Clinical Pharmacology for Carbaglu
Mechanism Of Action
Carglumic acid is a synthetic structural analogue of N-acetylglutamate (NAG) which is produced from glutamate and acetyl-CoA in a reaction catalyzed by N-acetylglutamate synthase (NAGS), a mitochondrial liver enzyme. NAG acts as the essential allosteric activator of carbamoyl phosphate synthetase 1 (CPS 1), a mitochondrial liver enzyme which catalyzes the first reaction of the urea cycle. The urea cycle, whose role is the disposition of ammonia, includes a series of biochemical reactions in the liver resulting in the conversion of ammonia into urea, which is then excreted through the urine. Carglumic acid acts as a CPS1 activator, improves or restores the function of the urea cycle, and facilitates ammonia detoxification and urea production.
Pharmacodynamics
In a retrospective review of the clinical course in 23 patients with NAGS deficiency, carglumic acid reduced plasma ammonia levels within 24 hours when administered with and without concomitant ammonia lowering therapies. No dose-response relationship has been identified.
Cardiac Electrophysiology
The effect of carglumic acid was evaluated in a Phase 1, randomized study in 76 healthy volunteers. The study suggests a lack of clinically relevant QT prolongation effect at the highest therapeutic dose level (250 mg/kg/day).
Pharmacokinetics
The pharmacokinetics of carglumic acid in healthy subjects following an intravenous (IV) infusion over 2 hours at 8 mg/kg or an oral administration at 100 mg/kg are summarized in Table 3.
Table 3: Mean (SD) Pharmacokinetic Parameter Values of Carglumic Acid in Healthy Subjects
| PK parameter |
IV infusion 8 mg/kg
(N=10) |
Oral 100 mg/kg
(N=12) |
| Cmax (ng/mL) |
8613 (558) |
3284 (321) |
| Tmax (hr)# |
2 (1-2) |
3 (2-4) |
| AUC (ng*hr/mL) |
24501 (1613) |
31426 (2150) |
| T1/2 (hr) |
31 (3) |
25 (2) |
| CL (L/hr/kg) |
0.34 (0.02) |
N/A |
| Vd (L/kg) |
15 (1) |
N/A |
| #Median (range); N/A, not applicable |
Absorption
Following an oral administration of CARBAGLU 100 mg/kg in healthy subjects, the absolute
bioavailability was approximately 10%.
Distribution
Carglumic acid is not bound to plasma proteins.
Elimination
Carglumic acid is predominantly excreted by the kidneys as unchanged product.
Metabolism
A proportion of carglumic acid may be metabolized by the intestinal bacterial flora.
The likely end product of carglumic acid metabolism is carbon dioxide, eliminated through the lungs.
Excretion
Following an oral administration of radiolabeled CARBAGLU at 100 mg/kg, 9% of the dose is excreted unchanged in the urine and up to 60% of the dose is recovered unchanged in the feces.
Specific Populations
Patients With Renal Impairment
The pharmacokinetics of carglumic acid in subjects with renal impairment were compared with healthy subjects with normal renal function following oral administration of a single dose of CARBAGLU 40 mg/kg or 80 mg/kg. The Cmax and AUC0-t of carglumic acid are summarized in Table 4. The geometric mean ratio (90% CI) of Cmax in subjects with mild, moderate, and severe renal impairment relative to those in their matched control subjects with normal renal function were approximately 1.3 (0.95, 1.86), 2.0 (1.62, 2.50), and 4.4 (3.11, 6.28), respectively. The geometric mean ratio (90% CI) of AUC0-t in subjects with mild, moderate, and severe renal impairment relative to those in their matched control subjects with normal renal function were approximately 1.4 (1.09, 1.73), 2.8 (2.27, 3.47), and 6.9 (5.21, 9.24), respectively [see DOSAGE AND ADMINISTRATION].
