A Phase 1 interventional study of ST-246 Days 1 - 3 and ST-246 Days 11 - 13 in Orthopoxviral Disease, Smallpox and Monkey Pox, sponsored by SIGA Technologies. Completed at 1 site in United States. Open to participants aged 18 Years to 50 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-10-01.
Sponsored by SIGA Technologies · Phase 1, Interventional, and Treatment
Among 49 studies in Smallpox with a site in United States — none open to participants now, 1 under way, none of them phase 3. Smallpox · United States.
Among the 49 studies in Smallpox with a site in United States, this one is the 40th largest by enrollment of the 43 interventional ones, is one of 5 that started in 2008, is one of 13 in phase 1, and was the 28th registered.
73 studies on the registry are indexed under Smallpox; 5 are open to participants now.
This study's enrollment of 12 is below the median of 150 across 61 interventional studies indexed under Smallpox.
Browse Smallpox studies →None of the 49 studies in Smallpox with a site in United States is open now.
Of the 2 Smallpox studies recruiting now, 0 (0%) set no upper age limit and 2 (100%) stop at 75 or younger; 0 take children under 18; 2 take healthy volunteers.
This study: 18 Years to 50 Years · all sexes · healthy volunteers too.
The full table on the hub →49 studies; the count open now beside each. This study's row is marked.
First in 2002; this study’s year is marked. 5 started in 2008.
Median enrollment 110 across the 43 interventional studies, 5,001 across the 5 observational. Of the 44 that completed or were terminated, 21 (48%) have results posted.
28 of 49 have an industry lead sponsor. The 10 most frequent:
SIGA Technologies is the lead sponsor of 9 studies on the registry; none are open to participants now.
SIGA Technologies has 8 studies filed under Smallpox — fewer than ten, so there is no comparison to draw.
1 of the studies in Smallpox with a site in United States that are under way reach primary completion within a year, 0 of them phase 3. Phase 3 first, then by date:
| Study | Primary completion |
|---|---|
| NCT04957485SIGA TechnologiesStudy to Assess the Safety and Immunogenicity of TPOXX® When Administered Orally for 28 Days With JYNNEOS | 2027-01-01 |
Among the 49 studies in Smallpox with a site in United States, from their registry updates:
Nothing recorded among them since 2026-09-25.
The purpose of this study was to evaluate the pharmacokinetic parameters and safety of a single dose of ST-246 400mg Form I versus ST-246 400mg Form V capsules in fed normal healthy volunteers.
This was a Phase I, double-blind, cross-over, single-dose study of the orally administered anti-orthopoxvirus compound, ST-246, to 12 healthy, fed volunteers between the ages of 18 and 50 years. Subjects were randomized such that 6 subjects received either ST-246 Form I (monohydrate) followed 10 days later after a wash-out period by Form V (hemihydrate), and 6 subjects received ST-246 Form V followed by Form I, as for the previous group.
Both forms of ST-246 were similar in the way they were manufactured. The only difference between Form I and Form V may be related to how it dissolves, and this may affect the way that it is absorbed in the human body. Information about any side-effects that may occur will also be collected in this study.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
History of any clinically significant conditions including:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
On an ECG, the QT interval is the time the heart’s lower chambers take to activate electrically and recover in each beat. QTc is that time adjusted for heart rate (QTcF by Fridericia’s formula, QTcB by Bazett’s). Some medicines lengthen it, and a long QTc can raise the risk of a dangerous heart rhythm.
The study may name a correction formula and a limit in milliseconds, often around 450–480.
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Hepatitis B is a virus that infects the liver. These are separate tests: HBsAg positive usually means a current infection (a recent vaccination can briefly cause it too); total anti-HBc (HBcAb) positive means an infection now or in the past; HBV DNA measures how much virus is in the blood.
Some studies accept a past infection if HBV DNA is undetectable, sometimes with antiviral medicine during the study. Check what this study allows.
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
QT and QTc
On an ECG, the QT interval is the time the heart’s lower chambers take to activate electrically and recover in each beat. QTc is that time adjusted for heart rate (QTcF by Fridericia’s formula, QTcB by Bazett’s). Some medicines lengthen it, and a long QTc can raise the risk of a dangerous heart rhythm.
The study may name a correction formula and a limit in milliseconds, often around 450–480.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ECG (electrocardiogram)
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hepatitis B tests
Hepatitis B is a virus that infects the liver. These are separate tests: HBsAg positive usually means a current infection (a recent vaccination can briefly cause it too); total anti-HBc (HBcAb) positive means an infection now or in the past; HBV DNA measures how much virus is in the blood.
