Antagonism of glycerol trinitrate activity by an inhibitor of glutathione S-transferase.

The in vitro spasmolytic activity of glycerol trinitrate was measured on the KCl-contraction of aorta strips from the rabbit. In the presence of sulphobromophthalein, a known inhibitor of glutathione S-transferase, the dose-activity curve for the nitrate was displaced to the right. Much smaller displacements were obtained with the control spasmolytic substances--papaverine and S-nitroso-N-acetylpenicillamine. It was confirmed that sulphobromophthalein inhibits glutathione S-transferase activity in aorta homogenates. Aorta extracts did not detectably catalyze the reaction between glutathione and sulphobromophthalein and the glutathione level was not decreased by treating the intact aorta with sulphobromophthalein. It is concluded that sulphobromophthalein acts as a specific antagonist of the spasmolytic activity of glycerol trinitrate, probably as a result of its inhibition of glutathione S-transferase. It thus seems probable that glutathione and glutathione S-transferase are involved in the pharmacological activation of the organic nitrates.

Comparison of isobutyl nitrate and isobutyl nitrite: tolerance and cross-tolerance to glyceryl trinitrate.

This study includes the first systematic comparison of an organic nitrate with the corresponding organic nitrite-isobutyl nitrate and isobutyl nitrite. The spasmolytic activity of the nitrite on isolated rabbit aortic strips was stronger, more rapid in onset, but less stable than the activity of the nitrate. In vitro tolerance to glyceryl trinitrate and isobutyl nitrite greatly weakened the activity of isobutyl nitrate, respectively, but had much less effect on isobutyl nitrite. Possible reasons for these differences are discussed.

Use of isosorbide dinitrate saliva concentrations for biopharmaceutical investigations.

The concentration of isosorbide dinitrate in paired samples of plasma and mixed saliva was monitored for up to 24 hr after oral administration of 60 mg of sustained-release isosorbide dinitrate to eight healthy volunteers. Measured isosorbide dinitrate plasma concentrations were mainly in the range of 0.1-10 ng/ml. Isosorbide dinitrate was excreted into saliva resulting in a mean (+/- SD) saliva-plasma concentration ratio of 0.68 +/- 0.37. A significant correlation between concentrations of isosorbide dinitrate in saliva and plasma was found (p less than 0.01). The sustained-release properties of the administered formulation were confirmed from the concentrations of isosorbide dinitrate found in both saliva and plasma. Saliva-plasma ratios were independent of the absolute concentrations of isosorbide dinitrate but showed a slight tendency to decrease with time. The principal factor relating saliva and plasma isosorbide dinitrate concentrations appeared to be the degree of plasma protein binding of the drug.

Effect of piroxicam on structure and function of joint cartilage.

In vitro experiments were performed on isolated articular chondrocytes under the influence of piroxicam. It was demonstrated that this non-steroidal anti-inflammatory agent affected neither cell proliferation nor the incorporation of 35SO4 into matrix macromolecules. Dogs were treated with piroxicam for 8 weeks. Morphological studies were performed on the tissues of the knee joints. Macroscopic and light microscopic investigations revealed no structural differences between the tissues (synovial membrane and articular cartilage) of control and treated dogs. Even at the ultrastructural level no alterations in the cartilage were observed. The capacity of chondrocytes to incorporate 35SO4 under in vitro conditions was identical in control and experimental animals. It is concluded that piroxicam has no adverse effect on chondrocytes under in vitro conditions or on articular cartilage structure in the in vivo model.

The pattern of glyceryl nitrates after oral administration of glyceryl trinitrate.

An oral dose of 20 mg sustained release glyceryl trinitrate (GTN, Nitro Mack Retard) was administered to 6 healthy human subjects. In the plasma of all subjects the metabolically generated glyceryl nitrates glyceryl 1,2-dinitrate (G-1,2-DN), glyceryl 1,3-dinitrate (G-1,3-DN), glyceryl 2-nitrate (G-2-N) and glyceryl (G-1-N) could be identified, but no intact GTN was found. The nitrate metabolites showed sustained plasma profiles which can be explained by a slow release of GTN with subsequent complete first-pass denitration. The plasma concentrations of the mononitrates were generally higher than those of the dinitrates. G-1,2-DN and G-2-N, the metabolites which contain a nitrate group in the central position, showed higher concentrations than the respective isomeric compounds. The combined glyceryl dinitrates reached concentrations between 10.2 and 21.7 ng/ml, the combined mononitrates varied from 70.4 to 106.8 ng/ml. The ratios of the areas under the curve G-1,3-DN:G-1,2-DN:G-1-N:G-2-N were 1:4:19:64, on average. Taking into consideration the relative vasodilator potencies of glyceryl nitrates in the animal, our results give rise to the hypothesis that the glyceryl dinitrate metabolites participate in the clinical efficacy of large oral doses of sustained release GTN.

