Disposition and metabolism of tenidap in the rat.

Tenidap is a new antirheumatic drug currently undergoing clinical evaluation. It inhibits production and activity of cytokines in vivo and causes significant reductions in plasma markers of disease activity in rheumatoid arthritis. After the oral administration of C-14 labeled tenidap, bile, urine and plasma were examined by HPLC and atmospheric pressure tandem mass spectrometry. Label is excreted primarily in bile/feces and the remainder in urine, with good recoveries. Numerous metabolites were identified and the structures of most were confirmed by comparison with authentic synthetic samples. Hydroxylation in several positions on both the oxindole and thienyl rings of tenidap represents the major routes of metabolism; most of these metabolites are subsequently conjugated. The glucuronide of 5'-hydroxytenidap, excreted primarily in bile, is the major metabolite, constituting about one third of the oral dose recovered. Other pathways include dihydroxylation and methoxylation on the thienyl ring. An unusual reduction of hydroxytenidap took place, resulting in the formation of a novel thiolactone analog. Anaerobic incubation with rat cecal contents generated the thiolactone metabolite, suggesting the involvement of gut microflora.

Discovery of the hemifumarate and (alpha-L-alanyloxy)methyl ether as prodrugs of an antirheumatic oxindole: prodrugs for the enolic OH group.

Ether, ester, and carbonate derivatives of the antirheumatic oxindole 1 were prepared and screened as potential prodrugs of 1. This effort led to the discovery of the (alpha-L-alanyloxy)-methyl ether and hemifumarate derivatives of 1 which deliver the drug efficiently into the circulation of test animals, are stable in the solid state, and possess good stability in solution at low pH as required to ensure gastric stability. Success in achieving acceptable bioavailabilities of 1 across species (rats, dogs, and monkeys) followed the inclusion of ionizable functionality within the promoiety to compensate for masking the polar enolic OH group of the free drug. However, the introduction of ionizable functionality was often associated with decreased stability, as demonstrated by the hemisuccinate, hemiadipate, hemisuberate, and alpha-amino ester derivatives of 1 which could not be isolated. A clear exception was the hemifumarate derivative of 1 which was not only isolable but actually more stable at neutral pH than the nonionizable ester analogues. The solution and solid state stability of the hemifumarate, together with its activity as a prodrug of 1, suggests that hemifumarate be considered as an alternative to hemisuccinate as a prodrug derivative for alcohols, particularly in situations where solution state stability is an issue.

Ampiroxicam, an anti-inflammatory agent which is a prodrug of piroxicam.

Ampiroxicam is a nonacidic ether carbonate prodrug of piroxicam. Our results demonstrate that, in contrast to piroxicam, ampiroxicam does not possess detectable prostaglandin synthesis inhibitory activity in vitro. Ampiroxicam, however, has similar in vivo potency to piroxicam in suppressing paw swelling in rat adjuvant arthritis. In an acute model of paw inflammation in rats, ampiroxicam is less potent than piroxicam itself: the ED50's of ampiroxicam are 9- and 3.5-fold higher than those of piroxicam following a single or multiple (5) daily oral doses, respectively. Using the phenylbenzoquinone stretching test as a method of evaluating acute analgetic activity, the ED50 for ampiroxicam is about 3-fold higher than that of piroxicam. These tests of activity share the property of being partially prostaglandin-dependent. Ampiroxicam itself is not observed in plasma after oral dosing to man, nor in the rat, dog, and monkey as reported here. Bioavailability studies show that conversion to piroxicam is about 100%, 90%, 70%, and 50% in these four species, respectively. These results indicate that ampiroxicam's anti-inflammatory activity is produced in vivo by conversion to piroxicam and support its credentials as an efficacious prodrug of piroxicam.

Simultaneous determination of tenidap and its stable isotope analog in serum by high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry.

A specific high-performance liquid chromatographic/atmospheric pressure chemical ionization tandem mass spectrometric assay for the quantitative determination of tenidap and its D3 analog in human serum is described. The assay exhibited a linear dynamic range of 0.1-25 micrograms ml-1. Its precision for the two analytes over the range was 17% or better. The assay validity and its utility to investigate changes in tenidap bioequivalence and pharmacokinetics are presented.

Disposition of ampiroxicam, a prodrug of piroxicam, in man.

1. Ampiroxicam, a prodrug of the effective anti-inflammatory agent piroxicam, was completely converted to piroxicam after oral administration to man. 2. At clinical doses there was no detectable portal or systemic exposure of man to ampiroxicam, indicating that conversion to piroxicam was complete during the absorption process. 3. The pharmacokinetics of piroxicam from ampiroxicam were essentially the same as those after piroxicam itself except that Cmax was slightly lower and tmax was slightly longer after administration of ampiroxicam.

