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Mechanism Of Action
Acute Hemodynamic Effects
Acute intravenous infusions of FLOLAN for up to 15 minutes in patients with idiopathic or heritable PAH or PAH/SSD produce dose-related increases in cardiac index (CI) and stroke volume (SV) and dose-related decreases in pulmonary vascular resistance (PVR), total pulmonary resistance (TPR), and mean systemic arterial pressure (SAPm). The effects of FLOLAN on mean pulmonary artery pressure (PAPm) were variable and minor.
In humans, hemodynamic changes due to epoprostenol (e.g., increased heart rate, facial flushing) returned to baseline within 10 minutes of termination of 60-minute infusions of 1 to 16 ng/kg/min. This pharmacodynamic behavior is consistent with a short in vivo half-life and rapid clearance in man, as suggested by the results of animal and in vitro studies.
In animals, the vasodilatory effects reduce right-and left-ventricular afterload and increase cardiac output and stroke volume. The effect of epoprostenol on heart rate in animals varies with dose. At low doses, there is vagally-mediated bradycardia, but at higher doses, epoprostenol causes reflex tachycardia in response to direct vasodilation and hypotension. No major effects on cardiac conduction have been observed. Additional pharmacologic effects of epoprostenol in animals include bronchodilation, inhibition of gastric acid secretion, and decreased gastric emptying.
When other antiplatelet agents or anticoagulants are used concomitantly, there is a potential for FLOLAN to increase the risk of bleeding. However, patients receiving infusions of FLOLAN in clinical trials were maintained on anticoagulants without evidence of increased bleeding.
Epoprostenol is rapidly hydrolyzed at neutral pH in blood and is also subject to enzymatic degradation. No available chemical assay is sufficiently sensitive and specific to assess the in vivo human pharmacokinetics of epoprostenol. Animal studies using tritium-labeled epoprostenol have indicated a high clearance (93 mL/kg/min), small volume of distribution (357 mL/kg), and a short half-life (2.7 minutes). During infusions in animals, steady-state plasma concentrations of tritium-labeled epoprostenol were reached within 15 minutes and were proportional to infusion rates.
Tritium-labeled epoprostenol has been administered to humans in order to identify the metabolic products of epoprostenol. Epoprostenol is metabolized to 2 primary metabolites: 6-keto-PGF1α (formed by spontaneous degradation) and 6,15-diketo-13,14-dihydro-PGF1α (enzymatically formed), both of which have pharmacological activity orders of magnitude less than epoprostenol in animal test systems. The recovery of radioactivity in urine and feces over a 1-week period was 82% and 4% of the administered dose, respectively. Fourteen additional minor metabolites have been isolated from urine, indicating that epoprostenol is extensively metabolized in humans.
The in vitro half-life of epoprostenol in human blood at 37°C and pH 7.4 is approximately 6 minutes; therefore, the in vivo half-life of epoprostenol in humans is expected to be no greater than 6 minutes.
In a pharmacokinetic substudy in patients with congestive heart failure receiving furosemide in whom therapy with FLOLAN was initiated, apparent oral clearance values for furosemide (n = 23) were decreased by 13% on the second day of therapy and returned to baseline values by Day 87. The change in furosemide clearance value is not likely to be clinically significant.
In a pharmacokinetic substudy in patients with congestive heart failure receiving digoxin in whom therapy with FLOLAN was initiated, apparent oral clearance values for digoxin (n = 30) were decreased by 15% on the second day of therapy and returned to baseline values by Day 87 . Clinical significance of this interaction is not known.
Chronic Infusion In Idiopathic Or Heritable PAH
Chronic continuous infusions of FLOLAN in patients with idiopathic or heritable PAH were studied in 2 prospective, open, randomized trials of 8 and 12 weeks' duration comparing FLOLAN plus conventional therapy with conventional therapy alone. Dosage of FLOLAN was determined as described in Dosage and Administration (2) and averaged 9.2 ng/kg/min at trials' end. Conventional therapy varied among patients and included some or all of the following: anticoagulants in essentially all patients; oral vasodilators, diuretics, and digoxin in one-half to two-thirds of patients; and supplemental oxygen in about half the patients. Except for 2 NYHA Functional Class II patients, all patients were either functional Class III or Class IV. As results were similar in the 2 trials, the pooled results are described.
Chronic hemodynamic effects were generally similar to acute effects. Increases in CI, SV, and arterial oxygen saturation and decreases in PAPm, mean right atrial pressure (RAPm), TPR, and systemic vascular resistance (SVR) were observed in patients who received FLOLAN chronically compared with those who did not. Table 4 illustrates the treatment-related hemodynamic changes in these patients after 8 or 12 weeks of treatment.
Table 4: Hemodynamics during Chronic Administration of
FLOLAN in Patients with Idiopathic or Heritable PAH
|Hemodynamic Parameter||Baseline||Mean Change from Baseline at End of Treatment Perioda|
(n = 52)
(n = 54)
(n = 48)
(n = 41)
|PAPm (mm Hg)||60||60||-5b||1|
|PVR (Wood U)||16||17||-4b||1|
|SAPm (mm Hg)||89||91||-4||-3|
|TPR (Wood U)||20||21||-5b||1|
|aAt 8 weeks: FLOLAN n = 10, conventional therapy n = 11 (n
is the number of patients with hemodynamic data). At 12 weeks: FLOLAN n = 38,
conventional therapy n = 30 (n is the number of patients with hemodynamic
bDenotes statistically significant difference between group receiving FLOLAN and group receiving conventional therapy. CI = Cardiac index, PAPm = Mean pulmonary arterial pressure, PVR = Pulmonary vascular resistance, SAPm = Mean systemic arterial pressure, SV = Stroke volume, TPR = Total pulmonary resistance.
