Eight healthy volunteers received a 5 min i.v. infusion of lysine theophylline, equivalent to 197 mg anhydrous theophylline, both before (day 1) and during (day 5) steady state chronic oral dosing with slow release nifedipine 20 mg 12 hourly. A theophylline pharmacokinetic profile was performed on day 1 and day 5 and a nifedipine pharmacokinetic profile was performed on day 4 and day 5. The greatest difference in serum theophylline concentrations was seen at the first sampling time (5 min after completion of the infusion) with a mean concentration of 9.9 mg l‐1 during nifedipine administration and 14.6 mg l‐1 with theophylline alone. Thereafter, the difference fell to approximately 1 mg l‐1 until 6 h when they became almost identical. Repeated measures analysis of variance using the theophylline serum concentrations at each of ten time points over 8 h as the repeated measures showed a small but significant effect of nifedipine (F(1,151) = 7.0, P less than 0.01) on serum theophylline concentrations. Mean volume of distribution (V) rose from 0.33 +/‐ 0.07 to 0.39 +/‐ 0.06 1 kg‐1 corrected body weight (CBW) in the presence of nifedipine (t = 2.23, P = 0.052). Theophylline clearance, area under the curve to 8 h AUC (0‐8), area under the curve to infinity AUC (0‐infinity) and elimination half‐life (t1/2) did not change appreciably. No statistically significant changes in nifedipine pharmacokinetics occurred in the presence of theophylline.
Eight healthy volunteers received slow release nifedipine 20 mg 12 hourly, for six doses. A nifedipine pharmacokinetic profile was performed after the fifth dosing interval using 12 sampling times over 12 h. A specific high pressure liquid chromatography (h.p.l.c.) nifedipine assay was used. Six of the volunteers subsequently received an i.v. infusion of 3.5 mg of nifedipine after an identical period (five dosing intervals) of chronic oral dosing with slow release nifedipine 20 mg 12 hourly. An identical pharmacokinetic profile was performed after the infusion. Bioavailability, clearance (CL), apparent volume of distribution (V), apparent half life (t1/2) and area under the curve (AUC) were calculated. The geometric mean apparent t1/2 for the slow release preparation was 6.3 +/‐ 2.0 h. In the six volunteers, the mean bioavailability was 46% (range 29‐86%), the mean CL was 588.0 +/‐ 67.1 ml min‐1, the mean apparent V was 160.1 +/‐ 61.7 l. The pharmacokinetics of slow release nifedipine during chronic dosing appear similar to those derived from single dose studies.
The effects of aspirin, soluble aspirin and lysine aspirin on buccal mucosal potential difference (p.d.) were compared in a double-blind trial. Placebo and three doses of each preparation containing 150, 300 and 600 mg of aspirin were allocated according to a latin square design. Six volunteer subjects were studied; each received a total of 10 treatments at least 24 h apart. All doses of each preparation considered, a significant treatment effect was seen [F (d.f. = 2,306) = 6.2, P<0.003]. Lysine aspirin showed the least effect of the active treatments on buccal p.d. with a change from baseline of +8.5 mV compared with +13.3 for soluble aspirin +14.4 for conventional aspirin and —5.2 mV for placebo.
The pharmacokinetics of two slow release theophylline preparations "Theo-Dur" (T) containing theophylline only and "Phyllocontin" (P) containing aminophylline have been compared in 12 patients with asthma. Each patient received both treatments in random order. The dose of treatment administered 12 hourly was increased or decreased to produce plasma theophylline concentrations of 10-20 mg/l at clinic visits normally 7 to 8 h after dosing. Pharmacokinetic studies were carried out after at least one week's treatment with this dose. After the first study day patients were crossed over to the second treatment at a dosage providing a similar amount of theophylline. They returned for a second study day after at least one week. Comparison of the dose corrected AUC, time to peak concentrations, within patient coefficients of variation (CV), number of concentration time points falling within 25% of Cmax and percentage fluctuations in plasma concentration showed no significant differences between the two preparations.
The purpose of this research and development was to develop the elevated susceptible, speedy, stable and reproducible extraction method with precise results. At the same time, this method would be efficient in analyzing the large numbers of plasma samples obtained for bioequivalence studies. The chromatography was performed by using column ZIC ® -HILIC, 4.6×150 mm, 5µ. Nimodipine was used as internal standard. The solid phase extraction was used to extract Acamprosate and Nimodipine (Internal standard) from plasma samples. The calibration curve was relied on the concentration of 10.01 ng/mL to 709.36 ng/mL for Acamprosate in human plasma
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