Final answer:
The drug most adversely affected by ingestion of antacids is tetracycline, as it requires an acidic environment for proper absorption, which is hindered by the neutralizing effect of antacids on stomach acid.
Step-by-step explanation:
The drug that is most adversely affected by the ingestion of antacids is C. Tetracycline. Antacids can increase the pH of the stomach, which negatively impacts the absorption of some antimicrobials. Tetracyclines, a group of broad-spectrum antibiotics such as doxycycline and others derived from Streptomyces spp., are best absorbed in an acidic environment in the stomach. When a patient takes antacids, the less acidic environment can significantly decrease the absorption of tetracycline antibiotics, reducing their effectiveness in treating infections. This is because antacids neutralize stomach acid and thus inhibit the dissolution of tetracycline compounds, which require a more acidic pH to dissolve properly and be absorbed into the bloodstream.