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AVMA Guidlines for drug use
- “Drugs restricted by federal law to use by or on the order of a licensed veterinarian” prescription drugs
- NOT - for vet use only, sold to vets only
- MUST HAVE A VALID DOCTOR-CLIENT PATIENT RELATIONSHIP!!!
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Prescription Drugs
- May be dispensed by non-vet staff AFTER they have received instructions from a vet
- Prescription drugs should be kept separately from OTC drugs and not accessible by the public
- Records must be kept of all prescriptions and updated quarterly or more often
- Prescriptions cannot be changed except by prescribing vet with a signature
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Prescription Drug Labels
- Doctor, clinic name, address, license number
- Date
- Patient name, owner name
- Drug name , strength and amount
- Explicit instructions
- Refills
- Withdrawal times
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Economics of Drug use
- Many drugs are not routinely used in large animals because the amounts needed are cost prohibitive and food animals have a set value (price of meat)
- Baytril (enrofloxacin) - 2.5 mg/kg BID
- Average bovine - 1300 pounds
- > 3 grams BID; 68mg tabs are $3 each > 44 tabs BID > $264 per day
- Penicillin - $7 per day
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Legend Drugs
- Prescription drugs and drugs in which there is some potential for abuse, misuse, side effects or the instructions are not easy for the lay person to understand
- Off label use
- Controlled drugs - CI - CV
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Controlled Drugs
- CI - research use only, special license required (LSD, heroin)
- CII - high abuse potential (morphine, carfentanil, pentobarbital)
- CIII - some abuse potential (telazol, ketamine, phenobarb, pentothal
- CIV - low abuse potential (butorphanol, diazepam)
- CV - state or local control – codeine
Meticulous records need to be kept for every drop C1-C4
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Technicians Role
- Vet techs can dispense legend drugs under the supervision of a vet only
- You need to use your training to make sure the drug and dose makes sense
- Knowledge of proper injection sites, amount per site, techniques of administration, withdrawal times, etc
- If there is any doubt, ASK! Vets do screw up!
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Drug Residues
- A big problem in the food animal industry (this does include some horses!)
- Any drug residues found in meat or milk are cause for a producer to lose his profits, his animals and/or his livelihood
- Different species metabolize drugs at different rates, differences between individuals within a species, physical condition of the individual, age of individual, concurrent drug use
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Drug Metabolism
- Liver is the key organ for drug metabolism
- Oxidized, reduced or hydrolyzed
- Cats - hard time with aspirin, dogs - hard time with sulfonamides
- Ruminants - hard time with sedatives/paralytics
- Concurrent drug use, age effects
- Half life
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Inflammation
- Mediated by several classes of chemicals that activate an “inflammatory cascade” that can be difficult to stop once started
- Histamine - vasodilation, bronchoconstriction, gastric secretion, sensitized nerve endings (pain)
- Kininogens - vasodilation, pain
- Prostaglandins - pain, vasodilation, gastric secretions
- All inflammatory responses begin with vasodilation, 5-10 minutes later blood vessels become leaky and mediators which are released from blood cells can enter the area
- 4 cardinal signs of inflammation
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Anti-inflammitory drugs
- Adrenocortical hormones
- Corticosteroids
- Anabolic steroids
- Non-steroidal anti-inflammatories (NSAIDS)
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Adrenocortical hormones
- Produced in the adrenal gland (ACTH)
- Mineralocorticoids - aldosterone - facilitates sodium and water retention by the kidneys (anti-diuretic)
- Glucocorticoids - cortisol - increases carbohydrate, protein, and fat metabolism - fight or flight
- Sex hormones – minor source of estrogen, progesterone and testosterone (FSH, LH not stimulated by ACTH)
- Epinephrine
