Overview of Drugs
and Dry Mouth
The Complexities of the Drug-Dry Mouth Relationship
Diagnosis of Dry Mouth: Symptoms, signs, causes
Dry Mouth and
Salivary Flow
Treatment of Drug-induced Xerostomia
Sources of Information/Abbreviations
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The Complexities of the Drug - Dry Mouth Relationship

Dry mouth is a subjective symptom. Quantitative, objective data regarding the capacity of drugs to induce dryness are usually obtained from responses given by patients in clinical studies. Unfortunately, few such studies have been conducted. This is hardly surprising. Dry mouth is often regarded as a petty complaint, so there is allegedly no compelling health-related reason to assess its presence. Moreover, even when noted as being present, most medical clinicians and pharmacologists place "dry mouth" in a category which usually "does not require the care of a physician". So the urgency to obtain specific information about the frequency and severity of oral dryness is simply not there.

But these are not the only problems. Most symptoms have a "home". Pain, for example, resides in the domain of neurology; palpitations, in cardiology; difficulty with breathing , in respiratory circles. But there is no common site for dry mouth. It is often included, along with other symptoms, in the list of adverse experiences associated with the gastrointestinal (G-I) system. But sometimes, it is listed under "autonomic responses"; sometimes, with the neurological system, at times under "dental complaints" or with the "special senses"; even under the respiratory system. Or, it may be simply listed under "other complaints". And to make matters worse, most of the time, the symptoms and/or complaints are not placed in a dedicated order or rank. One might expect, or at least hope, that the most severe symptoms would be ranked first. Sometimes this is done. But often, the listing of dry mouth in the "adverse event" sections of drug information handbooks bears little relation to the gravity of the complaint. In at least one well known case of oral dryness, where the offending drug is severely xerogenic, oral dryness is listed last. And this, simply because the term which was used to identify oral dryness was "xerostomia"--- and in the alphabetic rank order of presentation, the symptom was thus placed last on the list.

But matters get even worse. Dry mouth is often qualified as a "common" or "uncommon" complaint. There are, however, usually no numbers attached to define each of these parameters. In some cases, especially in recent drug studies, the actual percent of patients who develop oral dryness is shown. But we are frequently not told whether these percentages relate to the prevalence of dry mouth or, as is sometimes the case, to its severity. Moreover, many patients regularly consume many xerogenic drugs each day. Although we know that the frequency of onset of dry mouth is directly related to the total number of drugs taken per day, there is little information available to indicate what effect this has on the magnitude of the dryness.

And then, there is the matter of the formal listing of the complaint of oral dryness. "Dry Mouth" is listed in drug information handbooks under various headings: as an "adverse event, adverse effect, adverse experience, as an adverse reaction" or, it may simply be listed under the more general term "side effect". The term "adverse reaction" is frequently used where there is a causal association between the adverse event and the drug to which the patient was exposed. Since the objective of this portal is to identify the association between drugs and dry mouth, not to define the pharmacologic basis for the dryness, these terms will be used without regard to causality; in other words, we refer to adverse events.

Finally, there is the matter of the testing of drugs for their capacity to induce dry mouth. The markets in the industrialized world are virtually saturated with drugs. Moreover, the number of drugs available to the public increases rapidly each year. Indeed, in the Western World, barely a day goes by without the announcement of a new drug in the daily press, "online" or in the more formal publications of governments and the learned societies. In most countries, the state requires that each drug manufacturer conduct a series of more-or-less rigid pre-marketing tests to assess the efficacy and safety of each new medication. But test standards vary widely from country to country and even, in cases, within countries. To test drugs properly the tests should have input from the drug manufacturers, from relevant and appropriate governmental agencies and from independent science testing laboratories. The tests should be performed on large numbers of patients in a randomized, double blind manner. And final judgement should be rendered only after the new drug has been tested over a reasonably long period of time. Although there are a modest numbers of studies which have included dry mouth in their test protocol, few have made it their primary objective.

Clearly, the interpretation of data regarding the relationship between drugs and dry mouth is difficult. Generally, the data may be used to determine whether a drug is xerogenic or not. But, it is more difficult to determine how often dryness occurs and/or how grievous it is. The material presented in this portal is our best interpretation of the available data. However, it is important to note, that when an estimate of frequency is cited e.g. "dry mouth incidence = 10% or greater", this refers to the frequency which the event of dry mouth has been reported by patients taking the drug. Such assessments are a reasonably valid indicator of the likelihood of a complaint of xerostomia in treated patients . It does not necessarily follow that the drug concerned caused dry mouth in all those individuals.

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