Comparative viscosity and syringeability of five florfenicol injectable solutions

Easiness of injections is an important parameter for animal welfare and operators. This study was done to compare viscosity and syringeability of 5 florfenicol injectable solutions marketed in Mexico or Brazil, under laboratory conditions.

One 40% florfenicol injectable solution (Maxflor® LA, Virbac) was compared to four 30% florfenicol injectable solutions. Viscosity was measured at ambient temperature and 5°C by using a Brookfield viscosimeter. Syringeability was measured according to two tests: either as the time necessary to extract a 10 mL volume from a product vial by applying a constant strength of 19.6 N on a syringe or as the time necessary to empty a syringe containing a 10 ml volume of product by applying the same constant strength of 19.6 N. Two temperatures (ambient one ranging from 19 to 22°C and 5°C) and 2 types of needle (16G, 18G) were tested. Each measure was repeated 6 times with a chronometer. Times were then converted to the times corresponding to a volume necessary to treat a pig weighing 80 kg for a florfenicol dose regimen of 15 mg/kg, assuming a proportionality of the time according to the volume. For syringeability tests, each 30% florfenicol solution was compared to the 40% florfenicol solution by the t test with Bonferroni correction for pairwise multiple comparisons.

Viscosity ranged between 36 and 100 mPa.s at ambient temperature and between 96 and 328 mPa.s at 5°C, the 40% florfenicol solution having the lowest viscosity at both temperatures. The mean time to extract the defined volume at ambient temperature ranged from 2.2 to 7.0 s with a 16G needle and from 5.2 to 17.9 s with an 18G needle. The corresponding mean time at 5°C ranged from 5.0 to 19.9 s with a 16G needle and from 12.2 to 51.6 s with an 18G needle. The mean time to empty the syringe from the defined volume at ambient temperature ranged from 1.4 to 4.4 s with a 16G needle and from 3.3 to 10.4 s with an 18G needle. The corresponding mean time at 5°C ranged from 2.7 to 10.0 s with a 16G needle and from 6.4 to 23.2 s with an 18G needle. The 40% florfenicol solution showed the lowest times for all conditions, differences being statistically significant with all the 30% solutions.

Precision of the syringeability test was satisfactory. Measured times increased as viscosity of the product increased. Times were longer for the narrower gauge needle and at low temperature. Shortest times were recorded for the solution having both the highest florfenicol concentration and the lowest viscosity, reflecting influence of excipients. For this formulation, times appeared compatible with animal welfare and practical constraints (metaphylaxis, lower temperature in winter).

Disclosure of Interest: None Declared.