Automated extraction of drugs from biological fluids

An automated continuous flow liquid-liquid extraction procedure is described for the separation of the H2-antagonist loxtidine from plasma samples containing two metabolites which interfere in the radioimmunoassay of the drug. The extraction of the bronchodilator salbutamol was studied using the DuPont Prep I automated liquid solid extraction apparatus, with a 12 cartridge capacity, and a vacuum extraction box designed in this laboratory to hold 30 Sep-pak C-18 (Waters Associates) cartridges. Twenty-four plasma samples per hour can be automatically processed with the Prep I. Although the vacuum box is not fully automated 45 plasma samples per hour can be processed. The Prep I can only be used with DuPont XAD, strong cation and anion exchange cartridges. Cartridges containing alumina, silica, florisil, cation and anion exchange resins and reverse phase packings can all be used with the vacuum extraction box. The latter costs only a fraction of the Prep I and therefore each analyst can have his own unit.

Plasma ranitidine concentrations after intravenous administration in normal volunteers and haemodialysis patients

A comparison was made of the plasma concentrations of ranitidine base in 12 normal volunteers after the administration of 100 mg intravenously and in 6 patients with terminal renal failure after 40 mg intravenously off and then during haemodialysis. The plasma ranitidine concentrations were determined by radioimmunoassay. The results suggest that reduced elimination of the drug occurs in patients with severe renal failure and that there is significant removal of the drug during haemodialysis. It is suggested that dosage reduction is advisable in patients with severe renal failure and a suitable schedule for such patients is described.

Gastric acid response to topical or intravenous histamine and topical H2-receptor blockade in dogs

This study was undertaken to determine gastric acid surface and to examine the local effect f ranitidine, a histamine H2-receptor antagonist, on the gastric acid response to histamine. Histamine applied to the Heidenhain pouch (HP) mucosa resulted in a slight and dose-dependent stimulation of acid secretion without affecting acid secretion from the main stomach. Ranitidine given into the HP caused dose-dependent inhibition of the HP response to topical or intravenous histamine without affecting the acid response of the main stomach and without any significant change in the serum ranitidine level. Ranitidine applied to the main stomach with the pylorus occluded inhibited histamine-induced acid secretion also without any increase in the serum ranitidine level. This inhibition was about 30% of that obtained with the same dose of ranitidine given into the stomach with the pylorus left open during the experiment. This study provides evidence that topical histamine is a weak stimulant of gastric secretion and that topical ranitidine is capable of local inhibition of the acid response to both topical and intravenous histamine.

Ranitidine--a new H2-receptor antagonist

The pharmacokinetics and gastric antisecretory effects of a new histamine H2-receptor antagonist, ranitidine hydrochloride, have been investigated in healthy subjects. In the pharmacokinetic study six subjects received 20 mg, 40 mg, and 80 mg ranitidine, both orally and intravenously. Plasma levels of ranitidine were dose-related and in most subjects after oral drug the concentration time curve was bimodal. The estimated elimination half-life was 140 minutes and the bioavailability of the oral drug was about 50%. Five subjects received bolus intravenous injections of ranitidine 20 mg, 40 mg, and 80 mg during continuous gastric stimulation with pentagastrin. There was a dose-related reduction in acid output (P less than 0.05).

Affinity of labetalol for ocular melanin

1 The toxicity of labetalol has been studied in mice, rats, rabbits, and dogs, and reproductive studies have been carried out in rats and rabbits. Nothing was observed in any of these species to suggest that patients taking labetalol might be exposed to any toxic hazard. 2 During the reproductive studies 14C-labetalol was used to study placental transfer. Radioactivity was present in the uveal tract of the foetal eye. 3 Radioactive labetalol but not its metabolites was bound to the melanin pigment of the eye. This binding was reversible. It was not possible to saturate the melanin of the cat and dog eye even with prolonged dosing with labetalol. 4 Chloroquine, given orally at doses of 1.5-6 mg/kg/d for 4-7 weeks, produced changes in the cat retina. When oral doses of 20 mg labetalol/d were given to cats for 7 months, no oculotoxic effects were observed. 5 Detailed ophthalmological and histological examinations were carried out on the rats, rabbits, cats and dogs used in these studies. No changes indicative of oculotoxicity were observed. In the reproductive studies no effects were observed in the developing rat or rabbit eye, which could be consequent on the placental transfer of labetalol or its metabolites.

Fractures of the humeral shaft: a retrospective study of 240 adult fractures

Of 240 humeral fractures, 60 per cent occurred in patients under 35 years old, 39 per cent of fractures being in the middle third of the shaft, 28 per cent were open with an infection rate of 4 per cent. Radial nerve palsy was present in 18 per cent; midshaft fractures accounting for 69 per cent, with 60 per cent of radial nerves recovering spontaneously; 24 per cent after 12 weeks post injury. One hundred and eleven fractures had documentation greater than 3 months. Closed treatment in 100 patients resulted in 5 non-unions and 15 delayed unions; 11 primary internal fixations resulted in 3 non-unions and 2 delayed unions. Subsequent operative procedures reduced the total non-union rate to 5 per cent with 1 per cent delayed union and 4 per cent unknown. Fractures of the humeral shaft that have not begun to unite at 6 to 10 weeks probably will go on to non-union unless the treatment plan is changed. Closed methods of immobilization, other than the sling and swathe, should be used in chronic brain syndrome patients to avoid compounding their fractures. Sixty-three patients with 64 fractures were evaluated in follow-up using Cave's AEF system (92% excellent and satisfactory results) and a modification of Neer's protocol for proximal humeral fractures, (87% excellent and satisfactory results). A functional evaluation on the Cybex machine, (torque through range of motion) gave a useful graphic end result.

Photometric calibration of brief flash sources: technical note

From prior work is derived an equation for predicting errors incurred by the sole use of luminance values (0.05 of log factor of luminance increment above the calibrated value). A simple method was described for measuring the photometric result of a brief flash where peak candlepower is unknown.