Normal Plasma Ammonia

In patients treated with RAVICTI who experience neurologic symptoms (e.g. nausea, vomiting, headache, somnolence or confusion) in the absence of high plasma ammonia or other intercurrent illness to explain these symptoms, consider reducing the RAVICTI dosage and clinically monitor patients for potential neurotoxicity from high phenylacetate (PAA) concentrations. If available, obtain measurements of plasma PAA concentrations and plasma phenylacetylglutamine (PAGN) to calculate the ratio of plasma PAA to PAGN which may help to guide RAVICTI dosing. The PAA to PAGN ratio has generally been less than 1 in patients with UCDs who did not have significant plasma PAA accumulation. In general, a high PAA to PAGN ratio may indicate a slower or less efficient conjugation reaction to form PAGN, which may lead to increases in PAA without further conversion to PAGN [see Warnings and Precautions (5.1), Clinical Pharmacology (12.3)].

Elevated Plasma Ammonia

In patients 6 years and older, when plasma ammonia is elevated, increase the RAVICTI dosage to maintain fasting plasma ammonia to less than half the upper limit of normal (ULN). In infants and pediatric patients below 6 years of age, if obtaining fasting ammonia is problematic due to frequent feedings, adjust the RAVICTI dosage to keep the first ammonia of the morning below the ULN for age. If available, the ratio of PAA to PAGN in the same plasma sample may provide additional information to assist in dosage adjustment decisions [see Use in Specific Populations (8.7), Clinical Pharmacology (12.3)].

Dietary Protein Intake

If available, urinary phenylacetylglutamine (U-PAGN) measurements may be used to help guide RAVICTI dosage adjustment. Each gram of U-PAGN excreted over 24 hours covers waste nitrogen generated from 1.4 grams of dietary protein. If U-PAGN excretion is insufficient to cover daily dietary protein intake and the fasting ammonia is greater than half the ULN, the RAVICTI dosage should be increased. The amount of dosage adjustment should factor in the amount of dietary protein that has not been covered, as indicated by the 24-hour U-PAGN output, and the estimated RAVICTI dose needed per gram of dietary protein ingested and the maximum total daily dosage (i.e., 17.5 mL).

Consider a patient's use of concomitant medications, such as probenecid, when making dosage adjustment decisions based on U-PAGN. Probenecid may result in a decrease of the urinary excretion of PAGN [see Drug Interactions (7.2)].

Other Adverse Reactions

RAVICTI has been evaluated in 77 patients with UCDs (51 adult and 26 pediatric patients ages 2 years to 17 years) in 2 open-label long-term studies, in which 69 patients completed 12 months of treatment with RAVICTI (median exposure = 51 weeks). During these studies there were no deaths.

Adverse reactions reported in at least 10% of adult patients were nausea, vomiting, diarrhea, decreased appetite, dizziness, headache, and fatigue.

Adverse reactions reported in at least 10% of pediatric patients ages 2 years to 17 years were upper abdominal pain, rash, nausea, vomiting, diarrhea, decreased appetite, and headache.

RAVICTI has been evaluated in 17 patients with UCDs ages 2 months to less than 2 years in 3 open-label studies. The median exposure was 6 months (range 0.2 to 20 months). Adverse reactions reported in at least 10% of pediatric patients aged 2 months to less than 2 years were neutropenia, vomiting, constipation, diarrhea, pyrexia, hypophagia, cough, nasal congestion, rhinorrhea, rash, and papule.

RAVICTI has been evaluated in 16 patients with UCDs less than 2 months of age (age range 0.1 to 2 months, median age 0.5 months) in a single, open-label study. The median exposure was 10 months (range 2 to 20 months). Adverse reactions reported in at least 10% of pediatric patients aged less than 2 months were vomiting, rash, gastroesophageal reflux, increased hepatic enzymes, feeding disorder (decreased appetite, hypophagia), anemia, cough, dehydration, metabolic acidosis, thrombocytosis, thrombocytopenia, neutropenia, lymphocytosis, diarrhea, flatulence, constipation, pyrexia, lethargy, and irritability/agitation.

