Comparison of Physical Properties among Injectable Long-acting Amoxicillins

Vetrimoxin LA is the most easily handled amoxycillin product that can be prescribed by the veterinarian even for the mass application as a prophylactic treatment to small piglets, according to Krejci, P. Forget, N. Guerra and A. Lopez of Ceva, France.
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Injectable forms of antibiotics are more in favour instead of oral forms along with the trends to reduce the use of in-feed medications.

Amoxicillin-based products with prolonged activity are considered the best option in the first line treatments of infections such as Streptococcus suis (S. suis) or Haemophilus parasuis (H. parasuis ). Those bacteria are recognised as very early colonisers, they frequently infect already suckling piglets which may become clinically ill still in the farrowing unit with the signs of arthritis or septicaemia. Eventually, the disease can develop later in the nurseries.

From the standpoint of the prudent use of antimicrobials, the injectable forms of amoxicillin would be given the preference in comparison to in-water or in-feed treatment (de Paz, 2013).

Physical properties of such products are essential for easy handling and administration even via thin needles which would be necessary particularly in small piglets. This aspect considers not only the labour demand in the process of the drug administration, but also the welfare conditions for small pigs.

The aim of this study was to evaluate the re-suspendability and syringeability of various amoxicillin products in comparison to the world leading reference product, Vetrimoxin®LA (Ceva). The tests were performed under different conditions with the objective to mimic the real situations which can occur with the regards to the environment, especially the temperature during the storage and application of the products.

Figure 1. Suckling piglet with the arthritis due to S. suis

Materials and Methods


Vetrimoxin LA together with six other products was stored at rest to settle out for two weeks in the cool conditions. All products were then kept for 24 hours either at room temperature, at 4°C or at -20°C. Each product was re-suspended manually multiple times by shaking at five-second intervals. The number of five-second intervals was counted up and the final time-to-resuspension was calculated.


The syringeability was measured also after the exposure of the products to 20°C, 4°C and -20°C for 24 hours. Ten ml of each product was pushed through either 19G or 21G needles pressed by the constant force of 10N and the time by which 10ml of the liquid passed through was measured.

Each test was conducted in five replicates.

If the piston was blocked, 300 seconds were added to the total time of the corresponding sample for the statistical analysis. Fisher’s exact test and generalised linear model were used to compare the data.

Figure 2. Syringeability test


The time required for resuspending 100ml vial was the shortest for Vetrimoxin LA and product C in all temperature conditions. (Figures 1, 2 and 3). Product B became frozen at -20°C and thus could not be used for further testing.

Figure 3. Time of re-suspension (s) at 20°C

Figure 4. Time of re-suspension (s) at 4°C

Figure 5. Time of re-suspension (s) at -20°C

This indicator reflects the ease of preparation of the smooth suspension ready for being injected after the product was let sedimented in various storage conditions. Time and effort required for the re-suspension is important to the direct users of injectable amoxicillins in the high intensive pig production sites.

When the syringeability was assessed, Vetrimoxin LA was never blocked at 20°C and once each time at 4°C or -20°C, while other products were blocked in the syringe multiple times up to 100 per cent (Product A at 4°C and Product at -20° were frozen).

Table 1. Percentage of blockage in the syringe
Vetrimoxin®LA 0% 8.3% 8.3%
A 83.3% 100% 91.7%
B 41.7% 16.7% 100%
C 58.3% 41.7% 66.7%
D 91.7% 91.7% 91.7%
E 58.3% 75.0% 75.0%
F 41.7% 91.7% 66.7%

The difference was statistically significant between Vetrimoxin LA and all other products (p<0.002).

Once the suspension gets blocked inside the syringe or even worse in the automatic syringe, the latter needs to be disassembled, cleaned and dried off. As seen above, it may happen with some products when thin needles are used, mainly under the cold temperatures. The consequence on the fluent treatment process is evident.

Time required for injecting a 10-ml volume was the shortest for Vetrimoxin LA (Figure 5) with the statistically significant difference from all other products (GLM p< 0.0001).

Table 2. Mean (± sd) time required for injecting 10-ml volume
Vetrimoxin®LA 48.0 83.2 99.8
A 257.0 300.0 280.0
B 215.7 206.6 300.0
C 199.4 161.7 226.5
D 278.8 277.5 279.8
E 210.9 251.1 256.9
F 152.0 283.9 226.7

Even if the individual volume of the curative dose is low, the short time to inject becomes important in the mass prophylactic treatments. It gives also evidence about the low exertion required to push the piston and thus to treat larger numbers of animals.


It was already confirmed that Vetrimoxin LA administered to suckling piglets decreased significantly the mortality in the pre-weaning period due to sudden deaths, deaths after the acute disease and also because of crushing of weak, sick piglets. Healthy and more vital piglets may have better chance to evade crushing.

Time to re-suspension and time to inject a 10-ml volume was the shortest for Vetrimoxin LA among all tested products. Also the incidence of blockages was the lowest in various temperature conditions using both 19G and 21G needles.

This renders Vetrimoxin LA the easiest handled amoxycillin product which may be prescribed by the veterinarian even for the mass applications in prophylactic treatments of small piglets.


  • Amass S.F. et al. 1996. Swine Health and Production, 269-272.
  • De Paz X., 2013. Pig International, 16-19.

Further Reading

Find out more information on the diseases mentioned by clicking here.

October 2013

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