Bioavailability and metabolism of isosorbide dinitrate from a transdermal spray.

The plasma pharmacokinetics of isosorbide dinitrate (ISDN), isosorbide-2-nitrate (IS-2-N) and isosorbide-5-nitrate (IS-5-N) were investigated in 12 healthy volunteers after a single cutaneous administration of 60 mg ISDN (CAS 87-33-2) in the form of a solution sprayed onto the skin (TD Spray Iso Mack), in comparison with an intravenous infusion of 5 mg ISDN. After the intravenous dose, the apparent steady state volume of ISDN distribution came to 179.9 l, total body clearance was 3.14 l min-1, and terminal half-life was 79 min, on average. The transdermal absorption resulted in an average peak plasma concentration of 6.9 ng ISDN ml-1 at 5 h after the administration. ISDN concentrations between 1 and 5 ng ml-1 were maintained over at least 15 h. On average, 16.5% of the topically applied ISDN reached the systemic circulation. Total variations in Cmax (CV = 47.9%) and AUC (CV = 36.0%) of transdermal ISDN were similar to those usually observed after oral ISDN.

Glyceryl-1-nitrate pharmacokinetics in healthy volunteers.

The plasma kinetics and urinary excretion of glyceryl-1-nitrate (G-1-N), a metabolite of glyceryl trinitrate with antianginal potential, were investigated in 10 healthy male volunteers, after intravenous infusion and oral administration of 20 mg G-1-N. The apparent volume of G-1-N distribution was 601 corresponding to 0.761 kg-1 body weight, on average. It is suggested that total body water is the principal biological correlate of the hydrophilic drug. Mean intravenous clearance was 283 ml min-1 or 3.61 ml min-1 kg-1. The average of elimination half-lives were 2.50 +/- 0.36 (s.d.) h after the intravenous and 2.54 +/- 0.40 (s.d.) h after the oral dose. Inter-subject variances of pharmacokinetic parameters were low compared to variances reported for glyceryl trinitrate. The coefficient of intra-subject variation of the elimination half-lives was 8.8%. 5.5% (i.v.) and 5.4% (p.o.) of the administered dose were excreted into urine up to 48 h after the administration. 1% (i.v.) and 1.5% (p.o.) were in the conjugated form. The oral dose was rapidly and almost completely absorbed. The oral bioavailability on the basis of areas under the curve amounted to 88.6% on the average. For clinical use, owing to its high oral bioavailability, long residence in the body, inactivation by metabolic conversion, and good predictability of kinetic parameters, G-1-N offers advantage over glyceryl trinitrate.

[Influence of antianginal drugs on Lypressin induced T-wave enhancement in the electrocardiogram of the rat]. / Einfluss antianginöser Substanzen auf die durch Lypressin induzierte T-Wellenerhöhung im EKG der Ratte.

Lypressin enhances the T-wave in the ECG of the anesthetized Sprague-Dawley rat and this has been used in screening for antianginal activity. After oral administration the durations of action of the organic nitrates, glyceryl trinitrate, isosorbide dinitrate, glyceryl 1,2-dinitrate, glyceryl 1,3-dinitrate and of SIN-1 (3-morpholinosydnonimine), molsidomine and nicorandil were shorter than those of verapamil and nifedipine. The sequence of the durations of action of the substances examined was the same in the rat as in man.

The effect of activated charcoal on the bioavailability of piroxicam in man.

The effect of single and multiple oral doses of activated charcoal (a.c.) on the plasma concentrations of piroxicam was investigated in a cross-over study in 6 healthy volunteers after oral and rectal doses of 20 mg piroxicam. 50 g a.c. swallowed 5 min after the oral administration of one capsule of piroxicam almost completely prevented the absorption of the drug. 70 g a.c. per day were given in multiple doses over the interval of 10-58 h after the oral and 2-58 h after the rectal administration of piroxicam. This treatment reduced the mean bioavailability of piroxicam by 41.7% (oral) or 48.8% (rectal), relative to the control. The apparent total clearance increased significantly (p less than 0.05) to 163.6% (oral) or 187.9% (rectal) of the control. Half-lives of elimination were reduced on the average from 40.2 h to 19.6 h after the oral dose and from 40.7 h to 21.6 hours after the rectal dose under the a.c. treatment. It is inferred from these results that piroxicam is subject to enteral circulation. A.c. appears useful as an antidote in acute intoxications from piroxicam.

