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Polyacrylamide Hydrogel (PAAG or PAHG) Use in Horses With Osteoarthritis
Polyacrylamide Hydrogel (PAAG or PAHG), Arthramid® Vet and Noltrex®Vet, Use in Horses With Osteoarthritis
Introduction
Before we start let's be clear, these products are not currently approved by the Food and Drug Administration but available to veterinarians from foreign manufacturers and then imported and sold through US veterinary distributors. Two products are manufactured for veterinary use and seen in research articles, Arthramid® Vet and Noltrex®Vet. These products have been in use since around 2010.
Polyacrylamide hydrogel is used in the treatment of mild to moderate osteoarthritis in both humans and horses. Similar to hyaluronate, polyacrylamide hydrogel (PAAG or PAHG) is injected directly into the joint and is proposed to provide lubrication and cushioning to the joint to help restore a more normal joint environment. A significant difference is PAAG does not degrade as quickly over time. In this way they may provide significant long term therapy and support for compromised joints. On the other hand one proposed mechanism of HA is that it's degradation helps lower, use up, the inflammatory chemicals causing the arthritis. This article looks at the state of human and equine research including, clinical results, proposed mechanisms of action, precautions, and proposed dosages. Looking at the information currently available these products look promising, even exciting.
Support for it's Use
When I first came across a study comparing PAAG with HA I was surprised at the results that PAAG was shown to have significant clinical benefits as opposed to the much more iffy improvements with HA. I was not surprised at the HA results as I have been reading such report for 40 years. Yes positive significant lab and statistical benefits can be found with intra-articular HA but it it is hard to document a significant clinical improvement despite many anecdotal reports of such. But intra-articular PAAG showed significant clinical improvement that lasted over time in mild to moderate osteoarthritis. So going to find other reports on the use of PAAG I was again surprised to find a handful of research papers that supported the conclusions that PAAG will take horses lame from osteoarthritis and make them noticeable less lame and even sound for up to two years. Here are summaries of two such papers:
The above studies were done with the Arthramid® Vet product however there have been similar studies with similar results using Noltrex®Vet:
Acta Vet Scand. 2015 Apr 15;57(1):20.
An international multi-centre prospective study on the efficacy of an intra-articular polyacrylamide hydrogel in horses with osteoarthritis: a 24 months follow-up.
Aziz Tnibar 1, Hans Schougaard 2, Linus Camitz 3, Jonas Rasmussen 4, Marc Koene 5, Werner Jahn 6, Bo Markussen 7Background: Polyacrylamide hydrogel (PAAG) was evaluated recently to treat osteoarthritis (OA) in horses with highly encouraging results; however no long term field-study was done to explore its clinical efficacy and lasting effect. The objective of this study was to evaluate the efficacy of PAAG in improving clinical signs of OA in horses. We hypothesized that lameness grade would significantly improve and the effect would last at least 2 years in osteoarthritic joints treated with PAAG. Forty three horses older than 2 years with OA in only one joint based on clinical evaluation, intra-articular anaesthesia and imaging (radiography) were included in this study. Horses were injected with 2 ml of PAAG into the affected joint and were followed up at 1, 3, 6, 12 and 24 months. Efficacy of PAAG was evaluated by blinded clinical assessment of lameness. Adverse reactions to joint injection were assessed. Data relating to case details, type of activity, joint and limb involved, lameness duration, lameness grading, previous joint treatment, joint effusion grading, radiographic grading, and owner assessment were recorded. Factors associated with the outcome measure "lameness grading" were analyzed using generalized linear mixed model for logistic regression.
Results: At 1, 3, 6, 12 and 24 months follow-up, 59%, 69%, 79%, 81/% and 82.5% of horses were non-lame respectively. Reduction of joint effusion was observed over time. No side effect was observed in the treated joints. There was a significant decrease in lameness grade from baseline to 1, 3, 6, 12 and 24 months (P less than 0.0001) and a significant positive association with joint effusion (P less than 0.0001). Estimates for odds ratio (OR) showed that the effect of treatment increased over time (OR for lower lameness from month 1 to month 24 relative to baseline increased from 20 to 58).
Conclusions: PAAG significantly alleviated lameness and joint effusion in osteoarthritic joints. PAAG is a safe and lasting (at least 24 months) OA treatment in horses. PAAG is a promising new treatment for OA in horses.
An assessment of the effectiveness of hyaluronic acid and polyacrylamide hydrogel in horses with osteoarthritis: Systematic review and network meta-analysis
Res Vet Sci. 2020 Nov 20;134:42-50.
Authors
Amanda Azambuja da Silva Xavier 1 , Patrícia Pinto da Rosa 2 , Laurett de Brum Mackmill 2 , Victor Fernando Buttow Roll 3
Abstract
For several years, hyaluronic acid (HyA) and, more recently, polyacrylamide hydrogel (PHyd) have been used to reduce lameness and pain caused by osteoarthritis. However, there is still a lack of scientific evidence of the efficacy of these substances to allow veterinary experts to make decisions about their use in horses. The objective of this study was to evaluate, through a systematic review and network meta-analysis (NMA), the efficacy of HyA, associated or not with other drugs, and PHyd in relieving lameness in horses with osteoarthritis. The searches for primary studies were conducted on four search platforms. The efficacy of HyA and PHyd was estimated through the relative risk difference method. Heterogeneity was observed in the efficacy of HyA, indicating long-term ineffectiveness of this drug when associated or not with anti-inflammatory drugs. In contrast, the results indicate that PHyd is an effective alternative therapy, with a long period of action in reducing lameness in horses with osteoarthritis. This study provides evidence that the application of PHyd and HyA is effective in reducing lameness caused by osteoarthritis in horses at different time periods, where PHyd has a longer time of action.
- “A Preliminary Field Trial Evaluating the Efficacy of 4% Polyacrylamide Hydrogel in Horses With Osteoarthritis.” Principal Investigator: Dr. Scott McClure, DVM, PhD, Dipl. ACVS
- Clinical and Histologic Evaluation of Polyacrylamide Gel in Normal Equine Metacarpal /Metatarsal-Phalangeal Joints.” Principal Investigator: Dr. Scott McClure, DVM, PhD, Dipl. ACVS.
There are several more human prospective studies all which support the positive results seen above. noticeably there are very few adverse events associated with PAAG use. Occasionally I could find a report of mild heat, tenderness, and/or swelling but these all were treated successfully with a short course of NSAID's. There is one case of an exception in a person that is reported below.
There is one more important piece of information. In a study of goats using and induced arthritis model, PAAG was shown to marker reduce the amount of osteoarthritis and synovitis in the PAAG treated joints versus the untreated joints. Most of the treated joints did not show signs of lameness. While the study was small (6) the standardization of the joint disease and complete pathological examination of all the joints is unique and very strong evidence for the efficacy of this treatment.
Tnibar A, Persson A, Jensen HE, Svalastoga E, Westrup U, McEvoy F, et al. Evaluation of a polyacrylamide hydrogel in the treatment of induced osteoarthritis in a goat model: A pilot randomized controlled Study [abstract] Osteoarthritis and Cartilage. 2014;22:s477
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