The oral LD₅₀ in mice is 5000 mg/kg. The median lethal intravenous dose is 319 mg/kg in rats and 400 mg/kg in mice. FDA Label

Conversely, the most common adverse effects associated with vancomycin appear to be nausea, abdominal pain, and hypokalemia FDA Label. In particular, incidences of hypokalemia, urinary tracy infection, peripheral edema, insomnia, constipation, anemia, depression, vomiting, and hypotension are higher among subjects >65 years of than in those that are 65 years old or younger FDA Label.

Additionally, nephrotoxicity involving reports of renal failure, renal impairment, elevated blood creatinine, and others has also occurred with vancomycin therapy during studies, and can occur during or after completion of a course of therapy FDA Label. Risk of such nephrotoxicity is increased in patients greater than 65 years of age FDA Label.

Ototoxicity has also occurred in patients receiving vancomycin treatment, and it can be transient or permanent. This effect has been reported primarily in patients who have been given excessive intravenous doses, who have kidney dysfunction, who have an underlying hearing loss, or who are receiving concomitant therapy with another ototoxic agent like an aminoglycoside FDA Label. Potentially related adverse effects like vertigo, dizziness, and tinnitus have also been reported FDA Label.

Neutropenia, often beginning one week or more after onset of intravenous vancomycin therapy or after a total dose of more than 25 mg has been observed for several dozen patients as well. This neutropenia however, appears to be promptly reversible when the vancomycin treatment is discontinued. Alternatively, thrombocytopenia has also been reported FDA Label.

Additionally, a condition has been reported that is described as being similar to IV-induced symptoms involving symptoms consistent with anaphylactoid reactions, including hypotension, wheezing, dyspnea, urticaria, pruritus, flushing of the upper body (in what is known as the so-called 'Red Man Syndrome'), pain and muscle spasm of the chest and back. Although on average such reactions usually resolve within 20 minutes, they are just as likely to persist for hours FDA Label, A760.

In a controlled clinical study, the potential ototoxic and nephrotoxic effects of vancomycin on infants were assessed when the drug was given intravenously to pregnant women for serious staphylococcal infections complicating intravenous drug abuse. The results obtained demonstrated that vancomycin was found in cord blood but that no sensorineural hearing loss or nephrotoxicity attributable to vancomycin was noted. Ultimately however, because the number of subjects treated in this study was limited and vancomycin was administered only in the second and third trimesters, it is not formally known whether vancomycin causes fetal harm. Subsequently, vancomycin should be given to a pregnant woman only if clearly needed FDA Label.

Although it is known that vancomycin is excreted in human milk based on information obtained from the intravenous administration of the medication, it is not known if vancomycin is excreted into human milk after oral administration. However, because of the overall potential for adverse events, caution must be exercised when vancomycin is given to a nursing woman and a decision must be made whether to discontinue nursing or discontinue the drug, taking into consideration the importance of the drug to the mother FDA Label.

The safety and effectiveness in pediatric patients have not been formally established FDA Label.

Patients older than 65 years of age may take longer to respond to therapy compared to patients aged 65 year or younger. Vancomycin treatment in patients aged older than 65 years subsequently should not be discontinued or switched to an alternative treatment prematurely FDA Label.

Furthermore, clinical studies have demonstrated that geriatric patients are at increased risk of developing nephrotoxicity following treatment with oral vancomycin, which can occur during or after completion of therapy. In patients aged older than 65 years, including those with normal renal function prior to treatment, renal function should be monitored during and following treatment with vancomycin to detect any potential vancomycin induced nephrotoxicity FDA Label.