前兩篇,把降磷的三大重點、透析清除磷離子的極限、以及使用鋁片的隱憂,都討論過了,這一篇的重點是:“作為磷結合劑的鈣片”。
“可以用”且最常用的鈣片有兩種,就是“碳酸鈣”與“醋酸鈣”,不能用的鈣片是啥?“檸檬酸鈣”不能用,為什麼?上一篇的最後一段有寫,趕快回去複習!
其實,該注意的細節很多,讓我們一項一項來討論……
鈣片的疑慮
就和鋁片一樣的道理,鈣片的原罪就是本身所含有的鈣,若吸收太多,對身體有害,血管的鈣化、硬化、或是軟組織的鈣化沉積,都是鈣太多所導致。而且根據統計,使用鈣片的腎友中,有50%會產生高血鈣,尤其是合併使用活性維他命D的時候。
因此,之前討論透析液的鈣離子濃度,就是希望能讓腎友少一點鈣的負擔,同樣的,若選用鈣片來降磷,就得把這兩種鈣片比較一下,誰讓身體的鈣負擔較少,誰的降磷的效果比較好。
哪一個比較好?
種類 | 鈣被吸收比例 | 每吸收1毫克的鈣 可結合多少的磷 | 每一克的鈣片 可結合多少的磷 | 每一顆鈣片 可結合多少磷 |
---|
碳酸鈣(500毫克/顆) Calcium carbonate | 約20-30% | 0.125毫克 | 39毫克 | 19.5毫克 |
醋酸鈣(667毫克/顆) Calcium acetate | ☆ 約21%(隨餐吃) 約40%(沒有隨餐吃) | ☆ 0.345毫克 | ☆ 45毫克 | ☆ 30毫克 |
打星星的,就是贏家,從表格看的很清楚,醋酸鈣,鈣的吸收比例少,結合磷的效果稍好,比碳酸鈣更優一些!
為什麼會這樣?
磷結合劑的大師,在這篇回顧性文章中提到,碳酸鈣的崩解時間較長–因此建議腎友要咬碎吃,更麻煩的是,碳酸鈣在酸性環境下,比較容易溶解,與食糜混合,但是在鹼性環境下,對磷的結合力比較強,比較容易把磷抓住,讓磷不被身體吸收,兩者無法兼顧的情況下,自然降磷的效果較差。
醋酸鈣的崩解速度快–因此建議腎友整顆吞服,而且比較不受胃酸的影響,或許是這樣的緣故,造成上表兩種鈣片的差異。這篇文章也持相同的看法,不管是磷的結合力,或者是鈣的吸收比率,就是醋酸鈣優於碳酸鈣。
最多可以吃幾顆?
營養狀況好的情形下,血中的磷是降的越低越好,但是用來降低磷的鈣片,可不能劑量越加越大,理由在前面講過不再贅述,那麼,最多只能吃幾顆,才不會過量呢?底下的表格是專家的建議。
種類 | 含元素鈣的比例 | 一顆鈣片含多少元素鈣 | 一天最多能吃幾顆 (上限1500毫克元素鈣) |
---|
碳酸鈣(500毫克/顆) Calcium carbonate | 40% | 200毫克 | 7.5顆 |
醋酸鈣(667毫克/顆) Calcium acetate | 25% | 169毫克 | 8.8顆 |
2010年五月,KDOQI對於KDIGO治療指引的意見回饋中提到,這些劑量的建議,不是絕對的鐵律,當腎友血中鈣濃度較低,或副甲狀腺功能過高(亢進)時,可考慮更大的劑量來使用鈣片。
甚麼情況要考慮限制鈣片的使用呢?一、副甲狀腺功能過低時,鈣片的用量須減少,免得過多的鈣會更加抑制副甲狀腺的機能;二、當腎友身體中的血管,有明顯鈣化的現象時,也要盡量限制鈣片的使用。怎麼知道身體血管有鈣化呢?每年一次的胸部X光可以看主動脈弓是否鈣化(如下圖,點圖可放大)。
另外,腹部側面照的X光,能夠評估腹主動脈的鈣化情況(如下圖,點圖可放大)。
總結
使用鈣片的疑慮,是身體的鈣負擔增加,因此,注意鈣片的正確服用方法,小心鈣片的總用量,以及使用X光追蹤身體血管鈣化的情形。不管如何,還是得把血中的磷濃度降下來,這才是使用鈣片的目的。然而,如果還是沒辦法把磷降到目標範圍內,該怎麼辦?那就要靠“不含鋁或鈣的新磷結合劑”了,請待下篇分曉。
參考文獻:
KDOQI GUIDELINE 5. USE OF PHOSPHATE BINDERS IN CKD (2003)
KDIGO Clinical Practice Guideline for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD) (2009)
KDOQI US Commentary on the 2009 KDIGO Clinical Practice Guideline for the Diagnosis, Evaluation, and Treatment of CKD–Mineral and Bone Disorder (CKD-MBD) (2010)
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