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Modelling of the binding of two non-steroidal anti-inflammatory drugs, indometacin (CAS 53-86-1) and diclofenac sodium (CAS 15307-79-6) to the molecule of human serum albumin is presented. The models are based on the data obtained using difference spectroscopic technique. Speculations were made concerning the structural properties of the drugs and albumin molecules as well as the type of chemical interactions taking part in the drug-albumin binding. The proposed approach represents a more detailed investigation on the mechanism of drug-protein interactions.

After cutaneous application to rabbits of a solution containing 1% of indomethacin (Elmetacin), concentration-time curves were determined in the skin-layers, in the subcutaneous tissue, in the superficial musculature, in the knee-joint capsule and in plasma. The quantitative assay used on-line fluorimetric detection after separation by HPLC and alkaline hydrolysis. Levels of indomethacin decreased with the depth of the tissue layers at the site of application. Indomethacin concentrations in the examined tissues exceeded plasma concentration at least twice for up to 8 h. Indomethacin was also detectable in the contralateral untreated tissue specimens and in the knee joint capsule.

The bisphasic time-concentration course of the total plasma activity can be ascribed to 2 metabolites--oxametacine-glucuronide and desmethylindometacinamid(DMA)-glucuronide. The rate of biotransformation for oxametacine (1-p-chlorbenzoyl-2-methyl-5-methoxy-3-indolylacethydroxamic acid) is high. In contrast to laboratory animals the metabolic degradation of the mother substance to indometacine is negligible. Oxametacine is therefore not a pro-drug for indometacine in man. The main routes of biotransformation in man are: demethylation, conjugation, with active glucuronic acid, reduction to the acid amide and debenzoylation. For the 75 mg single dose urinary recoveries of the main metabolites, DMA-glucuronide and desbenzoyldesmethylmetacinamide (DBDMA)-glucuronide are 22.9% and 9.2%, respectively. The total recovery was found to be 97.55% of the dose, this being made up of 48.49% renal and 49.06% fecal excretion.

Pharmacokinetics of graded doses of sulindac were studied on 9 healthy volunteers. Serum concentrations of sulindac (inactive prodrug), sulindac sulfide (active metabolite) and sulindac sulfone (inactive metabolite) were measured both after a single dose of 150 mg, 175 mg or 200 mg and on the 6th and 7th days after b.i.d. administration of the same doses. The peak and minimum concentrations of sulindac were practically not dependent on the dose. The concentration-time curves remained similar after a single dose and after the repetitive dosing. On the contrary, both sulindac sulfide and sulfone gave about twice as high serum levels at steady-state as after a single dose. As judged from several pharmacokinetic parameters, a dose of 150 mg gave significantly smaller values than the higher doses but there was no significant difference between 175 mg and 200 mg in sulindac sulfide and sulfone concentrations. The average half-lives of sulindac, sulindac sulfide and sulfone were 1.7 -4.2 h, 15.3-16.1 h and 16.6-19.6 h, respectively. Both sulindac sulfide and sulfone tended to accumulate at a repetitive dose of 200 mg. The appropriate dose of sulindac appears to be 175 mg twice daily.

1. Analytical methods (isolation, TLC, UV-spectroscopic and preferably fluorimetric determination) of [1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetoxy] acetic acid (acemetacin, TV 1322, Rantudil), its analogues, hydrolysis-products and metabolites from biological material are described. 2. Stability is also dealt with. Hydrolysis of the p-chlorobenzoyl group results in strongly fluorescing compounds and can be used in determination of acemetacin, indometacin and derivatives 3. Proof is given that in in vitro studies, such as e.g. Mizushima's protein turbidity test or the test for inhibition of prostaglandin-synthetase, only intact acemetacin (and none of its potential break-down products) is present and is active. 4. In in vitro studies, such as the inhibition of total complement and of the increase in activity of serum sulfhydryl groups, acemetacin and a series of its salts proved to be at least as effective as indometacin. 5. In comparing protein binding, acemetacin, like indometacin, is found to bind strongly to albumin. The portion of free, non-protein bound acemetacin, which thus remains available for the pharmacological action, is found to be approx. 60% higher than the corresponding portion of free indometacin.

