Abstract
There is controversy concerning the effect of pilocarpine in the reversal of radio-induced xerostomia; however, the tests are usually performed at the end of radiotherapy. The present study evaluated the radioprotective effects of pilocarpine when ingested during radiation treatment. Eleven patients (recently diagnosed with head and neck cancer who were not undergoing radiotherapy) were divided into two groups: the control group (saline solution intake n=6) and the pilocarpine-treated (5 mg pilocarpine three times daily, n=5) group, in a prospective and double-blinded study. For five weeks, oral conditions, unstimulated salivary flow and stimulated saliva flow were collected weekly, with the first collection occurring prior to radiation therapy. As early as the second week, the control group exhibited oral complications and greater reduction in salivary flow rate. At the end of the study, the pilocarpine-treated group presented mean values of salivary flow greater than those of the control group. Pilocarpine intake applied simultaneously with radiotherapy demonstrated encouraging results with regard to lowering salivary flow reduction and incidence of xerostomia, as well as of oral complications.
- Radiotherapy
- pilocarpine
- xerostomia
Radiation therapy has been frequently used in the treatment of patients with cancer. Head and neck cancer patients undergoing radiotherapy become susceptible to secondary side-effects, such as oral mucositis, candidiasis, dysphagia, periodontitis, osteoradionecrosis, and reduced salivary flow, which represents the most significant change reported by patients (1-3). Reduced salivary flow is characterized by the sensation of a dry mouth (xerostomia) and is also caused by damage to the secretory glands located in the areas under radiation.
Saliva performs an essential role in the mouth, and the absence or even the reduction of salivary flow can affect speech patterns, mastication, and deglutition. It can also cause dental decay, periodontal diseases, and mucosal fragility (1, 3), all of which can lead to diminishing patient quality of life and dietary intake (4, 5). Even at lower doses (6), radiation therapy damages salivary glands through a change in the viscosity and flow of the saliva, negatively-affecting the lubrication of ingested food. Furthermore, it causes atrophy of the taste buds, a fact that alters the patient's sense of taste, making food less palatable. Because of a poor diet, these patients may suffer an impairment of their general condition, resulting in immunocompromised condition and an increase in morbidity, facilitating the emergence of opportunistic infections such as Candidiasis (7). A reduction in salivary flow also reduces bacterial action and self-cleaning properties, a fact that facilitates, in turn, the onset of tooth cavities, known as ‘radiation cavities’ (8-10).
Under radiotherapy, salivary flow decreases progressively, and this occurs during the first weeks of treatment (11, 12). Changes in the salivary glands start during the first and second weeks of treatment and are characterized by reduction or even complete absence of salivary secretion. This situation can sometimes be reversed; nevertheless, after completion of radiation treatment (13), it can take months for the salivary glands to start producing saliva again. However, there are palliative substances to help restore saliva and minimize discomfort (14, 15).
Given the importance of maintaining a stable and regular salivary flow in patients undergoing radiation therapy, much research has been performed regarding the need to offset radiation effects on glandular tissues, and to assist patients in preserving a good quality of life (5, 6, 16, 17). Clinical studies have demonstrated that pilocarpine is highly effective in the treatment of xerostomia (18). In addition to increasing salivary secretion, pilocarpine also intensifies the production of proteins. Compared to pilocarpine (5, 19), the surgical transfer of the submandibular gland to areas of lesser incidence of radiation has led to positive results; however, these procedures cannot be applied to all involved salivary glands.
Positive results have been achieved experimentally using pilocarpine hydrochloride in animals. A study on the direct effect of pilocarpine on secretion of saliva, using the submandibular glands from rats, demonstrated that pilocarpine has a direct effect on salivary fluid secretion (20). A similar study using rats evaluated the effect of pilocarpine on reversing xerostomia induced by anti-depressants, and it also demonstrated positive effects with regard to reversal of hyposalivation caused by Venlafaxine. Pilocarpine is a parasympathomimetic agent that acts as a non-selective muscarinic receptor agonist. It promotes the stimulation of exocrine glands, as well as salivary secretion, and it is effective in the treatment of patients with mild glandular destruction (21).
