Veterinary Antibiotic Dose & Choice Calculator
Empirical antibiotic selection when you do not have a culture and sensitivity yet: pick the species and the presentation, and get the stewardship-ranked first choice, the dose at your patient’s weight, when culture is non-negotiable, and the warnings that actually matter. 12 species, 101 presentations. By Dr Duncan Houston.
For veterinary professionals only. Built on an Australian stewardship and regulatory context: verify the current product label, formulary, local law and culture results against the individual patient before prescribing.
Build the plan
Species
Who is on the table? Safety rules and drug choices change completely between species.
Presentation
Filter by body system, then pick the clinical presentation.
Patient
Weight drives the dose; patient factors drive the warnings.
Used to calculate the mg per dose. Decimal point or comma both accepted.
Empirical plan
Choosing an antibiotic without a culture and sensitivity
Quick answer: Empirical antibiotic choice is a three-step decision. First, does this patient need an antibiotic at all? (7 of the 101 presentations in this tool are best treated with none.) Second, what organisms live at this body site in this species, and which lowest-importance drug reliably covers them? Third, is this one of the situations where a culture must be collected before the first dose: recurrent disease, deep or surgical-site infection, sepsis, or any reserve-tier drug. Green before orange before red, narrowest that works, shortest course that cures.
How to use this veterinary antibiotic calculator
- Pick the species and presentation. Filter by body system first to shorten the list; the safety rules change completely between species, so this is not a cosmetic step.
- Enter an accurate current weight. Then tick the patient factors that apply: they drive the renal, hepatic, pregnancy, age, allergy and food-chain warnings.
- Read the whole plan, not just the drug name. The gate (does this patient need an antibiotic at all), the culture rule, the dose with working shown, the duration and the warnings are all part of the answer.
- Verify before prescribing. Check the current label, formulary and local law, and note the tool reports mg per dose, never millilitres: calculate the volume from the concentration on the actual bottle.
How this calculator decides
Every recommendation follows the stewardship sequence used in hospital antimicrobial guidelines: microbiology should guide therapy where possible; the indication must be evidence-based with a plausible bacterial cause; the narrowest effective spectrum is chosen; the dose is appropriate to species, site and infection type; duration is minimised; and monotherapy is preferred over combinations wherever possible. Each drug then carries a traffic-light importance tier. Green drugs (penicillins, tetracyclines, sulfonamides, older macrolides, amphenicols) are first-line choices. Orange drugs (potentiated amoxicillin, first and second generation cephalosporins, lincosamides, nitroimidazoles, gentamicin) are second line. Red drugs (third and later generation cephalosporins, fluoroquinolones, amikacin, rifampicin, and the never-in-animals group such as carbapenems and vancomycin) are reserve: high-importance antimicrobials for human health, defensible empirically only with a culture sample already in the lab. The tiers describe antimicrobial importance and stewardship caution, not a rigid prescribing sequence: where several options are clinically suitable, favour the narrowest effective agent in the lowest tier, then de-escalate or stop when results allow.
The cases where culture is not optional
Pyelonephritis, prostatitis, recurrent urinary infection, deep pyoderma, otitis media, pyothorax, osteomyelitis and septic arthritis, sepsis of unknown source, any confirmed methicillin-resistant staphylococcal infection, and every plan that starts a red-tier drug. In these, the sample comes before the first dose. Starting antibiotics first does not just muddy the culture, it removes your ability to de-escalate later, which is how patients end up on six weeks of the wrong drug.
Species that punish reflex prescribing
Rabbits, guinea pigs, hamsters and chinchillas die from oral penicillins, cephalosporins, clindamycin, lincomycin and erythromycin: fatal clostridial enterotoxaemia, and in guinea pigs even injectable penicillin is off the table. Injectable penicillin is acceptable in rabbits. Adult horses die from oral lincosamides and macrolides (colitis) and from intravenous doxycycline, and foals must never get fluoroquinolones (cartilage). Cats go irreversibly blind above 5 mg/kg/day of enrofloxacin, and dry-pilled doxycycline or clindamycin causes feline oesophageal stricture. Tilmicosin kills goats, horses and pigs, and has killed people through accidental self-injection. Every one of these is enforced automatically in the calculator.
Food-producing animals
Cattle, sheep, goats, pigs and poultry add residue law on top of stewardship. Chloramphenicol, nitroimidazoles and nitrofurans are prohibited outright; fluoroquinolones are not permitted in food animals in Australia. Everything else follows the registered label: the withholding period and export slaughter interval printed on the product apply at the label dose, and off-label dosing extends them, which is a formal residue-advice conversation, not a guess. Eggs from treated backyard hens are their own trap: very few products carry an egg withhold at all, so assume discard and check the specific product.
