Metabolic fate of the new anti-ulcer drug enprostil in animals. 3rd communication: tissue accumulation after consecutive oral administration of [3H]-enprostil in rats.

Accumulation characteristics of radioactivity in organs and tissues were investigated after oral administration of [3H]-enprostil ((+/-)-11a,15a-dihydroxy-9-oxo-16-phenoxy-17,18,19,20-tetranorp r osta-4,5,13(t)- trienoic acid methyl ester, TA-84135) to male rats once a day (20 micrograms/kg/d) for 1, 7 or 14 days. [3H]-Enprostil was found to be partially metabolized in vivo to volatile tritium (3H2O). The ratios of volatile tritium to total radioactivity in plasma increased with repeated administration of [3H]-enprostil and the levels of volatile tritium were almost equilibrated within 7 days of drug administration. The formation rate of volatile tritium was estimated to be 1-2% of the single dose. The blood levels of non-volatile radioactivity at 1 h after each daily dosing were nearly constant. The levels at 24 h, however, increased with repeated dosing. The levels of non-volatile radioactivity in most tissues at 1 h after the multiple administration (7 and 14 times) were higher than those after the single dose. At 24 h, levels were noticeable after multiple dosing even in the tissues in which levels below the detection limit were found after the single dose. From the comparison of the multiple-dose groups, the levels in most tissues attained steady state within 7 times dosing. The daily excretions of radioactivity in the urine, feces and expired air were constant throughout the period of consecutive administration. The total recovery of administered dose was 92%, which was similar to that achieved in the single-dosing group. As described above, the retention of non-volatile radioactivity was observed in most tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and antisecretory activity of trimoprostil in Heidenhain-pouch dogs.

Trimoprostil, a prostaglandin E2 analog, was evaluated to determine if there was a relationship between plasma concentrations and inhibition of histamine-stimulated gastric acid secretion in dogs prepared with Heidenhain pouches. Trimoprostil was given p.o. followed by collection (drainage) of gastric juice from the pouch to determine acid output. In addition, serial blood samples were withdrawn to determine trimoprostil plasma concentrations. Trimoprostil was absorbed rapidly and eliminated with T1/2 ranging from 25 to 37 min. Trimoprostil was effective in inhibiting acid output compared with control. The maximal response and duration of activity were dependent on the concentration-time profile of trimoprostil. Trimoprostil produced a maximum inhibition of 98% and suppressed acid output for at least 3 hr. When plasma concentrations were related to the antisecretory response using a modified Hill equation, the response was found to lag behind plasma concentrations as evidenced by hysteresis loops. The predicted plasma concentration associated with a 50% inhibition of acid secretion (IC50) ranged from 0.58 to 0.79 ng/ml.

Prostaglandin metabolism and intraocular pressure.

The plasma lipid alterations characteristic of essential fatty acid deficiency (EFAD) generally appear one to two weeks after the initiation of fat free parenteral nutritional (PN), and may be associated with a reduction in prostaglandin (PG) formation. In the present study the relationship between exclusion of fat from the diet and changes in intraocular pressure (IOP) and PGE2 plasma levels were studied in 28 patients. The results indicated that three weeks after the omission of dietary fat a significant reduction in IOP levels occurred which persisted throughout the follow-up period of 7 (SD 1.2) weeks. Plasma PGE2 levels were also significantly reduced in patients on fat free PN for three weeks as compared with levels measured while patients were on a fat containing diet. This clinical observation is not yet understood and might be related to changes exerted by fatty acid deficiency.

Plasma levels of the prodrug, arbaprostil, [(15R)-15-methylprostaglandin E2], and its active, antiulcer (15S) epimer in humans after single dose oral administration.

