An extension study continues treatment and follow-up for people who finished a parent trial, usually with fewer visits and a heavier focus on long-term safety. The difficult part is the join: who is eligible, how they consent again for a new document, and how their earlier data sits alongside the new.
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Parent study completed
Last visit done, primary data locked or in review
Rollover eligibility check
Parent completion, tolerability, consent to continue
Extension consent signed
New consent document for the extension
Extension baseline
Carry-over of key parent values, concomitant medicines
Maintenance visits
Every 12 weeks: safety, exposure, selected assessments
End of treatment and safety follow-up
Final assessments, 30-day follow-up
The short answer
What an extension study is
Participants who finish a Phase 2 or Phase 3 trial often benefit from the treatment, or want to know whether it is still safe after longer use. An extension study answers both. For the sponsor it adds long-term safety data and durability of effect beyond the parent study's primary endpoint. For participants it provides access to the treatment until it is approved and available, or until a stopping rule is met. Some extensions run inside the parent protocol as an additional phase; others are separate protocols with their own consent, schedule and objectives. This page deals mostly with the separate-protocol form, since it gives the most design work.
The differences from the parent study are practical. Eligibility is mostly about completing the parent study and continuing to benefit and tolerate treatment. Allocation is typically open label, with everyone on the active drug, although a few designs continue blinded dosing for a period to protect the parent study's integrity. Visits are spaced out, often every 8 to 16 weeks, with safety labs and an adverse event review at each. Data volume per participant falls, but the duration grows, so audit and query workload spreads over a long time and the database stays open much longer.
Related reading: the extension is a normal use case for EDC for Phase 3 clinical trials and many sponsor-investigator teams run them in an academic setting; see EDC for investigator-initiated trials. If the extension is mostly passive follow-up, the long-term follow-up consent template is a useful reference for what the consent has to say.
Side by side
| Aspect | Parent study | Extension study | Data capture consequence |
|---|---|---|---|
| Eligibility | Full inclusion and exclusion criteria | Completed parent study, tolerating treatment, willing to continue | A short rollover eligibility form that references the parent outcome. |
| Consent | Parent informed consent | New consent document with extension-specific information | Separate consent record and signature date for the extension. |
| Allocation | Randomized, often blinded | Open-label active treatment, in most designs | Treatment recorded as received; unblinding handled according to your plan. |
| Visit frequency | Weekly to monthly early on | Every 8 to 16 weeks | Longer visit windows and fewer forms per visit. |
| Primary focus | Efficacy endpoint | Long-term safety and durability | Adverse event, laboratory and concomitant medication forms dominate. |
| Duration | Months | Years, sometimes open-ended | Database remains open; interim locks and periodic exports are needed. |
| Monitoring | Intensive early | Risk-based, centred on safety | Targeted source data verification on safety fields. |
| Reporting | Study report at database lock | Periodic safety updates and a final report | Repeatable exports of cumulative data. |
General pattern. The protocol of any particular extension may differ, and local regulations decide the minimum safety exposure required.
The rollover
The rollover is the highest-risk moment because it joins two protocols, two consent documents and often two databases. Four questions need written answers before the first participant crosses over.
What identifies the participant in both studies? Decide the rule, such as keeping the parent subject number as a field in the extension, or assigning a new number and recording the parent number beside it. Whichever you pick, do not rely on names or dates of birth. Capture has site-level participant numbering such as 001-0042; record the parent identifier in a dedicated field on the rollover form and make it required.
Which parent values must carry over? Usually the last visit's weight, key labs, the treatment received, the date of the last dose and the list of ongoing adverse events and concomitant medicines. These form the extension baseline. They can be entered by staff from the parent record, with edit checks to catch obvious errors, instead of being retyped from memory.
How does consent work? The extension usually needs its own informed consent, because the risks, duration, procedures and rights differ. Capture's eConsent supports on-screen participant signing with email one-time-password verification, investigator countersignature and exportable PDFs with the audit trail. Start from the long-term follow-up consent template and adapt it; see eConsent and the guide to electronic informed consent regulations.
What happens between the studies? Real life often leaves a gap of weeks while an extension is approved and sites are opened. Decide whether participants stay on treatment, are followed for safety, or stop. The extension protocol should say, and the data system should record the gap, not ignore it.
Parent completers
96
Rolled over
84
Not rolled over
12
Consent pending
3
e.g. lab criteria
Create the rollover eligibility form, the extension consent and a maintenance visit in the free sandbox. Every feature, no credit card, no time limit.
The reduced schedule
Most extension schedules replace dense efficacy assessments with a short list repeated at each visit. In Capture, each visit is a set of approved forms, and you can set a visit window so that a visit planned for week 12 may be done within an allowed range. Visit windows help sites schedule and let the monitor see out-of-window visits without calculating them by hand.
| Assessment | Ext BL | Wk 12 | Wk 24 | Wk 36 | Wk 48 | EoT | Safety FU |
|---|---|---|---|---|---|---|---|
| Extension consent | |||||||
| Adverse events and con meds | |||||||
| Vital signs and weight | |||||||
| Safety laboratory panel | |||||||
| ECG | |||||||
| Efficacy measure (short form) | |||||||
| Exposure and dosing log |
x = form expected at this visit.