Empirical first-choice reference tables
The tables below are generated from the same data the calculator runs on, and the page checks them against the live data every time it loads. Doses are per administration for an adult of the species unless stated.
Dog: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Superficial pyoderma | Cephalexin 22-30 mg/kg PO q12h; Clindamycin 5.5-11 mg/kg PO q12h; Amoxicillin / clavulanate 12.5-25 mg/kg PO q12h | orange | Recommended | 21 days, or 7 days beyond clinical resolution. Recheck at 2 weeks. |
| Deep pyoderma / furunculosis | Cephalexin 30 mg/kg PO q12h; Amoxicillin / clavulanate 20-25 mg/kg PO q12h | orange | Strongly recommended | 4-6 weeks; continue 14 days beyond clinical resolution. Reassess at 2-3 weeks. |
| Abscess / bite wound | Amoxicillin / clavulanate 12.5-25 mg/kg PO q12h | orange | Ideal | 5-7 days after drainage established. |
| Otitis externa | Antibiotics not indicated | - | Ideal | Topical therapy 1-2 weeks beyond cytological cure; recheck with cytology. |
| Otitis media | Amoxicillin / clavulanate 20-25 mg/kg PO q12h | orange | Required | 4-6 weeks systemic, guided by re-imaging/rechecks. |
| Sporadic bacterial cystitis | Amoxicillin 11-15 mg/kg PO q8-12h; Trimethoprim / sulfonamide 15 mg/kg PO q12h | green | Ideal | 3-5 days. Short course is the evidence-based standard, not the old 7-14 days. |
| Recurrent cystitis (3+ episodes/year) | Amoxicillin 11-15 mg/kg PO q8-12h | green | Required | Per culture; typically 3-5 days for reinfection, longer only for relapse with an identified nidus. |
| Subclinical bacteriuria | Antibiotics not indicated | - | Ideal | - |
| Pyelonephritis | Enrofloxacin 10-20 mg/kg PO/IV q24h; Marbofloxacin 2.75-5.5 mg/kg PO q24h | red | Sample before first dose | 10-14 days (ISCAID), reculture 1-2 weeks after finishing. |
| Bacterial prostatitis | Trimethoprim / sulfonamide 15-30 mg/kg PO q12h; Enrofloxacin 10-20 mg/kg PO q24h | green / red | Strongly recommended | Acute: 2-4 weeks. Chronic: 4-6 weeks minimum. Castration is part of the treatment. |
| Pyometra | Amoxicillin / clavulanate 20 mg/kg IV (as amoxicillin/clav or ampicillin) q8h; Ampicillin 22 mg/kg IV q8h | orange / green | Recommended | Stop at or shortly after surgery in an uncomplicated case; 5-7 days only if peritonitis/sepsis. |
| CIRDC (kennel cough) | Doxycycline 5 mg/kg PO q12h | green | Ideal | 7-10 days. |
| Bacterial pneumonia (stable patient) | Doxycycline 5 mg/kg PO q12h; Amoxicillin / clavulanate 12.5-25 mg/kg PO q12h | green / orange | Strongly recommended | 2 weeks is usually enough in uncomplicated cases (re-evaluate with imaging rather than defaulting to 4-6 weeks). |
| Severe pneumonia / aspiration with sepsis | Ampicillin 22 mg/kg IV q8h; Enrofloxacin 10 mg/kg IV slow q24h | green / red | Sample before first dose | IV until eating and afebrile 24-48 h, then oral de-escalation guided by culture; total commonly 2-3 weeks. |
| Pyothorax | Ampicillin 22 mg/kg IV q8h | green | Required | 4-6 weeks total, oral after drainage resolves. |
| Acute diarrhoea / gastroenteritis | Antibiotics not indicated | - | Ideal | - |
| AHDS (haemorrhagic gastroenteritis) | Amoxicillin / clavulanate 20 mg/kg IV q8h | orange | Ideal | Sepsis subset: 5-7 days. |
| Giardiasis | Fenbendazole 50 mg/kg PO q24h | green | Ideal | Fenbendazole 3-5 days; retest 1-2 weeks after treatment; bathe the dog and clean the environment on the last day. |
| Campylobacteriosis (confirmed, clinical) | Erythromycin 10-15 mg/kg PO q8h | green | Recommended | 5-7 days (azithromycin 3-5 days). |
| Chronic enteropathy / 'ARD' | Tylosin 25 mg/kg PO q12h | green | Ideal | If used: 4-6 weeks, then taper to the lowest effective strategy while pursuing the real diagnosis. |
| Parvoviral enteritis | Ampicillin 22 mg/kg IV q8h; Cefazolin 22 mg/kg IV q8h | green / orange | Ideal | Until neutrophil recovery and clinical resolution, typically 3-5 days IV. |
