Glycine1.5%

Glycine 1.5% w/v solution is a non-electrolyte, isosmotic irrigating fluid used to distend and irrigate the surgical field during certain electrosurgical endoscopic procedures. Its main established (labeled) use is as a genitourinary irrigant, since it does not conduct electricity and therefore does not disperse energy during monopolar electrocautery.

Established uses

• Bladder/urethral irrigation during transurethral resection of the prostate (TURP) and transurethral resection of bladder tumors (TURBT).
• Uterine cavity distension/irrigation during operative hysteroscopy (e.g., resection of fibroids, polyps, or endometrial ablation) using monopolar electrosurgical instruments.

Other use (nutritional/off-label)

Glycine is also used orally in some settings as a nutritional/dietary amino acid supplement; preliminary evidence has explored its use for sleep quality and as an adjunct in certain metabolic and psychiatric contexts, but such uses are not formally approved indications and evidence remains limited.

Each 100 mL of Glycine irrigation solution contains 1.5 g of glycine (1.5% w/v) in water for irrigation, of pharmacopoeial-grade quality, sterile and non-pyrogenic. The solution is a non-electrolyte and is hypotonic relative to plasma (osmolarity approximately 200 mOsm/L), formulated specifically for use with electrosurgical (monopolar) endoscopic equipment.

Glycine is the simplest amino acid and also functions as an inhibitory neurotransmitter in the central nervous system. In its medical/pharmaceutical form, Glycine is formulated as a sterile 1.5% irrigating solution used during certain urologic and gynecologic endoscopic surgeries. Because it is a non-electrolyte fluid, it does not conduct electrical current, which makes it suitable for irrigation during procedures that use monopolar electrocautery, unlike saline-based fluids. Glycine is also naturally present in the body and is used in other formulations as a nutritional amino acid supplement.

Glycine belongs to the therapeutic class of genitourinary/surgical irrigating solutions (non-electrolyte irrigants). In its supplement form, it is classified as an amino acid nutritional product.

Glycine solution acts locally as a distension and irrigation medium; because it lacks electrolytes, it does not disperse the electrical current used in monopolar resectoscopes, allowing a clear surgical field and effective cutting/coagulation.

Systemically, absorbed Glycine is metabolized primarily in the liver, partly via the glycine cleavage system, generating serine, ammonia, and other metabolites. Glycine is also an inhibitory neurotransmitter acting on glycine receptors in the spinal cord and brainstem, and functions as a co-agonist at NMDA receptors. Significant systemic absorption of the irrigation fluid during prolonged procedures can cause dilutional hyponatremia, hyperammonemia, and transient visual disturbances (collectively part of "TURP syndrome").

Glycine irrigation solution is for external irrigation/instillation into the bladder or uterine cavity by trained medical personnel using appropriate endoscopic equipment during the surgical procedure only. It is not for intravenous injection or systemic administration. The solution should be inspected for particulate matter and discoloration before use, and only clear solution in an intact container should be used. Oral Glycine supplement forms (powder/tablet) are taken by mouth, typically dissolved in water, as directed by a physician or dietitian.

Formal drug-interaction studies with Glycine irrigation solution are limited because it is used topically/locally during surgery. However:

• Concurrent use of diuretics, desmopressin, or other drugs that predispose to hyponatremia may increase the risk of clinically significant hyponatremia if substantial systemic absorption of Glycine solution occurs during a prolonged procedure.
• General anesthetic and sedative agents may have additive central nervous system depressant effects if large volumes of Glycine are systemically absorbed.
• Patients on medications that affect ammonia metabolism (e.g., valproate) may be at increased risk of hyperammonemia if significant Glycine absorption occurs.

