Impact of cetuximab conventional dosing on cetuximab-induced magnesium concentration under haemodialysis in head and neck cancer

Correction of metabolic acidosis after conversion from sevelamer hydrochloride to lanthanum carbonate Sir, We recently introduced lanthanum carbonate as an alternative phosphate binder to sevelamer hydrochloride in patients with elevated serum calcium. Lanthanum carbonate has a higher affinity for phosphate than sevelamer HCl, so fewer lanthanum carbonate tablets are required to achieve the same phosphate control. To reduce the pill burden in patients on high doses of sevelamer HCl, a policy of converting patients who were prescribed 8–12 sevelamer per day, and patients currently on 6 sevelamer per day but in need of a dose increase, to 3 × 750 mg lanthanum car-bonate per day was established. Conversions were made at the discretion of the doctor, so that well-controlled patients were less likely to switch. In October 2007, 60 haemodialysis patients converted according to the above criteria. Of these, 13 patients who disliked or were intolerant of lanthanum carbonate reverted to sevelamer HCl within 3 months. Forty-seven patients (68% male, median age 47 years, range 21–79) continued to take lanthanum carbonate. Several studies have suggested that sevelamer HCl contributes to metabolic acidosis [1,2], while lanthanum car-bonate would be expected to have an antacid effect. A comparison of the median of three routine (monthly) pre-dialysis serum bicarbonate and phosphate measurements immediately before and after conversion for each patient showed an increase in serum bicarbonate from a mean of 20.3 ± 2.3 to 22.2 ± 2.4 mmol/l (P < 0.0001, paired t-test), see Figure 1. There was no wash-out period for these patients, so it is not clear whether the change in bicarbonate was due to the discontinuation of sevelamer or the initiation of lanthanum carbonate. It is noteworthy that the increase in bicarbonate was significantly lower in the 15 patients that were prescribed 6 sevelamer per day prior to the conversion (0.7 ± 1.9 versus 2.3 ± 2.6 mmol/l, P = 0.04, unpaired t-test). This is in keeping with previous data suggesting that the degree of acidosis is related to the dose of sevelamer [2]. Phosphate levels were unchanged (mean before and after conversion 2.02 ± 0.53 and 1.97 ± 0.50 mmol/l, respectively). At the time of this analysis, the dose of lanthanum had not been titrated. Phosphate levels increased by an average of 0.25 mmol/l in the six patients who were on the maximum dose of sevelamer, suggesting that patients taking more than 9 sevelamer per day should convert to …