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  • 1
    ISSN: 1432-1041
    Keywords: cimetidine ; ranitidine ; carbamazepine ; sodium valproate ; pharmacokinetics ; drug metabolism ; inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The pharmacokinetics of a single oral dose (400 mg) of carbamazepine and sodium valproate were compared in peptic ulcer patients before and after four weeks of a therapeutic course of either cimetidine (1 g/day, n=6 subjects) or ranitidine (300 mg/day, n=6 subjects). There was a small (up to 20%) but statistically significant decrease in oral clearance of carbamazepine after cimetidine treatment. A similar fall in sodium valproate clearance in five cimetidine-treated patients was accompanied by a significantly prolonged elimination half-life. No such trends were demonstrated during ranitidine treatment. Since both anticonvulsants are partly metabolized by hepatic mixed function oxidases, an inhibition by cimetidine at this level may be responsible for the observed impairment of clearance. Thus a potentially important clinical interaction may occur in patients taking anticonvulsants and cimetidine concurrently.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    European journal of clinical pharmacology 16 (1979), S. 23-29 
    ISSN: 1432-1041
    Keywords: valproate ; epilepsy ; pharmacokinetics ; drug interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary In four refractory epileptic patients, peak plasma levels of sodium valproate occurred within 1.5 to 3 h after a single oral dose of valproate and the decline in plasma levels followed a monoexponential course with a t1/2 of 11.4 ± 0.1 h. The mean value for apparent volume of distribution was 0.176 ± 0.013 l/kg and for total plasma clearance 0.0106 ± 0.0009 l/h/kg. Steady state plasma levels were predicted using the method of superposition utilizing pharmacokinetic parameters determined following a single dose of valproate and were 78–123% of the predicted values for two patients receiving valproate alone, and 37–64% of the predicted values for the two patients receiving carbamazepine in addition to valproate. In a further group of 20 patients the mean daily doses of valproate for 8 patients receiving valproate alone (25.4 ± 4.9 mg/kg) was significantly less than those for the 12 patients receiving concomitant anticonvulsant therapy (41.6 ± 12.3 mg/kg) (p〈0.005). In addition, the steady state predose plasma levels of valproate were significantly higher in the valproate alone patients (90.3 ± 8.7 µg/ml) compared to the patients receiving additional anticonvulsants (75.3 ± 13.8 µg/ml) (p〈0.01). The higher dose requirements of valproate and lower predose and steady state plasma levels for those patients on multiple anticonvulsants indicate an interaction between valproate and other anticonvulsants.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1041
    Keywords: cimetidine ; intravenous infusion ; pharmacokinetics ; peptic ulcer ; duration of infusion ; acute dose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The use of cimetidine administered by bolus intravenous injection to critically ill patients has been associated with serious cardiac arrhythmias, due presumably to high initial plasma concentrations. The aim of this study was to determine the range of infusion times of a single 200 mg dose of cimetidine which would avoid high initial drug concentrations while maintaining a duration of effective concentrations no less than that resulting from bolus injection. Computer simulations of both maximum plasma cimetidine concentrations and duration of effective plasma cimetidine concentrations versus duration of infusion were based on mean pharmacokinetic date from 6 peptic ulcer patients who had received cimetidine 200 mg i.v. over 5 min. The simulations indicated that to reduce maximum plasma cimetidine concentrations by at least 50%, while maintaining the duration of effective plasma concentrations, the infusion time should be at least 30 min and no longer than 4.5 h. The validity of the simulations was subsequently tested in 4 of the patients, who received cimetidine 200 mg i.v. over 30 min. The mean maximum plasma concentration for the 30 min infusion (4.57±0.53 µg/ml) was, as predicted, approximately half that corresponding to bolus administration in these patients (8.97±1.96 µg/ml). Moreover, the duration of effective concentrations for the infusion (1.43±0.28 h) was significantly greater than that for the 5 min infusion (1.21±0.31 h). We suggest that where an acute intravenous dose of cimetidine (200 mg) is indicated, it should be administered over at least 30 min rather than as a bolus.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Clinical and experimental pharmacology and physiology 11 (1984), S. 0 
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effect of increased bile flow and hepatic bile acid flux on the systemic clearance and hepatic elimination of intravenously administered sodium valproate was studied in the bile fistula cat. Taurochenodeoxycholic acid (TCDC), tauro-3α, 7β-dihydroxy-12-keto-5β-cholanoic acid (T12K), SC-2644, and secretin were infused intravenously to vary bile flow and biliary bile acid secretion. Control animals were infused with 0.15 mol/l NaCl.2. Less than 1% of the drug administered to controls appeared as unchanged valproate in the bile over 6 h. Although SC-2644, T12K, and secretin significantly increased biliary excretion of valproate, it did not exceed 2% of the intravenous dose. Biliary clearance was directly related to the rate of bile flow, but not to the bile acid flux.3. By contrast, 18–19% of the dose appeared in bile as metabolite in controls, and none of the choleretic agents significantly increased this percentage. As a result, systemic clearance of valproate was unaltered.4. We conclude that the movement of unchanged valproate into bile is consistent with a process of simple diffusion. The fact that choleretic agents do not increase metabolite excretion into bile suggests that metabolite formation may be the rate-limiting step in the hepatic elimination of valproate, rather than transport and excretion of metabolites into bile.
    Type of Medium: Electronic Resource
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