Biliary elimination of aspirin after oral and intravenous administration in patients.

Five patients suffering from various diseases were investigated for biliary elimination of aspirin given i.v. (500 mg, n = 3; 1500 mg, n = 1) or orally (500 mg, n = 2). Two bile draining systems, t-tube and naso-biliary tube, were used to collect the bile fluid. The analysis of biliary secretion of salicylates revealed only small amounts of salicylic acid and its conjugates undergoing biliary elimination and subsequent enterohepatic circulation ranging between 0.02 and 1.89% of the given dose (median 0.18%). Urinary recovery was calculated between 22.4 and 101.78% (median 92.27%). From these data it is concluded that biliary elimination and subsequent enterohepatic circulation plays no (aspirin) or only a minor role (salicylic acid) in the excretion of aspirin in man.

Heterogeneity of three electrophoretically distinct Go alpha-subunits in mammalian brain.

So far three splice variants of the alpha o-gene coding for two alpha o proteins have been identified by molecular cloning, and the corresponding proteins purified. In the present study subtype-specific peptide antibodies revealed the existence of an electrophoretically distinct third form of alpha o in mammalian brain membranes which migrates more slowly on SDS-PAGE and shows a more acidic pI value than the other alpha o-subunits. Each of the three alpha o-subunits is detected as two isoforms when enriched from brain membranes. Rodent alpha o-subunits differ from non-rodent species in their electrophoretic mobilities. The results suggest that (i) there may exist a novel alpha o-subunit which reacts with an alpha o1-subunit-specific antibody, (ii) each alpha o-subunit may exist in more than one co- or posttranslationally modified isoform in brain membranes, and (iii) differences between alpha o-subunits from different species exist which are detectable by gel electrophoretic methods.

Pharmacokinetics of diflunisal in patients.

There are few pharmacokinetic data available on the disposition of diflunisal in patients; this study, therefore, looked at the oral absorption, distribution and elimination of this drug. Ten pharmacokinetic profiles obtained from 8 patients showed a maximum plasma diflunisal concentration of 62.0 +/- 26.5 mg/L after 2.76 +/- 1.87 hours, and an area under the plasma concentration-time curve (AUC) of 678.3 +/- 362.3 mg/L.h. Significant intra- and intersubject variability was observed in this group of patients. Analysis of biliary secretion of diflunisal in 4 patients suggested a biliary elimination and subsequent enterohepatic circulation ranging between 2.4 and 15.1%. The AUC for diflunisal in synovial fluid collected from 66 patients was about 70% of that for plasma. In none of 28 patients studied could any trace of diflunisal be observed in cerebrospinal fluid, even though the sensitivity of the assay allowed detection of concentrations as low as 0.01 mg/L.

Diflunisal disposition. Role of gastric absorption in the development of mucosal damage and anti-inflammatory potency in rodents.

Aspirin shows a high incidence of gastric side effects. These are thought to result from both systemic and local effects during drug absorption. In contrast, a lipophilic derivative of salicylic acid, diflunisal, causes significantly fewer adverse gastric effects. This is thought to be due to a lack of gastric absorption. To test this hypothesis, three types of experiments were performed with diflunisal: 1. Transgastric permeation was quantified under different pH conditions, using an isolated mouse stomach model. 2. Ulcerogenic potencies of buffered and unbuffered drug solutions were determined in rats. 3. The time course of its anti-inflammatory effect and the serum concentrations of diflunisal, given alone and with neutralizing buffer, were measured in rats with carrageenan-induced paw edema. Corresponding to the low gastric ulcerogenicity, absorption of diflunisal in the isolated stomach preparations was very small. However, absorption was pH-dependent and ranged between 0.69 and 8.73% with a maximum at pH 4.5. Gastric lesions were found to be more evident 24 hr after drug administration than after 5 hr. Comparing buffered vs. unbuffered diflunisal preparations, no difference in ulcerogenicity was detectable. However, using a buffered preparation, the anti-inflammatory effect of diflunisal was enhanced significantly (p less than 0.01), and elevated serum concentrations were found (p less than 0.05). The results show that raising the solubility of diflunisal does not influence gastric absorption or gastric toxicity considerably. However, its serum concentrations and systemic anti-inflammatory effects were significantly enhanced.

Biliary elimination of low-dose methotrexate in humans.

We studied the pharmacokinetics of methotrexate (MTX) in a 64-year-old man with rheumatoid arthritis. After 6 months of treatment, acute clinical complications arose, requiring emergency laparotomy and cholecystotomy. A biliary tube was inserted, and this allowed for direct analysis of the bile. The pharmacokinetics of 2 separate doses of MTX (orally and intravenously) were assessed (dosage 10 mg/m2). No substantive differences in the pharmacokinetics were found between pre- and post-cholecystotomy MTX treatment, including clearance rates, volumes of distribution, and terminal half-lives. The results, however, demonstrated a change in the bioavailability of the drug (decreasing from 84.7% to 38.9%). Based on extrapolations of the data, with assumed rates of bile flow, the findings also suggest that there is substantial biliary elimination of MTX (8.7-26.0%) and its principal 7-hydroxy metabolite (1.5-4.6%).

Effects of pentazocine and acetylsalicylic acid on pain-rating, pain-related evoked potentials and vigilance in relationship to pharmacokinetic parameters.

