Pegvaliase

Risk Summary

Based on findings in studies of pregnant animals without PKU treated with pegvaliase-pqpz, pegvaliase may cause fetal harm when administered to a pregnant woman. Limited available data with pegvaliase-pqpz use in pregnant women are insufficient to inform a drug-associated risk of adverse developmental outcomes. There are risks to the fetus associated with poorly controlled phenylalanine concentrations in women with PKU during pregnancy including increased risk for miscarriage, major birth defects (including microcephaly, major cardiac malformations), intrauterine fetal growth retardation, and future intellectual disability with low IQ; therefore, phenylalanine concentrations should be closely monitored in women with PKU during pregnancy. Advise pregnant women of the potential risks to the fetus.

A reproduction study in pregnant rabbits treated with pegvaliase‑pqpz demonstrated a high incidence of fetal malformations throughout the skeletal system, and in kidneys, lungs, and eyes. Embryo‑fetal toxicity (increased resorptions and reduced fetal weight) was also observed. These effects occurred at 5 times the maximum recommended daily dose and were associated with strong signs of maternal toxicity, including marked reductions in weight gain and food consumption, and death. A reproduction study in pregnant rats treated with pegvaliase‑pqpz demonstrated an increase in skeletal variations, with no malformations observed. The effects in rats occurred at 2.8 times the maximum recommended daily dose. In a pre-/post-natal development study in rats, pegvaliase‑pqpz produced reduced survival of offspring during lactation, decreases in pup weight and litter size, and delayed sexual maturation of offspring when administered daily at 13 times the maximum recommended daily dose. The effects on rat embryo‑fetal and post-natal development were also associated with maternal toxicity.

All pregnancies have a background risk of major birth defects, pregnancy loss, or other adverse pregnancy outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively. The estimated background risk of major birth defects and miscarriage in pregnant women with PKU who maintain blood phenylalanine concentrations greater than 600 micromol/L during pregnancy is greater than the corresponding background risk for pregnant women without PKU.

There is a pregnancy surveillance program for pegvaliase. If pegvaliase is administered during pregnancy, or if a patient becomes pregnant while receiving pegvaliase or within one month following the last dose of pegvaliase, healthcare providers should report pegvaliase exposure by calling 1-866-906-6100.

Clinical Considerations

Disease-Associated Maternal and/or Embryo-Fetal Risk

Uncontrolled blood phenylalanine concentrations before and during pregnancy are associated with an increased risk of adverse pregnancy outcomes and fetal adverse effects. To reduce the risk of hyperphenylalaninemia-induced fetal adverse effects, blood phenylalanine concentrations should be maintained between 120 and 360 micromol/L during pregnancy and during the 3 months before conception.

Dose Adjustments During Pregnancy and the Postpartum Period

Phenylalanine concentrations below 30 micromol/L in pregnant women with PKU treated with pegvaliase may be associated with adverse fetal outcomes. Monitor blood phenylalanine concentrations during pregnancy and adjust the dosage of pegvaliase or modify dietary protein and phenylalanine intake to avoid blood phenylalanine concentrations below 30 micromol/L.

Data

Human Data

Uncontrolled Maternal PKU: Available data from the Maternal Phenylketonuria Collaborative Study on 468 pregnancies and 331 live births in pregnant women with PKU demonstrated that uncontrolled phenylalanine concentrations above 600 micromol/L are associated with an increased risk for miscarriage, major birth defects (including microcephaly, major cardiac malformations), intrauterine fetal growth retardation, and future intellectual disability with low IQ.

Limited data from case reports of pegvaliase use in pregnant women are insufficient to determine a drug‑associated risk of adverse developmental outcomes.

Animal Data

All developmental toxicity studies were conducted in animals (rats and rabbits) without PKU, in which treatment with pegvaliase-pqpz produced a dose-dependent reduction in maternal blood phenylalanine concentrations. At doses that produced maternal toxicity and/or effects on embryo-fetal development, the maternal plasma phenylalanine concentrations were markedly reduced compared to the control group. The contribution of maternal phenylalanine depletion to the incidence of embryo‑fetal developmental effects was not evaluated.