Research on pilocarpine has been conducted after the patient had been submitted to the treatment, i.e. after the problem had already been created, instead of during treatment, when it can be prevented. Based on this point, our purpose was to analyze the radioprotective effect of the continuous use of pilocarpine hydrochloride in the salivary glands during the treatment of head and neck cancer in patients undergoing radiotherapy, with its use coinciding with the beginning of the radiation process.
Patients and Methods
Ethical considerations. This was a prospective, double-blind, randomized clinical study. The Ethics Committee for Research in Humans approved it under Protocol No. 79/06/07 and all patients signed an informed consent form.
Patient cohort. The sample included patients newly-diagnosed with head and neck cancer beginning treatment with radiotherapy. The main inclusion criterion was no previous exposure of patients to radiotherapy. The total radiation levels ranged from 35 to 50 Gy, with daily doses of about 2 Gy. The radiation doses were individualized according to each lesion's progression, since dose standardization remains impossible among patients. The sample consisted of both genders: eight men (72.7%) and three women (27.3%), with a mean age of 60 years.
In the sample, we excluded patients undergoing concomitant chemotherapy, or patients who had been diagnosed with cardiopathy, hypertension, diabetes, allergy to pilocarpine, Sjögren syndrome, tumors in the salivary glands, chronic lung disease, glaucoma, peptic ulcer, or who were taking β-blockers or drugs that could alter salivary flow.
Data collection. Were established five contacts with each patient. During the first contact, we collected personal data and evidence of co-morbidities, and oral and systemic changes. Data related to the malignancy, staging, and proposed treatment were collected from the medical records. We conducted a clinical and radiographical evaluation of the remaining teeth to detect the need for dental treatment prior to radiotherapy. We also searched for oral complications, such as mucositis or candidiasis. The initial collection of unstimulated saliva flow (USF) and stimulated saliva flow (SSF) were performed prior to any radiation exposure. Mevatron Linear Accelerator VI or Theratron 60Co was employed as radiation sources. The collected data were standardized and individually recorded for each patient.
Our second contact with patients occurred after one week of radiotherapy, when saliva was collected early in the morning, so as to evaluate their salivary flow (unstimulated flow - USF and stimulated flow - SSF). We questioned the patients about any reductions in the amount of saliva and the feeling of dry mouth. The emergence of oral complications such as oral mucositis, ulcers or difficulty to eat was clinically verified and classified according to the World Health Organization, (22) in degrees ranging from 0 to 4, (“absent”, “mild”, “moderate” and “severe”) as reported by Miller et al. (23). Fungal infections, such as candidiasis, was also identified. Patients were contacted at each subsequent week of radiation exposure, with new collections and clinical examinations being undertaken.
Group division. Due to the double-blind character of the study, a dispensing pharmacy held custody of the samples, separating those from the group who took pilocarpine solution from those which took the placebo. All patients were assigned a number corresponding to the medicine bottle. Researchers were not granted access to that information prior to the end of the survey. Therefore, two groups were formed: a control/irradiated group who ingested a saline solution (placebo) and the pilocarpine/irradiated group who ingested the radioprotective medication during the treatment.
Collection of saliva at rest and under stimulation. The first sample from both groups was collected at the start of the radiation process. The USF and SSF rates were determined using the salivary sputum method. For the unstimulated saliva collection, we asked patients to swallow all the saliva present in the mouth. We also asked them to abstain from both moving the tongue and from ingesting saliva for one minute. Afterwards, the patient was instructed to spit into a graduated tube, repeating the cycle every minute until completing a total of five minutes.
The final calculations resulted from the sum of the total volume obtained divided by the total collection time allowing calculation of a milliliter per minute final rate. Mechanical stimulation was used for achieving stimulated saliva rates; it consisted of chewing a hyperboloid, a non-toxic, tasteless, and odorless silicone instrument with a hyperbolic form. Patients were instructed to open and close the mouth, manipulating the object with the tongue, in addition to chewing the material. They performed one-minute repetitions three times. The produced saliva was spat into a graduated tube, and was maintained at rest for 30 min on a test tube holder. Foam content was disregarded, and the results were recorded in ml/min, following the same mathematical calculation.
After one week of radiation therapy, patients were asked to return for another collection, repeating the same process for another four weeks in order to verify any changes in the salivary flow. These data were recorded weekly on individual cards.
