Evaluation of Cariogenic and Erosive Potential of Anti-tussive Lozenges: An In Vitro Study

Introduction

Anti-tussive lozenges are often consumed by individuals suffering from sore throat and upper respiratory tract infections due to their cough suppressant and soothing effect on the oro-pharynx. There is indiscriminate use of lozenges due to their easy availability and affordability. The active ingredients in most of these lozenges are amylmetacresol, dichlorobenzy alcohol and/or dextromethorphan and they impart an unpleasant This work is licensed under a Creative Commons Attribution-NonCommercial 4.0. taste.^1,2 In order to make the lozenges palatable, large amounts of sugars are added to them.^3,4 Besides sugars, these lozenges also contain acids that contribute to their inherent pH. On consumption, lozenges slowly dissolve in the oral fluids releasing large amounts of sugars which have a prolonged contact with the tooth surface. These sugars are readily fermented by oral bacteria into acids leading to a drop in intra oral pH, thereby enhancing the risk of dental caries.⁵ Dental erosion is a pathologic, chronic localized loss of dental hard tissue that is chemically etched away from the tooth surface by acid and/or chelation without bacterial involvement.⁶ Both dental erosion and dental caries are caused by different processes; however, both the conditions may occur together causing deleterious effects to the teeth.⁷

Several studies have evaluated the cariogenic and erosive potential of paediatric liquid medications.^2,5,8 However, to our knowledge there is a paucity in literature regarding the physico-chemical properties of anti-tussive lozenges. The null hypothesis was that anti- tussive lozenges do not exhibit properties that are detrimental to teeth. Hence, the aim of this study was to determine the cariogenic and erosive potential of commonly available anti- tussive lozenges. The objectives were to assess their endogenous pH, titratable acidity, type and concentration of sugars present in these lozenges.

Materials and Methods

Six anti-tussive lozenges that are commonly and easily available over-the-counter at pharmacies in India were selected (Table 1). These lozenges were assessed for their endogenous pH, titratable acidity and sugar concentration (sucrose, fructose, glucose, sorbitol and saccharin).

Each lozenge was powdered using a mortar and pestle and 2.5 g of each lozenge was dissolved in 250 mL of deionized water to form 1% solution. The digital pH meter (Eutech Tutor pH meter, Eutech Instruments Pte Ltd., Singapore) accurate to 0.1 was first calibrated according to the manufacturer’s instructions. The endogenous pH of each lozenge was determined at room temperature by placing it directly into 30 mL solution of each sample. It was done in triplicates.^2,5,8 Titratable acidity was measured in triplicate for each lozenge using the same pH meter with addition of 0.02N sodium hydroxide (NaOH) solution and titrated until neutrality (pH 7.0) was reached. The volume of spent NaOH was recorded and the acid percentage of the substance was determined.^2,5,8

Analysis of Type and Concentration of Sugars^5,8

Analysis of sugars (sucrose, glucose, fructose and sorbitol) was performed using High Performance Liquid chromatography (HPLC) (Shimadzu LC-20 AD, Japan). 0.5 g of each lozenge was taken in a 50 mL centrifuge tube to which 2.5 mL of extraction solvent (acetonitrile: water, 70:30) was added and sonicated for 10 minutes. The solvent was then passed through Whatman filter paper. The supernatant was collected in a HPLC vial, then injected into HPLC-RID (Refractive index detector). All samples were prepared in triplicates. The chromatographic conditions were maintained as follows:

Column: Shim-pack C18 100 mm X 4.6 mm, 3µ

Flow rate: 1.0 mL/min

Injection volume: 20 µl

Detector: Refractive Index Detector 20 A

Run time: 15 minutes

Column Temperature: 25°C

Mobile phase A: Acetonitrile; Mobile phase B: Water

Analysis of saccharin was performed using Indian standard method of test for saccharin, food grade (IS 6385:1997).⁹ Each lozenge (5 g) was dissolved in 75 mL of hot water. Phenolphthalein indicator was added. Sample was titrated with 0.1N sodium hydroxide solution. Each mL of 0.1 N sodium hydroxide = 18.32 mg of saccharin.

