What are the adverse effects of boric acid?

Adverse Effects of Boric Acid

Boric acid is generally safe when used topically at appropriate concentrations and durations, but systemic absorption through inflamed skin or mucosa can cause serious toxicity including metabolic acidosis, acute renal failure, and death—particularly in children and with high-dose or prolonged exposure.

Topical Application Adverse Effects

Dermatologic and Local Reactions

• Vaginal burning sensation occurs in <10% of patients using intravaginal boric acid for vulvovaginal candidiasis 1
• Watery vaginal discharge during treatment is commonly reported 1
• Vaginal erythema can develop with intravaginal use 1
• Dermatitis toxica faciei has been documented in a 2-year-old after topical application of 2% boric acid solution, demonstrating that topical side effects can occur despite limited literature reporting 2

Otic Administration Risks

• Boric acid powder insufflation for otologic conditions delivers highly variable doses ranging from 2.1 mg to 730.8 mg depending on the insufflator device used 3
• The pneumatic powder blower delivers a mean dose of 192.8 mg per application, and the accordion insufflator delivers 284.1 mg—both exceeding the 50 mg/day threshold thought to cause systemic toxicity 3
• Inflamed skin and mucosal surfaces in the ear canal readily absorb boric acid, increasing systemic exposure risk 3

Systemic Toxicity

Acute Poisoning Manifestations

• Metabolic acidosis is a hallmark of boric acid poisoning 4
• Acute renal failure develops with significant ingestion 4
• Shock can occur in severe cases 4
• Death has been reported, especially in children who are more vulnerable to toxicity 5

Pharmacokinetics Contributing to Toxicity

• Boric acid is well absorbed orally and through damaged skin/mucosa 5
• The biological half-life is approximately 21 hours in humans, allowing accumulation with repeated exposure 5
• Boric acid has affinity for certain tissues, especially bone 5
• Slow elimination increases the risk of systemic side effects with repeated topical use 2

Dose-Related Toxicity Thresholds

• Exposure to 50 mg per day is considered the threshold for systemic toxicity in humans 3
• In a documented case of massive poisoning, serum boric acid levels reached 1800 μg/mL after large ingestion 4

Reproductive and Developmental Toxicity

• Reductions in male sperm counts have been noted in animal studies 5
• This reproductive toxicity raises concerns about chronic low-level exposure 5

Age-Specific Vulnerabilities

Pediatric Populations

• Children are at particularly high risk for toxicity and death from boric acid exposure 5
• Topical boric acid is licensed only for children above age 10 in some countries (e.g., Czech Republic), yet it is often used in younger children due to over-the-counter availability 2
• Fast absorption and slow elimination create disproportionate risk in pediatric patients 2

Drug Interactions and Chemical Reactivity

• Boric acid reacts reversibly with alcohols (especially 1,2-diols), carbohydrates, carboxylic acids, thiols, and amines 5
• These reactions form esters/adducts that are also Lewis acids with lower pKa values 5
• Boric acid can stabilize some pharmaceutical materials while catalyzing degradation of others, creating formulation challenges 5

Management of Toxicity

• Early treatment with forced diuresis and hemodialysis should be considered for boric acid poisoning, even before signs of renal dysfunction appear, to prevent severe renal damage 4
• During hemodialysis, boric acid clearance averages 235 mL/min with a 70% extraction ratio 4
• In documented cases, serum levels decreased from 1800 to 530 μg/mL after hemodialysis and from 530 to 30 μg/mL during forced diuresis 4

Clinical Context and Safety Considerations

When Boric Acid May Be Appropriate

• Boric acid is a safe, alternative, economic option for recurrent vulvovaginal candidiasis when conventional azole treatment fails due to non-albicans Candida species or azole-resistant strains 1
• Mycologic cure rates range from 40% to 100% in treated patients 1
• It demonstrates mild antibacterial and antifungal activity suitable for dermal and women's hygiene products 5

Critical Safety Warnings

• Avoid use in children under 10 years of age given the documented toxicity risk 2
• Limit otic insufflation to manual devices (DeVilbiss or House-Sheehy insufflators) that deliver <30 mg per application rather than pneumatic or accordion devices 3
• Monitor for signs of systemic absorption (nausea, vomiting, diarrhea, renal dysfunction) with any topical use on inflamed or abraded skin 4, 5
• Parenteral use should be avoided or used only at very low doses given the toxicity profile 5