Administered dose. Pilocarpine 5 mg (Dilecta Pharmacy Manipulation - Joao Pessoa, Paraiba, Brazil) was orally administered three times daily (17, 24, 25). Ingestion of pilocarpine started on the same day of the first radiation treatment. It was recommended that the medication should be taken an hour before each main meal (breakfast, lunch, and dinner), since its effect would begin one hour after the ingestion, lasting up to three hours (14). Every week, patients were given a dropper bottle containing the solution and were instructed to return it at the end of the week. The solution remaining in the vial was measured and checked for breaches of the ingestion protocol. We considered the following values as hyposalivation in the salivary flow analysis: USF ≤0.1 ml/min.; SSF ≤0.7 ml/min (2).
Results
We pre-selected twenty-nine patients; however, the careful selection of the population was directly reflected in the number of enrolled patients and in the end, only 11 were included in the survey. We consider that this low number is a result not only of the exclusion stemming from previously-established eligibility criteria, but also from the breach of protocol. All patients in the present study were smokers, and for more than half of them, this habit was associated with alcoholism.
The oropharynx and larynx were the areas mostly affected by cancer. The total radiation treatment ranged from 3,500-7,040 cGy, with an average of 4,829 cGy, standard deviation of ±1.017. This dosage was divided into daily doses ranging from 90 to 200 cGy. Thus, there was a variation in the accumulated radiation dose for each patient and radiation field. Table I shows the location of the tumor, histopathological diagnosis, and the prescribed radiation levels for each patient. At the end of the fourth week, the total radiation dosage ranged from 2,100 to 4,400 cGy, with a mean of 3,612 cGy.
The salivary flow was collected weekly (Tables II and III). All patients in the control group, starting from week 2, reported xerostomia and some type of oral alteration (represented by the presence of mucositis with/without candidiasis), except for patient 4 who was not subjected to facial radiation, being irradiated only in the right and left cervical fields (Table II). This fact, in turn, led to lower levels of salivary flow losses.
Hyposalivation was detected in all patients who did not receive pilocarpine; 5 of them reported xerostomia and oral complications, which started on the second week of treatment. For the majority of the patients of this group, this scenario remained unchanged for the duration of the study. It is worth noting that patients 8 and 9 had lower salivary reduction; however, it must be stated that patient 9 already had low salivary flow prior to radiation therapy, while patient 8 had not shown hyposalivation; he had laryngeal cancer and the higher doses of radiation were concentrated in the cervical areas.
The pilocarpine group had lower rates of salivary flow loss (Table III). As for oral changes, patients 4 and 10 showed no oral complications, the opposite being true for patients 3 and 7, who not only suffered salivary reductions, but also presented oral alterations, which started on the second week of treatment. Patients 1 and 7, whose tumors were located in the floor of the mouth, presented significant evidence of hyposalivation. We detected xerostomia in 2 patients, while the hyposalivation and oral complications were found in 3 of them. There was no evidence of side-effects in these patients.
At the conclusion of the four weeks of radiation, we observed that in the pilocarpine-treated group, only 1 of the patients presented hyposalivation in the USF and 2 of them in the SSF. These rates were 2 and 4 patients respectively, in the control group. Patients taking pilocarpine had, on average, a reduction of 0.21 ml/min in USF and 0.55 ml/min in SSF compared to initial rates, while in the placebo group these values were higher, averaging 0.34 ml/min for the USF and 1.43 ml/min for the SSF.
The weekly mean values of salivary flow per group demonstrated that patients from the control group had a lower salivary flow at the end of the four weeks of treatment, as well as greater variation in salivary flow during treatment; while patients who took the medication had higher values of salivary flow at the end of the four weeks. The latter also presented smaller flow variation throughout the treatment (Table IV). Figure 1 presents the average of salivary flow loss per group.
Discussion
The longitudinal character of the study, even in the short term, was a determining factor for the small number of volunteers. The five sample collections and the follow-ups required the weekly presence of the patient for a month. The small size of our sample was also due to several factors, such as patient, death, difficulty in the maintenance of weekly contact, slow radiotherapy service, presence of systemic alterations, misuse of medication, delay in initiating the treatment, exposure to radiation prior to the first collection of salivary flow, the wait for dental treatment required prior to the radiotherapy, and patients' refusal to participate. This is a problem faced in clinical work with small sample sizes.
