Vancomycin – Uses, Dosage, Side Effects, Interactions

Vancomycin is a tricyclic glycopeptide antibiotic originally derived from the organism Streptococcus orientalis. Vancomycin is used for the treatment and prevention of various bacterial infections caused by gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). It is also effective for streptococci, enterococci, and methicillin-susceptible Staphylococcus aureus (MSSA) infections. Vancomycin has numerous FDA-approved and off-label clinical uses.[rx][rx][rx]

FDA-approved Clinical Uses of Vancomycin

• Clostridium difficile-associated diarrhea (oral administration)
• Staphylococcus enterocolitis
• Pseudomembranous colitis
• Endocarditis: Diphtheroid, Enterococcal, Staphylococcal, and Streptococcal species
• Staphylococcal infections: septicemia, skin and soft tissue infections, bone infections, lower respiratory tract infections, etc.

Off-Label Clinical Uses of Vancomycin include

• Catheter-related infections
• Community-acquired bacterial pneumonia
• Clostridium difficile infection
• Neonatal prophylaxis for Group B streptococcus
• Intra-abdominal infections due to MRSA or ampicillin-resistant enterococci
• Bacterial meningitis
• Bacterial endophthalmitis (systemic or intravitreal administration)
• Native vertebral osteomyelitis
• Peritonitis
• Prosthetic joint infection
• Necrotizing skin and soft tissue infections
• Surgical prophylaxis
• Surgical-site infections

Mechanism of Action

Vancomycin is a glycopeptide antibiotic that exerts its bactericidal effect by inhibiting the polymerization of peptidoglycans in the bacterial cell wall. The bacterial cell wall contains a rigid peptidoglycan layer that has a highly cross-linked structure composed of long polymers of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG). Vancomycin binds to D-alanyl D-alanine, which inhibits glucosyltransferase (peptidoglycan synthase) and the P-phospholipid carrier, thereby preventing the synthesis and polymerization of NAM and NAG within in the peptidoglycan layer. This inhibition weakens bacterial cell walls and ultimately causes leakage of intracellular components, resulting in bacterial cell death. Vancomycin is only active against gram-positive bacteria.[rx][rx]

Administration

Vancomycin is FDA-approved for administration by either intravenous injection or oral route. Rectal administration is an off-label use of vancomycin useful in treating Clostridium difficile infection. The administration is dependent on the type and location of the infection. Vancomycin has poor oral bioavailability; therefore, its administration must be via the intravenous route to treat most infections.[rx][rx]

Intravenous vancomycin injection can treat MRSA infections as well as other susceptible gram-positive organisms. The dose of vancomycin required is dependent on the type and severity of infection, the patient’s overall clinical presentation, renal function, and body weight. The desired intravenous dose should be administered slowly over at least 60 minutes. The frequency of administration ranges from every 8 to 24 hours and should be adjusted based on renal function, age, and serum trough concentrations. Serum trough concentrations require close monitoring in all patients.

Oral vancomycin has low systemic absorption and is only effective for treating intestinal infections. Therefore, its only indications are for the treatment of Clostridium difficile-associated diarrhea (CDAD), pseudomembranous colitis, and Staphylococcal enterocolitis. Oral vancomycin is not an appropriate treatment option for systemic infections affecting other organs or parts of the body. Oral vancomycin is currently available as capsules and an oral solution. It is typically administered four times a day for a period of 7 to 10 days. However, the determination of the exact dose and length of therapy are dependant on multiple factors, including indication, assessment of the patient’s clinical presentation, and the severity of an infection. Oral vancomycin does not require dosage adjustment for renal impairment due to its low systemic absorption. Moreover, routine serum trough monitoring is not a recommendation for patients who are only receiving oral vancomycin.[rx]

Pharmacodynamics/Kinetics

• Route of administration: Intravenous, oral, rectal administration (off-label)
• Inhibition of bacterial growth: Slowly bactericidal
• PK/PD parameter: AUC: MIC
• Absorption: Oral vancomycin has a bioavailability of less than 10%.
• The onset of action: Vancomycin has a rapid onset of action with a serum peak concentration immediately following the completion of the intravenous infusion. The onset of action of oral vancomycin is currently unknown.
• Distribution: Large volume of distribution (0.4 L/kg to 1.0 L/kg) in body tissues and fluids, excluding cerebrospinal fluid (CSF) with non-inflamed meninges
• Protein Binding:  approximately 55%
• Metabolism: No evident metabolism (excreted unchanged)
• Clearance: 0.71 mL/minute/kg to 1.31 mL/minute/kg in adults with normal renal function
• Half-life: Vancomycin has a bi-phasic elimination half-life with its initial half-life being relatively quick and a terminal half-life of 4 to 6 hours in healthy adults with normal renal function. The elimination half-life is significantly prolonged in patients with renal dysfunction. Close monitoring is necessary for these patients.
• Excretion:  Intravenous vancomycin injection is primarily eliminated by glomerular filtration in the kidney (75% via urine). Oral vancomycin predominantly gets excreted in feces.

Contraindications of Vancomycin

Vancomycin is contraindicated in patients with a known hypersensitivity reaction to the drug or any component within the formulation.[rx]

Clinical Considerations

Although vancomycin does not have many contraindications, there are some important clinical considerations to keep in mind during patient care.

Geriatric Considerations: Elderly patients are more prone to vancomycin toxicity with IV administration due to age-related changes in renal function, the volume of distribution, and accumulation. These patients need to be carefully monitored and may require a more conservative dosage regimen.

