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Biomedical subjects

M Rowland

Publications and source records attributed to M Rowland.

At least 235 records · Page 13Linked to original sources
PubMed1977

Influence of acute viral hepatitis on disposition and plasma binding of tolbutamide.

To study the influence of acute hepatic disease on the disposition of tolbutamide, we measured tolbutamide plasma protein binding and pharmacokinetic parameters after intravenous administration of the drug to 5 subjects during and after apparent recovery from acute viral hepatitis. Although during the acute phase of illness protein binding of the drug decreased in all, volume of distribution of tolbutamide (0.15 +/- 0.03 L/kg) did not change. Clearance based on total concentration of tolbutamide in plasma increased in all subjects during the acute phase of study (26 +/- 5.4 ml/hr/kg) in comparison to the recovery phase (18 +/- 2.8 ml/hr/kg, p less than 0.02). Protein binding decreased after unconjugated bilirubin was added to plasma from the recovery phase, but not to the extent observed during the acute phase of illness at comparable levels of bilirubin. Clearance based on unbound drug concentration, calculated by dividing the observed plasma clearance by the fraction of unbound drug in plasma, did not differ significantly between the 2 study phases (300 +/- 47 and 260 +/- 39 ml/hr/kg). These observations suggest that the increase in clearance based on total drug concentration in plasma during hepatitis can be attributed solely to decreased plasma binding. This decrease in binding may be attributed in part, but not entirely, to increased combination of bilirubin during illness. The concentration of unbound drug in plasma at steady-state is determined by the rate of drug administration and the clearance based on unbound drug. If this clearance does not change during hepatic disease, no dosage alterations for tolbutamide and other comparable drugs are necessary to maintain a constant concentration of unbound drug.

Acute Disease↗
PubMed1977

Application of salivary concentration data to pharmacokinetic studies with antipyrine.

The concentrations of antipyrine in plasma and saliva were equivalent in normal volunteers and in patients with acute viral hepatitis following oral doses of antipyrine. Estimates of clearance, volume of distribution, and half-life made from either plasma or saliva samples were not statistically different in these subjects. Differences in the disposition kinetics of anticted using either plasma or saliva samples.

Acute Disease↗
PubMed1977

Kinetics of drug-drug interactions in sheep: tolbutamide and sulfadimethoxine.

The interaction between sulfadimethoxine and tolbutamide in sheep involving displacement from protein binding sites was investigated quantitatively. A 52% increase in the unbound plasma concentration of tolbutamide was observed in vitro at 37 degrees after the addition of sulfadimethoxine (100 microgram/ml) to sheep plasma containing tolbutamide (50 microgram/ml). Transient changes in tolbutamide's unbound and total plasma concentrations were noted after acute intravenous administration of sulfadimethoxine to sheep receiving a constant intravenous infusion of tolbutamide. These observations were consistent with displacement of tolbutamide from plasma and tissue binding sites and redistribution of the displaced tolbutamide into body water spaces. The steady state of both agents featured little change in the total plasma tolbutamide concentration, a 150% increase in the unbound plasma tolbutamide concentration, and an inhibition of tolbutamide oxidation by sulfadimethoxine. A model is presented and mathematical relationships are derived that permit a quantitation of the interaction and that indicate the sulfadimethoxine's constant of metabolic inhibition (K1) for tolbutamide metabolism is 65 microgram/ml.

Animals↗
PubMed1977

Aspirin.

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Aspirin↗
PubMed1977

Clinical and electrophysiological effects of intravenous quinidine in man.

Quinidine gluconate (total dose 4-4 to 9-1 mg/kg) was infused intravenously over 22 minutes in 20 patients with either frequent premature ventricular contractions or supraventricular arrhythmias, 16 of whom had bundle-branch block. Therapeutic plasma quinidine levels (3 to 7 mg/l) were achieved in 15. Heart rate, atrioventricular nodal, and infranodal conduction times did not change significantly. The QRS duration increased significantly from 128+/-30 to 134+/-29 ms at peak plasma quinidine levels (P less than 0.01). Mild hypotension occurred during infusion in most patients. Two patients had a severe but transient toxic response characterised by hypotension, nausea, vomiting, and diaphoresis. Atrioventricular dissociation with escape His bundle or fascicular rhythm occurred in 1 patient with sinus bradycardia. Bundle-branch block does not contraindicate administration of quinidine. Quinidine gluconate administered intravenously (0-3 to 0-4 mg/kg per min) is frequently associated with hypotenstion and should be used only in an intensive care setting and with careful monitoring of blood pressure.

Arrhythmias, Cardiac↗
PubMed1977

Concentration-time effects of quinidine disposition kinetics in rhesus monkeys.

