A prospective, double-blind, randomized, placebo and active controlled, multi-center, parallel group study comparing remimazolam to placebo, with an additional open-label arm for midazolam, in American Society of Anesthesiologists (ASA) Grade III and IV patients (ASA status evaluated by an anesthesiologist not otherwise involved in the study) undergoing a colonoscopy for diagnostic or therapeutic reasons.

Inclusion Criteria:

1. Male and female patients, aged ≥18, scheduled to undergo a diagnostic or therapeutic colonoscopy (therapeutic procedures may include hemostasis, resection, ablation decompression, and foreign body extraction, for example).

2. ASA grade III/IV

   1. ASA III patients are patients with severe systemic disease eg patients who, in the judgment of the Principal Investigator (PI), have significant enough systemic disease to warrant performing the colonoscopy procedure only in a facility which has post-procedure inpatient capability. ASA III physical status classification encompasses a wide range of potential patient co-morbidities some of which may make the selection of a facility with post-procedure inpatient capability preferable. By definition, ASA III patients have one or more moderate to severe systemic diseases which potentially cause substantial functional limitation. Examples may include poorly controlled diabetes or hypertension, moderate to severe chronic obstructive pulmonary disease, active hepatitis, heart failure or coronary artery disease (including implanted pacemaker and/or stent, recent myocardial infarction) cerebrovascular accident, or end stage renal disease requiring dialysis.
   2. ASA IV patients are patients with severe systemic disease that is a constant threat to life eg at least one severe disease that is poorly controlled or at end stage; possible risk of death; unstable angina; symptomatic chronic obstructive pulmonary disease; symptomatic chronic heart failure; hepatorenal failure.

3. For all female patients, negative result of urine or serum pregnancy test. Additionally, for women with child-bearing potential only, use of birth control during the study period (from the time of consent until all specified observations are completed).

4. Patient voluntarily signs and dates an informed consent form (ICF) that is approved by an investigational review board (IRB) prior to the conduct of any study procedure.

5. Patient is willing and able to comply with study requirements and will be available for a Follow-up Visit on Day 1 (+ 1 day) and Follow-up Phone call (Day 4 +/- 3 days) after the colonoscopy.

Exclusion Criteria:

1. Patients with a known sensitivity to benzodiazepines, flumazenil, opioids, naloxone, or a medical condition such that these agents are contraindicated.
2. Female patients with a positive pregnancy test at screening or baseline and lactating female patients.
3. Patients clearly acutely intoxicated with alcohol or drugs of abuse at baseline.
4. Patients in receipt of any investigational drug within 30 days or less than 7 half-lives (whichever is longer) before Screening, or scheduled to receive one during the study period.
5. Participation in any previous clinical trial with remimazolam.
6. Patients with an inability to communicate well with the Investigator, or deemed unsuitable according to the Investigator (in each case providing a reason).

Baseline Analysis Population is the Safety Population

Treatment-emergent Adverse Events (TEAEs) were collected from first dose of study drug medication until Day 4 (+ 3 days), and were followed until events resolved, became stable, or could be explained by another known cause(s)

Total number of participants affected with Other (Not Including Serious) Adverse Events represents any participant in the trial with a TEAE. The number of participants with Preferred Term (PT)TEAEs represents participants with TEAEs reported with a threshold of 5% in any of the arms