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Biomedical subjects

D N Robertson

Publications and source records attributed to D N Robertson.

At least 37 records · Page 2Linked to original sources
PubMed1985

Cholesterol and HDL-cholesterol values in women during use of subdermal implants releasing levonorgestrel.

Plasma concentrations of cholesterol, HDL-cholesterol, and levonorgestrel were determined in two groups of women using levonorgestrel-releasing subdermal implants. One group used six capsules (NORPLANT)*; the other six covered rods. Plasma concentrations of levonorgestrel among NORPLANT users averaged 700 pg/ml in the first two weeks of use, decreased to 300 pg/ml at 8 weeks, and to about 230 pg/ml by 50 weeks. Concentrations among covered rod users were 1.4 to 1.7 times higher at comparable time periods. Total serum cholesterol and HDL-cholesterol were decreased as compared with controls at all sampling intervals during the 114 weeks of the trial, although the differences did not meet tests of significance at all time periods. Decreases during the test period were of the order of 10 percent, except for total cholesterol among covered rod users where the decrease was less. Cholesterol to HDL-cholesterol ratios did not differ significantly from control values at any sampling period.

Adult↗
PubMed1984

Long-term reversible contraception with levonorgestrel-releasing Silastic rods.

Subcutaneously placed Silastic capsules containing levonorgestrel are effective for 5 years and have a higher continuation rate than other methods of reversible contraception. Six 3 cm capsules are required to achieve satisfactory circulating levels of levonorgestrel. Two 4 cm covered Silastic rods containing levonorgestrel, which are easier to manufacture, insert, and remove than the capsules, produce similar in vitro release rates. This study compared clinical and metabolic effects as well as bleeding patterns in 23 women using either six capsules (n = 11) or two covered rods (n = 12). Serum levels of levonorgestrel, lipids, and lipoproteins as well as frequency of elevated progesterone levels were compared in serum samples obtained before treatment and 1, 6, 12, 18, and 24 months after insertion with the two systems. While bleeding patterns were similar for users of the two systems, rod users had slightly higher serum levels of levonorgestrel and a lower incidence of cycles with elevated progesterone levels. Therefore, rods could replace capsules as a long-term, reversible contraceptive method.

Adolescent↗
PubMed1984

Long-term experience with Norplant implants in international clinical trials.

Norplant subdermal implants containing levonorgestrel were used for contraception and compared with the Copper T, Model T Cu 200, during 42 months of use in an open study in Chile, the Dominican Republic, and Finland. Among 324 women enrolled for the implant regimen, there were no pregnancies in the 1st 2.5 years, and 2 by the end of 42 months. 1st segment net and gross cumulative pregnancy rates were 0.7 and 1.2/100 respectively, at 3.5 years. Cumulative pregnancy rates for the T Cu 200 group were 2.9, net and 3.5/100, gross at 42 months. More than 1/2 of the implant acceptors, 51.6/100 were continuing use at 3.5 years, somewhat above the continuation rate of the T Cu acceptors, 43.5/100, but not significantly so.

Americas↗
PubMed1983

Clinical chemistry in women treated with levonorgestrel implants (Norplant) or a TCu 200 IUD.

Two groups of implant users and two groups of IUD users participated in the study at different times. In the first groups, fractionation of lipoproteins was performed on serum samples from 28 subjects who had used the implants for 37 months and from 26 subjects who had used the Copper TCu 200 for 30 months. Users of the implants had significantly lower levels of total cholesterol, triglycerides and LDL-cholesterol than users of the IUDs. HDL-cholesterol levels were not different between the groups. In the other groups of women, general chemistries and selected hormone assays were carried out on samples from 30 subjects who had used implants for 51 months and from 24 subjects who had used the TCu 200 IUDs for 43 months. The parameters studied were the SM-12 chemistry group profile, estradiol, cortisol, testosterone, triiodothyronine, thyroxine and thyroid stimulating hormone. In the implant group, mean serum glucose levels were statistically significantly elevated and inorganic phosphorus levels were significantly reduced as compared to the IUD group. In both cases all individual measurements were within the normal range for the population. Testosterone and triiodothyronine levels in the implant group were significantly lower than in the IUD group, but no individual values were outside the normal range for the population. Mean values for all other parameters were not significantly different between the groups.

Adult↗
PubMed1983

Release rates of levonorgestrel from Silastic capsules, homogeneous rods and covered rods in humans.