Enantioselective disposition of oral amlodipine in healthy volunteers.

Plasma concentrations of (R)- and (S)-amlodipine were measured after single oral administrations to 18 healthy volunteers of 20 mg amlodipine racemate. The contribution of the pharmacologically active (S)-enantiomer to the concentrations of total amlodipine (sum of enantiomers) was significantly higher than that of the inactive (R)-enantiomer, with mean values of 47% R to 53% S for the Cmax and 41% R to 59% S for the AUC (range between 24% R:76% S and 50% R:50% S). The oral clearance of the active (S)-form was subject to much less intersubject variation (25% CV) than that of the inactive (R)-form (52% CV). (R)-Amlodipine was more rapidly eliminated from plasma than (S)-amlodipine, with mean terminal half-lives of 34.9 h (R) and 49.6 h (S). The terminal half-lives of total amlodipine (mean 44.2 h) were strongly correlated with--and thus highly predictive for--the half-lives of the (S)-enantiomer. It is proposed that the observed enantioselectivity of oral amlodipine is due to differences in the systemic blood clearance of the enantiomers.

[Comparative antianginal, hemodynamic and pharmacokinetic effects of isosorbide-2-mononitrate and isosorbide dinitrate in the rat]. / Vergleichende antianginöse, hämodynamische und pharmakokinetische Wirkung von Isosorbid-2-mononitrat und Isosorbiddinitrat an der Ratte.

The effect of isosorbide 2-mononitrate (IS-2-MN) was compared with that of isosorbide dinitrate (ISDN) in rats regarding the antianginal, haemodynamic and pharmacokinetic properties. The antianginal effect of IS-2-MN in equal oral dose persisted 3 times longer in the rat than did ISDN. In the same oral dosage, the two compounds caused the equal reduction of the number of deaths after an acute myocardial infarction. The intravenous or enteral administration of a single IS-2-MN dose caused an increasingly dose-dependent reduction of the systolic and mean arterial blood pressure in anaesthetized rats. The amounts of IS-2-MN required for the purpose were identical for both kinds of application. The fall of the systolic and mean arterial blood pressure due to ISDN is approx. 22 times weaker after enteral administration than it is after intravenous application. The hypotensive effect of ISDN or IS-2-MN could be antagonized by pre-treatment of the animals with i.v. dihydroergotamine (DHE). The half-life of IS-2-MN in the rat was unchanged after increase of the oral doses. The bioavailability of IS-2-MN in the rat was 100%. 1 h after oral or intravenous administration of IS-2-MN to the rat, the concentrations in the walls of aorta abdominalis and aorta thoracica and in the walls of vena cava caudalis and vena thoracica were distinctly greater than in the blood or in the other tissues examined.

Comparative pharmacokinetics of isosorbide nitrates after repeated doses of sustained release isosorbide dinitrate.

The plasma kinetics of isosorbide dinitrate (ISDN), isosorbide-5-nitrate (IS-5-N) and isosorbide-2-nitrate (IS-2-N) were investigated in 20 healthy male and female volunteers, after b.i.d. administration over 2 days of sustained release ISDN 20 mg and 40 mg capsules (Iso Mack Retard 20 mg and 40 mg) and of a 40 mg sustained release ISDN tablet as reference formulation. The means of the individual maximum ISDN concentrations during the complete 2-day treatment amounted to 10.4 ng/ml after the 40 mg capsule, 5.3 ng/ml after the 20 mg capsule and 5.3 ng/ml after the reference tablet. The corresponding figures of the metabolically generated IS-5-N were 355.5 ng/ml, 168.8 ng/ml and 161.5 ng/ml, respectively. The measured amounts of IS-5-N are expected to contribute to the overall antianginal effect of at least the 40 mg capsule. According to the b.i.d. schedule, ISDN and the two mononitrates accumulated in the plasma after all three tested formulations. However, during the treatment with the 20 mg and the 40 mg capsules, accumulation was practically completed at the second day, while it was found to be more extended during treatment with the reference product. In terms of areas under the curve, the mean bioavailability of the 40 mg sustained release capsule relative to the reference formulation was 198% with respect to ISDN, and 197% both with respect to IS-2-N and IS-5-N. On the other hand, perfect dose-linearity of all relevant pharmacokinetic parameters of all three measured isosorbide nitrates was observed for the 20 mg and the 40 mg dose of the capsule.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-ulcer and secretion-inhibitory properties of the tricyclic derivative doxepin in rats and dogs.

