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A.
Rational Use of Drugs
National Standard Veterinary Treatment Guideline (SVTG)
is important to rationalize treatment of animal diseases,
utilization of drugs properly and protecting the public from
exposure to unnecessary drug residues. Drugs should be used
only when required at the required amount and combination.
Improper use of drugs may result in ineffective treatment,
unnecessary wastage of resources, and may harm the patient.
In using veterinary drugs, certain steps have to be followed
before deciding on what procedures have to be used. One
way of promoting such a practice is developing SVTG.
Rational approach to therapeutics requires careful evaluation
of the health problem in each species of animal and selecting
appropriate therapeutic strategies. Proper diagnosis of animal
diseases requires extensive discussions with owners and
clinical examinations and confirmed by appropriate
laboratory procedures. The efficacy of treatment largely
relies on correct diagnosis. Whenever the alternatives exist,
non-pharmacological treatment should be given priority to
chemical treatment. In veterinary medicine, preventive
measures are the option of the day than treatment. Thus
possible preventive measures should be given attention to
check the spread of animal diseases.
Selection of treatment requires cost/benefit analysis
particularly in food animals. Uneconomical treatment is
basically avoided unless and otherwise the animals have
special attachment with the owner (e.g. dogs and cats) or the
genetic make up of the animal should be conserved. Apart
from the cost of a particular drug, its efficacy and safey with
minimal adverse effects and minimal residues in food
animals should be given due attention. Drug choice depends
on individual patient and prescription; whenever written it
should clearly indicate the species of animal, the age,
sometimes breed, the dose of the drug in the formulations
available locally and the duration of treatment. In food
animals, considerations have to be given to the withdrawal
period of drugs in case an emergency slaughter is
recommended (included in prescription writing).
B.
Prescription writing
A prescription is an instruction from a prescriber to a
dispenser. The prescription is the link between the prescriber,
the drug dispenser and the patient. Appropriate prescription
should give relevant information, instruction and warning to
the patient. Currently veterinary doctors, animal health
assistants and sometimes animal health technicians could
prescribe to veterinary drugs dispensary and pharmacies.
Prescriptions should be clear, legible and indicate precisely
what should be given. It should include the following:
 Date of the prescription
 Name, form and strength of the drug. Generic name of
the drug should be used.
 Formulation of the drug (e.g. tablet, oral solutions, feed
additive, or ointment) should also be stated.
 Strength of the drug should be stated in standard units.
 Dose, route of administration and frequency should be
clear and explicit; use of phrases such as “take as
directed” or “take as before” should be avoided.
 Quantity of the medical product to be supplied should
be stated. Alternatively, the length of treatment course
should be stated.
C.
Adherence (compliance) with drug treatment
Once drugs are dispensed according to the prescription,
the owners or those who administer it should stick to the
dose and frequency of treatment. Poor adherence
(compliance) with the treatment plan is one of the most
important reason for treatment failure so long as the the
drug is well tolerated. In fact there may be mistakes in
prescriptions, which might result is errors in calculations
or different formulations have been quoted. It is not
uncommon to find Veterinary drugs in Ethiopia whose
active ingredient is one fifth or even less than the
concentrations recommended in the British Pharmacopenia
or other standards but the bolus size remains the same. In
these circumstances, those lower level professionals may
prescribe a bolus whose active ingredient is very low.
Non-compliance in veterinary medicine is also more
common than in humans and particularly over the counter
drugs where livestock owners have access.. The owners
usually divide the drug between other animals of the group
in order to save money. In this case the owners have to be
informed on the hazards and disadvantages arising from
such practices.
D.
Veterinary considerations in drugs use
The types of drugs to be used in veterinary medicines are
chemically similar to those used in humans. However, certain
conditions have to be considered before deciding to use a
certain drug. These include: whether treatment is economical,
if there are regulatory and public health concerns,
compatibility, stability and compounding process, and
pharmacokinetics of the active ingredient.
Apart from the diversity of animal species, the range of size
of animals varies within each species of animals. For
example, in cattle, the weighs of an adult animal ranges from
200-250kg in zebu and 700 or more for certain improved
breeds. Setting a standard dose for each group may be
therefore difficult. It is thus imperative that a veterinary
professional with sufficient experience should be involved in
prescription of drugs. On the other hand some drugs may be
applied to certain species but not to others requiring good
knowledge of adverse effects on a particular species of
animals. The type of feed is also another consideration.
Drugs formulated as feed additives are preferred but these
drugs could only be given to certain species of animals or
age groups if they may not adversely affect the microflora.
For example, tetracyclines in feed are more recommended to
calves and not to adults.
E.
Adverse drug reactions and drug interactions
An adverse drug reaction may be defined as any unwanted
response to a drug which is noxious, unintended and occurs
at doses normally used for prophylaxis, diagnosis, or therapy.
These reactions are mainly individual and thus closer
attentions should be given to drugs with known adverse
reactions. Adverse reactions may arise from old age.
Drug interactions (drug-drug interactions) on the other hand
are reactions that occur between two or more drugs when
they are used to treat pathophysiologically distinct illnesses
or a single illness in a patient. Interactions can occur between
drugs competing for the same receptor or acting on the same
physiological system. They may also occur indirectly when a
drug-induced disease or a change in fluid or electrolyte
balance alters the response to another drug. Interactions may
also occur when one drug alters the absorption, distribution
or elimination of another drug, such that the amount, which
reaches the site of action, is increased or decreased.
When two drugs are administered to an animal, they may
either act independently of each other, or interact with each
other. Interactions may decrease or increase the action of the
interacting drugs. In general, the combination of bactericidal
and bacteristatic drugs is not recommended, as it results
antagonistic effects.
F. Drug residues
By eating animals and animal products, humans are liable to
consume whatever chemicals the animal has consumed or
been exposed to. Such chemicals include veterinary drugs,
insecticides or herbicides. The residue limits and the
withdrawal periods of these chemicals and drugs have been
established though controversy still surrounds this issue.
Withdrawal period is the time between the application of the
drug and clearance to a level of its residue limit. Thus, the
withdrawal period should be considered during treatment of
food animals including livestock, honeybee and fish.