Table 4: Mean (SD) Cmax and AUC0-t of Carglumic Acid Following Single Oral Dose Administration of CARBAGLU 80 mg/kg or 40 mg/kg in Subjects with Renal Impairment and Matched Healthy Control Subjects with Normal Renal Function
PK
Parameters |
Normal Renal Function 1a:
eGFR ≥90 mL/min/1.73m2
(N=8) |
Mild Renal Impairment:
eGFR 60-89 mL/min/1.73m2
(N=8) |
Moderate Renal Impairment:
eGFR 30-59 mL/min/1.73m2
(N=8) |
Normal Renal Function 1b:
eGFR ≥90 mL/min/1.73m2
(N=8) |
Severe Renal Impairment:
eGFR 15-29 mL/min/1.73m2
(N=8) |
| 80 mg/kg |
40 mg/kg |
Cmax
(ng/mL) |
2983 (552) |
4310 (1937) |
6129 (1854) |
1890 (901) |
8377 (3815) |
AUC0-t
(ng*hr/mL) |
28313 (6204) |
39545 (12109) |
79766 (19708) |
20212 (6186) |
143075 (55910) |
| Treatment groups 1a and 1b represent two separate matched control groups of healthy subjects with normal renal function. |
Drug Interaction Studies
Based on in vitro studies, carglumic acid is not an inducer of CYP1A1/2, CYP2B6, CYP2C, and CYP3A4/5 enzymes, and not an inhibitor of CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4/5 enzymes.
Based on in vitro studies, carglumic acid is a substrate of the human OAT1 transporter.
Carglumic acid is not a substrate of MDR1, BCRP, MATE1, MATE2-K, OAT1, OAT3, OATP1B1, OATP1B3, OCT1, and OCT2. Carglumic acid is not an inhibitor of human BSEP, BCRP, MDR1, MATE1, MATE2-K, OAT1, OAT3, OATP1B1, OATP1B3, OCT1, and OCT2 transporters.
Clinical Studies
Acute And Chronic Hyperammonemia Due To NAGS Deficiency
The efficacy of CARBAGLU in the treatment of acute and chronic hyperammonemia due to NAGS deficiency was evaluated in a retrospective case series of 23 NAGS deficiency patients treated with CARBAGLU over a median duration of 7.9 years (range 0.6 to 20.8 years). For acute treatment, patients received CARBAGLU at 100 mg/kg/day to 250 mg/kg/day orally administered in 2 to 4 divided doses. For maintenance treatment, the dosage was reduced over time based on plasma ammonia level and clinical response.
The baseline characteristics of the patient population are shown in Table 5.
Table 5: Baseline Characteristics of 23 NAGS Deficiency Patients Treated with CARBAGLU
|
|
Patients
N=23 |
| Sex |
Male |
14 (61%) |
| Female |
9 (39%) |
| Age at initiation of CARBAGLU therapy (years) |
Mean (SD) |
2 (4) |
| Min-Max |
0-13 |
| Age groups at initiation of CARBAGLU therapy |
<30 days |
9 (39%) |
| >30 days - 11 months |
9 (39%) |
| ≥1 - 13 years |
5 (22%) |
| NAGS gene mutations by DNA testing |
Homozygous |
14 (61%) |
| Heterozygous |
4 (17%) |
| Not available |
5 (22%) |
| Patients current treatment status |
On-going |
18 (78%) |
| Discontinued |
5 (22%) |
The clinical and biochemical data in the 23-patient case series were retrospectively collected, unblinded, and uncontrolled and preclude formal statistical testing. Short-term efficacy was evaluated using mean and median change in plasma ammonia levels from baseline to days 1 to 3. Persistence of the effect was evaluated using long-term mean and median change in plasma ammonia level. Of the 23 NAGS deficiency patients in the case series, 13 patients had documented plasma ammonia levels prior to CARBAGLU treatment and after long-term treatment with CARBAGLU and were evaluable. Table 5 summarizes the plasma ammonia levels at baseline, days 1 to 3 post-CARBAGLU treatment, and long-term CARBAGLU treatment (mean 8 years) in the 13 evaluable patients.
