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# Hyaluronic acid
## Overview
Hyaluronic acid (HA) is a naturally occurring glycosaminoglycan found in various tissues, including synovial fluid and cartilage. It acts as a lubricant and shock absorber. When administered exogenously, it aims to supplement the natural viscoelastic properties of synovial fluid.
## Primary Indications
* Osteoarthritis of the knee (viscosupplementation)
* Ophthalmic surgery (e.g., cataract surgery, corneal transplantation) as a viscoelastic agent to maintain space and protect tissues.
## Adult Dosing
### Osteoarthritis of the Knee
Dosing and frequency vary significantly by product and manufacturer. Common regimens include:
* **Single injection:** 60 mg (6 mL) once.
* **Three weekly injections:** 20 mg (2 mL) once weekly for 3 weeks.
* **Five weekly injections:** 20 mg (2 mL) once weekly for 5 weeks.
The maximum number of treatment cycles per year is generally not well-defined and may depend on clinical response and local protocols.
### Ophthalmic Surgery
Dosing is highly dependent on the specific surgical procedure and the HA product used. It is typically administered intraocularly by the surgeon during the procedure.
## Pediatric Dosing
Hyaluronic acid is generally not recommended for pediatric patients for the treatment of osteoarthritis of the knee due to a lack of established efficacy and safety data. Limited use in ophthalmic procedures may occur at the discretion of the ophthalmologist.
## Dose Adjustments
No specific dose adjustments are typically required for hepatic or renal impairment. However, caution is advised in patients with severe hepatic or renal disease, though data are limited.
## Contraindications
* Known hypersensitivity to hyaluronic acid or any component of the formulation.
* Active infection at or near the injection site.
* Skin infections in the region of the proposed injection.
## Adverse Effects
### Osteoarthritis of the Knee
* **Common:** Pain, swelling, stiffness, and effusion at the injection site. Headache, back pain, arthralgia, and dizziness have also been reported.
* **Less Common/Rare:** Allergic reactions, localized edema, pruritus, rash, urticaria. Transient joint inflammation.
### Ophthalmic Surgery
* **Common:** Transient intraocular pressure (IOP) elevation, inflammation, pain.
* **Less Common/Rare:** Corneal edema, iritis, cystoid macular edema, endophthalmitis (rare but serious).
## Key Drug Interactions
No significant drug interactions are expected with systemically administered medications when used for intra-articular injections. Concurrent use of other intra-articular medications should be avoided due to potential for unknown interactions or altered efficacy.
## Monitoring
* **Osteoarthritis of the Knee:** Monitor for joint pain, swelling, and signs of infection at the injection site. Assess for improvement in pain and function.
* **Ophthalmic Surgery:** Post-operative monitoring of intraocular pressure, visual acuity, and signs of inflammation or infection.
## Clinical Pearls
* For knee osteoarthritis, HA is intended to supplement rather than replace the natural synovial fluid.
* Multiple products exist with varying molecular weights and formulations; consult product-specific information.
* Aspiration of excess synovial fluid prior to injection may be beneficial.
* Strict aseptic technique is crucial during administration to prevent infection.
* Patients should be advised to avoid strenuous activity (e.g., jogging, tennis, high-impact sports) for 48 hours after injection.
* For ophthalmic use, the viscoelastic properties protect ocular tissues during surgery.
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***Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for definitive guidance. Patient-specific factors must be considered for all treatment decisions.*
