Assessing the clinical impact of sodium content in medicines

When sodium in medicines matters

Sodium is an essential component of a healthy lifestyle. It has several important roles, including maintaining fluid balance and acid-base balance. High levels may be associated with increased cardiovascular complications such as hypertension and strokes.

Consider the sodium content of medicines for all people who take medicines. However, it is most relevant to consider for people with conditions associated with sodium retention, who require a low-sodium diet, or who take long-term medication.

Conditions associated with sodium retention include:

• hypertension
• heart failure
• peripheral oedema
• pulmonary oedema
• renal impairment
• pre-eclampsia
• liver cirrhosis

Acceptable limits

There is no evidence to suggest what level of sodium in medicines is acceptable. This will vary between individuals and requires a risk assessment based on:

• indication for the medicine
• formations available
• total dietary sodium intake
• any person-specific acceptable limits

The NHS recommends adults should consume no more than 6g of salt (sodium chloride) per day. This is roughly equivalent to 1 level teaspoon of salt. Check specific limits for individuals following a salt (sodium) restricted diet with their dietician or specialist.

Equivalence

1g of salt (sodium chloride) contains 400mg (17.1mmol) of sodium

1mmol of sodium is equivalent to 23mg of sodium

Why is sodium in medicines

Sodium may be present in medicines as:

• an active ingredient (such as sodium bicarbonate or sodium chloride)
• part of the active ingredient (such as diclofenac sodium, which is the salt form of the drug)
• an excipient in a medicine (such as sodium benzoate or sodium citrate)
• as a component of any additive required to prepare the medicine (such as the use of sodium chloride as a diluent for injection or infusion)

Sodium salts increase the solubility of medicines. All sodium salts are soluble and, therefore, even sodium bound in complex molecules is expected to dissolve and exert a physiological effect. Used as an excipient, sodium also has other roles, including:

• improving disintegration
• binding
• lubrication
• chelation
• antimicrobial properties

Formulations of concern

Effervescent, dispersible and soluble formulations often have a higher sodium content than other formulations. This is because sodium is used to increase solubility or aid in disintegration.

Intravenous preparation may be high in sodium, either due to the preparation itself or due to the diluent used for reconstitution or dilution.

Checking sodium content of medicines

For licensed medicines, use the Summary of Product Characteristics (SmPC) or Patient Information Leaflet (PIL) to check whether sodium is present as an active ingredient or an excipient.

See our article that covers searching for the presence or absence of an ingredient in medicines if you require further support.

Labelling regulations

If a product contains 1mmol (23mg) or more of sodium, the content will be listed in the product literature. 

Medicines containing less than 1mmol of sodium per ‘single dose’ are considered essentially ‘sodium-free’.

Medicines are considered ‘high in sodium’ if they contain 17mmol of sodium, or more, in the ‘maximum daily dose’ of a product. This is outlined in the product information for medicines intended for regular or long-term use.

Long-term use

Medicines intended to be used continuously for more than 1 month

Regular use

Repeated use of a medicine for more than 2 days every week.

Exceptions to labelling

The ‘high’ dose threshold does not apply to medicines indicated for short-term use only, such as sodium-containing effervescent and soluble products for:

• cystitis
• cold and flu
• diarrhoea
• bowel preparations

Tips to reduce medicine sodium intake

If sodium content is likely to have a significant impact for an individual, such as those following salt-restricted diets:

• avoid or limit use of effervescent, soluble or dispersible formulations where possible
• counsel individuals to seek advice from a pharmacist if purchasing over-the-counter (OTC) and pharmacy (P) medicines
• check the impact of sodium intake resulting from all medicines at their total daily doses
• consider the sodium burden from fluids used to reconstitute or dilute parenteral preparations (for example, 100mL of 0.9% sodium chloride contains 15.4 mmol of sodium)

Swallowing difficulties

Effervescent and dispersible formulations are often considered for patients with swallowing difficulties. To limit exposure to sodium, consider whether altering formulations, such as crushing tablets or opening capsules may be a suitable option.

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