The anti-ulcer and antisecretory properties of 3-(dibenz[b,e] oxepin - 11(6H)-ylidene)-N,N- dimethylpropylamine hydrochloride (doxepin) were investigated in a series of acute experiments in rats with gastric and duodenal ulcer. Acute gastric ulceration induced by immobilisation and stress (waterbath), and by non-steroidal anti-inflammatory agents, was reduced by doxepin to the same extent as by pirenzepine and cimetidine. Doxepin and cimetidine showed a weak but significant effect against serotonin-induced ulcers in the rat, but pirenzepine did not. Duodenal ulcer caused by increased acid production (pentagastrin plus carbachol induced) was suppressed by pirenzepine, doxepin and cimetidine. The inhibition of gastric secretion by doxepin was studied in anaesthetised rats and conscious dogs. In the Lai rat, doxepin decreased carbachol-induced secretion of hydrochloric acid more effectively than cimetidine. Doxepin was as ineffective as pirenzepine against histamine- or pentagastrin-induced secretion. In the dog with gastric fistula, doxepin inhibited the acid production induced by 2-desoxy-d-glucose more effectively, and for longer periods, than that induced by pentagastrin or histamine. In the dog with a Heidenhain pouch, doxepin reduced the acid secretion stimulated by pentagastrin and carbachol, and by histamine, less effectively and for a shorter time, than cimetidine. The antagonism of doxepin to the action of carbachol in the rat and that of 2-desoxy-d-glucose in the dog appears to be an important factor in its mode of action. To inhibit the secretion of saliva and to delay intestinal transport, a dose of doxepin 3-10 times greater than that required for anti-ulcerative and secretion-inhibitory effects was necessary.

[Pharmacology of isosorbide dinitrate after transdermal application]. / Pharmakologie von Isosorbiddinitrat nach transdermaler Applikation.

Different organic nitrates exhibit markedly different in vitro partition coefficients, P. The lipophilic character, of which P is a measure, is the most important physico-chemical property which influences the penetration of nitrate molecules through the skin. It follows that there are several possibilities for developing formulations in which the diffusion of the molecules through the layers of the epidermis is furthered. A transdermal spray of isosorbide dinitrate (ISDN, TD Spray Iso Mack) was administered to volunteers and blood concentrations of the nitrate were measured. The results demonstrate that therapeutically effective amounts of the nitrate do in fact penetrate through the various levels of the skin. In addition pharmacokinetic measurements confirm that ISDN penetrates from the sprayed on film into the surface of the skin within 20 min and is then slowly released from the epidermis into the capillaries of the corium. An advantage of the administration of ISDN through the skin lies in the avoidance of the rapid metabolism of the drug which takes place during its first passage through the liver (first-pass effect). The protracted efficacy of the transdermal spray in the treatment of patients with coronary disease is, therefore, due to the unchanged ISDN and not, as with oral treatment, to pharmacologically active metabolites.

Oral absorption and disposition of isosorbide dinitrate and isosorbide mononitrates in man.

The plasma concentrations of isosorbide dinitrate (ISDN) and its two pharmacologically active metabolites isosorbide 2-mononitrate (IS-2-MN) and isosorbide 5-mononitrate (IS-5-MN) were determined after oral administration of 20 mg ISDN and 20 mg of each of the mononitrates. The mean concentration-time curve of ISDN showed a peak of 51.6 ng/ml 15 min after drug intake, and declined bi-exponentially with a terminal half-life of 36.5 min. The mean concentrations of the simultaneously measured metabolic products IS-2-MN and IS-5-MN reached a maximum of 40.5 ng/ml and 144.4 ng/ml, respectively. In contrast, after the direct ingestion of isosorbide mononitrates, peaks of 409.1 ng/ml (IS-2-MN) and 483.2 ng/ml (IS-5-MN) were observed in the corresponding mean curves. Mean half-lives of 1.72 h for IS-2-MN and 4.20 h for IS-5-MN were calculated. The mean apparent volumes of distribution were 44.5 l (IS-2-MN) and 34.4 l (IS-5-MN), suggesting that the isosorbide mononitrates are distributed throughout the whole body fluid. After ISDN administration, it was estimated that 3.0 mg IS-2-MN and 7.8 mg IS-5-MN reached the systemic circulation. This corresponds to 63% of the ISDN dose being converted to isosorbide mononitrates by metabolic processes.

