Review question
To assess the effects of treatment with drugs in order to prevent damage to salivary glands following radiotherapy to the head and neck
Background
Problems with saliva production and salivary glands are a significant and mostly permanent side effect for people after radiotherapy treatment to the head and neck. When this occurs the condition is known as dry mouth or xerostomia. Dry mouth is not measurable and is a subjective or personal expression of how the mouth feels. It can have other causes and is a consequence of the production of less saliva or by the consistency of saliva. The rate of flow of saliva in an individual's mouth however can be measured. People who have dry mouth have a reduced quality of life. They can experience issues with taste and general discomfort, difficulties chewing, swallowing and speaking as well as tooth decay, thrush and other infections of the mouth. A wide range of drugs that work in different ways have been used to try and prevent problems with salivary glands caused by radiotherapy. Unfortunately there is currently not enough evidence to show which drugs or which type of drugs are most effective.
Study characteristics
The evidence in this review is current up to 14 September 2016. 39 studies were included with a total of 3520 participants. Participants were male and female, all ages and ethnic origins, out patients or in patients, who were scheduled to have radiation therapy with or without chemotherapy to the head and neck.
Drugs included were any prescribed to prevent salivary gland problems and given before or during radiotherapy. Information was collected from the end of radiotherapy except for that about adverse effects. Different techniques for giving radiation treatment that might reduce damage were not included.
The main outcomes measured were participant's own assessment of dry mouth and the measurement of salivary flow. Secondary outcomes measured included adverse or unwanted effects such as sweating, crying, watery discharge from the nose, diarrhoea and nausea.
Key results
There is some low-quality evidence to suggest that the drug amifostine prevents the feeling of dry mouth in people receiving radiotherapy to the head and neck (with or without chemotherapy) in the short- (end of radiotherapy) to medium-term (three months after radiotherapy). However it is less clear whether or not this effect is sustained to 12 months after radiotherapy. The benefits of amifostine should be weighed against its high costs and side effects. Adverse effects of vomiting, low blood pressure, feeling of sickness and allergic response were all more frequent in those receiving amifostine. There was insufficient evidence to show that any other treatment is beneficial.
Quality of the evidence
The quality of evidence for amifostine was found to be low because of risk of bias, inconsistency and imprecision caused by the small number of studies in the comparison or sample size. A standardized scale for measuring participant's experience of dry mouth would in future allow comparison and pooling together of results.
There is some low-quality evidence to suggest that amifostine prevents the feeling of dry mouth in people receiving radiotherapy to the head and neck (with or without chemotherapy) in the short- (end of radiotherapy) to medium-term (three months postradiotherapy). However, it is less clear whether or not this effect is sustained to 12 months postradiotherapy. The benefits of amifostine should be weighed against its high cost and side effects. There was insufficient evidence to show that any other intervention is beneficial.
Salivary gland dysfunction is an 'umbrella' term for the presence of either xerostomia (subjective sensation of dryness), or salivary gland hypofunction (reduction in saliva production). It is a predictable side effect of radiotherapy to the head and neck region, and is associated with a significant impairment of quality of life. A wide range of pharmacological interventions, with varying mechanisms of action, have been used for the prevention of radiation-induced salivary gland dysfunction.
To assess the effects of pharmacological interventions for the prevention of radiation-induced salivary gland dysfunction.
Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 14 September 2016); the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 8) in the Cochrane Library (searched 14 September 2016); MEDLINE Ovid (1946 to 14 September 2016); Embase Ovid (1980 to 14 September 2016); CINAHL EBSCO (Cumulative Index to Nursing and Allied Health Literature; 1937 to 14 September 2016); LILACS BIREME Virtual Health Library (Latin American and Caribbean Health Science Information database; 1982 to 14 September 2016); Zetoc Conference Proceedings (1993 to 14 September 2016); and OpenGrey (1997 to 14 September 2016). We searched the US National Institutes of Health Ongoing Trials Register (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases.
We included randomised controlled trials, irrespective of their language of publication or publication status. Trials included participants of all ages, ethnic origin and gender, scheduled to receive radiotherapy on its own or in addition to chemotherapy to the head and neck region. Participants could be outpatients or inpatients. We included trials comparing any pharmacological agent regimen, prescribed prophylactically for salivary gland dysfunction prior to or during radiotherapy, with placebo, no intervention or an alternative pharmacological intervention. Comparisons of radiation techniques were excluded.
We used standard methodological procedures expected by Cochrane.
We included 39 studies that randomised 3520 participants; the number of participants analysed varied by outcome and time point. The studies were ordered into 14 separate comparisons with meta-analysis only being possible in three of those.
We found low-quality evidence to show that amifostine, when compared to a placebo or no treatment control, might reduce the risk of moderate to severe xerostomia (grade 2 or higher on a 0 to 4 scale) at the end of radiotherapy (risk ratio (RR) 0.35, 95% confidence interval (CI) 0.19 to 0.67; P = 0.001, 3 studies, 119 participants), and up to three months after radiotherapy (RR 0.66, 95% CI 0.48 to 0.92; P = 0.01, 5 studies, 687 participants), but there is insufficient evidence that the effect is sustained up to 12 months after radiotherapy (RR 0.70, 95% CI 0.40 to 1.23; P = 0.21, 7 studies, 682 participants). We found very low-quality evidence that amifostine increased unstimulated salivary flow rate up to 12 months after radiotherapy, both in terms of mg of saliva per 5 minutes (mean difference (MD) 0.32, 95% CI 0.09 to 0.55; P = 0.006, 1 study, 27 participants), and incidence of producing greater than 0.1 g of saliva over 5 minutes (RR 1.45, 95% CI 1.13 to 1.86; P = 0.004, 1 study, 175 participants). However, there was insufficient evidence to show a difference when looking at stimulated salivary flow rates. There was insufficient (very low-quality) evidence to show that amifostine compromised the effects of cancer treatment when looking at survival measures. There was some very low-quality evidence of a small benefit for amifostine in terms of quality of life (10-point scale) at 12 months after radiotherapy (MD 0.70, 95% CI 0.20 to 1.20; P = 0.006, 1 study, 180 participants), but insufficient evidence at the end of and up to three months postradiotherapy. A further study showed no evidence of a difference at 6, 12, 18 and 24 months postradiotherapy. There was low-quality evidence that amifostine is associated with increases in: vomiting (RR 4.90, 95% CI 2.87 to 8.38; P < 0.00001, 5 studies, 601 participants); hypotension (RR 9.20, 95% CI 2.84 to 29.83; P = 0.0002, 3 studies, 376 participants); nausea (RR 2.60, 95% CI 1.81 to 3.74; P < 0.00001, 4 studies, 556 participants); and allergic response (RR 7.51, 95% CI 1.40 to 40.39; P = 0.02, 3 studies, 524 participants).
We found insufficient evidence (that was of very low quality) to determine whether or not pilocarpine performed better or worse than a placebo or no treatment control for the outcomes: xerostomia, salivary flow rate, survival, and quality of life. There was some low-quality evidence that pilocarpine was associated with an increase in sweating (RR 2.98, 95% CI 1.43 to 6.22; P = 0.004, 5 studies, 389 participants).
We found insufficient evidence to determine whether or not palifermin performed better or worse than placebo for: xerostomia (low quality); survival (moderate quality); and any adverse effects.
There was also insufficient evidence to determine the effects of the following interventions: biperiden plus pilocarpine, Chinese medicines, bethanechol, artificial saliva, selenium, antiseptic mouthrinse, antimicrobial lozenge, polaprezinc, azulene rinse, and Venalot Depot (coumarin plus troxerutin).