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.
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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.