SINGAPORE MEDICAL JOURNAL DRUG MONOGRAPH AN OVERVIEW OF ISOXICAM: A NEW NONSTEROIDAL ANTI-INFLAMMATORY DRUG W W Downie SYNOPSIS Isoxicam Is effective and well tolerated in all the major rheumatic diseases. It has been shown to be more efficacious than most cur- rently available NSAIDs, and at least as well tolerated. Its elimination half-life of 31 hours suits it ideally for once daily administration, and also allows occasional omission of a dose without loss of therapeu- tic control. The pharmacokinetic disposition of isoxicam is com- parable in young and elderly subjects, as well as in patients with renal or hepatic impairment. This isokinetic profile allows a standard dosing regimen to be employed across all age groups (except child- ren) and also in patients with major organ dysfunction. No unusual drug interactions have been noted, and the frequency of side -effects is low. Isoxicam is as well tolerated by elderly patients as by younger age groups, reflecting the constancy of the pharmacokinetic dis- position with age. INTRODUCTION Isoxicam (Maxicam® ) is the product of an independent drug discovery program, set up in 1966 by Warner-Lambert, to search for novel non - steroidal anti-inflammatory drugs (NSAIDs) of the non -carboxylic acid type. Isoxicam is an enolic acid and a benzothiazine derivative of the oxicam class of drugs, other members of which are piroxicam, tenoxicam and sudoxicam. Its full chemical name is [4hydroxy-2-methyl-n-(5-methyl-3- isoxolyl)-2H-1, 2-benzothiazine-3-carboximide 1,1-dioxide](1). The structural formula is shown in Fig. I. PHARMACOLOGY In standard animal models, isoxicam has shown anti-inflammatory, anal- Clinical Research Warner-Lambert International gesic and antipyretic activity. In particular, it has been demonstrated to pro- 201 Tabor Road of Morris Plains duce long-lasting inhibition carrageenan-induced paw oedema, and New Jersey 07950 also of adjuvant-induced arthritis, both in prophlactic and in therapeutic USA studies(2). In addition, isoxicam was also effective in inhibiting collagen - induced arthritis(3). In comparison with other NSAIDs, isoxicam is only a W W Downie, BSc, MB, ChB, MRCP (UK), FRCP (G) week inhibitor of cyclo-oxygenase, and demonstrates no inhibitory activity Director against 5-lipoxygenase(4). 29 VOLUME 26, NO. 1 FEBRUARY 1985 OH O -Ó-NM SOZN,CHg NAO CH3 Figure 1. The structure of isoxicam. PHARMACOKINETICS population in respect to the pharmacodynamic expression and pharmacokinetic disposition of drugs. A number of well - Following oral administration, peak plasma levels occur with- recognised age -related physiological changes may signi- in 4-8 hours. The drug is virtually 100 percent bioavailable, ficantly alter the biological handling and effects of drugs in and demonstrates linear pharmacokinetics over the recom- the elderly subject(7). The pharmacokinetics of isoxicam mended therapeutic dosage range. Like other NSAIDs, isox- have been intensively investigated in a series of single and icam is highly bound to plasma proteins (98 percent at nor- repeated dose pharmacokinetic studies in healthy young and mal dosing levels). It is extensively metabolised in the liver, elderly subjects as well as elderly patients with rheumatoid with only approximately 2 percent of parent drug appearing arthritis. Results from these studies have indicated that the unchanged in the urine. In common with other drugs of the pharmacokinetic disposition of isoxicam does not alter, with oxicam class, isoxicam has a low total body clearance re- age. Table I shows results obtained from a 21 -day repeated sulting in a long elimination half-life(2). The mean value is 31 dose study of 200mg isoxicam given once daily to young and hours, based on single and repeated dose studies making elderly subjects(8). There were no significant differences isoxicam ideally suited for once daily administration. In between the two age groups in any of the pharmacokinetic patients with hepatic disease, there is some reduction in variables. This constancy of the kinetic disposition of isox- plasma protein binding resulting in slightly more rapid elimin- icam has been termed the "isokinetic" phenomenon, and ation(5). Even in patients with severe impairment of renal indicates that no dosage modification is necessary in the function, there is no excessive accumulation of isoxicam with treatment of the elderly patient. The relatively slow elimina- repeated dosing(6). This is undoubtedly a reflection of the tion of isoxicam allows maintenance of the plasma level at 65 extensive metabolism to polar metabolites, which are readily percent of the steady state value, even if a dose is missed(9). excreted even in patients with severe impairment of renal In a clinical study in patients with rheumatoid arthritis, sub- function. stitution of placebo for active isoxicam did not result in wor- sening of the patients' pain for 48 hours, further indicating There has been a growing awareness, in recent years, maintenance of adequate plasma (and tissue) levels of isox- that the elderly may constitute a distinct subgroup of the icam when one or even two