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Pet Rat Drug Dosing: A Vet Reference

PublishedJuly 31, 2026Reading time6 minExoticRx Editorial

Editorially reviewed against published veterinary references. Awaiting credentialed clinical reviewer — our editorial process.

Most pet rats die of respiratory disease, and most respiratory disease in pet rats is Mycoplasma pulmonis. That's the one-line rat-medicine summary; everything else about drug selection in this species follows from it. Pet rats live 2–3 years, the lung disease usually starts at 6 months, and by 18 months you're managing acute exacerbations of a chronic background infection rather than curing anything. The right drug choice is the one that the patient tolerates long-term — not the one with the cleanest single-course MIC.

This article is the practical reference: what to reach for, what to avoid, and the dose ranges modern small-mammal exotics specialists actually use.

ExoticRx maintains an actively curated pet rat formulary. Browse the rat formulary for live, source-cited data; this article is the editorial overview.

The Mycoplasma context

M. pulmonis is endemic in nearly all colony rats and most pet rats. It causes chronic respiratory disease (CRD), often with secondary Streptococcus pneumoniae / Pasteurella pneumotropica / Bordetella bronchiseptica / CAR bacillus (cilia-associated respiratory bacillus) co-infections. Antibiotic choice in a coughing rat is essentially a Mycoplasma + secondary-pathogen co-cover decision.

The drugs that work against Mycoplasma are limited (it has no cell wall, so β-lactams don't touch it):

And the drugs that DON'T work against Mycoplasma but are sometimes given anyway:

Antibiotics

Enrofloxacin: 5–10 mg/kg PO, SC, or in drinking water q12h. The first-line drug for acute respiratory exacerbation. Add doxycycline for synergy in moderate-severe cases (the combination protocol is often called "Baytril–Doxy" by rat fanciers and has solid clinical-experience data). Keep on for 14–21 days minimum.

Doxycycline: 5 mg/kg PO q12h. Cornerstone of CRD management. Often paired with enrofloxacin for the first 14 days, then doxycycline alone for chronic suppression. Tolerated long-term in this species. The water-bottle delivery (50 mg in 250 mL water, refreshed daily) works for owners who can't reliably PO-dose twice daily — the rat's habitual drinking gets the dose.

Azithromycin: 30 mg/kg PO q24h × 5 days, then twice weekly for chronic. Useful as a third-line addition or rotation when doxycycline + enrofloxacin isn't holding. Long elimination half-life means twice-weekly maintenance dosing is feasible.

Chloramphenicol: 50 mg/kg PO q12h. Reserved for resistant cases or where co-infection with sulfonamide-resistant pathogens is suspected. Wear gloves when compounding (human aplastic anemia warning).

TMS (trimethoprim-sulfa): 30 mg/kg PO q12h. Useful for confirmed Streptococcus pneumoniae or skin infections; not effective against Mycoplasma alone but valuable as part of the secondary-pathogen cover.

Amoxicillin / amoxicillin-clavulanate: tolerated orally in rats (unlike rabbits — they're not hindgut fermenters). Useful for confirmed bite-wound abscess or non-respiratory bacterial disease. Don't reach for this in respiratory disease — no Mycoplasma activity.

Analgesia

Meloxicam: 1–2 mg/kg PO or SC q24h. Higher than the canine dose, similar to rabbit. Rats tolerate this well; the upper end is often needed for post-surgical analgesia or chronic mammary tumor pain. Hydration must be adequate.

Buprenorphine: 0.05–0.1 mg/kg SC q6–12h. Short-acting; the longer-duration depot formulations (Buprenorphine SR) at 0.6–1 mg/kg SC q72h are increasingly used for post-surgical pain and chronic tumor management — fewer handling stresses for the same coverage.

Tramadol: 5–10 mg/kg PO q12h. Adjunct for chronic musculoskeletal or tumor pain. Less reliable monotherapy than buprenorphine.