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Corticosteriods
- Uses - anti-inflammatory, anti-pruritic, immune suppression, vasoconstriction, anti-pyretic
- Problems - decreased immune function, PU/PD (inhibits ADH), muscle catabolism, laminitis in horses, ulcers, slows wound healing
- Water soluble - fast and short acting;
- water insoluble - slow and long acting
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Corticosteriod activity
- Cortisol/cortisone - base standard
- Prednisone, prednisolone - 4X cortisol, 12-36 hr onset
- Methylprednisolone (Depo Medrol) - 5X cortisol, 12-36 hours onset
- Trimacinolone (Vetalog) - 5X cortisol, 12 -36 hour onset
- Betamethasone (Celestone) - 30X cortisol, 36-72 hour onset
- Dexamethasone (Azium, Voren) - 30X cortisol, 36-72 hour onset
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Anabolic Steroids
- CIII
- Stimulates appetite, bone marrow and muscle anabolism
- Stanozolol (Winstrol),
- Boldenone (Equipoise)
- Hard on liver, kidneys and physes
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Non-Steroidal-Ani-Inflammatory-Drugs (NSAIDs)
- Uses - anti-inflammatory, anti-pyretic, analgesic, anti-endotoxic
- Contraindications - GI ulcers or diarrhea, kidney disease, dehydration, anemia, liver disease
- Mechanism of action - inhibits migration of inflammatory cells from the blood vessels, blocks prostaglandin production, inhibits phagocytocis
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Aspirin
- Acetylsalicylic acid
- Short half life in horses so not used much
- Large boluses used frequently in food animals
- Has some anticoagulant effects with long term use
- Acetominophen (Tylenol) - too expensive
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Flunixin
- Banamine
- Excellent visceral analgesic - #1 choice for colic
- Anti-endotoxic at low doses (1/4 of anti-inflammatory dose, but TID vs BID)
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Phenylbutazone
- Bute
- Excellent analgesic for musculoskeletal pain, less so for visceral pain
- Can be used for long periods of time at a reasonable dose
- NSAID most likely to cause toxicity (ulcers, colitis, major kidney damage)
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Prostiglandin and Hormones
- Prostaglandin
- Progesterone
- HCG
- Oxytocin
- Deslorelin
- Used almost exclusively to manipulate the estrous cycle to facilitate breeding
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Prostaglandins- PGF2a
- Lutalyse
- Use to lyse a CL, brings mare back into heat within 5 days IF CL is responsive (>5 days post ovulation)
- Used for abortion
- Causes signs of colic, sweating and severe cramping within 10-15 minutes - effects will pass
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Progesterone
- Regumate
- Maintains the uterus during pregnancy, prevents mares from coming into estrus, may reduce objectionable behavior in stallions
- DO NOT GET REGUMATE ON YOUR SKIN - IF YOU ARE PREGNANT, DON’T EVEN GET NEAR IT!!!!
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Human Chorionic Gonadotropin
- HCG
- Causes a mature follicle (>35mm in size) to ovulate within 36-48 hours
- Used to time ovulation with semen availability
- Only works once in any given breeding
- season - they develop antibodies!
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Deslorelin
- Ovuplant - subcutaneous implant
- GNRH analogue - causes increase in LH levels
- Causes ovulation of a follicle >32 mm in size within 36 hours
- Can be used multiple times in a season
- $$$$
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Oxytocin
- Stimulates smooth muscle contraction
- Milk letdown
- Retained placenta
- Induction of labor
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Anthelmintics
- Many different classes that treat different types of parasites
- Cestodes, nematodes, trematodes
- Coccidia
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Coccidiostats
- Amprolium - mimics vitamin B1 and binds to vB receptors on the schizonts, thereby retarding the schizonts development
- Sulfonamides - inhibits folic acid synthesis
- These are both coccidiostats - they do not kill the coccidia, just stop its development
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Organophosphates
- Dichlorvos, Trichlorfon
- Blocks nervous conduction in the parasite - if the dose is too high, it will block conduction in the host as well!
