessively anticoagulated with the recommended or lower starting doses of argatroban during treatment for heparin-induced thrombocytopenia type II (HIT-II) in a cardiothoracic intensive care unit.

CASE SUMMARY

Four patients were treated with argatroban after confirmation of HIT-II after cardiac surgery. In 3 patients, argatroban was initiated at the recommended starting dose of 2 micro g/kg/min; in 1 patient, therapy was initiated at 1 micro g/kg/min. All patients had relatively normal hepatic function. In all cases, the resulting activated partial thromboplastin time was supertherapeutic and exceeded 100 seconds in 3 patients. Additionally, argatroban clearance appeared to be prolonged upon discontinuation.

DISCUSSION

Argatroban pharmacokinetics in critically ill patients have not been investigated. Our case series demonstrates the potential over-anticoagulation that can occur in this patient population despite relatively normal hepatic function. An objective causality assessment revealed that the adverse drug event in these patients was probably caused by administration of argatroban.

CONCLUSIONS

Formal pharmacokinetic studies of argatroban are needed in critically ill patients in order to optimize therapy.

Direct thrombin inhibitors

This review deals with a newly-developed category of antithrombotic drugs - the direct thrombin inhibitors. These agents interact with thrombin and block its catalytic activity on fibrinogen, platelets and other substrates. Heparin and its derivatives (low molecular weight heparins and the active pentasaccharide) inhibit thrombin and/or other coagulation serine proteases indirectly via antithrombin, and the warfarin-type drugs interfere with the synthesis of the precursors of the coagulation serine proteases. The direct thrombin inhibitors approved for clinical use at present (lepirudin, desirudin, bivalirudin, argatroban) and another in the advanced clinical testing stage (melagatran/ximelagatran), are the subject of this review. The chemical structure; kinetics of thrombin inhibition; pharmacokinetics and clinical use of each of these is discussed.

Delayed argatroban treatment reduces edema in a rat model of intracerebral hemorrhage

BACKGROUND AND PURPOSE

Studies indicate that thrombin plays an important role in intracerebral hemorrhage (ICH)-induced edema formation. Although thrombin is produced as the blood clots, it may be bound to fibrin and only gradually released from the clot. The time window for administration of a thrombin inhibitor to reduce ICH-induced edema is unknown. Whether this time window extends beyond the period when a thrombin inhibitor might exacerbate rebleeding is also unknown.

METHODS

This study examines (1) whether argatroban, an inhibitor of both free and fibrin-bound thrombin, can reduce edema formation after intracerebral infusion of 100 micro L of blood in the rat; (2) the therapeutic time window for argatroban; and (3) whether argatroban promotes rebleeding in a model in which ICH was induced by intracerebral injection of collagenase.

RESULTS

Intracerebral infusion of blood caused a marked increase in perihematomal water content. Intracerebral injection of argatroban 3 hours after ICH caused a significant reduction in edema measured at 48 hours (80.9+/-1.0% versus 82.6+/-0.8%; P<0.01). The systemic administration of high-dose argatroban (0.9 mg/h) starting 6 hours after ICH also significantly reduced edema (80.3+/-1.1% versus 82.0+/-1.3% in vehicle controls; P<0.05). There was no protection when the onset of argatroban administration was delayed to 24 hours after ICH or if a lower dose of argatroban (0.3 mg/h) was used. Argatroban did not increase collagenase-induced hematoma volume when given into the clot after 3 hours or given systemically at 6 hours.

CONCLUSIONS

Our data suggest that argatroban may be an effective therapy for ICH-induced edema.

Lack of pharmacokinetic interactions between argatroban and warfarin

The potential for pharmacokinetic interactions between argatroban and warfarin was studied. In a randomized, crossover study, healthy volunteers participated in three treatment periods, each separated by a nine-day washout interval. Drug regimens consisted of a single oral 7.5-mg dose of warfarin, intravenous argatroban infused at a rate of 1.25 micrograms/kg/min for 100 hours, or both. Blood samples were collected at intervals up to 104 hours to determine clearance (CL) and the apparent first-order elimination rate constant (kel) for argatroban and the area under the concentration-versus-time curve (AUC) and maximum concentration (Cmax) for R- and S-warfarin. An interaction was defined as a > 25% difference in the magnitude of the pharmacokinetic values between administration of one drug alone and coadministration with the other agent. Twelve adult subjects were enrolled. The mean CL and lel for argatroban administered alone differed by < 7% from the mean values when the two drugs were coadministered. When warfarin was administered alone, the mean Cmax and AUC of R- and S-warfarin differed from the mean values when the two drugs were coadministered by < 10%. Prothrombin time was prolonged comparably when argatroban was administered alone and with warfarin. No deaths or serious adverse events were reported. No significant pharmacokinetic interactions were detected between i.v. argatroban 1.25 micrograms/kg/min and a single 7.5-mg oral dose of warfarin. Argatroban was well tolerated when administered alone or with warfarin.

