Shinya Shinozawa

Effect of temperature on serum protein binding characteristics of phenytoin in monotherapy paediatric patients with epilepsy

Objectives: To determine the effects of temperature on binding characteristics of phenytoin to serum proteins in paediatric patients with epilepsy.

Serum protein binding kinetics of phenytoin in monotherapy patients

Objectives: To determine the binding characteristics of phenytoin to serum proteins in the Japanese population and to compare these with those reported by other investigators. Method: Serum samples examined in the study were obtained from 72 patients (35 males, 37 females) receiving phenytoin monotherapy. The patients’ ages ranged from 1 to 73 years (1–15 years, 36 subjects; 16–44 years, 20 subjects; 45–64 years, 13 subjects; ≥65 years, 3 subjects). Results: The in vivo population binding parameters of phenytoin to serum proteins and theoretical minimal unbound serum phenytoin fraction ( fu) were determined using the Scatchard equation. The association constant ( K) was 0·020 l/μmol, while the total concentration of binding sites ( n(Pt) was 556 μmol/l. The number of binding sites per albumin molecule ( n) was 0·85, while binding ability (n · K) was 0·017 l/μmol. The fu was 0·083. The n · K is approximately 1·1 times higher in patients of Pospíšil et al. ( 26 ) (i.e. 0·0191 l/μmol) than in all our patients. The association contant is approximately 1·1 times higher in our study than in the in vitro study of Monks et al. ( 23 ) (i.e. 0·0186 l/μmol), while n is similar between the two studies. The fu in our patients is similar to the unbound serum phenytoin fraction in adult patients receiving phenytoin therapy reported by Richens ( 2) (i.e. 0·1). Conclusion: Our results suggest that there may be small differences in the binding characteristics of phenytoin to serum proteins between Japanese and non‐Japanese subjects. The unbound serum fraction of phenytoin in our patients with epilepsy can be assumed to be relatively constant in the therapeutic concentration range of phenytoin.

Protection against cis-diamminedichloroplatinum-induced nephrotoxicity by 2,3-dimercaptosuccinic acid in rats.

The present study was designed to examine the usefulness of 2,3-dimercaptosuccinic acid (DMSA) for the purpose of reducing cis-diamminedichloroplatinum (DDP)-induced nephrotoxicity and effective clinical use of DDP and safe. The effectiveness of DMSA on the DDP-excretion in rat kidney was observed by measuring the platinum concentration using Atomic Absorption Instrument. Co-administration of DMSA (1.0 or 2.0 mmol/kg) 1 hour after DDP injection (20 mumol/kg) showed more decrease in the platinum concentration than that immediately after DDP injection. The alleviating effect of DMSA on DDP toxicity was evaluated by lipid peroxidation, enzymatic antioxidants, and glutathione levels. The administration of DDP alone caused a significant increase in lipid peroxidation and significant decreases in enzymatic antioxidants and glutathione levels in the kidney. Co-administration of DMSA (2.0 mmol/kg) 1 hour after DDP injection showed the most effective reduction of these enzymatic damages caused by DDP. These findings suggested that the co-administration of DMSA (2.0 mmol/kg) 1 hour after DDP injection leads DDP to effective excrete from renal tissue and suppresses the lipid peroxide reaction and results in reduction of nephrotoxicity.

Temperature effect on serum protein binding kinetics of phenytoin in monotherapy patients with epilepsy

The effects of temperature on the binding kinetics of phenytoin (PHT) to serum proteins were determined in patients with epilepsy. Serum samples examined in the study were obtained from 59 patients (31 male, 28 female) with epilepsy on PHT monotherapy. Their age ranged from 3 to 64 years (mean (SD), 23.3 (16.3) years). Protein binding of PHT was evaluated by ultrafiltration under current routine laboratory conditions (25 +/- 3 degrees C) or at a temperature of 37 degrees C. The in vivo binding parameters of PHT to serum proteins were determined using a binding equation derived from the Scatchard equation for a one-site binding model. Significant differences were observed in serum concentrations of unbound PHT between paired data (P < 0.05). The mean association constant (K) of PHT to serum proteins is 0.011 microM-1 at 25 +/- 3 degrees C and 0.006 microM-1 at 37 degrees C, while mean total concentration of binding sites (n(Pt)) is 1002 microM for 25 +/- 3 degrees C and 1112 microM for 37 degrees C. Significant differences were observed in the binding kinetics of PHT to serum proteins for the different temperature conditions of ultrafiltration (P < 0.05). Our study confirms that binding affinity for PHT-serum protein interaction is approximately 45% lower at 37 degrees C than at 25 +/- 3 degrees C and consequently, binding potential (K.n(Pt)) is approximately 39% lower at 37 degrees C than at 25 +/- 3 degrees C.

Effect of temperature on binding characteristics of phenytoin to serum proteins in monotherapy adult patients with epilepsy.

&NA; The effects of temperature on binding characteristics of phenytoin (PHT) to serum proteins were determined in adult patients with epilepsy. Serum samples examined in the study were obtained from 47 adult patients (29 men, 18 women) with epilepsy on PHT monotherapy. Ages ranged from 18 to 64 years (mean [SD], 36.8 [12.1] years). Protein binding of PHT was evaluated by ultrafiltration under current laboratory routine conditions (25 ± 3°C) or at a temperature of 37°C. The in vivo binding parameters of PHT to serum proteins were determined using a binding equation derived from the Scatchard equation for a one-site binding model. Significant differences were observed in serum concentrations of unbound PHT between paired data (P < .05). The mean association constants (K) of PHT to serum proteins are 0.009 L &mgr;mol−1 at 25 ± 3°C and 0.003 L &mgr;mol−1 at 37°C, whereas mean total concentrations of binding sites [n(Pt)] are 1215 &mgr;mol L−1 for 25 ± 3°C and 2263 &mgr;mol L−1 for 37°C. Significant differences were observed in binding characteristics of PHT to serum proteins between the data determined in different conditions of ultrafiltration (P < .05). Our study confirms that binding affinity for PHT-serum protein interaction is approximately 67% lower at 37°C than at 25 ± 3°C, and, consequently, binding potential [K •n(Pt)] is approximately 38% lower at 37°C than at 25 ± 3°C.

No gender effect on binding characteristics of phenytoin to serum proteins in monotherapy for adult patients with epilepsy.

&NA; The aim of the present study was to determine the gender-related binding characteristics of phenytoin (PHT) to serum proteins in adult patients with epilepsy. Serum samples examined in the study were obtained from 80 adult patients (40 men and 40 women) with epilepsy on PHT monotherapy. Their age ranged from 16 to 64 years (mean [SD], 36.0 [11.7] years). Protein binding of PHT was evaluated by ultrafiltration under current laboratory routine conditions (25 ± 3°C). The in vivo binding parameters of PHT to serum proteins were determined using a binding equation derived from the Scatchard equation for a one-site binding model. No significant differences were observed in age and serum concentrations of albumin between male and female patients (p > 0.05), but significant differences were observed in serum concentrations of total and unbound PHT between the two groups (p < 0.05). The mean association constant of PHT to serum proteins is the same value of 0.008 L &mgr;mol−1 between male and female patients, whereas total concentration of binding sites seems to be similar between the two groups (1389 &mgr;mol L−1 for men and 1345 &mgr;mol L−1 for women). No significant differences were observed in binding characteristics of PHT to serum proteins between male and female patients (p > 0.05). Our results show that gender does not have a significant effect on the binding characteristics of PHT to serum proteins in adult patients receiving monotherapy under normal pathophysiologic conditions.