Pharmacokinetics of azithromycin in rats and dogs.

After intravenous or oral administration to rats and dogs, azithromycin was rapidly distributed into the tissues, where concentrations frequently exceeded those in serum by 100-fold or more within 24 h of a single dose. Tissue concentrations were proportional to the dose following single administrations of 10 to 40 mg/kg in rats and dogs. Tissue concentrations were higher after multiple dosing and became greater as the dose was increased from 10 to 40 mg/kg. Elimination half-lives were similar in most tissues and were about 40 h in rats after seven doses of 20 mg/kg and about 90 h in dogs after five doses of 30 mg/kg. Serum concentrations declined in a multi-exponential manner, reflecting initial rapid distribution into tissues and then slow return to serum from tissues. Azithromycin had good oral bioavailability in rats and dogs (46% and 97%, respectively). Rapid uptake of azithromycin by tissues from serum and slow redistribution from tissues to serum are apparently factors governing the pharmacokinetics of azithromycin in rats and dogs. Serum concentrations do not reflect the availability of azithromycin in tissues.

Doxazosin in patients with hypertension.

The antihypertensive effects and steady-state pharmacokinetics of doxazosin, as well as the bioequivalence of four dosage forms, were studied in 25 hypertensive patients. For an 8 mg daily dose mean Cmax at steady-state for all patients was 108 ng/ml; the mean tmax was 1.8 h. The mean terminal elimination half-life was 22 h. The four tablets containing 1, 2, 4, or 8 mg of doxazosin were bioequivalent in delivering the 8 mg dose. In patients with mild to moderate hypertension, 26-day treatment with doxazosin resulted in blood pressure reduction of 10/7 mmHg in the supine and 13/18 mmHg in the standing position. Adverse effects were generally mild and of brief duration.

A gas chromatographic/mass spectrometric assay for flutroline, a gamma-carboline antipsychotic agent, with direct derivatization on a moving needle injector.

A method has been developed for the determination of flutroline in plasma using capillary gas chromatography and selected ion monitoring detection of the TMS derivative. The method is linear over the concentration range of 3-60 ng ml-1 and was used to define the drug pharmacokinetics and bioavailability in animals and man. A novel method for direct derivatization on the tip of a moving needle injector is described.

Profile of trimazosin: an effective and safe antihypertensive agent.

Trimazosin, a selective alpha-1-adrenoceptor-blocking agent, has been extensively evaluated in over 1000 patients. In hypertensive patients, reduction in elevated blood pressure in both supine and standing positions, consequent to a reduction in systemic vascular resistance, persisted in long-term therapy. Progression of hypertension target organ damage did not occur. Improvement in blood lipids with decreased total serum cholesterol was noted in long-term therapy. In long-term studies, 74% of patients responded at a trimazosin dose of 300 mg/day or less; the maximum dose was 300 mg/day or less in 52% of patients and 200 mg/day or less in 36%. Most patients received twice a day therapy. The side effect profile of trimazosin was comparable to placebo and significantly better than that of either methyldopa or propranolol. Concomitant disease or therapy did not adversely affect the trimazosin safety profile. Hematology, clinical chemistry, and urinary parameters did not indicate deleterious effects. Because of its excellent safety and toleration profile, trimazosin may be particularly suitable in first-line therapy of patients with mild or moderate hypertension.

Metabolism of the prostaglandin fertility regulator sulprostone in monkeys.

The prostaglandin imide analog sulprostone (I) was labeled with tritium in the phenoxy ring to trace the fate of the prostanoic acid portion of the molecule and with carbon-14 in the methanesulfonimide moiety to trace the fate of that portion of the molecule. Disposition was studied after intravenous administration to female cynomolgus monkeys. The excretion and plasma pharmacokinetics of total radioactivity indicated that the prostanoic acid and methanesulfonimide moieties were disposed of differently, implying that hydrolysis of sulprostone was extensive and that the hydrolysis products were treated independently. The urinary excretion of tritium (prostanoic acid) was consistent with that observed for other prostaglandins. The urinary excretion and plasma pharmacokinetics of carbon-14 were consistent with those expected for methanesulfonamide. Urinary metabolites identified in 0-2 hr urine included a trace amount of unchanged drug, methanesulfonamide, and two products of beta-oxidation - the tetranor and dihydrotetranor prostanoic acids.

Radioimmunoassay for sulprostone.