Corticosteroids

Use of corticosteroids may cause the breakdown of body protein and increase plasma ammonia levels. Monitor ammonia levels closely when corticosteroids and RAVICTI are used concomitantly.

Valproic Acid and Haloperidol

Hyperammonemia may be induced by haloperidol and by valproic acid. Monitor ammonia levels closely when use of valproic acid or haloperidol is necessary in patients with UCDs.

Probenecid

Probenecid may inhibit the renal excretion of metabolites of RAVICTI including PAGN and PAA.

Drugs with narrow therapeutic index that are substrates of CYP3A4

RAVICTI is a weak inducer of CYP3A4 in humans. Concomitant use of RAVICTI may decrease the systemic exposure to drugs that are substrates of CYP3A4. Monitor for decreased efficacy of drugs with narrow therapeutic index (e.g., alfentanil, quinidine, cyclosporine) [see Clinical Pharmacology (12.3)].

Midazolam

Concomitant use of RAVICTI decreased the systemic exposure of midazolam. Monitor for suboptimal effect of midazolam in patients who are being treated with RAVICTI.

Risk Summary

Limited available data with RAVICTI use in pregnant women are insufficient to inform a drug-associated risk of major birth defects and miscarriage. In an animal reproduction study, administration of oral glycerol phenylbutyrate to pregnant rabbits during organogenesis at doses up to 2.7–times the dose of 6.87 mL/m2/day in adult patients resulted in maternal toxicity, but had no effects on embryo-fetal development. In addition, there were no adverse developmental effects with administration of oral glycerol phenylbutyrate to pregnant rats during organogenesis at 1.9 times the dose of 6.87 mL/m2/day in adult patients; however, maternal toxicity, reduced fetal weights, and variations in skeletal development were observed in pregnant rats administered oral glycerol phenylbutyrate during organogenesis at doses greater than or equal to 5.7 times the dose of 6.87 mL/m2/day in adult patients [see Data]. Report pregnancies to Horizon at 1-866-479-6742.

The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss or other adverse 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.

Data

Risk Summary

There are no data on the presence of RAVICTI in human milk, the effects on the breastfed infant, or the effects on milk production. Because of the potential for serious adverse reactions, including neurotoxicity and tumorigenicity in a breastfed infant, advise patients that breastfeeding is not recommended during treatment with RAVICTI.

Patients 2 Years to 17 Years of Age

The safety and effectiveness of RAVICTI in patients 2 years to less than 18 years of age have been established in 3 clinical studies: 2 open-label, fixed-sequence, switchover clinical studies from sodium phenylbutyrate to RAVICTI, and 1 long-term, open label safety study [see Adverse Reactions (6.1), Clinical Studies (14.2)].

Patients Less Than 2 Years of Age

The safety and effectiveness of RAVICTI in patients with UCDs less than 2 years of age have been established in 3 open-label studies. Pharmacokinetics and pharmacodynamics (plasma ammonia), and safety were studied in 17 patients aged 2 months to less than 2 years of age and in 16 patients less than 2 months of age [see Adverse Reactions (6.1), Clinical Studies (14.3)].

Juvenile Animal Toxicity Data

In a juvenile rat study with daily oral dosing performed on postpartum day 2 through mating and pregnancy after maturation, terminal body weight was dose-dependently reduced by up to 16% in males and 12% in females at 900 mg/kg/day or higher (3 times the dose of 6.87 mL/m2/day in adult patients, based on combined AUCs for PBA and PAA). Learning, memory, and motor activity endpoints were not affected. However, fertility (number of pregnant rats) was decreased by up to 25% at 650 mg/kg/day or higher (2.6 times the dose of 6.87 mL/m2/day in adult patients, based on combined AUCs for PBA and PAA).

