Perflutren Protein-Type A Microspheres

OPTISON™ (Perflutren Protein-Type A Microspheres Injectable Suspension, USP) is a sterile non-pyrogenic suspension of microspheres of human serum albumin with perflutren for contrast enhancement during the indicated ultrasound imaging procedures. The vial contains a clear liquid lower layer and a white upper layer that, after resuspension by gentle mixing, provides a homogeneous, opaque, milky-white suspension for intravenous injection.

Perflutren is chemically characterized as 1,1,1,2,2,3,3,3-perflutren with a molecular weight of 188, an empirical formula of C3F8 and it has the following structural formula:

Each mL of OPTISON contains 5.0-8.0x108 protein-type A microspheres, 10 mg Albumin Human, USP, 0.22 ±0.11 mg/mL perflutren, 0.2 mg N-acetyltryptophan, and 0.12 mg caprylic acid in 0.9% aqueous sodium chloride. The headspace of the vial is filled with perflutren gas. The pH is adjusted to 6.4-7.4. The protein in the microsphere shell makes up approximately 5-7% (w/w) of the total protein in the liquid. The microsphere particle size parameters are listed in Table 1.

Table 1: Microsphere Particle Size Parameters

Optison is indicated for use in patients with suboptimal echocardiograms to opacify the left ventricle and to improve the delineation of the left ventricular endocardial borders.

Serious Cardiopulmonary Reactions

Serious cardiopulmonary reactions including fatalities have occurred uncommonly during or shortly following perflutren-containing microsphere administration, typically within 30 minutes of administration. The risk for these reactions may be increased among patients with unstable cardiopulmonary conditions (acute myocardial infarction, acute coronary artery syndromes, worsening or unstable congestive heart failure, or serious ventricular arrhythmias).

The reported reactions to perflutren-containing microspheres include: fatal cardiac or respiratory arrest, shock, syncope, symptomatic arrhythmias (atrial fibrillation, tachycardia, bradycardia, supraventricular tachycardia, ventricular fibrillation, ventricular tachycardia), hypertension, hypotension, dyspnea, hypoxia, chest pain, respiratory distress, stridor, wheezing, loss of consciousness and convulsions (see ADVERSE REACTIONS).

Always have cardiopulmonary resuscitation personnel and equipment readily available prior to OPTISON administration and monitor all patients for acute reactions.

Anaphylactoid Reactions

In postmarketing use, uncommon but serious anaphylactoid reactions were observed during or shortly following perflutren-containing microsphere administration including:

Shock, hypersensitivity, bronchospasm, throat tightness, angioedema, edema (pharyngeal, palatal, mouth, peripheral, localized), swelling (face, eye, lip, tongue upper airway), facial hypoesthesia, rash, urticaria, pruritus, flushing, and erythema have occurred in patients with no prior exposure to perflutren-containing microsphere products (see ADVERSE REACTIONS).

Systemic Embolization of OPTISON in Patients with Cardiac Shunts

In patients with right-to-left, bi-directional, or transient right-to-left cardiac shunts perflutren-containing microspheres can bypass the pulmonary particle-filtering mechanisms and directly enter the arterial circulation resulting in microvascular occlusion and ischemia. Do not administer OPTISON by intra-arterial injection (see CONTRAINDICATIONS).

High Ultrasound Mechanical Index

High ultrasound mechanical index values may cause microsphere cavitation or rupture and lead to ventricular arrhythmias. Additionally, end-systolic triggering with high mechanical indices has been reported to cause ventricular arrhythmias. The safety of OPTISON at mechanical indices greater than 0.8 has not been evaluated. The safety of OPTISON with the use of end-systolic triggering has not been evaluated.

No information provided.

Mechanism Of Action

The Optison microspheres create an echogenic contrast effect in the blood. The acoustic impedance of the Optison microspheres is much lower than that of the blood. Therefore, impinging ultrasound waves are scattered and reflected at the microsphere-blood interface and ultimately may be visualized in the ultrasound image. At the frequencies used in adult echocardiography (2-5 MHz), the microspheres resonate which further increases the extent of ultrasound scattering and reflection.

