Work out exactly how much medicine to give a pet roof rat, in the drinking water, mixed into food, or by oral syringe. Choose a medicine and a route, enter your medicine’s strength, and the calculator does the math. The usual method is to make a premixed bottle of dissolved medicine, then dose by volume. This is general guidance, not veterinary advice; always confirm the drug, dose, and route with an exotics vet.
Medicines and supplements it covers
General starting-point doses for healthy adult roof rats (milligrams per kilogram of body weight per day, unless noted), cross-checked against Rat Guide, which has a medication page for most of them, and against the published rat literature where it does not. Linco-Spect, fluconazole and NAC have neither, and the calculator says so when you pick one; the yucca figure is our own. Confirm with your vet before use.
- Ambroxol: 10 mg/kg/day (a mucolytic that thins mucus; a helper, not a substitute for antibiotics)
- Amoxicillin / Clavamox: 20–50 mg/kg/day. Beta-lactams do not work against mycoplasma, the usual cause of rat respiratory disease, so this is not the drug for sneezing
- Azithromycin: 30 mg/kg/day (mycoplasma; best in drinking water)
- Cabergoline: tumor prevention 0.6 mg/kg once every 3 days; active pituitary tumor 10–50 mcg/kg every 12–24 h (a special schedule, not a daily dose; see the health hub). Both figures are the Rat Guide’s, and the 0.6 mg/kg every 72 hours schedule is the one that shrank a pituitary adenoma in a published pet-rat case
- Carprofen: 2–5 mg/kg/day (NSAID pain relief)
- Doxycycline: 10–20 mg/kg/day (10 mild, 20 moderate to advanced; best in drinking water). Our own sneezing FAQ puts the same caution on it as on Baytril: adult rats only unless your vet says otherwise, and avoid it in a nursing or pregnant doe. Dairy is fine, and this page used to say the opposite: the Rat Guide says doxycycline may be given with food or dairy, hindered by about 20 percent and not deemed clinically significant, so hiding it in yoghurt costs you very little. What does impair the tetracyclines is an antacid or a multivitamin containing aluminium, calcium, zinc, magnesium or iron, and doxycycline has the least affinity for calcium of the class
- Enrofloxacin (Baytril): 10–30 mg/kg/day (10 to 20 general, 30 aggressive respiratory; oral-syringe bolus). Not the first choice for a pregnant or nursing doe, or a rat under about 4 months old: fluoroquinolones carry a cartilage risk in young rats, and the Rat Guide recommends azithromycin or tylosin instead
- Ivermectin / Selamectin / Fenbendazole: antiparasitics (ivermectin 0.2–0.4 mg/kg repeated weekly, and fenbendazole 20 mg/kg/day for worms, are in the calculator; selamectin is a topical spot-on at 6–15 mg/kg)
- Meloxicam: 1–2 mg/kg/day (NSAID pain relief; oral syringe; avoid with kidney failure)
- Metronidazole: about 20–30 mg/kg/day
- SMX-TMP (Septra / Bactrim): 40–50 mg/kg/day. The Rat Guide gives 15 to 30 mg/kg every 12 to 24 hours for the trimethoprim plus sulfa total, which brackets this figure; confirm it with your vet
- Tylosin: 500 mg/L of drinking water, mixed fresh every three days (about 50 mg/kg/day at the drinking-water intake below), or 10 mg/kg by mouth once or twice a day. Both figures are the Rat Guide’s, which also lists tylosin as safe for pregnant does and rats under 4 months. Mixing it fresh matters: when that recipe was measured, the concentration in the bottle reached 70 to 79 mg/L and fell quickly. The same study found no tylosin at all in the blood while lung tissue held more than ten times the level needed against mycoplasma, so this route treats a chest infection and not a body-wide one. This page used to give 10 mg/kg/day in water, our own reading of that study; the documented dose is the one to use
- Plus Linco-Spect, Fluconazole, NAC, and yucca. None of these four has a Rat Guide page, so there is no rat dose authority behind their figures and the calculator says so when you pick one. The yucca water figure is our own, about 100 mg of extract per litre of drinking water, from our yucca lesson; its food figure, 200 mg of extract per kg of feed, is the rate fed to rats in a published feeding study, and the two agree once you allow for how much a rat eats and drinks
- Daily supportive supplements (in drinking water): EGT (ergothioneine) ⅛ tsp, taurine ½ tsp, betaine ⅛ tsp per US gallon. Measured by the spoon, which is what we actually do; that works out to roughly 105 mg/L, 460–590 mg/L and 80–115 mg/L, approximate because powders vary in how densely they pack
- By-weight supportive supplements (mixed into food): acetyl-L-carnitine ~150 mg/kg/day, R-alpha-lipoic acid ~38 mg/kg/day, methylcobalamin (B12) ~0.5 mg/kg/day, studied doses from research, not proven prescriptions (see the evidence)
Frequently asked questions
How do I put medicine in a pet rat’s drinking water?
Make a premixed solution: dissolve the tablet, or measure the liquid medicine, into a little water, then add the calculated volume to a known amount of drinking water and mix it fresh daily. Dosing by volume from a premix is the easiest way to measure the tiny amounts a rat needs.
How much doxycycline does a pet rat need?
A common starting point is 5–10 mg/kg every 12 hours (about 10–20 mg/kg/day). This calculator uses 20 mg/kg/day for steady drinking-water dosing. Always confirm the dose with an exotics vet.
What is the ambroxol dose for a rat?
About 10 mg/kg/day, split into two doses; this tool uses 10 mg/kg/day. That is not scaled from a human dose: it is the lowest of the three oral doses, 10, 50 and 100 mg/kg, given daily to rats for 21 days in the published rat study. Ambroxol is a mucolytic that thins mucus, a helper paired with antibiotics for respiratory disease, not a substitute for them. More on ambroxol for rats →
How much water does a rat drink, and why does the calculator need to know?
About 10 ml per 100 g of body weight per day, which is 100 ml per kg. For a 250 g rat that is roughly 25 ml a day. The calculator needs it because the drinking-water route has no other way to know how much medicine a rat actually swallows. It works backwards from the dose you want to the strength the water has to be, and every step of that runs through the intake figure. A National Research Council report assumes 30 ml a day for a 300 g rat, the same 100 ml per kg.
Until 17 August 2026 this page assumed 150 ml/kg/day, from the rat and mouse consumption table that has always been linked here. That table is built for environmental risk assessment, where the figure is set high on purpose so that a contaminant dissolved in drinking water is never under-estimated. Running it backwards to deliver a medicine turns that caution upside down: assuming a rat drinks a lot means mixing the medicine thin, so a rat drinking a normal amount was getting about two thirds of the intended dose. Correcting it raised every drinking-water amount this page gives by half. Two practical consequences: medicated water is now stronger-tasting than it was, and if a rat starts refusing her bottle, dilute it and tell your vet rather than pushing on; and a sick rat who is barely drinking still will not reach the target dose at any concentration, which is why the oral syringe stays the reliable route when the exact dose matters.
Is this veterinary advice?
No. These are general starting points for healthy adult roof rats. A sick rat needs an exotics vet to confirm the drug, dose, route, and duration, and you should weigh your rat.