Check your answers on page 48210.12968/jprp.2023.5.11.454
All medications designed for administration necessarily contain additional ingredients in their formulation to provide characteristics to produce a usable dosage form. These can be relatively few in the case of injectable medications or increasingly complex for other routes, particularly oral liquids which may require several compounds to improve stability or palatability. Some additives are included for a single reason; e.g. a flavouring, but other compounds may perform several roles. Sometimes, the additives can also provide physiological effects in their own right, which may be helpful or a hindrance depending on the clinical situation.
Polyols may commonly be found in oral liquid preparations where they can act as humectants, sugar sparing sweeteners and viscosity modifiers. Being poorly absorbed but osmotically active they also have the chance of causing osmotic effects in the gut, which can lead to a laxative effect if present in sufficient quantities. Examples of polyols commonly encountered in medications and foods include sorbitol, maltitol and xylitol.
Occasionally, sorbitol may be encountered as a medication in its own right, where it may be used to treat constipation, although it is not currently used for this indication in the UK. For this indication an oral 70% w/v solution may be administered in a dose of 30–50 ml, and can be expected to produce effects in less than 2 hours (Medscape, 2023).
QUESTION 1
Based on the information above, what is the minimum expected amount of sorbitol (in g) for an adult that could produce a laxative effect?
QUESTION 2
Assuming the dose from Q1 is effective for a 70 kg adult, calculate a dose, in g/kg, that could be extrapolated for use in patients of different sizes.
Early research into the thresholds for effect of sorbitol showed a distinct gender difference in sensitivity such that 0.24 to1 g/kg body weight for females and 0.17 to 0.4 g/kg body weight for males (Koizumi et al, 1983; Oku and Okazaki 1996), so you may wish to compare your answer here to these values.
In contrast to sorbitol, maltitol shows no difference in gender difference and tends to produce laxative effects at doses above 0.8 g/kg (Koizumi et al, 1983).
As has been previously mentioned, many medications may contain significant amounts of sorbitol and maltitol as sweeteners, or to ensure acceptably shelf stability. One such product is Clarityn syrup (Bayer, 2018), in which the active ingredient is loratadine.
Clarityn syrup may be dosed at 5 ml daily for patients under 30 kg, and contains 140 mg/ml of sorbitol and 600 mg/ml of maltitol.
QUESTION 3
What is the daily dose of each polyol that a 2-year-old boy would receive if treated with Clarityn syrup?
QUESTION 4
If the 2 year old weighs 12 kg what is the dose per kg of each polyol?
QUESTION 5
What proportion of the usually pharmacologically effective dose of each polyol will this child receive?
Bear in mind that the laxative effects of polyols are additive and patients may be using several products (both foods and medicines), which may contribute to their total dose and can collectively contribute to laxative effects. For patients on several medications the additive amounts of polyols may need to be considered, and it may be necessary to warn patients regarding foods containing significant amounts as they may push them over their limit of tolerance.