Subcutaneous administration of 5 mg/kg/day pegvaliase‑pqpz (5 times the maximum recommended daily dose based on bodyweight [mg/kg]) in pregnant rabbits during the period of organogenesis produced embryo‑lethality (increased resorptions), marked reduction in fetal weight, and fetal malformations. The malformations included multiple external abnormalities of the head, body and limbs, multiple soft tissue malformations (reduced size or absence of kidneys, diaphragmatic hernia, corneal opacity, discoloration or reduced size of eyes, and reduced size of lungs) and multiple skeletal malformations of the craniofacial bones, vertebrae, sternebrae, ribs, pelvis, limbs, and digits. An increase in variations and delayed ossification was also observed in all skeletal regions. The adverse developmental effects were associated with maternal toxicity, as indicated by marked impairment of weight gain and food consumption. Deaths associated with weight loss and abortion occurred in 8% of the pregnant rabbits treated with 5 mg/kg/day pegvaliase‑pqpz.

Subcutaneous administration of 2 mg/kg/day pegvaliase‑pqpz (2 times the maximum recommended daily dose based on bodyweight [mg/kg]) in pregnant rabbits had no adverse effects on embryo-fetal development. Systemic exposure to pegvaliase‑pqpz was detected in fetuses from rabbits treated with 2 or 5 mg/kg/day.

Pegvaliase‑pqpz increased fetal alterations when administered daily in pregnant rats at doses of 8 mg/kg subcutaneously and higher (2.8 times the human steady-state area under the curve [AUC] at the maximum recommended daily dose) during a 28‑day premating period, mating, and through the period of organogenesis. The fetal alterations were limited to skeletal variations such as cervical ribs, bifid centra of lumbar and thoracic vertebrae, and incomplete ossification of squamosal bones, frontal bones, lumbar vertebra arch, and ribs. Daily administration of 20 mg/kg subcutaneously (13 times the human steady-state AUC at the recommended maximum daily dose) to pregnant rats produced reductions in litter sizes and fetal weights, which was associated with maternal toxicity (decreased body weight, ovarian weight, and food consumption). The decrease in litter sizes at 20 mg/kg subcutaneously was secondary to reductions in corpora lutea and implantations. Systemic exposure to pegvaliase‑pqpz was detected in fetuses from rats treated with 20 mg/kg of pegvaliase‑pqpz (13 times the human steady-state AUC at the recommended maximum daily dose). Subcutaneous administration of 2 mg/kg/day pegvaliase‑pqpz (less than the human steady state AUC at the maximum recommended daily dose) in pregnant rats had no adverse effects on embryo‑fetal development.

Pegvaliase-pqpz decreased pup weight, litter size, and survival of offspring during lactation, and delayed sexual maturation of offspring when administered daily in rats at 20 mg/kg subcutaneously (13 times the human steady-state AUC at the recommended maximum daily dose), with dosing starting before mating and continuing through lactation. The effects in offspring were associated with maternal toxicity. No effects in offspring were observed at 8 mg/kg/day subcutaneously (2.8 times the human steady-state AUC at the recommended maximum daily dose). This study lacked a complete evaluation of physical and neurobehavioral development in offspring; however, no effects of pegvaliase‑pqpz were noted in tests of learning and memory.

Risk Summary

There are no data on the presence of pegvaliase-pqpz in human milk, the effects on the breastfed infant, or the effects on milk production. A pre-/post-natal study in rats showed that pegvaliase-pqpz is present in rat milk and that administration of pegvaliase-pqpz during lactation decreased pup weight and survival. However, systemic absorption of pegvaliase-pqpz was not detected in the rat pups. Pegvaliase may cause low phenylalanine concentrations in human milk. The developmental and health benefits of breastfeeding should be considered along with the clinical need for pegvaliase treatment and any potential adverse effect on the breastfed infant from pegvaliase or from the underlying condition.

Clinical Considerations

Monitor blood phenylalanine concentrations in breastfeeding women treated with pegvaliase.

Carcinogenicity and genotoxicity studies have not been performed with pegvaliase‑pqpz. Based on its mechanism of action, pegvaliase‑pqpz is not expected to be tumorigenic.

Pegvaliase-pqpz produced impaired fertility in female rats at 20 mg/kg/day subcutaneously (13 times the human steady-state AUC at the maximum recommended daily dose), as indicated by decreases in corpora lutea, implantations, and litter size. These effects were associated with maternal toxicity (decreased body weight, ovarian weight, and food consumption). No effects on mating or fertility were observed in female rats with 8 mg/kg/day subcutaneously (2.8 times the human steady-state AUC at the maximum recommended daily dose) or in male rats with 20 mg/kg/day subcutaneously.

