A comparison of salicylic acid levels in normal subjects after rectal versus oral dosing

OBJECTIVES

The common practice is to use 162 mg of aspirin orally in the emergency department (ED) for patients presenting with myocardial infarction. If the patient cannot take aspirin orally in the authors' facility, then 600 mg of aspirin is given rectally. However, no strong evidence exists as to whether the oral and rectal doses provide equivalent risk protection. The authors hypothesized that the salicylic acid levels for orally and rectally administered aspirin will not be similar, because of the different dosages used and the different routes of administration.

METHODS

The study sample consisted of healthy, nonpregnant, adult volunteers without active illness, who did not take any medication regularly. Each subject served as his or her own control to account for any confounding factors. The study was conducted on 2 days, separated by a 1-week washout period. On the first day, 162 mg of oral aspirin was chewed and swallowed. Salicylic acid levels were obtained at baseline (i.e., before taking the aspirin) and then 30, 60, and 90 minutes after dosing. The 600-mg aspirin suppository was self-administered 1 week later with a sample for laboratory measures again drawn at baseline and then 30, 60, and 90 minutes after dosing.

RESULTS

Twenty-four subjects completed the study. The rectal suppository provided significantly more salicylic acid into the blood than the oral tablets over 90 minutes (p < 0.001). No statistical difference was noted between oral and rectal administration from baseline to 30 minutes (p > 0.05). However, mean salicylic acid levels from the rectal suppository were statistically higher than from the oral tablets from 30 to 60 minutes (p < 0.001) and from 60 to 90 minutes (p = 0.002). More than 60% of the subjects had an increasing salicylic acid level response over time to the rectal suppository. The salicylic acid level response to the oral administration was more evenly divided between those subjects whose salicylic acid levels peaked quickly and then fell or held steady (33%), those whose salicylic acid levels increased over time (29%), and those whose salicylic acid levels were measureable only after 60 minutes (25%). Although not statistically significant, these differences in group distributions for the type of salicylic acid level response between oral and rectal doses suggested the possibility of a rectal advantage.

CONCLUSIONS

Whether the higher salicylic acid levels and faster absorption of the rectal aspirin translate into better clinical outcomes is unknown and cannot be concluded from our study. Previous evidence, however, has shown that 162 mg of aspirin chewed and swallowed provided lower mortality in patients presenting with myocardial infarction. Our results suggested the rectal administration of a 600-mg suppository provides sufficient levels of salicylic acid within 90 minutes to meet or exceed that of oral aspirin.

The release of isoconazole nitrate from different suppository bases: in-vitro dissolution, physicochemical and microbiological studies

The influence of the suppository base on the in-vitro release of isoconazole nitrate was studied by dissolution, physicochemical diffusion and microbiological disk-diffusion methods. Vaginal suppository formulations containing 25 mg isoconazole nitrate for local treatment of vaginitis were prepared by a fusion method, using different hydrophilic and lypophilic suppository bases (PEG 6000, PEG 4000, PEG 1500, Witepsol H15, Novata BD and Cremao). In-vitro release rates were examined by dissolution, physicochemical diffusion and microbiological disk-diffusion methods. In the physicochemical investigations the pH indicators (pH 1-14) erythrosin B, thymol blue, bromocresol green, chlorophenol red, phenol red, and alkali blue were added to agar gels. The discs were placed onto the agar gels and 21 h later, the coloured zone diameters were measured. In the microbiological investigations, the discs were put on the inoculated plates with the suspension of Candida albicans (Institute Pasteur 628). The inoculated plates were incubated at 37 degrees C for 3 days, then the diameters of inhibition zones were measured. In the dissolution investigations release rates were in the order PEG 6000 > PEG 4000 > PEG 1500 > > Witepsol H15 > Cremao > Novata BD. The diffusion distance of isoconazole nitrate in the physicochemical investigation was in the order polyethylene glycols > Witepsol H15 > Novata BD. In the microbiological studies release rates were found with polyethylene glycols > Witepsol H15 > Novata BD > Cremao. The findings in the in-vitro studies suggested that polyethylene glycols are suitable bases for vaginal suppositories.

Continuous flow bead-bed dissolution apparatus for suppositories

A bead-bed dissolution apparatus for suppositories was evaluated by measuring the release of benzocaine from various vehicles. During dissolution, suppositories soften, deform, disintegrate, and eventually pass through a phase change from a solid to an oil. The control of the interfacial area during dissolution is a key factor in obtaining experimentally reproducible release data. The proposed suppository dissolution apparatus was designed to provide greater constancy of the exposed suppository area for dissolution. The apparatus consisted of a glass bead-bed containing the suppository. A continuous flow of liquid was passed through the bead-bed at a constant rate. Direct contact of the suppository was maintained with the dissolution medium, confining the suppository within the beads.

Influence of food and fluid ingestion on aspirin bioavailability

The influence of test meals and accompanying fluid volume on aspirin bioavailability from commercial tablets was determined following single oral doses to healthy male volunteers. Plasma aspirin and salicylate levels were determined simultaneously using a GLC end-point. Area analysis indicated that approximately 5--8% of absorbed drug entered the systemic circulation as unchanged aspirin in nonfasted subjects compared to 16--18% in fasted individuals. Food tended to reduce the appearance rate of aspirin into the circulation, resulting in lower and somewhat more sustained levels than with fasting. Plasma salicylate levels were not influenced markedly by the various treatments, although levels were higher in fasted than in nonfasted subjects during the 1st hr after dosing. After this time, fat pretreatment tended to produce higher levels than other treatments.