Some studies accept a past infection if HBV DNA is undetectable, sometimes with antiviral medicine during the study. Check what this study allows.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hepatitis C tests
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Each of six subjects receive a single oral 400 mg dose (2×200 mg) of ST-246 Form I (monohydrate) in the first intervention period, followed 10 days later (3 days post-treatment monitoring and 7 days wash-out period) in the second intervention period by a single oral 400 mg dose (2×200 mg) of ST-246 Form V (hemihydrate). Both forms of drug are orally administered within 30 minutes after a standard light meal consisting of 400-450 calories and approximately 25% fat.
Drug: ST-246 Days 1 - 3 · Drug: ST-246 Days 11 - 13
Each of six subjects receive a single oral 400 mg dose (2×200 mg) of ST-246 Form V (hemihydrate) in the first intervention period, followed 10 days later (3 days post-treatment monitoring and 7 days wash-out period) in the second intervention period by a single oral 400 mg dose (2×200 mg) of ST-246 Form I (monohydrate). Both forms of drug are orally administered within 30 minutes after a standard light meal consisting of 400-450 calories and approximately 25% fat.
Drug: ST-246 Days 1 - 3 · Drug: ST-246 Days 11 - 13
First Intervention is on Days 1 - 3, and includes 6 patients dosed once orally with ST-246 Form I (Arm 1), and 6 patients dosed once orally with ST-246 Form V (Arm 2).
Also known as: Tecovirimat
Second Intervention is on Days 11 - 13 (after a 3 day post-treatment monitoring and 7 day wash-out period) where the 6 patients previously given ST-246 Form I (Arm 1) are now dosed once orally with ST-246 Form V, and the 6 patients previously given ST-246 Form V (Arm 2) are now dosed once orally with ST-246 Form I.
Also known as: Tecovirimat
Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: t½
Mean terminal half-life (t½; hrs) for Forms I and V were calculated from \[plasma\] vs time profiles.
Time frame: Post-dose samples at 0.5,1,2,3,4,8,12,24,36,48,72 hrs
Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: AUC0-τ
Area under the drug concentration-time curve from time zero to time t, where t is the last timepoint with a drug concentration ≥ lowest obtainable quantification (AUC0-τ; ng\*hr/mL).
Time frame: Post-dose samples at 0.5,1,2,3,4,8,12,24,36,48,72 hrs
Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: AUC0-∞
Area under the drug concentration-time curve from time zero to infinity (AUC0-∞; ng\*hr/mL).
Time frame: Post-dose samples at 0.5,1,2,3,4,8,12,24,36,48,72 hrs
Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: Cmax
Maximum drug concentration in plasma, determined directly from individual concentration-time data (Cmax)
Time frame: Post-dose samples at 0.5,1,2,3,4,8,12,24,36,48,72 hrs
Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: Tmax
Time to maximum plasma concentration(Tmax; hrs) for Forms I and V were calculated from \[plasma\] vs time profiles.
Time frame: Post-dose samples at 0.5,1,2,3,4,8,12,24,36,48,72 hrs
Number of Study Participants Who Tolerated a Single Dose of ST-246 Form I vs. Form V as Determined by No Clinically Significant Changes in Safety Parameters
Evaluated safety parameters included: 1. physical examination/vital signs 2. electrocardiograms (heart rate, PR interval, QRS duration, QT interval, and QTc Bazett) 3. laboratory safety tests (hematology, chemistry, urinalysis) 4. adverse events For a), b) and c), summary statistics (mean,SD, median, minm, maxm)for values, and changes from baseline(Day 1 pre-dose) to each timepoint, were measured and compared to laboratory normal reference ranges. Values for a)- d) were assigned grades according to DAIDS AE Grading Table. Any Grade of 3 or higher was considered severe and significant.
Time frame: 4 weeks
Study period was approximately 2 weeks (from August 26, 2008 to September 8, 2008), plus a 30-day post-treatment follow up. The study was conducted at a Phase I Study Unit of a Clinical Research Center in Orlando, FL.
