Disposition of topically applied sodium cromoglycate in the albino rabbit eye

4 Final Report on the Safety Assessment of Phenethyl Alcohol

Phenethyl Alcohol (PEA) is an aromatic alcohol that is used as a fragrance and an antimicrobial preservative in cosmetic formulations. PEA is metabolized to phenyl-acetic acid in mammals. In humans, it is excreted in urine as the conjugate phenylacetylglutamine.

The acute oral LD50s of PEA to rats ranged from 2.5 to 3.1 ml/kg, and for mice and guinea pigs was 0.8 to 1.5 g/kg and 0.4 to 0.8 g/kg, respectively. The dermal LD50s for rabbits and guinea pigs were 0.8 g/kg and 5 g/kg, respectively. PEA was slightly to moderately irritating to the skin of rabbits and guinea pigs and was not a guinea pig sensitizer. PEA, in concentrations of 1 % or greater, was irritating to the eyes of rabbits. PEA was neither an irritant nor a sensitizer in human studies.

PEA was not mutagenic in the Ames test or in an Escherichia coli DNA-polymerase-deficient assay system. PEA did inhibit the repair of radiation-induced breaks in the DNA of E. coli. PEA did not increase the number of sister chromatid exchanges in human lymphocytes.

Maternal exposure to PEA, microencapsulated in the feed, at concentrations of 1000, 3000, and 10,000 ppm had no effect on embryo-fetal loss, or embryo-fetal development and morphology. There was an increased incidence of incomplete ossification in the 10,000 ppm PEA group litters. Doses of 0.14, 0.43, and 1.40 ml/kg of PEA were applied to the skin of pregnant rats. Maternal toxicity was marked at the highest dose, Morphological abnormalities in fetuses in the 1.40 ml/kg PEA group were observed. The number of fetuses with moderate degrees of reduced ossification and with cervical rib(s) was significantly greater in the 0.43 ml/kg PEA group than in the controls. The incidence of structural changes was slightly greater in 0.14 ml/kg PEA-treated rats than in control rats. Dermal doses of 0.07,0.14,0.28,0.43, and 0.70 ml/kg/day PEA to pregnant rats significantly increased cervical ribs in the 0.70 ml/kg/day group litters.

The highest no observed adverse effect level (NOAEL) was 0.43 ml/kg/day for cervical rib malformation (teratogenic effect). The dermal applied teratogenicity NOAEL of 0.43 ml/kg/day was used to estimate a safe use level of 1.0% PEA in cosmetic products.

Methylxanthines and pain

Caffeine, an antagonist of adenosine A(1), A(2A) and A(2B) receptors, is known as an adjuvant analgesic in combination with non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen in humans. In preclinical studies, caffeine produces intrinsic antinociceptive effects in several rodent models, and augments the actions of NSAIDs and acetaminophen. Antagonism of adenosine A(2A) and A(2B) receptors, as well as inhibition of cyclooxygenase activity at some sites, may explain intrinsic antinociceptive and adjuvant actions. When combined with morphine, caffeine can augment, inhibit or have no effect depending on the dose, route of administration, nociceptive test and species; inhibition reflects spinal inhibition of adenosine A(1) receptors, while augmentation may reflect the intrinsic effects noted above. Low doses of caffeine given systemically inhibit antinociception by several analgesics (acetaminophen, amitriptyline, oxcarbazepine, cizolirtine), probably reflecting block of a component of action involving adenosine A(1) receptors. Clinical studies have demonstrated adjuvant analgesia, as well as some intrinsic analgesia, in the treatment of headache conditions, but not in the treatment of postoperative pain. Caffeine clearly exhibits complex effects on pain transmission; knowledge of such effects is important for understanding adjuvant analgesia as well as considering situations in which dietary caffeine intake may have an impact on analgesic regimens.