Arbaprostil [(15R)-15-methylprostaglandin E2] is an antiulcer prodrug being evaluated for the treatment of gastric and duodenal ulcers in humans. It epimerizes in acidic gastric fluid to produce the biologically active form, (15S)-15-methyl-PGE2, which acts directly on the gastric mucosa and possesses both gastric acid antisecretory and cytoprotective properties. Because of its local mode of action, plasma levels of the two epimers may have greater relevance to drug safety than to therapeutic efficacy. In the present study, plasma concentrations of both 15-methyl-PGE2 epimers resulting from a gastric acid antisecretory dose of arbaprostil oral solution (50 micrograms) were measured in eight male volunteers having sufficient gastric acidity for prodrug activation (pH less than 3). Arbaprostil was determined with a newly developed RIA having a sensitivity of 10 pg X mL-1. The accuracy of the RIA was confirmed by parallel analysis of plasma samples by HPLC. (15S)-15-Methyl-PGE2 was also determined by HPLC. Arbaprostil was both rapidly absorbed and eliminated (tmax of 15-30 min and plasma t1/2 of 20 min), but there was large intersubject variability in its observed maximum plasma concentration (38 to 348 pg X mL-1). The concentration of (15S)-15-methyl-PGE2 did not exceed 25 pg X mL-1 In six subjects and 50 pg X mL-1 in the remaining two subjects. The significance of these results is discussed.

Trimoprostil plasma concentration-gastric acid inhibition relationships in duodenal ulcer patients.

The effect of single 0.25 mg, 0.75 mg, 1.5 mg, and 3.0-mg oral doses of trimoprostil and placebo on the inhibition of meal-stimulated gastric acid secretion was investigated in duodenal ulcer patients. Drug and placebo were administered in a double-blind, randomized, crossover study under fasting conditions. A bactopeptone meal was administered 30 minutes after dosing. Gastric acid output was measured by intragastric titation (pH 5.5) and trimoprostil plasma concentrations were measured by a specific gas chromatography-negative chemical ionization-mass spectrometric method. Meal-stimulated gastric acid secretion was significantly reduced when compared to placebo for one hour after 0.25 mg, 1.5 hours after 0.75 mg, and for 2.5-3.0 hours after both 1.5 mg and 3.0 mg doses. The maximal inhibition of gastric acid ranged from 65% reduction after 0.75 mg to 74% after 1.5 mg to 82% after 3.0-mg doses. Trimoprostil was rapidly absorbed and eliminated; terminal elimination half-life ranged from 21 to 45 minutes. Both maximum concentration and area under the plasma concentration-time curve increased proportionately with an increase in the dose. The concentration-effect data at a given dose were simultaneously fit to a pharmacokinetic/pharmacologic effect model. An IC50 (plasma concentration needed to elicit a 50% inhibition effect) value of 0.2 ng/mL was observed at doses of 0.75 mg to 3.0 mg. Overall, trimoprostil was effective in inhibiting acid output in a dose-related manner in duodenal ulcer patients.

Determination of (15R)- and (15S)-15-methylprostaglandin E2 in human plasma with picogram per milliliter sensitivity by column-switching high-performance liquid chromatography.

(15R)-15-Methylprostaglandin E2 (PGE2) is a pro-drug under evaluation for the treatment of acute upper gastrointestinal hemorrhage and gastrointestinal cytoprotection. It is converted in acid (e.g., gastric fluid) to its active 15S epimer. Both epimers are found in human plasma at low pg/ml levels following oral dosing. A high-performance liquid chromatographic (HPLC) method was developed for the simultaneous analysis of (15R)- and (15S)-15-methyl-PGE2 in human plasma. The method combined off-line solid-phase extraction and reversed-phase HPLC clean-up with panacyl bromide derivatization and subsequent analysis using a heteromodal column-switching technique. Assay linearity was demonstrated over a range of 10-200 pg/ml for both 15-methyl-PGE2 epimers (r greater than or equal to 0.995). There were no significant inter-day differences in assay results for either epimer at 50 and 25 pg/ml (p greater than 0.05), with pooled estimates of precision at these levels producing relative standard deviations of less than or equal to 8% and less than or equal to 12%, respectively. The method quantitation limit (signal-to-noise ratio 5:1) for both epimers was 10 pg/ml when processing 3 ml of plasma. The analysis procedure was shown to be useful for quantifying at or below 10% of the (15R)-15-methyl-PGE2 maximum plasma concentration following a 50-micrograms oral dose in three human volunteers. For the same three subjects, however, the plasma concentration of (15S)-15-methyl-PGE2 did not exceed the quantitation limit of 10 pg/ml.

Determination of acetyltrimoprostil and its metabolite trimoprostil in human or dog plasma by gas chromatography-negative-ion chemical ionization mass spectrometry.

