Andrew Acheampong

Pharmacokinetics and Pharmacodynamics of a Sustained-Release Dexamethasone Intravitreal Implant

PURPOSE To determine the pharmacokinetics and pharmacodynamics of a sustained-release dexamethasone (DEX) intravitreal implant (Ozurdex; Allergan, Inc.). METHODS Thirty-four male monkeys (Macaca fascicularis) received bilateral 0.7-mg DEX implants. Blood, vitreous humor, and retina samples were collected at predetermined intervals up to 270 days after administration. DEX was quantified by liquid chromatography-tandem mass spectrometry, and cytochrome P450 3A8 (CYP3A8) gene expression was analyzed by real-time reverse transcription-polymerase chain reaction. RESULTS DEX was detected in the retina and vitreous humor for 6 months, with peak concentrations during the first 2 months. After 6 months, DEX was below the limit of quantitation. The C(max) (T(max)) and AUC for the retina were 1110 ng/g (day 60) and 47,200 ng · d/g, and for the vitreous humor were 213 ng/mL (day 60) and 11,300 ng · d/mL, respectively. The C(max) (T(max)) of DEX in plasma was 1.11 ng/mL (day 60). Compared with the level in the control eyes (no DEX implant), CYP3A8 expression in the retina was upregulated threefold up to 6 months after injection of the implant (0.969 ± 0.0565 vs. 3.07 ± 0.438; P < 0.05 up to 2-month samples). CONCLUSIONS The in vivo release profile of the DEX implant in an animal eye was similar to the pharmacokinetics achieved with pulse administration of corticosteroids (high initial drug concentration, followed by a prolonged period of low concentration). These results are consistent with those in clinical studies supporting the use of the DEX implant for the extended management of posterior segment diseases.

Ocular Pharmacokinetics and Safety of Ciclosporin, a Novel Topical Treatment for Dry Eye

Ciclosporin is a potent immunomodulator that acts selectively and locally when administered at the ocular surface. 0.05% ciclosporin ophthalmic emulsion has recently been approved by the US FDA for treatment of keratoconjunctivitis sicca (KCS) [dry-eye disease].After topical application, ciclosporin accumulates at the ocular surface and cornea, achieving concentrations (≥0.236 μg/g) that are sufficient for immunomodulation. Very little drug penetrates through the ocular surface to intraocular tissues. Ciclosporin is not metabolised in rabbit or dog eyes and may not be prone to metabolism in human eyes. Cultured human corneal endothelial and stromal cells exposed to ciclosporin in vitro exhibited no adverse effects and only minor effects on DNA synthesis. No ocular or systemic toxicity was seen with long-term ocular administration of ciclosporin at concentrations up to 0.4%, given as many as six times daily for 6 months in rabbits and 1 year in dogs. Systemic blood ciclosporin concentration after ocular administration was extremely low or undetectable in rabbits, dogs and humans, obviating concerns about systemic toxicity. In 12-week and 1-year clinical safety studies in dry-eye patients, the most common adverse event associated with the ophthalmic use of ciclosporin emulsion was ocular burning. No serious drug-related adverse events occurred.These data from in vitro, nonclinical and clinical studies indicate effective topical delivery of ciclosporin to desired target tissues along with a favourable safety profile, making 0.05% ciclosporin ophthalmic emulsion a promising treatment for KCS.

Blood Concentrations of Cyclosporin A During Long-Term Treatment With Cyclosporin A Ophthalmic Emulsions in Patients With Moderate to Severe Dry Eye Disease

