The combination of tetracycline and penicillin is not allowed. Tetracycline and penicillin are both natural antibiotics. Penicillin mainly kills bacteria by interfering with the synthesis of bacterial cell walls, causing bacterial disintegration and autolysis, and is a bactericidal agent, and is a reproductive bactericidal agent, and has a weaker effect on bacteria in a resting state. Tetracycline mainly inhibits the growth and reproduction of bacteria by interfering with bacterial protein synthesis, and is a bacteriostatic agent, and is a rapid bacteriostatic agent. When penicillin and tetracycline are used together, tetracycline can rapidly inhibit bacterial protein synthesis, resulting in bacteria in a quiescent state, which will affect and weaken the bactericidal effect of penicillin. When tetracycline and penicillin are used together, they do not produce additive or synergistic effects, but antagonistic effects, so they are not suitable for use.