Effects of N-acetyl-aspartyl glutamic acid and sodium cromoglycate on leukotriene B4 secretion by human leukocytes

Peripheral leukocytes from allergic subjects were treated for 30 min with sodium cromoglycate (SCG) or with N-acetyl-aspartyl glutamic acid (NAAGA) and challenged for leukotriene B4 (LTB4) production with calcium ionophore A 23187. NAAGA significantly inhibits LTB4 release at concentrations of 10(-2) M (-86%), 5 x 10(-3) M (-49%) and 10(-3) M (-34%), while SCG was not able to block LTB4 production within the range of 10(-2)-10(-4) M. In spite of the fact that SCG and NAAGA are chemically unrelated and that both show antiallergic properties, only NAAGA is able in this model to block production of LTB4, a chemical mediator strongly involved in inflammatory and hypersensitivity reactions.

A gamma scintigraphic evaluation of the precorneal residence of liposomal formulations in the rabbit

Multilamellar liposomes were prepared from dipalmitoyl phosphatidylcholine or egg lecithin in combination with cholesterol and either dicetyl phosphate or stearylamine. The size and charge of the colloidal preparations were characterized before labelling with [111In]8-hydroxyquinoline. Freshly labelled liposomes were instilled into the eyes of unanaesthetized NZW rabbits and their disposition and drainage followed using gamma scintigraphy. A positive surface charge was found to affect significantly liposomal drainage rate, whereas an increase in size restricted drainage from the inner canthal region. Drainage of the suspending medium was directly compared with liposomes by labelling the medium with [99mTc] sodium pertechnetate and following the simultaneous change in removal of 99mTc and 111In from the precorneal area. Slower drainage rates were obtained for the suspending medium compared with solutions of the isotopes suggesting that the liposomes restricted solution drainage.

Ocular sodium cromoglycate. An overview of its therapeutic efficacy in allergic eye disease

Sodium cromoglycate stabilizes mast cell membranes and prevents the release of histamine and other biochemical mediators. When topically applied to the eye before allergen exposure, ocular sodium cromoglycate prevents many of the signs and symptoms associated with type I allergic reactions (which includes hayfever, acute allergic and chronic allergic conjunctivitis, and vernal keratoconjunctivitis) and giant papillary conjunctivitis. Although difficulties exist in evaluating clinical trials in allergic eye disease, both open and controlled studies have shown ocular sodium cromoglycate to be very effective in relieving the subjective symptoms and clinical signs of the above ocular disorders. In addition, ocular sodium cromoglycate may decrease the need for supplementary oral antihistamines and, more importantly, the need for ocular corticosteroids, thus decreasing the incidence of steroid-induced ocular side effects. However, in severe cases and in instances of acute exacerbation of symptoms, the combined ocular application of sodium cromoglycate and corticosteroids may be very effective. No systemic or severe adverse reactions have been attributed to ocular sodium cromoglycate, which is not surprising since systemic drug absorption from the eye is minimal. However, transient local stinging and burning have been reported. Thus, although further studies in giant papillary conjunctivitis and comparative studies with corticosteroids in allergic conjunctivitis and vernal keratoconjunctivitis are needed to more clearly define the extent of benefits that may be obtained from ocular sodium cromoglycate, it is clear that the safety and efficacy of the drug in type I allergic eye diseases is such that it should be considered as a first-line agent when drug therapy of these disorders is indicated.

Ocular allergy and mast cell stabilizers

The role of the mast cell in ocular allergy is becoming understood. As a result, the therapeutic effects of agents that stabilize the mast cell have been evaluated in the treatment of seasonal allergic conjunctivitis, vernal keratoconjunctivitis, atopic keratoconjunctivitis, and giant papillary conjunctivitis. At present, cromolyn sodium is the only available mast cell stabilizer of known effectiveness. Clinical and laboratory investigations of the effectiveness of cromolyn sodium in the treatment of ocular allergy are reviewed in the present article.

Topical ocular drug delivery: recent developments and future challenges

Existing ocular drug delivery systems are fairly primitive and inefficient, but the stage is set for the rational design of newer and significantly improved systems. The focus of this review is on recent developments in topical ocular drug delivery systems relative to their success in overcoming the constraints imposed by the eye and to the improvements that have yet to be made. In addition, this review attempts to place in perspective the importance of pharmacokinetic modeling, ocular drug pharmacokinetic and bioavailability studies, and choice of animal models in the design and evaluation of these delivery systems. Five future challenges are perceived to confront the field. These are: (a) The extent to which the protective mechanisms of the eye can be safely altered to facilitate drug absorption, (b) Delivery of drugs to the posterior portion of the eye from topical dosing, (c) Topical delivery of macromolecular drugs including those derived from biotechnology, (d) Improved technology which will permit non-invasive monitoring of ocular drug movement, and (e) Predictive animal models in all phases of ocular drug evaluation.

