Treatment
Another pressing question for clinicians concerns artificial saliva. Although 23.2% of patients with dry mouth in this xerostomia cohort used artificial saliva, the efficacy of this treatment is still unproven. Saliva substitutes are often used by patients who cannot produce sufficient amounts of natural saliva. In practice, artificial saliva produces, at best, modest temporary improvement in dry mouth symptoms in up to 40% of patients. At worst, as put forth by the Cochrane Review, artificial saliva may be no better than placebo in treating dry mouth.37,38 The volumes needed for symptom relief are large, ranging between 40 mL and 150 mL per day depending on the substitute’s composition. Saliva substitutes also must be reapplied throughout each day. This is particularly bothersome when patients must wake up repeatedly to reapply the treatment at night.37 In short, these substances do not seem wholly effective in managing dry mouth, and other options must be made available to patients with refractory xerostomia when artificial saliva and lifestyle modifications fail.
For now, few alternatives exist. Chewing gums and lozenges help to stimulate salivary flow, as do muscarinic agonists like pilocarpine. Unfortunately, muscarinic agonists are seldom used due to cholinergic AEs. Humidifiers are effective in increasing nighttime moisture but are contraindicated in patients with dust mite allergies.39 Reservoir-based devices with automated pumps funnel water and/or salivary substitutes from a fanny pack into patients’ mouths for lubrication.37 Other more esoteric pharmacologic treatments include D-limonene, yohimbine, and amifostine, which purportedly protect salivary progenitor cells, increase peripheral cholinergic activity, and protect salivary glands from free-radical damage during radiation treatment, respectively. Although these agents have shown some promise, D-limonene is difficult to administer given the high dosage required for treatment, yohimbine hasn’t been seriously investigated for improving salivary secretion since 1997, and amifostine isn’t used widely due to its AE profile despite its US Food and Drug Administration approval for prevention of xerostomia.39
Substance Abuse
The impact of smoking on xerostomia remains controversial. Some studies report an association between active smoking and xerostomia; others suggest that the local irritant effect of tobacco smoke may increase salivary gland output.40,41 The same may be true for chronic alcohol use as there are no epidemiologic studies showing a causal relationship between alcohol use and xerostomia. Studies with rats that are chronically exposed to ethanol have found increased salivary flow rates.42 In the xerostomia cohort presented here, 30 patients (21.7%) had a documented history of substance misuse. That percentage is likely underestimated, as substance misuse is often underreported, and frequent use may not always constitute misuse. Therefore, nicotine exposure, alcohol exposure, illicit drug use, and vaping all should be considered during the workup of a patient with xerostomia.
Limitations
It is common for medications to remain in a patient’s health record long after that patient stops taking them. Developing methods to track when patients discontinue their prescriptions will be essential for clearing up uncertainty in our data and in other similar studies. This study also did not account for patients’ medication adherence and the duration of exposure to medications and illicit substances. Furthermore, the results of this veteran study are not easily generalizable as this cohort is disproportionately male, of advanced age, and especially prone to exhibiting both substance use and psychiatric diagnoses relative to the general population. As described by Viljakainen and colleagues, risk factors for xerostomia include advanced age, female gender, low body mass index (BMI), malnutrition, and depressive symptoms, but because the demographic scope of this veteran population was narrow, it was not possible to discern the impact of, for example, gender.33 Data on variables like BMI, malnutrition, and depressive symptoms were not available. For this study, xerostomia could only be considered as an all-or-nothing phenomenon because the dataset did not describe different levels of dry mouth severity (eg, mild, moderate, severe).