VTNE

Antimicrobials include antibiotics, antifungals, antivirals, and antiparasitics. Bactericidal drugs kill bacteria; bacteriostatic drugs inhibit growth and rely on the immune system. The minimum inhibitory concentration (MIC) is the lowest concentration that prevents visible growth. Time-dependent drugs (beta-lactams) work best when levels stay above the MIC, so dosing intervals matter; concentration-dependent drugs (fluoroquinolones, aminoglycosides) work best with high peaks. Selection should be based on culture and sensitivity whenever possible, and clients must finish the full course to limit resistance.

Penicillins

Penicillin G, ampicillin,

Cell wall synthesis

Hypersensitivity; clavulanate inhibits beta-

amoxicillin, amoxicillin-

(penicillin-binding

lactamase; procaine penicillin is IM only

clavulanate

proteins); bactericidal

(procaine reactions in horses)

Cephalosporins

1st: cephalexin, cefazolin;

Cell wall; bactericidal

Higher generations add gram-negative

3rd: cefpodoxime,

coverage; cefazolin for surgical prophylaxis;

cefovecin, ceftiofur

cefovecin injection lasts up to 14 days

Fluoroquinolones

Enrofloxacin,

DNA gyrase and

Cartilage damage in growing animals; retinal

marbofloxacin,

topoisomerase IV;

degeneration and blindness in cats at high

pradofloxacin

concentration-dependent

enrofloxacin doses; lower seizure threshold

Aminoglycosides

Gentamicin, amikacin,

30S ribosome;

Nephrotoxicity (monitor urine for casts,

neomycin

bactericidal,

creatinine) and ototoxicity; poor oral

concentration-dependent

absorption, so given parenterally

Tetracyclines

Doxycycline,

30S ribosome;

Tooth discoloration in young animals; chelated

oxytetracycline,

bacteriostatic

by calcium, antacids, iron; doxycycline tablets

minocycline

can cause esophageal stricture in cats (follow with water)

Macrolides and

Erythromycin,

50S ribosome

GI upset; erythromycin is prokinetic;

lincosamides

azithromycin, tylosin;

clindamycin penetrates bone (osteomyelitis,

clindamycin, lincomycin

dental infections, toxoplasmosis)

Potentiated

Trimethoprim-

Folic acid synthesis

Keratoconjunctivitis sicca in dogs, crystalluria

sulfonamides

sulfamethoxazole

(keep hydrated), bone marrow suppression, hypersensitivity (Doberman pinschers)

Nitroimidazoles

Metronidazole

DNA damage in anaerobes

Anaerobes and Giardia; crosses the blood-brain

and protozoa

barrier; high doses cause ataxia, nystagmus, seizures; prohibited in food animals

Amphenicols

Chloramphenicol,

50S ribosome;

Chloramphenicol causes rare, fatal aplastic

florfenicol

bacteriostatic

anemia in people: wear gloves; banned in food-producing animals; florfenicol is the approved cattle alternative

Oral penicillins, cephalosporins, macrolides, and especially lincosamides can kill rabbits, guinea pigs, hamsters, and chinchillas by disrupting cecal flora and causing fatal clostridial enterotoxemia. Lincomycin and clindamycin also cause severe colitis in horses.

Antifungals and Antivirals

Drug	ActionandUse	KeyCautions
Azoles:ketoconazole ,	Inhibitergosterolsynthesis;systemic	Ketoconazole:hepatotoxicityandmanydruginteractions;
itraconazole fluconazole ,	andskinfungi	fluconazolepenetratestheCNSandurine
Terbinafine	Allylamine;dermatophytes	GIupset;generallywelltolerated
AmphotericinB	Bindsergosterolinfungal	Nephrotoxic;monitorrenalvalues
	membranes;severesystemic
	mycoses
Nystatin	Polyene;topicalororalforyeast	NotabsorbedfromtheGItract
	(Candida)
Griseofulvin	Dermatophytes;givewithafattymeal	Teratogenic(neverinpregnantanimals);bonemarrow
		suppression especially in FIV -positive cats ,
Famciclovir;interferons	Antivirals;famciclovirforfeline	Supportivecareremainsthecoreofviraldiseasetreatment
	herpesvirus-1

