Caffeine metabolism in premature infants

Caffeine has been used frequently in the treatment and prevention of apnea of prematurity. The metabolism of caffeine depends on the activities of the hepatic enzymes that vary from one infant to another. The objective of this study was to determine the influence of postnatal age (PNA), birth weight (BW), study weight (SW), gestational age (GA), postconceptual age (PCA), and gender on the maturation of caffeine metabolism in premature infants. The caffeine base was administered orally as a loading dose of 10 mg/kg, followed by a maintenance dose of 2 mg/kg every 24 hours. The steady-state concentration of caffeine and metabolites was measured in plasma taken on the 5th-day postloading dose. The molar concentration ratios for the N3 (N3-), N7 (N7-), N1 (N1-), and all methyl (Nall-) demethylation processes; clearance (CL); and the percentage of molar concentration of caffeine found in plasma to that of the total caffeine and metabolites (%CAF) were calculated from samples collected from 80 neonatal infants. The 48 male and 32 female premature infants had median (range) BW (g), GA (weeks), SW (g), PCA (weeks), and PNA (days) of 1300 (650-2260), 30 (24-34), 1630 (980-2670), 34 (29-40), and 28 (5-60), respectively. The median (range) of the ratios for the %CAF, CL, and the N3-, N7-, N1-, and Nall- were 86.9 (52.9-99.0), 0.127 (0.046-0.503) ml.kg-1.min-1, 0.032 (0-0.438), 0.070 (0.007-0.471), 0.026 (0-0.283), and 0.0463 (0.003-0.303), respectively. When the patients were stratified into four PNA age groups, each older group showed a consistently higher level of caffeine metabolic activity for the N3-, N7-, and Nall- pathways with a corresponding decrease in the %CAF, whereas no significant differences were seen for the N1-pathway or for CL. No pattern of significant differences between the demethylation process ratios, %CAF, or CL was seen between groups of infants when they were stratified according to BW, SW, PCA, or GA. The female infants were found to have significantly higher rates of caffeine metabolism as shown by %CAF, N1-, N3-, and Nall- processes but not the N7-. Multivariate linear regression analysis by two methods demonstrated that PNA is significantly related to %CAF and Nall-, whereas the female patients had higher levels of metabolic activity for the %CAF and N1- process. The authors conclude that the N7-demethy-lation process is the predominate caffeine metabolic process in premature infants. Furthermore, the maturation of the caffeine metabolism in premature infants with a PNA of less than 60 days increases with postnatal age, regardless of birth weight, gestational age, postconceptual age, and study weight. The female neonatal patients demonstrated a higher rate of caffeine metabolism than the males.

Pharmacokinetics of mesna and dimesna after simultaneous intravenous bolus and infusion administration in patients undergoing bone marrow transplantation

This study was undertaken to examine the pharmacokinetics of mesna and its dimer form, dimesna, in the plasma and urine of patients undergoing bone marrow transplantation who received 130 mg/kg of mesna divided intravenously into a 30-mg/kg bolus dose followed immediately by 100 mg/kg infused over 12 hours for uroprotection. The relationship between and urinary excretion of mesna and dimesna also was examined by comparing the data obtained in patients who developed hemorrhagic cystitis versus those who did not. Blood and urine samples were collected at different time intervals after administration, and the plasma or urine was analyzed by liquid chromatography with electrochemical detection. Dimesna was analyzed in these samples after reduction back to mesna with sodium borohydride. The concentration-time data of mesna exhibited the characteristics of the two-compartment model well, and the mean +/-SD values of the distributive phase half-life (t1/2 alpha), postdistributive phase half-life (t1/2 beta), volume of distribution of the central compartment (Vdc), volume of distribution at steady state (Vdss), volume of distribution during the postdistributive phase (Vd beta), total clearance (Cl), and mean residence time (MRT) observed were 0.12 +/- 0.15 hours, 2.12 +/- 1.61 hours, 0.324 +/- 0.336 L/kg, 1.09 +/- 1.18 L/kg, 2.09 +/- 3.0 L/kg, 0.755 +/- 0.507 L/hr.kg, and 6.77 +/- 0.72 hours, respectively. The mean +/-SD values of t1/2 and MRT of dimesna were 1.29 +/- 0.6 hours and 6.68 +/- 1.05 hours, respectively, and the ratio of the area under the concentration-time curve (AUC) of mesna to that of dimesna was 1.21 +/- 0.57. The fractions of dose excreted in urine in the form of mesna and dimesna in 20 hours (fu) were 0.361 +/- 0.15 and 0.482 +/- 0.25, and the renal clearance (ClR) values were 0.244 +/- 0.201 L/hr.kg and 0.157 +/- 0.156 L/hr.kg, respectively. The urinary excretion of mesna in these patients was higher than that required for uroprotection for the whole duration of infusion, and there was no significant difference in the pharmacokinetics of mesna between patients who developed hemorrhagic cystitis and those who did not. This was not the case with dimesna, in which patients with hemorrhagic cystitis excreted in urine less than 50% of the amount of dimesna excreted by those without hemorrhagic cystitis.

