Starting Dose of Sevelamer for Dialysis Patients
For dialysis patients not currently taking a phosphate binder, start sevelamer at 800-1600 mg (one to two 800 mg tablets or two to four 400 mg tablets) three times daily with meals, with the specific dose determined by the baseline serum phosphorus level. 1
Dose Selection Based on Serum Phosphorus Level
The FDA-approved starting dose algorithm is straightforward and based solely on the patient's serum phosphorus concentration 1:
Serum phosphorus >5.5 and <7.5 mg/dL: Start with 800 mg (one 800 mg tablet or two 400 mg tablets) three times daily with meals 1
Serum phosphorus ≥7.5 and <9 mg/dL: Start with 1600 mg (two 800 mg tablets or three 400 mg tablets) three times daily with meals 1
Serum phosphorus ≥9 mg/dL: Start with 1600 mg (two 800 mg tablets or four 400 mg tablets) three times daily with meals 1
Critical Considerations for This Patient
The history of hypocalcemia makes sevelamer an ideal choice because it contains no calcium and will not worsen hypocalcemia, unlike calcium-based binders 2. In fact, sevelamer is specifically preferred in patients with hypercalcemia, low PTH levels (<150 pg/mL on two consecutive measurements), or when calcium intake needs restriction 3, 2.
The impaired PTH levels require careful attention: If PTH is low (<150 pg/mL), calcium-based binders should be avoided entirely 4, making sevelamer the appropriate first-line agent 3. However, sevelamer alone may cause PTH to rise further 5, so concurrent vitamin D metabolite therapy should be considered to jointly control both hyperphosphatemia and hyperparathyroidism 5.
Administration and Titration
Sevelamer must be taken 10-15 minutes before or during meals to maximize phosphate binding efficacy, as it works by binding dietary phosphorus in the gastrointestinal tract 2.
After initiating therapy, adjust the dose based on serum phosphorus response 1:
- Target serum phosphorus: 3.5-5.5 mg/dL for dialysis patients 4, 3
- If phosphorus >5.5 mg/dL: Increase by one tablet per meal at 2-week intervals 1
- If phosphorus 3.5-5.5 mg/dL: Maintain current dose 1
- If phosphorus <3.5 mg/dL: Decrease by one tablet per meal 1
The average effective dose in clinical trials was approximately three 800 mg tablets per meal (7.2 g/day total), with a maximum studied dose of 13 g/day 1.
Monitoring Requirements
Monitor serum phosphorus monthly following initiation 4. Given the patient's history of hypocalcemia and impaired PTH, also monitor 6:
- Serum calcium and phosphorus every 2 weeks for the first month, then monthly 6
- Intact PTH monthly for at least 3 months 6
- Calcium-phosphorus product (target <55 mg²/dL²) 3
Important Caveats
Gastrointestinal side effects are the primary concern with sevelamer, including constipation, nausea, and rarely bowel obstruction 1. Patients with dysphagia or severe GI motility disorders were excluded from clinical trials 1.
Metabolic acidosis may transiently worsen when switching from calcium carbonate to sevelamer due to loss of the alkaline calcium salt 7. Monitor serum bicarbonate levels.
Vitamin D depletion can occur with sevelamer, though not more than with calcium-based binders 7. The patient may require vitamin D supplementation, particularly given the impaired PTH levels 5.