Statistical Analysis

Data obtained was subjected to statistical analysis using Statistical Package for Social Sciences [SPSS] for Windows, Version 22.0. (released 2013; Armonk, NY: IBM Corp). The data was entered in Excel software, analysed and presented by descriptive statistics (means and standard deviation) and subjected to Kruskal Wallis test followed by Mann Whitney Post hoc analysis to compare the mean pH, titratable acidity. One-way ANOVA test followed by Bonferroni's Post hoc Analysis was used to compare sugar concentration of the lozenges. The level of significance (P value) was set at <0.05 as statistically significant.

Results

All the lozenges were found to have an endogenous pH of less than 7. The lowest mean pH (3.17±0.020) and highest mean titratable acidity (0.277±0.006) was observed with Strepsils® (Table 2). Multivariate analysis showed a statistically significant difference in pH and titratable acidity of all the lozenges except in the comparison of titratable acidity between Koflet® and Vicks® (Table 3). The concentration of total fermentable sugars was highest in Koflet® (74.78%). Sucrose concentration was more than 50 g% in all the lozenges. While glucose concentration was found to be highest in Cofsils® (11.00 g%), sucrose concentration was highest in Koflet® (68.67 g%) and Alex® had the highest fructose concentration (3.32 g%) (Table 4). Highest concentration of non-fermentable sugars, like saccharin and sorbitol were found in Cofsils® (3.46 g%) and Alex® (5.64 g%), respectively (Table 4).

Multiple comparisons of the fermentable sugar concentrations between the lozenges showed a significant difference in the concentrations of glucose and fructose between Cofsils® and the other lozenges (P <0.05). Sucrose concentration in Cofsils® differed significantly on comparison with Strepsils®, Tus-Q® and Koflet® (Table 5). With regard to non-fermentable sugars, saccharin concentration present in Vicks® and Koflet® differed significantly from that of the other lozenges. A significant difference in the concentration of sorbitol was seen between Strepsils® and the other lozenges (P <0.05) (Table 6).

Multiple comparisons of the fermentable sugar concentrations between the lozenges showed a significant difference in the concentrations of glucose and fructose between Cofsils® and the other lozenges (P <0.05). Sucrose concentration in Cofsils® differed significantly on comparison with Strepsils®, Tus-Q® and Koflet® (Table 5). With regard to non-fermentable sugars, saccharin concentration present in Vicks® and Koflet® differed significantly from that of the other lozenges. A significant difference in the concentration of sorbitol was seen between Strepsils® and the other lozenges (P <0.05) (Table 6).

Discussion

In a developing country like India, lozenges are sold over-the-counter, without the need for a prescription. Children are not restricted by parents from having lozenges and they are often given for symptomatic relief of pain associated with tonsillitis and laryngitis. At times, they may be consumed in the same manner as mints or candy. It is a common practice to see pharmacists offer lozenges as a substitute for tendering the balance amount, following receipt of payment for other medicines. Since anti-tussive lozenges are easily affordable and have an immediate soothing action on an irritable throat, they are likely to be consumed several times in a day.

In chronic respiratory conditions, drugs including antihistamines, cough suppressants, or bronchodilators are prescribed. In these medications, the pharmaceutical ingredient per se and the underlying respiratory condition can have an effect on salivary flow and viscosity.¹⁰ In children, these drugs are commonly given as liquid formulations which can predispose them to oral dryness, particularly at night. The use of anti-tussive lozenges at bedtime is a common practice.^2,5

Lozenges can stimulate salivary secretion due to the presence of other ingredients such as weak organic acids, flavouring agents and preservatives. The bicarbonate content in stimulated saliva is mainly responsible for buffering the acidic pH created by the lozenges. However, placement of the lozenge in the vestibule, until it completely dissolves is a cause of concern considering its close proximity to teeth surfaces and reduced salivary flow rate during sleep.² Therefore, the buffering action of salivary constituents such as bicarbonates, phosphates, and peptides is lower during the night. The quantity of saliva in children is also lesser than that of adults and the use of lozenges increases the risk of exposing their teeth to a cariogenic environment.