Investigation of the interaction between argatroban and acetaminophen, lidocaine, or digoxin

The potential pharmacokinetic interactions between argatroban and acetaminophen, lidocaine, or digoxin were examined. Three randomized crossover studies were conducted. In the first study, 11 subjects completed three sessions (with a five-day washout period between sessions), receiving two 500-mg acetaminophen caplets at 0, 6, 12, 18, and 24 hours; i.v. argatroban 1.5 micrograms/kg/min from hours 12 to 30; or a combination of both. In the second study, 12 subjects completed three sessions (with a five-day washout period between sessions), receiving lidocaine hydrochloride injection 2 mg/kg/hr for 16 hours (after receiving a loading dose of 1.5 mg/kg over 10 minutes), i.v. argatroban 1.5 micrograms/kg/min for 16 hours, or a combination of both. In the third study, 12 subjects completed two sessions (with a seven-day washout period between sessions), receiving oral digoxin 0.375 mg/day for 15 days and either i.v. placebo or argatroban 2 micrograms/kg/min on days 11 through 15. Primary pharmacokinetic values in each study included area under the drug concentration versus time curve and steady-state concentrations of argatroban and the concomitantly administered drug. Lack of a pharmacokinetic interaction (individually defined for each study) was demonstrated in each study. Argatroban, regardless of acetaminophen or lidocaine administration, prolonged activated partial thromboplastin time values approximately 1.6-1.8 times the baseline values. No deaths, unexpected adverse events, or clinically significant changes in safety laboratory values occurred. No pharmacokinetic interaction was detected between argatroban and acetaminophen, lidocaine, or digoxin. Argatroban is well tolerated during coadministration with these drugs. In practice, argatroban coadministered with these frequently prescribed drugs should require no dosage adjustments.

Argatroban

Antithrombotic and antiplatelet therapies are the cornerstones of management of cardiovascular disorders today. Due to the safety and efficacy limitations of the classic antithrombotic, unfractionated heparin, considerable effort has been directed at developing novel anticoagulants. Direct thrombin inhibitors as a class of drugs offer inhibition of clot-bound as well as fluid-phase thrombin and a more predictable anticoagulant response. Specifically, argatroban, a synthetic small molecule direct thrombin inhibitor, selectively inhibits the catalytic site of thrombin in a reversible manner. Overall, argatroban's short half-life, ease of monitoring with an activated partial thromboplastin time, and safety in renal failure patients make this drug the preferable mode therapy for prevention of thrombosis in heparin-induced thrombocytopenia. The role of adjunctive argatroban therapy in acute coronary syndromes and during percutaneous coronary intervention is currently being studied.

A synopsis of the clinical uses of argatroban

Argatroban, a direct thrombin inhibitor, has been used in Japan since the early 1980's and was recently approved for use in the United States for patients with heparin-induced thrombocytopenia. However, its use has been studied in other clinical settings including, myocardial infarction, percutaneous coronary intervention and cerebral thrombosis. The doses used in the different clinical situations vary, but argatroban offers the advantage of not requiring renal adjustment. Because of its small molecular weight, argatroban has the ability to inhibit both clot bound and soluble thrombin. This paper provides a comprehensive review of both indicated and off label uses of argatroban. Pharmacology, pharmacokinetics, adverse events and drug interactions with argatroban are also discussed.

Argatroban

Argatroban is a direct thrombin inhibitor synthesised to bind to the catalytic site of the thrombin molecule. It binds rapidly and reversibly to both clot-bound and soluble thrombin. The relatively short elimination half-life of argatroban (39 to 51 minutes) and its reversible binding allow rapid achievement of therapeutic effect on initiation of therapy and rapid restoration of normal haemostasis upon cessation of therapy. Argatroban produces a predictable dose response that is well correlated with changes in anticoagulant parameters. Argatroban, given to patients with heparin-induced thrombocytopenia (HIT) and heparin-induced thrombocytopenia with thrombosis (HITTS) in a large scale, nonrandomised, prospective trial, reduced a combined end-point of morbidity and mortality when compared with historical controls. Argatroban was well tolerated in clinical trials of patients with HIT and caused no increase in bleeding risk compared with historical controls.

Argatroban for prevention and treatment of thromboembolism in heparin-induced thrombocytopenia

OBJECTIVE

To renew the pharmacology, pharmacokinetics, efficacy adverse events, and cost of argatroban in the prevention and treatment of thromboembolism in patients with heparin-induced thrombocytopenia (HIT).

DATA SOURCES

A MEDLINE search (1980 to August 2000) of English-language literature was conducted using the search term argatroban to identify pertinent case reports, clinical trials, abstracts, and review articles. Additional reports were identified from the reference lists compiled in the literature reviewed, as well as from the manufacturer.