| Cholangitis / hepatobiliary infection | Amoxicillin / clavulanate 12.5-25 mg/kg PO q12h | orange | Strongly recommended | 4-6 weeks, guided by recheck ultrasound and liver values. |
| Periodontal disease / tooth root abscess | Amoxicillin / clavulanate 12.5-25 mg/kg PO q12h; Clindamycin 5.5-11 mg/kg PO q12h | orange | Ideal | 5-7 days around definitive dental treatment. |
| Osteomyelitis / septic arthritis | Cefazolin 22 mg/kg IV q8h; Cephalexin 22-30 mg/kg PO q12h | orange | Required | Septic arthritis 4-6 weeks; osteomyelitis 6-8 weeks or beyond radiographic resolution. |
| Surgical prophylaxis | Cefazolin 22 mg/kg IV at induction redose q90min intra-op | orange | Ideal | Ends at closure. Continuing past 24 hours is treatment, not prophylaxis, and needs a diagnosis to justify it. |
| Leptospirosis | Doxycycline 5 mg/kg PO q12h; Ampicillin 22 mg/kg IV q8h | green | Recommended | Doxycycline 14 days total. |
| Ehrlichia / Anaplasma | Doxycycline 10 mg/kg PO q24h | green | Ideal | 28 days for Ehrlichia; 14-28 days for Anaplasma. |
| Sepsis, source unknown | Ampicillin 22 mg/kg IV q8h; Enrofloxacin 10 mg/kg IV slow q24h | green / red | Sample before first dose | De-escalate to the narrowest effective single agent within 48-72 hours on culture; total duration per source. |
| Confirmed MRSP infection | Only per susceptibility: Chloramphenicol 40-50 mg/kg PO q8h; Clindamycin 11 mg/kg PO q12h; Trimethoprim / sulfonamide 15-30 mg/kg PO q12h | green / orange | Required | Per site; topical chlorhexidine does much of the work in skin MRSP. |
Cat: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Cat bite abscess | Amoxicillin 11-22 mg/kg PO q12h; Amoxicillin / clavulanate 12.5 mg/kg PO q12h | green / orange | Ideal | 5-7 days after drainage. |
| LUTS in a cat under 10 years | Antibiotics not indicated | - | Recommended | - |
| Bacterial cystitis (confirmed or older cat with risk factors) | Amoxicillin 11-15 mg/kg PO q12h | green | Recommended | 3-5 days. |
| Pyelonephritis | Marbofloxacin 2.75-5.5 mg/kg PO q24h; Pradofloxacin 5-7.5 mg/kg PO (oral suspension) q24h | red | Sample before first dose | 10-14 days, reculture after finishing. |
| Upper respiratory infection (URI complex) | Doxycycline 10 mg/kg PO q24h | green | Ideal | 7-10 days (Chlamydia: extend to 4 weeks). |
| Chlamydia felis conjunctivitis | Doxycycline 10 mg/kg PO q24h | green | Ideal | 4 weeks (shorter courses relapse). |
| Mycoplasma haemofelis (haemotropic mycoplasmosis) | Doxycycline 10 mg/kg PO q24h | green | Ideal | 14 days minimum (some continue 2-4 weeks); glucocorticoids only if immune-mediated destruction dominates. |
| Bacterial pneumonia | Doxycycline 10 mg/kg PO q24h; Amoxicillin / clavulanate 12.5 mg/kg PO q12h | green / orange | Strongly recommended | 2 weeks typical for uncomplicated; re-image rather than defaulting long. |
| Pyothorax | Ampicillin 22 mg/kg IV q8h | green | Required | 3-4 weeks oral after drainage (amoxicillin/clavulanate is a rational oral continuation). |
| Gingivostomatitis / severe dental disease | Amoxicillin / clavulanate 12.5 mg/kg PO q12h; Clindamycin 5.5-11 mg/kg PO q12h | orange | Ideal | 5-7 days around definitive dental treatment. |
| Acute diarrhoea | Antibiotics not indicated | - | Ideal | - |
| Tritrichomonas foetus colitis | Ronidazole 30 mg/kg PO q24h | orange | Recommended | 14 days. |
| Neutrophilic cholangitis | Amoxicillin / clavulanate 12.5 mg/kg PO q12h | orange | Strongly recommended | 4-6 weeks guided by rechecks. |
| Pyometra | Amoxicillin / clavulanate 20 mg/kg IV formulation q8h | orange | Recommended | Stop at/shortly after surgery unless peritonitis. |
| Surgical prophylaxis | Cefazolin 22 mg/kg IV at induction redose q90min intra-op | orange | Ideal | Ends at closure. |
| Sepsis, source unknown | Ampicillin 22 mg/kg IV q8h; Marbofloxacin 2.75-5.5 mg/kg IV/PO q24h | green / red | Sample before first dose | De-escalate on culture at 48-72 h. |
