1. Clinical Overview
Vancomycin is a tricyclic glycopeptide antibiotic derived from *Amycolatopsis orientalis*. It is a bactericidal agent primarily used for serious, life-threatening Gram-positive bacterial infections, particularly those caused by methicillin-resistant *Staphylococcus aureus* (MRSA) and other multidrug-resistant organisms. In the Indian context, it is a critical last-line antibiotic, heavily regulated to prevent resistance. It is poorly absorbed orally and is primarily administered intravenously for systemic infections; an oral formulation is used only for *Clostridioides difficile* colitis.
| Onset | Duration | Bioavailability |
|---|---|---|
| Rapid bactericidal effect begins within hours of achieving therapeutic serum concentrations. Peak serum concentrations are reached immediately after the end of a 60-minute intravenous infusion. | Dosing interval is typically every 6 to 12 hours (q6-12h) in patients with normal renal function, due to a half-life of 4-6 hours. The post-antibiotic effect against Staphylococci is 1-2 hours. | Oral: Negligible (<5%) for systemic effect; used for local gut action in *C. difficile* infection. Intravenous: 100% (bioavailability by definition). Intramuscular: Not recommended due to pain and tissue necrosis. |
2. Mechanism of Action
Vancomycin inhibits the second stage of cell wall synthesis in Gram-positive bacteria by binding with high affinity to the D-alanyl-D-alanine terminus of cell wall precursor units (lipid II). This binding prevents the transglycosylation and transpeptidation reactions catalyzed by penicillin-binding proteins (PBPs), thereby inhibiting peptidoglycan polymerization and cross-linking. This leads to weakening of the cell wall and ultimately causes bacterial cell lysis and death.
3. Indications & Uses
- Serious infections caused by Methicillin-resistant *Staphylococcus aureus* (MRSA)
- Infections caused by other Gram-positive bacteria in patients with severe beta-lactam allergy
- Empiric therapy for suspected MRSA in healthcare-associated pneumonia, bacteremia, or skin/soft tissue infections
- Surgical prophylaxis (as per specific guidelines, e.g., cardiac surgery) in patients with beta-lactam allergy or known MRSA colonization
4. Dosage & Administration
Adult Dosage: **IV for normal renal function (CrCl >90 mL/min):** 15-20 mg/kg/dose (actual body weight) every 8-12 hours. A typical 500mg dose is often used for a 60-70kg patient. **Loading dose:** 25-30 mg/kg may be used in critically ill patients to rapidly achieve target trough levels. **Oral for *C. difficile*:** 125 mg orally four times daily for 10 days (standard dose; 500mg oral dose is not standard and may be used in severe/complicated cases as per IDSA guidelines).
Administration: **IV Administration:** MUST be infused slowly. 500mg should be diluted in at least 100 mL of compatible fluid (NS, D5W) and infused over **at least 60 minutes** (minimum 1 hour) to minimize risk of 'Red Man Syndrome' and phlebitis. Faster infusions (e.g., over 30 min) may be used in some protocols with pre-medication. **Oral Administration:** For *C. difficile*, the oral solution is prepared from the IV powder and must be taken as directed, not for systemic infection.
5. Side Effects
Common side effects may include:
- 'Red Man Syndrome' (erythema, flushing, pruritus, rash on face, neck, upper torso - infusion rate related)
- Phlebitis at injection site
- Nausea
- Chills
- Fever
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Aminoglycosides (Gentamicin, Amikacin) | Additive/synergistic nephrotoxicity and ototoxicity. | Major |
| Loop Diuretics (Furosemide, Torsemide) | Increased risk of ototoxicity. | Major |
| Amphotericin B | Increased risk of nephrotoxicity. | Major |
| NSAIDs (e.g., Ibuprofen, Diclofenac) | Increased risk of nephrotoxicity. | Moderate |
| Anesthetic agents | May enhance neuromuscular blockade. | Moderate |
| Cholestyramine, Colestipol | May bind oral vancomycin in GI tract, reducing efficacy for *C. difficile* if administered concurrently. | Moderate |
7. Patient Counselling
- Do report any ringing in ears, hearing difficulty, dizziness, or changes in urine output immediately.
- Do inform all healthcare providers you are on vancomycin, especially before any surgery or new medication.
- Do complete the full course of therapy even if you feel better.
- Don't stop the medication without consulting your doctor.
- Don't take any over-the-counter painkillers (NSAIDs like ibuprofen) without asking your doctor or pharmacist.
8. Toxicology & Storage
Overdose: Manifestations of overdose are extensions of its adverse effects: severe ototoxicity (tinnitus, hearing loss, vertigo), acute renal failure, and possible neuromuscular blockade.
Storage: **Unreconstituted Powder:** Store below 25°C, protected from light and moisture. **Reconstituted Solution (IV):** When diluted in compatible IV fluids, it is stable for up to 96 hours at 2-8°C (refrigerated) and for 24 hours at room temperature (25°C). **Oral Solution:** When prepared from IV powder, it is stable for 14 days when refrigerated (2-8°C) in an amber bottle. Do not freeze. Always check product-specific literature from the manufacturer.