Pharmacokinetics of intra-amniotically administered hyperosmolar urea in rhesus monkeys

Final report of the safety assessment of Urea

Although Urea is officially described as a buffering agent, humectant, and skin-conditioning agent-humectant for use in cosmetic products, there is a report stating that Urea also is used in cosmetics for its desquamating and antimicrobial action. In 2001, the Food and Drug Administration (FDA) reported that Urea was used in 239 formulations. Concentrations of use for Urea ranged from 0.01% to 10%. Urea is generally recognized as safe by FDA for the following uses: side-seam cements for food contact; an inhibitor or stabilizer in pesticide formulations and formulations applied to animals; internal sizing for paper and paperboard and surface sizing and coating of paper and paper board that contact water-in-oil dairy emulsions, low-moisture fats and oils, moist bakery products, dry solids with surface containing no free fats or oil, and dry solids with the surface of fat or oil; and to facilitate fermentation of wine. Urea is the end product of mammalian protein metabolism and the chief nitrogenous compound of urine. Urea concentrations in muscle, liver, and fetuses of rats increased after a subcutaneous injection of Urea. Urea diffused readily through the placenta and into other maternal and fetal organs. The half-life of Urea injected into rabbits was on the order of several hours, and the reutilization rate was 32.2% to 88.8%. Urea given to rats by a bolus injection or continuous infusion resulted in distribution to the following brain regions: frontal lobe, caudate nucleus, hippocampus, thalamus plus hypothalamus, pons and white matter (corpus callosum). The permeability constant after treatment with Urea of whole skin and the dermis of rabbits was 2.37 +/- 0.13 (x 10(6)) and 1.20 +/- 0.09 (x10(3)) cm/min, respectively. The absorption of Urea across normal and abraded human skin was 9.5% +/- 2.3% and 67.9% +/- 5.6%, respectively. Urea increased the skin penetration of other compounds, including hydrocortisone. No toxicity was observed for Urea at levels as high as 2000 mg/kg in acute oral studies using female rats or mice. No signs of toxicity were observed in male piglets dosed orally with up to 4 g/kg Urea for 5 days. Dogs dosed orally with 5 to 30 g/L Urea for 4 to 10 days had signs of toxicity, including weakness, anorexia, vomiting and retching, diarrhea and a decreased body temperature, which led to a deep torpor or coma. No significant microscopic changes were observed in the skin of male nude mice dermally exposed to 100% Urea for 24 h. No observable effect on fetal development was seen in rats and mice dosed orally with an aqueous solution of Urea (2000 mg/kg) on days 10 and 12 of gestation. The mean number of implants, live fetuses, percent fetal resorptions, mean fetal weight, and percent fetuses malformed were comparable to control group. A detergent containing 15% Urea was injected into pregnant ICR-JCl mice and dams and fetuses had no significant differences when compared to control animals. Urea given orally did not enhance the developmental toxicity of N-nitrosomethylurea. Female Sprague-Dawley rats injected in the uterine horn with 0.05 ml Urea on day 3 (preimplantation) or on day 7 (post implantation) exhibited no maternal mortality or morbidity; a dose-dependent reduction in embryo survival was seen with preimplantation treatment. Urea injected intra-amniotically induces mid-trimester abortions in humans. Urea was not genotoxic in several bacterial and mammalian assays; although in assays where Urea was used at a high concentration, genotoxicity was found, many in in vitro assays. Urea is commonly used in studies of DNA because it causes uncoiling of DNA molecules. Urea was not carcinogenic in Fisher 344 rats or C57B1/6 mice fed diets containing up to 4.5% Urea. Exposure of normal human skin to 60% Urea produced no significant irritation in one study, but 5% Urea was slightly irritating and 20% Urea was irritating in other reports. Burning sensations are the most frequently reported effect of Urea used alone or with other agents in treatment of diseased skin. Overall, there are few reports of sensitization among the many clinical studies that report use of Urea in treatment of diseased skin. The Cosmetic Ingredient Review (CIR) Expert Panel determined the data provided in this report to be sufficient to assess the safety of Urea. The Panel did note that Urea can cause uncoiling of DNA, a property used in many DNA studies, but concluded that this in vitro activity is not linked to any in vivo genotoxic activity. Although noting that formulators should be aware that Urea can increase the percutaneous absorption of other chemicals, the CIR Expert Panel concluded that Urea is safe as used in cosmetic products.