A sensitive and specific procedure is described for the determination of the antisecretory prostaglandin acetyltrimoprostil and its metabolite trimoprostil in human or dog plasma using gas chromatography--negative-ion chemical ionization mass spectrometry (GC--NICI-MS). Trideuterated analogues of both compounds are added to plasma as the internal standards. The plasma is extracted at pH 7.3 with benzene--dichloromethane (9:1), and the residue of the organic extract is reacted at room temperature with pentafluorobenzyl bromide in the presence of 18-crown-6-ether and potassium acetate. The derivatives are reconstituted in heptane, and appropriate aliquots are analyzed by GC--NICI-MS with selected-ion monitoring of the intense (M--C6F5CH2)- fragment ions of acetyltrimoprostil (m/z 419), trimoprostil (m/z 377), and their respective trideuterated analogues (m/z 422 and m/z 380, respectively). Quantitation of an experimental plasma sample is based on a comparison of the m/z 419 versus m/z 422 and m/z 377 versus m/z 380 ion ratios in each sample to that obtained from the analysis of drug-free plasma fortified with various amounts of both protio compounds, and a fixed amount of each trideuterated internal standard. The limit of quantitation of the assay for human plasma is 0.2 ng ml-1 with mean relative standard deviations at this concentration of 15.5% and 9.7% for acetyltrimoprostil and trimoprostil, respectively.

Trimoprostil plasma concentration--gastric acid inhibition relationships: potentiation by food.

A single, oral, 1.5-mg dose of trimoprostil was taken before a standard meal and a matching placebo was taken after a standard meal by 10 subjects (group A). A second group of 10 subjects took placebo before a meal and trimoprostil after the meal (group B), while a third group took placebo both before and after the standard meal (group C). Food-stimulated gastric acid production was measured by intragastric titration for 6.5 hr after dosing. Trimoprostil taken after the meal had a greater effect on gastric acid secretion than when taken before the meal: Duration of effect was 5 to 5.5 hr in group B and 2 to 2.5 hr in group A. Blood samples were drawn and assayed for trimoprostil by gas chromatography-mass spectrometry. Mean trimoprostil plasma concentration and mean inhibition of gastric acid secretion data were fit to two models by the Hill equation. The mean plasma concentration associated with 50% inhibition of gastric acid secretion was 1.25 ng/ml. Trimoprostil plasma concentrations between 3 and 4 ng/ml were associated with 70% to 80% gastric acid inhibition. Overall, there appears to be a pharmacokinetic-pharmacologic correlation between trimoprostil plasma concentrations and inhibition of gastric acid secretion. Trimoprostil (1.5 mg) in the presence of food appears to have a therapeutic advantage, in that it decreases acid secretion longer than when taken without food and suffers no loss of bioavailability.

Capillary gas chromatographic-mass spectrometric analysis of 15-deoxy-16-hydroxy-16-vinylprostaglandin E2.

A new topically active antihypertensive agent, the methyl ester of 15-deoxy-16-hydroxy-16-vinylprostaglandin E2 (1), rapidly hydrolyzes in blood to the carboxylic acid 2, which also has antihypertensive activity. A capillary gas chromatographic-mass spectrometric method is described for measuring 2 in human plasma or serum at expected experimental blood levels of 75-1500 pg/mL. The assay is based on selected-ion monitoring of the carboxylate anion formed from negative ion chemical ionization of the trimethylsilylpentafluorobenzyl ester of 2, using a trideuterated analogue of 2 as internal standard. The method has been used to analyze samples from subjects following topical application of 1-2 mg of 1. Sample preparation included isolation from 1 mL of plasma or serum and purification of the ester derivative with C18 cartridges, followed by a two-step trimethylsilylation.

Influence of food on the bioavailability of trimoprostil: an overview.

The influence of food on the bioavailability of trimoprostil , a new antiulcer prostaglandin E2 derivative, was investigated in healthy male volunteers in four separate studies. Doses of 0.75, 1.5, and 3.0 mg were administered orally in both the presence and absence of food followed by serial blood sampling through 24 hours. Plasma trimoprostil concentrations were determined by a gas chromatograph-negative chemical ionization-mass spectrometric method for pharmacokinetic evaluation. Food decreased the absorption rate of trimoprostil as indicated by a later tmax (P less than 0.01) and corresponding lower Cmax at each dose. However, the food effect on tmax diminished as the dose increased. Although Cmax was reduced, food did not alter the extent of absorption, indicated by similar AUC (P greater than 0.05) between fed and fasted states. Both Cmax and AUC increased proportionately with an increase in dose. The harmonic mean half-lives of elimination were similar (P greater than 0.05) across all doses and ranged from 27 to 55 minutes.