At some instances, the patient's health status became a limiting factor. There were situations where the collection of the saliva through the sputum method became impossible either because of a painful mouth, or due to some other indisposition, resulting from intensive treatment. The data on patient 11 demonstrate this; however, this fact was not the reason for exclusion from the research since the variations in the salivary flow were numerically and clinically confirmed. It is worth mentioning that the data corresponding to patients 1 and 7, who were both diagnosed with hyposalivation (pilocarpine-treated group). This can be explained by the existing lower salivary flow prior to the first radiation exposure during radiotherapy. In addition to the higher concentration of the doses to specific areas of the face, the lesion being located in the floor of the mouth interfered with collection, what might also have lead to low rates of salivation.
Often, only a part of the parotid gland is within the radiation field, ranging from 25% to more than 75% of the total volume of the gland. In this case, the larger the glandular exposure, the greater the damage, and areas with less than 25% exposure do not seem to have a significant effect on salivary production (26).
A reduction in salivary secretion was noticed in the first and second weeks of treatment, as previously reported (13). This decrease in salivary flow is progressive, and starts during the first weeks of therapy. During this treatment, physical changes induced by radiation therapy started occurring in the salivary glands. These changes manifest as a reduction or sometimes a complete absence of salivary secretion (11, 12). This fact was identified in the study, and during the second week, oral complications began to appear in the majority of the patients who took the placebo, whereas similar complications were persistent in only two patients in the group which was treated with pilocarpine. Patient 4 showed no oral complications and had little salivary loss, even when taking the placebo; nonetheless, he had no radiation field in the face, since the radiation was restricted to his cervical fossa, which may explain the better influence of radiotherapy.
The result was similar for patient 10, who did not show any evidence of reduction in salivary flow. The mean USF values for the control group before and during radiotherapy were 0.56 and 0.22 ml/min, respectively, which are values comparable to those already reported (12). The pilocarpine group had a higher mean USF value during treatment.
Very importantly, our study shows encouraging results, since the association of radioprotective drugs with cancer treatment had a positive impact in minimizing damage caused to the glands. The available treatments to reverse these post-radiation impairments are merly palliative, and do not produce significant improvements (16). Our results show the situations during the first four weeks of treatment. The extrapolation or continuity of these indexes during all treatment are unpredictable. The accumulated doses have a tendency to exacerbate the effects. Although the salivary flow data for the period following radiotherapy is not available, the final rates of salivary flow are reported as being similar to the salivary flow during treatment (12). Longitudinal and double-blind studies, conducted with a more significant sample size have also suggested that the use of pilocarpine concomitant with radiotherapy can have beneficial results in cases where the parotid gland is subjected to radiation levels greater 40 Gy, especially when permanent damage is to be assessed twelve months after the start of the radiotherapy (26).
Although the results from the pilocarpine-treated group were better than those presented by patients who took the placebo, at the concentration used, pilocarpine did not effectively block radiation effects on the salivary glands, yet it does seem to attenuate the damage incurred. More detailed studies should be conducted, using increased dosages. Serious adverse effects have been rare and there are reports of side-effects associated with continuous use of this medication (27, 28), as well as secondary effects of moderate intensity and short duration, such as sweating, frequent urination, and red skin (27). No noticeable side-effects were observed nor reported during this study, which is probably a result of short-term use (four consecutive weeks) of pilocarpine.
Conclusion
We conclude that daily intake of pilocarpine, in divided doses, led to maintenance of a higher salivary flow when compared to the control group. Pilocarpine intake also reduced the incidence of xerostomia and oral complications, even though it was unable to effectively block the local effects of radiation exposure during radiotherapy.
Acknowledgements
We express our thanks the Napoleao Laureano Hospital (Joao Pessoa/PB) that granted the physical space to perform this research and medical monitoring to the all voluntaries, and The National Research Council (CNPq) that granted financial support (PIBIC) to Marcele Pimentel and Mariângela Araújo.
- Received November 6, 2013.
- Revision received January 26, 2014.
- Accepted January 28, 2014.
- Copyright© 2014 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved