Model-Informed Support of Dose Selection for Prophylactic Treatment with Dalcinonacog Alfa in Adult and Paediatric Hemophilia B Patients

INTRODUCTION

Dalcinonacog alfa (DalcA), a novel subcutaneously administered recombinant human factor IX (FIX) variant is being developed for adult and paediatric patients with hemophilia B (HB). DalcA has been shown to raise FIX to clinically meaningful levels in adults with HB. This work aimed to support dosing regimen selection in adults and perform first-in-paediatric dose extrapolations using a model-based pharmacokinetic (PK) approach.

METHODS

A population PK model was built using adult data from two clinical trials (NCT03186677, NCT03995784). With allometry in the model, clinical trial simulations were performed to study alternative dosing regimens in adults and children. Steady-state trough levels and the time-to-reach target were derived to inform dose selection.

RESULTS

Almost 90% of the adults were predicted to achieve desirable FIX levels, i.e. 10% FIX activity, following daily 100 IU/kg dosing, with 90% of the subjects reaching target within 1.6-7.1 days. No every-other-day regimen met the target. A dose of 125 IU/kg resulted in adequate FIX levels down to 6 years, whereas a 150 IU/kg dose was needed below 6 down to 2 years of age. For subjects down to 6 years that did not reach target with 125 IU/kg, a dose escalation to 150 IU/kg was appropriate. The children below 6 to 2 years were shown to need a dose escalation to 200 IU/kg if 150 IU/kg given daily was insufficient.

CONCLUSION

This study supported the adult dose selection for DalcA in the presence of sparse data and enabled first-in-paediatric dose selection to achieve FIX levels that reduce risk of spontaneous bleeds.

Sucrose Formulated Recombinant Human Antihemophilic Factor VIII Is Safe and Efficacious for Treatment of Hemophilia A in Home Therapy

To add an increased level of safety to antihemophilic factor replacement therapy, a full-length, recombinant Factor VIII (rFVIII) product has been developed without human-derived plasma proteins during purification and formulation and using an additional solvent/detergent viral inactivation step. This first clinical trial of a sucrose-formulated full-length rFVIII (rFVIII-FS) was conducted in previously treated patients (≥100 prior exposure days) with severe (<2% FVIII) hemophilia A in North America (NA) and Europe (EU). Pharmacokinetic profiles for rFVIII-FS were compared with those of currently licensed rFVIII product (Kogenate®) in 35 patients. Safety and efficacy during home therapy were evaluated in 71 patients. The new formulation displayed a pharmacokinetic profile similar to that of rFVIII. Patients on home therapy received a cumulative total of 11,867 exposure days, 12,546 infusions, and 22,443,694 IU of rFVIII-FS. Of 2585 bleeds, 93.5% were treated with 1-2 infusions and 80.5% of responses were rated as excellent or good. No evidence of de novo inhibitor formation was observed. Only 0.27% of infusions were associated with any drugrelated adverse event. Except for an episode of intermittent chest pain with palpitations which ceased after treatment with analgesics, associated adverse events were mild or moderate. Overall, rFVIII-FS provided excellent hemostatic control, was well-tolerated, and caused no significant adverse effects, thus demonstrating safety and efficacy for treatment of bleeds in patients with hemophilia A.

Full-length sucrose-formulated recombinant factor VIII for treatment of previously untreated or minimally treated young children with severe haemophilia A

The safety and efficacy of a full-length sucrose-formulated recombinant factor VIII product (rFVIII-FS; KogenateFS; Kogenate Bayer) was evaluated in previously untreated (PUPs) and minimally treated (MTP) patients with severe haemophilia A (FVIII < 2%). Patients (37 PUPs; 24 MTPs) aged 0.1–25.7 months were treated with rFVIII-FS for a cumulative of 9,141 exposure days (EDs), median 114 EDs (range 4–478), on prophylactic or on-demand therapy. Eighty-nine percent of all treated bleeding episodes were successfully treated with 1 (74%) or 2 (15%) infusions. Clinical response to first infusion for each bleeding episode was rated as ‘excellent’ in 58%, or ‘good’ in 33%, of all cases. Recombinant FVIII-FS was used in 27 surgical procedures, mainly catheter implantations, which were all conducted without bleeding complications. FVIII recovery mean values (~2%/kg/ IU) were as expected for any licensed FVIII concentrate. FVIII neutralizing antibody formation was 15% (9/60). Aside from inhibitor formation, three adverse events were rated as ‘at least possibly drug-related’ for a total drug-related adverse event rate of 0.14%. No viral seroconversions were observed. Overall, excellent safety and efficacy were demonstrated with rFVIII-FS for therapy of young children with severe haemophilia A.