13.2 Animal Toxicology and/or Pharmacology

In rats without PKU treated with pegvaliase-pqpz, dose-dependent vacuolation in multiple organs and tissues was observed in the 4‑ and 26‑week repeat dose toxicity studies at doses of 8 mg/kg subcutaneously or greater administered twice weekly (less than the human steady state AUC at the maximum recommended daily dose). Vacuolation occurred in renal tubule cells and in histiocytic cells of the liver, spleen, testes, adrenal cortex, mesenteric lymph node, and mandibular lymph node. Vacuolation in histiocytes of the affected organs and tissues persisted after cessation of treatment. The vacuolation observed in these studies was not associated with organ‑related toxicities as determined by clinical chemistry/urinalysis and histopathological examination. The clinical significance of these findings and functional consequences are unknown.

In the 39‑week repeat dose toxicity study in monkeys, pegvaliase-pqpz 3 mg/kg subcutaneously twice weekly (2 times the human steady state AUC at the maximum recommended daily dose) produced systemic arteritis involving small arteries and arterioles in a wide range of organs and tissues (kidney, urinary bladder, pancreas, gallbladder, esophagus, stomach, duodenum, jejunum, ileum, cecum, colon, rectum, lung, heart, sciatic nerve, lacrimal gland, mandibular lymph node, epididymis, seminal vesicle, ovary, uterus, cervix, and vagina) and in subcutaneous injection sites. Arteritis was likely due to the immune-mediated response (e.g., immune complex deposition in blood vessels) associated with chronic administration of a foreign protein to the animals. The incidence and severity of systemic arteritis was dose-dependent. The vascular inflammation observed in this study was not associated with organ related toxicities as determined by clinical pathology parameters (hematology, clinical chemistry, and urinalysis) and histopathological examination.

Studies of longer duration in rats and monkeys treated with pegvaliase‑pqpz have not been conducted.

• Anaphylaxis
• Other Hypersensitivity Reactions

Clinical Trials Experience

Because clinical trials are conducted under widely 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 data described below reflect a total treatment exposure of 789 patient-years in 285 patients who received pegvaliase in an induction/titration/maintenance regimen in clinical trials. Of the 285 patients, 229 patients were exposed to pegvaliase for 24 weeks, 209 patients were exposed for 1 year, 181 patients were exposed for 2 years, and 160 patients were exposed for 3 years or longer. The patient population was evenly distributed between male and female patients, the mean age was 29 years (range: 16 to 56 years), and 98% of patients were White.

The most common adverse reactions (at least 20% of patients in either treatment phase) were injection site reactions, arthralgia, hypersensitivity reactions, headache, generalized skin reactions lasting at least 14 days, nausea, abdominal pain, vomiting, cough, oropharyngeal pain, pruritus, diarrhea, nasal congestion, fatigue, dizziness, and anxiety.

Of the 285 patients exposed to pegvaliase in an induction/titration/maintenance regimen in clinical trials, 44 (15%) patients discontinued treatment due to adverse reactions. The most common adverse reactions leading to treatment discontinuation were hypersensitivity reactions (6% of patients) including anaphylaxis (3% of patients), angioedema (1% of patients), arthralgia (4% of patients), generalized skin reactions lasting at least 14 days (2% of patients), and injection site reactions (1% of patients).

The most common adverse reactions leading to dosage reduction were arthralgia (15% of patients), hypersensitivity reactions (9% of patients), injection site reactions (4% of patients), alopecia (3% of patients), and generalized skin reactions lasting at least 14 days (2% of patients).

The most common adverse reactions leading to temporary drug interruption were hypersensitivity reactions (14% of patients), arthralgia (13% of patients), anaphylaxis (4% of patients), and injection site reactions (4% of patients).

Table 1 lists adverse reactions reported in at least 15% of patients treated with pegvaliase in an induction/titration/maintenance dosage regimen in clinical trials, and illustrates the adverse reaction rates over time by treatment phase. Table 2 lists laboratory abnormalities reported in at least 10% of patients treated with pegvaliase in an induction/titration/maintenance dosage regimen in clinical trials.

For these analyses, the induction/titration phase was defined as the time prior to reaching a stable dose (completing an 8‑week phase at the same dose level). Once a stable dosage was reached, patients were considered to be in the maintenance phase thereafter. Safety data for patients who reached the maintenance phase are included within either the induction/titration or maintenance phases depending on the onset date of the adverse reaction. Safety data for patients who did not reach the maintenance phase are included within the induction/titration phase. The maintenance phase includes data for patients who were previously on pegvaliase and transitioned to placebo during the randomized withdrawal period of Study 302.

