Physiochemical Properties and Cytotoxicity of a Benzalkonium Chloride-Free, Micellar Emulsion Ophthalmic Formulation of Latanoprost

Figures & data

Figure 1 Formation of the micellar formulation. The micellar formulation consists of latanoprost, an NIS, castor oil, a buffering agent, and a safer sorbate-based preservative system. NIS functions as the primary solubilizer, while castor oil has a dual function of a demulcent and stabilizer.

Abbreviation: NIS, nonionic surfactant.

Figure 2 Optimization of the concentrations of (A) castor oil and (B) total lipid concentration. (A) The optimum concentration is located at the intersection of the zone of clarity and the zone producing the micellar formulation. (B) The optical transmission of total lipid concentrations 0.4% to 1.6% were measured against the total lipid concentration. The intersection of these 2 lines identifies the optimal total lipid concentration for the micellar formulation.

Table 1 Characteristics of Surfactant-Oil Pairs

Surfactant-Oil Pair	% Optical Transmission	Droplet Size
Solutol HS 15-castor oil	90%	<100 nm
Polysorbate 80-castor oil	35%	173 nm
Solutol HS 15-arachis oil	<35%	>200 nm

Note: Pairs tested in single batches.

Table 2 Interbatch Particle Size Distribution

Characteristics	Batch 1 (1 L)	Batch 2 (20 L)	Batch 3 (20 L)	Batch 4 (20 L)	Batch 5 (20 L)	Batch 6 (20 L)
D10	34.71 (1.09)	30.72 (2.22)	34.03 (2.06)	36.11 (3.40)	34.28 (4.82)	32.19 (1.89)
D50	57.54 (1.94)	51.46 (2.42)	55.78 (1.99)	59.15 (2.83)	58.71 (7.14)	52.37 (1.74)
D90	89.49 (3.52)	82.36 (7.44)	84.95 (1.85)	89.84 (2.46)	98.83 (12.27)	80.87 (1.79)
Mean (nm)	60.33 (2.00)	54.57 (3.24)	57.99 (1.95)	61.44 (2.69)	63.39 (7.55)	54.8 (1.64)
Span	0.95	1.01	0.91	0.91	1.10	0.93

Notes: Data shown as mean (SD). Total of 10 bottles per batch tested.

Abbreviation: SD, standard deviation.

Table 3 Physicochemical Characteristics of the Micellar Formulation Across the 6 Batches

Characteristics	Batch 1 (1 L)	Batch 2^a (20 L)	Batch 3^a (20 L)	Batch 4 (20 L)	Batch 5 (20 L)	Batch 6 (20 L)
Viscosity (cps)	0.997	0.997	0.996	0.996	0.998	0.993
Zeta potential (mV)	−3.29	−4.31	−3.14	−4.31	−5.94	−4.54
Surface tension	38.94	39.03	39.40	39.06	39.06	39.07
pH	7.03	6.89	7.05	7.04	6.99	6.91
Osmolality (mOsm/kg)	368	375	361	361	361	–
% optical transmission	91.36	90.34	90.65	88.37	91.62	91.48

Note: ^aControl batch. Single analysis for each batch.

Table 4 Average Potency of Latanoprost in Stability Study

	0 month	3 months	6 months	9 months	12 months	18 months	24 months
25°C/40% RH	102.4 (0.7)	99.7 (2.1)	100.2 (2.3)	98.0 (3.0)	99.0 (0.8)	100.1 (2.4)	101.9 (2.1)
	0 month	1 months	2 months	3 months	6 months
40°C/25% RH	102.4 (0.7)	98.3 (4.7)	97.2 (3.1)	100.5 (2.3)	100.8 (2.9)	–	–

Notes: Data show as mean (SD) % of label claim. Data averaged over 3 batches.

Abbreviations: RH, relative humidity; SD, standard deviation.

Table 5 In vitro Dilution Study

Batch	Time Point (Hours)
	0.5	1	2	4	6	8	10	12
Batch 1	27.3 (3.87)	41.6 (4.60)	64.9 (5.73)	86.5 (4.20)	97.8 (2.88)	102.3 (1.68)	104.7 (1.14)	105.5 (0.61)
Batch 2	22.8 (1.68)	37.9 (2.63)	59.7 (2.82)	79.7 (2.07)	86.2 (1.33)	88.9 (0.64)	90.4 (0.68)	91.6 (1.56)
Batch 3	21.7 (1.56)	35.7 (2.18)	56.5 (2.68)	80.4 (2.16)	88.8 (2.23)	93.0 (2.00)	95.2 (2.25)	95.7 (2.26)
Batch 4	31.7 (2.08)	45.9 (2.69)	62.0 (3.45)	83.2 (2.73)	90.5 (2.02)	94.5 (1.26)	95.7 (1.45)	96.6 (0.85)
Batch 5	29.5 (2.75)	44.4 (3.01)	60.4 (3.36)	81.9 (2.62)	89.6 (2.16)	93.0 (1.44)	94.1 (1.03)	94.8 (1.06)
Batch 6	33.4 (2.24)	48.7 (3.25)	64.3 (3.46)	84.2 (3.18)	91.3 (2.19)	94.8 (1.44)	96.0 (1.40)	95.4 (3.00)

Note: Data shown as mean (standard deviation), %.

Table 6 Cytotoxicity of Positive and Negative Controls and Micellar Formulation with Latanoprost 0.005% and Latanoprost 0.005% with BAK in Neutral Red Assay

Sample	Microscopic Observation	Neat	1:10	1:100	Rating^a
Positive control (BAK)	Cytotoxic	51.19	–	–	Severe
Negative control	Not cytotoxic	0	–	–	None
Latanoprost 0.005% with BAK	Moderate cytotoxicity	42.75	0	0	Moderate
Solution with latanoprost batch 060	Moderate cytotoxicity	31.73	0	0	Moderate
Placebo batch 060	No cytotoxicity	2.09	0	0	None
Micelle formulation with latanoprost batch 064	Slight cytotoxicity	15.59	10.53	0	Slight
Placebo batch 064	Slight cytotoxicity	17.02	4.58	0	Slight

Notes: ^aReactivity rating scale was per the 2004 The United States Pharmacopeia Convention, Inc. 0%–10%, None; 10%–20%, Slight; 20%–30%, Mild; 30%–50%, Moderate; 50%–100%, Severe.

Abbreviation: BAK, benzalkonium chloride.