2.1  Recommended Dosing

The recommended dose of KALBITOR is 30 mg (3 mL), administered subcutaneously in three 10 mg (1 mL) injections.  If the attack persists, an additional dose of 30 mg may be administered within a 24 hour period.

2.2  Administration Instructions

KALBITOR should only be administered by a healthcare professional with appropriate medical support to manage anaphylaxis and hereditary angioedema. 

KALBITOR should be refrigerated and protected from the light.  KALBITOR is a clear, colorless liquid; visually inspect each vial for particulate matter and discoloration prior to administration.  If there is particulate matter or discoloration, the vial should not be used.

Using aseptic technique, withdraw 1 mL (10 mg) of KALBITOR from the vial using a large bore needle.  Change the needle on the syringe to a needle suitable for subcutaneous injection.  The recommended needle size is 27 gauge.  Inject KALBITOR into the skin of the abdomen, thigh, or upper arm.  Repeat the procedure for each of the 3 vials comprising the KALBITOR dose.  The injection site for each of the injections may be in the same or in different anatomic locations (abdomen, thigh, upper arm).  There is no need for site rotation.  Injection sites should be separated by at least 2 inches (5 cm) and away from the anatomical site of attack.

The same instructions apply to an additional dose administered within 24 hours.  Different injection sites or the same anatomical location (as used for the first administration) may be used.

5.1  Hypersensitivity Reactions, Including Anaphylaxis

Potentially serious hypersensitivity reactions, including anaphylaxis, have occurred in patients treated with KALBITOR.  In 255 HAE patients treated with intravenous or subcutaneous KALBITOR in clinical studies, 10 patients (3.9%) experienced anaphylaxis.  For the subgroup of 187 patients treated with subcutaneous KALBITOR, 5 patients (2.7%) experienced anaphylaxis.  Symptoms associated with these reactions have included chest discomfort, flushing, pharyngeal edema, pruritus, rhinorrhea, sneezing, nasal congestion, throat irritation, urticaria, wheezing, and hypotension.  These reactions occurred within the first hour after dosing.

Other adverse reactions indicative of hypersensitivity reactions included the following: pruritus (5.1%), rash (3.1%), and urticaria (2.0%).

Patients should be observed for an appropriate period of time after administration of KALBITOR, taking into account the time to onset of anaphylaxis seen in clinical trials.  Given the similarity in hypersensitivity symptoms and acute HAE symptoms, patients should be monitored closely in the event of a hypersensitivity reaction.

KALBITOR should not be administered to any patients with known clinical hypersensitivity to KALBITOR [see Contraindications (4)].

6.1  Clinical Trials Experience

Because clinical trials are conducted under varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The safety data described below reflect exposure to KALBITOR in 255 patients with HAE treated with either intravenous or subcutaneous KALBITOR.  Of the 255 patients, 66% of patients were female and 86% were Caucasian.  Patients treated with KALBITOR were between the ages of 10 and 78 years. 

Overall, the most common adverse reactions in 255 patients with HAE were headache (16.1%), nausea (12.9%), fatigue (11.8%), diarrhea (10.6%), upper respiratory tract infection (8.2%), injection site reactions (7.4%), nasopharyngitis (5.9%), vomiting (5.5%), pruritus (5.1%), upper abdominal pain (5.1%), and pyrexia (4.7%).  Anaphylaxis was reported in 3.9% of patients with HAE.  Injection site reactions were characterized by local pruritus, erythema, pain, irritation, urticaria, and/or bruising.

The incidence of adverse reactions below is based upon 2 placebo-controlled, clinical trials (EDEMA3® and EDEMA4® ) in a total of 143 unique patients with HAE. Patients were treated with KALBITOR 30 mg subcutaneous or placebo.  Patients were permitted to participate sequentially in both placebo-controlled trials; safety data collected during exposure to KALBITOR was attributed to treatment with KALBITOR, and safety data collected during exposure to placebo was attributed to treatment with placebo.  Table 1 shows adverse reactions occurring in ≥3% of KALBITOR-treated patients that also occurred at a higher rate than in the placebo-treated patients in the two controlled trials (EDEMA3 and EDEMA4) of the 30 mg subcutaneous dose.

Some patients in EDEMA3 and EDEMA4 received a second, open-label 30 mg subcutaneous dose of KALBITOR within 24 hours following the initial dose.  Adverse reactions reported by these patients who received the additional 30 mg subcutaneous dose of KALBITOR were consistent with those reported in the patients receiving a single dose.

6.2  Immunogenicity

In the KALBITOR HAE program, patients developed antibodies to KALBITOR.  Rates of seroconversion increased with exposure to KALBITOR over time.  Overall, 7.4% of patients seroconverted to anti-ecallantide antibodies.  Neutralizing antibodies to ecallantide were determined in vitro to be present in 4.7% of patients.

Anti-ecallantide and anti-P. pastoris IgE antibodies were also detected.  Patients who seroconvert may be at a higher risk of a hypersensitivity reaction.  The long-term effects of antibodies to KALBITOR are not known.  

The test results for the ecallantide program were determined using one of two assay formats: ELISA and bridging electrochemiluminescence (ECL).  As with all therapeutic proteins, there is a potential for immunogenicity with the use of KALBITOR.  The incidence of antibody formation is highly dependent on the sensitivity and specificity of the assay.  Additionally, the observed incidence of antibody (including neutralizing antibody) positivity in an assay may be influenced by several factors, including assay methodology, sample handling, timing of sample collection, concomitant medications, and underlying disease.  For these reasons, comparison of the incidence of antibodies to KALBITOR with the incidence of antibodies to other products may be misleading.