13,14-Dihydro-15-keto-PGF2 alpha (PGFM) and sulprostone serum levels after application of sulprostone to postpartum women.

13 ,14 -Dihydro-15-keto-PGF2 alpha (PGFM) serum levels were determined by radioimmunoassay in 101 postpartum women who were treated with 200 micrograms methergin, 5 I.U. oxytocin and 500 micrograms sulprostone, respectively, 30 min after expulsion of placenta. All patients had normal deliveries. The present radioimmunoassay system did not show cross-reactivity with sulprostone. In addition, radioimmunoassayable sulprostone serum levels were monitored. Covariance analysis of area under PGFM serum levels between time zero and 180 min after application of oxytocics was performed. A higher but statistically not significantly PGFM serum level was maintained in subjects treated with sulprostone. Sulprostone serum levels are rapidly attained after application. Decrease of radioimmunoassayable sulprostone indicates a half-life of 75 min. These data corroborate clinical findings of an accompanying paper and combine to suggest that sulprostone may be a useful alternative therapy in high-risk patients with severe postpartum atony and hemorrhage in whom prior preventive measures have failed.

Gas chromatographic--mass spectrometric quantitation of 16, 16-dimethyl-trans-delta 2-PGE1.

Di-deuterated and di-tritiated 16,16-dimethyl-trans-delta 2-PGE1 has been synthesized and used for development of a GC-MS method for quantitation of corresponding unlabelled drug in patient plasma. Although these carrier/internal standard molecules only contain 2 deuterium atoms the lower limit of detection at each injection is as low as about 40 pg. The maximum plasma levels of this drug following administration of vaginal suppositories used in clinical studies (1 mg 16,16-dimethyl-trans-delta 2-PGE1 methyl ester in 0.8 g Witepsol S-52) were 100-350 pg/ml i.e. in the same order of magnitude as earlier seen for 16,16-dimethyl-PGE2.

Plasma levels of 9-deoxo-16,16-dimethyl-9-methylene-PGE2 in connection with its development as an abortifacient.

Gaschromatographic-mass spectrometric quantitation of 9-deoxo-16,16-dimethyl-9-methylene-PGE2 in plasma samples obtained during constant intravenous infusion of the drug revealed that a plasma level of about 20 ng/ml was associated with high enough uterine contractility for induction of second trimester abortions. This level was therefore aimed for during the development of formulations and dose schedules for interruption of pregnancy with this drug. For the first time it was possible to induce second trimester abortions through oral administration of a prostaglandin analog, although the plasma levels were low giving a moderate success rate (about 50%) within 25 hours. Rectal administration of 20 mg of the drug at 6 hours intervals resulted in high enough plasma levels for second trimester abortions. Highly efficient dose schedules for interruption of early first trimester ("menses induction") and second trimester pregnancies through vaginal administration were developed. The frequency of side effects in the early first trimester were so low that "home treatment" was possible. Formulations suitable for 3, 6 or 12 hours preoperative dilatation of the cervix were also developed.

Biological action and half life in plasma or intramuscular sulprostone for termination of second trimester pregnancy.

Sulprostone levels in plasma, platelet function and clinical effects were examined in four patients after intramuscular injection of 500 microgram sulprostone for induction of missed and therapeutic abortion in the second trimester of pregnancy. The half life of sulprostone in plasma was 34 (30-45) minutes. The highest sulprostone levels were found 10 to 20 minutes after injection (0.25-0.77 ng/ml) and after 120-240 minutes the values in plasma were no longer distinguishable from zero. Platelet count remained constant. 20 minutes after the injection platelet aggregation was slightly decreased, but not to a significant level. There was no correlation between sulprostone levels in plasma and pain of labour or induction abortion times. Side effects were minimal.

PIP: Plasma levels of sulprostone, a synthetic prostaglandin E2 derivative, were measured along with assessment of platelet function and clinical effects of intramuscular injection in 4 patients. The 4 patients were given 500 mcgm, intramuscularly, of sulprostone to induce missed and therapeutic abortion in the second trimester of pregnancy. Half-life of sulprostone in plasma was 34 minutes (range 30-45), and the highest drug levels were found 10-20 minutes after injection (levels ranged from .25-.77 ngm/ml). Plasma levels diminished to zero after 120-240 minutes. Platelet count was unaltered throughout, although platelet aggregation did decrease slightly, but not significantly, about 20 minutes after injection. Side effects were gastrointestinal and adjudged minimal. An attempt to correlate plasma levels of sulprostone and labor pain or abortion-induction time was fruitless.