Three forms of subdermal implants containing levonorgestrel are described. These are: capsules, in which the powdered drug is sealed inside of lengths of Medical Grade Silastic tubing; homogeneous rods, in which the drug is uniformly dispersed in Silastic 382 Medical Grade Elastomer; and covered rods, in which a core rod of drug and filler-free polydimethylsiloxane polymer (50:50, Wt:Wt) are sealed inside thin-walled Silastic tubing. Long-term in vivo release rates from human subjects are presented; 6.5 years for capsules, 3.6 years for homogeneous rods and 4 years for covered rods. Sets of six capsules release a decreasing amount of drug through the first few hundred days in situ and after 500 days a fairly constant rate of about 35 micrograms per day is released (2 micrograms/cm). Homogeneous rods deliver a continuously declining amount of drug during the entire time studied. In the first 100 days the release averages 136 micrograms per day from a set of three 3-cm rods (15 micrograms/cm), gradually declining to 30 micrograms per day (3.3 micrograms/cm) from day 800 to day 1300. The covered rods deliver at a constant rate of 17.5 micrograms per day for a 3-cm rod (5.83 micrograms/cm) through 4 years.

Capsules↗
PubMed1983

Scanning electron microscopy and X-ray microanalysis of foreign bodies associated with Silastic implants in humans.

Polydimethylsiloxane (Silastic) capsules containing megestrol acetate have been implanted in subcutaneous tissue as a method of long-term contraception. Histological studies revealed a granulomatous foreign body reaction around these capsules with birefringent crystals in multinucleated giant cells. Although several authors had interpreted these crystals as steroids, this seemed unlikely since the tissue had been processed with organic solvents. Analysis of these crystals by polarization microscopy, scanning electron microscopy, and X-ray microanalysis demonstrated that the material was talc. The talc was probably introduced as a contaminant from gloves during the implantation. Further analysis showed that capsule fragmentation could not have produced the material since Silastic particles could not be detected.

Contraceptive Agents↗
PubMed1983

Three-year experience with NORPLANT subdermal contraception.

NORPLANTTM (Laboratorios Gutfol, S.A., Mexico City, Mexico) subdermal implants containing levonorgestrel were accepted by 816 women in a two-phase study initiated in 1975 and augmented in 1978. Through 3 years of first-segment use, acceptors experienced five pregnancies, a cumulative net rate of 0.7 per 100, and a gross pregnancy rate of 1.1 per 100. First-segment continuation at 3 years was at the rate of 44.6 per 100, an annual average of 76 per 100. NORPLANT users experienced irregular menstruation, with high interindividual variation, but with normal average numbers of bleeding days and of bleeding episodes. Hemoglobin levels increased moderately during implant use. The incidence of systolic blood pressure readings above 145 mm Hg or diastolic readings above 95 mm Hg was similar to that observed among users of the TCu 200 intrauterine device enrolled under the same selection criteria in the same clinics between the two phases of the NORPLANT study. Comparative data on pregnancy and other rates are also given for these intrauterine device acceptors.

Adolescent↗
PubMed1982

A five-year clinical trial of levonorgestrel silastic implants (Norplant TM).

Silastic implants containing the progestin, levonorgestrel, were tested as a long-term contraceptive system in 101 women. During five full years of use, no pregnancies occurred. The 5-year continuation rate was 54%. Menstrual irregularities were the most frequent reason for termination of use but only during the first year. More than half of the terminations for this reason were in the first year. Some of the subjects elected to continue use of the implants beyond 5 years, allowing release rate data to be obtained through 6 years. From the second through the sixth year of use, the implants delivered a constant 30 micrograms per day of levonorgestrel to the subjects, and even after six years 57% of the original steroid content remained in the capsules. Return of fertility following removal was essentially immediate and not related to time of use. Medical reasons for removal were infrequent and no pattern was discernible.

Adult↗
PubMed1981

Lipoprotein patterns in women in Santo Domingo using a levonorgestrel/estradiol contraceptive ring.

Ten healthy, normally menstruating women attending a family planning clinic in Santo Domingo Participated in a study to determine the effects on plasma lipid levels of levonorgestrel and estradiol released from a contraceptive ring. A schedule of 21 days of use followed by 7 days of non-use was followed for 6 cycles. During the first two cycles of use, concentrations of cholesterol, HDL cholesterol, triglycerides and LDL cholesterol declined significantly from control levels, up to 25% for cholesterol, 28% for HDL cholesterol, 45% for friglycerides and 24% for LDL cholesterol. There were no subsequent changes with continued use. These declines are similar in direction but of lesser magnitude than those reported from clinics in other countries where pretreatment plasma levels of the same lipids are considerably higher. There was no significant change in the total cholesterol to HDL cholesterol ratio during treatment.

