Saturday, December 22, 2007

calcium và loãng xương

Đài ABC bên Úc có một cuộc tranh luận thú vị về vai trò của calcium và loãng xương. Hai người "đối nghịch" nhau là giáo sư Philip Sambrook và Christopher Nordin. Tôi quen cả hai người. Sambrook là thầy cũ của tôi, còn Nordin là "sư phụ" của thầy tôi. Xem hai thầy trò tranh cãi nhau vui ra phết. Ông Nordin tin vào calcium và vitamin D, còn ông Sambrook thì không. Trước khi tranh luận 1 ngày, ông Sambrook có gọi điện tôi để "cầu cứu" vài thủ thuật dịch tễ học để tranh luận với thầy Nordin. Thú thật, trong vấn đề phòng chống loãng xương, tôi thấy calcium và vitamin D cũng có hiệu quả chứ đâu phải vô dụng.

Ali Moore talks to Professors Philip Sambrook and Chris Nordin

Broadcast: 21/12/2007

Reporter: Ali Moore

Ali Moore speaks to Professor Philip Sambrook, the Medical Director of Osteoporosis Australia, and Professor Chris Nordin, the man credited with drawing the medical community's attention back to the link between calcium deficiency and osteoporosis.
ALI MOORE: Last week we brought you a story about a class of drugs called bisphosphonates, used to maintain bone density in patients with cancer and osteoporosis.

In the story we discussed how these drugs can, in certain circumstances, cause a disfiguring side effect called osteonecrosis of the jaw or ONJ, also known as dead jaw. It causes the jawbone to dissolve and is a side effect most often associated with having dental work while on the drug.

The story caused quite a controversy, with some in the medical profession concerned we did not clearly distinguish when a patient may be at risk. So in the spirit of clarity, tonight one of those most concerned about our report, Professor Philip Sambrook, joined me in our Sydney studio, along with a veteran in the treatment of osteoporosis, Professor Chris Nordin form our Adelaide studio.

Professor Sambrook is the President of the Australia and New Zealand Bone and Mineral Society, Professor Nordin is a senior specialist at the Institute of Medical and Veterinary Science in Adelaide.

Gentlemen, thank you very much for joining us.

There is evidence linking bisphosphonates with what's known as osteonecrosis or ONJ. The question we're asking is what's the evidence? In what cases does it apply to? What's the risk - benefit equation?

Professor Sambrook to you first.

In your view, how big is the risk and when does the benefit outweigh that risk?

PHILIP SAMBROOK, AUSTRALIA AND NEW ZEALAND BONE AND MINERAL SOCIETY PRESIDENT: So the bisphosphonates get used to treat two main conditions, cancer and osteoporosis. Now in cancer we use quite high doses. This is after all a life saving therapy. We do know there is a moderate incidence of this in cancer.

In osteoporosis we use much smaller doses and the risk is quite rare.

ALI MOORE: So would you say quite rare, can you actually quantify the risk in the two cases?

PHILIP SAMBROOK: It's about one in ten thousand to one in one hundred thousand.

Now people need to be aware of that, but then again, the risk of dying after a hip fracture is probably about one in five in the first six to 12 months. So people need to know the benefits and the risks.

ALI MOORE: And in terms of the patients who have cancer, can you quantify that risk?

PHILIP SAMBROOK: Well there are estimates of about one in ten but we still don't know that for sure. It is certainly more common in cancer but then it stops the spread of cancer to the skeleton, which is a very serious condition.

ALI MOORE: So in essence you're saying that with osteoporosis the risk is negligible compared to the benefit, that would be your contention?

PHILIP SAMBROOK: I think patients need to know about it, and I warn all my patients about it, but it is a very low risk, it seems to only occur after a tooth extraction which is not that common. So I tell my patients to be aware of that and let their dentist know if they're taking this medication and they face a tooth extraction. But it is still rare even in that context.

ALI MOORE: Professor Nordin, is that a fair assessment, rare?

CHRIS NORDIN, INSTITUTE OF MEDICAL AND VETERINARY SCIENCE SENIOR SPECIALIST: I think so, yes. It's the intravenous use of bisphosphonates, mainly in cancer and high doses that's a problem. The ordinary use of bisphosphonates in osteoporosis, the risk is negligible.

ALI MOORE: Let's look at the benefits for osteoporosis patients. Professor Sambrook, is it of benefit to all patients, or only if you have what you might call a medium to severe case of osteoporosis?

PHILIP SAMBROOK: Well my view is that it's worthwhile for people with moderate or severe osteoporosis. Currently the Government restricts it to people who have had a fracture already, a low trauma fracture, or older people with very low bone densities. And I think that's appropriate. In milder cases you can probably get by with simpler therapies including calcium and vitamin D.

ALI MOORE: How do you assess what's a minor case of osteoporosis? What's the measurement?

PHILIP SAMBROOK: We mainly use a bone density to make that judgment. If a patient has had a fracture, however, that is a signal often that there is a more severe form of osteoporosis present. And that's really why the PBAC has recommended its use in that situation.

ALI MOORE: You're talking about the Public Health Scheme and being able to get it on a PBS scheme?

