Tigecycline is categorised as a glycylcycline and differs from classic tetracyclines in being active against tetracycline-resistant organisms. The resistance mechanisms it overcomes are:
- A Active efflux (tet efflux pumps) and ribosomal protection proteins ✓
- B Enzymatic inactivation and target modification (ribosomal protection)
- C Target modification (mutated 30S) and altered outer membrane permeability
- D β-Lactamase production and efflux pumps
Correct answer: A. Active efflux (tet efflux pumps) and ribosomal protection proteins
Explanation
The two classic tetracycline resistance mechanisms are: (1) energy-dependent efflux pumps encoded by tet genes that pump tetracycline out of the cell; (2) ribosomal protection proteins (e.g., TetM, TetO) that displace tetracycline from the ribosome. Tigecycline's bulky 9-t-butylglycylamido side chain sterically blocks both mechanisms — it is a poor substrate for tet efflux pumps and is not displaced by ribosomal protection proteins. It therefore retains activity against many tetracycline-resistant gram-positive and gram-negative organisms.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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