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Biomedical subjects

M Pfeffer

Publications and source records attributed to M Pfeffer.

At least 91 records · Page 5Linked to original sources
PubMed1988

Clinical pharmacokinetics of oral buspirone in patients with impaired renal function.

12 patients with mild to moderate impairment of renal function and 12 healthy subjects each received 20mg buspirone as a single dose in this acute study. Six anuric patients with chronic renal failure were given two 20mg doses of buspirone, the first 2 days before haemodialysis (between dialyses) and the second during hemodialysis (2 hours before dialysis began). The differences between the median pharmacokinetic values of buspirone for healthy subjects, patients with mild to moderate renal impairment, and anuric patients were not statistically significant. Similarly, there were no significant differences between values in mild to moderate renal failure vs healthy subjects. Some of the median pharmacokinetic values for the active buspirone metabolite 1-(2-pyrimidinyl)-piperazine (1-PP), however, differed significantly for anuric patients, compared with healthy subjects or patients with mild to moderate renal impairment. When assessed between and during haemodialysis, the anuric patients had significantly (p less than 0.05) greater pharmacokinetic median values: half-life (t 1/2) = 15.2 vs 9.8 hours; area under the concentration-time curve (AUC) = 604 vs 404 nmol/L.h; and mean residence time (MRT) = 9.28 vs 6.96 hours. No firm recommendation for specific dosage can be made based on the present data. However, it does appear that in patients with mild to moderate renal impairment, the pharmacokinetics of buspirone and its active metabolite 1-PP are similar to those in individuals with normal renal function. For anuric patients higher concentrations of the 1-PP metabolite are attained while they are not undergoing haemodialysis. A dosage reduction of 25 to 50% might be necessary when buspirone is given to anuric patients.

Administration, Oral↗
PubMed1987

[Therapy of urticaria with H1 and H2 antihistaminics. Results of clinical and experimental studies].

The antipruritic effect of modern H1- and H2-receptor blockers in chronic urticaria, that had been clinically proved, was experimentally studied by means of the histamine weal test. The H2-antihistamine preparation ranidine alone did not clearly reduce weals or erythemas induced by histamine when compared with a placebo. As expected, both parameters were markedly reduced by the H1-antihistamine preparation terfenadine. After combined administration of both drugs, the effect of the H1-blocker proved to be significantly increased. We discuss the possible mode of action and the consequences for anti-allergic therapy.

Benzhydryl Compounds↗
PubMed1987

Lack of interaction between cimetidine and buspirone.

Simultaneous administration of cimetidine and many benzodiazepine anxiolytics has resulted in decreased body clearance and marked prolongation of the half-life of these agents. The pharmacokinetic interaction of buspirone, a new nonbenzodiazepine anxiolytic, and cimetidine was studied in 10 healthy male volunteers. Each received, in order, buspirone 45 mg/day (days 1-7), no drug (days 8-14), cimetidine 1 g/day (days 15-21), buspirone 45 mg/day plus cimetidine 1 g/day (days 22-28), and cimetidine 1 g/day (days 29-31). Buspirone and 1-pyrimidinyl piperazine (1-PP), an active metabolite, pharmacokinetics, urinary excretion of cimetidine, a manual dexterity test, the Stroop color-word interference test, and a visual analog mood scale were evaluated on each treatment. There were no significant (p greater than 0.05) differences among treatments for any measurement except for a slight (31%) but significant (p less than 0.05) increase in the 1-PP Cmax value. These results suggest that within the normal therapeutic dosage ranges for both drugs, it is unlikely that a clinically significant interaction between them will occur.

Adult↗
PubMed1987

Buspirone pharmacokinetics in patients with cirrhosis.

The pharmacokinetics of a single oral dose of buspirone (20 mg) were determined in 12 patients with cirrhosis and 12 normal subjects. The mean AUC of buspirone was 55 +/- 38 s.d. ng ml-1 h in cirrhotics and 3.5 +/- 2.4 s.d. ng ml-1 h in normals. The time until maximum concentration (tmax) attained was similar in the two groups (0.6 vs 0.7 h), but mean maximum concentration Cmax was higher in patients (18.8 +/- 16.3 s.d. ng ml-1) than in normals (1.2 +/- 0.8 s.d. ng ml-1). Mean elimination half-life of buspirone was greater in cirrhotics, but this difference was marginally significant statistically (cirrhotics, 6.1 +/- 3.5 s.d. h, normals 3.2 +/- 1.5 s.d. h, P = 0.05). Eight of 12 patients and seven of 12 normal subjects had a second peak in the plasma concentrations of buspirone. In patients this occurred at 10.8 +/- 7.4 s.d. h after the dose, and its mean concentration was 3.1 +/- 6.6 ng ml-1. In normal subjects the second peak occurred at 4.3 +/- 2.1 h after the dose and its mean concentration was 0.5 +/- 0.3 ng ml-1. On the kinetic evidence buspirone should be used with caution in liver disease.