DATA SYNTHESIS

Argatroban is a synthetic direct thrombin inhibitor indicated for parenteral use in the prevention and treatment of thromboembolism in patients with HIT. Its elimination half-life is approximately 40-50 minutes, and it is primarily eliminated by hepatic metabolism and biliary secretion. Compared with historical controls, argatroban-treated patients with HIT or HIT with thrombosis (HITTS) experienced lower rates of the composite end point of death, amputation, and new thrombosis. Dosing is initiated at 2 microg/kg/min and adjusted to maintain the activated partial thromboplastin time at 1.5-3 times the patient's baseline. In Japan, argatroban is approved for use in acute ischemic stroke and chronic peripheral occlusive disease. It has also been used as an alternative to unfractionated heparin (UFH) in patients with a history of HIT or HITTS undergoing percutaneous coronary intervention and other procedures. Additionally, argatroban has been compared with UFH in patients with acute myocardial infarction who were receiving thrombolytic therapy. Hemorrhage is the primary adverse event associated with argatroban. Argatroban increases the prothrombin time, making assessment of the intensity of warfarin therapy during concurrent administration more complex.

CONCLUSIONS

The use of argatroban in patients with HIT and HITTS is associated with improvement in clinical outcomes compared with historical controls. Argatroban offers several practical advantages over other available agents with respect to dosing, monitoring, reversibility of effect with discontinuation of the drug, and cost.

Argatroban and alteplase in patients with acute myocardial infarction: the ARGAMI Study

ARGAMI was designed to assess safety and efficacy of argatroban compared with heparin as adjunctive treatment to alteplase in the treatment of patients with acute myocardial infarction. ARGAMI consisted of an open-dose finding study (35 patients) followed by a placebo-controlled study with double dummy technique and 2:1 (argatroban:heparin) randomization. An argatroban dosage of 100 microg/kg bolus plus 3 microg/kg/min infusion for 72 hours was selected for the randomized study in which 82 patients were allocated to argatroban and 45 to heparin (5000 U intravenous bolus, 1000 U/h infusion). Patency of the infarct-related artery (Thrombolysis in Myocardial Infarction [TIMI] grade 2 or 3 flow) after 90 minutes was obtained in 62 patients (76%) allocated to argatroban versus 37 patients (82%) allocated to heparin (p=ns). Angiograms after 24 hours and 5 to 10 days showed low reocclusion rates in both groups. Bleeding complications were observed in 16 patients allocated to argatroban (19.5%) and in 9 patients allocated to heparin (20.0%). One patient allocated to heparin suffered from hemorrhage stroke. Argatroban, given as adjunctive treatment to alteplase, is tolerated well in patients with acute myocardial infarction. Safety and efficacy of the combination alteplase and argatroban (with this dose regimen) are similar to those of alteplase and heparin.

Anticoagulant activity and pharmacokinetic properties of a sub-cutaneously administered mixed micellar formulation of argatroban in experimental animals

We have studied the anticoagulant properties of a novel mixed micellar formulation containing 14 mg/ml argatroban administered by the sub-cutaneous (s.c.) route to rats, rabbits, dogs and primates. Blood samples were taken at various times post-treatment for the determination of the thrombin time (TT), Ecarin clotting time (ECT) and the activated partial thromboplastin time (aPTT). Plasma levels of argatroban were determined in the dog and primate. Mixed micelles alone (0.15 M sodium glycocholate and 0.15 M egg lecithin) were without effect on the clotting parameters. The mixed micellar formulation of argatroban dose-dependently increased all three clotting parameters in the rat (1-4 mg/kg), the rabbit (1 and 2 mg/kg), the dog (1 and 2 mg/kg) and the primate (0.25 and 0.5 mg/kg). In each case the TT was the most sensitive parameter, followed by the ECT and the aPTT. The duration of action of argatroban in each species was dose dependent and varied from 3 h in the rat to 6 h in the dog. In the latter, the mixed micelle formulation had a significantly increased plasma half-life and mean residence time without affecting the overall area under the curve. The increases in the clotting time were strongly correlated with the plasma levels of argatroban and were linear across the range of concentrations obtained in the dog and the primate, although the aPTT plasma concentration response curve was very flat. Species differences were noted between the increase in clotting time for a given plasma concentration, with the primate being more sensitive than the dog (e.g. 4.7 times more so in terms of the ECT). Thus, a mixed micellar formulation of argatroban, which markedly enhances its solubility, could be useful as a potential anticoagulant for sub-cutaneous administration.

Comparison of anticoagulant effects and safety of argatroban and heparin in healthy subjects

STUDY OBJECTIVE

To evaluate and compare the relationship between dosage and coagulation parameters, as well as safety profiles, of ascending bolus and infusion dosages of argatroban versus heparin in three phase I studies.

DESIGN

Two randomized, double-blind studies compared argatroban and heparin, and one open-label, dose-escalation study further evaluated argatroban.

SETTING

University teaching hospital clinical research unit.

PATIENTS

Healthy men (aged 22-62 yrs).