Local blocks (lidocaine 1–2 mg/kg + bupivacaine 1 mg/kg) for any procedure with a clear nerve target. Greatly reduces the systemic analgesia burden.

Antiparasitics

Ivermectin: 0.4 mg/kg SC, repeated in 14 days. Standard for fur mites (Radfordia ensifera, Ornithonyssus bacoti) and ear mites. Rats tolerate the topical formulation poorly — the oral solution diluted in water for SC injection is the practitioner default.

Selamectin: 6–12 mg/kg topical. Spot-on for external parasites; well-tolerated and avoids the injection.

Fenbendazole: 20 mg/kg PO q24h × 5 days. Routine intestinal nematodes; uncommon as a primary need in pet rats but useful for refractory pruritus when mites have been excluded.

Anaesthesia

Isoflurane: 3–4% mask induction → 1.5–2.5% maintenance via mask. Standard. Mask induction is straightforward. Some practitioners intubate with a 2.0–2.5 mm uncuffed tube; others manage on mask.

Pre-med: midazolam 0.5–1 mg/kg + buprenorphine 0.05 mg/kg SC, 30 minutes before. Reduces handling stress, lowers iso requirements, provides peri-operative analgesia.

Ketamine + xylazine: 60–90 mg/kg ketamine + 5–10 mg/kg xylazine IM. Older protocol, still used in some settings. Reverse with atipamezole or yohimbine at published rat/small-mammal doses (do not scale to 5× the xylazine dose — that ratio applies only to medetomidine); see the formulary. Slower recovery than mask induction.

Recovery: warm, dark, quiet. Rats are easy to recover but easy to dehydrate post-op — give SC fluids (10–25 mL/kg warmed Hartmann's) before discharge.

Mammary tumor management — the other big rat-medicine topic

Roughly 50% of intact female rats develop mammary tumors by 18 months. They're usually fibroadenomas (benign) but recur in 30–50% of patients post-surgical removal. Drug-side considerations:

Cabergoline: 0.6 mg/kg PO q72h. Reduces prolactin-driven tumor growth in confirmed prolactinomas. Off-label in rats but well-tolerated. Useful when surgical removal isn't feasible.

Deslorelin (Suprelorin): 4.7 mg implant SC. Suppresses estrogen and reduces recurrence risk in spayed or intact female rats. Newer but increasingly used.

Surgical removal is the primary treatment; drugs above are adjunct. Pre-op meloxicam + buprenorphine, post-op continued for 5 days.

What kills rats you shouldn't reach for

Quick reference

IndicationDrug / doseRouteCadence
Mycoplasma respiratory (acute)Enrofloxacin 5–10 mg/kg + Doxycycline 5 mg/kgPO or SCBoth q12h
Chronic respiratory suppressionDoxycycline 5 mg/kgPOq12h, long-term
Resistant respiratoryAzithromycin 30 mg/kg × 5d, then twice weeklyPOq24h initially
Strep / secondaryTMS 30 mg/kgPOq12h
Bite wound / abscessAmoxicillin-clavulanate 10–20 mg/kgPOq12h
Pain (NSAID)Meloxicam 1–2 mg/kgPO or SCq24h
Pain (opioid, repeat)Buprenorphine 0.05–0.1 mg/kgSCq6–12h
Pain (opioid, long-acting)Buprenorphine SR 0.6–1 mg/kgSCq72h
MitesIvermectin 0.4 mg/kgSCRepeat at 14 days
Mites (alternate)Selamectin 6–12 mg/kgTopicalOnce
Mammary tumour adjunctCabergoline 0.6 mg/kgPOq72h
Anaesthesia pre-medMidazolam 0.5–1 + buprenorphine 0.05 mg/kgSC30 min before
Anaesthesia maintenanceIsoflurane 1.5–2.5%InhalationalContinuous

For per-drug live data, browse the rat formulary or calculate by weight directly against the source-cited database.

Sources

Pet Rat Drug Dosing: A Vet Reference | ExoticRx