New research validates clinical value of treating Copperhead envenomation with CroFab®

BTG plc (LSE: BTG), the global healthcare company, announced that research published today in PLOS ONE establishes the Patient-Specific Functional Scale (PSFS) as a valid, reliable, and clinically mea

BTG plc (LSE: BTG), the global healthcare company, announced that research published today in PLOS ONE establishes the Patient-Specific Functional Scale (PSFS) as a valid, reliable, and clinically meaningful measure for assessing quality of life and functionality in snake envenomation studies.

The research is based on a secondary analysis of BTG-sponsored studies which used PSFS to show that administering CroFab® Crotalidae Polyvalent Immune Fab (Ovine) to patients envenomated by copperhead snakes can aid the recovery of a patient’s affected limb function as compared with placebo. Today’s paper shows that not only was there a statistically significant difference between patients treated with CroFab® and the placebo group in the Copperhead trial, but that the difference is also clinically meaningful.

Study author Charles Gerardo, M.D., said “This study establishes a valid and reliable measure of the ability to perform activities that are important to snakebite patients. Additionally, it demonstrates that the effect of CroFab® found in the Copperhead trial is clinically significant.”

Copperhead envenomations are often thought to be less severe than other North American Pit Viper snakebites. By using PSFS, the Copperhead trial revealed that in addition to significant pain and swelling of the injured limb, and other soft tissue injury, envenomation also limited the daily activities of patients such as driving, climbing stairs, brushing their teeth, or using a cell phone.

Christon Hill, Vice President of R&D for BTG Pharmaceuticals, said: “CroFab® is the only FDA-approved product to treat all North American pit viper envenomations, including copperheads, in adult and pediatric patients. This new data continues to support our indicated use by showing that patients bitten by copperheads recover limb function faster when treated with CroFab®. Clinically meaningful patient-reported outcomes are important for physicians considering how best to treat their patients.”

Patient-Specific Functional Scale

PSFS offers an important patient-centered outcome measure that yields informative and clinically relevant information beyond the diagnosis-oriented endpoints that are commonly used to evaluate antivenom. Patients are asked to rate their ability to perform a short list of activities limited by their disease. While this tool is widely used in other diseases and clinical populations, this is the first study to establish the reliability and temporal stability of this patient reported outcome for patients with snake envenomation.

This study also established and validated the minimally clinically important difference (MCID) in the PSFS specifically for snake envenomation as approximately 1.0 using multiple methodologies. The MCID indicates the minimal difference needed in a numeric scale that reflects a patient perception of change in a given health status. Defining the MCID gives added credibility and rigor to PSFS as a patient-reported outcome in clinical trials.

About the Study

The researchers performed a post-hoc, secondary analysis of two BTG-sponsored trials of CroFab® in patients suffering copperhead envenomation. They compared PSFS with other quality of life and functional assessment data collected in these studies. Their analysis showed the reliability of the PSFS was adequate with good internal consistency (a Cronbach’s alpha of 0.91; 95% CI 0.88, 0.95) and good temporal stability (ICC value for the unchanged patients of 0.83; 95% CI 0.72, 0.89). External validity was demonstrated with a strong correlation of the PSFS scores with other quality of life and extremity functional assessments. The MCID calculated using the standard error of measurement of the individual scale responses was 1.04. When using the pooled standard deviation of the differences between the scale responses at baseline and follow-up, the MCID was 1.05.

Click here to read the full published article on PLOS ONE.

For further information contact:


Chris Sampson, Corporate Communications Director

+44 (0)20 7575 1595; Mobile: +44 (0)7773 251 178

About BTG Pharmaceuticals.

BTG Pharmaceuticals provides antidotes that counteract the potentially life-threatening effects associated with exposure or overexposure to certain toxins. These acute care products are typically used in emergency rooms and intensive care units to treat patients for whom there are limited or no existing treatment options. We are dedicated to delivering quality medicines that make a real difference to patients through the development, manufacture, and commercialisation of pharmaceutical products. To learn more about BTG Pharmaceuticals, please visit:



Do not administer CroFab® to patients with a known history of hypersensitivity to any of its components, or to papaya or papain unless the benefits outweigh the risks and appropriate management for anaphylactic reactions is readily available.


Coagulopathy: In clinical trials, recurrent coagulopathy (the return of a coagulation abnormality after it has been successfully treated with antivenin), characterized by decreased fibrinogen, decreased platelets, and elevated prothrombin time, occurred in approximately half of the patients studied; one patient required re-hospitalization and additional antivenin administration. Recurrent coagulopathy may persist for 1 to 2 weeks or more. Patients who experience coagulopathy due to snakebite should be monitored for recurrent coagulopathy for up to 1 week or longer. During this period, the physician should carefully assess the need for re-treatment with CroFab® and use of any type of anticoagulant or anti-platelet drug.

Hypersensitivity Reactions: Severe hypersensitivity reactions may occur with CroFab®. In case of acute hypersensitivity reactions, including anaphylaxis and anaphylactoid reactions, discontinue infusion and institute appropriate emergency treatment. Patients allergic to papain, chymopapain, other papaya extracts, or the pineapple enzyme bromelain may also have an allergic reaction to CroFab®. Follow-up all patients for signs and symptoms of delayed allergic reactions or serum sickness (e.g., rash, fever, myalgia, arthralgia).


The most common adverse reactions (incidence ≥ 5% of subjects) reported in the clinical studies were urticaria, rash, nausea, pruritus and back pain. Adverse reactions involving the skin and appendages (primarily rash, urticaria, and pruritus) were reported in 12 of the 42 patients. Two patients had a severe allergic reaction (severe hives and a severe rash and pruritus) following treatment and one patient discontinued CroFab® due to an allergic reaction. Recurrent coagulopathy due to envenomation and requiring additional treatment may occur.

To report suspected adverse reactions, contact 1-877-377-3784 or FDA at 1-800-FDA-1088 or

Please see the full Prescribing Information for CroFab®.

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