bactericidal
Bactericidal describes a drug that actively kills bacteria rather than just stopping them from multiplying. If a bacteriostatic drug puts bacteria in handcuffs, a bactericidal drug delivers a knockout blow — the bacteria die whether or not the immune system shows up.
Drugs are usually called bactericidal when they reduce a starting bacterial population by at least 99.9% under standard conditions, or when their minimum bactericidal concentration sits close to their MIC. They tend to act on processes that, when sabotaged, are directly lethal — beta-lactams shatter the cell wall, fluoroquinolones break the DNA, and aminoglycosides cripple the ribosome irreversibly.
Bactericidal action matters most when the patient cannot rely on their own defenses — in meningitis, endocarditis, or severe infection in someone with a weak immune system — where merely pausing bacterial growth would not be enough. The honest nuance is that the labels are not absolute: a drug can be bactericidal against one species and only bacteriostatic against another, and clinical outcome often depends as much on dosing and site as on the label.
Bacterial endocarditis is treated with bactericidal antibiotics because the infected heart valve has poor immune access and bacteria must be killed outright.
Where the immune system cannot reach, killing must be complete.
The minimum bactericidal concentration (MBC) is the lab counterpart to MIC: the lowest concentration that kills 99.9% of bacteria, not merely stops their growth.