INTERVENTION

In the first study, 36 subjects received an argatroban 30-, 60-, 120-, or 240-microg/kg bolus, or a heparin 30-, 60-, 120-, or 240-U/kg bolus for three subjects, then amended to 15, 30, 60, or 120 U/kg. In the second study, 37 subjects received argatroban 1.25, 2.5, 5, or 10 microg/kg/minute with or without a 250-microg/kg bolus, or heparin 0.15, 0.20, 0.25, or 0.30 U/kg/minute with or without a 125-U/kg bolus. In the third study (open-label), nine subjects received an argatroban 250-microg/kg bolus plus an infusion of 15, 20, 30, and 40 microg/kg/minute.

MEASUREMENTS AND MAIN RESULTS

When administered as a bolus dose in the first study, argatroban and heparin both produced dose-related increases in activated clotting time (ACT) and activated partial thromboplastin time (aPTT) within 10 minutes of administration. Dissipation of anticoagulant effect was approximately 4-fold faster for argatroban than for heparin. When administered by infusion with or without a bolus in the second study, argatroban, but not heparin, produced predictable dose-related increases in ACT and aPTT that were generally consistent across both effect measures and modes of administration. Effect steady state was attained by five or more subjects per dosing group receiving argatroban (5-9) but typically two or fewer subjects per group receiving heparin (0-7). Furthermore, upon cessation of infusion, anticoagulant effects dissipated faster for argatroban (effect half-life 18-41 min) than for heparin (effect half-life 23-134 min). When argatroban was infused without a bolus, peak and effect steady-state values for ACT and aPTT generally were attained within 1-3 hours. Data from the second and third studies show that for argatroban dosages up to 40 microg/kg/minute, plasma drug concentrations attained at 4 hours of infusion increased linearly with dose, and weight-adjusted plasma clearance was dose independent. In all studies, argatroban and heparin were well tolerated.

CONCLUSION

Anticoagulation was more predictable with argatroban than with heparin as measured by ACT and aPTT, with comparable safety profiles.

Pharmacokinetics of argatroban in primates: evidence on endogenous uptake

BACKGROUND

Antithrombin agent, argatroban, is currently undergoing several clinical trials for cardiovascular indications. Because of its solubility, this drug is usually administered via an intravenous bolus followed by infusion. The purpose of this study was to determine the pharmacokinetics of argatroban after intravenous bolus injection in primates.

METHODS

Parallel in vitro studies in primate whole blood were carried out to simulate a one-compartment system. Argatroban (range 1.0-7.5 mg/kg) was administered to four groups of primates and blood samples were drawn at various time periods. Argatroban measurements were made in plasma using functional (aPTT, Heptest, TT) and HPLC methods.

RESULTS

In vitro, argatroban primarily distributed in the plasma in proportionate amounts. Relative uptake of argatroban to the blood cells (leukocytes and erythrocytes) was minimum. However, in vivo, argatroban followed a complex pharmacokinetics. Within 5 min after the bolus administration, only <20% of argatroban was recovered. The recovered amount was proportionate to the dosage and followed the expected kinetics with a half-life of <20 min. Simultaneous quantitation of M1-metabolite of argatroban revealed only a fraction of recovered argatroban (approximately 25%) converted into M1 in these experimental settings. Results obtained from the functional and absolute methods correlated well. HPLC profile did not reveal the presence of any other metabolite(s).

CONCLUSIONS

These observations suggest that argatroban may be endogenously taken up by the vascular or other sites and may exhibit a complex kinetics. In acute settings, the metabolic transformation of argatroban to M1 is relatively low. To further clarify the pharmacokinetics/pharmacodynamics of this drug, additional studies are warranted.

Estimating data transformations in nonlinear mixed effects models

A routine practice in the analysis of repeated measurement data is to represent individual responses by a mixed effects model on some transformed scale. For example, for pharmacokinetic, growth, and other data, both the response and the regression model are typically transformed to achieve approximate within-individual normality and constant variance on the new scale; however, the choice of transformation is often made subjectively or by default, with adoption of a standard choice such as the log. We propose a mixed effects framework based on the transform-both-sides model, where the transformation is represented by a monotone parametric function and is estimated from the data. For this model, we describe a practical fitting strategy based on approximation of the marginal likelihood. Inference is complicated by the fact that estimation of the transformation requires modification of the usual standard errors for estimators of fixed effects; however, we show that, under conditions relevant to common applications, this complication is asymptotically negligible, allowing straightforward implementation via standard software.

The pharmacokinetics and pharmacodynamics of argatroban: effects of age, gender, and hepatic or renal dysfunction

STUDY OBJECTIVE

To determine the pharmacokinetics and pharmacodynamics of argatroban in healthy volunteers and patients with hepatic or renal dysfunction.

DESIGN

Prospective, open-label study (studies 1 and 3); prospective, open-label, parallel-group study (study 2).

SETTINGS

Two research centers and an inpatient clinic.

SUBJECTS

Study 1, healthy volunteers; study 2, healthy volunteers and volunteers with hepatic disease; study 3, volunteers with normal to severely impaired renal function assigned to one of four groups based on creatinine clearance.

