Clinical Pharmacology for Endari
Mechanism Of Action
The mechanism of action of the amino acid L-glutamine in treating sickle cell disease (SCD) is not fully understood. Oxidative stress phenomena are involved in the pathophysiology of SCD. Sickle red blood cells (RBCs) are more susceptible to oxidative damage than normal RBCs, which may contribute to the chronic hemolysis and vaso-occlusive events associated with SCD. The pyridine nucleotides, NAD+ and its reduced form NADH, play roles in regulating and preventing oxidative damage in RBCs. L-glutamine may improve the NAD redox potential in sickle RBCs through increasing the availability of reduced glutathione.
Pharmacodynamics
In vivo analyses demonstrated that L-glutamine supplementation improved NAD redox potential.
Pharmacokinetics
The pharmacokinetics of L-glutamine has been studied in healthy subjects and a variety of disease states. Relevant results from published literature are summarized below.
Absorption
Following single-dose oral administration of L-glutamine at 0.1 g/kg, mean peak L-glutamine concentration was 1028 μM (or 150 mcg/mL) occurring approximately 30 minutes after administration.
The pharmacokinetics following multiple oral doses has not been characterized.
Distribution
After an intravenous (IV) bolus dose, the volume of distribution was estimated to be approximately 200 mL/kg.
Elimination
After an intravenous bolus dose, the terminal half-life of L-glutamine was approximately one hour.
Metabolism
Endogenous L-glutamine participates in various metabolic activities, including the formation of glutamate, and synthesis of proteins, nucleotides, and amino sugars. Exogenous L-glutamine is anticipated to undergo similar metabolism.
Excretion
Metabolism is the major route of elimination for L-glutamine. Although L-glutamine is eliminated by glomerular filtration, it is almost completely reabsorbed by the renal tubules.
Specific Populations
The safety of Endari has not been established in patients with renal or hepatic impairment.
Drug Interactions
No drug interaction studies have been conducted.
Clinical Studies
The efficacy of Endari in sickle cell disease was evaluated in a randomized, double-blind, placebo-controlled, multi-center clinical trial entitled “A Phase III Safety and Efficacy Study of L-Glutamine to Treat Sickle Cell Disease or Sickle βo-thalassemia” [NCT01179217] (see Table 3).
The clinical trial evaluated the efficacy and safety of Endari in 230 patients (5 to 58 years of age) with sickle cell anemia or sickle β0-thalassemia who had 2 or more painful crises within 12 months prior to enrollment. Eligible patients stabilized on hydroxyurea for at least 3 months continued their therapy throughout the study. The trial excluded patients who had received blood products within 3 weeks, had renal insufficiency or uncontrolled liver disease, or were pregnant (or planning pregnancy) or lactating. Study patients received Endari or placebo for a treatment duration of 48 weeks followed by 3 weeks of tapering.
Efficacy was demonstrated by a reduction in the number of sickle cell crises through Week 48 and prior to the start of tapering among patients that received Endari compared to patients who received placebo. This clinical benefit was observed irrespective of hydroxyurea use. A sickle cell crisis was defined as a visit to an emergency room/medical facility for sickle cell disease-related pain which was treated with a parenterally administered narcotic or parenterally administered ketorolac. In addition, the occurrence of chest syndrome, priapism, and splenic sequestration were considered sickle cell crises. Treatment with Endari also resulted in fewer hospitalizations due to sickle cell pain at Week 48, fewer cumulative days in hospital and a lower incidence of acute chest syndrome.
Table 3. Results from the Endari Clinical Trial in Sickle Cell Disease
| Event | Endari (n = 152) | Placebo (n = 78) |
| Median number of sickle cell crises (min, max)1 | 3 (0, 15) | 4 (0, 15) |
| Median number of hospitalizations for sickle cell pain (min, max)1 | 2 (0, 14) | 3 (0, 13) |
| Median cumulative days hospitalized (min, max)1 | 6.5 (0, 94) | 11 (0, 187) |
| Median time (days) to first sickle cell crisis (95% CI)1,2 | 84 (62, 109) | 54 (31, 73) |
| Patients with occurrences of acute chest syndrome (%)1 | 13 (8.6%) | 18 (23.1%) |
1. Measured through 48 weeks of treatment 2. Hazard Ratio=0.69 (95% CI=0.52, 0.93), estimated based on unstratified Cox’s proportional model. Median time and 95% CI were estimated based on the Kaplan Meier method. |
The recurrent crisis event time analysis (Figure 1) yielded an intensity rate ratio (IRR) value of 0.75 with 95% CI= (0.62, 0.90) and (0.55, 1.01) based on unstratified models using the Andersen-Gill and Lin, Wei, Yang and Ying methods, respectively in favor of Endari, suggesting that over the entire 48week period, the average cumulative crisis count was reduced by 25% from the Endari group over the placebo group.
Figure 1. Recurrent Event Time for Sickle Cell Crises by Treatment Group
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| *Andersen-Gill: 95% CI (0.62, 0.90); Lin-Wei-Yang-Ying: 95% CI (0.55, 1.01) |