Hemostasis in patients with normal and impaired renal function under treatment with cefodizime

Ten patients (two with normal, eight with impaired renal function) on their usual diet were treated with cefodizime (HR 221) for seven days. The dosage was 4 g/day, adapted to renal function as appropriate. Platelet function, plasma coagulation and vitamin K metabolism were investigated before and on day 7 of therapy. Platelet function and plasma coagulation remained unchanged, regardless of the size of the serum antibiotic trough levels, in both normal and impaired renal function. Vitamin K1 metabolism remained unaffected, since no increase in vitamin K1 2,3 epoxide in the circulation was observed during the therapy. Cefodizime (HR 221), a parenteral aminothiazole cephalosporin, does not affect hemostasis.

Drug interaction between propafenone and metoprolol

1 The steady-state plasma concentrations of metoprolol and propafenone were determined in patients being treated with one of these drugs alone and during combined treatment with both drugs. In addition, single dose studies with metoprolol, propafenone and the combination of both drugs were performed in healthy volunteers to determine the pharmacokinetics and the time course of beta-adrenoceptor blocking activity. 2 In four patients being treated with metoprolol first and subsequently with propafenone in addition steady-state levels of metoprolol increased two to five fold with simultaneous treatment with propafenone. 3 In four patients being treated with the drug combination first and thereafter with propafenone alone no changes in the steady-state levels of propafenone were observed between both treatment periods. 4 Adverse effects of the drug combination were observed in two patients (one patient experienced severe nightmares and the other left ventricular failure). 5 When single oral doses of metoprolol (50 mg) and propafenone (150 mg) and the combination of both were administered to healthy subjects, an approximately two-fold decrease of the oral clearance of metoprolol was seen when propafenone was given in addition. No conclusive changes in the pharmacokinetics of propafenone could be detected in the presence of metoprolol. 6 Duration of beta-adrenoceptor blocking activity of a single dose of metoprolol in healthy volunteers as measured by reduction of exercise-induced tachycardia increased when propafenone was given in addition. 7 The dose of metoprolol should be reduced when propafenone is given in addition.

Factors responsible for interindividual differences in the dose requirement of phenprocoumon

The total and unbound plasma concentrations of phenprocoumon and the prothrombin complex activity were determined in 51 patients on phenprocoumon. A 7-fold difference in the dosing rate (10-70 micrograms/kg/day) was required to maintain the prothrombin complex activity at 11-30% of normal. The variation in dosing requirement was mainly due to interindividual differences in the intrinsic clearance of phenprocoumon and only to a minor degree to differences in sensitivity to it. On average patients with myocardial infarction required only 2/3 of the daily dose of phenprocoumon of post cardiac surgery patients and patients with thrombosis and emboli. That difference appeared to be due to higher clearance in surgical patients and to greater resistance to phenprocoumon in patients with thrombosis and emboli. The total clearance in patients varied approximately 5-fold. It was better predicted by the interindividual intrinsic clearance (r = 0.84) than by the unbound fraction (r = 0.15).

Double-blind comparison of haloperidol decanoate and fluphenazine decanoate effectiveness, side-effects, dosage and serum levels during a six months' treatment for relapse prevention

In this present study 31 schizophrenic patients were treated for six months for relapse prevention under double-blind conditions with either haloperidol decanoate (22) or fluphenazine decanoate (9). In respect of the prophylactic action, both depot neuroleptics proved to be equal during the comparatively short period of observation. In both groups a psychotic relapse occurred that could not be managed by increasing the depot dosage. No side-effects worth mentioning appeared in either group of patients; patients under haloperidol decanoate, however, only required half the quantity of anti-parkinson medication as compared with patients treated with fluphenazine decanoate, and also displayed extrapyramidal motor symptoms (EPMS) to a lesser degree. Patients received a mean monthly injection of 80 mg of Haloperidol, reaching steady-state serum levels of about 3 ng/ml in the third injection interval. Fluphenazine serum levels known so far for seven patients amount to 0.8 ng/ml after fluphenazine injections of 21 mg every 14 days.

Relationship between pharmacokinetics and pharmacodynamics of molsidomine and its metabolites in humans

