Vitamin B6 and hemodialysis: the impact of high-flux/high-efficiency dialysis and review of the literature.

High-flux/high-efficiency (HF/HE) dialysis is associated with improved clearance for larger molecules, which include a wide variety of middle molecules and water-soluble vitamins. Our study attempted to measure in vivo clearances of serum pyridoxal-5'-phosphate (PLP), the active metabolite of vitamin B6, on standard cuprophan versus cellulose triacetate HF/HE dialysis for patients maintained on 10 mg daily pyridoxine supplements. A longitudinal evaluation of PLP after 3 months on HF/HE dialysis was performed simultaneously. The average in vivo PLP clearance for six patients on standard hemodialysis increased by more than 50%, from 86 +/- 61.7 mL/min using a cuprophan membrane to 173 +/- 90.2 mL/min using a cellulose triacetate dialyzer, at average blood flows of 375 mL/min (P < 0.05). Levels of PLP decreased from a baseline of 50 +/- 13.8 ng/mL to 24 +/- 9.7 ng/mL (P < 0.05) after 3 months of HF/HE treatments; the levels returned to 45 +/- 6.4 ng/mL on resumption of standard dialysis treatments. Although not achieving statistical significance, the average hematocrit increased from 31.2% +/- 1.66% to 32.7% +/- 1.24% while on HF/HE dialysis without an increase in erythropoietin requirements. We conclude that HF/HE dialysis treatments can have a dramatic impact on vitamin B6 homeostasis. Further investigation to evaluate the effects of different membranes and reprocessing should be performed on more heterogeneous patient populations in whom compliance problems with diet and vitamin supplementation may exist. The increased clearance of vitamin B6 may have significantly more detrimental effects in these settings.

Cimetidine-induced acute interstitial nephritis.

Cimetidine is responsible for changes in serum creatinine. Previously reported, this has been thought to be related to an alteration in the manner in which the kidney handles creatinine. Herein a case of acute interstitial nephritis attributable to the ingestion of routine doses of cimeditine is detailed. Review of the changes in serum creatinine and renal function in patients taking cimetidine reveals that as many as 60% of the patients taking cimetidine may have changes in serum creatinine. In none of those series, however, have changes in urinary protein excretion or urinary sediment been followed. Recently several reports have been published in which patients have developed acute interstitial nephritis while taking cimetidine. However, in no previously reported case has the diagnosis been proved by rechallenging the patient with that drug. In our study the patient had moderate to severe renal insufficiency with acute interstitial nephritis while on cimetidine. Rechallenging the patient with cimetidine resulted in prompt return of clinical signs and symptoms as well as changes in serum creatinine and urinary sediment characteristics diagnostic of interstitial nephritis.

The effect of renal transplantation on plasma protein binding.

The in vitro plasma protein binding was determined in nine maintenance hemodialysis patients who later underwent renal transplantation. The organic acid fluorescein (10 micrograms/ml) or the organic base quinidine (5 micrograms/ml) was added to the pre and post transplant serum of these patients. Drug concentrations were measured spectrophotofluorometrically after equilibrium dialysis. The results were compared with the plasma protein binding of eight normal volunteers. The patients on maintenance hemodialysis had lower plasma protein binding of fluorescein than normals (78 +/- 5% vs 89 +/- 4, p less than 0.001). Plasma protein binding improved significantly after renal transplantation (85 +/- 3, p less than 0.01) but was still lower than in normals (p 0.05). Plasma protein binding of quinidine was not significantly different than in normal volunteers (77 +/- 8%) either prior to (72 +/- 10%) or after (73 +/- 12%) kidney transplantation. Plasma protein binding of quinidine remains unaffected by renal transplantation. However, the abnormal plasma protein binding or organic acids in chronic renal failure may be significantly improved by renal transplantation.

Timolol kinetics in chronic renal insufficiency.

A single-dose kinetic study of oral timolol, 20 mg, was undertaken in 3 groups of volunteers with varying degrees of renal function--(1) 10 normal subjects (N); (2) 9 patients with moderate chronic renal insufficiency (MCRI; C cr, 20 to 50 ml/min); (3) 4 patients with end-stage renal disease (ESRD)--to assess the need for dosage modification as renal function diminishes. There were borderline statistical differences in absorption between groups. The mean peak concentration (C max) was 84.3 +/- 44.8 ng/ml at 0.8 +/- 0.4 hr for N and 87.1 +/- 22.8 ng/ml at 1.7 +/- 1.2 hr (p, NS) for MCRI. N and MCRI mean half-lives (5.2 +/- 2.6 hr and 4.0 +/- 1.2 hr) were not statistically different. Salivary levels correlated with plasma levels in 3 N and 1 MCRI patient. Group differences in blood pressure and pulse response to timolol seems to reflect differences present at baseline with percent change from baseline identical for the two groups except at 12 to 24 hr. Administration of timolol on an interdialysis day revealed similar kinetic and physiologic response in the normal and the MCRI group. During dialysis, timolol, 20 mg, induced significant hypotension and bradycardia.