Safety and efficacy of sucrose-formulated full-length recombinant factor VIII: Experience in the standard clinical setting

The safety of full-length sucrose-formulated recombinant factor VIII (rFVIII-FS; KOGENATE® FS) for up to 24 months of use was evaluated in a postmarketing observational study in Europe. Long-term safety and efficacy data were available for 212 patients with severe haemophilia A, including 13 previously untreated patients (PUPs) and 12 patients with 1–19 exposure days (EDs). Patients accumulated a mean (± SD) of 187 (121) EDs to rFVIII-FS and received a total of 39,627 infusions, mainly for prophylaxis and for the treatment of 4,283 spontaneous or trauma-related bleeds during an average observation time of 710 (136) days. Of these bleeding episodes, 85.4% were successfully treated with one or two infusions of rFVIII-FS. Haemostasis was also evaluated during 46 minor to major surgical pro- cedures, and the response to infusion was “excellent” or “good” in all cases. FVIII inhibitor formation was observed in six patients (two de novo; four persistent or recurrent). The de novo cases represent 8.0% (2 of 25) of patients who reported 0–19 previous EDs at study entry. Four of the five patients who reported possible drug-related adverse effects developed inhibitors. The results of this observational study demonstrate the efficacy and safety of rFVIII-FS during normal clinical use in the treatment of patients with severe haemophilia A. Furthermore, these findings are consistent with those of previous phase III clinical studies with rFVIII-FS, particularly with regard to its efficacy and low incidence of inhibitor formation.

Efficacy of pirfenidone in patients with idiopathic pulmonary fibrosis with more preserved lung function

This post hoc analysis examined the differences in idiopathic pulmonary fibrosis disease progression and the effects of pirfenidone in patients stratified by more preserved versus less preserved baseline lung function status using forced vital capacity (FVC) or GAP (gender, age and physiology) index stage.

Efficacy outcomes, i.e. FVC, 6-min walking distance (6MWD) and dyspnoea (University of California San Diego Shortness of Breath Questionnaire (UCSD SOBQ)), were analysed at 12 months in patients randomised to pirfenidone 2403 mg·day−1 or placebo in the pooled phase 3 CAPACITY/ASCEND population (n=1247), with subgroups stratified by baseline FVC ≥80% versus <80% or GAP stage I versus II–III. Treatment-by-subgroup interaction was tested based on a rank ANCOVA model; factors in the model included study, region, treatment, subgroup and treatment-by-subgroup interaction term.

Patients with both more preserved (FVC ≥80% or GAP stage I) and less preserved (FVC <80% or GAP stage II–III) lung function at baseline demonstrated clinically significant disease progression at 12 months in terms of categorical decline in FVC, 6MWD and UCSD SOBQ. The magnitude of pirfenidone treatment effect was comparable between subgroups, regardless of whether lung function was classified using FVC or GAP index stage.

These findings support the initiation of treatment with pirfenidone, irrespective of stage of baseline lung function in this patient population.

An Open-label, Phase II Study of the Safety and Tolerability of Pirfenidone in Patients with Scleroderma-associated Interstitial Lung Disease: the LOTUSS Trial

OBJECTIVE

Systemic sclerosis-associated interstitial lung disease (SSc-ILD) shares a number of clinical features and pathogenic mechanisms with idiopathic pulmonary fibrosis (IPF). This study was designed to evaluate the tolerability of the IPF treatment pirfenidone in SSc-ILD. The known gastrointestinal, skin, and liver adverse events (AE) of pirfenidone are of importance given the involvement of these organs in SSc.

METHODS

All patients received pirfenidone and were randomized 1:1 to either a 2- or 4-week titration starting at 801 mg/day and finishing at a maintenance dose of 2403 mg/day. Patients received pirfenidone for 16 weeks in total. Assessments included treatment-emergent AE (TEAE) and exploratory disease outcomes.