Adult↗
PubMed1986

Prefeeding-dependent anaerobic metabolization of xenobiotics by intestinal bacteria--methods for acarbose metabolites in an artificial colon.

The biotransformation of Acarbose (Bay g 5421) by an artificial in vitro system with viable intestinal microorganisms was investigated. The bacteria were obtained from the colon of man or from the caecum and colon of rats and were incubated anaerobically with 14C-Acarbose in a nutrient solution. The metabolites were separated and purified by chromatographic methods and identified by nuclear magnetic resonance (1H; 13C) spectrometry and by mass spectrometry. Metabolites in man and rat are component 2 (minus the terminal glucose of Acarbose), a basic disaccharide consisting of rings B and C, and component 1. This latter substance is formed, after hydrolytic cleavage of the internal glucose of Acarbose, by spontaneous rearrangement of rings A and B (Acarviosine) into a tricyclic oxazolidine. The metabolite pattern of Acarbose is changed profoundly after several weeks of pretreatment of man or rat with this compound. The microflora adapted in such a manner yields in addition methylated, hexosylated, and n-butyroylated derivatives of Acarbose and/or component 2.

Acarbose↗
PubMed1985

Acesulfame K, cyclamate and saccharin inhibit the anaerobic fermentation of glucose by intestinal bacteria.

The caecal microflora of Cara rats was incubated in the pH stat with glucose under anaerobic conditions, and the acid production was measured. In the presence of the sweeteners Acesulfame K, Cyclamate and Saccharin, inhibition of the fermentation of glucose was observed with ED50 values of 260, 251, and 140 mM, respectively. The nutritional relevance of these observations is probably slight; an interpretation in terms of bacterial physiology leads to the proposal that the sweeteners may act on glucose transport systems at the bacterial cytomembrane.

Anaerobiosis↗
PubMed1985

Bioavailability and pharmacokinetics of etoposide (VP-16).

The absolute oral bioavailability of etoposide (VePesid) was determined in cancer patients based on a comparison of intravenous and oral administration. The oral dosage unit was etoposide solubilized in a polyethylene glycol-based vehicle in a soft gelatin capsule formulation. The intravenous dose was 80 mg/m2 as a one-hour infusion and the oral dose was 160 mg/m2. The absolute bioavailability based on plasma concentrations or urinary excretion of etoposide was 48% to 57%. The plasma elimination half-life was 5.3 hours, total body clearance 21.4 mL/min/m2, and renal clearance 7.7 mL/min/m2. Significant intersubject and intrasubject variation was observed in intravenous and oral pharmacokinetics and oral bioavailability. This variability could be related to intrapatient and interpatient differences in nonrenal clearance and the inherent patient and disease status problems in evaluating the pharmacokinetics of anticancer drugs. This variability is characteristic of many classes of cytotoxic drugs and indicative of the requirements of individual dose optimization.

Aged↗
PubMed1984

Comparative effects of propranolol and nadolol on renal blood flow in normal rats and rats with congestive heart failure.

Mean arterial blood pressure (MAP), heart rate (HR), renal blood flow (RBF), and renal vascular resistance (RVR) were determined before and during an infusion of propranolol (18 mg/kg/hr) or nadolol (30 mg/kg/hr) in anesthetized Munich-Wistar rats with normal cardiac function. Eight rats treated with propranolol had significant reductions in MAP (110 to 98 mm Hg; p less than 0.05) and HR (316 to 242 bpm; p less than 0.01), accompanied by a 24% decrease in RBF (5.9 to 4.5 ml/min; p less than 0.05) and a 22% increase in RVR (19.4 to 23.7 mm Hg/ml/min; p less than 0.05). Although nadolol also reduced MAP (104 to 93 mm Hg; p less than 0.01) and HR (315 to 268 bpm; p less than 0.05) in eight other rats, RBF and RVR remained unchanged from baseline levels. Thus, despite similar decrements in MAP and HR, propranolol decreased renal perfusion, whereas nadolol maintained it in animals with noninfarcted myocardium. These parameters were also evaluated in rats with congestive heart failure induced by myocardial infarction at least 3 weeks prior to their receiving either propranolol (18 mg/kg/hr; n = 6) or nadolol (30 mg/kg/hr; n = 6). In the basal state, rats with congestive heart failure had significantly (p less than 0.05) lower MAP, HR, and RBF and higher (p less than 0.01) RVR compared with control rats. Propranolol and nadolol induced comparable falls (p less than 0.05) in MAP and HR. Whereas RBF tended to fall with propranolol (3.3 to 2.4 ml/min), renal perfusion was well maintained with nadolol (3.4 to 3.8 ml/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1984

Studies of mitomycin C absorption after intravesical treatment of superficial bladder tumors.

