To evaluate the safety and efficacy of self-titration to effective analgesia with inhaled AeroLEF in patients with moderate/severe acute pain in the post-surgical setting.

After elective ACL knee surgery, consented patients will receive a single dose of AeroLEF for moderate/severe acute pain. Patients stop dosing if they achieve analgesia, complete the maximum available dose, or experience dose-limiting side effects.

Inclusion Criteria:

1. Male or female between ages 18 years and 60 years.
2. A body mass index of between 18 and 30, inclusive.
3. If a female of child-bearing potential, the patient must have a negative urine pregnancy test at screening and baseline.
4. Scheduled for elective ACL arthroscopic knee repair surgery, and meet the criteria of the American Society of Anesthesiologists [ASA] Physical Status Criteria of Class I or Class II, and suitability for an anesthetic plan limited to general anesthesia (inhalation/IV) with post-operative PCA initiated in a PACU setting and not requiring CPM before the 12 hours post surgery observation is completed.
5. Scheduled for a morning surgery and anticipating remaining in the hospital for an overnight stay.
6. Normal laboratory values for clinical chemistry, haematology and urinalysis. If a patient has abnormal clinically significant laboratory values, inclusion will be permitted at the discretion of the investigator .
7. Physical examination with no clinically relevant findings as determined by the investigator.
8. Able to demonstrate the ability to understand the requirements of the study, willingness to provide written informed consent (prior to any study-related procedures being performed) and able to adhere to the study restrictions, and return for the required assessments.

Exclusion Criteria:

1. History of addiction to drugs or alcohol.
2. Exposure to any investigational drug within the 30 days prior to enrolment.
3. Documented hypersensitivity to fentanyl or other opioid analgesics
4. Documented hypersensitivity/allergy to the components of the liposomes used in the AeroLEF formulation
5. History of pulmonary, cardiovascular, neurologic, endocrine, hepatic, GI, or kidney disease or therapy that would jeopardize the patient's well-being by participation in this study (excluded by ASA I and II categories)
6. Currently receiving treatment, or have received treatment in the previous two weeks, with antidepressant or antipsychotic drugs (including monoamine oxidase inhibitors).
7. Clinically significant ongoing medical conditions.
8. Currently receiving treatment for chronic pain.
9. Current therapy with narcotic or CNS-depressant medications.
10. Current chronic therapy with NSAIDs, ASA or acetaminophen within the previous 7 days.
11. Patient, who in the opinion of the investigator, is mentally or emotionally unsuitable to participate, or unable/unwilling to comply with the study assessments.
12. Blood donation or other blood loss within 45 days prior to enrolment in the study totalling 100 mL or greater.