Simultaneous determination of carboprost methylate and its active metabolite carboprost in dog plasma by liquid chromatography-tandem mass spectrometry with positive/negative ion-switching electrospray ionization and its application to a pharmacokinetic study.

A liquid chromatography-tandem mass spectrometric (LC-MS/MS) method using positive/negative electrospray ionization (ESI) switching for the simultaneous quantitation of carboprost methylate and carboprost in dog plasma has been developed and validated. After screening, the esterase inhibitor, dichlorvos was added to the whole blood at a ratio of 1:99 (v/v) to stabilize carboprost methylate during blood collection, sample storage and LLE. Indomethacin was added to plasma to inhibit prostaglandins synthesis after sampling. After liquid-liquid extraction of 500µL plasma with ethyl ether-dichloromethane (75:25, v/v), analytes and internal standard (IS), alprostadil-d4, were chromatographed on a CAPCELL PAK Phenyl column (150×2.0mm, 5µm) using acetonitrile-5mM ammonium acetate as mobile phase. Carboprost methylate was detected by positive ion electrospray ionization followed by multiple reaction monitoring (MRM) of the transition at m/z 400.5→329.3; the carboprost and IS were detected by negative ion electrospray ionization followed by MRM of the transitions at m/z 367.2→323.2, and 357.1→321.2, respectively. The method was linear for both analytes in the concentration range 0.05-30ng/mL with intra- and inter-day precisions (as relative standard deviation) of ≤6.75% and accuracy (as relative error) of ≤7.21% and limit of detection (LOD) values were 10 and 20pg/mL, respectively. The method was successfully applied to a pharmacokinetic study of the analytes in beagle dogs after intravaginal administration of a suppository containing 0.5mg carboprost methylate.

Pharmacokinetics of prostaglandins.

Naturally occurring prostaglandins (PGs) are rapidly metabolized in the human circulation. For clinical use a number of PG analogues have therefore been developed which are resistant to rapid inactivation. Among these are carboprost, gemeprost and misoprostol. Following intramuscular injection of carboprost, plasma levels peaked after 20 minutes and declined slowly thereafter. In amniotic fluid the half-life was between 31 and 37 hours. Gemeprost is administered vaginally, and maximum plasma levels were reached after 2-3 hours, with detectable levels for at least 6-8 hours. Pharmacokinetic data on misoprostol are available following oral, vaginal and sublingual administration. Following oral treatment, plasma levels peaked at about 30 minutes, while after vaginal administration of the tablets the levels increased gradually and reached maximum levels after 70-80 minutes, but remained detectable for a significantly longer time. After sublingual administration the peak concentration was the same as for oral treatment but declined significantly more slowly. Endocervical administration of PGE(2) might be regarded as a local therapy, while following vaginal administration increased plasma levels of metabolites can generally be found. The plasma profile varies with the vehicle used.

Menses induction in rhesus monkeys using a controlled-release vaginal delivery system containing (15S) 15-methyl prostaglandin F2 alpha methyl ester.

Polymeric controlled-release vaginal delivery systems were designed for (15S)15-methyl prostaglandin (PG)F2 alpha methyl ester (carboprost methyl). The drug was incorporated into a highly permeable reservoir membrane that was bound to a relatively nonpermeable support membrane. The rate of drug release was controlled by coating the reservoir membrane with a less permeable rate-controlling membrane. Vaginal devices were prepared with in vitro steady-state release rates from 5 to 180 microgram/hour. The release curves were characterized by an initial, transient rapid release of the drug, followed by a linear zero-order release phase. Pregnancy was terminated in rhesus monkeys following a 24-hour treatment with vaginal devices having release rates of carboprost methyl of 45 microgram/hour or greater. Successful menses induction was associated with peripheral plasma concentrations of (15S)15-methyl PGF2 alpha between 2000 and 3000 pg/ml. Peripheral plasma concentrations of progesterone declined very rapidly to less than 1.0 ng/ml in monkeys in which pregnancy was terminated. These studies demonstrate the feasibility of manufacturing controlled-release vaginal delivery systems containing carboprost methyl for use in early pregnancy termination.

Pulmonary prostaglandin metabolism during normobaric hyperoxia.

Prostaglandin metabolism by rat lung tissue was measured following exposures of 6, 24 and 48 hours to either pure oxygen or air at one atmosphere. Tissue concentrations of PGE1, PGE2 and PGF2 alpha were not altered by oxygen exposures. Prostaglandin synthetase activity decreased between 24 and 48 hours but was not significantly different from control at 48 hours. Combined prostaglandin dehydrogenase/reductase activity decreased between 24 and 48 hours to 13% of control values and was significantly lower than in air at 48 hours. The plasma concentration of 13, 14 dihydro-15-keto PGF2 alpha, a catabolite of PGF2 alpha, was significantly lower in oxygen-exposed rats at 24 and 48 hours. We conclude that endogenous pulmonary prostaglandin concentrations are maintained during hyperoxia but that catabolism of prostaglandins by the lungs may be impaired.

Termination of pregnancy by intramuscular administration of 15 (S)-15-methyl-prostaglandin in F2 alpha.

The use of 15 (S)-15-methyl-prostaglandin F2 alpha for second-trimester termination of pregnancy, induction of labor in the presence of a dead or severely malformed fetus, and the management of molar pregnancy was investigated in 212 women. The dosage regime was 250 microgram of the prostaglandin analogue every 1 to 3 hours. Cumulative expulsion rates amounted to 94 and 97% after 24 to 36 hours, respectively. Gastrointestinal side effects occurred in 48% of the patients, and both the number and intensity of the episodes were significantly reduced by antiemetic and antidiarrheal drugs. No serious complications occurred.