INTERVENTION

Study 1, argatroban 125-microg/kg bolus followed by 4-hour continuous infusion of 2.5 microg/kg/minute; study 2, 4-hour infusion of 2.5 microg/kg/minute (1.25 microg/kg/minute in one patient with hepatic impairment); study 3, 5-microg/kg/minute continuous infusion over 4 hours.

MEASUREMENTS AND MAIN RESULTS

Blood samples were obtained to assess plasma argatroban concentration, plasma activated partial thromboplastin time (aPTT), and whole blood activated clotting time (ACT). Study 1: the pharmacokinetic profile was well described by a two-compartment model with first-order elimination; effect response and plasma argatroban concentrations were well correlated. Mean +/- SD clearance, steady-state volume of distribution, and half-life values (40 healthy volunteers) were 4.7 +/- 1.1 ml/minute/kg, 179.5 +/- 33.0 ml/kg, and 46.2 +/- 10.2 minutes, respectively. The only effect of age or gender was the approximately 20% lower clearance in elderly men versus elderly women, which did not translate to clinically or statistically significant differences in pharmacodynamic response. Study 2: in patients with hepatic impairment, area under the concentration versus time curve (AUC) from time zero (t0) to last measurable concentration, AUC from t0 to infinity, maximum concentration, and half-life of argatroban were increased approximately 2- to 3-fold; clearance was one-fourth that of healthy volunteers. For aPTT and ACT, AUC over time for mean effect and mean maximum effect was higher in these volunteers. Study 3: no significant differences were detected. All four groups had predictable response profiles over time.

CONCLUSION

Argatroban should be easy to monitor and control, with little potential for underdosing or overdosing, regardless of age, gender, or renal function. Dosing precautions are recommended, however, in patients with hepatic dysfunction.

Simultaneous monitoring of argatroban and its major metabolite using an HPLC method: potential clinical applications

Argatroban is a peptidomimetic inhibitor of thrombin that is currently undergoing extensive clinical trials as a heparin substitute for thrombotic complications. Argatroban is readily metabolized into a major derivative, M1, that has pharmacological characteristics distinct from its parent compound. The currently available clot-based assays measure the cumulative anticoagulant effect of argatroban and its metabolite(s). Available HPLC methods do not differentiate between argatroban and M1-metabolite. A modified method was developed to simultaneouly quantitate M1-metabolite and argatroban in biological fluids. Initial validation studies for the method included clinical trials of argatroban in patients with heparin-induced thrombocytopenia, (ARG 911 Study) and coronary interventional procedures (ARG 310 Study). Plasma samples were extracted with acetonitrile and reconstituted in a mobile phase. Calibration curves were prepared by running known standards of argatroban and M1-metabolite in normal human plasma. Ultraviolet detection was made at 320 nm. The retention times for argatroban and M1-metabolite peaks were found to be 10.5 +/- 0.3 minutes and 3.9 +/- 0.1 minutes, respectively. The extraction efficiency was > 95% (r2 = 0.99). In heparin-induced thrombocytopenia patients with major bleeding complications (n = 30), the relative increase in M1-metabolite compared to argatroban varied widely (two- to eight-fold). The mean concentration of argatroban during the steady infusion period was found to be 0.7 +/- 0.35 microgram/mL, and for M1-metabolite, it was 5.5 +/- 2.8 micrograms/mL. Proportionate results were not seen when higher dosages of argatroban were administered (coronary angioplasty studies). Argatroban and M1-metabolite levels also compared well with the results in global clotting assays. Owing to the simultaneous quantitation of argatroban and M1-metabolite, this method provides a rapid assessment of the pharmacokinetics and pharmacodynamics of argatroban. The differential quantitation may be useful in the assessment of relative metabolic turnover of argatroban that can be related to the hepatic and renal functions in a given patient.

Heparin induced thrombocytopenia: diagnosis and contemporary antithrombin management

Heparin-induced thrombocytopenia (HIT) may be complicated by severe thrombotic complications and death. Currently no specific laboratory test is available to make the diagnosis. When HIT is clinically suspected, heparin should be discontinued immediately. While no specific therapy for HIT exists, there is increasing evidence that acute antithrombin therapy may significantly reduce morbidity and mortality. Among several agents, the direct antithrombins, such as r-hirudin and argatroban, look the most promising for acute treatment.

SPD 502: a water-soluble and in vivo long-lasting AMPA antagonist with neuroprotective activity