To quantify blood cyclosporin A (CsA) concentrations during treatment with CsA topical ophthalmic emulsions, blood was collected from 128 patients enrolled in a Phase 3, multicenter, double-masked, randomized, parallel-group study of CsA eyedrops for treatment of moderate to severe dry eye disease. Patients received 0.05% CsA, 0.1% CsA, or vehicle b.i.d. for 6 months; vehicle-treated patients then crossed over to 0.1% CsA b.i.d. for 6 months. CsA concentrations were measured using a validated LC/MS-MS assay (quantitation limit = 0.1 ng/mL). No patient receiving 0.05% CsA had any quantifiable CsA in the blood (n = 96 samples). All but 7 of 128 (5.5%) trough blood samples from the 0.1% CsA group were below the quantitation limit for CsA; none exceeded 0.3 ng/mL. CsA was also below the limit of quantitation in 205 of 208 (98.6%) of serial postdose blood samples collected from 26 patients during 1 dosing interval between months 9 and 12. The highest C(max) measured, 0.105 ng/mL at 3 hours postdose, occurred in a 0.1% CsA-treated patient. These results indicate that long-term use of topical CsA ophthalmic emulsions at doses that are clinically efficacious for treating dry eye will not cause any system-wide effects.

Formulation effects on ocular absorption of brimonidine in rabbit eyes

Purite (stabilized oxychloro complex) and benzalkonium chloride (BAK) are preservatives. We investigated formulation effects on ocular absorption of brimonidine in rabbit eyes. The formulations compared were: Alphagan (0.2% brimonidine tartrate/0.005% BAK, pH 6.4), Brimonidine-Purite (0.2% brimonidine tartrate/0.005% Purite, pH 7.2), and Brimonidine-PF (0.2% brimonidine tartrate, preservative-free (PF), pH 6.4) solutions. The study was conducted in a cross-over fashion; albino rabbits (n = 18) were given a single 35 microl drop of each test formulation in each eye. Aqueous humor samples were collected at selected times post-dose from subgroups of 2 rabbits per timepoint and analyzed for brimonidine concentrations by LC-MS/MS. The AUC and Cmax were calculated. The results showed rapid ocular absorption of brimonidine, with peak concentrations at 0.33-1 hr. The AUC(0-5hr) values were 3.78 +/- 0.38, 2.77 +/- 0.22, and 2.49 +/- 0.22 microg-hr/ml (mean +/- SEM) for Brimonidine-Purite, Alphagan and Brimonidine-PF, respectively. The corresponding Cmax values were 2.69 +/- 0.72, 1.74 +/- 0.13, and 1.24 +/- 0.22 microg/ml (mean +/- SEM). Brimonidine-Purite provided significantly higher AUC(0-5hr) than Alphagan (p < 0.05). No statistical significant difference in AUC(0-5hr) was found between Alphagan and Brimonidine-PF. In conclusion, 0.2% Brimonidine-Purite was 1.4 and 1.5 times more ocularly bioavailable in rabbits than 0.2% Alphagan and 0.2% Brimonidine-PF, respectively.

Measurement of brimonidine concentrations in human plasma by a highly sensitive gas chromatography/mass spectrometric assay

Brimonidine is an alpha 2-adrenergic agonist that is efficacious in lowering intraocular pressure in humans. A highly sensitive and selective gas chromatography/mass spectrometry (GC/MS) assay is described for quantitation of brimonidine in human plasma following ocular installation. Brimonidine in 1 ml of plasma was extracted together with tetradeuterated brimonidine (internal standard) and clonidine (carrier) by solvent extraction. After solvent evaporation, 3,5-bis(trifluoromethyl)benzoyl derivatives were formed and injected onto a GC/MS apparatus under negative chemical ionization conditions. The ions monitored for derivatized brimonidine and tetradeuterated brimonidine were m/z 691 [M-HBr] and m/z 694 [M-DBr], respectively. Calibration curves were linear from 2 to 1000 pg ml-1 (r2 = 0.981-0.996). The method was specific for brimonidine relative to endogenous compounds in plasma. The inter-day relative standard deviation for analysis of quality controls was 12% or less, and the inter-day assay accuracy ranged from 97 to 104% of nominals. The GC/MS assay showed adequate sensitivity for analysis of human samples from volunteers ocularly dosed with 0.5% brimonidine tartrate solution. Overall, the GC/MS assay showed excellent precision and accuracy, and a minimum quantifiable concentration of 2 pg ml-1.

Levels of bimatoprost acid in the aqueous humour after bimatoprost treatment of patients with cataract.