PHILIP SAMBROOK: That's right. So the Federal Government provides a subsidy in the context of a low trauma fracture.

ALI MOORE: Professor Nordin, why do you think it is over prescribed, given that assessment of when it is suitable?

CHRIS NORDIN: Well, although a lot of people with osteoporosis get fractures, it does not mean that everybody with a fracture has osteoporosis.

The requirement for bisphosphonate according to the rules of the PBAC is that you can have a fracture and a low bone density. It's called established osteoporosis and that's what it means.

It is not being enforced for a variety of reasons. Neither Medicare nor the PBAC have seen fit to enforce their own regulations and the result is anyone with a fracture is now getting bisphosphonates and something like two thirds of these people do not have osteoporosis.

You have to remember that although a lot of people with anaemia are breathless, it does not mean everyone who is breathless has got anaemia.

ALI MOORE: Professor Sambrook, on what Professor Nordin just said, are we prescribing bisphosphonates to people who don't have osteoporosis and may simply have had a fracture?

PHILIP SAMBROOK: See I would disagree with Chris on that point. There's about 2.2 million Australians with osteoporosis, Access Economics has shown that.

We're treating about 20 per cent of those patients so I think we're vastly under-treating. We know that the people who have fractures, only about 20 per cent of those are being treated.

Now some of these people will have what we call osteopenia, but if it's moderate reductions in bone density, they still should be treated.

ALI MOORE: But I guess the question is, let's say you have a fracture, what else do you have to present with when you go to your GP, to be eligible to get a bisphosphonate?

PHILIP SAMBROOK: You only have to have a low trauma fracture. And although Chris says established osteoporosis by bone density, in fact the Government has not mandated a bone density. They reconsidered it last year and they agreed to leave it as a fracture, a low trauma fracture.

ALI MOORE: Professor Nordin, you say up to two thirds of people could potentially be using bisphosphonates when they don't in fact have osteoporosis.

CHRIS NORDIN: That is what's actually happening. Yes.

ALI MOORE: What do you think is the answer to that, if in fact you are right?

CHRIS NORDIN: Of course I'm right, I mean, the facts are perfectly clear. If you use fracture as your indication for bisphosphonates, then two thirds of those people, depending precisely how you define osteoporosis, if it's defined by the World Health Organisation standards, then between two thirds and three quarters of these people do not have osteoporosis.

You have got to understand it's like assuming that everybody with a stroke has got a high blood pressure. A lot of people with high blood pressure get strokes but not everybody with a stroke has high blood pressure.

ALI MOORE: But as Professor Sambrook just says, you're actually only treating 20 per cent of those with osteoporosis.

CHRIS NORDIN: That's a completely different argument, it had nothing to do with the situation at all. I'm talking about who is getting bisphosphonates at the moment.

PHILIP SAMBROOK: The Government has defined established osteoporosis as a low trauma fracture. They don't require a bone density test.

ALI MOORE: Let's agree, between the two of you, to agree to disagree, if you like on that issue of whether or not we're looking at over subscribing of this medication.

But I want to raise another question. Professor Nordin, do you think there is a viable alternative to bisphosphonates for those with osteoporosis, I suppose perhaps those with a low level osteoporosis versus those with a more severe case?

CHRIS NORDIN: Calcium is first of all the first line in prevention and there should be no question about that.

Whether people need bisphosphonates depends partly on what they've got. The spinal fracture cases - bisphosphonates are far more effective in treating spinal fractures and peripheral fractures and spinal fractures should be getting far more attention. That's the first thing.

The second thing is that the bisphosphonates do one very specific thing - they cut down the rate of bone break down by (inaudible). That is actually what they do.

ALI MOORE: I presume, Professor Sambrook, you would agree with that, that at a very low level you can start with calcium but you move on?

PHILIP SAMBROOK: I make sure all my patients have got adequate calcium and vitamin D. But we do know, if you look at the data, that the reduction in fractures is about 15 per cent with calcium, it's about 50 per cent with the bisphosphonates.

ALI MOORE: I would like to return to one of the issues that was in the initial story on the 7:30 Report, and that's the question of what information patients are given about warnings of potential risks.

Professor Nordin, do you believe there is sufficient evidence out there about what people should be taking into account before they take these therapies?

CHRIS NORDIN: Well I think the sensible thing to do for osteoporosis is to make sure that there's no dental problem, that the patient's not proposing to have a tooth transplant or tooth extraction in the near future.

But apart from that, the risk is so low that we mustn't get lost in frightening everybody about side effects.

You have got to understand there are many over the counter drugs such as Nurofen and even Aspirin, that carry more risk than the risk of bisphosphonates in ordinary osteoporosis.

And if we spend all our time explaining all the risks about every drug to every patient, the entire medical system would come to a grinding halt.

ALI MOORE: That said of course, every patient has the right to make their own decision. Professor Sambrook, do you believe that there is sufficient?

PHILIP SAMBROOK: I think the new information that the TJ is requiring is worthwhile. But the most important thing the patient must remember is that it a rare, it virtually only ever occurs after a tooth extraction, so they should let their dentist know if that is planned.

ALI MOORE: Gentlemen, thank you very much for joining us.


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