Acemetacin was given to 14 volunteers in a randomized cross-over arrangement as one single administration of 90 mg (1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetoxyacetic acid) (as Rantudil, Rantudil forte and Rantudil retard) and the courses of blood levels curves compared. Half-life of absorption was considerably higher with the retard formulation (2.01 instead of 0.58 h). The blood level maximum (tmax) was significantly (p less than 0.05) delayed by the retardation, blood levels were lower after 2 h (p less than 0.01), not significantly different 3-4 h after administration and higher (p less than 0.05) than the immediate release form after 6-10 h. AUC's are 5.82 +/- 4.04 (normal) and 6.75 +/- 3.24 (mumol X l-1 X h retarded). The mean residence time was prolonged from 4.1 to 6.3 h, yielding a sustained release quotient of 1.54. After multiple administration (2 retard capsules/d for 8 d) cmax corresponded to the results obtained after single application, maximum levels at 1.24 mumol X l-1 (mean) being somewhat higher than after single application (1.11 mumol X l-1), which is the usual steady-state behavior. Minimum levels in the steady-state (cmin) were 0.24-0.53 mumol X l-1. Bioavailability (AUC's between applications) was not significantly different. No accumulation was found. Levels measured during 8 days of administration of the Rantudil retard formulation corresponded to blood levels from computer simulations. Biological half-life was 4.03 h, which was similar to data obtained with Rantudil (3 X 60 mg/d) in rheumatic patients.

1. [14C]-Indometacin and [14C]-Acemetacin are synthesized starting from carboxyl-[14C]-levulinic acid. 2. Renal, biliary and fecal elimination of both compounds occurs mainly within 24 h after intravenous or intraduodenal application to rats and after degradation to N-des-p-chlorobenzoyl- and O-des-methyl compounds and various conjugations. Main metabolite in urine and feces after both compounds is O-desmethyl-indometacin. A high percentage of unchanged indometacin besides small amounts of des-p-chlorobenzoylindometacin (DBI) and des-p-chlorobenzoyl-O-desmethylindometacin (DBMI) are found in bile. Both metabolites exist also in urine, bile and feces following administration of acemetacin. 3. After application of [1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetoxy]-acetic acid (acemetacin, TV 1322, Rantudil) free acemetacin is found to be 2.4% in urine, 7% in the bile and 3.5% in feces. In urine and bile additional amounts are present as conjugates. 4. Conjugation to sulfuric acid was found besides glucuronidation, i.e., O-desmethylindometacinsulfate (urine, bile) and des-p-chlorobenzoyl-O-desmethylindometacinsulfate (bile). indometacin glycine, a new conjugate, is formed after application of either acemetacin or indometacin. The renal proportion of this metabolite is three times higher after acemetacin than after indometacin, this can explain the better tolerance of acemetacin in comparison to indometacin. 5. metabolism of acemetacin and indometacin in the rat, as manifested by excretion into urine, bile and feces, is comparable on a qualitative basis if excretion of free acemetacin is neglected; there exist, however, quantitative differences.

A single dose each of two brands of indometacin (INN; in some pharmacopoeias called indomethacin) containing suppositories, made with different vehicula , was administered rectally - in a cross over design - to ten healthy volunteers. Product A ( Dolcidium ) was made of a new waxy excipient which emulsifies at body temperature; product B was a leading brand of indometacin containing suppository, made of a hydrophilic polyethyleneglycol basis, which dissolves in body fluid. Plasma indometacin concentrations were measured frequently during a period of 9 h after dosing. Both products showed rather consistent absorption profiles. The maximum plasma indometacin concentration after administration of the product A 50 mg suppository was found after 62 +/- 18 min (mean +/- S.D.), and measured 2.0 +/- 0.5 mg X l-1. After dosing with the reference product those values were 66 +/- 21 min and 1.8 +/- 0.4 mg X l-1, respectively. The area under the plasma indometacin concentration-time curve was found to be 384 +/- 130 mg X l-1 X min for product A 50 mg suppositories and 372 +/- 62 mg X l-1 X min for the reference product. This results in a relative bioavailability of the product A 50 mg suppositories of 1.02, after correction for actual amount of indometacin in each dosage form. None of the above mentioned pharmacokinetic parameters were statistically significantly different (p greater than 0.05), indicating bioequivalence of the two products.

Metabolism and pharmacokinetics of [1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetoxy]-acetic acid (acemetacin, TV 1322, Rantudil) in comparison to equimolar doses of indometacin was investigated in human volunteers after a single oral application and in rheumatic patients after multiple application. After multiple application (t.i.d. for 10 days) of equimolar doses of acemetacin and indometacin, mean blood level curves. The bioavailability of acemetacin derived from these data, corresponds to that of indometacin, i.e., approx. 100%, whereas after a single dose bioavailability of acemetcin is found to be smaller (66% from blood level, 64% from urine). This difference between single and multiple application is explained by slow filling-up of compartments. Degradation of acemetacin occurs by esterolytic cleavage to indometacin, by O-demethylation and N-desacylation and by partial conjugation of all these compounds to glucuronic acid. Blood level ratios of acemetacin and indometacin are equal after single and after multiple application of acemetacin. Therefore, degradation of acemetacin is not induced after multiple application. After a steady-state has been reached half-life of elimination is 4.5 +/- 2.8 h, which is longer than for indometacin (2.2 +/- 0.5 h). Interindividual differences are in the same range as described for indometacin.