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Biomedical subjects

K Chan

Publications and source records attributed to K Chan.

At least 271 records · Page 15Linked to original sources
PubMed1980

Kinetics and metabolism of intramuscular neostigmine in myasthenia gravis.

Neostigmine kinetics and metabolism were studied after intracellular administration to 8 patients with myasthenia gravis. The plasma neostigmine level declined monoexponentially from 21 +/- 2 to 9 +/- 1 ng/ml between 30 and 120 min. The data were interpreted in terms of a 1-compartment model. Estimates of plasma half-life (t1/2) ranged from 51.1 to 90.5 min; apparent volume of distribution varied from 32.0 to 60.6 1; and total body clearance from 434 to 549 ml/min. Approximately 80% of the drug was eliminated in urine within 24 hr either as unchanged neostigmine or its metabolites. Approximately 50% of the dose was eliminated as the unchanged drug, 15% as 3-hydroxyphenyltrimethylammonium, and 15% as other unidentified metabolites. The neostigmine t1/2, based on the urinary excretion of the unchanged drug, ranged from 90.2 to 118.7 min. It was concluded that neostigmine was eliminated by renal and extrarenal mechanisms.

Half-Life↗
PubMed1980

Plasma concentration and metabolism of phenoperidine in man.

The plasma concentrations of phenoperidine were measured in five patients during general anaesthesia. The concentration of the drug decreased rapidly between 2 and 40 min and then declined more slowly. Detectable concentrations of phenoperidine were present in plasma for at least 3 h. In the five patients, the distribution half-life of the drug ranged from 3.19 to 14.23 min and the elimination half-life from 47.31 to 162.30 min. Unchanged phenoperidine and two identified metabolites (pethidine and norpethidine) were present in urine.

Adjuvants, Anesthesia↗
PubMed1980

The simultaneous monitoring of plasma levels of neostigmine and pyridostigmine in man.

The synthesis of a series of pyridostigmine analogues wa reported. From these analogues N,N-dipropylcarbamoyloxy-1-methylpyridinium bromide was considered the most suitable compound for use as a common internal marker for the simultaneous determination of neostigmine and pyridostigmine in human plasma. The assay involved a preliminary ion-pair extraction of the drugs and the internal marker from plasma using potassium-iodide glycine buffer. The extract was analysed by a GC system (10% OV-17 on chromosorb W-AW, 100-120 mesh) linked to a nitrogensensitive detector. The calibration graphs of neostigmine and pyridostigmine were linear and reproducible over the range 5 ng to 100 ng per ml in 3 ml plasma samples. This assay procedure has been used to monitor simultaneously the plasma levels of neostigmine (4.7 to 33 ng per ml) and pyridostigmine (2.7 to 18.6 ng per ml) of a myasthenic patient over a period of twelve hours with repeated dosing of neostigmine bromide (30 mg) and pyridostigmine bromide (60 mg).

Biotransformation↗
PubMed1980

The effect of indomethacin on renal function in man.

Twenty-one patients with rheumatoid arthritis were given indomethacin 25 mg t.i.d. by mouth for 3 weeks followed by indomethacin 25 mg t.i.d. plus a 100 mg suppository at night, after a 5-day period on placebo capsules. The mean (+/- S.E.) 24-hour creatinine clearance was 57.8 +/- 5.7 ml/min in the placebo period and was not significantly altered during indomethacin therapy, 53.1 +/- 5.5 ml/min in the oral period and 56.6 +/- 6.4 ml/min in the oral plus suppository period (P greater than 0.1). In 6 volunteers, duplicate 2-hour creatinine clearances were performed after a single oral dose of 50 mg indomethacin. After placebo capsules the mean creatinine clearance was 133.7 +/- 9.5 ml/min and after 50 mg indomethacin it was 126.5 +/- 8.9 ml/min (P greater than 0.1). In 4 of the volunteers the mean creatinine clearance after 8 days on indomethacin 25 mg q.i.d. was 117.1+/- 5.3 ml/min (P greater than 0.1). Indomethacin plasma concentrations were in the usual range for the dose given. Indomethacin caused no reduction in the creatinine clearance in spite of causing significant inhibition of prostaglandin E synthesis.

Administration, Oral↗
PubMed1979

Pharmacokinetics and pharmacological effects of neostigmine in man.

1 The pharmacokinetics of neostigmine was studied in six patients during the reversal of neuromuscular block induced by tubocurarine chloride. The effect of the drug on neuromuscular function was simultaneously assessed by electromyography. 2 Neostigmine was rapidly eliminated from plasma after intravenous administration. The decline in the plasma concentration of the drug was invariably resolved into two exponential components. The fast disposition (distribution) half-life of the drug was invariably less than 1 min; the slow disposition (elimination) half-life ranged from 15.4--31.7 min. 3 Neostigmine usually increased the amplitude of the compound muscle action potential and diminished electromyographic decrement within 2 min of intravenous injection. The pharmacological effect of neostigmine was usually maximal between 7 and 15 min. There was an inverse relationship between the plasma concentration of the drug and the facilitation of neuromuscular transmission. 4 Red cell acetylcholinesterase activity was almost completely inhibited within 2--3 min of intravenous injection of neostigmine. Enzyme activity recovered to approximately 28% of control values by 30 min and to 55% by 60 min.

Acetylcholinesterase↗
PubMed1979

The effects of physiocochemical properties of pethidine and its basic metabolites on their buccal absorption and renal elimination.

