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Calcium carbonate with magnesium carbonate

Updated 2 Feb 2023 | Indigestion remedies


Tablets containing 680mg calcium carbonate and 80mg heavy magnesium carbonate

Drugs List

  • calcium carbonate 680mg and magnesium carbonate 80mg chewable tablet
  • calcium carbonate 680mg and magnesium carbonate 80mg chewable tablets sugar-free
  • RENNIE chewable tablet
  • RENNIE ICE chewable tablet
  • RENNIE SUGAR FREE chewable tablet
  • Therapeutic Indications


    For the relief of indigestion, heartburn, nervous indigestion, hyperacidity, flatulence, upset stomach, dyspepsia, biliousness, gastritis, overindulgence in food and drink, indigestion during pregnancy.



    Two tablets as required, to a maximum of sixteen tablets a day.


    No dosage adjustment necessary (see Adult dosage)

    Caution is advised in the elderly due to the increased possibility of renal impairment.


    Children under 6 years
    Not recommended for children under 6 years of age

    Children 6-12 years
    1 tablet as required, up to a maximum of 8 tablets a day

    Children over 12 years
    No dosage adjustment necessary (see Adult dosage)

    Patients with Renal Impairment

    Contraindicated in severe renal impairment.

    Caution should be exercised in patients with renal impairment. Plasma calcium and magnesium levels should be monitored regularly in these patients.
    Avoid prolonged use in patients with renal impairment as this may possibly increase the risk for the development of renal calculi.

    Precautions and Warnings

    Pregnancy (see Pregnancy section)

    Breastfeeding (see Lactation section)

    Use with caution in elderly patients ( see Dosage, Elderly section )

    Renal impairment. Avoid prolonged use in patients with renal impairment as this may possibly increase the risk for the development of renal calculi ( see Dosage, Renal Impairment section )

    Alkalosis, hypercalcaemia, hypermagnesaemia, milk-alkali syndrome, acid rebound and constipation can result following long term use at high doses especially in patients with renal insufficiency.

    Patient should consult their doctor if symptoms persist despite treatment.

    Antacids are known to reduce absorption of certain medicines. Patients should be advised not to take the preparation at the same time as other drugs.

    Some tablets contain sucrose and therefore should not be taken by patients with fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency.

    Pregnancy and Lactation


    There is consensus that antacids may be used during all phases of pregnancy and have been widely prescribed without evidence of adverse effects at normal therapeutic use. Occasional case reports following excessive doses taken during pregnancy have raised concerns over the possible effects of metals, including calcium, absorbed from antacids. The unrestricted and long term use of antacids during pregnancy should be avoided.

    It should be noted that the preparation is licensed for indigestion during pregnancy, however, as with all medicines the preparation should only be taken during pregnancy when considered necessary.

    The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14-17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password at ( ) or if this is unavailable at the backup site ( ).


    Antacids as a group, are generally not considered to cause adverse effects in breastfed infants, and the UK Drugs in Lactation Advisory Service consider that they are usually compatible with breastfeeding. Calcium carbonate is only absorbed to a limited extent following oral administration. There is a possibility that magnesium salts may also enter breast milk and cause diarrhoea in infants although it is poorly absorbed from the gastrointestinal tract.

    The manufacturer advises that the preparation may be taken during breastfeeding, however, as with all medicines, it should only be taken during breastfeeding when considered necessary.

    Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
    Specialist advice is available from the UK Drugs in Lactation Advisory Service at

    UK Drugs in Lactation Advisory Service Classification - Commonly prescribed antacids are suitable for use in lactation.

    Effects on Ability to Drive and Operate Machinery

    There are no known effects on the ability to drive or operate machinery.


    Advise patients that the tablets should be sucked or chewed.

    Advise patients that they should seek medical advice if symptoms persist.

    Advise the patient not to take at the same time as other medicines.

    Side Effects

    Hypersensitivity reactions

    The following side effects have been reported following larger than recommended doses:

    Rebound acid
    Milk alkali syndrome
    Renal impairment
    Abnormal muscular weakness


    It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.

    The following number will direct the caller to the relevant local centre (0844) 892 0111

    Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Shelf Life and Storage

    Do not store above 25 degrees C

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