The goal of this clinical trial is to investigate biomarkers of non-IgE-mediated immediate hypersensitivity reactions during infusion of intravenous vancomycin. The main question it aims to answer is:

• Identifying novel biomarkers in blood that occur during infusion reaction

Participants will:

• Have allergy skin testing for vancomycin
• Receive an infusion of vancomycin

Inclusion Criteria:

• Male or female age ≥ 18 years.
• Adequate kidney function as defined by creatinine level within normal institutional limits at the participant's first visit.
• Women of child bearing potential must agree to a reliable form of highly effective contraception (hormonal, device, or barrier method of birth control; abstinence) prior to study entry, for the duration of study participation, and for 7 days following completion of vancomycin therapy. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform the Principal Investigator and her treating physician immediately.
• Ability to understand and the willingness to sign a written informed consent.
• Ability to clearly understand and speak English at an 8th grade reading level. For safety reasons, participants must speak English due to the anticipated need for clear and timely communication with investigators and the study team in emergency situations, since the investigators and study team are English speaking.

Exclusion Criteria:

• Participants who have previously received vancomycin in any formulation, including oral or intravenous.
• History of allergic reactions to study drug or reactions attributed to compounds of similar chemical or biologic composition to vancomycin, including active product or excipients.
• Concurrent use of medications thought to cause non-specific mast cell activation (e.g. opioids)
• Baseline serum tryptase over 8.0 ng/mL and/or known mast cell disorder, including, but not limited to, mastocytosis, idiopathic mast cell activation syndrome, and hereditary alpha tryptasemia
• Active infection or immunodeficiency
• Unstable cardiovascular disease
• Renal insufficiency
• Current hearing deficit
• Current use of beta-blockers
• Use of immunomodulatory therapies or oral corticosteroids within the previous 1 month
• Use of biologics in the previous 6 months, including omalizumab
• Participants taking antihistamines must stop these drugs for one week prior to enrollment and must refrain from taking antihistamines during the duration of the study so as not to interfere with responses during drug challenge