### 17. Trimethoprim-Sulfonamide Combinations and Warfarin
- Interaction: Trimethoprim-sulfonamide combinations can potentiate the effects of warfarin.
- Effect: Increased risk of bleeding.

### 18. Colistin and Aminoglycosides
- Interaction: Concurrent use of colistin and aminoglycosides can increase the risk of nephrotoxicity.
- Effect: Kidney damage.

### 19. Doxycycline and Antacids
- Interaction: Antacids containing aluminum, magnesium, or calcium can reduce the absorption of doxycycline.
- Effect: Decreased efficacy of doxycycline.

### 20. Metronidazole and Alcohol
- Interaction: Metronidazole can cause a disulfiram-like reaction when combined with alcohol.
- Effect: Vomiting, tachycardia, and other adverse effects.

### Key Considerations:
- Always consult a veterinarian before administering multiple drugs to poultry.
- Follow withdrawal periods to avoid residues in meat and eggs.
- Monitor birds for signs of adverse effects when using multiple medications.

This list is not exhaustive, and interactions may vary depending on the specific drugs, dosages, and individual bird factors.