Achieving objective and quantitative measurement of experimental pain in human volunteers and establishing the impact of drugs remains a difficult task. This problem may be overcome by employing a method which allows the simultaneous measurement of pain ratings elicited by standardized stimulation of the nasal mucosa by carbon dioxide, together with pain-related chemo-somatosensory evoked potentials (CSSEP) and vigilance. We assessed the effect of pentazocine and acetylsalicylic acid on these parameters in 14 human volunteers and related the effects to the pharmacokinetic parameters of the drugs measured at the same time. Pentazocine was found to reduce the pain ratings as well as the amplitudes of the pain-related evoked potentials and to increase their latencies. Vigilance (measured by EEG power spectra and performance of a tracking task) was also significantly reduced. These effects were observed during the distribution phase and the first period of the terminal elimination phase of the drug. Acetylsalicylic acid had no significant effects on pain ratings, but reduced the amplitudes of the event-related potentials when compared to placebo controls. At the same time a slight, but significant, effect on vigilance (reduced performance of the tracking task) was observed. These effects could not be related to the presence of unmetabolized acetylsalicylic acid in the plasma. They appeared at later times when only salicylic acid was left. It is concluded that chemical stimuli of sufficient intensity produce pain which may be suppressed by opioid analgesics such as pentazocine. The effect of acetylsalicylic acid on this experimental pain did not reach significance for all measured parameters under the experimental conditions chosen. The changes in vigilance and in the amplitudes of pain-related chemo-somatosensory evoked potentials indicated as yet unknown CNS-effects of this non-steroidal anti-inflammatory drug.

Biliary elimination of non-steroidal anti-inflammatory drugs in patients.

In view of evidence in animals that enterohepatic recirculation of non-steroidal anti-inflammatory drugs contributes to small intestinal mucosal damage we have investigated the extent of biliary elimination of three nonsteroidals. Ibuprofen (n = 3), diclofenac (n = 2) and indomethacin (n = 3) were given to six patients with a percutaneous transhepatic cholangiodrainage placed in the bile duct system. One patient received all three drugs. The mean biliary elimination of ibuprofen was 0.82% of the given dose compared with 50.41% urinary excretion. When diclofenac or indomethacin was administered 4.62% and 6.40% of the dose were found in bile, whereas 34.73% and 32.22% (means) were recovered from urine, respectively. The mean percentage eliminated in bile as unchanged drug and active phase II metabolites was 0.15% for ibuprofen, 1.09% for diclofenac and 5.02% for indomethacin.

Gastrointestinal ulcerations induced by anti-inflammatory drugs in rats. Physicochemical and biochemical factors involved.

Aspirin, diclofenac, diflunisal, ibuprofen and indomethacin were given orally or intravenously to fasted or fed rats. The resulting gastric and intestinal damage was assessed using standard methods. The same drugs were administered to rats with biliary fistulas, and the fraction of drug excreted in bile was quantified using HPLC methods. We found that gastric damage occurred only in the fasted animals and was found to be dose-dependent and related to the amount (r = 0.871) and solubility (r = 0.909) of the individual drug. As far as acute gastric toxicity is concerned, neither the potency of a drug as an inhibitor of cyclo-oxygenase nor the fraction of unchanged or conjugated agent excreted in bile appeared to be relevant. Secondly, ulcerations of the small intestine occurred in fed animals only. The degree of damage was related to the amount of unchanged or conjugated drug excreted in bile and cyclo-oxygenase inhibitory potency (r = 0.873). The administered dose (within the range investigated) and drug solubility appeared not to contribute to intestinal toxicity. It is concluded that, in the rat, acute gastric and intestinal toxicity of non-steroidal anti-inflammatory drugs are due to different mechanisms. Whereas gastric toxicity is strongly influenced by the amount of drug dissolved under the pH conditions in the stomach, intestinal toxicity appears to depend on biliary excretion and enterohepatic circulation of a drug as well as on its potency as an inhibitor of prostaglandin synthesis.

Therapeutically relevant differences in the pharmacokinetical and pharmaceutical behavior of ibuprofen lysinate as compared to ibuprofen acid.

The pharmacokinetic properties of ibuprofen p.o. given either as a lysine salt or as acid to eight young, healthy male volunteers was investigated. Ibuprofen lysinate, administered after overnight fasting, produced peak plasma concentrations significantly earlier and higher than ibuprofen acid. A similar difference was observed when the drugs were given following a standardized breakfast. Under these conditions the lat-time was significantly shorter for the lysine salt than for the acid. The pharmacokinetic differences are likely to result from the faster dissolution rate of ibuprofen lysinate. They indicate that the administration of ibuprofen as lysine salt before meals may be advantageous if rapid and reliable onset of pain relief is required.

Buffering the stomach content enhances the absorption of diflunisal in man.

Diflunisal, a lipophilic salicylate, is absorbed more slowly in healthy volunteers than aspirin. In this paper we report on attempts to influence diflunisal absorption by buffering the gastric milieu. Sodium bicarbonate given together and 30 min after diflunisal tablets significantly (p less than 0.05) shortened the time to reach peak plasma concentration (tmax greater than 15 per cent), raised maximum plasma concentration slightly (Cmax 6 per cent) and increased the area under the plasma concentration-time curve (AUC greater than 8 per cent). Other pharmacokinetic parameters, including terminal half-life and renal elimination of the compound, were not considerably influenced. These findings indicate that the absorption of diflunisal was enhanced by increased gastric pH, presumably a result of an increased solubility of diflunisal in the stomach together with faster transport into the small intestine. In one volunteer, after intravenous administration diflunisal plasma concentrations declined in a triphasic manner with a terminal half-life of 12.8 h. The volume of distribution was approximately 10 per cent of body weight. Based on the ratio of AUC after equivalent i.v. and oral diflunisal doses, the absolute bioavailability was 89.5 per cent.