The dentition can be affected by the use of lozenges due to their inherent properties that can have an effect on intra-oral pH. The pH of a formulation is one of the properties to be determined in order to understand its erosive potential. The pH values of medications have been reported to range from 2.5 to 7.04.^2,11,8,5 In this study, five out of six lozenges showed an acidic pH that was below 5.5, which is the critical pH for onset of enamel dissolution.^2,8

The introduction of solid candies into the mouth has been shown to immediately stimulate salivary flow that increases with active sucking of the candies,^12,13 and to decrease intra-oral pH to about 4.5 and also the surface hardness of enamel.^13,14 Similarly, with lozenges there could be an immediate stimulation of saliva secretion, but passive retention of the lozenge causes longer exposure of the teeth to acid and less time for remineralisation. The orange flavour of lozenges, Strepsils®, Cofsils® and Tus-Q® indicate the presence of citric acid or malic acid in them. These lozenges also showed significantly lower endogenous pH as compared to the menthol flavoured lozenge (Vicks®). Citric acid is known to have a chelating action on dental hard tissues.^2,8,15 There is no mechanical stimulation with lozenges as they are not chewed. Prolonged presence of lozenges in the oral cavity increases the need for buffering action of saliva in order to neutralize these acids. Stimulated flow of saliva is influenced by the intensity and frequency of sucking or chewing on the product and also by the secretory capacity of the salivary glands. If the lozenges are highly acidic and there is prolonged or frequent exposure, saliva will not be able to overcome the acidic challenge. The size of the lozenges should also be taken into consideration because the mass of acidic lozenges has been shown to be associated with the degree of enamel softening in situ.16 In a study on adults, the time taken for lozenges to dissolve completely was 4 to 17 minutes.¹⁷

The erosive potential of lozenges is also dependent on its ability to neutralise acid or its "buffering capacity". Estimation of titratable acidity allows for an indirect measurement of the amount of saliva required to buffer the acidic environment following the use of lozenges.^5,18,19 Titratable acidity represents the total acidic content and is indicative of strength of the erosive potential. In the present study, the citric flavoured lozenges, Strepsils®, Cofsils®, Tus-Q® and Alex® had a significantly higher titratable acidity, whereas Vicks® (menthol) had the least. The greater the buffering capacity or titratable acidity of the lozenge, the longer it will take for saliva to neutralise it. Primary teeth are smaller in dimension and are more susceptible to erosion because of the thinner enamel and dentin. Newly erupted permanent teeth are also likely to be affected.

Sugars are added to pharmaceutical formulations in order to make them more palatable and mask the taste of the other ingredients. Lozenges are a mixture of different sugars and other carbohydrates in an amorphous state.²⁰ Lozenges are akin to hard-boiled sweets and contain sugars such as sucrose, glucose and fructose. In this study, all the lozenges contained more than 52% of sucrose, a fermentable disaccharide that is known to be a causative agent of dental caries. The presence of sucrose allows for oral microorganisms to produce acids. Although the lozenge Koflet® had the highest sucrose content, the presence of other ingredients like pepper and clove, could be the reason for its slightly higher endogenous pH. Among the sugars, sucrose is widely used because of its lower cost and easy processing.^3,4 In earlier studies on liquid preparations, the sugar content in anti-tussives was around 50% and it varied from 18% to 100% for other medications.^21,2,5,8 Additionally, most of the lozenges also contained non-fermentable sugars, including saccharin and sugar alcohols, which contribute to their sweetness.

The outcome of this study disapproved the null hypothesis that anti-tussive lozenges do not exhibit properties that are detrimental to teeth. The use of lozenges can be potentially erosive to dentition in children and particularly in individuals with xerostomia, slow oral clearance, and low salivary buffer capacity. Clinical investigations need to be carried out to further validate the findings of this study.

Conclusion

The endogenous pH, titratable acidity and sugar content of all the lozenges strongly indicate the cariogenic and erosive potential of lozenges and its possible detrimental effect on the dentition. Oral health professionals should spread awareness among parents, pharmacists and the community on the ill effects of indiscriminate use of anti-tussive lozenges on the teeth.

Conflict of interest

Nil