Ketorolac Other names: Ketorolac trometamol

Ketorolac is a non-steroidal anti-inflammatory agent demonstrating analgesic and anti-inflammatory activity. Ketorolac inhibits the cyclo-oxygenase enzyme essential for biosynthesis of prostaglandins. Ketorolac has been shown to reduce prostaglandin levels in the aqueous humour after topical ophthalmic administration.

Ketorolac given systemically does not cause pupil constriction. Results from clinical studies indicate that ketorolac has no significant effect on intra-ocular pressure.

General characteristics

Absorption

Rabbit aqueous humor bioavailability:

After topical ocular doses in the rabbit the half life of total radioactivity in aqueous humor was longer than after intracameral injection. This suggests that topical dosing may lead to a “reservoir” effect in the corneal epithelium and continued flux of drug from the reservoir into the aqueous humor.

Distribution

After ophthalmic doses were administered to rabbits, peak concentrations of radioactivity were achieved within 1 hour in the ocular tissues and were highest in the cornea (6.06 mcg-eq/ml). At 1 hour, the majority of the radioactivity (0.9% of administered dose) was recovered from the sclera (0.58%) and cornea (0.24%), and smaller amounts were recovered from the aqueous humor (0.026%), vitreous humor (0.023%), retina-choroid (0.018%), iris-ciliary body (0.007%) and lens (0.002%).

Relative to plasma AUC values, the AUC’s in rabbits were higher for cornea (104 fold), sclera (27 fold), iris-ciliary body (5.8 fold), retina-choroid (5.6 fold), aqueous humor (3.3 fold) and approximately one-half in the vitreous humor and lens. After ophthalmic administration, concentrations of drug-related radioactivity were higher in the ocular tissues and lower in plasma compared with those after IV dosing.

Systemic Absorption

After ophthalmic doses in the rabbit, ketorolac was absorbed rapidly into the systemic circulation (T_max, 15 min). Plasma half-lives after ophthalmic doses (6.6-6.9 hr) were longer than those after IV administration (1.1 hr), suggesting that removal of drug from eye into the venous circulation may be rate-limiting. By comparison of drug levels in aqueous humor after intracameral injection vs. plasma levels after IV administration, ketorolac was shown to clear more rapidly from plasma (6 ml/min) than from the anterior chamber (11 mcl/min).

In the cynomolgus monkey, peak plasma levels of ketorolac occurred at 1.1 hr after the ophthalmic dose. The plasma half-life of ketorolac was similar after ophthalmic (1.8 hr) and IV doses (1.6 hr).

The majority of the ophthalmic dose was excreted in urine (66% in rabbit and 75% in monkey) and a small amount in faeces (11% in rabbit and 2% in monkey). The extent of systemic absorption after ophthalmic dosing averaged 73% in the rabbit and 76% in the cynomolgus monkey.

Metabolism

After ophthalmic administration in rabbits, ketorolac represented the major component (more than 90%) of radioactivity in aqueous humor and plasma and the p-hydroxy metabolite accounted for 5% of radioactivity in plasma. Ketorolac was also the major component (96%) of plasma radioactivity after ophthalmic dosing in monkeys.

After ophthalmic dosing in the rabbit, 72%, 17% and 6% of the total radioactivity in urine was comprised of intact ketorolac, p-hydroxy ketorolac and other polar metabolites, respectively. After IV dosing, the relative proportions of total radioactivity in urine averaged 6% as intact ketorolac, 68% as p-hydroxy ketorolac and 22% as polar metabolites.

In the monkey, intact ketorolac and its polar metabolite accounted for 32% and 65% of the total radioactivity in urine, respectively, after ophthalmic dosing, and 50% and 49% of the radioactivity in urine, respectively, after IV dosing. Thus, the metabolism of ketorolac was qualitatively similar after ophthalmic and IV administration in the monkey and rabbit.

Characteristics in patients

Ketorolac solutions (0.1% or 0.5%) or vehicle were instilled into the eyes of patients approximately 12 hours and 1 hour prior to surgery. Concentrations of ketorolac in aqueous humor sampled at the time of surgery were at the lower limit of detection (40 ng/ml) in 1 patient and below the quantitation limit in 7 patients dosed with 0.1% ketorolac. The average aqueous humor level of ketorolac in patients treated with 0.5% ketorolac was 95 ng/ml. Concentrations of PGE2 in aqueous humor were 80 pg/ml, 40 pg/ml and 28 pg/ml in patients treated with vehicle, 0.1% ketorolac and 0.5% ketorolac, respectively.

In the 21-day multiple dose (TID) tolerance study in healthy subjects, only 1 of 13 subjects had a detectable plasma level pre-dose (0.021 μg/ml). In another group of 13 subjects, only 4 subjects showed very low plasma levels of ketorolac (0.011 to 0.023 μg/ml) 15 minutes after the ocular dose.

Thus, higher levels of ketorolac in the aqueous humor and very low or no detectable plasma levels after ophthalmic doses, suggest that the use of ketorolac by the ophthalmic route in treatment of ocular disorders results in quite low systemic absorption in patients.

Non-clinical data reveal no special hazard for humans based on conventional studies of safety pharmacology, repeated dose toxicity, genotoxicity, carcinogenic potential, toxicity to reproduction and development.

Acute, sub-acute and chronic studies of ketorolac in experimental animals have established the safety of the drug. In addition, octoxinol 40 was separately evaluated for its ocular safety. Ketorolac was found to be non-irritating, it did not demonstrate a local anaesthetic effect, it did not influence the healing of experimental corneal wounds in rabbits, it did not enhance the spread of experimental ocular infections of Candida albicans, Herpes simplex virus type one, or Pseudomonas aeruginosa in rabbits, and it did not increase the ocular pressure of normal rabbit eyes.