Oral Antimicrobial Medication
Pharmacokinetics in Chickens
DGS Burch BVetmed MRCVS
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Notes to assist use of this spreadsheet:
These data give an overall pattern for an antimicrobial, obviously each reference or study has been carried out in a different way so the results may vary between studies.
1. Dose rate is usually given by gavage as a bolus dose in classical pharmacokinetic studies but for practical use in water studies are described. Estimated dose rates have an 'e' denoting them for comparative use.
2. Cmax is the peak level found in serum after administration and is the highest level that can be achieved with a certain antimicrobial at a certain dose.
Administration by water usually gives a much lower figure because the drug is given over a 24-hour period and feed slows the passage and sometimes affects the absorption of some compounds.
3. C 12hours is the level of antimicrobial found in the blood 12 hours after administration. Products with a fast clearance usually have gone by 12 hours. When given in water levels may be lower but can persist for longer periods.
4. Steady state is the level achieved after in water medication and the average level that is achieved over a 24 hour period.This is the most important level for many antimicrobials as they act by inhibiting the growth of the bacteria and require a prolonged exposure. Concentrations in other target tissues like lung or airsac are also important when dealing with infections in those areas.
5. Protein binding of an antimicrobial is important as it can affect the effective concentration of that particular antimicrobial against an organism. High binding is therefore not usually good.
6. Bioavailability is the comparison of the absorption of a product from the gut in comparison with a dose given intravenously (assumed 100%). It is important if you want an antimicrobial to go from the gut to a target in the body. A high bioavailability means a drug is likely to work systemically although other factors can affect this. Feed may interfere with the absorption and bioavailability of a product.
7. Lung concentration is important if you want to treat an infection in the lung. Some antibiotics specifically concentrate in lung tissue and air sacs.
Overall, understanding the pharmacokinetics of an antimicrobial, knowing its level at the site of infection and the Minimal Inhibitory Concentration (MIC) of an organism to treat, can help the veterinarian to decide on what product, what dose, how it should be administered, for how long and improve the therapeutic control of the disease and thereby reduce the chances of developing antimicrobial resistance.
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