All 13 patients had increased plasma ammonia levels at baseline (mean 271 micromol/L; normal range: 5 to 50 micromol/L). By day 3 and with long-term treatment, normal plasma ammonia levels were attained (Table 6).
Table 6: Plasma Ammonia Levels in NAGS Deficiency Patients at Baseline and After Treatment with CARBAGLU
| Timepoint |
Patients (N = 13) |
Ammonia level (micromol/L) |
Baseline
(prior to first dose of CARBAGLU) |
N |
13 |
| Mean (SD) |
271 (359) |
| Median |
157 |
| Range |
72-1428 |
| Missing Data |
0 |
| Day 1 |
N |
10 |
| Mean (SD) |
181 (358) |
| Median |
65 |
| Range |
25-1190 |
| Missing Data |
3 |
| Day 2 |
N |
8 |
| Mean (SD) |
69 (78) |
| Median |
44 |
| Range |
11-255 |
| Missing Data |
5 |
| Day 3 |
N |
5 |
| Mean (SD) |
27 (11) |
| Median |
25 |
| Range |
12-42 |
| Missing Data |
8 |
Long-term treatment
(mean duration 8 years; median duration 6
years; range 1-16 years based on
last available value while
on CARBAGLU treatment) |
N |
13 |
| Mean (SD) |
23 (7) |
| Median |
24 |
| Range |
9-34 |
| Missing Data |
0 |
The mean plasma ammonia level at baseline and the decline that is observed after treatment with CARBAGLU in 13 evaluable patients with NAGS deficiency is illustrated in Figure 1.
Figure 1: Mean Plasma Ammonia in 13 Evaluable NAGS Deficiency Patients at Baseline and After Treatment with CARBAGLU
Acute Hyperammonemia Due To PA And MMA
A randomized, double-blind, placebo-controlled, multicenter clinical trial evaluated the efficacy of CARBAGLU in the treatment of hyperammonemia in patients with PA and MMA (NCT01599286).
Eligible hyperammonemic episodes, defined as an admission to the hospital with a plasma ammonia level ≥ 70 micromol/L, were randomized 1:1 to receive either CARBAGLU or placebo for 7 days or until hospital discharge, whichever occurred earlier. All patients received standard of care, including a combination of protein restriction, intravenous glucose, insulin, and/or Lcarnitine; the use of alternative pathway medications (e.g., sodium benzoate and medications with phenylacetate as an active metabolite) was prohibited. CARBAGLU was dosed orally at 150 mg/kg/day for patients ≤ 15 kg or 3.3 g/m2/day for patients > 15 kg and was divided into 2 equal doses administered 12 hours apart by NG tube, G-tube, or oral syringe. Plasma ammonia testing was performed at pre-randomization and at post-dosing intervals of every 6 -12 hours for the first 48 hours and every day thereafter if the ammonia level was ≥ 50 micromol/L.
The efficacy evaluation was based on 90 hyperammonemic episodes (42 treated with CARBAGLU and 48 with placebo) in 24 patients (12 male and 12 female) with PA (n = 15) or MMA (n = 9). The median patient age was 8 years (range 4 days to 29 years). The primary endpoint was the time from the first dose of drug to the earlier of plasma ammonia level ≤ 50 micromol/L (normal range) or hospital discharge. The median time to reach the primary endpoint was 1.5 days in the CARBAGLU group compared to 2.0 days in the placebo group, a difference of 0.5 days (95% confidence interval: -1.2, 0.1), driven by an effect on plasma ammonia normalization. Throughout the first three days of treatment, a higher proportion of CARBAGLUtreated episodes reached the primary endpoint compared to placebo-treated episodes (Figure 2).
Figure 2: Episodes Reaching the Earlier of Plasma Ammonia Level ≤ 50 micromol/L or Hospital Discharge in Patients with PA or MMA Treated with CARBAGLU or Placebo for up to 7 days