Timing of Second Invega Sustenna Dose After Initial Loading
The second dose of Invega Sustenna should be administered one week (Day 8) after the first dose, with a permissible window of ±4 days (Days 4-12). 1
Standard Dosing Schedule
- First dose (Day 1): 234 mg administered into the deltoid muscle 1
- Second dose (Day 8): 156 mg administered into the deltoid muscle, ideally one week after the first injection 1
- Flexible window: The second dose may be given 4 days before or after the one-week timepoint (i.e., anywhere from Day 4 to Day 12) without clinically significant impact on plasma concentrations 1, 2
This expanded ±4-day window (recently approved based on pharmacokinetic modeling) provides scheduling flexibility while maintaining therapeutic paliperidone exposure, with only ±3 ng/mL variation in median peak concentrations across this range 2.
Rationale for the One-Week Interval
The Day 8 deltoid injection is critical for rapidly achieving therapeutic concentrations because:
- Deltoid administration produces approximately 28% higher peak concentrations compared to gluteal injection 3
- The two initial deltoid doses create a loading regimen that eliminates the need for oral antipsychotic supplementation 1, 4, 5
- Drug release begins as early as Day 1, reaches maximum plasma concentrations at 13 days, and provides sustained release for up to 126 days 3
Management of Missed Second Dose
If the Day 8 window (±4 days) is missed, dosing strategy depends on elapsed time since the first injection 1:
Less than 4 weeks since first injection:
- Administer the 156 mg second dose in the deltoid muscle as soon as possible 1
- Give the third injection (117 mg) in either deltoid or gluteal muscle 5 weeks after the first injection, regardless of when the second dose was actually given 1
- Resume regular monthly dosing thereafter 1
4 to 7 weeks since first injection:
- Resume with two 156 mg deltoid injections: one immediately, then a second one week later 1
- Resume regular monthly dosing in either deltoid or gluteal muscle thereafter 1
More than 7 weeks since first injection:
- Restart the complete initiation regimen: 234 mg on Day 1, then 156 mg one week later, both in the deltoid 1
Common Pitfalls
Avoid gluteal administration for the first two doses: Both initiation doses must be given in the deltoid muscle to achieve adequate loading; gluteal injections produce lower peak concentrations and would delay therapeutic effect 1, 3.
Do not add oral supplementation: The approved loading regimen is designed to achieve therapeutic levels without oral antipsychotic overlap, unlike some other long-acting injectables 1, 4, 5.
Needle selection matters: Use weight-adjusted needles for deltoid injections (1-inch 23-gauge for patients <90 kg; 1.5-inch 22-gauge for ≥90 kg) to ensure proper intramuscular delivery 1.
Subsequent Maintenance Dosing
After the second initiation dose, monthly maintenance injections begin 5 weeks after the first injection (approximately 4 weeks after the second dose), with a recommended dose of 117 mg that can be administered in either the deltoid or gluteal muscle 1.