[Effect of piroxicam on the structure and function of joint cartilage]. / Der Einfluss von Piroxicam auf Struktur und Funktionen des Gelenkknorpels.

Experimental studies on the dog were performed to investigate possible deleterious effects of non steroidal anti-inflammatory agents, in particular piroxicam, on healthy articular cartilage. Piroxicam, diclofenac, and indomethacin were administered orally to beagles over an 8-week period. Control animals received empty capsules during the same period. A variety of morphological investigations were carried out on the tissues of the knee joint following treatment. Macroscopically and at light microscopical level no differences in the structure of cartilage or synovial membrane were detected between control and test animals. Similarly, with the transmission electron microscope, no structural changes were observed between control and test groups (piroxicam-treated). The incorporation of radioactively labeled sulfur into cartilage proteoglycans was similar in piroxicam-treated and control dogs. Related studies involving the addition of piroxicam to isolated chondrocytes in vitro showed that the proliferative capacity and proteoglycan synthesis of chondrocytes were unaffected by this antirheumatic agent. It is concluded that piroxicam exerts no damaging effect on normal cartilage in the knee joint of the dog.

Enantioselective gas chromatographic assay with electron-capture detection for amlodipine in biological samples.

A sensitive enantioselective gas chromatographic assay has been developed for amlodipine, 2-[(2-aminoethoxy)-methyl]-4-(2-chlorophenyl)-3-ethoxycarbonyl-5- methoxycarbonyl-6-methyl-1,4-dihydropyridine, a calcium channel blocking therapeutic agent. The assay involves conversion of the (+)-(R)- and (-)-(S)-enantiomers of amlodipine into their acyl derivatives with the chiral reagent (+)-(S)-alpha-methoxy-alpha-trifluoromethylphenylacetyl chloride (Mosher's reagent). Peak separation after chromatography of the diastereomers was larger than 85%, and the lower limit of detection in blood plasma was 0.02 ng/ml for each enantiomer. The method has been used for the measurement of amlodipine enantiomers in human, rat and dog plasma, and in various organs of the rat.

Preliminary study of the pharmacokinetics of desmethyldiazepam administered as drops or tablets.

Desmethyldiazepam (Vegesan) was administered in the form of 5-mg and 10-mg tablets and of 10-mg drops to 4 male and 4 female young healthy volunteers. The plasma levels of desmethyldiazepam were measured over 168 h. The time courses could be fitted to the one- or to the two-compartment model. The mean half-lives of elimination came to 75.3 +/- 32.0 (SD) h (5-mg tablets), 66.5 +/- 21.0 (SD) h (10-mg tablets) and 78.4 +/- 33.2 (SD) h (10-mg drops). The bioavailability of desmethyldiazepam from tablets and from drops was practically the same. The bioavailability appeared to be independent of dose in this range. A significantly higher total plasma clearance was calculated for the male than for the female volunteers after all three dosage forms (p less than 0.05). The total plasma clearance lay between 4.8 and 13.0 ml/min for the female and 12.4 and 24.3 ml/min for the male volunteers. Ingestion of the contraceptive pill is suggested as a possible cause of the sex differences.

[Comparative hemodynamics action of glycero-2-nitrate and glycerol trinitrate in various species and the pharmacokinetics of glycerol-2-nitrate in the dog]. / Vergleichende hämodynamische Wirkung von Glycerol-2-nitrat und Glyceroltrinitrat an verschiedenen Tierarten und Pharmakokinetik von Glycerol-2-nitrat am Hund.

Comparative Hemodynamic Activity of Glyceryl 2-Nitrate and Glyceryl Trinitrate in Various Species and Pharmacokinetics of Glyceryl 2-Nitrate in Dog A single dose of glyceryl 2-nitrate (G-2-N) had practically identical hypotensive and cardiovascular activity when administered intravenously or enterally to the anaesthetized rabbit, cat or dog. In all three species the hypotensive and also cardiovascular activity of G-2-N lasted much longer than that of glyceryl trinitrate (GTN, Nitro Mack). In the rabbit, cat and dog enterally active doses of GTN were 500-1000 times greater than parenterally active doses. In all species enterally administered GTN was about 8 times more active than enterally administered G-2-N. G-2-N is 100% bioavailable in the conscious dog.