doses of isoxicam are omitted (10). TABLE 1 Age Pharmacokinetic 18-64 (years) 65-88 (years) Variable n = 34 n = 15 Elimination half-life (hours) 31.4 31.2 Maximum concentration (ug/MI) 40.8 43.6 Area under plasma concentration/ 663.7 714.3 time curve (ug. hours. ml -1) Pharmacokinetic variables following 21 day repeated dosing with isoxicam 200mg once daily (mean values) 30 SINGAPORE MEDICAL JOURNAL duration of action of isoxicam is complemented . The long DRUG INTERACTIONS by a rapid. onset of action of analgesia. Significant pain patient self -rating pan scales, was reduction, based on Many patients receiving NSAIDs are often taking additional isoxicam dose in observed 3 hours after the first 200mg medication for concomitant diseases. Under such circum- patients with rheumatoid arthritis(11), and as early as 2 hours stances, the potential for drug -drug interactions requires to dose in patients with acute gouty arth- after a single 400mg be assessed. In an extensive investigational program using pain relief is likely to enhance ritis(12). This rapid onset of a variety of pharmacodynamic and pharmacokinetic designs, patient confidence in the drug and also promote compliance. no clinically significant interactions have been noted with ant- acids, cimetidine(16), digoxin, propranolol, glibenclamide(17), In order to reduce the frequency of dosing of short half-life phenytoin or alcohol(18). On the other hand, isoxicam did drugs, it is common pharmaceutical practice to reformulate potentiate the anticoagulant effect of warfarin(16), a pheno- such agents in a "slow-release" or "retard" preparation. menon common to other NSAIDs. Furthermore, the isoxicam However, the release characteristics of such preparations plasma level was reduced in the presence of anti-inflamma- may be altered by changes in the gastrointestinal milieu, tory doses of aspirin(19). This also happens with other resulting in erratic or incomplete liberation of active drug NSAIDs, but is of dubious clinical significance. substance. In a'double-blind comparative study, isoxicam (200mg once daily) was compared with diclofenac retard CLINICAL TRIAL PROGRAM (100mg once daily) in patients with rheumatoid arthritis. Both drugs produced rapid relief to the cardinal symptoms of pain OPEN -LABEL STUDIES and joint tenderness following the first dose. However, at the pre -dose assessments after 2 and 4 weeks, the scores for Studies conducted in the open -label format are primarily pain and joint tenderness were not significantly different from designed to provide information about long-term safety, baseline (pre-treatment) in the patients on diclofenac retard. rather than efficacy. However, the latter may be inferred by On the other hand, significant reductions in these clinical the fact that patients choose to remain on trial medication for variables were maintained at the pre -dose assessments in months or even years. In the case of isoxicam more than the patients receiving isoxicam. The results are summarized 1500 patients entered long-term open -label studies, and to in Table 2. These data indicate that the once -daily administra- date over 300 have been on the drug for longer than 3 years tion of the retard formulation of diclofenac does not provide for the treatment of rheumatoid arthritis or osteoarthritis. 24 -hour relief of symptoms or signs at the recommended dosage, and supports the contention that round-the-clock COMPARATIVE STUDIES relief with a once -a -day dosing regimen can only be relief upon by using a drug with an intrinsic long half-life, such as Studies comparing isoxicam with other commonly -used isoxicam (13). NSAIDs have been carried out in the clinical indications of TABLE 2 Diclofenac Retard isoxicam Clinical Base- 2 4 Base- 2 4 Variable line weeks weeks line weeks weeks Pain Scale 14.30 10.44 10.89 11.18 5,91 5.91 p* NS NS <0.05 <0.05 Joint Tenderness 19.30 13.67 14.56 14.55 5.64 5.64 <0.001 p NS NS <0.001 Results of clinical variables immediately prior to dosing at baseline, and after 2 and 4 weeks treatment with diclofenac retard (100mg once daily) or isoxicam (200mg once daily). 'p = significance level compared with baseline (Wilcoxon matched pairs signed ranks test) NS = not significant (p<0.05 CLINICAL PHARMACOLOGY rheumatoid arthritis, osteoarthritis, ankylosing spondylitis and acute musculoskeletal disorders. With the exception of one In a four week study using chromium -tagged red cells, occult single-blind trial in musculoskeletal disease, all studies were gastrointestinal blood loss during isoxicam administration conducted on a double-blind basis, utilizing, where necess- ranged between 0.6 and 1.1 ml daily, values comparable with ary, the double -dummy technique. Most of the studies were those obtained following naproxen administration(14). of the parallel group format, but several employed a cross- over design. In a further four week study of renal function, isoxicam administration resulted in a significant increase in creatinine Rheumatoid Arthritis clearance after two and four weeks of therapy, as well as significant reduction in serum uric acid levels(15).