One-Alpha capsules, drops and injection all contain the active ingredient alfacalcidol, which is a form of vitamin D.

What is it used for?

  • Correcting calcium levels and weakening of bone caused by kidney failure (renal osteodystrophy).
  • Softening of the bones due to lack of vitamin D and hence calcium in the body (rickets and osteomalacia).
  • Correcting the level of calcium in the blood in people who have overactive or underactive parathyroid glands (hypo or hyperparathyroidism). These glands produce parathyroid hormone, which helps control the metabolism of calcium and phosphate in the body.
  • Correcting low blood calcium levels (hypocalcaemia) in newborn babies.

How does it work?

  • One-Alpha capsules, drops and injection all contain the active ingredient alfacalcidol, which is a form of vitamin D. (Alfacalcidol capsules are also available without a brand name, ie as the generic medicine.)
  • Vitamin D is normally obtained primarily from sunlight acting on the skin.
It is also consumed in the diet in oily fish and milk products. This vitamin is converted first in the liver and then in the kidneys to its active form, calcitriol. Calcitriol acts as a hormone in the body, controlling the absorption of calcium and phosphate from the gut, the levels of calcium and phosphate in the blood and the normal healthy turnover of bone.
  • People who have reduced kidney function can't convert enough vitamin D into calcitriol. This can lead to problems with calcium and phosphate metabolism, reduced absorption of calcium and phosphate from the gut, low levels of calcium in the blood and various bone disorders.
  • Standard vitamin D supplements are no use for people with reduced kidney function, because their kidneys can't convert the vitamin into its active form. However, alfacalcidol is rapidly converted in the liver directly to calcitriol. This bypasses the step required by the kidneys and means the vitamin can then be used by the body. Taking alfacalcidol increases the amount of active vitamin D in the body, which in turn increases the level of calcium and phosphate in the blood and helps reduce bone breakdown.
  • Alfacalcidol is also given to provide a more rapid increase in active vitamin D and hence calcium, in people with various bone diseases. As this form of vitamin D only requires one conversion to become calcitriol, it provides a quicker response than giving normal dietary vitamin D supplements.
  • How do I take it?

    • One-Alpha capsules and drops can be taken either with or without food.
    • The medicine is taken once a day. The dose prescribed will depend on the amount of calcium in your blood. Follow the instructions given by your doctor.


    • You will need to have regular blood tests to check the level of calcium in your blood while you are taking this medicine. Initially these will be once a week. Tell your doctor if you get any of the following symptoms while taking this medicine, as these could suggest that the level of calcium in your blood has risen too high: needing to pass urine more often than usual, feeling thirsty, dry mouth, metallic taste in your mouth, headache, feeling weak, pain in your muscles or bones, feeling sick or vomiting, constipation.

    Use with caution in

    • Decreased kidney function.
    • People with kidney stones.
    • People taking digoxin.

    Not to be used in

    • People who have a high level of calcium in their blood (hypercalcaemia).
    • People with a high level of calcium in their body tissues (calcification).
    • One-Alpha drops contain sorbitol and are not suitable for people with rare hereditary problems of fructose intolerance.
    • This medicine should not be used if you are allergic to any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

    If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

    Pregnancy and breastfeeding

    Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

    • The safety of this medicine in pregnancy has not been established. It should be used with caution during pregnancy, and only if the benefits to the mother outweigh any possible risks to the developing baby. Seek medical advice from your doctor or pharmacist.
    • This medicine may pass into breast milk in small amounts. This could affect calcium levels in a nursing infant so it is important to get advice from your doctor before taking this medicine if you are breastfeeding.

    Side effects

    Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

    • High level of calcium in the blood (hypercalcaemia).
    • High blood phosphate content (hyperphosphataemia).
    • Rash or hives.
    • Itching.
    • Deposition of calcium in the kidneys (nephrocalcinosis).

    The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.

    For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

    How can this medicine affect other medicines?

    It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while having treatment with this one, to make sure that the combination is safe.

    Thiazide diuretics, such as bendroflumethiazide, reduce the amount of calcium excreted in the urine, and this can increase the amount of calcium in the blood. If you are taking a thiazide diuretic in combination with this medicine you should have regular blood tests to monitor the level of calcium in your blood.

    People taking digoxin or other cardiac glycosides may have an increased risk of abnormal heart rhythms if they experience abnormally high blood calcium levels while taking this medicine.

    The following medicines may decrease the absorption of vitamin D from the gut and should not be taken at the same time of day as this medicine:

    • colestipol
    • colestyramine
    • orlistat.

    If you are taking any of the following medicines you may need a larger than normal dose of vitamin D. Ask your doctor for advice:

    • carbamazepine
    • phenobarbital
    • phenytoin.