| Skin/soft tissue infection in a genuinely un-medicatable cat | Cefovecin 8 mg/kg SC once (repeat at 14 days only if clearly indicated) | red | Sample before first dose | One injection covers 14 days; reassess before any repeat. |
Rabbit: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Pasteurellosis / 'snuffles' (URT) | Enrofloxacin 10-20 mg/kg PO q24h; Trimethoprim / sulfonamide 30 mg/kg PO q12h | red / green | Strongly recommended | 14-30 days; chronic cases may need longer with husbandry overhaul (ventilation, dust, ammonia). |
| Abscess (facial / dental / subcutaneous) | Penicillin G 40,000-60,000 IU/kg SC injection ONLY q24-48h | green | Recommended | 2-6 weeks alongside surgical treatment. |
| Rabbit syphilis (Treponema paraluisleporidarum) | Penicillin G 40,000-80,000 IU/kg SC injection ONLY once weekly x3 | green | Ideal | 3 weekly injections. |
| GI stasis | Antibiotics not indicated | - | Ideal | - |
| Enterotoxaemia / clostridial dysbiosis | Metronidazole 20 mg/kg PO q12h | orange | Ideal | 5-7 days with intensive support. |
| Cystitis / urinary infection | Trimethoprim / sulfonamide 30 mg/kg PO q12h | green | Recommended | 7-14 days. |
Guinea pig & rodents: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Guinea pig pneumonia / URT | Enrofloxacin 5-10 mg/kg PO q12h; Trimethoprim / sulfonamide 30 mg/kg PO q12h | red / green | Strongly recommended | 10-14 days; separate in-contact animals (Bordetella carrier rabbits should not live with guinea pigs). |
| Rat mycoplasmosis (chronic respiratory disease) | Doxycycline 5 mg/kg PO q12h; Enrofloxacin 5-10 mg/kg PO q12h | green / red | Strongly recommended | Flares: 2-4 weeks of the combination; some rats need pulse or continuous therapy. |
| Cystitis (guinea pig / rat) | Trimethoprim / sulfonamide 30 mg/kg PO q12h | green | Recommended | 7-14 days. |
| Pododermatitis (bumblefoot) | Trimethoprim / sulfonamide 30 mg/kg PO q12h | green | Recommended | 2-6 weeks by grade; husbandry decides the outcome. |
| Antibiotic-associated enterotoxaemia | Metronidazole 20 mg/kg PO q12h | orange | Ideal | 5-7 days with intensive support; guarded prognosis. |
Ferret: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Helicobacter mustelae gastritis / ulcers | Amoxicillin 20 mg/kg PO q12h; Metronidazole 20 mg/kg PO q12h | green / orange | Ideal | 21-28 days of the full combination; partial courses breed resistant Helicobacter. |
| Pneumonia / severe URT | Amoxicillin / clavulanate 12.5-25 mg/kg PO q12h | orange | Recommended | 10-14 days. |
| UTI / prostatomegaly-related | Trimethoprim / sulfonamide 15-30 mg/kg PO q12h | green | Recommended | 2-4 weeks with the underlying disease treated. |
| Bite wound / abscess | Amoxicillin / clavulanate 12.5-25 mg/kg PO q12h | orange | Ideal | 5-7 days. |
Bird (companion): empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Avian chlamydiosis (psittacosis) | Doxycycline 25-35 mg/kg PO q24h | green | Recommended | 45 days. Shorter courses relapse and keep shedding. |
| Bacterial sinusitis / URT | Trimethoprim / sulfonamide 25 mg/kg PO q12h | green | Recommended | 10-21 days plus sinus flushing. |
| Pododermatitis (bumblefoot) | Amoxicillin / clavulanate 125 mg/kg PO q12h | orange | Strongly recommended | 2-6 weeks by grade alongside surgical and husbandry treatment. |
| Gram-negative enteritis | Trimethoprim / sulfonamide 25 mg/kg PO q12h | green | Recommended | 7-10 days. |
| Egg-related coelomitis | Enrofloxacin 15-20 mg/kg PO/IM q12-24h | red | Strongly recommended | 2-4 weeks with definitive reproductive management. |
Reptile: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Septicaemia / systemic infection | Ceftazidime 20 mg/kg IM/SC q72h | red | Strongly recommended | 2-4 weeks minimum at corrected POTZ. |
| Respiratory infection | Ceftazidime 20 mg/kg IM/SC q72h | red | Strongly recommended | 3-6 weeks; ectotherm courses run long. |
