To compare the plasma concentration (bioavailability) and safety of a single naloxone 5 mg autoinjector intramuscular (IM) injection to a single 2 mg IM injection (an approved safe dose) and to a single 2 mg bolus intravenous (IV) injection (an approved safe dose)

A randomized, open-label, 3-treatment, 6-sequences, 3-period Williams Square crossover single-dose, relative bioavailability study in healthy adult participants. The study includes Screening period, a Treatment period and a Follow-up contact (SoA). At least twelve (12) participants will be enrolled. If the number of evaluable participants falls below 12, participants may be replaced.

Inclusion Criteria:

Participants are eligible to be included in the study only if all of the following criteria apply:

Age and Sex:

1. Healthy male and/or female participants of non-childbearing potential, who, at the time of screening, are between the ages of 18 and 55 years, inclusive.

   Refer to protocol for reproductive criteria for male and female participants.

   Type of Participant and Disease Characteristics:

2. Male and female participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, vital signs, 12-lead ECG, and/or clinical laboratory tests.

3. Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations, and other study procedures.

   Weight:

4. BMI of 17.5 to 30.5 kg/m2; and a total body weight > 50 kg (110 lb).

Informed Consent:

5. Capable of giving signed informed consent as described in Appendix 1, which includes compliance with the requirements and restrictions listed in the ICD and in this protocol.

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Exclusion Criteria:

Participants are excluded from the study if any of the following criteria apply:

Medical Conditions:

1. Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.

2. Current or past diagnosis of any type of drug dependence within the past year will not be eligible to participate. History of alcohol abuse, dependence or binge drinking and/or any other illicit drug use within 6 months of screening. Binge drinking is hours. As a general rule, alcohol intake should not exceed 14 units per week (1 unit = 8 ounces (240 mL) beer, 1 ounce (30 mL) of 40% spirit or 3 ounces (90 mL) of wine).

3. If fever is present within 7 days of admission or screening.

4. Evidence or history of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurological, or allergic disease (including drug allergies, but excluding untreated, asymptomatic, seasonal allergies at the time of dosing).

5. History of HIV infection, hepatitis B, or hepatitis C, positive testing for HIV, HBsAg, or HCVAb. Hepatitis B vaccination is allowed.

6. Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.

   Prior/Concomitant Therapy:

7. Use of prescription or nonprescription drugs and dietary and herbal supplements within 14 days or 5 half-lives (whichever is longer) prior to the first dose of study intervention. Prior/Concurrent Clinical Study Experience:

8. Previous administration with an investigational drug within 30 days (or as determined by the local requirement) or 5 half-lives preceding the first dose of study intervention used in this study (whichever is longer).

   Diagnostic Assessments:

9. A positive urine drug test.

10. Has participated in, is currently participating in, or is seeking treatment for substance-and/or alcohol-related disorders (excluding nicotine and caffeine).

11. Has a positive alcohol breathalyzer test at screening or upon admission to the study center of Treatment Period. Positive results may be repeated and/or participants re-scheduled at the investigator's discretions.

12. Screening supine BP ≥140 mm Hg (systolic) or ≥90 mm Hg (diastolic), following at least 5 minutes of supine rest. If BP is ≥140 mm Hg (systolic) or ≥90 mm Hg (diastolic), the BP should be repeated 2 more times and the average of the 3 BP values should be used to determine the participant's eligibility. Repeated BP tests should be spaced at least 5 minutes apart.

13. Screening supine 12-lead ECG demonstrating a QTc interval > 450 msec or a QRS interval > 120 msec. If QTc exceeds 450 msec, or QRS exceeds 120 msec, the ECG should be repeated 2 more times and the average of the 3 QTc or QRS values should be used to determine the participant's eligibility.

14. Participants with ANY of the following abnormalities in clinical laboratory tests at screening, as assessed by the study-specific laboratory and confirmed by a single repeat test, if deemed necessary:

    Abnormal platelet count and/or PT/INR; AST or ALT level ≥1.5 × ULN; Total bilirubin level ≥1.5 × ULN; participants with a history of Gilbert's syndrome may have direct bilirubin measured and would be eligible for this study provided the direct bilirubin level is ≤ ULN.

    Other Exclusions:

15. Blood donation (excluding plasma donations) of approximately 1 pint (500 mL) or more within 60 days prior to dosing.

16. History of sensitivity to heparin or heparin-induced thrombocytopenia.

17. Unwilling or unable to comply with the criteria in the Lifestyle Considerations section of this protocol.

18. History of hypersensitivity to naloxone or any of the components in the formulation of the study products.

19. Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.

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Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.