Antimicrobials · Glycylcyclines
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Tigecycline is a glycylcycline antibiotic that functions by binding to the 30S ribosomal subunit to inhibit bacterial protein synthesis.
Tigecycline provides broad-spectrum coverage including MRSA, VRE, and multidrug-resistant Gram-negative organisms.
Tigecycline lacks activity against the '3 Ps': Pseudomonas, Proteus, and Providencia species.
The FDA issued a black box warning for increased all-cause mortality compared to other antibiotics, reserving it for situations where alternative treatments are not suitable.
Tigecycline achieves poor serum concentrations due to rapid distribution into tissues, making it ineffective for bacteremia or bloodstream infections.
The most common adverse effect of tigecycline is severe nausea and vomiting, which occurs in a significant percentage of patients.
Tigecycline is structurally related to tetracyclines and shares the potential for photosensitivity and tooth discoloration in developing children.
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A 58-year-old male is hospitalized for a complex intra-abdominal infection following a perforated diverticulum. He has a history of severe penicillin allergy and is currently colonized with vancomycin-resistant Enterococcus (VRE). The medical team initiates tigecycline therapy. On day three, the patient remains hemodynamically stable but complains of persistent, severe nausea and vomiting. Blood cultures drawn at admission and today remain negative for bacterial growth.
Which pharmacokinetic property best explains why tigecycline is an inappropriate choice for this patient's potential systemic infection?
Low serum concentrations due to rapid tissue distribution
Tigecycline has a large volume of distribution and low serum levels, making it ineffective for treating bacteremia or systemic bloodstream infections, which is a classic board-tested limitation.
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Classification
Glycylcycline antibiotic; structurally related to tetracyclines.
Indications
Complicated skin and soft tissue infections, complicated intra-abdominal infections, and community-acquired bacterial pneumonia.
Mechanism of Action
Binds to the 30S ribosomal subunit, inhibiting bacterial protein synthesis.
Side Effects
Nausea, vomiting, increased all-cause mortality, pancreatitis.
Contraindications / Monitoring
Pregnancy (tetracycline class). Monitor LFTs and serum amylase/lipase.
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Mechanism of Action
Tigecycline binds with high affinity to the 30S ribosomal subunit, effectively blocking the entry of aminoacyl-tRNA into the A site of the ribosome. This action prevents the elongation of the peptide chain, halting bacterial protein synthesis. It is designed to evade common resistance mechanisms like efflux pumps and ribosomal protection proteins.
Unique Properties
It possesses a broad spectrum of activity, including MRSA, VRE, and many multidrug-resistant Gram-negative organisms. Notably, it lacks activity against Pseudomonas aeruginosa and Proteus species, which are classic board distractors.
Indications
Indicated for complicated skin and soft tissue infections and complicated intra-abdominal infections. It is also used for community-acquired bacterial pneumonia. It is generally reserved as a salvage therapy when other agents are ineffective.
Pharmacokinetics
Tigecycline is administered via IV infusion only. It undergoes extensive biliary/fecal excretion, meaning no dosage adjustment is required for renal impairment. It has a large volume of distribution, resulting in low serum concentrations, making it ineffective for bacteremia.
Side Effects & Adverse Events
The most common adverse effects are nausea and vomiting, which are often dose-limiting. Pancreatitis has been reported, requiring monitoring of lipase. Most critically, the FDA issued a warning regarding increased all-cause mortality compared to other antibiotics, limiting its use to situations where alternatives are unsuitable.
Contraindications
Pregnancy is an absolute contraindication due to the risk of permanent tooth discoloration and inhibition of bone growth in the fetus. It should be avoided in patients with known hypersensitivity to tetracyclines.
Monitoring
Monitor serum amylase and lipase if the patient develops symptoms of pancreatitis. Baseline and periodic LFTs are recommended. Monitor for signs of superinfection due to its broad-spectrum nature.
Clinical Pearls
Always remember the 'No Pseudomonas' rule for Tigecycline. Because of its poor serum penetration, it is a failed choice for treating bloodstream infections or sepsis. If a board question asks for a drug for MRSA/VRE that avoids renal dosing, this is your answer.