Accumulating preclinical data suggest that compounds that block the excitatory effect of glutamate on excitatory amino acid receptors may have neuroprotective effects and utility for the treatment of neurodegeneration after brain ischemia. In the present study, the in vitro and in vivo pharmacological properties of the novel glutamate antagonist SPD 502 [8-methyl-5(4-(N,N-dimethylsulfamoyl)phenyl)-6,7, 8,9,-tetrahydro-1H-pyrrolo[3,2-h]-isoquinoline-2, 3-dione-3-O-(4-hydroxybutyric acid-2-yl)oxime] are described. In binding studies, SPD 502 was shown to display selectivity for the [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-binding site (IC50 = 0.043 microM) compared with the [3H]kainate- (IC50 = 81 microM), [3H]cis-4-phosphonomethyl-2-piperidine carboxylic acid-(CGS 19755), and [3H]glycine-binding sites (IC50 > 30 microM) in rat cortical membranes. In an in vitro functional assay, SPD 502 blocked the AMPA-induced release of [3H]gamma-aminobutyric acid from cultured mouse cortical neurons in a competitive manner with an IC50 value of 0.23 microM. Furthermore, SPD 502 potently and selectively inhibited AMPA-induced currents in cortical neurons with an IC50 value of 0.15 microM. In in vivo electrophysiology, SPD 502 blocked AMPA-evoked spike activity in rat hippocampus after i.v. administration with an ED50 value of 6.1 mg/kg and with a duration of action of more than 1 h. Furthermore, SPD 502 increased the seizure threshold for electroshock-induced tonic seizures in mice at i.v doses of 40 mg/kg and higher. In the two-vessel occlusion model of transient forebrain ischemia in gerbils, SPD 502 (10 mg/kg bolus injection followed by a 10 mg/kg/h infusion for 2 h) resulted in a highly significant protection against the ischemia-induced damage in the hippocampal CA1 pyramidal neurons.

Assessment of the potential pharmacokinetic and pharmacodynamic interactions between erythromycin and argatroban

Argatroban, a direct thrombin inhibitor, is metabolized in vitro by CYP3A4/5 and therefore may be susceptible to clinically relevant CYP3A drug interactions. The effect of erythromycin, a potent CYP3A4/5 inhibitor, on the pharmacokinetics and pharmacodynamics of argatroban was evaluated in 14 healthy male volunteers in an open-label, crossover study with a 5-day washout between regimens. Argatroban 1 microgram/kg/min was infused alone for 5 hours (regimen A) and again on day 6 of a 7-day oral regimen of 500 mg erythromycin four times daily (regimen B). Serial blood samples for the determination of activated partial thromboplastin time (aPTT) and argatroban concentrations were collected for up to 48 hours following infusion. Mean values for argatroban area under the concentration-time curves (AUC0-inf), maximum concentration (Cmax), and half-life (t1/2) were similar between regimens. Mean aPTT values were not affected significantly by the concomitant administration of argatroban and erythromycin compared to argatroban alone. No serious adverse events or bleeding episodes occurred during the study. These results suggest that oxidative metabolism by CYP3A4/5 is unlikely to be an important in vivo elimination pathway for argatroban. Therefore, coadministration of CYP3A4/5 inhibitors should not require a modification in the dosage of argatroban.

Effects of locally administered argatroban on restenosis after balloon angioplasty: experimental and clinical study

1. This study was undertaken to evaluate the preventive effects of locally administered argatroban, a competitive inhibitor of thrombin-induced platelet activation, on restenosis after balloon angioplasty. 2. A hydrogel-coated balloon catheter was immersed three times in argatroban/saline solution (1 mg/mL) for 60 s, inflated to a pressure of 606 kPa and left in the rabbit common carotid artery for 1 min. The same procedure was performed, without drug, as a control. The pharmacokinetics of delivered argatroban in the arterial wall were assessed using [14C]-argatroban. Platelet deposition 2 h after balloon injury was quantified by fluorescence studies using antiplatelet antibody. Vascular smooth muscle cell (VSMC) proliferation 3 days after balloon injury was assessed by immunohistochemical staining for proliferative cell nuclear antigen (PCNA). In a clinical study, we divided 50 elective patients into two groups: argatroban and control. 3. In the experimental study, the mean quantities of argatroban at 0, 2 and 6 h after deflation were 24.63, 0.49 and 0.11 nmol/g wet weight of artery, respectively. Argatroban was undetected 24 h after deflation. Two hours after deflation, argatroban-treated arteries showed less platelet adhesion than saline-treated controls. The mean number of PCNA-positive cells was 16.9 and 43.8% in the argatroban and control groups, respectively (P < 0.01). In the clinical study, the mean late gain loss was 8.2 and 27.3% in the argatroban and control groups, respectively (P < 0.05). The mean late restenosis rate was 11.1 and 41.4% in the argatroban and control groups, respectively (P < 0.05). 4. These data suggest that blood coagulation plays a significant role in VSMC proliferation after balloon injury and that locally administered argatroban using hydrogel-coated balloon catheter may prevent post-percutaneous transluminal coronary angioplasty restenosis.

