The attrition rate for analgesic compounds remains stubbornly high. By some estimates, fewer than 2% of preclinical pain candidates reach approval, a failure rate that outpaces most other therapeutic areas. While the reasons are multifactorial, one persistent contributor is the translational gap between standard rodent models and human pain pathophysiology.
A growing body of evidence suggests that porcine models may close this gap in ways that matter for clinical decision-making.
Rodent pain models like CCI, SNL, SNI, and Brennan plantar incision have been workhorses of analgesic drug development for decades. They are well-characterized, reproducible, and cost-effective. They have also failed, repeatedly, to predict clinical outcomes.
The reasons are both anatomical and behavioral. Rodents have fundamentally different skin architecture, peripheral nerve density, and pain expression compared to humans. They do not exhibit the spontaneous, observable pain behaviors that characterize human pain states. And the primary endpoint in most rodent pain studies, evoked withdrawal reflexes, captures only one dimension of a multidimensional clinical experience.
This is not a new observation. But the implications are still underappreciated in preclinical program design.
Pig skin is structurally and functionally identical to human skin across five key parameters: thickness, hair follicle content, pigmentation, collagen composition, and lipid content. A 2021 systematic review of porcine pain models (Meijs et al., Lab Animal) confirmed near-complete overlap between pig and human peripheral neurophysiology.
More importantly, pigs express spontaneous pain behaviors such as guarding, weight shifting, altered gait, reduced social interaction, and avoidance. These parallel clinical presentations in ways rodent reflexive endpoints simply cannot. These behaviors can be quantified using validated tools like the distress behavior score (DBS), human approach test (HAT), and computerized open field analysis.
This combination of human-like peripheral neurobiology and clinically relevant behavioral readouts is what makes the translational argument for porcine models so compelling.
The strongest evidence for any preclinical model is retrospective clinical validation, meaning instances where the model's predictions were confirmed in human trials.
Consider the ZYNRELEF story. HTX-011, a bupivacaine-meloxicam extended-release formulation developed by Heron Therapeutics, was tested in a pig postoperative pain (POP) flank model. The pig data revealed a specific pH-dependent mechanism: surgical inflammation lowers tissue pH, reducing unionized bupivacaine to just 0.6%. Meloxicam restores pH, increasing the unionized fraction to 7.5% and enabling 72-hour analgesia. This mechanism, characterized preclinically in the pig model, was subsequently confirmed in a 237-subject Phase II human bunionectomy trial (Ottoboni et al., 2019, Reg Anesth Pain Med). ZYNRELEF went on to receive FDA approval.
Equally telling is the negative control. Aprepitant, an NK1 receptor antagonist, showed no analgesic effect in a pig peripheral neuropathic pain (PNT) model. The same compound failed in human clinical trials for neuropathic pain.
Castel et al., 2016, The Journal of Pain, 17(1): 36-49
A model that predicts clinical failure, not just success, is a model you can trust for decision-making.
Drug ranking data adds further weight. In a head-to-head comparison of local anesthetics in pig POP (Castel et al., 2017, J Pain Res), Exparel outperformed Marcaine, which outperformed Naropin. That AUC ranking mirrors human postoperative analgesic data exactly.
The translational fidelity extends to tissue pathology. Skin biopsies from pigs with peripheral neuritis show reduced intraepidermal nerve fiber (IENF) density, elevated CGRP and NaV1.7 in keratinocytes, and altered endothelin receptor expression (ETA↑, ETB↓). This pattern mirrors human neuropathic pain biopsies precisely (Rice et al., 2019, Neurobiology of Pain).
This is not a superficial resemblance. It is a histopathological match at the molecular level.
Rodent models remain valuable for mechanism-of-action studies, target engagement, and early screening. However, pain programs targeting postoperative, neuropathic, or chronic pain benefit from incorporating a translational species that captures the endpoints regulators and clinicians care about.
The question isn't whether to use pig models. It's whether your program can afford not to.
MD Biosciences operates translational pig pain models — including PNT, POP, and neuroma models — with integrated behavioral, electrophysiological, and histological endpoints. To discuss study design for your pain program, reach out at neuro@mdbiosciences.com.