The question asks about the substance used as an effective sedative and painkiller for treating post-surgery patients. Let's analyze the options provided and determine the correct answer with proper reasoning:

1. Antibiotics: These are drugs used to treat bacterial infections. They are not used for pain relief or sedation. Therefore, antibiotics are not the correct answer.
2. Morphine: This is a well-known opioid analgesic, which is used for pain relief, including severe pain management after surgery. It also has sedative properties, making it an effective choice for post-surgical pain management. Hence, this is the correct answer.
3. Anti-retroviral drugs: These are medications used to treat viral infections, specifically HIV. They play no role in sedation or pain relief. Thus, they are not relevant to the question.
4. Interferon: This is a type of protein used for treating viral infections and certain types of cancers. It does not have any sedative or painkiller properties and, therefore, is not the answer to this question.

The correct answer is Morphine.

Morphine works by binding to the opioid receptors in the brain, blocking the transmission of pain signals, and inducing a state of sedation, which makes it particularly effective in a post-surgical context where pain management is crucial for patient comfort and recovery.

Conclusion: In post-operative care, morphine is preferred due to its ability to effectively manage pain and provide sedation, making it the best choice among the given options.