Rat Dose Planner

Common Laboratory Rat Strains

The choice of rat strain has major implications for dosing math, drug metabolism, and study interpretation. The most commonly used strains in US biomedical research:

Outbred white rat. Adult males ~300–500 g, females ~225–325 g. The default rat strain at most US academic vivariums and the most common rat in pharmacology, toxicology, and behavior studies. Heterogeneous response is a feature for some studies and a confound for others.

Outbred white rat, slightly smaller and more docile than SD. Adult ~250–350 g. The most widely used rat strain in Europe and Asia. Often interchangeable with SD for routine pharmacology.

Outbred hooded rat (white body, dark head). Adult ~300–400 g. The most common rat strain in behavioral neuroscience because the pigmented eyes give better visual acuity than albino strains.

Inbred. Adult ~225–325 g. Widely used in autoimmunity, transplantation, and stress research. More sensitive to pain stimuli than SD and Wistar.

Inbred. Adult ~225–325 g. The historical NIA aging colony strain. Used heavily in carcinogenicity studies and longevity research.

Inbred. Adult ~250–350 g. Used in respiratory allergy models and as the genetic background for several disease models.

Diehl et al. (2001) Rat Route Limits

The Diehl guide is the most cited source for rodent injection volumes in IACUC and AAALAC documentation. Rat-specific limits:

• PO (oral gavage): 10
• IP (intraperitoneal): 10
• SC (subcutaneous, single site): 5
• IV bolus (lateral tail vein): 5
• IM (intramuscular, single site): 0.1 — very small per site

The rat IP limit is half the mouse IP limit (10 vs 20 mL/kg). The rat SC limit is half the mouse SC limit (5 vs 10 mL/kg). The rat IM limit is 2× the mouse IM limit (0.1 vs 0.05 mL) — but rats also have larger muscle masses, so the absolute volume that fits is much larger.

When porting a mouse protocol to a rat study, do NOT just scale the dose by mg/kg — re-check the volume against the rat-specific limit, because the rat ceiling is more restrictive on most routes.