Diflunisal, a new-acting analgesic and prostaglandin inhibitor: effect of concomitant acetylsalicylic acid therapy on ototoxicity and on disposition of both drugs

Ototoxicity associated with salicylates. A brief review

Aspirin, the prototype of the salicylates, is a ubiquitous agent. The availability of aspirin, other salicylates and nonsteroidal anti-inflammatory drugs (NSAIDs) as prescription and over-the-counter medications means there is a wealth of clinical experience with these agents. Among the documented adverse effects of aspirin is the potential for ototoxicity. Tinnitus and hearing loss, usually reversible, are associated with acute intoxication and long term administration of salicylates. A range of measured serum concentrations are reported as correlating with documented ototoxicity (19.6 to > 67 mg/dl). Most case reports are based on total serum salicylate concentrations whereas unbound serum salicylate concentrations appear to reflect more closely the risk of ototoxicity. The pathophysiology of toxicity may be related to biochemical and subsequent electrophysiological changes in the inner ear and eighth cranial nerve impulse transmission. Localised drug accumulation and vasoconstriction in auditory microvasculature may be mediated by the antiprostaglandin activity of these agents. Ototoxicity, although not life-threatening, may add to the morbidity of patients taking salicylates or NSAIDs in therapeutic and toxic doses.

Influence of renal failure, rheumatoid arthritis and old age on the pharmacokinetics of diflunisal

The single-dose plasma kinetics of diflunisal was studied in healthy young and old subjects, in patients with rheumatoid arthritis, and in patients with renal failure. The plasma and urine kinetics of the glucuronidated metabolites of diflunisal were studied in the healthy elderly subjects and in the patients with renal failure. In addition, the multiple-dose plasma kinetics of diflunisal was assessed in healthy volunteers and in patients with rheumatoid arthritis. After a single dose of diflunisal the terminal plasma half-life, mean residence time and apparent volume of distribution were higher in elderly subjects than in young adults. No difference was observed in any pharmacokinetic parameter between age-matched healthy subjects and patients with rheumatoid arthritis. The elimination half-life of unchanged diflunisal was correlated with the creatinine clearance (r = +0.89) and its apparent total body clearance exhibited linear dependence on creatinine clearance (r = +0.78). In patients with renal failure, the terminal plasma half-life and mean residence time of diflunisal were prolonged. The renal and apparent total body clearances were lower, the mean apparent volume of distribution was higher and the mean area under the concentration-time curve extrapolated to infinity (AUC) was greater in the renal failure patients than in controls. The plasma concentration of the glucuronidated metabolites rapidly rose to levels above those of unchanged drug in renal patients, whereas they were lower than those of unchanged diflunisal in controls. The AUC (0-96 h) of diflunisal glucuronides in the patients was four-times that in controls, and the terminal elimination half-life of the glucuronides was prolonged in them. The renal excretion and clearance of diflunisal glucuronides were reduced when renal function was impaired. After multiple dosing, the pre-dose steady-state plasma-concentration increased with decreasing creatinine clearance (r = -0.79). When the plasma concentration exceeded 200 mumols.l-1, the elimination half-life was doubled, due to partial saturation of diflunisal conjugation. This finding suggests that lower doses could be used in long-term treatment. Thus, old age and arthritic disease appear to have little influence on the kinetics of diflunisal in the absence of renal functional impairment. Ordinary doses can be given for short term treatment of elderly patients with or without RA. In patients with renal failure, however, reduced doses of diflunisal are recommended.

A diflunisal related fatality: a case report

A case is reported where the death of an individual resulted from the ingestion of diflunisal. Diflunisal was identified by a combination of liquid chromatography, UV spectrophotometry and colorimetry. Diflunisal was quantified in blood (260 mg/l), bile (71 mg/l), kidney (350 mg/kg), liver (400 mg/kg), stomach contents (34 mg) and urine (78 mg/l). No previous literature references discussing diflunisal related fatalities were available.

Steady-state disposition of diflunisal: once- versus twice-daily administration

To evaluate the steady-state bioequivalence of the nonsteroidal antiinflammatory analgesic agent, diflunisal, administered once versus twice daily, 13 healthy volunteers received diflunisal as follows: 1000 mg at 8:00 AM and 500 mg at 8:00 AM and 8:00 PM, each for 14 days in a randomized crossover study. The mean (+/- SD) steady-state peak plasma concentrations were significantly greater after once-daily dosing (186 +/- 25 micrograms/ml vs 150 +/- 37 micrograms/ml; p less than 0.01). The time to peak concentration was also longer after the single-dose regimen (2.5 +/- 0.8 vs 1.9 +/- 0.9 hr; p less than 0.05). The regimens were similar with respect to the mean 24-hour area under the plasma concentration-time curve at steady state (2839 +/- 612 vs 2782 +/- 778 micrograms.hr.ml-1), steady-state plasma concentrations (118 +/- 25 vs 116 +/- 32 micrograms/ml), trough plasma concentration (85 +/- 27 vs 92 +/- 28 micrograms/ml) as well as 24-hour urinary excretion (776 +/- 79 vs 771 +/- 89 mg) of diflunisal. Based on urinary recoveries, the bioequivalence ratio (once vs twice daily) was 1.01 +/- 0.08. These results indicate that diflunisal administered once daily might offer comparable therapeutic effects but be more convenient than a twice-daily regimen.

Diflunisal: a review of its pharmacological properties and therapeutic use in pain and musculoskeletal strains and sprains and pain in osteoarthritis

Diflunisal is a salicylic acid derivative with analgesic and anti-inflammatory activity. It has been studied in osteoarthritis, pain resulting from musculoskeketal sprains and strains and from minor surgery and cancer. The duration of its analgesic effect is longer than that of aspirin and diflunisal is effective when given twice daily. Diflunisal is not metabolised to salicylic acid and has a lesser effect than aspirin on platelet function in vivo. In osteoarthritis, diflunisal appears comparable in efficacy to moderate doses of aspirin (2 to 3g daily), but is better tolerated. It has not been compared with the most active phenylalkanoic acid derivatives such as naproxen in adequate numbers of patients. Diflunisal is comparable with glafenine in pain and with propoxyphene/paracetamol combinations and oxyphenbutazone in pain and in musculoskeletal strains and sprains. As with other non-steroidal agents, gastrointestinal complaints are the most frequently reported side effects.