Pharmacological Effects

In clinical studies, total 24-hour area under the plasma concentration-time curve (AUC) of ammonia levels was comparable at steady state during the switchover period between RAVICTI and sodium phenylbutyrate [see Clinical Studies (14)].

Cardiac Electrophysiology

The effect of multiple doses of RAVICTI 13.2 g/day and 19.8 g/day (approximately 69% and 104% of the maximum recommended daily dosage) on QTc interval was evaluated in a randomized, placebo- and active-controlled (moxifloxacin 400 mg), four-treatment-arm, crossover study in 57 healthy subjects. The upper bound of the one-sided 95% CI for the largest placebo-adjusted, baseline-corrected QTc, based on individual correction method (QTcI) for RAVICTI, was below 10 ms.

Absorption

RAVICTI is a pro-drug of PBA. Upon oral ingestion, PBA is released from the glycerol backbone in the gastrointestinal tract by lipases. PBA derived from RAVICTI is further converted by β-oxidation to PAA.

In healthy, fasting adult subjects receiving a single oral dose of 2.9 mL/m2 of RAVICTI, peak plasma levels of PBA, PAA, and PAGN occurred at 2 hours, 4 hours, and 4 hours, respectively. Upon single-dose administration of RAVICTI, plasma concentrations of PBA were quantifiable in 15 of 22 participants at the first sample time postdose (0.25 hours). Mean maximum concentration (Cmax) for PBA, PAA, and PAGN was 37.0 micrograms/mL, 14.9 micrograms/mL, and 30.2 micrograms/mL, respectively. In healthy subjects, intact glycerol phenylbutyrate was detected in plasma. While the study was inconclusive, the incomplete hydrolysis of glycerol phenylbutyrate cannot be ruled out.

In healthy subjects, the systemic exposure to PAA, PBA, and PAGN increased in a dose-dependent manner. Following 4 mL of RAVICTI 3 times a day for 3 days, the mean Cmax and AUC were 66 micrograms/mL and 930 micrograms∙h/mL for PBA and 28 micrograms/mL and 942 micrograms∙h/mL for PAA, respectively. In the same study, following 6 mL of RAVICTI three times a day for 3 days, mean Cmax and AUC were 100 micrograms/mL and 1400 micrograms∙h/mL for PBA and 65 μg/mL and 2064 micrograms∙h/mL for PAA, respectively.

In adult patients with UCDs receiving multiple doses of RAVICTI, maximum plasma concentrations at steady state (Cmax,ss) of PBA, PAA, and PAGN occurred at 8 hours, 12 hours, and 10 hours, respectively, after the first dose in the day. Intact glycerol phenylbutyrate was not detectable in plasma in patients with UCDs.

In clinical studies of RAVICTI in patients with UCDs, the peak observed PAA concentrations by age group are shown in Table 2.

Distribution

In vitro, the extent of plasma protein binding for 14C-labeled metabolites was 81% to 98% for PBA (over 1 to 250 micrograms/mL), and 37% to 66% for PAA (over 5 to 500 micrograms/mL). The protein binding for PAGN was 7% to 12% and no concentration effects were noted.

Elimination

Specific Populations

Drug Interaction Studies

In vitro PBA or PAA did not induce CYP1A2, suggesting that in vivo drug interactions via induction of CYP1A2 is unlikely.

In in vitro studies, PBA at a concentration of 800 micrograms/mL caused greater than 60% reversible inhibition of cytochrome P450 isoenzymes CYP2C9, CYP2D6, and CYP3A4/5 (testosterone 6β-hydroxylase activity). The in vitro study suggested that in vivo drug interactions with substrates of CYP2D6 cannot be ruled out. The inhibition of CYP isoenzymes 1A2, 2C8, 2C19, and 2D6 by PAA at the concentration of 2.8 mg/mL was observed in vitro. Clinical implication of these results is unknown.