8.1  Pregnancy

Pregnancy Category C

There are no adequate and well-controlled trials of KALBITOR in pregnant women.  KALBITOR has been shown to cause developmental toxicity in rats, but not rabbits. Because animal reproductive studies are not always predictive of human response, KALBITOR should be used during pregnancy only if clearly needed.

In rats, intravenous KALBITOR at an intravenous dose approximately 13 times the maximum recommended human dose (MRHD) on a mg/kg basis caused increased numbers of early resorptions and percentages of resorbed conceptuses per litter in the presence of mild maternal toxicity.  No development toxicity was observed in rats that received an intravenous dose approximately 8 times the MRHD on a mg/kg basis.  There were no adverse effects of KALBITOR on embryofetal development in rats that received subcutaneous doses up to approximately 2.4 times the MRHD on an AUC basis, and in rabbits that received intravenous doses up to approximately 6 times the MRHD on an AUC basis.

8.2  Labor and Delivery

No information is available on the effects of KALBITOR during labor and delivery.

8.3  Nursing Mothers

It is not known whether ecallantide is excreted in human milk.  Caution should be exercised when ecallantide is administered to a nursing woman.

8.4  Pediatric Use

Safety and effectiveness of KALBITOR in patients below 16 years of age have not been established.

8.5  Geriatric Use

Clinical trials of KALBITOR did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects.  In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

12.1  Mechanism of Action

Hereditary angioedema (HAE) is a rare genetic disorder caused by mutations to C1‑esterase-inhibitor (C1-INH) located on Chromosome 11q and inherited as an autosomal dominant trait.  HAE is characterized by low levels of C1-INH activity and low levels of C4.  C1-INH functions to regulate the activation of the complement and intrinsic coagulation (contact system pathway) and is a major endogenous inhibitor of plasma kallikrein.  The kallikrein-kinin system is a complex proteolytic cascade involved in the initiation of both inflammatory and coagulation pathways.  One critical aspect of this pathway is the conversion of High Molecular Weight (HMW) kininogen to bradykinin by the protease plasma kallikrein. In HAE, normal regulation of plasma kallikrein activity and the classical complement cascade is therefore not present.  During attacks, unregulated activity of plasma kallikrein results in excessive bradykinin generation.  Bradykinin is a vasodilator which is thought by some to be responsible for the characteristic HAE symptoms of localized swelling, inflammation, and pain.

KALBITOR is a potent (Ki = 25 pM), selective, reversible inhibitor of plasma kallikrein.  KALBITOR binds to plasma kallikrein and blocks its binding site, inhibiting the conversion of HMW kininogen to bradykinin.  By directly inhibiting plasma kallikrein, KALBITOR reduces the conversion of HMW kininogen to bradykinin and thereby treats symptoms of the disease during acute episodic attacks of HAE.

12.2  Pharmacodynamics

No exposure-response relationships for KALBITOR to components of the complement or kallikrein-kinin pathways have been established.  

The effect of KALBITOR on activated partial thromboplastin time (aPTT) was measured because of potential effect on the intrinsic coagulation pathway.  Prolongation of aPTT has been observed following intravenous dosing of KALBITOR at doses ≥20 mg/m2.  At 80 mg administered intravenously in healthy subjects, aPTT values were prolonged approximately two-fold over baseline values and returned to normal by 4 hours post-dose.

For patients taking KALBITOR, no significant QT prolongation has been seen.  In a randomized, placebo-controlled trial (EDEMA4) studying the 30 mg subcutaneous dose versus placebo, 12-lead ECGs were obtained at baseline, 2 hours and 4 hours post-dose (covering the time of expected Cmax), and at follow-up (day 7).  ECGs were evaluated for PR interval, QRS complex, and QTc interval.  KALBITOR had no significant effect on the QTc interval, heart rate, or any other components of the ECG.

12.3  Pharmacokinetics

Following the administration of a single 30 mg subcutaneous dose of KALBITOR to healthy subjects, a mean (± standard deviation) maximum plasma concentration of 586 ± 106 ng/mL was observed approximately 2 to 3 hours post-dose.  The mean area under the concentration-time curve was 3017 ± 402 ng*hr/mL.  Following administration, plasma concentration declined with a mean elimination half-life of 2.0 ± 0.5 hours.  Plasma clearance was 153 ± 20 mL/min and the volume of distribution was 26.4 ± 7.8 L.  Based on a population pharmacokinetic analysis, body weight, age, and gender were not found to affect KALBITOR exposure significantly.  Ecallantide is a small protein (7054 Da) and renal elimination in the urine of treated subjects has been demonstrated. 

No pharmacokinetic data are available in patients or subjects with hepatic or renal impairment. 

13.1  Carcinogenesis, Mutagenesis, Impairment of Fertility

There are no animal or human studies to assess the carcinogenic or mutagenic potential of KALBITOR (ecallantide).

KALBITOR had no effects on fertility and reproductive performance in rats at subcutaneous doses up to 25 mg/kg/day (approximately 21 times the MRHD on a mg/kg basis).

13.2  Animal Toxicology

Reproductive Toxicology Studies

KALBITOR has been shown to cause developmental toxicity in rats, but not rabbits. Treatment of rats with an intravenous dose of 15 mg/kg/day (approximately 13 times the MRHD on a mg/kg basis) caused increased numbers of early resorptions and percentages of resorbed conceptuses per litter in the presence of mild maternal toxicity.  However, no development toxicity was observed in rats that received an intravenous dose of 10 mg/kg/day (approximately 8 times the MRHD on a mg/kg basis).  KALBITOR was not teratogenic in rats at subcutaneous doses up to 20 mg/kg/day (approximately 2.4 times the MRHD on an AUC basis) and rabbits that received intravenous doses up to 5 mg/kg/day (approximately 6 times the MRHD on an AUC basis).