Aim: To determine the aqueous humour concentration of the acid hydrolysis products of bimatoprost and latanoprost after a single topical dose of bimatoprost 0.03% or latanoprost 0.005% in humans. Methods: Randomised, controlled, double-masked, prospective study. 48 eyes of 48 patients scheduled for routine cataract surgery were randomised in an 8:2:2 ratio to treatment with a single 30 μl drop of bimatoprost 0.03%, latanoprost 0.005% or placebo at 1, 3, 6 or 12 h before the scheduled cataract surgery. Aqueous humour samples were withdrawn at the beginning of the surgical procedure and analysed using high-performance liquid chromatography–tandem mass spectrometry. Results: Bimatoprost acid (17-phenyl trinor prostaglandin F2α) was detected in aqueous samples at a mean concentration of 5.0 nM at hour 1, 6.7 nM at hour 3 and 1.9 nM at hour 6 after bimatoprost treatment. After latanoprost treatment, the mean concentration of latanoprost acid (13,14-dihydro-17-phenyl trinor prostaglandin F2α) in aqueous samples was 29.1 nM at hour 1, 41.3 nM at hour 3 and 2.5 nM at hour 6. Acid metabolites were below the limit of quantitation in all samples taken 12 h after dosing and in all samples from placebo-treated patients. None of the samples from latanoprost-treated patients contained quantifiable levels of non-metabolised latanoprost. Non-metabolised bimatoprost was detected in aqueous samples at a mean concentration of 6.6 nM at hour 1 and 2.4 nM at hour 3 after bimatoprost treatment. Conclusions: Low levels of bimatoprost acid were detected in aqueous humour samples from patients with cataract treated with a single dose of bimatoprost. Latanoprost acid concentrations in samples from patients treated with latanoprost were at least sixfold higher. These results suggest that bimatoprost acid in the aqueous humour does not sufficiently account for the ocular hypotensive efficacy of bimatoprost.

Effects of the Preservative Purite® on the Bioavailability of Brimonidine in the Aqueous Humor of Rabbits

PURPOSE To determine aqueous humor concentrations of brimonidine given the following ophthalmic formulations in female New Zealand White Rabbits: (1) BAK-preserved brimonidine tartrate 0.20% at a pH of 6.4; (2) BAK-preserved brimonidine tartrate 0.15% at a pH of 6.4, and (3) Purite((R))-preserved brimonidine tartrate 0.15% at a pH of 7.3. METHODS Eighteen (18) animals were given a 35-microL drop of formulation into each eye. Aqueous humor samples were collected at 9 time points over 8 hours. Brimonidine concentrations were quantified using LC-MS/MS. RESULTS The C(max) was achieved between 0.33-0.67 hours postdosing for all 3 formulations. Mean C(max) after Purite-preserved brimonidine tartrate 0.15% was 88% higher than that after BAK-preserved brimonidine tartrate 0.15% (p = 0.040), and 44% higher than that after BAK-preserved brimonidine tartrate 0.20% (p = 0.0784). AUC(0-3 hr) values were comparable for all 3 formulations. CONCLUSIONS Purite-preserved brimonidine tartrate 0.15% produced higher peak concentrations than BAK-preserved brimonidine tartrate 0.15%. It also had a concentration that was comparable to BAK-preserved brimonidine tartrate 0.20%. The differences in safety may result from the change in preservative.