- DO NOT use in pregnant animals or young animals
- Very toxic - causes diarrhea, cramping and colic
- Used to kill bot larvae
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Avermectins
- Ivermectin (Eqvalan, Zimectrin), moxidectin (Quest), “Heartgard”
- Dosed orally, IM or pour-on
- Blocks the neurotransmitter GABA in the worm’s nervous system, thereby paralyzing it so it can be passed
- Used for nematodes and bots - no effect on trematodes and cestodes, they have no GABA
- NOT FOR use in animals intended for food or lactating dairy cattle
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Benzimidazoles
- Very large group - all drups end in ‘-azole’
- Very safe drugs (80 times recc dose)
- Affects the microtubules (strength and movement) and glucose levels (decreases) of the parasites, thereby killing nematodes and trematodes
- Thiabendazole - TBZ
- Fenbendazole - ‘Panacur’, ‘Safeguard’ - 8 day withdrawl, not for breeding dairy cows - also kills cestodes at double dose
- Mebendazole - ‘Telmintic’
- Oxyfenbendazole - ‘Anthelcide’
- Levamisole- ‘Levasole’, not for horses
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Phenothiazines
- Affects the nervous system of nematodes
- Very harsh on the host
- Not used much in large animals
- Also used as a tranquilizer (acepromazine)
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Piperazine
- Affects nervous system of nematodes, causing paralysis
- Affects adults only, retreat in 2-4 weeks to get newly molted larvae
- Can cause diarrhea and neuro signs
- Not used much in large animal but is used in pigs
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Pyrantel - "Strongid"
- Paralyzes adult nematodes at recc dose, paralyzes tapeworms at double dose (springtime)
- Safe up to 20X recc dose
- Can be fed daily - ‘Strongid C’
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Praziquantel
- “Droncit”
- Just recently approved for use in horses
- Effective against cestodes and some trematodes
- Causes paralysis of parasite and results in digestion
- Used in combination with an avermectin as an “all in one” dewormer
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Combination of Anthelmintics
- Many anthelmintics combine classes and are sold under a new name
- Be sure all of the ingredients are safe in the animal you are treating
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Beta-Lactam Antibiotics
- All drugs in this group are based on a b-lactam ring
- Penicillins and cephalosporins
- Mechanism of action - binds to bacterial cell wall proteins to cause holes in the cell walls, resulting in cell death
- Bacteria can become resistant by developing “b-lactamases” that destroy the b-lactam ring
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Penicillins
- Discovered in 1928
- Bacteriocidal to Gram (+)bacteria, aerobic and anaerobic
- Dosed in international units (IU) - amount of activity in 0.6mg of pure crystalline penicillin
- Rapidly absorbed IM; not given orally in large animals (diarrhea and GI upset)
- Excreted by the kidney
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Penicillin - types
- Pen G benzathine - IM only, longer acting (q 48 hour dosing)
- Pen G procaine - IM only, contains anesthetic due to large doses used, slows absorption
- Label dose is WRONG! 10,000 IU/lb = 3cc per 100lb body weight
- Sodium pen, potassium pen, ampicillin - IV only, good for resistant bacteria
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Penicillin - toxicity
- Toxicity - not routinely seen
- Hypersensitivity reactions - can be immediate - anaphylaxis, seizuring, collapse, hypersalivation, temporary blindness
- Contraindications - known allergy to B-lactam antibiotics (including cephalosporins); concurrent use of bacteriostatic antibiotics (tetracycline)
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Clavulanic Acid
- Added to some penicillins to prevent destruction of the drug by penicillinases (Clavamox)
- ‘Potentiated’ penicillin
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Cephalosporins
- First isolated in 1945 from sewage
- Modified penicillins - same mechanism of action
- 1st, 2nd and 3rd generations
- Broader spectrum than pens, more Gram (+) and some Gram (-), 3rd generation less effective against Staph
- More expensive
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Cephalosporins - types
- Cephalexin (Keflex) - 1st generation, oral
- Cefazolin - 1st generation, oral
- Ceftiofur (Naxcel) - 3rd generation, IM or IV
- Exceed new long acting Ceftiofur
- Excreted by the kidney
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Cephalosporins - toxicity
- Ceftiofur is the only cephalosporin used in large animals - orally causes diarrhea and GI upset
- Toxicity - high doses can cause pain at injection sites, diarrhea and ataxia