Pregnancy Considerations: Oral vancomycin capsules are categorized as a category B drug for use in pregnancy. In contrast, intravenous vancomycin injection is as category C. Vancomycin should not be used during pregnancy unless the benefits outweigh the risks of the medication. If treatment with vancomycin is necessary, close monitoring of maternal blood is a recommendation to reduce the risk of ototoxicity and nephrotoxicity in the fetus. Animal studies have not yet determined any evidence of fetal harm from maternal vancomycin use. However, vancomycin crosses the placenta, and researchers have detected it in fetal serum, amniotic fluid, and cord blood. Patients who become pregnant while taking vancomycin should contact their healthcare provider immediately. Moreover, it is essential to note that pregnant patients may require higher doses of vancomycin to achieve therapeutic concentrations due to alterations in pharmacokinetics, such as an increased volume of distribution and total plasma clearance.

Renal Impairment – The reduced renal function can cause vancomycin to accumulate in the body, thereby increasing the risk of adverse effects. Dosing adjustments are necessary for renal impairment. Close monitoring of vancomycin trough concentrations is necessary for all patients with renal impairment. Patients should receive counsel to contact their provider if they experience symptoms of reduced kidney function, such as decreased urine output, swelling, and abdominal pain as vancomycin may exacerbate renal impairment.

Bacterial Resistance – Similar to other antimicrobials, prolonged or inappropriate treatment with vancomycin can lead to bacterial resistance, such as vancomycin-resistant enterococci (VRE). Providers need to be aware of increased antimicrobial resistance patterns and practice appropriate antimicrobial stewardship. Moreover, patients should receive counseling on the importance of medication adherence to prevent the development of multidrug-resistant infections.

Adverse Effects of Oral Vancomycin

Adverse Effects of Intravenous Vancomycin Injection

Common adverse effects of intravenous vancomycin injection include nephrotoxicity, hypotension, and hypersensitivity reactions. Anaphylaxis is a type of hypersensitivity reaction that can occur with vancomycin.[rx][rx][rx]

Redman syndrome is an infusion-related reaction associated with rapid intravenous infusion of vancomycin. Symptoms include flushing, pruritus, and an erythematous rash on the face, neck, and upper torso. Signs of red man syndrome often appear 4 to 10 minutes after starting or shortly after the completion of an infusion. The incidence of red man syndrome varies between 3.7% and 47% in patients. However, there is a direct correlation between the increased incidence of red man syndrome with faster rates of vancomycin administration. Rapid infusion of vancomycin can lead to angioedema and hypotension, which accompany red man syndrome. Reports show the most severe forms of this reaction frequently occur in children and patients younger than the age of 40. Prolonging the infusion time is the primary management strategy used to mitigate red man syndrome. Nevertheless, premedication with antihistamines, such as diphenhydramine or hydroxyzine, can be useful in preventing the occurrence of red man syndrome.

Less common adverse effects include local phlebitis, chills, drug fever, skin rash, eosinophilia, and reversible neutropenia.

In rare situations, patients have reported DRES’s syndrome (drug rash with eosinophilia and systemic symptoms), ototoxicity, thrombocytopenia, vasculitis, and Stevens-Johnson syndrome.

Gastrointestinal adverse effects, such as abdominal pain and nausea, are commonly seen with oral vancomycin. Dysgeusia or distorted sense of taste is a common adverse effect unique to vancomycin oral solution. Patients should seek medical attention if these adverse effects are severe and bothersome. Note that many of these adverse effects are temporary.

Less common adverse effects of oral vancomycin include peripheral edema, fatigue, headache, diarrhea, flatulence, vomiting, back pain, urinary tract infection, and fever.

Reports exist of rare cases of increased serum creatinine, red man syndrome, interstitial nephritis, nephrotoxicity, ototoxicity, thrombocytopenia, and vasculitis with the use of oral vancomycin.

Drug Interactions of Vancomycin

Co-administration of other medications, along with vancomycin, may increase the risk of adverse effects and toxicity. Therefore dosing adjustments, additional monitoring, and consideration of alternative treatment should merit attention when combining vancomycin with certain medications. Caution is necessary when administering vancomycin with other nephrotoxic agents such as aminoglycosides, amphotericin products, and IV contrast.

Monitoring

Patients receiving vancomycin therapy require monitoring to ensure the safety and efficacy of the medication. Periodic renal function tests and complete blood cell counts can help to monitor the patient’s response to the drug.[rx]

Assessment of vancomycin trough concentrations is a strong recommendation in the following patients receiving intravenous vancomycin injection:

• A severe or invasive infection
• Critical illness
• Impaired or unstable renal function
• Morbid obesity (body mass index greater than or equal to 40 kg/m)
• Advanced age
• Inadequate response to therapy after three to five days
• Concomitant use of nephrotoxic agents (i.e., aminoglycosides, piperacillin-tazobactam, amphotericin B, cyclosporine, loop diuretics, nonsteroidal anti-inflammatory drugs, contrast dye).

Monitoring vancomycin trough concentrations in stable patients with normal renal function is also recommended to assess satisfactory clinical response. Obtaining vancomycin serum trough concentrations allows healthcare professionals to evaluate the efficacy of the vancomycin dosing regimen and clearance of the drug by the individual patient. The target therapeutic serum trough concentration varies depending on the indication and typically ranges between 10 mcg/mL to 20 mcg/mL.

Serum trough concentrations should ideally be drawn immediately (30 minutes or less) before administration of a dose at steady-state conditions. Typically, steady-state occurs after the third dose of vancomycin.

Unlike intravenous vancomycin injection, oral vancomycin typically does not require serum concentration monitoring due to a lack of systemic absorption.