Mitomycin C is an active drug in the treatment of superficial bladder cancer. Although clinical safety of intravesical mitomycin C has been well accepted there are no data on absorption of this drug from the bladder in patients with damaged bladder mucosa. We studied 18 patients for evidence of absorption of mitomycin C after transurethral resection and/or radiation therapy. Mitomycin C is absorbed on intravesical instillation and the degree of absorption depends on the degree of damage to the bladder. Despite some evidence of absorption no systemic effect on bone marrow was observed and no evidence of deoxyribonucleic acid damage was found in any of these patients. Mitomycin C appears to be a safe drug but further studies are indicated to document its safety when used for maintenance therapy.

Antibiotics, Antineoplastic↗
PubMed1983

Human intravenous pharmacokinetics and absolute oral bioavailability of cefatrizine.

Cefatrizine was administered intravenously and orally at dose levels of 250, 500, and 1,000 mg to normal male volunteers in a crossover study. Intravenous pharmacokinetics were dose linear over this range; mean peak plasma concentrations at the end of 30-min infusions were, respectively, 18, 37, and 75 micrograms/ml, total body clearance was 218 ml/min per 1.73 m2, renal clearance was 176 ml/min per 1.73 m2, and mean retention time in the body was 1.11 h. Cumulative urinary excretion of intact cefatrizine was 80% of the dose, and half-lives ranged from 1 to 1.4 h. Steady-state volume of distribution was 0.22 liters/kg. On oral administration, the absolute bioavailabilities of cefatrizine were 75% at 250 and 500 mg and 50% at 1,000 mg. The mean peak plasma concentrations and peak times were, respectively, 4.9, 8.6, and 10.2 micrograms/ml at 1.4, 1.6, and 2.0 h, mean residence times were 2.4, 2.6, and 3.1 h, and mean absorption times were 1.3, 1.6, and 1.9 h. Oral renal clearance and half-life values corresponded well to the intravenous values. Cumulative urinary excretion of intact cefatrizine (as percentage of dose) was 60 at 250 mg, 56 at 500 mg, and 42 at 1,000 mg. It is hypothesized that the lack of oral dose linearity between the 500- and 1,000-mg doses is due to a component of cefatrizine absorption by a saturable transport process. Relative absorption at the high dose would be sufficiently slow that an absorption "window" would be passed before maximum bioavailability could be attained. It is not expected that the observed bioavailability decrease at doses exceeding 500 mg will have any therapeutic significance, since clinical studies are establishing efficacy for a recommended unit dosage regimen of 500 mg.

Administration, Oral↗
PubMed1982

Pharmacokinetics of intramuscular ceforanide in infants, children, and adolescents.

We studied the pharmacokinetics of intramuscular ceforanide in 46 infants, children, and adolescents, ranging in age from 1 month to 17 years. After the subjects were given 20-mg doses of ceforanide per kg, the mean peak plasma concentration was 56.3 microgram/ml (range, 27.0 to 95.0), the mean 8-h level was 5.9 microgram/ml (range, 1.5 to 13.5), and the mean 12-h level was 1.5 microgram/ml (range, 0.2 to 4.2). Ceforanide half-life varied with the ages of the patients: in 1- to 2-year-old children, in half-life was significantly shorter (1.5 h) than in younger or older children. Plasma concentrations at 8 and 12 h after a dose were lowest in 1- to 2-year-old children. There was no relationship between the area under the curve, the volume of distribution, or the body clearance of ceforanide to the ages of the patients. Within 6 h of administration of the drug, a mean of 77.5% of a dose was excreted in urine, and at the end of 12 h, virtually all (93.9%) of the administered dose was recovered in urine samples. The administration of ceforanide every 12 h did not result in drug accumulation. A dose of 20 mg of ceforanide per kg every 12 h is recommended for most pediatric patients. Dosage recommendations for 1- to 2 year-old children are presented.

Adolescent↗
PubMed1982

Pharmacokinetics of cefadroxil after oral administration in humans.

