Frequently Asked Questions About DIFICID^® (fidaxomicin)

DIFICID is a macrolide antibacterial drug indicated in adult and pediatric patients 6 months of age and older for treatment of Clostridioides difficile-associated diarrhea (CDAD).

To reduce the development of drug-resistant bacteria and maintain the effectiveness of DIFICID and other antibacterial drugs, DIFICID should be used only to treat infections that are proven or strongly suspected to be caused by C. difficile.

The recommended dose of DIFICID for adults and pediatric patients weighing at least 12.5 kg and able to swallow tablets is one 200 mg tablet orally twice daily for 10 days, with or without food. The recommended dosage of the oral suspension in pediatric patients (weighing at least 4 kg) is weight-based and is twice daily for 10 days.

• No dose adjustment is recommended for patients ≥ 65 years of age.
• No dose adjustment is recommended for patients with renal impairment.
• No dosage adjustments are recommended when co-administering fidaxomicin with substrates of P-gp or CYP enzymes.
• The impact of hepatic impairment on the pharmacokinetics of fidaxomicin has not been evaluated; however, because fidaxomicin and its active metabolite (OP-1118) do not appear to undergo significant hepatic metabolism, elimination of fidaxomicin and OP-1118 is not expected to be significantly affected by hepatic impairment.

• DIFICID is contraindicated in patients who have known hypersensitivity to fidaxomicin or any other ingredient in DIFICID.
• Acute hypersensitivity reactions, including dyspnea, rash, pruritus, and angioedema of the mouth, throat, and face have been reported with DIFICID. If a severe hypersensitivity reaction occurs, DIFICID should be discontinued and appropriate therapy should be instituted.
• DIFICID is not expected to be effective for the treatment of other types of infections due to minimal systemic absorption of fidaxomicin. DIFICID has not been studied for the treatment of infections other than CDAD. DIFICID should only be used for the treatment of CDAD.
• Only use DIFICID for infection proven or strongly suspected to be caused by C. difficile. Prescribing DIFICID in the absence of a proven or strongly suspected C. difficile infection is unlikely to provide benefit to the patient and increases the risk of development of drug-resistant bacteria.
• The most common adverse reactions in adults reported in clinical trials are nausea (11%), vomiting (7%), abdominal pain (6%), gastrointestinal hemorrhage (4%), anemia (2%), and neutropenia (2%).
• Among adult patients receiving DIFICID, 33 (5.9%) withdrew from trials as a result of adverse reactions. Vomiting was the primary adverse reaction leading to discontinuation of dosing (incidence of 0.5% for both DIFICID and vancomycin patients).
• The most common adverse reactions in pediatric patients treated with DIFICID are pyrexia (13.3%), abdominal pain (8.2%), vomiting (7.1%), diarrhea (7.1%), constipation (5.1%), increased aminotransferases (5.1%), and rash (5.1%).
• The safety and effectiveness of DIFICID in patients <6 months of age have not been established.
• The recommended dose of DIFICID for adults and pediatric patients weighing at least 12.5 kg and able to swallow tablets is one 200 mg tablet orally twice daily for 10 days, with or without food. The recommended weight-based dosage of the oral suspension in pediatric patients (weighing at least 4 kg) is twice daily for 10 days.
• No dose adjustment is recommended for patients ≥ 65 years of age.
• No dose adjustment is recommended for patients with renal impairment.
• No dosage adjustments are recommended when co-administering fidaxomicin with substrates of P-gp or CYP enzymes.
• The impact of hepatic impairment on the pharmacokinetics of fidaxomicin has not been evaluated; however, because fidaxomicin and its active metabolite (OP-1118) do not appear to undergo significant hepatic metabolism, elimination of fidaxomicin and OP-1118 is not expected to be significantly affected by hepatic impairment.

Yes. Your eligible, privately insured patients may save on their out-of-pocket prescription costs for DIFICID, paying as little as $50 per prescription on each of up to 4 qualifying prescriptions for either up to 20 tablets or one bottle of DIFICID Oral Suspension. Maximum savings is $3,400 per prescription.

The coupon is not valid for patients who are uninsured or patients with Medicare or other Government Program insurance. Not all patients are eligible. Certain restrictions apply. Tell your eligible, privately insured patients to visit DIFICID.com to review the Terms and Conditions.

Your patients can visit DIFICID.com to request a coupon, and if eligible, activate and bring to their pharmacy along with their prescription.

Also, eligible health care professionals may request coupons for DIFICID for use with their appropriate patients.

Request coupons for DIFICID

DIFICID was studied in adults vs vancomycin in two phase 3 trials. To view the study design and clinical end points, click the link below.

View study data on the efficacy of DIFICID

Possible relevant ICD-10 codes for DIFICID

The above codes may be potentially relevant when billing for DIFICID and its administration. Consult the relevant manual and/or other guidelines for a description of each code to determine the appropriateness of its use and for information on additional codes. Diagnosis codes should be selected only by a health care professional. Please consult with the applicable payer to understand the payer’s specific billing requirements. This information is subject to change.

You are solely responsible for determining the appropriate codes and for any action you take in billing. The information provided here is not intended to be definitive or exhaustive, and is not intended to replace the guidance of a qualified professional advisor. Merck and its agents make no warranties or guarantees, expressed or implied, concerning the accuracy or appropriateness of this information for your particular use given the frequent changes in public and private payer billing. The use of this information does not guarantee payment or that any payment received will cover your costs.

View excerpts from the 2021 IDSA/SHEA clinical practice guidelines for adult patients with Clostridioides difficile infection (CDI)
IDSA, Infectious Diseases Society of America
SHEA, Society for Healthcare Epidemiology of America

Click to download guidelines

View excerpts from 2021 ACG clinical guidelines for patients with Clostridioides difficile infection (CDI)
2021 ACG, American College of Gastroenterology

Click to download guidelines

DIFICID is bactericidal therapy that targets Clostridioides difficile.
DIFICID has been shown to be active against most isolates of C. difficile, both in vitro and in clinical infections.

• Macrolide antibiotic bactericidal against C. difficile in vitro, inhibiting RNA synthesis by binding to RNA polymerases
• Acts locally in the gastrointestinal tract

• The most common adverse reactions in adults reported in clinical trials are nausea (11%), vomiting (7%), abdominal pain (6%), gastrointestinal hemorrhage (4%), anemia (2%), and neutropenia (2%).
• Among adult patients receiving DIFICID, 33 (5.9%) withdrew from trials as a result of adverse reactions. Vomiting was the primary adverse reaction leading to discontinuation of dosing (incidence of 0.5% for both DIFICID and vancomycin patients).
• The most common adverse reactions in pediatric patients treated with DIFICID are pyrexia (13.3%), abdominal pain (8.2%), vomiting (7.1%), diarrhea (7.1%), constipation (5.1%), increased aminotransferases (5.1%), and rash (5.1%).