RESULTS

Sixty-three patients were randomized; 96.8% experienced a TEAE and more patients reported TEAE during the titration versus the maintenance period. The most commonly reported TEAE were consistent with those observed for pirfenidone in IPF (nausea, headache, fatigue) and were similar regardless of titration schedule. More patients discontinued treatment because of TEAE in the 2- versus 4-week titration group (5 vs 1, respectively); all discontinuation events occurred > 3 weeks after reaching the full dose of pirfenidone. Mycophenolate mofetil (MMF), taken by 63.5% of patients in addition to pirfenidone, did not appear to affect tolerability. Exploratory disease outcomes remained largely unchanged.

CONCLUSION

Pirfenidone showed an acceptable tolerability profile in SSc-ILD, although a longer titration may be associated with better tolerability. Tolerability was not affected by concomitant MMF. The present findings support further investigation of pirfenidone in future clinical trials in patients with SSc-ILD.

TRIAL REGISTRATION

ClinicalTrials.gov; www.clinicaltrials.gov NCT01933334.

A phase 3 trial of pirfenidone in patients with idiopathic pulmonary fibrosis

BACKGROUND

In two of three phase 3 trials, pirfenidone, an oral antifibrotic therapy, reduced disease progression, as measured by the decline in forced vital capacity (FVC) or vital capacity, in patients with idiopathic pulmonary fibrosis; in the third trial, this end point was not achieved. We sought to confirm the beneficial effect of pirfenidone on disease progression in such patients.

METHODS

In this phase 3 study, we randomly assigned 555 patients with idiopathic pulmonary fibrosis to receive either oral pirfenidone (2403 mg per day) or placebo for 52 weeks. The primary end point was the change in FVC or death at week 52. Secondary end points were the 6-minute walk distance, progression-free survival, dyspnea, and death from any cause or from idiopathic pulmonary fibrosis.

RESULTS

In the pirfenidone group, as compared with the placebo group, there was a relative reduction of 47.9% in the proportion of patients who had an absolute decline of 10 percentage points or more in the percentage of the predicted FVC or who died; there was also a relative increase of 132.5% in the proportion of patients with no decline in FVC (P<0.001). Pirfenidone reduced the decline in the 6-minute walk distance (P=0.04) and improved progression-free survival (P<0.001). There was no significant between-group difference in dyspnea scores (P=0.16) or in rates of death from any cause (P=0.10) or from idiopathic pulmonary fibrosis (P=0.23). However, in a prespecified pooled analysis incorporating results from two previous phase 3 trials, the between-group difference favoring pirfenidone was significant for death from any cause (P=0.01) and from idiopathic pulmonary fibrosis (P=0.006). Gastrointestinal and skin-related adverse events were more common in the pirfenidone group than in the placebo group but rarely led to treatment discontinuation.

CONCLUSIONS

Pirfenidone, as compared with placebo, reduced disease progression, as reflected by lung function, exercise tolerance, and progression-free survival, in patients with idiopathic pulmonary fibrosis. Treatment was associated with an acceptable side-effect profile and fewer deaths. (Funded by InterMune; ASCEND ClinicalTrials.gov number, NCT01366209.).

Psychometric evaluation of a patient-reported symptom assessment tool for adults with haemophilia (the HAEMO-SYM)

In patients with haemophilia, repeated bleeding events result in significant comorbid conditions that can degrade health-related quality of life. Clinician-reported symptom measures are available for use in patients with haemophilia A or B; however, there has not been a validated patient-reported symptom evaluation instrument available for haemophilia to date. The objective of this study was to develop and evaluate a self-report instrument, the HAEMO-SYM, for measuring symptom severity in patients with haemophilia. Eighty-four haemophilic subjects from Canada and the USA were enrolled and completed the HAEMO-SYM, SF-36, and Health Assessment Questionnaire-Functional Disability Index (HAQ-FDI). Four-week reproducibility was evaluated in 72 stable subjects. Construct validity was assessed by correlating subscale scores with the SF-36, HAQ-FDI, a coping questionnaire and clinical scores. The final 17-item HAEMO-SYM has two subscales: pain and bleeds. Internal consistency reliability was good (Cronbach's alphas, 0.86-0.94) and test-retest reliability was good (Intraclass Correlation Coefficients, 0.75-0.94). HAEMO-SYM subscale scores were significantly correlated with SF-36 scores (P < 0.05 for all except HAEMO-SYM Pain and SF-36 Mental Health), HAQ-FDI scores (P < 0.05 for all but HAEMO-SYM Bleeds with HAQ-FDI Hygiene and Reach), Gilbert scale (P < 0.01), coping (P < 0.05) and global pain (P < 0.001). Mean HAEMO-SYM scores varied significantly in groups defined by severity, HIV status and treatment regimen. Greater symptom severity was associated with more severe disease, HIV-positive status and prophylaxis treatment. The results of this study suggest that the HAEMO-SYM, a haemophilia-specific symptom severity instrument, has good reliability and provides evidence that supports construct validity in patients with haemophilia.