The effects of dose and duration of drug administration (time) on the disposition kinetics of quinidine were investigated in unanesthetized rhesus monkeys. A specific thin-layer chromatography-fluorometric assay was developed for the determination of quinidine in plasma, blood and urine. After the monkeys receive an i.v. bolus dose of 3 to 7 mg/kg, quinidine distributes rapidly in the body (T 1/2alpha = 2 minutes). The half-life associated with elimination (T 1/2 beta) was 27 to 35 minutes and primarily involved metabolic transformation. The volume of distribution varied between 0.2 and 0.65 liters/kg and total clearance between 4.8 and 13 ml/min/kg. Similar estimates of T 1/2 beta, clearance and volume of distribution were obtained following constant infusions producing steady-state concentrations less than 6 microng/ml. Prolonged infusion of quinidine at rates producing plasma concentrations in the range of 6 to 13 microng/ml resulted in increases in the elimination half-life whereas drug clearance remained constant. This observation suggests an increased volume of distribution. Both concentration and time were demonstrated to be important in producing changes in quinidine disposition kinetics. The precise mechanism underlying this phenomenon remains unanswered.

Animals↗
PubMed1976

Disposition kinetics of quinidine.

The disposition kinetics of quinidine in 12 hospitalized patients in whom oral quinidine therapy was to be initiated is described. Quinidine in doses of 2.6 to 5.2 mg/kg base were infused intravenously over 22 min. Plasma samples were collected during the postinfusion for 24 hr and analyzed by a specific and sensitive assay procedure. In the 12 hr after administration, postinfusion plasma quinidine concentration decay was described by a biexponential equation. Attempts to include the 24-hr data point in the fitting procedures resulted in poorer agreements between the theoretical and experimental curves. A 2-compartment open model is proposed to describe the disposition of quinidine. The volume of the central pool (Vc) and steady-state volume of distribution (Vdss) were 0.91 +/- 0.11 L/kg and 3.03 +/- 0.25 L/kg, respectively, and indicate that quinidine distribution is predominantly extravascular. Quinidine distribution was quite rapid (t1/2alpha = 7.19 +/- 0.70 min), while the apparent elimination half-life (t1/2beta) was considerably longer, 6.333 +/- 0.47 hr. Total body plasma clearance ranged from 1.49 to 7.15 ml/min/kg (mean 4.70) and is primarily associated with nonrenal mechanisms of drug elimination. Urine specimens collected for 48 hr indicated that 17% of the dose is excreted intact and that urinary excretion was essentially complete within 24 hr. Renal clearance (Clr) was 0.80 +/- 0.18 ml/min/kg. The study demonstrated that there is substantial interpatient variability with respect to quinidine disposition.

Adult↗
PubMed1976

Influence of acute viral hepatitis on disposition and pharmacologic effect of warfarin.

Five patients received a small oral dose of warfarin during and after recovery from acute viral hepatitis. Mean (+/- SD) clearance, volume of distribution, and half-life of the drug were 6.1 +/- 0.9 ml/hr/kg, 0.09 +/- 0.04 L/kg, and 23 +/- 5 hr, respectively, during the acute period. After apparent recovery, observed values were 6.1 +/- 0.7 ml/hr/kg, 0.21 +/- 0.02 L/kg, and 25 +/- 3 hr. These differences were not significant. Pattern of renal elimination of warfarin metabolites and drug protein binding did not change between the two phases. During the acute period of illness, prothrombin time increased in 2 of the 5 subjects, but remained within normal limits in all participants during the recovery period. This study shows that warfarin disposition may not change as a consequence of mild or moderate hepatic impairment.

Adult↗
PubMed1976

Influence of viral hepatitis on the disposition of two compounds with high hepatic clearance: lidocaine and indocyanine green.

The disposition of lidocaine and indocyanine green was studied in 6 individuals during and after recovery from an episode of acute viral hepatitis. Both compounds are highly cleared from the blood by the liver so that clearance of both should be sensitive to changes in hepatic blood flow. During the acute phase of illness, clearance of indocyanine green decreased without apparent change in volume of distribution, whereas clearance of lidocaine, decreased in 4, did not change in 1, and increased in 1 during the acute phase of hepatitis. Volume changes for lidocaine were also variable. We observed no significant correlation between any parameters of lidocaine disposition and any of several tests of liver function or any parameters of indocyanine green disposition. The absence of correlation between pharmacokinetic parameters of the disposition of lidocaine and indocyanine green indicates that the influence of hepatic disease on the hepatic processes that lead to the elimination of each compound is not predictable. No useful clinical correlates are now available by means of which to predict lidocaine disposition in patients with altered hepatic function.

Acute Disease↗
PubMed1975

Influence of congestive heart failure on blood vessels of lidocaine and its active monodeethylated metabolite.

The blood concentrations of lidocfaine and its active monodeethylated metabolite, monethylglycinexylidide (MEGX), were measured in 31 patients who were receiving infusiions of lidocaine intravenously. In 3 patients who were studied intensively, the elimination half-life of MEGX was 120 min, which was similar to the elimination half-life of lidocaine (139 min). An addition 3 patients demonstrated a higher ratio of the concentration in blood of MEGX to lidocaine, and the MEGX may have contributed, in 1 patient, to the central nervous system toxicity that occurred during the infusion. Elevated concentrations of MEGX in blood were associated with congestive heart failure (r equalto 0.5, p equal to 0.004). Our data suggest that the elimination of MEGX may be decreased in patients with depressed cardiac output and sympathomimetic compensation.

Adult↗