Enantioselective determination of selfotel in human urine by high-performance liquid chromatography on a chiral stationary phase after derivatization with 9-fluorenylmethyl chloroformate

An analytical method for the enantioselective determination of selfotel in human urine has been developed and validated. The method is based on high-performance liquid chromatography and utilizes CGS 20005 (a selfotel analog) as the internal standard. Urine samples were derivatized in situ with o-phthalic dicarboxaldehyde-3-mercaptopropionic acid and 9-fluorenylmethyl chloroformate (FMOC). Chromatographic separations of the FMOC derivatives of selfotel enantiomers and the internal standard were achieved using a column switching system consisting of an Inertsil ODS-2 column (75x4.6 mm I.D., 5 microm) and a Chiralcel OD-R column (250x4.6 mm I.D., 10 microm). The composition of the mobile phase was acetonitrile-0.1 M phosphate buffer, pH 2.50 (35:65) for the Inertsil ODS-2 column and acetonitrile-0.1 M phosphate buffer, pH 2.00 (35:65) for the Chiralcel OD-R column. The analytes were monitored using fluorescence detection at an excitation wavelength of 262 nm and an emission wavelength of 314 nm. The limit of quantification (LOQ) for this method is 0.25 microg/ml for each selfotel enantiomer. The method was successfully utilized to determine preliminary selfotel stereospecific pharmacokinetics.

Strategies for neuroprotection with glutamate antagonists. Extrapolating from evidence taken from the first stroke and head injury studies

Over fifty patients with severe head injury, and one hundred with stroke, have now been treated with the competitive NMDA antagonist CGS 19755 (selfotel). Preliminary analysis has shown possible evidence of benefit for both these clinical indications, and several other glutamate antagonists are now being evaluated for these indications in Phase II trials. The optimal dose of CGS 19755 (selfotel) for efficacy for severe head trauma has not yet been identified, but may be > 3 mg/kg, as at this dose there was evidence of an ICP lowering effect and improved CPP. For stroke, however, the maximal tolerated dose was 1.5 mg/kg, because these conscious patients developed hallucinations and agitation. There were no other significant drug-associated adverse events in either of these studies. It is difficult to determine the "neuroprotective" dose for this compound in humans. By extrapolating from animal studies the "best estimate" would be around 5 mg/kg in patients with severe head trauma. For stroke, behavioral side effects were the major limiting factor for dosing. Although several NMDA antagonists, including CGS 19755 (selfotel), are currently entering efficacy trials for stroke, based upon their tremendous potency in animal models, the problem of psychomimetic effects may necessitate the use of additional management strategies, e.g., more intensive monitoring and concomitant medications.

Correlation of CGS 19755 neuroprotection against in vitro excitotoxicity and focal cerebral ischemia

The in vivo neuroprotective effect and brain levels of cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755), a competitive N-methyl-D-aspartate (NMDA) antagonist, were compared with its in vitro neuroprotective effects. The dose-response for in vitro neuroprotection against both NMDA toxicity and combined oxygen-glucose deprivation (OGD) was determined in murine neocortical cultures. Primary cultures of neocortical cells from feta mice were injured by exposure to 500 microM NMDA for 10 min or to OGD for 45 min. The effect of CGS 19755 in both injury paradigms was assessed morphologically and quantitated by determination of lactate dehydrogenase release. Near complete neuroprotection was found at high doses of CGS 19755. The ED50 for protection against NMDA toxicity was 25.4 micro M, and against OGD the ED50 was 15.2 microM. For the in vivo paradigm rabbits underwent 2 h of left internal carotid, anterior cerebral, and middle cerebral artery occlusion followed by 4 h reperfusion; ischemic injury was assessed by magnetic resonance imaging and histopathology. The rabbits were treated with 40 mg/kg i.v. CGS 19755 or saline 10 min after arterial occlusion. CSF and brain levels of CGS 19755 were 12 microM and 5 microM, respectively, at 1 h, 6 microM and 5 microM at 2 h, and 13 microM and 7 microM at 4 h. These levels were neuroprotective in this model, reducing cortical ischemic edema by 48% and ischemic neuronal damage by 76%. These results suggest that a single i.v. dose penetrates the blood-brain barrier, attaining sustained neuroprotective levels that are in the range for in vitro neuroprotection.

Safety and tolerability of the glutamate antagonist CGS 19755 (Selfotel) in patients with acute ischemic stroke. Results of a phase IIa randomized trial

BACKGROUND AND PURPOSE

CGS 19755 is a competitive N-methyl-D-aspartate (NMDA) receptor antagonist that limits neuronal damage in animal stroke models. The objectives of this multicenter (7 centers), randomized, double-blind, placebo-controlled, ascending-dose phase IIa study were to evaluate the safety and tolerability of CGS 19755 and obtain pharmacokinetic and preliminary data on its efficacious dose range in patients treated within 12 hours of hemispheric ischemic stroke.

METHODS

At each dose level, 6 patients were randomized to one or two intravenous bolus doses of CGS 19755, and 2 patients were randomized to placebo. An unblinded safety and monitoring committee-evaluated results at each dose before ascending to the next level. All patients at the first level (1 mg/kg) received two doses separated by 12 hours. The first 2 patients at 2 mg/kg received two doses, but adverse experiences occurred in both; subsequent patient groups received single doses of 2.0, 1.75, or 1.5 mg/kg.