Comparison of Human Ocular Distribution of Bimatoprost and Latanoprost

PURPOSE This study investigated the ocular distribution of bimatoprost, latanoprost, and their acid hydrolysis products in the aqueous humor, cornea, sclera, iris, and ciliary body of patients treated with a single topical dose of 0.03% bimatoprost or 0.005% latanoprost for understanding concentration-activity relationships. METHODS Thirty-one patients undergoing enucleation for an intraocular tumor not affecting the anterior part of the globe were randomized to treatment with bimatoprost or latanoprost at 1, 3, 6 or 12 h prior to surgery. Concentrations of bimatoprost, bimatoprost acid, latanoprost, and latanoprost acid in the human aqueous and ocular tissues were measured using liquid chromatography tandem mass spectrometry. RESULTS Following topical administration, intact bimatoprost was distributed in human eyes with a rank order of cornea/sclera >iris/ciliary body >aqueous humor. Bimatoprost acid was also detected in these tissues, where its low levels in the cornea relative to that of latanoprost acid indicated that bimatoprost hydrolysis was limited. Latanoprost behaved as a prodrug that entered eyes predominantly via the corneal route. Levels of latanoprost acid were distributed as cornea >>aqueous humor>iris>sclera>ciliary body. CONCLUSIONS Our study provided experimental evidence that levels of bimatoprost in relevant ocular tissues, and not only aqueous humor, are needed to understand the mechanisms by which bimatoprost lowers intraocular pressure (IOP) in human subjects. The data suggest that bimatoprost reached the target tissues favoring the conjunctival/scleral absorption route. Findings of intact bimatoprost in the target ciliary body indicated its direct involvement in reducing IOP. However, bimatoprost acid may have only a limited contribution on the basis that bimatoprost has greater/similar IOP-lowering efficacy than latanoprost, yet bimatoprost acid levels were a fraction of latanoprost acid levels in the aqueous humor and cornea and only sporadically detectable in the ciliary body. In this report, human ocular tissues were examined concurrently with aqueous humor for the in vivo distribution of bimatoprost, bimatoprost acid, latanoprost, and latanoprost acid.

Characterization of benzimidazole and other oxidative and conjugative metabolites of brimonidine in vitro and in rats in vivo using on-line H/D exchange LC-MS/MS and stable-isotope tracer techniques

The characterization of brimonidine metabolites presents some challenges since brimonidine and its metabolites generate few structurally informative fragment ions in the LC-MS/MS spectra. The objective of the current study is to use on-line hydrogen/deuterium (H/D) exchange LC-MS/MS and stable-isotope tracer techniques to further characterize unknown brimonidine metabolites in vitro and in vivo. Brimonidine and D4-brimonidine were co-incubated in rat and human microsomes and rabbit aldehyde oxidase in vitro. In addition, the urine was collected from rats co-administered orally with brimonidine and D4-brimonidine. The hepatic microsomal and urinary metabolites were then characterized by H/D LC-MS/MS system. In addition to previously characterized 2-oxobrimonidine, 3-oxobrimonidine and 2,3-dioxobrimonidine, the results show that oxidation occurs at quinoxaline ring producing oxo-hydroxybrimonidine and hydroxyquinoxaline metabolites. The hydroxyquinoxaline metabolite was only observed in microsomal incubations with hydroxylation at the 7- or 8- position. The dehydro-hydroxybrimonidine metabolites were characterized as 2-oxo or 3-oxo -4′, 5′-dehydrobrimonidine. A novel metabolite ((4-bromo-1H-benzoimidazol-5-yl)-imidazolidin-2-ylidene-amine) of benzimidazole derivative of brimonidine in rats in vivo was identified and confirmed with reference standard. In conclusion, on-line H/D exchange LC-MS/MS and stable-isotope tracer techniques are useful for the characterization of brimonidine metabolites.

Cyclosporine Distribution into the Conjunctiva, Cornea, Lacrimal Gland, and Systemic Blood Following Topical Dosing of Cyclosporine to Rabbit, Dog, and Human Eyes

Cyclosporine is an immune modulator that inhibits T-lymphocyte-mediated immunoreactivity. Allergan is currently evaluating the clinical efficacy of 0.05%–0.4% cyclosporine emulsion for the treatment of immuno-inflammatory eye diseases, such as keratoconjunctivitis sicca, or dry eye syndrome. Topical ocular application of cyclosporine, formulated as 2% cyclosporine in olive oil, 0.2% cyclosporine in corn oil ointment (Schering-Plough), or 0.2% cyclosporine emulsion (Allergan), was found to reduce ocular surface inflammation and improve lacrimal gland secretion in dogs with KCS.1–3