Intrauterine administration of drugs for termination of pregnancy in the second trimester

Medical methods have been used for many years to terminate mid-trimester pregnancy, ranging from irritant chemicals and traditional plants to ecbolic agents and solutions instilled locally into the uterus. These methods had serious limitations, with relatively high rates of maternal mortality and morbidity. Surgical evacuation requires special skills not available to all practitioners and many doctors consider second trimester dilatation and evacuation as a surgical taboo. In recent years several approaches evolved and reached the clinics, presenting safer and more effective options. Intra-amniotic instillation of hypertonic solutions, particularly saline or urea, proved in many hands to be a good method for pregnancies beyond 15 weeks of gestation. Due to a long latency period after instillation, these agents are often supplemented by an intravenous oxytocin infusion. Extraovular hypertonic saline or ethacridine (Rivanol) have their advocates, particularly in the grey-zone of pregnancy range from 13-15 weeks. In the last two decades, intrauterine prostaglandins were added to the methods in current use. Extra-amniotic prostaglandins (E2, F2 alpha or 15-methyl F2 alpha) were originally given in repeated doses or as a continuous local drip, but later a single instillation was used, usually mixing the drug with a viscous solution or gel. Intra-amniotic prostaglandins, in much higher doses, particularly the 15-methyl analogue, proved highly effective and relatively safe, especially when combined with laminaria tent insertion in the cervix. Various combinations of methods have provided a wide spectrum of data which is difficult to evaluate at present. Studies comparing different methods were mainly attempted in the mid-seventies. The outcome raised many pertinent questions and left many major issues unresolved. Most of the comparisons were not randomized or well-controlled and only referred to the natural prostaglandin compounds. The analogues, however, seem to offer several advantages and the role of additional methods such as laminaria or antiprogestins remains to be further evaluated.

Evaluation of intra-amniotic administration of 120 gm of urea with 5 mg of prostaglandin F2 alpha for midtrimester termination of pregnancy between 20 and 24 weeks' gestation

The occasional finding of signs of life in fetuses delivered following intra-amniotic administration of 80 gm of urea and 5 mg of prostaglandin F2 alpha suggested that the dose of 80 gm of urea was inadequate beyond the nineteenth week. Protocol modifications were made, and the metabolic effects of intra-amniotic administration of 120 gm of urea used beyond the nineteenth week were compared to those of the 80 gm dose of urea used in patients prior to the twentieth week. The 120 gm urea dose was well tolerated. The peak blood urea nitrogen (at 4 hours after instillation) was higher with 120 gm of urea (36.4 mg/dl) than with 80 gm of urea (24.6 mg/dl) (p less than 0.05). Small decreases in the platelet count (14% of control) and serum fibrinogen (11%), sodium (2%), potassium (7%), and carbon dioxide (11%) levels and a 5% increase in peak serum osmolality were found. Following the change in protocol, fetal heart activity has been absent at 3 hours after instillation in all cases less than 24 weeks from the last menstrual period.

13, 14-dihydro-15-keto-prostaglandin F2alpha concentrations in human plasma and amniotic fluid

An antiserum to 13,14-dihydro-15-keto-prostaglandin F2alpha (PGF2alphaM) was prepared and a radioimmunoassay evaluated in various reproductive states. PGF2alphaM plasma concentration was 63.6 +/- 10.3 pg/ml (mean +/- SEM) in cycling women. The concentration fluctuated throughout the menstrual cycle and pregnancy, but no discernible patterns were noted. PGF2alphaM concentrations were elevated at the time of urea + oxytocin induced abortion (238 +/- 54 pg/ml) and during late stages of normal labor (352 +/- 107 pg/ml) but were not elevated during labor prior to 7 cm dilatation. Following intra-amniotic instillation of 5 mg of PGF2alpha tromethamine into the amniotic sac, PGF2alphaM concentration increased in the amniotic fluid. In the plasma of these patients there was an eighteenfold rise in plasma PGF2alphaM concentration compared to a 3.5-fold rise in PGF2alpha at 1 hour, suggesting changes in PGF2alphaM may be more easily detected than the parent compound. While PGF2alphaM may be a useful index of PGF2alpha production, it appears that PGF2alphaM is of little value in predicting the occurrence of uterine contraction.

Hyperosmolar urea for elective midtrimester abortion. Experience in 1,913 cases

Intra-amniotic hyperosmolar urea (59.7 per cent) augmented by intravenous oxytocin (332 millimicron per minute), prostaglandin F2alpha (20 mg.), prostaglandin F2alpha (10 mg.), or prostaglandin F2alpha (5 mg.) was utilized for 1,913 patients requesting elective midtrimester abortion. Injection-abortion intervals ranging from 13.70 to 21.49 hours were achieved with failure rates of 0.7 to 6.7 per cent. Despite frequent pre-existing medical conditions, the complication rate compared favorably with those of other methods for terminating midtrimester pregnancy such as saline amnioinfusion or dilatation and evacuation.

Intra-amniotic urea and prostaglandin F2alpha for midtrimester abortion: clinical and laboratory evaluation

The clinical management of the elective midtrimester abortion continues to be unsatisfactory as judged by either national mortality or morbidity rates. This report documents the results of a randomized series of 19 midtrimester abortions induced by either intra-amniotic hyperosmolar urea and 5 mg. of prostaglandin F2alpha (PGF2alpha) or intra-amniotic hyperosmolar urea alone. Pertinent clinical characteristics and biochemical determinations were compared between these two groups. A series of 150 patients were then treated with urea and 5 mg. of PGF2alpha. The clinical results of this series of patients are presented and compared with a previous group who had urea and 10 mg. of PGF2alpha. These studies demonstrate that 5 mg. of PGF2alpha with 80 Gm. of urea achieves injection-abortion intervals that are less than 24 hours.