This study investigates the use of low doses of ketamine, along with opiate pain medication, is more effective at controlling the acute pain of patients in the emergency department than opiate pain medication alone. In addition, this study examines whether patients treated with low doses of ketamine, along with opiate pain medication, will require less opiate pain medication to control their pain, and whether these patients are equally happy with their pain control as patients who receive only opiate pain medication.

This randomized, double blinded, placebo controlled study investigates the use of low-dose ketamine, in conjunction to standard opiate treatment, as compared to placebo plus standard opiate treatment, for acute painful conditions in the ED setting. The investigators hypothesize that patients treated with ketamine will require less opiate for similar levels of pain relief up to 2 hours from initiation of treatment, with similar levels of patient satisfaction and an acceptable side effect profile.

Once seen by a physician, potential patients will receive provider-determined opiate treatment for their painful condition, prior to the informed consent process to ensure that treatment is not delayed. Once identified for inclusion, patients will receive informed consent and, upon consent, will subsequently be randomized through block randomization into one of two study groups. Each study group will contain at least 50 subjects. Randomization will be determined using a table of random numbers, using a restricted randomization scheme to ensure roughly equal numbers in each group. Group assignments will be sealed in opaque envelopes to be opened sequentially by the investigators. Group assignments will not indicate whether it is the treatment or the control group. At this time (T0), an initial NRS-11 score will be obtained. The NRS-11 is an 11-point scale on which patients rate their level of pain from 0 ("no pain") to 10 ("worst pain imaginable"). If, after initial analgesic, pain level is <6, patients will be asked again in 15 min. If at this time it is still <6, they will not proceed in the study. The intervention group will receive 0.1 mg/kg of ketamine given over 1 minute, and the control group will receive an equivalent volume of normal saline; both groups will have received a provider-determined dose of opiate analgesia prior to enrollment. At thirty-minute intervals, subjects will be asked their level of pain, if they need more pain control and will be evaluated for the presence of side effects (hallucinations, dysphoria, weakness, diplopia, nausea, vomiting, dizziness, itching and bradypnea) as well as sedation as defined by Ramsay score of greater than 2. Repeat doses of pain medication will be given as 0.05 mg/kg morphine or equivalent dose of opioid analgesic. Total opiate dosage and number of repeat doses given at the end of 120 minutes will be recorded. At each time interval, as well as at the end of 120 minutes (T120), patient satisfaction with pain control will be recoded on the 4-point Likert scale, with 0 being "completely unsatisfied" and 3 being "very satisfied".

Inclusion Criteria:

• Greater than 18 years but less than 70 years old.
• Exhibiting pain defined on a numerical rating scale (NRS-11 [Farrar et al. 2001]) score of equal to or greater than 6 out of 10
• Deemed by the treating EM physician to require opioid analgesia.

Exclusion Criteria:

• Respiratory, hemodynamic or neurologic compromise, as determined by observation of signs of respiratory distress, systolic blood pressure less than 90 mmHg or systolic/diastolic blood pressure greater than 160/90, or a Glasgow -Coma Score less than 15.
• A history of chronic ventilation, dialysis or with previously diagnosed cirrhosis or hepatitis by istory.
• Active psychosis.
• Clinical intoxication.
• Known sensitivity to any study drug.
• An inability to understand the NRS-11 pain measurement scale.
• Presentation with headache or chest pain.
• Pregnancy.
• A lack of decision-making capacity.
• A pain score less than 6 on the NRS-11 scale.
• A concern by the treating physician or study personnel of current or prior history of narcotic abuse, or other secondary gain.
• Previously participated in the study.

Collection approach for adverse events: regular investigator assessment.

This study was conducted in a busy ED in the general patient population, without special conditions, locations, or providers for study patients. The cohort includes subjects with chronic pain and long-term outpatient opioid use, as well as patients with new-onset acute pain; it is possible that the former patient population may react quite differently to the adjunctive ketamine usage than the latter.