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Biomedical subjects

D J Back

Publications and source records attributed to D J Back.

At least 199 records · Page 11Linked to original sources
PubMed1982

The gut wall metabolism of ethinyloestradiol and its contribution to the pre-systemic metabolism of ethinyloestradiol in humans.

1 Five patients have been studied to determine the contribution of the gut wall to the pre-systemic metabolism of ethinyloestradiol. All patients had a catheter inserted into their hepatic portal vein as part of their surgical management. 2 After an oral dose of 50 micrograms (65 microCi) ethinyloestradiol, blood samples were taken from the hepatic portal vein and from a peripheral vein at intervals for 1 h. 3 In each patient the concentration of conjugated ethinyloestradiol in the portal vein was considerably higher than in the peripheral vein. 4 Although a number of assumptions have been made, calculations showed that the gut wall appeared to be twice as effective as the liver in conjugating ethinyloestradiol on the first pass. 5 In two patients there was no evidence of major uptake or metabolism of ethinyloestradiol in the lung.

Aged↗
PubMed1982

The effects of ampicillin on oral contraceptive steroids in women.

1 Thirteen women taking long term oral contraceptive steroids were studied while taking ampicillin (500 mg three times daily) and compared to a control cycle while not taking ampicillin. 2 There were no significant changes in the plasma concentrations of ethinyloestradiol, levonorgestrel, follicle stimulating hormone or progesterone, although lower concentrations of ethinyloestradiol were noted in two women. 3 We conclude that most patients taking oral contraceptive steroids do not need to take alternative contraceptive precautions while taking ampicillin.

Adult↗
PubMed1981

Oral contraceptive steroid plasma concentrations in smokers and non-smokers.

A study was performed to find out whether the overall rate of metabolism of oral contraceptives is affected by smoking and whether this explains the increased incidence of cardiovascular disease in users of oral contraceptives who smoke. Plasma ethinyloestradiol and norgestrel concentrations in 311 women using oral contraceptives were similar in smokers and non-smokers. The overall rate of metabolism of contraceptive steroids does not therefore seem to be affected by cigarette smoking.

Adult↗
PubMed1981

The pharmacokinetics of levonorgestrel and ethynylestradiol in women - studies with Ovran and Ovranette.

A radioimmunoassay for levonorgestrel (Ng), which is applicable to plasma samples obtained from women who have taken a combination type oral contraceptive, has been developed and fully validated. Plasma concentrations of Ng rise to a peak of 3.6 ng/ml after an oral dose of 150 microgram and to 5.0 ng/ml after a 250 microgram dose. Following the intravenous administration of Ng, plasma concentrations of the steroid decline bi-exponentially with mean half-lives of 0.76 and 11.55 hours. Comparison of the results of the intravenous and oral administration of the steroid show a mean systemic bioavailability of 89% after the 150 microgram dose and 99% after a 250 microgram dose. This difference was not statistically significant. The values for volume of distribution were approximately half and the values for plasma clearance three times less than that previously reported for norethindrone. The plasma ethynylestradiol levels were also measured following administration of 30 microgram both intravenously and orally. The bioavailability and kinetics were similar to that previously reported for a 50 microgram dose. The peak values after oral dosing were 103 pg/ml and were reached by 1.0 hour in all subjects.

Adult↗
PubMed1981

Studies on the enzymatic cleavage of norethisterone oenanthate.

Norethisterone oenanthate (NET OEN) was extensively hydrolysed in rabbit, rat and guinea pig plasma (99.9%, 76.1% and 46.0% hydrolysed in 90 min, respectively). In contrast, there was negligible hydrolysis (less than 2.5%) in dog, goat and human plasma. Rabbit liver, kidney, gut wall, stomach, heart and muscle showed marked hydrolytic activity in vitro, but there was little hydrolysis of NET OEN by either human muscle or fat. It is proposed that following intramuscular administration of NET OEN to rabbits, the ester is rapidly hydrolysed at the injection site and in the circulation whereas in humans the liver is the main site of hydrolysis since neither muscle nor plasma cause significant breakdown of the ester. The rabbit is not a good model for predicting the pharmacokinetics of NET OEN in humans.

Adipose Tissue↗
PubMed1981

The in vitro metabolism of ethinyloestradiol, mestranol and levonorgestrel by human jejunal mucosa.

1 Ethinyloestradiol was extensively metabolised in vitro by human jejunal mucosa to form ethinyloestradiol sulphate. 2 The amount of conjugation was directly related to the weight of biopsy tissue. 3 The degree of conjugation of mestranol and levonorgestrel was much lower than for ethinyloestradiol suggesting that the 17-position of the steroid nucleus is relatively inaccessible for conjugation. 4 No Phase I metabolism of ethinyloestradiol or levonorgestrel was apparent in the conditions used in these experiments.

Adult↗
PubMed1981

Interindividual variation and drug interactions with hormonal steroid contraceptives.

Large interindividual differences occur in the plasma concentration of contraceptive steroids. With the present tendency to decrease the dose of progestagen and oestrogen any factor which reduces the bioavailability of the lower dose preparations becomes very important. The possibility that other drugs and environmental chemicals may interact with contraceptive steroids is currently being investigated. Clinical reports suggest that the most important interacting drugs are the antituberculosis agent rifampicin, anticonvulsants and antibiotics. In the case of the first two, evidence is available suggesting that microsomal enzyme induction, either in the liver or the gut wall, is the operative mechanism. Antibiotics interfere with the pharmacokinetics of contraceptive steroids by interfering with their enterohepatic circulation in animal species: whether this is operative in man is still unclear. Other environmental and constitutional factors such as smoking, variations in diet, and concurrent disease may alter the disposition of contraceptive steroids and affect response accordingly. Additional studies are needed to estimate the significance of such interactions.