- If allergic to penicillins, then considered allergic to cephalosporins
- Contraindications - known allergies
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Aminoglycosides
- Bacteriocidal to Gram (-) bacteria, aerobic only
- Inhibits bacterial protein synthesis by binding to the ribosome and rendering it useless
- Gentamycin (Gentocin), amikacin ($$), tobramycin ($$$)
- Given IV, IM or ophthalmic
- Resistance - on the increase due to ribosomal mutation
- Use VERY carefully in dehydrated animals - may be best to delay administration until dehydration is corrected
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Aminoglycosides - toxicity
- Toxicity - ototoxicity, nephrotoxicity, neuromuscular blockade (respiratory paralysis)
- SID dosing decreases negative effects
- Contraindications - concurrent diuretic and anesthetic use, dehydration, severe renal disease
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Tetracyclines
- Bacteriostatic
- Gram (-) and (+), aerobic and anaerobic and rickettsia, but considerable resistance exists
- Inhibits bacterial protein synthesis by ribosomal binding
- Resistance is widespread
- Given IV (SLOWLY) and orally, IM can be used, but is irritating
- If given orally, do not combine with milk, antacids or Maalox (binds to the calcium)
- Excreted by the kidney
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Tetracyclines - toxicity
- Toxicity - generally safe, can cause GI upset
- May cause diarrhea, yellow teeth (chelates calcium) - use very cautiously in young animals! New born foals for contracted tendons
- Doxycycline
- Contraindications - concurrent penicillin use, methoxyflurane use
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Chloramphenicol
- Was the 1st broad spectrum antibiotic
- Bacteriostatic against Gram (+) and (-), aerobes, anaerobes and rickettsia
- Inhibits protein synthesis by binding to ribosome - this is reversible and can infection can recur if drug is withdrawn too soon
- Given orally or IV, can cross the placenta, excreted by the kidney
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Chloramphenicol - toxicity
- BANNED IN ALL FOOD ANIMALS!!!!!
- Public health issues - blood dyscrasias (aplastic anemia) - handle the drug carefully (preferably wearing gloves)
- Toxicity - short term therapy (<10 days) rarely causes side effects; GI upset if given orally
- Contraindications - concurrent bacteriocidal drug use, phenobarbital
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Sulfonamides
- #1 cause of drug residue violations, esp in swine, veal and poultry
- 1st discovered in 1936
- Bacteriostatic - Gram (-) and (+), coccidia
- Bacteriocidal if combined with trimethoprim
- Inhibits bacterial production of folic acid - bacteria must produce their own, mammalian cells must acquire it elsewhere
- IV, IM and oral forms available (oral most common)
- Resistance has developed
- Excreted by liver and kidney
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Sulfonamides - toxicity
- Toxicity - skin rashes, thrombocytopenia, arthritis, urinary disease
- Contraindications - known allergy, folate deficiency, late term pregnancy, renal or liver diease
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Macrolides
- Erythromycin, Streptomycin
- Bacteriostatic (cidal at high doses) against Gram (+)
- Inhibits bacterial protein synthesis by binding to the ribosome
- May cause life threatening diarrhea in adult horses (can be used carefully in foals), rabbits and guinea pigs
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Macrolides - uses and toxicity
- Given orally only on an empty stomach
- IV or IM use is painful
- Can cross the placenta
- Excreted by the liver in bile
- Toxicity - generally safe in ruminants
- Contraindications - can interact with methylprednisolone (Depo-Medrol) and warfarin
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Fluroquinolones
- Ciprofloxacin, Enrofloxacin (Baytril)
- Bacteriocidal to Gram (+) and (-) aerobics; NO ANAEROBICS
- Inhibits bacterial DNA from coiling into its double helix
- Very useful in skin, respiratory and urinary tract infections
- BANNED IN LACTATING DAIRY CATTLE
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Fluroquinolones - toxicity
- Toxicity - GI upset
- Damaging to developing cartilage - do not use in growing animals!
- Contraindications - concurrent use of chloramphenicol or other fluroquinolones, magnesium containing antacids
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Drugs Banned in Food animals
- Chloramphenicol, Clenbuterol
- Diethylstilbestrol, Dimetridazole
- Furazolidone, Glycopeptide
- Ipronidazole, Nitrofurazone
- Nitrofurans, Nitroimidazoles
- Fluoroquinolones
- Phenylbutazone (female dairy cattle >20 months of age)
- Sulfonamides (lactating dairy cattle, except sulfadimethoxine)
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