Carcinogenesis

In a 2-year study in Sprague-Dawley rats, glycerol phenylbutyrate caused a statistically significant increase in the incidence of pancreatic acinar cell adenoma, carcinoma, and combined adenoma or carcinoma at a dose of 650 mg/kg/day in males (4.7 times the dose of 6.9 mL/m2/day in adult patients, based on combined AUCs for PBA and PAA) and 900 mg/kg/day in females (8.4 times the dose of 6.9 mL/m2/day in adult patients, based on combined AUCs for PBA and PAA). The incidence of the following tumors was also increased in female rats at a dose of 900 mg/kg/day: thyroid follicular cell adenoma, carcinoma and combined adenoma or carcinoma, adrenal cortical combined adenoma or carcinoma, uterine endometrial stromal polyp, and combined polyp or sarcoma. The dose of 650 mg/kg/day in male rats is 3 times the dose of 7.5 mL/m2/day in pediatric patients, based on combined AUCs for PBA and PAA. The dose of 900 mg/kg/day in female rats is 5.5 times the dose of 7.5 mL/m2/day in pediatric patients, based on combined AUCs for PBA and PAA. In a 26-week study in transgenic (Tg.rasH2) mice, glycerol phenylbutyrate was not tumorigenic at doses up to 1000 mg/kg/day.

Mutagenesis

Glycerol phenylbutyrate was not genotoxic in the Ames test, the in vitro chromosomal aberration test in human peripheral blood lymphocytes, or the in vivo rat micronucleus test. The metabolites PBA, PAA, PAGN, and phenylacetylglycine were not genotoxic in the Ames test or in vitro chromosome aberration test in Chinese hamster ovary cells.

Impairment of Fertility

Glycerol phenylbutyrate had no effect on fertility or reproductive function in male and female rats at oral doses up to 900 mg/kg/day. At doses of 1200 mg/kg/day (approximately 7 times the dose of 6.9 mL/m2/day in adult patients, based on combined AUCs for PBA and PAA), maternal toxicity was observed and the number of nonviable embryos was increased.

Active-Controlled, 4-Week, Noninferiority Study (Study 1)

A randomized, double-blind, active-controlled, crossover, noninferiority study (Study 1) compared RAVICTI to sodium phenylbutyrate by evaluating ammonia levels in patients with UCDs who had been on sodium phenylbutyrate prior to enrollment for control of their UCD. Patients were required to have a confirmed diagnosis of UCD involving deficiencies of CPS, OTC, or ASS, confirmed via enzymatic, biochemical, or genetic testing. Patients had to have no clinical evidence of hyperammonemia at enrollment and were not allowed to receive drugs known to increase ammonia levels (e.g., valproate), increase protein catabolism (e.g., corticosteroids), or significantly affect renal clearance (e.g., probenecid).

The primary endpoint was the 24-hour AUC (a measure of exposure to ammonia over 24 hours) for venous ammonia on days 14 and 28 when the drugs were expected to be at steady state. Statistical noninferiority would be established if the upper limit of the 2-sided 95% CI for the ratio of the geometric means (RAVICTI/sodium phenylbutyrate) for the endpoint was 1.25 or less.

Forty-five patients were randomized 1:1 to 1 of 2 treatment arms to receive either

–

Sodium phenylbutyrate for 2 weeks → RAVICTI for 2 weeks; or

–

RAVICTI for 2 weeks → sodium phenylbutyrate for 2 weeks.

Sodium phenylbutyrate or RAVICTI were administered three times daily with meals. The dose of RAVICTI was calculated to deliver the same amount of PBA as the sodium phenylbutyrate dose the patients were taking when they entered the study. Forty-four patients received at least 1 dose of RAVICTI in the study.

Patients adhered to a low-protein diet and received amino acid supplements throughout the study. After 2 weeks of dosing, by which time patients had reached steady state on each treatment, all patients had 24 hours of ammonia measurements.

Demographic characteristics of the 45 patients enrolled in Study 1 were as follows: mean age at enrollment was 33 years (range: 18 to 75 years); 69% were female; 33% had adult-onset disease; 89% had OTC deficiency; 7% had ASS deficiency; 4% had CPS deficiency.

