Q:A patient of mine whose calcium level is at the bottom of the acceptable band for osteoporosis has been prescribed Disodium Etridonate. As she is only 45 she is worried about side effects. Unfortunately her consultant is unable to answer her questions. Could you help, please? M.M., Merseyside.
A:We're amazed that your patient's consultant can't give her information about the side effects of Disodium Etridonate. This information is readily available to all doctors, if they bothered to crack open their copy of the Data Sheet Compendium, which I'm assuming that anyone at consultant level would have a copy of.Until recently, this drug, marketed as Didronel in the UK by Norwich Eaton Ltd, was only indicated for Paget's Disease of bone (osteitis deformans), which causes a softening, enlargement and deformity in the bones. What happens is that bone is laid down quickly and then dissolves in the pelvis, leg bones, spine or skull. Paget's Disease mainly strikes men and rarely before the age of 40. The drug works by slowing down the dissolving of bone.
In osteoporosis, on the other hand, the bone in the skeleton has decreased so that parts of it can no longer provide adequate support. The bones are thin and "honeycombed" and the cause of fractures of the wrist, spine and hips of some four out of every 10 women. It also produces the dowager's hump, caused by the vertebrae collapsing due to osteoporosis.
In November of last year, Norwich Eaton got the go ahead to use this drug to treat "established osteoporosis of the vertebrae". In theory the drug will slow down the bone dissolving mechanism and allow the repair systems to catch up. It is given in a kit called Didronel PMO (post menopausal osteoporosis), with the drug and a supply of calcium; 400 mg of the drug is taken each day for two week cycles, followed by a three month cycle of the calcium. This cycle is repeated for a minimum of three years.
When the drug is used for Paget's Disease, says Norwich Eaton, there is a point (depending on how long or how much you take) when the drug itself prevents the mineralization of bone. At 20 mg per kg of weight per day, "Didronel suppresses bone turnover and essentially greatly reduces mineralization of the uninvolved skeleton." At lower doses, the recommended 5 mg per kg of weight per day, this is "uncommon" with the general skeleton, although it may occur in certain localized places.
With the higher doses, this drug may increase bone pain and risk of fractures.Although a spokesman for Norwich Eaton says that this is unlikely with the dosage for osteoporosis (one sixth that of Paget's Disease) no one can say for certain.
One in 15 patients on even the lower doses of Didronel will experience gastrointestinal complaints such as diarrhoea or nausea. It should not be used by people with intestinal disorders or severely impaired kidney function, and indeed, patients on this drug should have their kidney function regularly tested.
Frankly, since your patient presumably hasn't yet been diagnosed as having true vertebrae osteoporosis, you might consider counselling your patient to come off this drug particularly as she is 45 years old and indeed is still inside the "normal" range for calcium. Rather than taking a drug with a litany of side effects, we recommend the usual prescription of lifestyle changes, a combination of weight bearing exercise (like walking, running, tennis anything on your feet), and a good diet not too high in protein with plenty of calcium and vitamin D.
Remember: one recent study (see Vol 2 No 11) proved that patients combining exercise and calcium had a similar outcome in preventing bone loss to those taking HRT, the usual osteoporosis drug.