Direct liquid chromatographic micro-measurement of tamoxifen in plasma of cancer patients

We describe in this report a sensitive and direct method for the analysis of tamoxifen (TAM) in microsamples of plasma. The drug and internal standard (quinine bisulfate, I.S.) were separated on a 10-microm particle, 10 cm X 8 mm CN cartridge in conjunction with a radial compression system. The mobile phase was a mixture of 0.1 M sodium acetate in 0.001 M tetrabutylammonium phosphate solution (pH 6) and methanol (30:70, v/v) at a flow-rate of 4 ml/min. After addition of I.S. and o-phosphoric acid in acetonitrile (0.6 M) to the plasma (30 microl), the mixture was placed in an ultraviolet shortwave transluminator for 2 min prior to injection into the chromatograph. The compounds were detected in the effluent fluorometrically at excitation and emission wavelengths of 258 and 378 nm, respectively. Under these conditions, no interference in the assay from any endogenous substance or other concurrently used drugs was observed and the retention times of I.S. and TAM were 4.4 and 10.15 min, respectively. The concentration of TAM in plasma was linearly (r>0.9983) related to the peak height ratio (TAM/I.S.) in the range 0.01-2.0 microg ml(-1) and C.V. at 0.075, 0.4 and 1.2 microg ml(-1) was < or = 4.96%. We are currently using this assay for monitoring TAM in plasma and investigating its pharmacokinetics in cancer patients receiving cytotoxic drugs in addition to TAM as a multi-drug resistance modifier.

Urinary selenium in healthy and diabetic Saudi Arabians

We examined Se in urine of 170 Saudi Arabian diabetics (19 insulin-dependent [type 1] and 151 insulin-independent [type 2]) and in an equal number of control subjects of the same origin by measuring the ratio of the concentration of this metal (C(Se)) to that of creatinine in urine (C(creat)) for each subject. The mean (and SEM) of C(Se) /C(creat) for the control subjects was 56 (2.9) mu mol/mol creat, whereas, the value for the diabetics combined or separated into type 1 and type 2 was 56.7 (3.2), 51.5 (6.3), and 57.4 (3.5) mu mol/mol creat, respectively. With the exception of type 2 diabetics who were treated with insulin in addition to oral hypoglycemic and diet (35 patients) (mean [SEM] = 43 (4.3) mu mol/mol creat), there was no significant difference in C(Se)/C(creat) between the diabetics and control subjects. Also, there was no significant correlation between C(Se)/C(creat) and age, sex, or weight of diabetics, whereas, the correlation with the degree of diabetic control was significant (p < 0.0136). Of all diabetes-associated disorders (cardiovascular diseases, neuropathy, ophthalmologic diseases, infections, and hepatic disease), only ophthalmologic diseases appears to cause a significant (p < 0.05) reduction in C(Se)/C(creat), but only among type 2 diabetics. Inasmuch as Se status is reflected by urinary Se, healthy Saudi Arabians appear to have Se status that is comparable or higher than those reported for other populations.