Concentration-dependent precorneal loss of pilocarpine in rabbit eyes

Precorneal loss of pilocarpine was studied in pigmented and albino rabbits. We instilled 25 microliter of isotonic pilocarpine solution, pH 6.4, into rabbit eyes and monitored drug concentration in the precorneal tear film. Increased concentration (0.2% - 2.0%) of pilocarpine accelerated precorneal drug loss from the tear film from 0.686 min-1 to 1.064 min-1. This increase was mainly due to induced lacrimation. Polyvinyl alcohol (1.4%) retarded precorneal loss of pilocarpine. The rate of loss was the same in pigmented and albino rabbits. The effects of the changed precorneal loss of pilocarpine on corneal drug absorption are discussed.

Influence of ophthalmic formulations on sodium cromoglycate disposition in the albino rabbit eye

The effect of different ophthalmic vehicles on the disposition of sodium cromoglycate in tears and ocular tissues of the rabbit eye has been studied over 6 h. The vehicles contained sodium cromoglycate, 2% in an aqueous solution, 2 and 4% in an oleaginous formulation of polyethylene and mineral oil (Plastibase 5W), and 4% in an absorption ointment base of 10% hypoallergenic acetylated lanolin (Modulan) in paraffins. The last formulation was superior to all others studied over 6 h in prolonging the retention of sodium cromoglycate in the precorneal area and the conjunctiva. The concentration of sodium cromoglycate in the tears, conjunctiva and cornea 6 h after administration of the acetylated lanolin base equalled or exceeded the concentrations obtained with the aqueous solution 1 h post-instillation.

Ocular drug bioavailability from topically applied liposomes

During the past decade liposomes have been investigated extensively for their ability to improve drug utilization by the body, first in the area of chemotherapeutics and most recently in the area of ophthalmology. Liposomes are vesicle-like structures with a concentric series of alternating compartments of aqueous spaces and phospholipid bilayers. To date, liposomes have been found to both promote and reduce ocular drug absorption, indicating that a definite need exists for further studies to evaluate the interplay of drug, liposomes, and the corneal surface in determining the effectiveness of liposomes as vehicles for topically applied ophthalmic drugs. The purpose of this review is to place in perspective the role of liposomes in topical ocular drug delivery. As background material, the factors influencing ocular drug bioavailability and the features of liposomes pertinent to their effectiveness as drug carriers are reviewed.

Possible mechanisms for the retention of topically applied vitamin A (retinol) in the albino rabbit eye

The concentration of vitamin A in various anterior segment tissues of the albino rabbit eye following topical instillation of a 1 mg/ml drug solution in peanut oil was determined using radiotracer techniques. It was found that 50-80% of the vitamin A absorbed into the albino rabbit eye was in the corneal epithelium and the conjunctiva and that over 50% of the vitamin A in the cornea was in its epithelial layers. While trace amounts of topically applied peanut oil remained in the precorneal area as late as 2 hours post-dosing, the vitamin A dissolved in it did not appear to play a major role in sustaining vitamin A concentration within the eye. Rather, solubilization of vitamin A by the proteins in tears as well as by the cellular lipids and retinol-binding proteins in the corneal epithelium appear to play a more important role. It is suggested that further work is necessary to delineate the specific involvement of retinol-binding proteins in ocular vitamin A pharmacokinetics.

The prolonged retention of sodium cromoglycate in the rabbit eye

The retention of sodium cromoglycate in the rabbit eye over a 6 h period following its administration in two different vehicles is reported. When formulated as a dispersion in a hypo-allergenic acetylated lanolin/paraffins base, prolonged retention was observed. Thus, the concentration of sodium cromoglycate in the tears, conjunctiva and cornea 6 h after administration equalled or exceeded the concentration obtained with an aqueous solution 1 h post-instillation.