Pharmacodynamics

The median duration of Optison contrast enhancement for each of the four doses of Optison, 0.2 (40% of recommended dose), 0.5, 3.0, and 5 mL , were approximately one, two, four, and five minutes, respectively [see Clinical Studies].

Pharmacokinetics

After injection of Optison, diffusion of the perflutren gas out of the microspheres is limited by the low partition coefficient of the gas in blood that contributes to the persistence of the microspheres.

The pharmacokinetics of the intact microspheres of Optison in humans are unknown.

The binding of perflutren to plasma proteins and its partitioning into blood cells are unknown. However, perflutren protein binding is expected to be minimal due to the low partition coefficient of the gas in blood.

Following intravenous injection, perflutren is cleared with a pulmonary elimination half-life of 1.3 ± 0.69 minutes (mean ± SD).

Metabolism

Perflutren is a stable gas that is not metabolized. The human albumin component of the microsphere is expected to be handled by the normal metabolic routes.

Excretion

Perflutren is eliminated through the lungs within 10 minutes. The mean ± SD recovery was 96% ± 23%. The perflutren concentration in expired air peaked approximately 30-40 seconds after administration.

Clinical Studies

Echocardiography

The efficacy of Optison was evaluated in two identical multicenter, controlled, dose escalation studies of 203 patients (Study A: n=101, Study B: n=102) with sub-optimal non-contrast echocardiography defined as having at least two out of six segments of the left ventricular endocardial border inadequately delineated in the apical four-chamber view. Among these patients there were 79% men, 21% women, 64% White, 25% Black, 10% Hispanic, and 1% other race or ethnic group. The patients had a mean age of 61 years (range: 21 to 83 years), a mean weight of 196 lbs. (range: 117 to 342 lbs.), a mean height of 68 inches (range: 47 to 78 inches), and a mean body surface area of 2.0m² (range: 1.4 to 2.6m²). Approximately 23% of the patients had chronic pulmonary disease, and 17% had congestive and dilated cardiomyopathy with left ventricular ejection fractions (LVEFs) of between 20% and 40% (by previous echocardiography). Patients with a LVEF of less than 20% or with New York Heart Association Class IV heart failure were not included in the studies.

After non-contrast imaging, Optison was administered in increasing increments as 4 doses (0.2, 0.5, 3.0 and 5 mL) with at least ten minutes between each dose. Ultrasound settings were optimized for the baseline (non-contrast) apical four-chamber view and remained unchanged for the contrast imaging. Static echocardiographic images and video-tape segments were interpreted by a reader who was blinded to the patient's clinical history and to the dose of Optison. Left ventricular endocardial border delineation and left ventricular opacification, were assessed before and after Optison administration by the measurement of visualized endocardial border length and ventricular opacification.

In comparison to non-contrast ultrasound, Optison significantly increased the length of endocardial border that could be visualized both at end-systole and end-diastole (see Table 3). In these patients there was a trend towards less visualization in women. Optison increased left ventricular opacification (peak intensity) in the mid-chamber and apical views (see Table 4). The imaging effects of Optison on endocardial border delineation and left ventricular opacification were similar at doses between 0.5 ml and 5 ml and were also similar among patients with or without pulmonary disease and dilated cardiomyopathy.

Table 3 : Left Ventricular Endocardial Border Length Before and After OPTISONa, b

Table 4 : Intensity of Left Ventricular Opacificationa Before and After OPTISON™ b,c

Pulmonary Hemodynamic Effects

The effect of Optison on pulmonary hemodynamics was studied in a prospective, open-label study of 30 patients scheduled for pulmonary artery catheterization, including 19 with an elevated baseline pulmonary arterial systolic pressure (PASP) ( > 35 mmHg) and 11 with a normal PASP ( ≤ 35 mmHg). Systemic hemodynamic parameters and ECGs were also evaluated. No clinically important pulmonary hemodynamic, systemic hemodynamic, or ECG changes were observed. This study did not assess the effect of Optison on visualization of cardiac or pulmonary structures.