Anti-Bacterial Agents↗
PubMed1980

Influence of environmental chemicals on drug therapy in humans: studies with contraceptive steroids.

The effects have been studied of various environmental factors on the variability in response to oral contraceptive steroid therapy in women. Ten- to thirty-fold variations in plasma concentrations of norethisterone, L-norgestrel and ethinyloestradiol have been shown in samples taken 12 h after administration of oral contraceptives in mid-menstrual cycle. Factors shown to be responsible for this variation include passage into the enterohepatic circulation, a variable first-pass effect, and changes in metabolism in the gut wall or liver due to diet, disease, smoking or administration of drugs. Phenobarbitone and the antibiotic rifampicin increase both oestrogen and progestogen metabolism in women and in experimental animals by increasing hepatic and gut wall metabolism. In animals, other antibiotics (ampicillin, neomycin and lincomycin) suppress the gut flora that normally hydrolyse steroid conjugates excreted in bile; enterohepatic circulation or oral contraceptive steroids is thus reduced and their plasma concentrations lowered by up to 90%. In the human, ampicillin has a variable but less dramatic effect on elimination of oral contraceptives. Samples of gut wall mucosa obtained from patients with coeliac disease are defective in their ability to metabolize oral contraceptives. Cigarette smokers eliminate ethinyloestradiol more rapidly than non-smokers; an increased production of reactive steroid metabolites may thus be a cause of vascular disease in women who smoke and take contraceptive steroids.

Animals↗
PubMed1980

The interaction of phenobarbital and other anticonvulsants with oral contraceptive steroid therapy.

In a group of 5 women on long-term anticonvulsant and oral contraceptive therapy, the plasma ethynylestradiol (EE) concentration on 50 microgram EE daily was 11.1 +/- 4.5 pg/ml. These values were at the lower end of the range found in normal women in this laboratory taking 30 microgram EE daily (6-190 pg/ml). Four women have been studied prospectively for 3 months, over 1 cycle before and 2 cycles during phenobarbital 30 mg b.i.d. therapy. Significant falls in the plasma EE concentration were seen in two women (from 104.8 +/- 13.4 to 37.7 +/- 2.0 pg/ml and from 125.6 +/- 23.8 to 34.8 +/- 6.7 pg/ml p less than 0.01) and breakthrough bleeding was seen in both women. No changes in plasma concentrations of follicle stimulating hormone, progesterone, norethindrone or norgestrel were seen. There was a significant increase in the sex hormone binding globulin capacity from 100.7 +/- 5.8 to 133.3 +/- 1.2 nmoles/1 (p less than 0.05). These changes are consistent with the known microsomal enzyme inducing effect of phenobarbital.

Adolescent↗
PubMed1980

The effect of rifampicin on the pharmacokinetics of ethynylestradiol in women.

A single dose of Minovlar (50 microgram ethynylestradiol (EE) and 1 mg norethindrone acetate) was given to seven women during treatment with rifampicin (450-600 mg/day) and again one month after stopping rifampicin. Blood samples were taken at intervals over a 24-hour period. The area under the plasma EE versus time curve increased significantly on stopping rifampicin from 1014 +/- 317 pg/ml x h (mean +/- SE) to 1747 +/- 218 pg/ml x h (p less than 0.01). The terminal plasma half-life increased from 2.9 +/- 0.8 h to 6.3 +/- 1.4 h (p less than 0.005). The sex hormone binding globulin (S.H.B.G.) capacity was also reduced from 213.4 +/- 11.5 nmoles to 129.0 +/- 7.7 nmoles/1 after stopping rifampicin. In one patient starting rifampicin who was taking Minovlar as a long-term oral contraceptive, a fall in the plasma EE concentration was associated with a rise in the plasma follicle stimulating hormone concentration. These effects of rifampicin on EE pharmacokinetics are consistent with induction of the microsomal enzymes that metabolise EE.

Adolescent↗
PubMed1980

The pharmacokinetics of a large (3 mg) oral dose of ethynylestradiol in women.

Plasma levels of ethynylestradiol (EE), EE sulphate (EES), EE glucuronide (EEG) and prolactin were measured in women up to 72 h following the oral administration of 3 mg of EE. The decline in plasma EE levels showed a sharp discontinuity at 10 h which is assumed to be due to the beginning of enterohepatic circulation (EHC). After this event, an apparently terminal monoexponential decline was eventually established with a half-life of 13.1 h. As a result of EHC, the volume of distribution was increased by 60% to 6.0 1.Kg-1 but it does not appear that any significant accumulation of EE would occur during multiple dosing. Plasma levels of EES were, on average, 22.5 times greater than those of EE and this circulating metabolite may act as a reservoir of EE. No circulating EEG could be detected. Comparing these results with those previously obtained with 50 microgram EE, there was no evidence of dose dependency in the pharmacokinetics of this steroid. Plasma prolactin levels were markedly enhanced by this single dose of oestrogen.

Adult↗