Safety and pharmacokinetics of a recombinant factor VIII with pegylated liposomes in severe hemophilia A

BACKGROUND

BAY 79-4980 is a sucrose-formulated recombinant factor VIII (rFVIII-FS) combined with pegylated liposomes to prolong activity.

OBJECTIVES

To investigate the safety, tolerability, bioavailability, pharmacokinetics and pharmacodynamics of a single administration of BAY 79-4980 compared with standard rFVIII-FS in patients with severe hemophilia A.

METHODS

This randomized, double-blind study consisted of two crossover substudies comparing two doses of liposomal rFVIII-FS with standard rFVIII-FS. Males (12-60 years) with severe hemophilia A received a single infusion of standard rFVIII-FS (35 IU kg(-1)) followed by a single infusion of BAY 79-4980 (13 or 22 mg kg(-1) pegylated liposomes) or vice versa, with 12 observation days and a 2-day washout period between treatments.

RESULTS

Twenty-six subjects were enrolled at two centers. No serious adverse events were reported. Transient increases in complement C3a, but not CH50, were seen in subjects receiving both the low- and high-liposome-dose BAY 79-4980. Mild transient elevations of total and low-density lipoprotein cholesterol were observed. There were no clinically significant differences in clotting or laboratory parameters or in pharmacokinetic behavior between BAY 79-4980 and standard rFVIII-FS. The number of subjects with spontaneous bleeds on days 1-14 postinfusion was low, and group comparisons were inconclusive.

CONCLUSIONS

Single-dose administration of BAY 79-4980 is well tolerated in patients with severe hemophilia A. Plasma pharmacokinetics of FVIII cannot explain the extended protection from bleeding observed previously with BAY 79-4980. Further studies of efficacy and long-term safety of chronic administration are planned.

Safety and pharmacokinetics of a recombinant factor VIII with pegylated liposomes in severe hemophilia A

BACKGROUND

BAY 79-4980 is a sucrose-formulated recombinant factor VIII (rFVIII-FS) combined with pegylated liposomes to prolong activity.

OBJECTIVES

To investigate the safety, tolerability, bioavailability, pharmacokinetics and pharmacodynamics of a single administration of BAY 79-4980 compared with standard rFVIII-FS in patients with severe hemophilia A.

METHODS

This randomized, double-blind study consisted of two crossover substudies comparing two doses of liposomal rFVIII-FS with standard rFVIII-FS. Males (12-60 years) with severe hemophilia A received a single infusion of standard rFVIII-FS (35 IU kg(-1)) followed by a single infusion of BAY 79-4980 (13 or 22 mg kg(-1) pegylated liposomes) or vice versa, with 12 observation days and a 2-day washout period between treatments.

RESULTS

Twenty-six subjects were enrolled at two centers. No serious adverse events were reported. Transient increases in complement C3a, but not CH50, were seen in subjects receiving both the low- and high-liposome-dose BAY 79-4980. Mild transient elevations of total and low-density lipoprotein cholesterol were observed. There were no clinically significant differences in clotting or laboratory parameters or in pharmacokinetic behavior between BAY 79-4980 and standard rFVIII-FS. The number of subjects with spontaneous bleeds on days 1-14 postinfusion was low, and group comparisons were inconclusive.

CONCLUSIONS

Single-dose administration of BAY 79-4980 is well tolerated in patients with severe hemophilia A. Plasma pharmacokinetics of FVIII cannot explain the extended protection from bleeding observed previously with BAY 79-4980. Further studies of efficacy and long-term safety of chronic administration are planned.

