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Biomedical subjects

D J Morgan

Publications and source records attributed to D J Morgan.

At least 199 records · Page 11Linked to original sources
PubMed1980

The effect of infusion time on the time course of drug concentration in blood.

We have studied by digital computer stimulation the relationship among the rate of intravenous infusion of the dose of a drug, the pharmacokinetic parameters of the drug, the maximum blood drug concentration achieved (Cmax) and the interval (TEff) during which the blood concentration of the drug is maintained above a selected minimum effective concentration (CEff) for the case of single dose administration of a drug with monoexponential pharmacokinetics. It was found that increasing the time during which the dose of the drug is infused results in a much smaller decrease in the maximum blood concentration attained. TEff, was found to be a fraction of the ratios infusion time/drug elimination half-life and zero-time intercept (Co)/CEff. The stimulations showed that TEff varies nonlinearly with increasing infusion time. However, the nature of the relationship between TEff and infusion time depends very much on the value of Co/CEff. At low values of Co/CEff, TEff decreased almost linearly with increasing infusion time, but at higher values of Co/CEff, TEff increased for a time with increasing infusion time. From these simulations, it should be possible to predict whether therapeutically effective blood concentrations of a drug may be achieved with the use of a slower infusion in situations where clinical considerations necessitate that the infusion time of the dose be increased.

Computers↗
PubMed1980

Evaluation of slow infusions of co-trimoxazole by using predictive pharmacokinetics.

Digital computer simulations of plasma concentration-time profiles of single intravenous infusions of trimethoprim (160 mg)/sulfamethoxazole (800 mg) based on data from other workers showed that increasing the infusion period from the hitherto generally recommended 1 to 1.5 h to 6 h did not significantly affect the interval (approximately 10 h and 8.5 h, respectively) during which trimethoprim and sulfamethoxazole plasma concentrations were maintained above their minimum effective plasma concentrations (selected as 0.6 microgram/ml and 25 microgram/ml, respectively). For the 6-h infusion, the simulated peak plasma concentration of trimethoprim was only approximately 27% less than for the 1-h infusion, and that for sulfamethoxazole was approximately 30% less. The validity of these predictions was confirmed by plasma concentration measurements of trimethoprim and sulfamethoxazole in six patients undergoing gynecological surgery, who received co-trimoxazole (160 mg of trimethoprim, 800 mg of sulfamethoxazole) postoperatively by constant-rate intravenous infusion over a 4-h period. It is concluded that infusions of the dose of intravenous co-trimoxazole over periods from 1 to at least 6 h are therapeutically equivalent.

Adult↗
PubMed1979

Occult aortic stenosis as cause of intractable heart failure.

During a three-year period 10 patients with critical aortic stenosis were referred to a cardiac referral centre with symptoms and signs of intractable cardiac failure and low cardiac output. In nine patients the correct diagnosis was not suspected at the referring hospital, and in the remaining patient the true severity of the aortic stenosis was not appreciated and cardiomyopathy was suggested as an additional diagnosis. The most common referral diagnoses were severe mitral regurgitation (four patients), congestive cardiomyopathy (two patients), or both (three patients). Only two patients had soft ejection systolic murmurs at the base of the heart radiating into the neck, and such a murmur appeared in a third patient during medical treatment. The carotid pulses were of small volume but the characteristic slow-rising, anacrotic nature of the pulse could not be appreciated clinically. The diagnosis was suspected in nine patients because of aortic valve calcification detected by lateral chest x-ray examination in seven patients and by x-ray screening of the heart in two, and because of abnormal aortic valve echoes in the echocardiogram of all five patients in whom the aortic valve could be seen. Eight patients underwent aortic valve replacement despite seemingly poor preoperative left ventricular function. Three patients died, of whom two had severe coexistent coronary artery disease. The five survivors all returned to normal lives and needed little or no medication.Critical aortic stenosis should be actively sought in patients with severe heart failure of unknown cause since surgery may enable them to resume their normal lives.

Aged↗
PubMed1979

Pharmacokinetics and pharmacodynamic studies of labetalol in hypertensive subjects.

1 The pharmacokinetics of labetalol were studied in twelve hypertensive patients, ten of whom were not receiving other therapy. 2 Following intravenous administration there was a three- to fourfold variation in terminal elimination half-life, volume of distribution and total plasma clearance. The mean elimination half-life was 3.25 hours. 3 Following oral administration the drug was absorbed rapidly. Systemic availability varied from 11-86% (mean 33%). 4 Plasma levels correlated poorly with the acute effect on BP, raising the possibility of labetalol acting in a deep tissue compartment or alternatively an active metabolite contributing to its effect.

Administration, Oral↗
PubMed1977

Cyclic metabolites of etidocaine in humans.

1. Three cyclic metabolites of etidocaine excreted in urine of man have been investigated by g.l.c.-mass spectrometry. 2. These metabolites have been identified as 3-(2,6-dimethylphenyl)-5-ethyl-2,4-imidazolidinedione, 1-(2,6-dimethylphenyl)-2-methyl-4-ethyl-2-imidazolin-5-one and 1-(2,6-dimethylphenyl)-2,4-diethyl-2-imidazoline-5-one. 3. Formation in vivo of two of the metabolites is proposed to proceed via carbinolamine intermediates.

Acetanilides↗
PubMed1975

The effect of sampling technique on some blood parameters in the rat.

When used to restrain rats while obtaining cardiac blood, there was little difference between the effects of ether, pentobarbitone sodium, and fentanyl plus droperidol on acid-base balance, haemoglobin, haematocrit, plasma protein, calcium and magnesium. The use of manual restraint increased blood acidity, plasma protein, calcium and magnesium, but decreased blood glucose. Haemoglobin and haematocrit values were higher for tail blood than for blood removed from the heart or abdominal aorta.

Anesthesia↗
PubMed1975

The effect of sampling technique on acid-base balance and other blood parameters in the sheep.

The effect of 4 sampling routines--venipuncture, intravenous cannula, intravenous cannula following the administration of a tranquiliser (xylidino dihydrothiazine hydrochloride), intravenous cannula following exercise--were compared. Blood pH and base excess values were similar after venipuncture and cannula sampling, but higher (P less than 0 with 05) after the administration of the tranquiliser and lower (P less than 3 with 05) following exercise. Blood haemoglobin, haematocrit and lactate levels followed this pattern, while plasma protein levels were similar for all treatments except after exercise, where they were higher (P less than 0 with 05). The recovery of various blood parameters to normal values after a period of exercise was also studied: acid-base balance had returned to near normal within 60 min, while haemoglobin and haematocrit levels had returned to normal within 10 min.

Acid-Base Equilibrium↗