RAVICTI was non-inferior to sodium phenylbutyrate with respect to the 24-hour AUC for ammonia. Forty-four patients were evaluated in this analysis. Mean 24-hour AUCs for ammonia during steady-state dosing were 866 micromol∙h/L and 977 micromol∙h/L with RAVICTI and sodium phenylbutyrate, respectively. The ratio of geometric means was 0.91 [95% CI 0.8, 1.04].

The mean ammonia levels over 24-hours after 2 weeks of dosing (on day 14 and 28) in the double-blind short-term study (Study 1) are displayed in Figure 2 below. The mean and median maximum ammonia levels (Cmax) over 24 hours and 24-hour AUC for ammonia are summarized in Table 3. Ammonia values across different laboratories were normalized to a common normal range of 9 to 35 micromol/L using the following formula after standardization of the units to micromol/L:

Normalized ammonia (micromol/L) = ammonia readout in micromol/L × (35/ULN of a laboratory reference range specified for each assay)

Figure 2: Ammonia Levels in Adult Patients with UCDs in Short-Term Treatment Study 1

Open-Label, Uncontrolled, Extension Study in Adults

A long-term (12-month), uncontrolled, open-label study (Study 2) was conducted to assess monthly ammonia control and hyperammonemic crisis over a 12-month period. A total of 51 adults were in the study and all but 6 had been converted from sodium phenylbutyrate to RAVICTI. Venous ammonia levels were monitored monthly. Mean fasting ammonia values in adults in Study 2 were within normal limits during long-term treatment with RAVICTI (range: 6 to 30 micromol/L). Of 51 adult patients participating in the 12-month, open-label treatment with RAVICTI, 7 patients (14%) reported a total of 10 hyperammonemic crises. The fasting ammonia measured during Study 2 is displayed in Figure 3. Ammonia values across different laboratories were normalized to a common normal range of 9 to 35 micromol/L.

Figure 3: Ammonia Levels in Adult Patients with UCDs in Long-Term Treatment Study 2

Open-Label, Long-Term Study in Adults

An open-label long-term, study (Study 5) was conducted to assess ammonia control in adult patients with UCDs. The study enrolled patients with UCDs who had completed the safety extensions of Study 1, Study 3 or Study 4 (Study 2, 3E and 4E, respectively). A total of 43 adult patients between the ages of 19 and 61 years were in the study. The median length of study participation was 1.9 years (range 0 to 4.5 years). Venous ammonia levels were monitored at a minimum of every 6 months. Mean fasting ammonia values in adult patients in Study 5 were within normal limits during long-term (24 months) treatment with RAVICTI (range: 24.2 to 31.4 micromol/L). Of the 43 adult patients participating in the open-label treatment with RAVICTI, 9 patients (21%) reported a total of 21 hyperammonemic crises. Ammonia values across different laboratories were normalized to a common normal range of 10 to 35 micromol/L.

Open-Label, Uncontrolled, Extension Studies in Pediatric Patients 2 Years to 17 Years of Age

Long-term (12-month), uncontrolled, open-label studies were conducted to assess monthly ammonia control and hyperammonemic crises over a 12-month period. In two studies (Study 2, which also enrolled adults, and an extension of Study 3, referred to here as Study 3E), a total of 26 pediatric patients ages 6 years to 17 years were enrolled and all but 1 had been converted from sodium phenylbutyrate to RAVICTI. Mean fasting venous ammonia levels were within normal limits (range 17 to 23 micromol/L) during long-term treatment with RAVICTI. Of the 26 pediatric patients 6 years to 17 years of age participating in these two trials, 5 patients (19%) reported a total of 5 hyperammonemic crises. The fasting ammonia levels measured during these two extension studies in patients 6 years to 17 years are displayed in Figure 5. Ammonia values across different laboratories were normalized to a common normal range of 9 to 35 micromol/L.