Health-related quality of life assessment in adult haemophilia patients: a systematic review and evaluation of instruments

The objective of this study was to review and evaluate the performance of health-related quality of life (HRQL) and other health status measures used in studies of adult haemophilia and provide recommendations for future research. A systematic literature review was performed to identify HRQL and health status measures used in haemophilia. Literature was identified using medical databases, Internet and manual searches. The search was restricted to articles published in English since 1986. Ninety-six abstracts were located; 19 relevant articles were selected for detailed review. Three main types of HRQL measures were identified: generic psychometric-based HRQL (SF-36 and SF-12), utility-based HRQL [EQ-5D and Health Utilities Index (HUI)], and musculoskeletal-specific HRQL (Arthritis Impact Measurement Scale 2, AIMS 2) instruments. No patient-rated haemophilia-specific HRQL instrument was found. The SF-36, the EQ-5D, and the HUI were able to discriminate haemophilia patient subgroups with respect to disease severity and HIV comorbidity status. Sixteen additional scales were identified that were used to measure the different aspects of physical, psychological, and social functioning of patients. There were no clinical studies of haemophilia carried out that employed HRQL instruments, thus responsiveness of these instruments could not be evaluated. The variety of instruments used in haemophilia studies highlights the need for a tool that can capture the full impact of haemophilia and its treatment on patients' HRQL. Developing such a tool poses the unique challenge of accounting for common comorbidities, such as HIV and chronic hepatitis that may have a greater HRQL impact than the underlying disease.

Results of an orthopaedic survey in young patients with severe haemophilia in Spain

This paper outlines the results obtained in a cross-sectional study of a group of young patients with severe haemophilia A and B. The primary aim of the study was to ascertain the level of orthopaedic complications in the group, the effects that these complications have on quality of life, and the medical resources used on these patients. The secondary aim was to relate their current orthopaedic state to the type of treatment received before the study. The study was carried out in 11 hospitals in Spain, where 70 severe haemophilia patients (factor VIII [FVIII] < 2%), with an average age of 21.6 and a median age of 22, and no inhibitors, were monitored. The percentage of patients suffering from articular complaints was 84.3% and 85.7% according to the Gilbert and Petterson scales, respectively. Furthermore, pain was reported in 16.1% of joints, most frequently in ankles. Using the SF-36 Health Survey, patients were observed to have a poorer quality of life relative to healthy controls. Despite high levels of both the coagulant factor given to patients and the financial resources dedicated to their treatment, the type of treatment (on demand and/or as secondary prophylaxis) provided to the young adults was found to be incapable of preventing haemophilic arthropathy and subsequent negative quality of life consequences.

Single-dose ciprofloxacin versus 3 days of norfloxacin in uncomplicated urinary tract infections in women

A double-blind, randomized controlled study to evaluate the efficacy and safety of a single dose of 500 mg of ciprofloxacin versus 3 days 400 mg twice-daily of norfloxacin in uncomplicated urinary tract infection in women was designed. Patients underwent four visits: baseline, and at 3, 7 and 28 days. The main efficacy variables were clinical and microbiological outcome at day 7. Analyses on both valid patients and intention-to-treat populations were performed. Two hundred and twenty-six patients (114 receiving ciprofloxacin and 112 receiving norfloxacin) were considered valid for efficacy evaluation. Bacteriologic cure was 91.2% in the ciprofloxacin group and 91.9% in the norfloxacin group. Clinical resolution was 91.2 and 93.8%, respectively. Both treatments were equally efficacious (P = 0.016).

Efficacy of a sucrose-formulated recombinant factor VIII used for 22 surgical procedures in patients with severe haemophilia A

A sucrose-formulated recombinant FVIII (rFVIII-SF) was investigated under clinical trial conditions during surgical procedures in previously treated patients (PTPs). Fifteen PTPs with severe haemophilia A (FVIII < or = 1%) underwent 22 surgical procedures. The procedures performed cover a spectrum from minor to major surgery. Haemostatic outcome was assessed by the investigators to be excellent in 16 procedures and good in the remaining six procedures. It is concluded that rFVIII-SF is efficacious and safe in severe haemophilia A patients undergoing minor or major surgery.

Sucrose formulated recombinant human antihemophilic factor VIII is safe and efficacious for treatment of hemophilia A in home therapy--International Kogenate-FS Study Group

