A Study of MK-6072 and MK-3415A in Participants Receiving Antibiotic Therapy for Clostridium Difficile Infection (MK-3415A-002)

An extended 9-month follow-up to assess for CDI recurrence through Month 12 will be
conducted in a subset of participants.

Inclusion Criteria:

- Participant has a diagnosis of CDI defined as: a) presence of diarrhea (passage of 3
or more loose stools in 24 or fewer hours); and b) positive test for toxigenic C.
difficile from a stool collected no more than 7 days before study infusion.

- Participant is receiving SOC therapy (i.e., oral metronidazole, oral vancomycin, IV
metronidazole concurrent with oral vancomycin, oral fidaxomicin, or oral fidaxomicin
concurrent with IV metronidazole) for CDI.

- Participant is highly unlikely to become pregnant or to impregnate a partner by
meeting at least one of the following criteria: a) females not of reproductive
potential (i.e., one who has either (1) reached natural menopause, defined as 6
months of spontaneous amenorrhea with serum follicle stimulating hormone [FSH] levels
in the postmenopausal range, or 12 months of spontaneous amenorrhea not including
cases with an underlying disease, such as anorexia nervosa, that causes amenorrhea;
(2) 6 weeks post surgical bilateral oophorectomy with or without hysterectomy; or (3)
bilateral tubal ligation); or b) participants of reproductive potential who agree to
remain abstinent or use (or have their partner use) two acceptable methods of birth
control (i.e., intrauterine device [IUD], diaphragm with spermicide; contraceptive
sponge, condom, vasectomy and any registered and marketed hormonal contraceptives
that contain an estrogen and/or progestational agent including oral, subcutaneous,
intrauterine, or intramuscular agents) starting at enrollment and throughout the
12-week study.

Exclusion Criteria:

- Participant with an uncontrolled chronic diarrheal illness such that their normal
24-hour bowel movement habit is 3 or more loose stools.

- Participant with planned surgery for CDI within 24 hours.

- Female participant with a positive pregnancy test in the 48 hours before infusion and
pre-menopausal females who are not sterilized and therefore have the potential to
bear a child who are unwilling to undergo pregnancy testing.

- Female participant breast feeding or planning to breast feed before completion of the
12-week study.

- Female participant planning to donate ova before completion of the 12-week study and
male participants planning to impregnate or donate sperm before completion of the
12-week study.

- Participant has previously participated in this study, has previously received
MK-3415 or MK-6072 (either alone or in combination), has received a C. difficile
vaccine, or has received another experimental monoclonal antibody against C.
difficile toxin A or B.

- Participant plans to donate blood and/or blood products within 6 months after
infusion.

- Participant has received immune globulin within 6 months before infusion or is
planning to receive immune globulin before completion of the 12-week study.

- Treatment with SOC therapy is planned for longer than 14 days.

- Participant has received more than a 24-hour regimen of cholestyramine, colestimide,
rifaximin, or nitazoxanide within 14 days before infusion or plans to receive these
medication before completion of the 12-week study period.

- Participant plans to take medications that are given to decrease gastrointestinal
peristalsis, such as loperamide (Imodium™) or diphenoxylate hydrochloride/atropine
sulfate (Lomotil™) any time during the 14 days after infusion. Participants receiving
opioid medications at the onset of diarrhea may be included if they are on a stable
dose or if there is anticipation of a dose decrease or cessation of use.

- Participant plans to take the probiotic Saccaromyces boulardii or plans to receive
fecal transplantation therapy, or any other therapies that have been demonstrated to
decrease CDI recurrence at any time after infusion (Day 1) and through completion of
the 12-week study period.

- Participant has received another investigational study agent within the past 30 days
or is currently participating in or scheduled to participate in any other clinical
study with an investigational agent during the 12-week study.

- Participant is not expected to survive for 72 hours.

- Participant has any other condition that, in the opinion of the investigator, would
jeopardize the safety or rights of the participant, would make it unlikely for the
participant to complete the study, or would confound the results of the study.