| Ulcerative stomatitis (mouth rot) | Ceftazidime 20 mg/kg IM/SC q72h | red | Strongly recommended | 2-4 weeks with local treatment and husbandry correction. |
| Abscess / SCUD (shell rot) | Ceftazidime 20 mg/kg IM/SC q72h | red | Strongly recommended | 2-6 weeks alongside surgery. |
Horse: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Strangles (Streptococcus equi) | Penicillin G 22,000 IU/kg IM (procaine) q12h | green | Recommended | Early cases: 5-7 days. Complicated cases per specialist guidance. |
| Pleuropneumonia / severe LRT infection | Penicillin G 22,000 IU/kg IV (K/Na salt) or IM (procaine) q6h IV / q12h IM; Gentamicin 6.6 mg/kg IV q24h | green / orange | Sample before first dose | Weeks, guided by ultrasound and repeat cytology; refer early. |
| Foal Rhodococcus equi pneumonia | Azithromycin 10 mg/kg PO q24h x5d then q48h; Rifampicin 5 mg/kg PO q12h | green / red | Strongly recommended | 3-6 weeks, until ultrasound and inflammatory markers resolve. |
| Cellulitis / infected wound | Penicillin G 22,000 IU/kg IM (procaine) q12h; Trimethoprim / sulfonamide 30 mg/kg PO q12h | green | Recommended | 5-10 days; any wound near a joint or sheath gets a synoviocentesis, not a longer course. |
| Post-partum metritis | Penicillin G 22,000 IU/kg IM (procaine) q12h; Gentamicin 6.6 mg/kg IV q24h | green / orange | Recommended | 3-7 days with lavage; laminitis watch is part of the treatment. |
| Diarrhoea / colitis | Metronidazole 15 mg/kg PO q8h; Oxytetracycline 6.6 mg/kg IV slow q24h | orange / green | Recommended | 3-5 days (PHF) / 5-7 days (clostridial). |
| Neonatal foal sepsis | Penicillin G 22,000 IU/kg IV (K/Na salt) q6h; Gentamicin 12 mg/kg IV q36h | green / orange | Sample before first dose | 7-14 days guided by culture and clinical course; IgG transfer check is part of the treatment. |
| Urinary tract infection | Trimethoprim / sulfonamide 30 mg/kg PO q12h | green | Strongly recommended | 7-14 days; image for stones and assess bladder function. |
Cattle: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Bovine respiratory disease (BRD) | Oxytetracycline 20 mg/kg SC/IM (long-acting) single dose, repeat per label at 48-72h; Florfenicol 40 mg/kg SC (single-dose product; 20 mg/kg IM q48h alternative) once | green | Recommended | Per label. Observe the withholding period and export slaughter interval on the product used at the dose used. |
| Clinical mastitis (mild to moderate) | Cloxacillin per label (Intramammary, per registered tube) | orange | Strongly recommended | Per label; strip affected quarters; severe/toxic mastitis is a fluids-first emergency. |
| Metritis (post-partum) | Penicillin G 22,000 IU/kg IM (procaine) q24h; Oxytetracycline 10 mg/kg IV/IM q24h | green | Recommended | 3-5 days. |
| Calf scours | Trimethoprim / sulfonamide 16-24 mg/kg IV/IM q24h; Ampicillin 10 mg/kg IM q12h | green | Recommended | 3-5 days in the systemically ill only. Colostrum management fixes next season. |
| Footrot (interdigital necrobacillosis) | Penicillin G 22,000 IU/kg IM (procaine) q24h; Oxytetracycline 20 mg/kg SC/IM (long-acting) single dose | green | Ideal | 3-5 days (penicillin); clean, examine and rule out deeper sepsis if not sound in 3 days. |
| Pinkeye (infectious bovine keratoconjunctivitis) | Oxytetracycline 20 mg/kg SC/IM (long-acting) single dose, repeat at 72h if needed | green | Ideal | 1-2 long-acting doses; patch the eye, control flies, manage grass seed and dust. |
| Toxic / septic cow (e.g. severe coliform mastitis, peritonitis) | Oxytetracycline 10 mg/kg IV slow q24h; Trimethoprim / sulfonamide 16-24 mg/kg IV q24h | green | Recommended | 3-5 days with aggressive fluids, calcium and NSAIDs per case. |
Sheep & goats: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Footrot | Oxytetracycline 20 mg/kg IM (long-acting) single dose | green | Ideal | Single LA dose plus flock-level control (footbath, cull chronic carriers, vaccinate where available). |