Figure 5: Ammonia Levels in Pediatric Patients 2 Years to 17 Years of Age with UCDs in Long-Term Treatment Studies 2 and 3E

In an extension of Study 4 (referred to as Study 4E), after a median time on study of 4.5 months (range: 1 to 5.7 months), 2 of 16 pediatric patients ages 2 years to 5 years had experienced three hyperammonemic crises.

Open-Label, Long-Term Study in Pediatric Patients 1 Year to 17 Years of Age

An open-label, long-term study (Study 5) was conducted to assess ammonia levels in pediatric patients with UCD. The study enrolled patients with UCDs who had completed Studies 2, 3E and 4E. A total of 45 pediatric patients ages 1 year to 17 years were included in the study. The median length of treatment was 1.7 years (range 0.2 to 4.6 years). Venous ammonia levels were monitored at a minimum every 6 months. Mean ammonia values in pediatric patients in Study 5 were within normal limits during long-term (24 months) treatment with RAVICTI (range: 15.4 to 25.1 micromol/L). Of the 45 pediatric patients participating in the open-label treatment with RAVICTI, 11 patients (24%) reported a total of 22 hyperammonemic crises. Ammonia values across different laboratories were normalized to a common normal range of 10 to 35 micromol/L.

Uncontrolled, Open-Label Studies in Pediatric Patients Aged 2 Months to Less than 2 Years of Age (Studies 4/4E, 5)

A total of 7 patients with UCDs aged 2 months to less than 2 years participated in Studies 4/4E and 5. In these studies, there were 7, 6, 6, 6 and 3 pediatric patients who completed 1, 6, 9, 12 and 18 months, respectively (mean and median exposure of 15 and 17 months, respectively). Patients were converted from sodium phenylbutyrate to RAVICTI. The dosage of RAVICTI was calculated to deliver the same amount of PBA as the sodium phenylbutyrate dosage the patients were taking when they entered the study.

Patients received a mean RAVICTI dose of 7.5 mL/m2/day (8.2 g/m2/day), with doses ranging from 3.3 to 12.3 mL/m2/day (3.7 to 13.5 g/m2/day). Patients were dosed three times per day (n=3) or four times per day (n = 4).

Venous ammonia levels were monitored on days 1, 3, and 10 in Study 4 and at week 1 in Study 4E. Two patients had elevated ammonia values on day 1 of treatment (122 micromol/L and 111 micromol/L respectively) and neither had associated signs and symptoms of hyperammonemia. At day 10/week 1, six of the 7 patients had normal ammonia levels (less than 100 micromol/L) while the remaining patient had an elevated ammonia value on day 10 (168 micromol/L) and was asymptomatic.

During the extension period, venous ammonia levels were monitored monthly. Ammonia values across different laboratories were normalized (transformed) to a common normal pediatric range of 28 to 57 micromol/L for comparability. The mean ammonia levels in pediatric patients at month 1, 3, 6, 9 and 12 were 58, 49, 34, 65, and 31 micromol/L during treatment with RAVICTI, respectively.

Three patients reported a total of 3 hyperammonemic crises defined as having signs and symptoms consistent with hyperammonemia (such as frequent vomiting, nausea, headache, lethargy, irritability, combativeness, and/or somnolence) associated with high ammonia levels (greater than 100 micromol/L) and requiring medical intervention. Hyperammonemic crises were precipitated by gastroenteritis, vomiting, infection or no precipitating event (one patient). There were 4 patients who had one ammonia level that exceeded 100 micromol/L which was not associated with a hyperammonemic crisis.

Uncontrolled, Open-Label Study in Pediatric Patients Less Than 2 Years of Age (Study 6)

Study 6 was an uncontrolled, open label study in pediatric patients less than 2 years of age. The primary efficacy endpoint was successful transition to RAVICTI within a period of 4 days followed by 3 days of observation for a total of 7 days, where successful transition was defined as no signs and symptoms of hyperammonemia and a venous ammonia level less than 100 micromol/L. Ammonia levels were monitored for up to 4 days during transition and on day 7.