Adolescent↗
PubMed1980

Plasma concentrations of levonorgestrel as a function of the release rate of levonorgestrel from medicated intra-uterine devices.

An effort was made to achieve different levels of plasma levonorgestrel (13-ethyl-17 alpha-ethynyl-17-hydroxy-gon-4-en-3-one) (Ng) concentrations by the intra-uterine admininistration of levonorgestrel-releasing intra-uterine devices (IUD). Three different models were designed to release different doses of Ng daily. Sixteen women volunteered for the study and had a Ng IUD inserted post-menstrually. The effect of the IUDs on the ovulatory pattern was studied by measuring plasma concentration of oestradiol and progesterone by radioimmunoassay. Ng plasma concentrations were also measured by radioimmunoassay. In vitro experiments to measure the release of Ng from each type of device were carried out. Although some overlapping of mean plasma levels of Ng occurred during use of the three models of the IUDs, suppression of ovulation was clearly dose-dependent. Wide variations in plasma levels of Ng were seen between individuals but quite uniform plasma levels were seen in each subject for up to one year. IUDs where in vitro release rates were equivalent to each other also resulted in wide individual variations in plasma concentrations of Ng.

Adult↗
PubMed1979

A three-year clinical trial with levonorgestrel silastic implants.

Silastic implants containing the progestin, levonorgestrel, were tested as long-term contraceptives in 101 women. After three full years of exposure and 2,998 woman-months of use, no pregnancies had occurred. The continuation rates were 87% at 12 months, 79% at 24 months and 66% at 36 months. The most important side effect was excessive or irregular bleeding during the first year. No treatment was offered for this side effect other than vitamins and iron or change of method, with the exception of 3 cases where ethinyl estradiol was used one time for 2 weeks each. Bleeding disturbances led 8 patients to ask for removal of implants. Other side effects were headache, acne and lower abdominal pain. Blood and urine analysis tested 17 different parameters and all but plasma cortisol remained within normal limits throughout the study. A general tendency toward lowered cortisol values was observed and two subjects had more than one value below the normal limit for the population during the study. Glucose tolerance tests during the second year were abnormal in two women with familial diabetes but they returned to normal values spontaneously at the next test. It is concluded that levonorgestrel implants offer effective protection against pregnancy during the first three years of continuous use. Their acceptability and few side effects justify larger trials, especially if treatment of bleeding irregularities is introduced.

Abdomen↗
PubMed1978

Release of contraceptive steroids from sustained release dosage forms and resulting plasma levels.

The correlations of plasma levels of levonorgestrel, megestrol acetate and norgestrienone with the doses delivered from subdermal implants and contraceptive rings have been examined. Differences in plasma levels as large as three-fold between different subjects receiving nearly identical doses were observed with all three steroids. The relative plasma levels seen from one subject to another showed high consistency over time. Part of the explanation may lie in differing levels of sex hormone binding globulin, but additional factors must be operative since megestrol acetate binds only weakly with this carrier.

Contraceptive Devices, Female↗
PubMed1978

Clinical trial with subdermal implants containing norgestrienone.

Norgestrienone implants delivering approximately 225 microgram/ day were tested clinically for contraceptive effectiveness and acceptability in 145 women. Five pregnancies occurred in 2259 woman-months of use, one in the 11th month, one in the 15th and three in the 16th month of use. Continuation rate at 12 months was 86.7. The number of bleeding runs and bleeding days was increased in approximately 12% of the subjects. Ten percent of the patients had no bleeding in the first 90 days of treatment. Changes in bleeding pattern led to closures in four cases. Headache and signs of mild androgenicity were among the leading side effects. Blood and urine analysis throughout the study showed normal values of 17 different parameters, but a tendency to lower cholesterolemia not associated with changes in thyroid hormone levels, was observed in several patients. Cortisol was found slightly under the lower normal range in one subject without clinical manifestations of hypoadrenalism. It is concluded that norgestrienone implants should be replaced every twelve months for maximal contraceptive effect and because of their efficacy and good acceptability, evaluation of their long term use is warranted.

Adolescent↗