| Pneumonia (pasteurellosis) | Oxytetracycline 20 mg/kg IM (long-acting) single dose, repeat per label | green | Recommended | Per label; ventilation and stocking density decide whether it comes back. |
| Listeriosis (circling disease) | Penicillin G 44,000 IU/kg IV as Na/K salt (NEVER IV procaine) or IM as procaine q12h | green | Ideal | 7-14 days; pull or fix the spoiled silage. Zoonotic: pregnant handlers stay clear of abortion material. |
| Caseous lymphadenitis (CLA) | Antibiotics not indicated | - | Ideal | - |
| Joint ill / navel ill (lambs & kids) | Penicillin G 22,000 IU/kg IM (procaine) q24h | green | Ideal | 5-7 days minimum; established joint infection carries a poor prognosis, so the real fix is navel dipping and colostrum next season. |
| Mastitis | Oxytetracycline 20 mg/kg IM (long-acting) single dose, repeat per label; Penicillin G 22,000 IU/kg IM (procaine) q24h | green | Recommended | 3-5 days; blue-bag (gangrenous) mastitis is a salvage/cull conversation, not an antibiotic one. |
Pig: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Erysipelas (diamond skin disease) | Penicillin G 22,000 IU/kg IM (procaine) q24h | green | Ideal | 3-5 days. |
| Respiratory disease (pleuropneumonia / enzootic pneumonia) | Amoxicillin 15 mg/kg IM (long-acting) q48h; Oxytetracycline 20 mg/kg IM (long-acting) single dose, repeat per label | green | Recommended | 3-5 days individual; ventilation and stocking are the herd cure. |
| Greasy pig disease (exudative epidermitis) | Amoxicillin 15 mg/kg IM (long-acting) q48h | green | Recommended | 3-5 days; piglet hydration decides survival. |
| Piglet scours (E. coli) | Trimethoprim / sulfonamide 15 mg/kg IM / oral per label q24h | green | Strongly recommended | 3 days typical; reassess against culture. |
| Joint ill / streptococcal arthritis (piglets) | Penicillin G 22,000 IU/kg IM (procaine) q24h; Amoxicillin 15 mg/kg IM (long-acting) q48h | green | Ideal | 3-5 days. |
Poultry: empirical first choices
| Presentation | Empirical first choice | Tier | Culture & susceptibility | Duration |
|---|---|---|---|---|
| Chronic respiratory disease (Mycoplasma) | Doxycycline 10-20 mg/kg PO q24h; Tylosin 25 mg/kg PO / in water per label q8-12h | green | Recommended | 7-14 days for flares. |
| Necrotic enteritis | Amoxicillin 15 mg/kg PO / in water per label q12h | green | Ideal | 5 days with coccidiosis control. |
| Bumblefoot (pet hen) | Amoxicillin / clavulanate 125 mg/kg PO q12h | orange | Recommended | 2-4 weeks by grade; eggs discarded during and after therapy per advice. |
| Egg yolk peritonitis (pet hen) | Trimethoprim / sulfonamide 25 mg/kg PO q12h | green | Strongly recommended | 2-4 weeks with definitive management of the reproductive disease. |
| Fowl cholera | Amoxicillin 15 mg/kg PO / in water per label q12h; Oxytetracycline 20 mg/kg PO / in water per label q24h | green | Recommended | 5-7 days; expect relapse in carrier flocks, discuss vaccination and rodent control. |
Antimicrobial stewardship tiers (the traffic-light chart)
| Antimicrobial | Class | Stewardship tier | Food animal status |
|---|---|---|---|
| Amoxicillin | Aminopenicillin | Green - first choice | Per label / registration |
| Ampicillin | Aminopenicillin | Green - first choice | Per label / registration |
| Azithromycin | Azalide macrolide | Green - first choice | Per label / registration |
| Chloramphenicol | Amphenicol | Green - first choice | Prohibited in food animals |
| Doxycycline | Tetracycline | Green - first choice | Per label / registration |
| Erythromycin | Macrolide | Green - first choice | Per label / registration |
| Fenbendazole (antiparasitic, not an antibiotic) | Benzimidazole | Green - first choice | Per label / registration |
| Florfenicol | Amphenicol | Green - first choice | Per label / registration |
| Minocycline | Tetracycline | Green - first choice | Per label / registration |
| Neomycin (oral / topical) | Aminoglycoside | Green - first choice | Per label / registration |