The human oral pharmacokinetics of cefadroxil were studied in parallel at doses of 250, 500, and 1,000 mg in three groups of 10 healthy young male volunteers. Renal excretion of intact cefadroxil, accounted for 82, 79, and 77% of the above doses. Mean peak serum levels were dose linear: 9, 18, and 35 microgram/ml at 250, 500, and 1,000 mg, respectively. However, overall pharmacokinetics were linear only in the 250- to 500-mg dose range; apparent serum clearances were 10 liters/h, and true renal clearances were 9 and 8 liters/h at 250 and 500 mg. At 1,000 mg, apparent serum clearance dropped to about 7 liters/h, true renal clearance, dropped to 6 liters/h, and the area under the curve increased disproportionately. At 250 and 500 mg, mean half-life was about 1.2 h; at 1,000 mg, however, it was 1.6h. The nonlinear decrease in clearance could be related to saturation of active renal tubular secretion of cefadroxil between the 500- and 1,000-mg doses. Previous results indicating that cefadroxil has greater persistence than other oral cephalosporins such as cephalexin, cephradine, cefaclor were confirmed.

Administration, Oral↗
PubMed1982

Pharmacokinetics of ceforanide.

The pharmacokinetic of ceforanide, a new parenteral cephalosporin antibiotic, were examined at intravenous and intramuscular doses of 250, 500, and 1,000 mg in healthy male volunteers. Over the above dosing range, ceforanide pharmacokinetics were essentially linear, with plasma clearances varying from 2.2 to 2.5 liters/h. The best present overall estimate of the drug's half-life was 2.9 h. Intramuscular ceforanide was 100% bioavailable, Peak intravenous serum levels were 39, 71, and 135 micrograms/ml at the end of 30-min infusions of 250, 500, and 1,000 mg; after intramuscular injections of 250, 500, and 1,000 mg, the respective peak serum levels were 21, 38, and 69 micrograms/ml. From 80 to 85% of the above doses were eliminated as unchanged.

Biological Availability↗
PubMed1981

Effect of dosing volume on intramuscular absorption rate of aminoglycosides.

The Loo-Riegelman method was applied to serum amikacin level data after intravenous and intramuscular administration. Intramuscular amikacin absorption can be described by first-order kinetics, but the absorption rate constant decreased from 1.95 hr-1 at a 125-mg dose to 1.00 hr-1 at a 750-mg dose. This rate change apparently is a physical phenomenon due to differing dosing volumes at different doses and attendant changes in the surface area to volume ratio at the injection site. Amikacin absorption rates on intramuscular injection can be maximized by giving several smaller injections rather than a single larger injection. This phenomenon should be generally observed with aminoglycoside antibiotics and could be partly responsible for reported variations in the absorption rate and the poor predictability of serum concentrations.

Absorption↗
PubMed1981

Ceforanide kinetics in renal insufficiency.

Ceforanide (500 mg) was infused intravenously over 30 min into six normal subjects, 10 nondialysis patients with renal insufficiency, and six hemodialysis patients. Dialysis patients received two ceforanide infusions, one immediately before dialysis and another during an interdialysis period. Sequential plasma samples over 24 to 72 hr were assayed for ceforanide. Peak ceforanide levels (mean = 69 +/- 12 micrograms/ml) and volumes of distribution did not vary with creatinine clearance (Clcr, ml/min/1.73 m2) and both plasma clearance and renal clearance decreased linearly as Clcr decreased. Mean nonrenal clearance (4.6 +/- 1.8 ml/min/1.73 m2) did not vary with Clcr. Mean half-life was 3 hr in the normal subjects, increasing to approximately 25 hr in patients with severe renal insufficiency. Hemodialysis resulted in a removal of approximately 21% of the dose of ceforanide. Dosing recommendations for patients with renal insufficiency are provided.

Adult↗
PubMed1981

Human pharmacokinetics and disposition of sarmoxicillin, a lipophilic amoxicillin prodrug.

Sarmoxicillin, an amoxicillin prodrug, is the methoxymethyl ester of hetamoxicillin. Esterification converted amoxicillin from an amphoteric to a cationic compound and resulted in a 30- to 600-fold increase in lipid partitioning. Oral absorption studies in normal subjects demonstrated that sarmoxicillin was only partially hydrolyzed by nonenzymatic and gut or hepatic first-pass metabolism and that significant quantities of intact ester appeared in the systemic circulation. Sarmoxicillin was converted to amoxicillin in plasma by hydrolysis of the acetone penicinate and the methoxymethyl ester bonds. Significant amoxicillin levels were demonstrated in saliva after administration of sarmoxicillin, but not amoxicillin, over a 250- to 1,000-mg dose range. Differences in the absorption, distribution, or metabolism of amoxicillin were also evident in the lower plasma amoxicillin maximum concentration and area under the curve and longer half-life after sarmoxicillin administration. Differences in the distribution of this lipophilic ester could result in a significant increase in tissue penetration and subsequent therapeutic efficacy of amoxicillin when administered as sarmoxicillin.

Amoxicillin↗