Rates of adverse reactions (adjusted for duration of exposure) generally decreased over time and for some stayed relatively stable. In the maintenance phase, the rate of adverse reactions (adjusted for duration of exposure) in patients who reached the maintenance phase was comparable across dosages evaluated. The types and rate of adverse reactions reported during the maintenance phase in patients who received 20 mg once daily, 40 mg once daily, and 60 mg once daily were similar. During long-term treatment (greater than 36 months), the exposure-adjusted rates of adverse reactions decreased.

Rates of laboratory abnormalities (adjusted for duration of exposure) stayed relatively stable over time, except for complement C4 below lower limit of normal (LLN) and hs-CRP above 0.287 mg/dL over a 6 month period (both decreased over time) and hypophenylalaninemia (blood phenylalanine concentration below 30 micromol/L) on a single measurement (increased over time). There were no dose‑related trends in type or rate of laboratory abnormalities (adjusted for duration of exposure) reported during the maintenance phase in patients receiving 20 mg once daily, 40 mg once daily, or 60 mg once daily.

Table 1. Adverse Reactions* Reported in at least 15% of PKU Patients Treated with Pegvaliase in an Induction/Titration/Maintenance Regimen in Clinical Trials – Incidence and Exposure-Adjusted Rates:

* ≥15% incidence in either treatment phase
^† N (%) = Number of patients with at least 1 Adverse Reaction (%); Rate = Exposure-Adjusted Rate of Adverse Reactions (Adverse Reactions/Person‑Years)
^‡ Includes injection site: reaction, erythema, pruritus, pain, bruising, rash, swelling, urticaria, induration, hemorrhage, edema, mass, inflammation, nodule, discoloration, warmth, hematoma, irritation, vesicles, hypersensitivity, papule, discomfort, scar, paresthesia, hypertrophy, extravasation, dryness, scab
^§ Includes arthralgia, pain in extremity, back pain, musculoskeletal pain, neck pain
^¶ Includes rash, urticaria, anaphylaxis, rash generalized, hypersensitivity, rash erythematous, rash maculo-papular, rash pruritic, serum sickness, swelling face, dermatitis contact, swollen tongue, lip swelling, rash macular, pharyngeal edema, injection site hypersensitivity, eczema, drug eruption, dermatitis allergic, dermatitis, tongue edema, palatal edema, edema mouth, multiple allergies, lip edema, eye edema, exfoliative rash, drug hypersensitivity, dermatitis atopic, dermatitis acneiform, pruritus allergic, mouth swelling, implant site rash, gingival swelling, face edema, eyelid edema, eye swelling, dermatitis psoriasiform, dermatitis infected, conjunctivitis allergic, bronchospasm, angioedema, allergic sinusitis, allergic cough, eczema nummular, rhinitis allergic
# Includes headache, migraine, sinus headache
^Þ Includes pruritus, rash, urticaria, dry skin, rash erythematous, erythema, cellulitis, rash macular, pruritus generalized, petechiae, dermatitis allergic, skin infection, skin induration, rash maculo-papular, rash generalized, pharyngeal edema, macule, granulomatous dermatitis, exfoliative rash, drug eruption, dermatitis atopic, dermatitis, xanthogranuloma, skin plaque, skin mass, skin lesion, skin hypopigmentation, skin hyperpigmentation, skin exfoliation, septal panniculitis,scar, rash pruritic, rash papular, psoriatic arthropathy, pruritus allergic, papule, necrobiosis lipoidica diabeticorum, furuncle, eczema, ecchymosis, dermatitis psoriasiform, dermatitis infected, blister, eczema nummular, granuloma, infected dermal cyst, lipohypertrophy, psoriasis, skin irritation
^SS Includes abdominal pain, abdominal pain upper, abdominal discomfort

Table 2. Laboratory Abnormalities Reported in at least 10% of PKU Patients Treated with Pegvaliase in an Induction/Titration/Maintenance Regimen in Clinical Trials – Incidence and Exposure-Adjusted Rates:

^* N (%) = Number of patients with at least 1 laboratory abnormality (%); Rate = Exposure-Adjusted Rate of Laboratory Abnormalities (Laboratory Abnormalities/Person‑Years)
^† Blood phenylalanine concentration below 30 micromol/L
LLN – lower limit of normal
ULN – upper limit of normal
Hs – high sensitivity

Description of Selected Adverse Reactions

Arthralgia

In clinical trials, 245 out of 285 (86%) patients experienced episodes consistent with arthralgia (includes back pain, musculoskeletal pain, pain in extremity, and neck pain).

