Characterization of the metabolites of alosetron in experimental animals and human.

The metabolism of radiolabelled alosetron was studied in rat, dog, rabbit, mouse and human. The metabolism in rat and dog was studied at a low and an elevated dose designed to generate sufficient quantities of metabolite for definitive identification. A strategy for the characterization of metabolites in cases of extensive metabolism was developed and demonstrated for alosetron. Semi-preparative high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), nuclear magnetic resonance (NMR) and liquid chromatography-nuclear magnetic resonance (HPLC-NMR) enabled the isolation and characterization of 28 metabolites of alosetron. The characterization of the metabolites in animal excreta facilitated the identification of human systemic metabolites.

off absorption, pharmacodynamics, metabolism and excretion of 14C-sumatriptan following intranasal administration to the beagle dog.

The pharmacodynamics, pharmacokinetics, metabolism, and excretion of 14C-sumatriptan have been studied in the beagle dog following administration by the intranasal and other routes. The pharmacological response which was monitored, an increase in carotid arterial vascular resistance, correlated with the plasma levels of unchanged sumatriptan following intranasal, intravenous, or intraduodenal administration to the anaesthetised dog. The pharmacokinetics and metabolism of sumatriptan were then confirmed in conscious male and female dogs. Intranasal administration of 14C-sumatriptan resulted in rapid absorption of part of the dose. The overall bioavailability of sumatriptan was 40-50%. Sumatriptan was eliminated from plasma with a half-life of 1.5 or 1.9 h after intravenous or intranasal dosage respectively. Radioactivity was largely excreted in urine (up to 75% of the dose) with small amounts in the bile and faeces after intravenous and intranasal dosing, as sumatriptan and a major metabolite. The results from these studies suggest that intranasal administration provides a viable method for delivering sumatriptan to the systemic circulation.

Naratriptan: biological profile in animal models relevant to migraine.

The biological profile of naratriptan (N-methyl-3-(1-methyl-4-piperidinyl)-1H-indole-5-ethane-sulphonamide), a novel 5HT1B/1D receptor agonist, was investigated in a variety of experimental models of relevance to migraine. Naratriptan has high affinity for human recombinant 5HT1B and 5HT1D receptors (pKi = 8.7 +/- 0.03 and 8.3 +/- 0.1, respectively) and causes contractions of dog isolated basilar and middle cerebral artery (EC50 values of 0.11 and 0.07 microM, respectively). Naratriptan causes small contractions of human isolated coronary arteries (EC50 value of 0.17 microM; maximum contraction equivalent to 33% of 5HT maximum). In anaesthetized dogs, naratriptan causes selective vasoconstriction of the carotid arterial bed (CD50 dose = 19 +/- 3 micrograms kg-1) and, in anaesthetized rats, naratriptan selectively inhibits neurogenic plasma protein extravasation in the dura (ID50 = 4.1 micrograms kg-1). In a variety of antinociceptive tests, naratriptan has no effect even at high doses. In conscious rats and dogs, naratriptan has high oral bioavailability (71% and 95%, respectively). The data show that naratriptan is a selective agonist at 5HT1B/1D receptors, with a pharmacological profile very similar to that of sumatriptan, albeit 2-3 fold more potent. These observations, coupled with high oral bioavailability in animals, suggest that naratriptan has the profile of an orally effective anti-migraine drug.

Disposition of sumatriptan in laboratory animals and humans.

Sumatriptan is a new 5HT1-like agonist that has proved a novel and effective treatment for migraine. The disposition of the 14C-radiolabeled drug in laboratory animals and humans after oral and parenteral administration is described. Oral absorption of sumatriptan is essentially complete in dogs and rabbits, but only approximately 50% in rat. In humans, at least 57% of an oral dose is absorbed. Bioavailabilities are species dependent (14, 23, 37, and 58% in humans, rabbits, rats, and dogs) reflecting differing degrees of first-pass metabolism. These data correlate well with hepatic extraction ratios, which are highest in rabbits and humans and lowest in dogs. Renal clearance is significant in all species and exceeds the glomerular filtration rate in rats, rabbits, and humans, but not in dogs. The compound is a weak base that shows widespread tissue distribution, including passage across the placental barrier and into milk, but low CNS penetration. Protein binding of sumatriptan is low in all species. Elimination half-lives of sumatriptan are approximately 1 hr in rats and rabbits, and approximately 2 hr in dogs and humans. In all species the majority of the absorbed dose is renally excreted, predominantly as the indole acetic acid metabolite and unchanged drug. Interesting species differences are evident in the metabolism of sumatriptan. Thus, in humans, the indole acetic acid metabolite is excreted partly as a glucuronide, whereas in animals conjugation of this metabolite is not apparent. In addition, demethylation of the sulfonamide side chain of the drug is evident in rodent and lagomorph species only.

Thermospray liquid chromatography-mass spectrometry for the characterisation of sulphate ester conjugates.

Formation of polar conjugates is a well documented metabolic pathway for xenobiotics containing phenolic hydroxyl groups. This paper describes the analysis of two sulphate ester conjugates by fast atom bombardment mass spectrometry and thermospray liquid chromatography-mass spectrometry. Thermospray liquid chromatography-mass spectrometry proved the more successful technique for obtaining the molecular weight of the intact conjugate, but only by removal of the buffer from the high-performance liquid chromatography eluent.

The metabolism of ondansetron.