Quantitative determination of 9-deoxo-16, 16-dimethyl-9-methylene-PGE2 in human plasma by GC-MS, RIA and HPLC.

Comparisons were made of 9-deoxo-16,16-dimethyl-9-methylene-PGE2 levels in plasma determined by three assay methods. Plasma samples from Rhesus monkeys treated with 200 micrograms/kg 9-deoxo-16,16-dimethyl-9-methylene-PGE2 intravenously were analyzed by radioimmunoassay (RIA) and by high pressure liquid chromatography (HPLC). In a second experiment known amounts of 11 beta-3H-9-deoxo-16,16-dimethyl-9-methylene-PGE2 were added to human plasma at several concentration levels. The samples were analyzed by RIA, HPLC and gas chromatography-mass spectrometry (GC-MS). A limited number of comparisons have been made between RIA and GC-MS analysis of plasma samples from human subjects treated wtih 9-deoxo-16,16-dimethyl-9-methylene-PGE2. The results indicated that the three assay methods generally give comparable estimations of 9-deoxo-16,16-dimethyl-9-methylene-PGE2 content in plasma.

Plasma concentrations of 9-deoxo-16-dimethyl-9-methylene-PGE2 in rhesus monkeys after administration by various routes.

A method is described for the estimation of 9-deoxo-16, 16-dimethyl-9-methylene-PGE2 by double antibody radioimmunoassay. Plasma samples obtained from animals treated with 9-methylene-16, 16-dimethyl-PGE2, 1-adamantanamic salt were extracted with diethyl ether to recover the prostaglandin. The validation of sample preparation and assay procedure are presented. Rhesus females were treated by several routes of administration and the samples assayed for drug content. Maximum blood levels were probably reached 30 minutes following subcutaneous injection and within 30 seconds of an intravenous injection. Results of the acute intravenous injection indicate an initial half-life of approximately one minute in peripheral circulation. Continuous intravenous infusion at 3 increasing doses of this compound resulted in a stepwise increase in plasma drug concentrations. Vaginal administration of 9-methylene-16, 16-dimethyl-PGE2, 1-adamantanamine salt in suppositories produced a dose dependent increase in plasma drug concentration. Higher plasma drug concentrations were produced when the prostaglandin was delivered in H-15 base suppositories than in E-76 base suppositories.

Hydrolysis of an orally active platelet inhibitory prostanoid amide in the plasma of several species.

The prostanoid 3-oxa-4,5,6-trinor-3,7-inter-m-phenylene-PGE1-amide (OI-PGE1-amide) has a prolonged duration of oral platelet aggregation inhibitory activity when compared to the parent free acid (OI-PGE1) in the rat. When incubated in rat plasma at 1 microgram/ml for 30 seconds prior to addition of ADP, OI-PGE1-amide inhibits in vitro rat platelet aggregation approximately 50%. OI-PGE1 inhibits at 1 ng/ml. Inhibition of platelet aggregation by plasma incubated with OI-PGE1-amide (1 microgram/ml) increases with time and the rate of this increase differs with species. Incubation of OI-PGE1 in plasma does not result in an increase of platelet inhibitory activity with time. The increase of platelet inhibitory activity was assumed to indicate hydrolysis of OI-PGE1-amide to the more active OI-PGE1. A compound, different from OI-PGE1-amide, was isolated by an ion exchange/silica gel separation sequence from an incubation of OI-PGE1-amide in rat plasma. It had potent platelet aggregation inhibitory activity. This material was shown to be OI-PGE1 by thin-layer chromatography, gas chromatography and mass spectral analysis. Studies with [3H]-OI-PGE1-amide confirmed the formation of OI-PGE1 in plasma incubations. Amide hydrolytic activity was significantly different between species, the rank order being: rat greater than guine pig greater than monkey = human greater than dog. This relationship corresponded with that determined by measuring the increase in platelet inhibitory activity with time in plasma incubations of OI-PGE1-amide reported above. Present data indicate that (a) OI-PGE1-amide is hydrolyzed to the parent acid by plasma enzymes of several species and (b) hydrolytic activity of plasma varies widely between species.