The pKa values, RF values, partition coefficients between n-heptane and phosphate buffer (pH = 7.4), and buccal absorption tests of pethidine and its basic metabolites, norpethidine and pethidine N-oxide, have been determined. The amounts of these compounds recovered in the 48 h urine samples after intramuscular administration of pethidine (1.5 mg kg-1) to six healthy subjects varies with urinary pH values: the recovery from acidic urine (pH 5.0) is 15.2 to 52.0%, 6.7 to 12.9% and 0.2 to 2.3% of dose for pethidine, norpethidine and pethidine N-oxide respectively; in alkaline urine (pH 8.0) the values are 0.8 to 1.8%, 0.6 to 2.8% and 0.3 to 2.1% respectively. The physicochemical properties (pKa values, RF values, partition coefficients) and buccal absorption of pethidine, norpethidine and pethidine N-oxide are in good agreement with the pattern of their renal elimination in acidic and alkaline urine conditions. The contribution of the physiocochemical properties of pethidine and its metabolites to the drug's disposition in the body and the effect of urinary pH on its metabolism should be taken into account in pharmacokinetic studies and interpretation of intersubject variation in response to pethidine.

Absorption↗
PubMed1979

Nutrition and growth of the moderately halophilic bacteria Micrococcus morrhuae K-17 and Micrococcus luteus K-15.

Chemically defined media have been developed for the growth of two moderately halophilic bacteria, Micrococcus morrhuae K-17 and Micrococcus luteus K-15. M. morrhuae K-17 grows well in a synthetic medium (SM-1) which contains a number of salts, 0.21 M KCl, 2 M NaCl, D-mannose, five vitamins and ten amino acids. The synthetic medium (SM-2) for M. luteus K-15 contains a number of salts, 0.21 M KCl, 1 M NaCl, D-fructose, nine vitamins and nine amino acids. Nutritional studies show that M. morrhuae K-17 can utilize a large number of organic compounds as carbon and energy source while the ability of M. luteus K-15 in utilizing the organic compounds is rather limited. The minimum salt requirement is 0.5 M NaCl for both strains when growth at the optimum temperature of 30 degrees C. However, this requirement can be lowered to 0.2 M in M. luteus K-15 when grown at a lower temperature of 25 degrees C. It is concluded that the ability to grow in a wider range of salt concentrations in response to temperature is species specific in moderate halophiles. The salt range for growth to occur can be extended when cells of both strains are grown in complex medium which might provide the amino acids and growth factors that cannot be synthesized by these strains at high salt concentrations.

Amino Acids↗
PubMed1978

Quantitative gas-liquid chromatographic method for the determination of indomethacin in biological fluids.

A sensitive and specific gas chromatographic method for the analysis of indomethacin has been developed. After extraction of the drug from blood or urine with ethylene dichrloride a derivative is formed with pentafluorobenzyl bromide. 5-Fluoro-indomethacin is used as an internal standard. The overall recovery of indomethacin is 85.1 +/- 2.3% and the method can detect 10 ng indomethacin in a 1 ml plasma or urine sample. No interference in the method is seen with some commonly used drugs. The method has been used to measure plasma indomethacin concentrations in 20 patients with rheumatoid arthritis, being treated with 25 mg indomethacin three times daily. The plasma concentration ranged from 168-596 ng/ml.

Animals↗
PubMed1978

Clearance of neostigmine from the circulation during the antagonism of neuromuscular block.

The plasma concentration of neostigmine was measured in five patients during the antagonism of neuromuscular block. The concentration of the drug decreased rapidly between 2 and 5 min after administration, and then more slowly. Detectable concentrations of neostigmine were present in plasma after 60 min. In the five patients the distribution half-life of neostigmine was less than 1 min; the elimination half-life ranged from 15.4 to 30.1 min.

Adult↗
PubMed1978

Plasma clearance of neostigmine and pyridostigmine in the dog.

1 The pharmacokinetics of neostigmine and pyridostigmine was studied in conscious dogs by the use of a cross-over design. 2 Both neostigmine and pyridostigmine were cleared from plasma in a biexponential manner. 3 The apparent volume of distribution of pyridostigmine was invariably greater than that of neostigmine, and its fast disposition half-life was approximately three times longer. 4 The whole body clearance and the urinary elimination of pyridostigmine was approximately twice that of neostigmine. 5 The slow disposition half-life of pyridostigmine was approximately three times longer than that of neostigmine, suggesting that the longer duration of action of pyridostigmine is related to the differential clearance of the two quarternary amines from plasma.

Animals↗
PubMed1977

Plasma pyridostigmine levels in patients with myasthenia gravis.

Plasma concentrations of pyridostigmine were measured in 7 patients with myasthenia gravis. Six subjects on oral pyridostigmine bromide were stabilized on widely different doses of the drug (60 to 660 mg/day). Nevertheless, the concentration of the quaternary amine in plasma was maintained within a relatively narrow range (usually between 20 and 60 ng/ml). In 3 myasthenic patients, the area under the plasma concentration-time curve was relatively constant for 4 hr after the same oral dose of pyridostigmine (60 mg). Despite this similarity, there were in general considerable interindividual differences in the bioavailability of pyridostigmine in myasthenic patients. In 1 subject, the bioavailability of the quaternary amine was increased sixfold by doubling the oral dose from 30 mg to 60 mg. After oral administration of pyridostigmine, the half-life of the drug in one subject (4.25 hr) was almost three times as great as after intramuscular administration in a different patient (1.49 hr).

Administration, Oral↗