To add an increased level of safety to antihemophilic factor replacement therapy, a full-length, recombinant Factor VIII (rFVIII) product has been developed without human-derived plasma proteins during purification and formulation and using an additional solvent/detergent viral inactivation step. This first clinical trial of a sucrose-formulated full-length rFVIII (rFVIII-FS) was conducted in previously treated patients (> or = 100 prior exposure days) with severe (<2% FVIII) hemophilia A in North America (NA) and Europe (EU). Pharmacokinetic profiles for rFVIII-FS were compared with those of currently licensed rFVIII product (Kogenate) in 35 patients. Safety and efficacy during home therapy were evaluated in 71 patients. The new formulation displayed a pharmacokinetic profile similar to that of rFVIII. Patients on home therapy received a cumulative total of 11,867 exposure days, 12,546 infusions, and 22,443,694 IU of rFVIII-FS. Of 2585 bleeds, 93.5% were treated with 1-2 infusions and 80.5% of responses were rated as excellent or good. No evidence of de novo inhibitor formation was observed. Only 0.27% of infusions were associated with any drug-related adverse event. Except for an episode of intermittent chest pain with palpitations which ceased after treatment with analgesics, associated adverse events were mild or moderate. Overall, rFVIII-FS provided excellent hemostatic control, was well-tolerated, and caused no significant adverse effects, thus demonstrating safety and efficacy for treatment of bleeds in patients with hemophilia A.

The orthopaedic status of severe haemophiliacs in Spain

This paper provides an outline of the results obtained in a cross-sectional study conducted primarily with the aim of ascertaining orthopaedic complications in a group of young severe A and B haemophiliacs, the effects which these complications have on the medical resources used with these patients, and the impact of severe haemophilia on their quality of life. Its secondary aim was to link their current orthopaedic status to the type of treatment they had received prior to the study. Eleven Spanish hospitals took part in this study, monitoring 70 severe haemophiliacs (FVIII:C <2%) without inhibitors who had a mean age of 21.6 years and a median age of 22. Retrospective data collected from birth to the conclusion of the study were used and, for certain variables, data from the last 12 months. The type of treatment given had been on-demand treatment, together with prophylaxis of variable time periods, which in 32 cases (45.7%) were prolonged (>6 months). In 40 cases (57.1%) the patients underwent one or more periods of prophylaxis. Thirty-three patients (47.8%) had over 1000 days of administration of factors VIII and IX. The analysis of the total study group reveal an average of 348 bleeding episodes per patient. The findings of this study revealed that 84.3% of these patients suffer from articular complaints on the Gilbert scale, and 85.7% on the Pettersson scale. In addition, pain was reported in 16.1% of the joints, the most frequently affected being the ankle joints. Twenty-six patients (37%) had undergone orthopaedic surgery from the time of birth to the conclusion of the study. The quality of life of the severe haemophiliacs reviewed seems to have been affected. During the last 12 months, there were 216 outpatient haematological visits and 176 orthopaedic-rehabilitation visits, as well as 12 radiological explorations and two hospitalizations. During these 12 months, medical expenditure totalled $55 473 per patient per year, the most important item being factor concentrates VIII/IX ($54 119 per patient per year). The type of treatment given to these patients (on-demand and/or as secondary prophylaxis) was found to be incapable of preventing haemophilic arthropathy or guaranteeing an acceptable quality of life, although both the administration of coagulant factor concentrate to such patients and the financial resources dedicated to their treatment was very high. Consequently, a strategic change is to be considered for the prevention of haemophilic arthropathy, based on the introduction of replacement treatment involving continuous administration of factors VIII and IX in primary prophylaxis regimens from the first years of life.

Pharmacokinetics of triflusal and its main metabolite HTB in healthy subjects following a single oral dose

The pharmacokinetic profile of triflusal (2-acetoxy-4-trifluoromethyl benzoic acid) and its main metabolite HTB (2-hydroxy-4-trifluoromethyl benzoic acid) has been studied in 8 healthy subjects (4 males and 4 females), after a single oral dose of 900 mg of triflusal. Plasma concentrations were determined by a sensitive HPLC method. Sampling was performed up to 120 h post medication. Triflusal displays a Cmax of 11.6 +/- 1.7 micrograms/ml and a tmax of 0.88 +/- 0.26 h. The elimination half-life (t1/2) was 0.55 h with a clearance (Cl/F) of 45.5 +/- 11.0 l/h. HTB kinetic parameters were: tmax 4.96 +/- 1.37 h and Cmax 92.7 +/- 17.1 micrograms/ml, with an elimination t1/2 of 34.3 +/- 5.3 and a clearance of 0.18 +/- 0.04 l/h. The results obtained in this study show a rapid absorption of triflusal and an immediate biotransformation into HTB. The long lasting platelet anti-aggregatory effect of triflusal in spite of its short t1/2, could be explained by the irreversible inhibition of platelet cyclo-oxygenase and the sustained levels of HTB, which also possess anti-aggregant properties.