Can isoniazide (INH) cause dry mouth?

Isoniazid and Dry Mouth: Clinical Implications and Management

Isoniazid (INH) is not specifically documented to cause dry mouth as a common side effect in major tuberculosis treatment guidelines. While INH is associated with several well-documented adverse effects, xerostomia (dry mouth) is not prominently mentioned among them 1.

Known Adverse Effects of Isoniazid

Isoniazid has several well-documented adverse effects that clinicians should monitor for:

1. Hepatotoxicity:

   • Incidence of clinical hepatitis is 0.1-0.6% 1
   • Risk increases with age, especially in persons over 50 years
   • Higher risk in those with underlying liver disease or alcohol consumption

2. Peripheral Neuropathy:

   • Dose-related and uncommon (<0.2%) at conventional doses 1
   • Higher risk in patients with nutritional deficiency, diabetes, HIV infection, renal failure, and alcoholism
   • Preventable with pyridoxine (vitamin B6) supplementation (25 mg/day) 1, 2

3. Central Nervous System Effects:

   • Dysarthria, irritability, seizures, dysphoria, and concentration problems 1

4. Other Documented Effects:

   • Lupus-like syndrome (rare, <1%)
   • Hypersensitivity reactions (fever, rash, Stevens-Johnson syndrome)
   • Monoamine poisoning (rare)
   • Diarrhea (with liquid formulation containing sorbitol) 1

Dry Mouth and Medications

While isoniazid is not specifically listed as causing xerostomia in the tuberculosis treatment guidelines, many medications can cause dry mouth through various mechanisms:

• Medications with anticholinergic effects are the most common culprits 3, 4
• Xerostomia can significantly impact oral health and quality of life 3, 5
• Drug-induced xerostomia is particularly common in elderly patients due to polypharmacy 3

Clinical Implications and Management

If a patient on isoniazid reports dry mouth symptoms:

1. Consider alternative causes:

   • Review the patient's complete medication list for other drugs with known xerogenic effects
   • Evaluate for other conditions that may cause dry mouth (Sjögren's syndrome, radiation therapy)

2. Management options if dry mouth persists:

   • Ensure adequate hydration
   • Consider saliva substitutes or stimulants 6, 5
   • Implement meticulous oral hygiene to prevent dental caries
   • Regular dental check-ups

3. Monitoring:

   • Continue to monitor for more common and serious adverse effects of isoniazid
   • Patients should be instructed to report symptoms of hepatitis immediately (loss of appetite, nausea, vomiting, jaundice, malaise) 1

Conclusion

Based on current tuberculosis treatment guidelines, dry mouth is not listed among the common or significant adverse effects of isoniazid. Clinicians should focus on monitoring for the well-documented adverse effects such as hepatotoxicity and peripheral neuropathy. If dry mouth occurs in a patient taking isoniazid, consider other medications or conditions as potential causes before attributing it to isoniazid therapy.