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Toropainen E, Fraser-Miller SJ, Novakovic D, Del Amo EM, Vellonen KS, Ruponen M, Viitala T, Korhonen O, Auriola S, Hellinen L, Reinisalo M, Tengvall U, Choi S, Absar M, Strachan C, Urtti A. Biopharmaceutics of Topical Ophthalmic Suspensions: Importance of Viscosity and Particle Size in Ocular Absorption of Indomethacin. Pharmaceutics 2021; 13:pharmaceutics13040452. [PMID: 33810564 PMCID: PMC8067094 DOI: 10.3390/pharmaceutics13040452] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 03/23/2021] [Accepted: 03/24/2021] [Indexed: 11/16/2022] Open
Abstract
Eye drops of poorly soluble drugs are frequently formulated as suspensions. Bioavailability of suspended drug depends on the retention and dissolution of drug particles in the tear fluid, but these factors are still poorly understood. We investigated seven ocular indomethacin suspensions (experimental suspensions with two particle sizes and three viscosities, one commercial suspension) in physical and biological tests. The median particle size (d50) categories of the experimental suspensions were 0.37–1.33 and 3.12–3.50 µm and their viscosity levels were 1.3, 7.0, and 15 mPa·s. Smaller particle size facilitated ocular absorption of indomethacin to the aqueous humor of albino rabbits. In aqueous humor the AUC values of indomethacin suspensions with different particle sizes, but equal viscosity, differed over a 1.5 to 2.3-fold range. Higher viscosity increased ocular absorption 3.4–4.3-fold for the suspensions with similar particle sizes. Overall, the bioavailability range for the suspensions was about 8-fold. Instillation of larger particles resulted in higher tear fluid AUC values of total indomethacin (suspended and dissolved) as compared to application of smaller particles. Despite these tear fluid AUC values of total indomethacin, instillation of the larger particles resulted in smaller AUC levels of indomethacin in the aqueous humor. This suggests that the small particles yielded higher concentrations of dissolved indomethacin in the tear fluid, thereby leading to improved ocular bioavailability. This new conclusion was supported by ocular pharmacokinetic modeling. Both particle size and viscosity have a significant impact on drug concentrations in the tear fluid and ocular drug bioavailability from topical suspensions. Viscosity and particle size are the key players in the complex interplay of drug retention and dissolution in the tear fluid, thereby defining ocular drug absorption and bioequivalence of ocular suspensions.
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Affiliation(s)
- Elisa Toropainen
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Sara J. Fraser-Miller
- Drug Research Program, Division of Pharmaceutical Chemistry and Technology, University of Helsinki, 00014 Helsinki, Finland; (S.J.F.-M.); (D.N.); (T.V.); (C.S.)
| | - Dunja Novakovic
- Drug Research Program, Division of Pharmaceutical Chemistry and Technology, University of Helsinki, 00014 Helsinki, Finland; (S.J.F.-M.); (D.N.); (T.V.); (C.S.)
| | - Eva M. Del Amo
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Kati-Sisko Vellonen
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Marika Ruponen
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Tapani Viitala
- Drug Research Program, Division of Pharmaceutical Chemistry and Technology, University of Helsinki, 00014 Helsinki, Finland; (S.J.F.-M.); (D.N.); (T.V.); (C.S.)
| | - Ossi Korhonen
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Seppo Auriola
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Laura Hellinen
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Mika Reinisalo
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Unni Tengvall
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
| | - Stephanie Choi
- Food and Drug Administration, Rockville, MD 20993, USA; (S.C.); (M.A.)
| | - Mohammad Absar
- Food and Drug Administration, Rockville, MD 20993, USA; (S.C.); (M.A.)
- AstraZeneca Pharmaceuticals, Rockville, MD 20878, USA
| | - Clare Strachan
- Drug Research Program, Division of Pharmaceutical Chemistry and Technology, University of Helsinki, 00014 Helsinki, Finland; (S.J.F.-M.); (D.N.); (T.V.); (C.S.)
| | - Arto Urtti
- School of Pharmacy, University of Eastern Finland, 70211 Kuopio, Finland; (E.T.); (E.M.D.A.); (K.-S.V.); (M.R.); (O.K.); (S.A.); (L.H.); (M.R.); (U.T.)
- Drug Research Program, Division of Pharmaceutical Biosciences, University of Helsinki, 00014 Helsinki, Finland
- Laboratory of Biohybrid Technologies, Institute of Chemistry, St. Petersburg State University, 198504 Peterhof, Russia
- Correspondence: ; Tel.: +35-840-5402-2279
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