Parasiticides

Class/Drug	Mechanism	Targets	Cautions
Benzimidazoles:	Inhibitparasitemicrotubule	Roundworms hookworms , ,	Widesafetymargin;fenbendazole
fenbendazole ,	(tubulin)formation	whipworms Taenia Giardia , ,	needs multiple-day dosing;
albendazole			albendazolecansuppressbone
			marrowandisteratogenic
Pyrantelpamoate	Depolarizingneuromuscular	Roundworms hookworms ,	Safeinpuppies kittens pregnant , ,
	blocker(spasticparalysis)		animals
Praziquantel epsiprantel ,	Tetaniccontractionand	Tapeworms(cestodes) ,	Verysafe;coversDipylidium Taenia , ,
	tegumentdamage	flukes(trematodes)	Echinococcus
Macrocycliclactones:	Open glutamate-gated and	Nematodes heartworm ,	MDR1(ABCB1)mutationdogs;toxic
ivermectin selamectin , ,	GABA -gated chloride channels	larvae(L3 L4) mites some , , ,	tochelonians;testforheartworm
milbemycin moxidectin ,	in invertebrates paralysis →	ectoparasites	beforestartingpreventive
Melarsomine	Arsenicaladulticide	AdultDirofilariaimmitisin	DeepIMintolumbarepaxialmuscles;
		dogs	strictexerciserestriction(embolism
Metronidazole , fenbendazole	Seeabove	Giardia	risk) 1 Bathetoremovecystsfromthe haircoat

Endoparasiticidesandantiprotozoals(Continued)

Class/Drug	Mechanism	Targets	Cautions
Ponazuril toltrazuril ,	Triazineantiprotozoals	Coccidia;ponazurilfor	Clindamycinistheusualfirstchoice
		equineprotozoal	forclinicaltoxoplasmosis
		myeloencephalitis
		(Sarcocystisneurona);
		activeagainstToxoplasma
Amprolium ,	Thiamineantagonist;	Coccidiosis	Amproliumoverdosecancause
sulfadimethoxine	sulfonamide		thiaminedeficiency
			(polioencephalomalacia)inruminants

Dogs with the MDR1 (ABCB1) mutation lack functional P-glycoprotein at the blood-brain barrier, so ivermectin and other substrates reach the brain. Signs are ataxia, mydriasis, blindness, tremors, coma, and death. At-risk breeds include Collies, Australian Shepherds, Shetland Sheepdogs, Old English Sheepdogs, Long-haired Whippets, and herding-breed crosses. Monthly heartworm-preventive doses are safe; high doses (mange treatment, livestock products) are not. Loperamide, acepromazine, butorphanol, and some chemotherapy drugs (vincristine, doxorubicin) also cause exaggerated effects in affected dogs.

Heartworm prevention with a macrocyclic lactone kills the L3 and L4 larvae transmitted in the previous month, so it must be given every month, year-round. Giving a preventive to a heavily microfilaremic dog can cause a shock-like reaction, which is why an antigen and microfilaria test comes first.

Drug/Class	Mechanism	Cautions
Fipronil	Blocks GABA -gated chloride channels in	Toxictorabbits
	insectsandarachnids
Imidacloprid nitenpyram ,	Nicotinicacetylcholinereceptoragonistsin	Widesafetymargin;nitenpyramkillsadultfleaswithin
(neonicotinoids)	insects	hours
Isoxazolines:fluralaner ,	Block GABA and glutamate-gated chloride -	Oralortopical;maycausetremors ataxia orseizures; , ,
afoxolaner sarolaner , ,	channels	cautionindogswithseizurehistory
lotilaner
Permethrin(pyrethroid)	Prolongssodiumchannelopeningininsect	Toxictocats(tremors seizures)becauseofdeficient ,
	nerves	glucuronidation;treatwithmethocarbamol bathingin ,
		dishdetergent supportivecare ,
Amitraz	Formamidine; alpha-2 agonist	Demodicosisdipsandcollars;causessedation ,
		bradycardia hyperglycemia(reversewith ,
		atipamezole);toxictohorses;notforcats
Organophosphates ,	Inhibitacetylcholinesterase	SLUDGEsigns(salivation lacrimation urination , , ,
carbamates Lufenuron;methoprene , pyriproxyfen	Insectgrowthregulators(chitininhibitor; juvenilehormoneanalogs)	defecation GI upset emesis); antidote is atropin1e , , Preventeggandlarvaldevelopment;noadulticide effect