The pharmacokinetic properties and hemodynamic effect of molsidomine and its pharmacologically active metabolite SIN-1 were investigated in 13 healthy volunteers following single oral doses. Hemodynamic changes were measured by finger plethysmography (peripheral arterial resistance), impedance plethysmography (venous distensibility), heart rate, and blood pressure. Plasma concentrations of molsidomine, SIN-1, and SIN-1C were measured by means of high-pressure liquid chromatography. Oral administration of rapidly dissolving tablets of molsidomine (2 tablets of 4 mg), a sustained-release form of molsidomine (8 mg), and SIN-1 (4 mg) caused an increase of the a/b ratio of the finger plethysmogram and an increase of the venous distensibility. Heart rate and blood pressure remained unaffected. The time course of the peripheral arterial effect mimicked the time course of plasma concentrations of molsidomine and SIN-1. Similar to the results in animals, molsidomine was metabolized in humans to SIN-1 and subsequently degraded to the inactive metabolite SIN-1C. The kinetic profile of both metabolites could be followed in the plasma. The rate-limiting step in the metabolic sequence of molsidomine was found to be enzymatic hydrolysis and decarboxylation of molsidomine to SIN-1. Concentration-response curves of the a/b ratio of the finger plethysmogram showed that the plasma concentrations required to produce a definite effect are much higher for molsidomine than for SIN-1. This shows that the pharmacodynamically active form of molsidomine in humans is the metabolite SIN-1. The changes in the finger plethysmogram produced by SIN-1 suggest that in addition to the effect on the venous site, SIN-1 also dilates the peripheral arterial site.

Possible coumarin-like mechanism of action for cephalosporins

In three patients treated with cephalosporins (one patient with latamoxef, two patients with cefazedone) vitamin K1 was injected to investigate whether this was followed by an increase in vitamin K1 2,3-epoxide plasma concentrations as compared to controls. Such a rise in K1-epoxide concentrations in the plasma can be demonstrated following treatment with coumarins. This reflects an inhibition of the vitamin K1-epoxide reductase in the liver. Coumarins are thought to induce hypoprothrombinaemia by such a mechanism. In all three patients we found a considerable increase in the vitamin K1-epoxide plasma concentrations following injection of 10 mg vitamin K1, whereas in normal subjects only traces of K1-epoxide could be detected (less than 0.030 micrograms/ml). The K1-epoxide concentrations found in our three patients treated with cephalosporins were 0.12, 0.16 and 0.19 micrograms/ml, respectively. This indicates that latamoxef or cefazedone might reduce clotting factor synthesis by a coumarin-like mechanism of action in these patients. Although the effect of cephalosporins in enhancing vitamin K1-epoxide plasma concentrations is less than that of coumarins, it might cause severe hypoprothrombinaemia in the presence of latent vitamin K deficiency.

Cyclic interconversion of vitamin K1 and vitamin K1 2,3-epoxide in man

The disposition of a single intravenous bolus dose of 10 mg vitamin K1 and vitamin K1-2,3-epoxide were studied in two healthy subjects without and with 12 h pretreatment dose of phenprocoumon (0.4 mg/kg). For each compound administered alone the plasma concentration-time profile was adequately fitted by a biexponential equation, with an average terminal half-life of 2.0 and 1.15 h for the administered vitamin K and its 2,3-epoxide respectively. While vitamin K1 was measurable in plasma following administration of vitamin K1-2,3-epoxide, the epoxide was not detectable following administration of vitamin K1. Following pretreatment with phenprocoumon and after intravenous administration of vitamin K1, both the average half-life and area under the plasma concentration-time profile of vitamin K1 were marginally reduced to 1.5 h and 1.76 mg l-1 h respectively, while the plasma concentration of vitamin K1-2,3-epoxide was readily measurable and its half-life markedly prolonged to 14.7 h. Following pretreatment with phenprocoumon and after oral administration of vitamin K1-2,3-epoxide, no vitamin K1 was detectable in plasma and the half-life of the epoxide was 13.8 h. Based on area considerations the data suggest that either phenprocoumon does more than just inhibit the reduction of vitamin K1-2,3-epoxide to vitamin K1, or that the simple model describing the interconversion between vitamin K1 and its epoxide is inadequate. The same conclusion is drawn from the analysis of comparable data in dogs, obtained by Carlisle & Blaschke (1981).

Pharmacokinetics and pharmacodynamics of the 5-HT2 receptor antagonist ketanserin in man

We determined the pharmacokinetics of ketanserin and its effects on blood pressure and heart rate in eight healthy volunteers following single-dose intravenous (10 mg) and oral (20 mg) administration of ketanserin. Following intravenous injection, plasma concentration-time data could most adequately be described by an open, three-compartment model. Plasma concentration declined with a mean terminal half-life of 15.6 +/- 6.2 h (mean +/- SD). Total clearance and volume of distribution at steady state were 0.39 +/- 0.07 L/kg/h and 3.3 +/- 1.1L/kg, respectively. The free fraction in plasma determined by equilibrium dialysis was 9.36 +/- 0.56%. Following single oral doses, a bioavailability of 0.51 +/- 0.06 was estimated. The half-life of the elimination phase tended to be somewhat longer (18.5 +/- 5.1 h, p greater than 0.05) than after intravenous administration. In addition, pharmacokinetics and effects of ketanserin on blood pressure and heart rate were investigated in two healthy volunteers after continuous treatment with ketanserin (20 mg three times a day) over a period of 5 days. No evidence of time-dependent nonlinear changes in pharmacokinetics was observed. Following single-dose as well as continuous treatment with ketanserin, no significant changes either in systolic and diastolic blood pressure or in pulse rate could be detected.

