PubMed Health⌕ Search

Biomedical subjects

R D Smyth

Publications and source records attributed to R D Smyth.

At least 55 records · Page 3Linked to original sources
PubMed1977

Calcium stimulation of gastrin and gastric acid secretion: effect of small doses of calcium carbonate.

Oral calcium carbonate (0-5 g, pH 9-4) increased serum gastrin and gastric acid output with slight but insignificant change in serum calcium. A similar rise in serum calcium during an intravenous infusion of calcium gluconate failed to increase serum gastrin and gastric acid output. Both intragastric calcium actions were abolished by acidification of the calcium carbonate solution (pH 1-0). The increase in serum gastrin and gastric acid output after intragastric calcium carbonate was not affected, however, by a simultaneous intraduodenal acid load. Equivalent neutralising doses of magnesium hydroxide (pH 9-4) did not increase serum gastrin and gastric acid output above basal levels, whereas antral acidification with 20 ml 0-1 N HCl resulted in a slight decrease in serum gastrin. Intraduodenal calcium carbonate (pH 3-0) also increased serum gastrin and gastric acid output, whereas an equivalent volume of intraduodenal saline (pH 3-0) had no effect. These findings indicate that calcium increases serum gastrin by local stimulation of antral and duodenal mucosa. They also suggest that the action of calcium on gastric secretion is partly mediated by gastrin.

Calcium↗
PubMed1976

Correlation between dissolution characteristics and absorption of methaqualone from solid dosage forms.

A methaqualone tablet in two strengths, 150 and 300 mg, was developed. The dissolution rate of an experimental formulation in pH 7.0 phosphate buffer, measured by the resin flask method, was shown to correlate with bioavailability in humans. The dissolution rate criterion was used to develop the final tablet formulation. Bioavailability of this formulation in two strengths was compared with a commercial capsule formulation and a slowly dissolving tablet formulation. Correlation between dissolution rate and bioavailability was shown in freshly prepared methaqualone tablet formulations. Bioavailability of tablets under accelerated stability testing conditions remained unaltered, whereas the dissolution rates in pH 7 phosphate buffer decreased, using the resin flask method. A rotating-flask method was developed, and dissolution in 0.1 N HCl at 2 rpm correlated with the bioavailability of both new and aged tablet formulations.

Absorption↗
PubMed1976

Correlation of in vitro and in vivo methodology for evaluation of antacids.

The rate and extent of acid consumption of an antacid suspension and tablet were evaluated by in vitro and in vivo techniques. Four different test procedures were used to estimate in vitro antacid reactivity. In vivo effects were determined in the fasted and postcibal states in normal human subjects by a radiotelemetry procedure. The duration of elevation of intragastric pH greater than 3 was in agreement with in vitro estimates of total acid consumption of the antacid. There was also good correlation between onset, extent, and duration of in vivo antacid activity and a modified in vitro Beekman antacid test procedure. There was no significant difference in antacid activity of the tablet or suspension in either in vitro or in vivo test procedures. A wide variation in antacid activity was observed between subjects and also in the fasted versus postcibal states. These studies emphasize the requirements for standardization of antacid products by comparactive in vitro and in vivo evaluations to facilitate individualized dose titration of the antacid in each patient and correlation of the acid secretion rate in various types of GI disease with the antacid dose.

Aluminum Hydroxide↗
PubMed1976

The antiphlogistic, antinociceptive and antipyretic properties of fenclorac.