| Oxytetracycline | Tetracycline | Green - first choice | Per label / registration |
| Penicillin G (benzylpenicillin / procaine penicillin) | Natural penicillin | Green - first choice | Per label / registration |
| Trimethoprim / sulfonamide | Potentiated sulfonamide | Green - first choice | Per label / registration |
| Tylosin | Macrolide | Green - first choice | Per label / registration |
| Amoxicillin / clavulanate | Potentiated aminopenicillin | Orange - second line | Per label / registration |
| Cefazolin | 1st generation cephalosporin | Orange - second line | Per label / registration |
| Cefoxitin | 2nd generation cephalosporin | Orange - second line | Per label / registration |
| Cephalexin | 1st generation cephalosporin | Orange - second line | Per label / registration |
| Cephalonium (intramammary) | 1st generation cephalosporin | Orange - second line | Per label / registration |
| Clindamycin | Lincosamide | Orange - second line | Per label / registration |
| Cloxacillin (intramammary) | Anti-staphylococcal penicillin | Orange - second line | Per label / registration |
| Gentamicin | Aminoglycoside | Orange - second line | Per label / registration |
| Lincomycin | Lincosamide | Orange - second line | Per label / registration |
| Metronidazole | Nitroimidazole | Orange - second line | Prohibited in food animals |
| Mupirocin (topical) | Pseudomonic acid | Orange - second line | Per label / registration |
| Ronidazole | Nitroimidazole | Orange - second line | Prohibited in food animals |
| Tiamulin | Pleuromutilin | Orange - second line | Per label / registration |
| Tilmicosin | Long-acting macrolide | Orange - second line | Per label / registration |
| Tulathromycin | Long-acting macrolide | Orange - second line | Per label / registration |
| Amikacin | Aminoglycoside | Red - reserve, C&S first | Per label / registration |
| Cefovecin (Convenia) | 3rd generation cephalosporin | Red - reserve, C&S first | Per label / registration |
| Cefpodoxime | 3rd generation cephalosporin (oral) | Red - reserve, C&S first | Per label / registration |
| Ceftazidime | 3rd generation cephalosporin | Red - reserve, C&S first | Per label / registration |
| Ceftiofur | 3rd generation cephalosporin | Red - reserve, C&S first | Per label / registration |
| Ceftriaxone / cefotaxime | 3rd generation cephalosporin | Red - reserve, C&S first | Per label / registration |
| Enrofloxacin | Fluoroquinolone | Red - reserve, C&S first | Not permitted in food animals (AU) |
| Imipenem / meropenem (carbapenems) | Carbapenem | Red - reserve, C&S first | Per label / registration |
| Isoniazid | Antimycobacterial | Red - reserve, C&S first | Per label / registration |
| Marbofloxacin | Fluoroquinolone | Red - reserve, C&S first | Not permitted in food animals (AU) |
| Piperacillin / tazobactam | Antipseudomonal penicillin | Red - reserve, C&S first | Per label / registration |
| Polymyxin B / colistin | Polymyxin | Red - reserve, C&S first | Per label / registration |
| Pradofloxacin | 3rd generation fluoroquinolone | Red - reserve, C&S first | Not permitted in food animals (AU) |
| Rifampicin | Rifamycin | Red - reserve, C&S first | Per label / registration |
| Ticarcillin / clavulanate | Antipseudomonal penicillin | Red - reserve, C&S first | Per label / registration |
| Vancomycin / teicoplanin | Glycopeptide | Red - reserve, C&S first | Per label / registration |
Veterinary antibiotic calculator FAQs
Can I choose an antibiotic without a culture and sensitivity?
Yes, for most first-episode, uncomplicated infections: empirical selection based on the expected organisms at that body site is standard practice. The discipline is in the exceptions. Recurrent infections, pyelonephritis, deep pyoderma, osteomyelitis, pyothorax, otitis media and any plan that reaches for a reserve-tier drug all need a sample collected before or alongside the first dose, because a culture taken after antibiotics have started is a culture wasted.