Arthralgia episodes were more frequent during the induction/titration phase (7.4 episodes/patient-year) and decreased over time (1.4 episodes/patient-year in the maintenance phase).

Forty-four out of 285 (15%) patients had one episode of arthralgia, 32 (11%) patients had 2 episodes of arthralgia, 18 (6%) had 3 episodes of arthralgia, and 146 (51%) had 4 or more episodes of arthralgia. Arthralgia occurred as early as after the first dose of pegvaliase and occurred at any time during treatment. The mean duration of arthralgia was 16 days (median: 3 days, range: 1 to 936 days), and 19% of arthralgia episodes had a duration of at least 14 days. Severe arthralgia (severe pain limiting self-care activities of daily living) was reported by 11 (4%) patients. In addition to arthralgia, other joint-related signs and symptoms reported were: joint swelling (24 patients; 8%), joint stiffness (22 patients; 8%), and musculoskeletal stiffness (20 patients; 7%). Arthralgia episodes were managed with medications (e.g., nonsteroidal anti-inflammatory drugs, glucocorticoids, and acetaminophen), pegvaliase dosage reduction (4% of episodes), pegvaliase interruption (4% of episodes), or pegvaliase withdrawal (0.6% of episodes). 97% of arthralgia episodes were reported as resolved at the time of last observation (up to 77 months of follow‑up).

Injection Site Reactions

Injection site reactions were reported as early as after the first dose of pegvaliase and occurred at any time during treatment. Injection site reactions were more frequent during the induction/titration phase (21 episodes/patient-years) and decreased over time (3 episodes/patient‑years in the maintenance phase). The mean duration of injection site reaction was 10 days (median: 2 days, range: 1 to 1612 days), and 8% of injection site reactions had a duration of at least 14 days. 99% of injection site reactions were reported as resolved at the time of last observation (up to 77 months of follow‑up).

Three injection site reactions consistent with granulomatous skin lesions were reported (each reaction occurring in one patient): granulomatous dermatitis (occurred after 464 days of pegvaliase treatment and lasted 16 days), xanthogranuloma (occurred after 378 days of pegvaliase treatment and lasted 638 days) was treated with a topical antihistamine, corticosteroid, and pegvaliase treatment was discontinued, and necrobiosis lipoidica diabeticorum (occurred after 281 days of pegvaliase treatment and lasted 281 days). Necrobiosis lipoidica diabeticorum was treated with steroid injections and complicated by Pseudomonas infection. All three injection site reactions resolved.

One patient reported soft tissue infection (occurred after 196 days of pegvaliase treatment and lasted 8 days) associated with mesenteric panniculitis treated with antibiotics, which resulted in treatment discontinuation.

Generalized Skin Reactions (not limited to the injection site) Lasting at Least 14 Days

In clinical trials, 134 out of 285 (47%) patients treated with pegvaliase experienced generalized skin reactions (not limited to the injection site) lasting at least 14 days. Mean duration of these reactions was 63 days (median: 37 days; range: 14 to 638 days). Generalized skin reactions were more frequent during the induction/titration phase (0.7 episodes/patient‑years), and decreased over time (0.3 episodes/patient-years in the maintenance phase).

The mean time from first dose of pegvaliase to onset of skin reactions was 373 days (median: 213 days; range: 2 to 1970 days). 5% of these reactions persisted at least 180 days, and 86% of these reactions were reported as resolved at the time of last observation (up to 77 months of follow‑up).

Angioedema

In clinical trials, 22 out of 285 (8%) patients experienced 45 episodes of angioedema (symptoms included: pharyngeal edema, swollen tongue, lip swelling, mouth swelling, eyelid edema and face edema) occurring independent of anaphylaxis. Angioedema (included under Hypersensitivity in Table 2) was more frequent during the induction/titration phase (0.14 episodes/patient-year) and decreased over time (0.04 episodes/patient-year in the maintenance phase). Three patients discontinued treatment. All episodes resolved. Angioedema can present as a symptom of anaphylaxis.

Serum Sickness

In clinical trials, serum sickness was reported in 7 out of 285 (2%) patients. Serum sickness episodes were more frequent during the induction/titration phase (0.04 episodes/patient-year) and decreased over time (less than 0.01 episodes/patient-year during the maintenance phase). All serum sickness reactions resolved without sequelae (duration of serum sickness ranged from 1 to 8 days). Out of the 7 patients who experienced serum sickness, 5 patients continued treatment without a recurrence, and managed serum sickness with drug interruption, dosage reduction and/or concomitant medication. Two patients discontinued treatment.

