Which Initial Invega Sustenna Dose is the Loading Dose?
Both initial doses function together as a loading regimen, but the Day 1 dose of 234 mg (150 mg eq) administered in the deltoid is specifically designed as the primary loading dose to rapidly achieve therapeutic concentrations. 1, 2
Understanding the Two-Dose Initiation Regimen
The recommended initiation protocol for Invega Sustenna consists of:
- Day 1: 234 mg (150 mg eq) deltoid injection - This is the loading dose that initiates rapid therapeutic blood levels 1, 2
- Day 8: 156 mg (100 mg eq) deltoid injection - This is the second initiation dose that maintains and continues the therapeutic effect 1, 2
Why Day 1 is Considered the Loading Dose
The 234 mg Day 1 injection achieves significantly greater symptom improvement compared to placebo by Day 8, demonstrating its role as the primary loading dose. 3 This design allows therapeutic concentrations to be reached rapidly without requiring oral antipsychotic supplementation, which distinguishes it from other long-acting injectable formulations. 1, 4
The pharmacokinetic profile shows that:
- Release begins as early as Day 1 following the initial injection 2
- Maximum plasma concentrations are reached at approximately 13 days 2
- The onset of clinical response occurs by Day 8 in patients receiving the 234 mg initial dose 4
Clinical Significance of Both Doses
While Day 1 serves as the loading dose, both injections must be administered in the deltoid muscle during initiation because deltoid injection produces approximately 28% higher maximum concentrations compared to gluteal injection. 2 This is critical for achieving rapid therapeutic levels.
After the Day 8 injection of 156 mg, continued symptom improvement is observed at Day 22 and Day 36, with evidence of a dose-dependent response trend. 3 This demonstrates that the Day 8 dose is essential for maintaining the therapeutic effect initiated by the loading dose.
Common Pitfall to Avoid
Do not administer either initiation dose in the gluteal muscle - both Day 1 and Day 8 injections must be given deltoid to ensure proper therapeutic concentrations are achieved rapidly. 2 Subsequent monthly maintenance doses (starting Day 36 onward) can be administered in either deltoid or gluteal sites. 1, 4