What is the first-choice antibiotic for a dog urinary tract infection?
For sporadic bacterial cystitis in dogs, amoxicillin at 11-15 mg/kg orally every 8-12 hours, or trimethoprim-sulfonamide at 15 mg/kg twice daily, for 3-5 days. Amoxicillin-clavulanate, cefovecin and fluoroquinolones are not first line for a simple UTI, and short courses now beat the old 7-14 day habit.
Why is cefovecin (Convenia) a reserve antibiotic?
It is a third-generation cephalosporin, a high-importance class for human medicine, and a single injection leaves sub-therapeutic tissue concentrations for around 65 days, which is close to a designed experiment in resistance selection. It has one legitimate niche: the patient that genuinely cannot be medicated any other way, ideally with a culture collected before injecting.
Which antibiotics kill rabbits and guinea pigs?
Oral penicillins (including amoxicillin and amoxicillin-clavulanate), cephalosporins, clindamycin, lincomycin and erythromycin cause fatal clostridial enterotoxaemia in rabbits, guinea pigs, hamsters and chinchillas. Injectable penicillin is acceptable in rabbits only; in guinea pigs avoid penicillins by any route. Safe oral options include enrofloxacin, trimethoprim-sulfonamide and metronidazole.
Which antibiotics are prohibited in food-producing animals?
Chloramphenicol, nitroimidazoles (metronidazole, ronidazole) and nitrofurans are prohibited outright in food animals in Australia and most jurisdictions, and fluoroquinolones must not be used in food-producing animals in Australia. For everything else, use a product registered for the species and observe the label withholding period and export slaughter interval, remembering that off-label doses extend withholds.
Why does my young cat's cystitis not need antibiotics?
Fewer than about 5% of cats under 10 years with lower urinary tract signs have a bacterial infection; the overwhelming majority have feline idiopathic cystitis, a sterile, stress-associated disease. The treatment is analgesia, environmental modification and water intake, not amoxicillin, and certainly not a long-acting cephalosporin injection.
What do the green, orange and red tiers mean?
They follow the antimicrobial importance-rating framework used in Australian stewardship guidance (ASTAG) and hospital traffic-light charts. Green drugs are first-line, low human-health-importance choices. Orange drugs are second line. Red drugs are high-importance reserve antimicrobials: empirical use is only defensible with a culture sample already collected, and some (carbapenems, vancomycin) have no place in routine practice at all.
How does the calculator work out mg per dose?
It multiplies body weight in kilograms by the published mg/kg (or IU/kg) range for that drug and indication, converting pounds to kilograms first if you toggled lb. When the dose is a range, you get the low and high total per administration, with the working shown so you can check the arithmetic yourself. Confirm the dose, route and interval suit your individual patient before prescribing.
Does the calculator convert the dose to millilitres?
No, deliberately. Product concentrations vary between brands, formulations and countries, so the tool reports the total active dose in mg or IU and leaves the volume calculation to the concentration printed on the bottle in your hand. Assuming a concentration for you is how tenfold errors happen.
Can I use these recommendations outside Australia?
The dose arithmetic is universal, but the stewardship tiers, prohibited-substance rules and withholding framework are built on the Australian context (ASTAG importance ratings, APVMA residue law). Drug registration, legal classifications and accepted protocols differ by country: treat the output as decision support and verify against your local label, formulary and law.
How long should an antibiotic course be?
Shorter than the habit. Uncomplicated cystitis: 3-5 days. Uncomplicated pneumonia: around 2 weeks with recheck imaging rather than a default 4-6 weeks. Superficial pyoderma: 3 weeks or 7 days past resolution. Surgical prophylaxis: ends at skin closure. The evidence has moved to shortest-effective courses; the calculator shows a duration with every plan.
Clinical sources and update policy
This tool synthesises published veterinary antimicrobial guidance, expected pathogens, Australian antimicrobial-importance ratings and residue law. The primary source hubs behind the methodology:
- ISCAID guidelines for canine and feline urinary, respiratory and skin infections.
- Australian Veterinary Association policy on antimicrobial use.
- Australian antibacterial importance ratings (ASTAG), the basis of the green, orange and red tiers.
- APVMA list of substances not permitted in food-producing animals.
Update policy: guidelines, registrations, labels and residue requirements change. Verify the current source on the day you prescribe, and report a suspected correction via the ASK A VET™ contact page. Authorship, sourcing and corrections standards live in the editorial guidelines.