When used appropriately as a surgical irrigant, local side effects are uncommon. The main safety concern is systemic absorption of Glycine solution during prolonged or extensive procedures, which can cause a constellation of effects sometimes called "TURP syndrome," including:

• Dilutional hyponatremia (nausea, vomiting, confusion, headache, and seizures in severe cases)
• Transient visual disturbances, including temporary blindness ("Glycine toxicity")
• Hyperammonemia (drowsiness, confusion)
• Bradycardia, hypertension or hypotension, and fluid overload/pulmonary edema in severe cases

Oral Glycine supplementation is generally well tolerated; mild gastrointestinal upset, nausea, or drowsiness have been reported infrequently at higher doses.

There are no well-controlled studies establishing the safety of Glycine irrigation solution or oral supplementation during pregnancy and lactation. Glycine should be used during pregnancy only if clearly needed and if the potential benefit justifies the potential risk to the fetus; use during operative hysteroscopy in a pregnant patient would require careful specialist judgment. Breastfeeding women should consult a physician before using oral Glycine supplements, as data on excretion into breast milk are limited.

Procedures using Glycine irrigation should be performed by experienced surgical teams with continuous monitoring of fluid input/output (fluid deficit) to detect excessive systemic absorption early. Procedure duration should be minimized where clinically feasible. Patients with hepatic impairment may be at increased risk of hyperammonemia-related toxicity, since Glycine metabolism can generate ammonia; extra caution and closer monitoring are advised in such patients. Patients with cardiac or renal impairment are at increased risk of fluid overload from absorbed irrigation fluid and should be monitored closely. If signs of TURP syndrome (confusion, visual changes, bradycardia, hypotension) develop, the procedure should be expedited to completion and appropriate supportive treatment instituted promptly.

Overdose in the conventional sense does not apply to a surgical irrigant, but excessive systemic absorption of Glycine solution during a procedure can produce a toxic syndrome (hyponatremia, hyperammonemia, visual disturbances, cardiovascular instability). If this is suspected, seek immediate medical attention; treatment is supportive and may include careful fluid and electrolyte correction, oxygen, and cardiovascular support in a monitored setting. For oral supplement overdose, contact a physician, hospital, or poison control center immediately rather than attempting home treatment.

Store at room temperature (below 30°C), protected from light, freezing, and excessive heat. Keep out of reach of children. Use only clear, particulate-free solution from an intact, undamaged container; discard any unused portion after opening.

Renal impairment: increased risk of fluid overload from absorbed irrigation fluid; use with caution and close monitoring.

Hepatic impairment: increased risk of hyperammonemia-related toxicity from absorbed Glycine; use with caution.

Elderly: may be more susceptible to fluid overload and cardiovascular effects of systemic absorption; monitor closely during and after the procedure.

Pediatric patients: safety and efficacy of Glycine irrigation have not been well established in children; use only when a pediatric urologic or gynecologic specialist determines it is necessary, with careful fluid monitoring.

Glycine irrigation solution is used only for the duration of the surgical procedure in which it is required, and procedure time is deliberately minimized where possible to reduce absorption risk. Oral Glycine supplementation duration should be determined by the prescribing physician or dietitian based on the reason for use; there is no universally established treatment duration for non-approved supplemental use.

Amino acids; genitourinary/surgical irrigating solutions (non-electrolyte irrigants); nutritional/dietary supplements.

Glycine solution is electrically non-conductive (a non-electrolyte), which allows it to be used as a distension/irrigation medium during monopolar electrosurgery without dispersing the cutting/coagulation current, unlike electrolyte-containing fluids such as normal saline. Physiologically, Glycine acts as an inhibitory neurotransmitter at glycine receptors in the spinal cord and brainstem and as an obligatory co-agonist (with glutamate) at the NMDA receptor in the central nervous system.

Safety and efficacy of Glycine irrigation solution have not been formally established in pediatric patients. It may be used off-label during pediatric urologic or gynecologic endoscopic procedures at the discretion of a specialist, with careful attention to total volume used and fluid balance monitoring, given children's smaller circulating volume and greater susceptibility to fluid/electrolyte disturbances. Oral Glycine supplements are not recommended for children without specific medical guidance.