RESULTS

Adverse experiences (agitation, hallucinations, confusion, paranoia, and delirium) occurred in all 6 patients treated with 2 mg/kg, and in 3 of 5 at 1.75 mg/kg. Similar but milder adverse experiences were noted in 4 of 7 patients at 1.5 mg/kg and 1 of 6 patients at 1.0 mg/kg. Adverse experiences began between 20 minutes and 22 hours (mean, 8 hours) after treatment and lasted 2 to 60 hours (mean, 24 hours). Mortality was 1 of 8 in patients receiving placebo and 3 of 24 in treated patients. In treated survivors, median and mean percent improvement in National Institutes of Health Stroke Scale scores from baseline to terminal visit (mean, 86 days) was comparable at all doses, and 95% of treated patients had Barthel Index scores of > or = 70 at the terminal visit.

CONCLUSIONS

We conclude that a single intravenous dose of 1.5 mg/kg CGS 19755 is safe and tolerable in patients with acute ischemic stroke. An efficacy trial is indicated.

Pipecolic acid is an osmoprotectant for Escherichia coli taken up by the general osmoporters ProU and ProP

Exogenously supplied L-pipecolic acid was accumulated by Escherichia coli cells and protected them while growing at inhibitory osmolarity. Using specific uptake mutants and competitive assays, we established that the imino acid enters the cells through the ProP and ProU systems with Km values of 225 and 53 microM, respectively. Surprisingly, in spite of the requirement for the wild-type proX gene for osmoprotective ability, no binding activity of labelled pipecolate with the periplasmic protein encoded by proX could be detected. In an attempt to demonstrate whether the two porters (ProP and ProU) are the only carriers involved in osmoregulation, a variety of molecules known for their intracellular osmolarity-dependent accumulation in various organisms were investigated. N-Dimethylproline (proline betaine), N-dimethylglycine, homobetaine (beta-alanine betaine), gamma-butyrobetaine and dimethylsulfoniopropionate were found to be capable of promoting the growth of osmotically stressed E. coli. All of these molecules enter bacterial cells via ProP and ProU porters. None of the osmoprotectants except N-dimethylproline was able to bind the periplasmic protein encoded by proX, while this protein was necessary for their uptake. Apparently, ProP and ProU are the sole osmoporters involved in osmolyte influx into E. coli cells.

Tissue distribution of two NMDA receptor antagonists, [3H]CGS 19755 and [3H]MK-801, after intrathecal injection in mice

The tissue distribution of [3H]cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755) and [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (NK-801) was investigated after a single IT injection into lumbar spinal cord of mice. The level of radioactivity was analyzed in the lumbar, thoracic, and cervical spinal cord, brainstem, frontal cortex, liver, lungs, kidneys, stomach, intestine, spleen, heart, and blood from 5 min up to 6 h after injection. Within the CNS, [3H]CGS 19755 redistributed slowly from the site of injection toward the brainstem and cortex, peaking in the cortex 3-4 h after IT injection. At no time, however, did the relative level per gram of tissue in the frontal cortex exceed 10% of the relative level in the lumbar region of the spinal cord. The highest peripheral level of [3H]CGS 19755 was found in the kidneys. [3H]MK-801 redistributed rapidly from the spinal cord injection site to the peripheral organs. The highest peripheral levels of [3H]MK-801 were found in the lungs and liver, where the radioactivity peaked at 10 and 30-60 min, respectively, after injection. The relative levels of [3H]CGS 19755 were consistently higher in CNS tissues (except for the first 15 min in the frontal cortex) and blood than the corresponding levels of [3H]MK-801. The opposite relationship was true in the liver, lungs, kidneys, stomach, intestine, spleen, and heart. The effect on the response latency in the hot-plate test was quantified in the same animals immediately prior to sacrifice for the distribution study.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo distribution of CGS-19755 within brain in a model of focal cerebral ischemia

The blood-brain barrier permeability of the competitive N-methyl-D-aspartate receptor antagonist CGS-19755 [cis-4-(phosphonomethyl)-2-piperidine carboxylic acid] was assessed in normal and ischemic rat brain. The brain uptake index of CGS-19755 relative to iodoantipyrine was assessed using the Oldendorf technique in normal brain. The average brain uptake index in brain regions supplied by the middle cerebral artery was 0.15 +/- 0.35% (mean +/- SEM). The unidirectional clearance of CGS-19755 from plasma across the blood-brain barrier was determined from measurements of the volume of distribution of CGS-19755 in brain. These studies were performed in normal rats and in rats with focal cerebral ischemia produced by combined occlusion of the proximal middle cerebral artery and ipsilateral common carotid artery. In normal rats the regional plasma clearance across the blood-brain barrier was low, averaging 0.015 ml 100 g-1 min-1. In ischemic rats this clearance value averaged 0.019 ml 100 g-1 min-1 in the ischemic hemisphere and 0.009 ml 100 g-1 min-1 in the nonischemic hemisphere. No significant regional differences in plasma clearance of CGS-19755 were observed in either normal or ischemic rats except in cortex injured by electrocautery where a 14-fold increase in clearance across the blood-brain barrier was measured. We conclude that CGS-19755 crosses the blood-brain barrier very slowly, even in acutely ischemic tissue.