Plasma protein binding of azapropazone in patients with kidney and liver disease

1 The free fraction of azapropazone in the plasma of 37 healthy volunteers ranged from 0.0027 to 0.0070 (0.0044 +/- 0.0009, mean +/- s.d.). The principal binding protein was found to be albumin. 2 In 27 patients with various degrees of renal failure the free fraction values of azapropazone were markedly enhanced (0.0260 +/- 0.0239, mean +/- s.d.) and increased more than tenfold in some patients. There was a weak correlation (r = 0.46, P less than 0.05) between the free fraction and the clearance of endogenous creatinine. Such correlation was not found for serum creatinine, serum albumin, serum uric acid and serum urea nitrogen. 3 In 32 patients with chronic liver disease the free fraction values of azapropazone were also markedly higher (0.0210 +/- 0.0242, mean +/- s.d.) than in healthy subjects. There were statistical significant correlation between free fraction values and the prothrombin complex activity in the plasma (r = 0.40, P less than 0.05) and the total bilirubin concentration in the plasma (r = 0.90, P less than 0.001), respectively. Such correlation was not found for serum albumin, serum glutamic oxalacetic transaminase, serum gamma-glutamyl transpeptidase and serum alkaline phosphatase. 4 In patients with kidney and liver disease the free fraction values of azapropazone correlated well with those of the anticoagulant drug phenprocoumon (r = 0.93, P less than 0.001). However, the binding of the latter drug was less impaired. Bilirubin, when added in vitro, displaced both drugs from plasma proteins but this displacing effect was much smaller than the binding changes observed in patients with liver disease. 5 Kidney and liver disease caused a marked impairment of the plasma protein binding of azapropazone. In patients with kidney disease the degree of impairment of azapropazone binding cannot or only poorly (creatinine clearance) be predicted from the biochemical parameters of kidney function whereas in patients with chronic liver disease the total bilirubin concentration in the plasma may serve as an index of the binding defect.

Age-dependent differences in the effect of phenprocoumon on the vitamin K1-epoxide cycle in rats

The anticoagulant activity and the pharmacokinetics of phenprocoumon as well as the effect of phenprocoumon on the vitamin K1-epoxide cycle in younger (12 weeks) and older (36 weeks) male inbred Lewis rats has been examined in a study of the mechanism responsible for the increase in the responsiveness to oral anticoagulant drugs (OAD's) with increasing age. After a single i.v.-dose of phenprocoumon (0†355 mg kg−1 the anticoagulant effect obtained was greater in older than in younger rats. There were no differences between younger and older rats in the rate of elimination, volume of distribution and in the free fraction and free concentration values of phenprocoumon in plasma and liver. After i.v.- injection of 64·3 μg kg−1 [3 H]vitamin K1 and different doses of phenprocoumon (0·02 to 3 mg kg−1) the [3 H]vitamin K1 concentration in the liver decreased and the [3 H] vitamin K1-2, 3-epoxide concentration increased dependent on the dose and the liver concentration of phenprocoumon. These changes were more pronounced in the older than in the younger rats. Concentration-response curves gave similar EC50-values for both age-groups but a 1·6-fold higher maximal response (expressed as vitamin K1-epoxide/vitamin K1 ratios) in the older rats. Since OAD's exert their anticoagulant effect most probably by inhibiting an enzyme (vitamin K1-epoxide reductase) which regenerates vitamin K1 from the epoxide metabolite and since the vitamin K1-epoxide/vitamin K1 ratios in the liver may reflect the degree of inhibition of the epoxide reductase by OAD's, our results may indicate that the inhibitory effect of phenprocoumon on this enzyme is more pronounced in older than in younger rats. This could explain the age-dependent differences in the anticoagulant activity.

Effect of induction and inhibition of drug metabolism on pharmacokinetics and anticoagulant activity of the enantiomers of phenprocoumon in rats

The elimination, distribution and anticoagulant activities of the enantiomers of phenprocoumon were studied in rats following enzyme induction by phenobarbital (pretreatment with 75 mg . kg-1 for 4 days) and enzyme inhibition by chloramphenicol (100 mg . kg-1 h prior to the injection of phenprocoumon and then 50 mg . kg-1 every 12 h). Pretreatment with phenobarbital increased the rate of elimination and decreased the total anticoagulant effect per dose of both enantiomers. It also caused a slight reduction of the liver/plasma concentration ratio of the enantiomers due to the increase of the liver weight and a significant enhancement of the synthesis rate of prothrombin complex activity in non-anticoagulated rats. Chloramphenicol decreased the rate of elimination and enhanced the total anticoagulant effect per dose of both enantiomers. The distribution between plasma and liver remained unaffected. Thus, in rats neither the induction of the phenprocoumon metabolism by phenobarbital nor its inhibition by chloramphenicol appears to be stereoselective.