A Dosage Based Approach to Water Soluble Medicating

The decision to treat a group of animals with water-soluble antibiotics is an everyday occurrence in pig production throughout the world. If there is a concern that a disease may be threatening the group, the veterinarian and producer need a way that all of the pigs can be treated easily. The obvious appeal of a water-based approach to treatment is that a single herds-person can treat a large group of animals at one time.

The label instructions on most water-soluble antibiotic products direct the user to create a stock solution of a specific concentration that is metered out at a set rate (i.e. 1:128 OR 1:100) into the drinking water line. This is the most commonly used approach in our current pig production systems. Some product labels actually direct the user to mix a specific amount of medication into a large reservoir of water and then deliver it directly to the target group via troughs or water lines. This method is not as commonly used in our current production systems.

Interestingly enough, most water-soluble antibiotic products, purchased for use in pig production in Canada, make no reference to the amount of product that should be delivered to the treatment group on the basis of weight (i.e. DOSE = 'mg per kg' OR 'IU per kg'). Most other types of antibiotic products direct the user to deliver a certain amount of product in this manner. The best example of this approach would be injectable antibiotics that are delivered directly into the muscle of the pig via an IntraMuscular (IM) injection. Usually, the label will indicate how many kilograms or pounds that a milliliter of the product will treat.

This presentation will explain why it is important to consider dose when delivering water-soluble antibiotics and how we have attempted to address this concern in an effective and practical manner for day-to-day pig production.

Why is it important to consider dose when treating pigs through the water?

Whenever we decide to treat a pig with an antibiotic, it is important that they receive the correct dosage or amount of product for their size. As the size of the pig increases, the amount of antibiotic required to effectively treat the pig also increases. Ultimately, we want to insure that the antibiotic reaches a high enough concentration in the pig's body so that it either stops bacterial multiplication (i.e. bacteriostatic) or kills the bacteria completely (i.e. bactericidal). If enough antibiotic is not delivered to the pig, the treatment may not be effective and an antibiotic that could have worked will have effectively failed.

How do the current label directions fail to insure a proper dose is delivered?

Even when a stock solution is properly mixed, according to label instructions, there are several factors that may cause variation in the 'real' final dose that the target animals receive. The amount of antibiotic consumed relies upon these factors and as a result the amount of stock solution (or antibiotic) that is used everyday may vary dramatically during a treatment period. As a result, it is very difficult to trust that the majority of the pigs are getting a consistent treatment dose each day.

     · Medicator Calibration --> If the medicator which meters the stock solution into the water line is not
      properly calibrated, the amount of antibiotic delivered may be higher or lower than intended.

     · Animal Health --> Sick animals may drink less than their healthy counterparts. If the majority of pigs
      in the group are not feeling well enough to get up and drink enough water, they may not receive enough
      antibiotic to actually treat or prevent the disease as intended. It is also important to understand that the
      body absorbs and distributes antibiotics to the tissues (i.e. muscle, joints, etc) differently in a sick state
      versus a healthy state.

     · Water Accessibility --> Drinkers may become blocked by excessive feed in wet/dry feeders. Nipple
      drinkers may become blocked by mineral deposits or other forms of blockage. If there is any impediment
      to water consumption due to accessibility, reaching an adequate dose will be more unlikely.

     · Palatability --> How the water tastes when the medication is added can effect the water consumed
      per day and, ultimately, the dose which the pig consumes.

     · Temperature --> The amount of water consumed per day is dramatically effected by the effective
      environmental temperature that the pig feels.

     · Stage of Production --> If the demands of production require more water intake on a daily basis,
      this will effect the amount of antibiotic consumed. The most obvious example in pig production would be
      the lactating sow that must consume more water as a result of milk production.

     · Weight --> As a pig grows, the amount of water consumed as a percentage of total body weight
      changes. As a rule of thumb, it is generally thought that a 'younger' pig will consume approximately 10%
      of its body weight in water (One litre of water = One kilogram) every day while an 'older' growing pig will
      comsume closer to 6 or 7% respectively on a daily basis.

What approach to water-soluble treatment can address these concerns?

The 'only' way to insure that 'every' pig in a target treatment group receives the correct dose of antibiotic is to weigh it and then deliver the correct amount of antibiotic into the vein, muscle, or mouth! Clearly, these approaches may not always be practical when treating a large number of pigs.

When treating pigs through the water, you can 'never' be certain that every pig will receive the correct dose of antibiotics. However, you can increase the likelihood that 'most' of the pigs in the group will have a better chance of receiving the correct dose. The hope is that this approach will result in an cost-effective preventative or therapeutic treatment program.

We have adopted a 'dosage-based' approach to insure that as many pigs as possible receive the 'intended' amount of antibiotics every day during the treatment period. A Water Soluble Calculator has been created to facilitate rapid calculations. The main functions of this calculator include the following:

1) Incorporate the desired dose for each product to be used
     · This requires a thorough literature search that will verify the target effective dose (i.e. 'mg per kg' OR
       'IU per kg').
     · Must be prescribed by a veterinarian since it is an off label usage.

2) Calculate the amount of product required per day for the group
     · This calculation requires: the total kgs (body weight) of the treatment group (number of pigs X average
      weight), target dose ('mg/kg' OR 'IU/kg'), and concentration of the product to be used ('mg per kg
      product' Or 'mg per container of product').

3) Calculate the amount of product required per treatment period
     · This calculation requires the amount required per day and the total number of days in the treatment
      period.

4) Calculate the cost of the treatment
     · The cost of the treatment should be calculated on both a total group and individual pig basis.
     · As well, it is good to calculate the costs on a 'per day' and 'per treatment period' basis.

5) Cost comparison between products
     · It is valuable to include a cost comparison between water-soluble antibiotic products so that a decision
      on cost effective treatments can be made.

Key Considerations for Implementation of the Dose Based Approach

     · Recognize that all treatments are 'Off Label' and require a prescription from the consulting veterinarian.

     · The veterinarian should prescribe both the dose and the withdrawal period. The Canadian Quality
      Assurance (CQA) also requires that this prescription be part of the production unit's CQA records.

     · The emphasis of this approach is on the 'total amount' of antibiotic consumed each day.

     · When the 'amount consumed' becomes the concern, most of the factors (listed above) effecting daily
      intake become 'non-issues'.

     · The only variable that is not addressed by this approach is variable water intake within the group (from
      pig to pig). When there is a large variation within a group, it is best to use the average of the heaviest
      pigs in the group as your average overall weight to insure that all pigs receive an adequate amount of
      antibiotic each day.
       Using too low a weight will under estimate the volume needed.

     · Once the target amount of antibiotic is consumed by the group for the treatment day, the treatment
      should stop. Generally speaking, it is desirable to deliver the antibiotic during the normal working day
      (8 to 9 hours) or over a 24-hour period.

     · For CQA program recording purposes, the number of pigs, weight of pigs, daily amount of antibiotic,
      route of administration (IW or PO), and withdrawal period must match the instruction sheet produced
      by the water-soluble calculator.

Conclusion

The proper use of antibiotics in pig production should ultimately be based on a scientifically determined dosage for the treatment group or individual. Unfortunately, when it comes to water-soluble antibiotic use in Canada, it is difficult to take this approach with the current labeling policies. Fortunately, Canadian veterinarians currently
have the ability to prescribe off label usage and this allows a safer and more defendable approach to antibiotic therapy.

Author: Dr Tim Snider (Elite Swine Inc.)
Proceedings of the 2005 Manitoba Swine Seminar
Prairie Swine Centre publication

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A Dosage Based Approach to Water Soluble Medicating