What were the design, patient population, dosing regimen, efficacy, and safety results of the BALANCE phase‑2 trial of olezarsen in adults with severe hypertriglyceridaemia (fasting triglycerides >500 mg/dL)?

BALANCE Phase 2 Trial of Olezarsen in Severe Hypertriglyceridemia

The BALANCE trial was actually a Phase 3 (not Phase 2) randomized, double-blind, placebo-controlled study that enrolled 66 patients with familial chylomicronemia syndrome (FCS) who had severe hypertriglyceridemia with fasting triglycerides >500 mg/dL, demonstrating that olezarsen 80 mg subcutaneously every 4 weeks reduced triglycerides by 43.5% compared to placebo at 6 months and dramatically reduced acute pancreatitis episodes. 1

Study Design

The trial randomized patients 1:1:1 to receive:

• Olezarsen 80 mg subcutaneously every 4 weeks (n=22)
• Olezarsen 50 mg subcutaneously every 4 weeks (n=21)
• Placebo (n=23)

Treatment duration was 49-53 weeks with primary endpoint assessment at 6 months (average of weeks 23,25, and 27). 12

Patient Population Characteristics

Baseline demographics:

• Mean fasting triglycerides: 2,630 ± 1,315 mg/dL (median 2,303 mg/dL; range 334-6,898 mg/dL)
• 71% had documented acute pancreatitis within the prior 10 years
• 32% had diabetes in the 80 mg group (26% in placebo)
• Background lipid therapies: 27% on statins, 42% on omega-3 fatty acids, 49% on fibrates, 13% on other lipid-lowering therapies
• All patients had genetically confirmed familial chylomicronemia syndrome 12

This represents a severely affected population with extremely elevated triglycerides and high pancreatitis risk, reflecting the real-world FCS patient burden.

Efficacy Results

Primary Endpoint (Triglyceride Reduction at 6 Months)

The 80 mg dose met the primary endpoint with statistical significance:

• Placebo-corrected reduction: -43.5% (95% CI: -69.1% to -17.9%; p<0.001)
• Absolute treatment difference: -43% (95% CI: -74%, -11%; p=0.0084) 12

The 50 mg dose failed to achieve statistical significance:

• Placebo-corrected reduction: -22.4% (95% CI: -47.2% to 2.5%; p=0.08) 1

This dose-response relationship established 80 mg as the appropriate therapeutic dose for FCS.

Secondary Lipid Parameters at 6 Months (80 mg dose)

• Apolipoprotein C-III: -73.7% vs placebo (95% CI: -94.6% to -52.8%)
• Non-HDL cholesterol: -23% vs placebo (95% CI: -45%, -2%)
• Apolipoprotein B-48: -76% vs placebo (95% CI: -150%, -2%)
• LDL cholesterol: +55% increase (95% CI: 1%, 109%) - though remained <70 mg/dL in 74% of patients 2

The substantial apoC-III reduction is mechanistically important, as this is the direct target of olezarsen's antisense oligonucleotide mechanism.

Sustained Effect Over Time

Median triglyceride levels remained consistently suppressed throughout the 12-month treatment period, with durable reductions observed from month 6 through month 12. 2

Critical Clinical Outcome: Acute Pancreatitis

By 53 weeks, olezarsen dramatically reduced pancreatitis episodes:

• Placebo group: 11 episodes (7 patients, 30% of group)
• Combined olezarsen groups: 2 episodes total (1 in each dose group)
• Rate ratio: 0.12 (95% CI: 0.02-0.66) - representing an 88% reduction in pancreatitis risk 12

This represents the most clinically meaningful outcome, as acute pancreatitis is the primary driver of morbidity and mortality in FCS patients. All patients who developed pancreatitis had prior history within 10 years of screening.

Safety Profile

Common Adverse Events

Injection site reactions were the most notable treatment-related adverse event:

• Occurred more frequently with olezarsen vs placebo (RR 3.93) 3

Platelet count reductions:

• Platelet counts <140,000/µL occurred more frequently (RR 4.76) 3
• This requires monitoring but was not associated with bleeding events

Moderate Severity Events

4 patients in the 80 mg group experienced moderate adverse events considered related to study drug by investigators 1

Serious Adverse Events

No significant increase in serious adverse events compared to placebo, and liver enzyme elevations were comparable to placebo 3

Immunogenicity

42% of FCS patients (18/43) developed treatment-emergent anti-drug antibodies through 53 weeks. While ADAs increased trough concentrations, they did not affect clinical efficacy, safety, or peak drug levels 2

Clinical Context and Caveats

Important considerations:

• The FDA label data 22 confirms this was designated as a Phase 3 trial (Trial 1 in the label), not Phase 2, though it may have been referred to as BALANCE
• The 50 mg dose is not recommended for FCS based on failure to meet primary endpoint; only 80 mg every 4 weeks is FDA-approved for this indication
• The LDL-C increase, while statistically significant, remained within acceptable range for most patients and should be monitored
• All efficacy was demonstrated on top of maximally tolerated conventional therapies, which are largely ineffective in FCS due to the genetic lipoprotein lipase deficiency
• The dramatic pancreatitis reduction occurred in a population with 71% prior pancreatitis history, representing the highest-risk patients

Per ACC guidelines 44, patients with triglycerides ≥1,000 mg/dL require extreme dietary fat restriction (10-15% of calories) and complete alcohol abstinence, which should continue alongside olezarsen therapy.