Post-conceptional induction of menses with a single vaginal suppository of (15S)-15-methyl prostaglandin F2 alpha methyl ester.

The induction of post-conceptional menses needs a technically simple method which would avoid instrumentation of the uterus. One possible method investigated in this study is the abortifacient effect of a single dose long-acting vaginal suppository containing 3.0 mg of (15S)-15-methyl prostaglandin F2 alpha methyl ester. Pregnancy was terminated successfully in 13 of the 14 subjects. Two successful patients required curettage for prolonged bleeding and retained products of conception. Prolonged vaginal bleeding and the uncertainty of endpoints with particular reference to human chorionic gonadotropin (HCG) constitute the major problem with this non-invasive method, and are discussed in the light of the data obtained.

PIP: The clinical characteristics and applicability of vaginal administration of a single suppository of (15S)-15-methyl prostaglandin F2alpha (PGF2alpha) methyl ester in postconceptional induction of menses was evaluated in 14 healthy women who were no more than 7 weeks pregnant and desired pregnancy termination. Each suppository contained 3.0 mg of 15S-15-methyl PGF2alpha methyl ester in a 2.2 gm base of Witepsol E-76-A. Blood samples were collected at 0, 4, 8, and 10 hours and again at the 14th day follow-up visit for analysis of serum chorionic gonadotropin (HCG) levels using the Beta subunit radioimmunoassay as described by Vaitukaitis et.al. and serum progesterone levels using the radioimmunoassay method of Kirton et.al. Pregnancy termination was successful in all but 1 patient. Vaginal bleeding persisted for at least 14 days in 8 cases; 2 of these patients necessitated curettage at 4 weeks and 9 weeks after the procedure. The failed case was an obese woman whose pregnancy persisted. HCG levels declined below the arbitrary limit of 1 I.U./ml within 2 weeks after therapy in 36% of the cases. Plasma progesterone levels declined below the baseline level of 5 ng/ml within 2 weeks. A wide range of values was observed at 4 and 8 hours. The 1 failure case had an initial value of 72 pg/ml at 4 and 8 hours; all cases with undetectable levels at 8 hours had initial values over 138 pg/ml. In patients with prolonged bleeding, serum HCG and progesterone showed a significantly slower decline than in patients with an uneventful abortion. Diarrhea occurred in 86% of the cases and vomiting in 36%. The study illustrates the effectiveness of administration of 1 vaginal suppository containing 3.0 mg of PGF2alpha methyl ester in 1st trimester abortion. However, the bleeding and gastrointestinal side effects associated with this method preclude its widespread use.

Termination of early gestation with a single vaginal suppository of (15S)-15-methyl-prostaglandin F2alpha methyl ester.

Abortion was induced in 20 women who were less than 49 days pregnant with a vaginal suppository containing 3.0 mg (15S)-15-methyl-prostaglandin F2alpha methyl ester. Peripheral serum levels of (15S)-15-methyl F2alpha free acid, beta hCG and progesterone were measured before, during the 10 hours after treatment and over the next 14 days. Eighteen of the subjects had a complete follow-up: ten were aborted (53%), three had incomplete abortions and five were failures. There was a correlation between serum levels of F2alpha (15S)-15-methyl-prostaglandin F2alpha free acid, and the incidence of success. Progesterone was significantly reduced in all three groups of subjects and, therefore, could not be utilized to judge the success of the procedure. A small but insignificant reduction of betahCG occurred in all subjects regardless of outcome during the ten-hour observation period. Since minor side effects of diarrhea and vomiting occurred in less than half of the aborted and only a few of the not aborted subjects, a larger amount of drug might improve the success rate.

PIP: Abortion was induced in 20 women who were less than 49 days pregnant with a vaginal suppository containing 3.0 mg (15S)-15-methyl-(PGF2alpha) prostaglandin F2 alpha methyl ester. Peripheral serum levels of (15S)-15-methylPGF2alpha free acid, betahCG, and progesterone were measured before, during the 10 hours after treatment, and over the next 14 days. 18 of the subjects had a complete follow-up; 10 were aborted (53%), 3 had incomplete abortions, and 5 were failures. There was a correlation between serum levels of F2alpha (15S)-15-methyl-PGF2alpha free acid, and the incidence of success. Progesterone was significantly reduced in all 3 groups of subjects and therefore could not be utilized to judge the success of the procedure. A small but insignificant reduction of betahCG occurred in all subjects regardless of outcome during the 18-hour observation period. Since minor side effects of diarrhea and vomiting occurred in less than 1/2 of the aborted and only a few of the nonaborted sujects, a larger amount of drug might improve the success rate.

Plasma levels of 15 (S) 15-methyl-PGF 2 alpha-methyl ester following vaginal administration for induction of abortion in women.

A single suppository containing 3.0 mg 15 (S)15-methyl-PGF2 alpha-methyl ester was administered vaginally in women to terminate mid-trimester pregnancy. Plasma levels of the drug (both methyl ester and free acid forms) were measured at different time intervals using deuterated carriers and gas chromatography-mass-spectrometry. 15(S)15-methyl PGF2 alpha (sum of methyl ester + free acid) was found to have a mean value of 1166 pg/ml plasma at 3 hrs after administration of the suppository. The mean levels were subsequently found to be maintained in the range of 1000 pg/ml. Preliminary studies showed that unlike the successfully aborted women, in those who did not abort within 30 hrs with this suppository, the plasma levels of the drug were not maintained for a sufficiently long time. The episodes of side effects, body surface area and the induction-abortion interval in relation to the plasma levels are discussed.