The metabolism of ondansetron has been studied in rat, dog and man. In laboratory animals absorption of the compound across the gastrointestinal tract is rapid and extensive, but due to high first-pass metabolism, the oral systemic bioavailability is low (less than 10%). The high systemic clearance of ondansetron results in a very short half-life in rat and dog. The renal clearance of ondansetron is low, indicating that the major route of systemic clearance is by metabolism. Routes of excretion of drug-related material differ between laboratory animals and man - the major route in the rat and dog is via the bile, while in man the predominant route is via the urine. However, the routes of metabolism are qualitatively similar in all species, indicating that the species used in toxicological testing of ondansetron were appropriate.

The kinetics of 14C-GR43175 in rat and dog.

GR43175 is a selective 5-HT 1-like receptor agonist which is effective in the acute treatment of migraine. Rats and dogs were dosed intravenously (iv) and orally (po) with 1 mg 14C-GR43175 base (as succinate salt)/kg bodyweight. GR43175 is rapidly absorbed after oral dosing. In dog, 95-100% of the dose is absorbed, but less (25-30%) is absorbed by the rat. The bioavailability is greater than 54% in dog, but lower in rat. Except for the CNS, drug-related material is widely distributed after iv dosing, but is mainly concentrated in the gastrointestinal tract and excretory organs after oral dosing. GR43175 is eliminated from plasma by a combination of renal and metabolic clearance. Some first-pass metabolism occurs in both species. In dog the major route of excretion is in urine (78-83% of the dose) after either route of administration. In rat, urine is also the major route of excretion (71%) after iv dosing. After oral dosing to the rat the major route of excretion is in the faeces (83%). GR43175 is extensively metabolized, after either route of administration, in both species. GR49336, the indole acetic acid derivative of GR43175, is the major metabolite in dog and a major metabolite in rat.

Determination of salbutamol in human plasma and urine by high-performance thin-layer chromatography.

A rapid, accurate and sensitive method for the determination of salbutamol in plasma and urine is described. Salbutamol is extracted using solid-phase techniques and converted to an indoaniline dye by reaction with dimethyl-p-phenylenediamine. The indoaniline is separated using high-performance thin-layer chromatography and quantified by absorption microdensitometry at 650 nm. The method is sensitive down to 20 ng/ml in urine and to 1 ng/ml in plasma and provides data in good agreement with that obtained by gas chromatography--mass spectrometry. The method can be used for analysis of pharmacokinetic studies.

Value of toxicological investigation in the diagnosis of acute drug poisoning in children.

In the 2 years 1978 and 1979 specimens from 287 children aged between 10 days and 14 years were received for general toxicological investigations. Of the 95 (33%) cases of confirmed poisoning, the diagnosis was established as a direct result of the analyses in 48 patients. No diagnosis was made in at least 85 (30%) of the remaining cases. Benzodiazepines were the drugs most commonly encountered (33%), followed by barbiturates, glutethimide, and meprobamate (15%), salicylate and paracetamol (15%), tricyclic antidepressants (12%), and ethanol (11%). 36 patients were severely poisoned (grade 3 or 4 coma, or convulsions), although only 1 patent died. There was evidence that drug(s) had been administered without authorisation in at least 7 instances, and in 51 (54%) of the poisoned patients there was sufficient concern about the safety of the child or the mode of administration of the drug(s) to institute legal proceedings (8 cases), involve the social services (25 cases), or arrange further medical appointments (18 cases). Drugs are readily available in most households and offer a means of inflicting injury that is less easily detectable than physical assault. For this reason, comprehensive toxicological investigations should be considered in children not only when they may assist in management but also in the presence of unusual or unexplained symptoms which could be drug-induced.

The effect of temperature on the growth and lipid composition of the extremely halophilic coccus, Sarcina marina.

Sarcina marina (NCMB 778) grew over the temperature range 20-45 degrees C but no growth was recorded at 15 degrees C or 50 degrees C. At the optimum growth temperature of 34 degrees C the doubling time was 14.5 h. The major polar lipid components, tentatively identified as the diether analogues of phosphatidyl glycerophosphate (PGP), phosphatidyl glycerol (PG), diglycosyl diglyceride (DGD) and triglycosyl diglyceride (TGD), and the major neutral lipid components, tentatively identified as squalene, dihydrosqualene, tetrahydrosqualene, vitamin MK8, geranyl geraniol and di-O-phytanyl glycerol, are identical to those found in other extremely halophilic rods and cocci. The total lipid content varied with growth conditions from 0.6-3.2% of the dry cell weight, polar lipids accounted for between 94.3 and 83.6% of the total lipid, the remainder being neutral lipid. In response to both the transition from exponential to stationary phase and a reduction of 14 degrees C in growth temperature, batch cultures showed: (i) an increase in total lipid content; (ii) a decrease in PG and (iii) an increase in PGP. Specific responses to the temperature decrease were (i) increased total lipid content; (ii) no decrease in neutral lipids in stationary phase; (iii) marked reduction in PG and (iv) raised DGD. (i) and (ii) could be mechanisms for increasing membrane fluidity. In common with all other extreme halophiles investigated the alkyl side chains of S. marina polar lipids were identified as the phytanyl (3R, 7R, 11R, 15-tetramethylhexadecyl) group. Its structure did not appear to vary with temperature so that the normal mechanisms for modifying the structure of lipid alkyl side chains to modulate membrane fluidity in response to temperature changes probably does not occur in this group of microorganisms.