What causes a metallic taste in an adult patient with a history of gastroesophageal reflux disease (GERD) and sinus infections, who is taking medications such as antibiotics, antihistamines, or decongestants?

Causes of Metallic Taste in Adults

In an adult patient with GERD and sinus infections taking antibiotics, antihistamines, or decongestants, the metallic taste is most likely medication-related, with antibiotics (particularly metronidazole) being the primary culprit, though GERD itself can contribute through acid reflux reaching the pharynx and nasopharynx. 1, 2

Medication-Induced Metallic Taste

Antibiotics as Primary Offenders

• Metronidazole causes a "sharp, unpleasant metallic taste" as one of its most characteristic adverse effects, occurring commonly during therapy. 1
• This metallic sensation is distinct from other gastrointestinal side effects and is specifically documented in FDA labeling as "not unusual." 1
• Other antibiotics used for tuberculosis treatment, particularly ethionamide, commonly cause metallic taste along with profound gastrointestinal effects including nausea and vomiting. 3

Other Medication Classes

• Antihistamines and decongestants can cause dry mouth, which may alter taste perception and contribute to dysgeusia. 3
• Eszopiclone (a sleep medication) demonstrates a +0.07 risk difference for unpleasant taste compared to placebo, with studies showing 15.2-26.1% incidence of metallic taste. 3
• Multiple medication classes including phenylbutazone, carbamazepine, and muscle relaxants have been documented to cause partial or complete loss of taste, taking weeks to months for recovery after discontinuation. 4

GERD-Related Mechanisms

Direct Acid Contact Pathway

• Gastric acid refluxes through the lower esophageal sphincter into the distal esophagus, then continues proximally through the upper esophageal sphincter into the pharynx and potentially the nasopharynx, where direct acid contact can alter taste perception. 2
• Dual-pH probe monitoring has objectively documented this mechanism, with 32% of children with chronic sinusitis showing nasopharyngeal reflux with acid detected in the nasopharynx itself. 2
• In adults with chronic sinusitis refractory to conventional therapy, 64% had documented gastroesophagopharyngeal reflux using 3-site ambulatory pH monitoring, compared to only 18% of healthy controls. 2

Clinical Presentation Without Typical GERD Symptoms

• Up to 75% of patients with reflux-related extraesophageal manifestations may lack typical symptoms such as heartburn or regurgitation. 5, 6
• Patients may present with chronic sore throat, throat clearing, or globus sensation without any gastrointestinal complaints, making the GERD connection less obvious. 5

Sinus Infection Contribution

Bidirectional Relationship

• The combination of GERD and chronic sinusitis creates a bidirectional relationship where conditions associated with extraesophageal reflux may themselves cause GERD or increase reflux episodes. 2
• Post-nasal drip sensations can result from GERD through both direct reflux pathways and reflex pathways, with acid in the esophagus triggering vagally-mediated airway reactions. 2

Diagnostic Approach

Initial Assessment

• Obtain detailed medication history focusing on recent antibiotic use (especially metronidazole), antihistamines, and decongestants as the most likely immediate causes. 1
• Assess for GERD symptoms including heartburn, regurgitation, dysphagia, or relief with antacids, though absence does not rule out GERD as a contributor. 3, 5
• Look for symptoms suggesting esophageal involvement: heartburn, regurgitation, dysphagia, odynophagia, or relief with antisecretory agents. 3

Empiric Treatment Trial

• If GERD is suspected, initiate a 4-8 week trial of PPI therapy, though extraesophageal manifestations typically require 8-12 weeks minimum for adequate response. 5, 6
• Consider discontinuing or substituting the suspected offending medication if clinically feasible, as medication-induced dysgeusia may take weeks to months to resolve after discontinuation. 4

When to Pursue Objective Testing

• If one PPI trial fails (up to 12 weeks), pursue objective testing with pH-impedance monitoring off PPI rather than trying additional empiric PPI trials, as further empiric therapy is low yield. 6
• Consider upper endoscopy if symptoms include dysphagia, odynophagia, gastrointestinal bleeding, unexplained iron deficiency anemia, weight loss, or recurrent vomiting. 3
• Objective reflux testing with prolonged wireless pH monitoring off medication (96-hour preferred) is required to confirm nasopharyngeal reflux and establish causation. 2

Important Clinical Pitfalls

Avoid Premature Closure

• Do not assume metallic taste is benign without considering medication review as the first step. 1
• Do not continue empiric PPI therapy beyond 12 weeks without objective testing, as 50-60% of patients with extraesophageal manifestations will not have GERD. 6

Multidisciplinary Approach

• A multidisciplinary approach with communication between gastroenterology, otolaryngology, and allergy/immunology produces the best outcomes for suspected extraesophageal reflux patients. 2
• No single diagnostic tool conclusively identifies reflux as the cause; diagnosis requires integrating symptoms, endoscopy findings, reflux monitoring results, and treatment response. 6

Rare but Serious Causes

• In extraordinary cases with chronic metallic taste unresponsive to standard measures, consider foreign body ingestion (such as copper-containing objects) with serum copper level testing and endoscopic evaluation. 7
• Chemotherapy and targeted cancer therapies cause metallic taste in 34% of patients experiencing taste changes, with women affected more frequently than men. 8