The development of a radioimmunoassay for measuring subnanogram amounts of the prostaglandin uterine stimulant, sulprostone (N-methanesulfonyl 16-phenoxy-omega-tetranor PGE2 carboxamide), is described. The 9-carboxymethoxime derivative of sulprostone was coupled to keyhole limpet hemocyanin to prepare the immunogen, and to tyramine to yield a precursor suitable for radioiodination. The antiserum generated from rabbits was specific for sulprostone, showing cross reactivities of less than 0.1% against PGE2, PGF2 alpha, and known sulprostone metabolites. The range for routine assay of sulprostone was 10-300 pg which corresponded to 50-1500 pg/ml of plasma. The coefficient of variation for replicate analyses on the same sample was 8-12%. The assay was used to measure the plasma levels of sulprostone in patients who had received the drug intramuscularly.

Metabolism of N-acetyl PGE2 carboxamide in the rat.

After intratracheal administration to rats, the bronchodilator N-acetyl PGE2 carboxamide was converted rapidly to PGE2 and 13,14-dihydro-15-keto-PGE2, the major plasma metabolite. Oxidation of the N-acetyl carboxamide by prostaglandin dehydrogenase and hydrolysis of the imide bond were demonstrated in vitro.

Disposition of guanethidine during chronic oral therapy.

The plasma level and urinary excretion rate of guanethidine have been measured in 30 patients during oral maintenance therapy, and in 5 patients following discontinuous of therapy. A significant correlation was found between the daily average urinary excretion and the maintenance dose, although wide interindividual variation was noted among patients maintained on the same dose. A statistically significant correlation was also observed between the area under the plasma level curve during the dose interval and the oral maintenance dose. After discontinuation of chronic therapy, the half-life of 1.5 days of the initial phase of elimination was essentially in agreement with the half-life of almost 2 days determined in acute studies. In addition, a second phase of elimination with a half-life of 4 to 8 days was observed.

A selective and sensitive assay for urinary metanephrine and normetanephrine using gas chromatography mass spectrometry with selected ion monitoring.

Vapor phase methodology for quantitative analysis of urine for metanephrine and normetanephrine as the pentafluoropropionyl derivative is described. The use of selected ion monitoring provided sufficient sensitivity and selectivity that milliliter aliquots of urine required only a simple scheme of sample processing; preliminary purification consisted of percolation through a column of XAD-2 followed by solvent extraction. The sample extracts were converted to the pentafluoropropionyl derivatives and analyzed by gas chromatography mass spectrometry with selected ion monitoring. Quantitative analysis was based on alpha[2H2]-beta-[2H1]metanephrine and alpha-[2H2]-beta-[2H1]normetanephrine which were added to the urine sample at the outset. The calibration plots for metanephrine and normetanephrine were linear from 10 ng ml-1 to 2000 ng ml-1 of urine permitting the detection of metanephrine and normetanephrine levels throughout the normal range and well into the subnormal range. Examples of application of the methodology to clinical investigation are described. The overall reproducibility of the sample processing methodology and instrumentation was assessed by replicate analyses of the same urine sample over a period of several weeks; the coefficient of variation was +/- 2.5% (n = 8).

Selected ion monitoring assay for meclizine in human plasma.

A method has been developed for the quantification of meclizine in human plasma using gas chromatography mass spectrometry. Pentadeuterated meclizine was synthesized and used as an internal standard. The method gave linear results over a concentration range of 5-200 ng ml-1 and was used to determine plasma levels of meclizine following administration to a male volunteer.

Selected ion monitoring assay for the bronchodilator pirbuterol.

A selected ion monitoring assay has been developed to measure plasma levels of the bronchodilator pirbuterol in animals and man. Pirbuterol is extracted from plasma with acetone + potassium carbonate and after further purification is converted to its trimethylacetyl derivative. With the use of the stable isotope labeled internal standard, pirbuterol-d9, precisions of 10% and 6% were achieved at plasma concentrations of 1 and 20 ng ml-1, respectively. The synthesis of the deuterium labeled internal standard is described.

Metabolism of digitoxin in man and its modification by spironolactone.

The effect of spironolactone on the metabolism of intravenously administered 3H-digitoxin (80 muCi) was investigated in eight patients. In three of them the labelled glycoside was given on a second occasion after spironolactone treatment had been discontinued for at least 65 days. Of total urinary radioactivity 79% was unaltered drug and 12% consisted of water soluble compounds. No digitoxigenin or digoxigenin and only trace amounts (less than 2 %) of digoxin and the bis- and monoglycosides of digoxigenin were found. After spironolactone total urinary radioactivity was unchanged but the fraction eliminated as unchanged digitoxin fell from 79 to 66 % and the water soluble compounds increased from 12 to 26 % (p less than 0.05). In addition spironolactone caused a 20 ( reduction in the half-life of serum radioactivity (p less than 0.01) and a 16 % reduction in the volume of distribution (p less than 0.05). Induction of hepatic enzymes by spironolactone is proposed to explain the alteration in the metabolism of digitoxin in man. Both the altered metabolic pattern and the reduction in the volume of distribution appear to contribute to the reduction in half-life.