Immunogenicity

As with all therapeutic proteins, there is potential for immunogenicity. The detection 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 pegvaliase in the studies described below with the incidence of antibodies in other studies or to other products may be misleading.

All patients treated with pegvaliase developed a sustained total anti-drug antibody (TAb) response with a majority of patients (91%; N=235/258) developing that response by Week 4 of treatment. Mean TAb titers peaked 2 weeks after pegvaliase initiation and remained elevated throughout treatment (greater than 3 years after treatment initiation). Anti-phenylalanine ammonia lyase (PAL) IgM antibodies were detected in a majority of patients (98%; N=265/270) by 2 months after treatment initiation, with incidence declining over time to 67% at 36 months (N=114/171). Anti‑PAL IgG antibodies were detected in almost all patients (N=226/227) by 4 months after treatment initiation. Mean anti-PAL IgM and IgG titers peaked at approximately 3 and 6 months, respectively, after treatment initiation and remained elevated throughout treatment (greater than 3 years after treatment initiation). Drug-induced anti-PEG IgM and IgG antibodies were detected in the majority of patients (98%; N=277/284 for IgM; and 278/284 for IgG) with mean titers for both peaking at 1 to 3 months after treatment initiation. Neutralizing antibodies (NAb) capable of inhibiting PAL enzyme activity were detected on at least one measurement in the majority of patients (89%; N=253/284) over time. Mean NAb titers peaked and reached a plateau at 16 to 20 weeks of treatment and then remained present throughout treatment (greater than 3 years after treatment initiation).

Twenty-seven of 29 patients who had anaphylaxis were tested for anti‑pegvaliase‑pqpz IgE antibodies, which recognize the PEGylated protein product. Of the 27 patients tested for anti‑pegvaliase‑pqpz IgE antibodies, 26 patients tested negative. The one patient who tested positive for anti‑pegvaliase‑pqpz IgE antibodies on the screening test did not have sufficient sample to confirm IgE positivity. This patient tested negative for anti‑pegvaliase‑pqpz IgE at routine visits prior to and after the anaphylaxis episode (not at times of anaphylaxis). Sixty‑seven of 285 patients in clinical trials were tested for both anti‑PAL IgE antibodies, which recognize the recombinant PAL protein, and for anti‑pegvaliase‑pqpz IgE antibodies during routine study visits (not at times of anaphylaxis episodes) or during additional visits for hypersensitivity reactions. Of those 67 patients, 5 (8%) tested positive at least once for anti‑PAL IgE antibodies but negative for anti‑pegvaliase‑pqpz IgE antibodies.

The highest frequency of hypersensitivity reactions (consistent with a Type III immune complex-mediated hypersensitivity mechanism) occurred within the first 6 months of pegvaliase treatment when the mean circulating immune complex (CIC) concentrations were at their highest and mean complement C3 and C4 concentrations were at their lowest. Mean CIC concentrations decreased and complement levels increased over time as the exposure-adjusted rate of hypersensitivity reactions decreased. IgG and IgM CIC concentrations were above the upper limit of normal in 63% (N=164/259) and 42% of patients (N=109/259), respectively, at 12 weeks of pegvaliase treatment and returned towards baseline with long-term treatment (greater than 3 years after treatment initiation). 61% of patients (N=110/180) had complement C3 concentrations less than lower limit of normal (LLN) at 6 months after treatment initiation and 38% of patients (N=94/248) had complement C4 concentrations less than LLN at 3 months after treatment initiation. The incidence of low complement C3 and C4 concentrations decreased over time, but approximately 35% (N=34/96) and 12% (N=11/96) of patients had low C3 and C4 concentrations, respectively, at 36 months after treatment initiation.

Higher antibody responses for all antibody analytes, including NAb, were associated with lower mean trough pegvaliase‑pqpz concentrations and with higher blood phenylalanine concentrations. Hypersensitivity reactions occurred more frequently in patients with higher antibody titers for some but not all antibody analytes. Patients with higher mean change in IgG CIC concentrations from pre-treatment baseline tended to have higher discontinuation rates than patients with lower mean change in IgG CIC concentrations. Mean antibody titers for anti‑PAL IgG and IgM, TAb, and NAb remained relatively stable with long-term treatment.