Fenclorac (a,m-dichloro-p-cyclohexlphenylacetic acid, diethylammonium salt) is a potent nonsteroidal anti-inflammatory agent with significant analgesic and antipyretic activity. Fenclorac had an ED50 of 7.9 mg/kg in the carrageenan paw edema assay and had a duration of action of 18-22 hours. Comparative tests in the carrageenan paw edema assay in the rat indicated that the potency of fenclorac was 13 times that of aspirin, 3.4 times phenylbutazone, 3 times ibuprofen and 0.3 times indomethacin. Fenclorac was less potent than indomethacin, but more potent than phenylbutazone or aspirin in treatment of developing or established adjuvant arthritis. The anti-inflammatory effectiveness of fenclorac did not depend upon the integrity of the adrenopituitary axis and was not affected by the route of administration or sex of the test animal. Fenclorac was 77 times more potent than aspirin and more than twice as potent as indomethacin in reducing fever in rats rendered hyperthermic with brewer's yeast. Fenclorac did not affect normal body temperatures. Fenclorac did not interfere with cellular immune mechanisms as measured by its lack of effectiveness in experimental allergic encephalomyelitis. Antinociceptive testing indicated that fenclorac had peripheral but not central analgesic activity. Fenclorac had an acute oral LD50 in rats and mice of 285 and 430 mg/kg, respectively. The acute gastric lesion UD50 for fenclorac was 7 mg/kg in the fasted rat. Studies using 51Cr-tagged erythrocytes indicated that fenclorac did not produce significant fecal blood loss in the rat at twice the therapeutic ED50 dose for up to 12 days after dosing. Extensive and prolonged fecal blood loss was observed with a corresponding dose of indomethacin for up to nine days after administration. Comparison of the anti-inflammatory pharmacology, Therapeutic Ratio and the data obtained from the 51Cr-fecal blood loss studies indicated that fenclorac was well tolerated after acute or subacute administration to the rat.

Adrenalectomy↗
PubMed1976

Induction of hepatic enzymes by methaqualone and effect on warfarin-induced hypoprothrombinemia.

The effect of methaqualone on the induction of hepatic enzymes was evaluated in rats and compared with that of phenobarbital by measuring effects on hexobarbital and methaqualone hypnosis, plasma and tissue levels of methaqualone, hepatic aniline hydroxylase and aminopyrine demethylase activity and warfarin-induced hypoprothrombinemia. Maximal reductions in hexobarbital hypnosis occurred 3 days after daily administration of 60 mg of methaqualone per kg per day. At this time, the activities of aniline hydroxylase and aminopyrine demethylase were increased 60 and 139%, respectively, and hepatic microsomal proteins increased 15% above controls in methaqualone-pretreated animals. Methaqualone altered its own metabolism as demonstrated by a 48% reduction in methaqualone hypnosis in pretreated animals. The extent and duration of induction by phenobarbital was considerably greater than methaqualone in all experiments. Methaqualone pretreatment did not affect warfarin-induced hypoprothrombinemia, whereas phenobarbital-pretreated animals showed a 32 to 64% reduction in response to the anticoagulant. These studies indicate that methaqualone is a relatively weak inducer of hepatic drug-metabolizing enzymes and has no effect on the anticoagulant acitivty of warfarin.

Aminopyrine N-Demethylase↗
PubMed1976

Blood levels in methaqualone in man following chronic therapeutic doses.

Human serum was analyzed for methaqualone (MTQ) and hydroxylated metabolites by gas liquid chromatographic (GLC), ultraviolet spectrophotometric (UV) and spectrofluorimetric (SF) procedures. Intact methaqualone was found to be the major circulating drug component after administration of multiple 300 mg daily doses over a 28-day period. Hydroxylated methaqualone metabolites, if present, were estimated to be in extremely low concentrations. After acute ingestion of large quantities of methaqualone (2.4-3.0 g), at least one methaqualone metabolite, [2-methyl-3-(2' hydroxymethylphenyl)-4(3H)-quinazolinone] was present in serum obtained from subjects with a history of chronic drug abuse.

Adult↗
PubMed1975

Age differences affecting induction of hepatic drug metabolizing enzymes by methaqualone and phenobarbital in the rat.

Methaqualone pretreatment for 3 or 6 days caused an induction of hepatic enzymes in the young male rat as measured by a reduction in hexobarbital-hypnosis. However, methaqualone pretreatment had no effect on the hexobarbital-hypnotic response in older male rats. Phenobarbital was a more potent enzyme inducer than methaqualone, and caused induction of liver enzymes in both age groups.

Age Factors↗