Safety focus
Long exposure changes which events matter. Events that are rare in a six-month parent study become visible in an extension: serious infections, malignancies, organ toxicity, abnormal laboratory trends, bone and cardiovascular signals depending on the drug class. The adverse event form needs consistent seriousness, severity, relatedness, outcome and action taken fields, and it should handle events that start in the parent study and continue into the extension without being counted twice.
Two design rules help. First, bring ongoing adverse events across at rollover by recording each with its original onset date and a "continuing" status, so the extension picture is complete. Second, record the exposure carefully: start and stop dates for each dose level, interruptions and reasons. Long-term safety summaries are usually reported per patient-year of exposure, and the denominators come from these records. If you plan to report to regulators, check which definitions and deadlines apply; SAE reporting timelines and the SAE deadline calculator are starting points, and the adverse event template provides a base form.
Plan monitoring for the long haul. A risk-based approach concentrates source data verification on safety fields, serious adverse events and dosing records rather than everything. Capture lets you set SDV per field, which makes a targeted plan practical; see risk-based monitoring and SDV software.
Joining the data
Each has trade-offs. Pick before the build, because the identifier choice is hard to change later.
Add extension visits and forms to the parent study after the primary visits. One participant record, one audit trail, one export. Best when the protocol is a single document and consent is an addition to the existing one. Requires the parent study to stay open.
Create a separate extension study. Record the parent identifier on the rollover form. Joined data are produced at analysis by matching on that identifier. Cleaner separation for a separate protocol and a separate lock, at the cost of a join step. Pricing is per live study, so check it against the pricing page.
Collect only new extension data and rely on the parent database for baseline. Simplest to build but hardest to analyse across both, and not advised where cumulative safety summaries are the goal.
Before go-live
Required parent identifier, completion status, last dose date, tolerability and willingness to continue.
Adapt the long-term follow-up template, test the signature and countersignature flow, and check the PDF export.
Forms with edit checks for last weight, labs, ongoing adverse events and concomitant medicines.
Dose level, start and stop dates, interruptions and reasons, for patient-years later.
Use the visit window calculator to check the windows your protocol implies.
Agree how often cumulative data are frozen for safety updates. See the database lock workflow.
If the parent was blinded, decide who sees what at rollover and test it.
Cumulative data
The reason for running an extension is usually the pooled picture: all adverse events across the parent and extension, exposure to date, and laboratory trends over time. That picture needs both datasets in the same structure. Capture exports CSV and Excel with a data dictionary, can filter by site and date range, and produces SDTM datasets as SAS XPT with Define-XML, so a programmer can stack parent and extension domains such as AE, EX and LB. See CDISC SDTM export software for how the datasets are produced.
If you chose the separate-study route, test the join with a dummy rollover participant before go-live: create the participant in both builds, export both, and confirm the identifier matches and that events spanning the boundary show once. It is an hour of work that saves weeks later.
It is a study that continues treatment or follow-up for participants who completed a parent trial, usually to collect long-term safety and durability data. Many are open label and run for years.
In most separate-protocol extensions participants sign a new informed consent that describes the extension. Your protocol and ethics committee decide the exact requirement. Capture eConsent supports the signature and countersignature flow for the new document.
Yes, as additional visits and forms after the parent visits, if the protocol is one document. The alternative is a separate study that records the parent identifier. The trade-offs are in the cards above.
Usually every 8 to 16 weeks, with safety labs and adverse event review at each visit, though your protocol decides. Visit windows in Capture let sites schedule within an allowed range.
Record start and stop dates for every dose period, including interruptions. Patient-years of exposure are derived from those dates by your statistician, so the dosing log must be complete.
Yes. Decide who stays blinded after the parent database is locked and set roles accordingly. Blinded roles in Capture do not receive treatment-arm values.
Capture is suitable for Phase 1 to 3 studies. Plan interim locks, exports and a monitoring approach for long duration, and model the study fee and participant fee for the full period on the pricing page.
There is no automatic import from another study. Carry-over values are entered on the rollover and baseline forms with edit checks, or joined at export through the parent identifier.
Keep exploring
EDC for Phase 3 clinical trials
The typical parent study setting.
Long-term follow-up consent template
Starting point for extension consent.
Adverse event reporting software
Safety capture for long exposure.
Risk-based monitoring and SDV
Targeted verification over years.
CDISC SDTM export software
Stacking parent and extension domains.
eConsent
Signature, countersignature and PDF export.
Open the free sandbox, build the rollover eligibility form, the extension consent and a maintenance visit, and test them with dummy participants. No credit card, and you pay only once you go live.