These hemodynamic improvements appeared to persist when FLOLAN was administered for at least 36 months in an open, nonrandomized trial.
The acute hemodynamic response to FLOLAN did not correlate well with improvement in exercise tolerance or survival during chronic use of FLOLAN.
A statistically significant improvement was observed in exercise capacity, as measured by the 6minute walk test in patients receiving continuous intravenous FLOLAN plus conventional therapy (n = 52) for 8 or 12 weeks compared with those receiving conventional therapy alone (n = 54). Improvements were apparent as early as the first week of therapy. Increases in exercise capacity were accompanied by statistically significant improvement in dyspnea and fatigue, as measured by the Chronic Heart Failure Questionnaire and the Dyspnea Fatigue Index, respectively.
Survival was improved in NYHA Functional Class III and Class IV patients with idiopathic or heritable PAH treated with FLOLAN for 12 weeks in a multicenter, open, randomized, parallel trial. At the end of the treatment period, 8 of 40 (20%) patients receiving conventional therapy alone died, whereas none of the 41 patients receiving FLOLAN died (P = 0.003).
Chronic Infusion In PAH/SSD
Chronic continuous infusions of FLOLAN in patients with PAH/SSD were studied in a prospective, open, randomized trial of 12 weeks' duration comparing FLOLAN plus conventional therapy (n = 56) with conventional therapy alone (n = 55). Except for 5 NYHA Functional Class II patients, all patients were either functional Class III or Class IV. In the controlled 12-week trial in PAH/SSD, for example, the dose increased from a mean starting dose of 2.2 ng/kg/min. During the first 7 days of treatment, the dose was increased daily to a mean dose of 4.1 ng/kg/min on Day 7 of treatment. At the end of Week 12, the mean dose was 11.2 ng/kg/min. The mean incremental increase was 2 to 3 ng/kg/min every 3 weeks.
Conventional therapy varied among patients and included some or all of the following: anticoagulants in essentially all patients, supplemental oxygen and diuretics in two-thirds of the patients, oral vasodilators in 40% of the patients, and digoxin in a third of the patients. A statistically significant increase in CI, and statistically significant decreases in PAPm, RAPm, PVR, and SAPm after 12 weeks of treatment were observed in patients who received FLOLAN chronically compared with those who did not. Table 5 illustrates the treatment-related hemodynamic changes in these patients after 12 weeks of treatment.
Table 5: Hemodynamics during Chronic Administration of
FLOLAN in Patients with PAH/SSD
|Hemodynamic Parameter||Baseline||Mean Change from Baseline at 12 Weeks|
(n = 56)
(n = 55)
(n = 50)
(n = 48)
|PAPm (mm Hg)||51||49||-5a||1|
|RAPm (mm Hg)||13||11||-1a||1|
|PVR (Wood U)||14||11||-5a||1|
|SAPm (mm Hg)||93||89||-8a||-1|
|aDenotes statistically significant difference between group receiving FLOLAN and group receiving conventional therapy (n is the number of patients with hemodynamic data). CI = Cardiac index, PAPm = Mean pulmonary arterial pressure, RAPm = Mean right arterial pressure, PVR = Pulmonary vascular resistance, SAPm = Mean systemic arterial pressure.|
Statistically significant improvement was observed in exercise capacity, as measured by the 6-minute walk, in patients receiving continuous intravenous FLOLAN plus conventional therapy for 12 weeks compared with those receiving conventional therapy alone. Improvements were apparent in some patients at the end of the first week of therapy. Increases in exercise capacity were accompanied by statistically significant improvements in dyspnea and fatigue, as measured by the Borg Dyspnea Index and Dyspnea Fatigue Index. At Week 12, NYHA functional class improved in 21 of 51 (41%) patients treated with FLOLAN compared with none of the 48 patients treated with conventional therapy alone. However, more patients in both treatment groups (28/51 [55%] with FLOLAN and 35/48 [73%] with conventional therapy alone) showed no change in functional class, and 2/51 (4%) with FLOLAN and 13/48 (27%) with conventional therapy alone worsened.
No statistical difference in survival over 12 weeks was observed in PAH/SSD patients treated with FLOLAN as compared with those receiving conventional therapy alone. At the end of the treatment period, 4 of 56 (7%) patients receiving FLOLAN died, whereas 5 of 55 (9%) patients receiving conventional therapy alone died.
Increased Mortality In Patients With Heart Failure Caused By Severe Left Ventricular Systolic Dysfunction
A large trial evaluating the effect of FLOLAN on survival in NYHA Class III and IV patients with congestive heart failure due to severe left ventricular systolic dysfunction was terminated after an interim analysis of 471 patients revealed a higher mortality in patients receiving FLOLAN plus conventional therapy than in those receiving conventional therapy alone. The chronic use of FLOLAN in patients with heart failure due to severe left ventricular systolic dysfunction is therefore contraindicated.
Last reviewed on RxList: 5/6/2015
This monograph has been modified to include the generic and brand name in many instances.
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