| Milestone | ST-246 Form I Followed by Form V | ST-246 Form V Followed by Form I |
|---|---|---|
| Started | 6 | 6 |
| Completed | 6 | 6 |
| Not completed | 0 | 0 |
| Milestone | ST-246 Form I Followed by Form V | ST-246 Form V Followed by Form I |
|---|---|---|
| Started | 6 | 6 |
| Completed | 5 | 6 |
| Not completed | 1 | 0 |
| Withdrew: Death in family | 1 | 0 |
| Milestone | ST-246 Form I Followed by Form V | ST-246 Form V Followed by Form I |
|---|---|---|
| Started | 5 | 6 |
| Completed | 5 | 6 |
| Not completed | 0 | 0 |
Evaluated safety parameters included: 1. physical examination/vital signs 2. electrocardiograms (heart rate, PR interval, QRS duration, QT interval, and QTc Bazett) 3. laboratory safety tests (hematology, chemistry, urinalysis) 4. adverse events For a), b) and c), summary statistics (mean,SD, median, minm, maxm)for values, and changes from baseline(Day 1 pre-dose) to each timepoint, were measured and compared to laboratory normal reference ranges. Values for a)- d) were assigned grades according to DAIDS AE Grading Table. Any Grade of 3 or higher was considered severe and significant.
| participants | ST-246 Form I | ST-246 Form V |
|---|---|---|
| Number of Study Participants Who Tolerated a Single Dose of ST-246 Form I vs. Form V as Determined by No Clinically Significant Changes in Safety Parameters | 12 | 11 |
Mean terminal half-life (t½; hrs) for Forms I and V were calculated from \[plasma\] vs time profiles.
| hours | ST-246 Form I | ST-246 Form V |
|---|---|---|
| Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: t½ | 27.446 ± 13.109 | 28.180 ± 21.992 |
Area under the drug concentration-time curve from time zero to time t, where t is the last timepoint with a drug concentration ≥ lowest obtainable quantification (AUC0-τ; ng\*hr/mL).
| ng*hr/mL | ST-246 Form I | ST-246 Form V |
|---|---|---|
| Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: AUC0-τ | 15624.495 ± 5449.188 | 20065.316 ± 6744.974 |
Area under the drug concentration-time curve from time zero to infinity (AUC0-∞; ng\*hr/mL).
| ng*hr/mL | ST-246 Form I | ST-246 Form V |
|---|---|---|
| Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: AUC0-∞ | 19922.017 ± 6543.563 | 21982.709 ± 9330.953 |
Maximum drug concentration in plasma, determined directly from individual concentration-time data (Cmax)
| ng/mL | ST-246 Form I | ST-246 Form V |
|---|---|---|
| Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: Cmax | 1068.9 ± 294.3 | 1230.2 ± 348.6 |
Time to maximum plasma concentration(Tmax; hrs) for Forms I and V were calculated from \[plasma\] vs time profiles.
| hours | ST-246 Form I | ST-246 Form V |
|---|---|---|
| Pharmacokinetic Parameters for a Single Dose of ST-246 Form I vs. Form V: Tmax | 3.8 ± 1.5 | 3.8 ± 1.6 |
Collected over 4 weeks. Non-serious events are listed at a 0% frequency threshold.
| Group | Deaths | Serious | Other |
|---|---|---|---|
| ST-246 Form I | — | 0/12 (0%) | 1/12 (8.3%) |
| ST-246 Form V | — | 0/11 (0%) | 2/11 (18.2%) |
| Event | ST-246 Form I | ST-246 Form V |
|---|---|---|
| HeadacheNervous system disorders | 0/12 | 1/11 |
| Neck painMusculoskeletal and connective tissue disorders | 0/12 | 1/11 |
| Underarm tendernessGeneral disorders and administration site conditions | 1/12 | 0/11 |
| Age, Categorical(Participants) | ST-246 Form I Followed by Form V | ST-246 Form V Followed by Form I | Total |
|---|---|---|---|
| <=18 years | 0 | 0 | 0 |
| Between 18 and 65 years | 6 | 6 | 12 |
| >=65 years | 0 | 0 | 0 |
| Age, Continuous(years) | ST-246 Form I Followed by Form V | ST-246 Form V Followed by Form I | Total |
|---|---|---|---|
| Mean | 34.7 ± 8 | 34.8 ± 9.4 | 34.8 ± 8.3 |
| Sex: Female, Male(Participants) | ST-246 Form I Followed by Form V | ST-246 Form V Followed by Form I | Total |
|---|---|---|---|
| Female | 4 | 6 | 10 |
| Male | 2 | 0 | 2 |
| Region of Enrollment(participants) | ST-246 Form I Followed by Form V | ST-246 Form V Followed by Form I | Total |
|---|---|---|---|
| United States | 6 | 6 | 12 |
The record gives a start of Aug 2008, a primary completion of Oct 2008 and a completion of Oct 2008. It does not say whether these dates are actual or estimated.
Results were first posted in Feb 2010, 1 year 4 months after primary completion.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is completed, as verified in Sep 2010. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: Tecovirimat
SIGA Technologies