Tiopronin
N-(2-Mercaptopropionyl)-glycine (MPG)
Also known as: Thiola · Acadione · Captimer · Epatiol · Mucolysin · Mucosyt · Sutilan · Thiosol · Tioglis · SF 522 · N-(2-Mercaptopropionyl)-glycine · 2-MPG · thiopronine
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Prophylactic treatment of cystine urinary calculi | 30 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Dissolution of uroliths | Approximately 40 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| In conjunction with an alkalinizing, protein and sodium restricted diet (e.g., u/d) | 30-40 mg/kg PO divided into two daily doses | PO | divided into two daily doses | — | 🌎 NA |
| Treatment of cystine urinary calculi | 20 mg/kg PO twice daily | PO | twice daily | 1-3 months | 🌎 NA |
| Prevention of cystine urinary calculi | 15 mg/kg PO twice daily | PO | twice daily | — | 🌎 NA |
- Prophylactic treatment of cystine urinary calculi: Increase water intake and urine diuresis. Alkalinize urine (pH 6.5-7.0) using potassium citrate. In cases with low cystine excretion and low urolith recurrence rate, tiopronin dose may be individually decreased (<30 mg/kg) or stopped.
- Dissolution of uroliths: Reevaluation of uroliths with ultrasound or radiography every 4th week. After urolith dissolution, give prophylactic dose. If urolith dissolution is not achieved after 2-3 months, surgery is recommended.
- Treatment of cystine urinary calculi: Relatively high incidence of adverse effects
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Tiopronin is a specialized antiurolithic agent primarily used in veterinary medicine to manage and prevent cystine urolithiasis (bladder stones) in dogs. Cystinuria is an inherited metabolic defect in the renal tubular reabsorption of certain amino acids, notably cystine, which is highly insoluble in acidic urine and prone to forming calculi.
Tiopronin is typically employed when dietary modifications (ultra-low protein, alkalinizing diets) and urinary alkalinization fail to dissolve or prevent the recurrence of these stones.
- Key Features:
- Acts as a chelating agent to increase cystine solubility in the urine.
- Often preferred over penicillamine due to a potentially lower incidence of adverse effects, though it remains relatively expensive.
- Requires lifelong therapy and strict owner compliance for prophylactic success.
Mechanism of action
Tiopronin is an active sulfhydryl (-SH) compound. In the urine, it undergoes a thiol-disulfide exchange with cystine (which is a cysteine-cysteine disulfide).
- Mechanism Pathway: Tiopronin + Cystine → Tiopronin-Cysteine Disulfide Complex + Cysteine.
- This newly formed complex is up to 50 times more water-soluble than cystine alone.
- By increasing the solubility of cystine in the urine, tiopronin prevents the precipitation of cystine crystals and facilitates the gradual dissolution of existing cystine calculi.
Safety & warnings
Contraindications
- Agranulocytosis
- Aplastic anemia
- Thrombocytopenia or other significant hematologic abnormality
- Impaired renal or hepatic function
- Sensitivity to either tiopronin or penicillamine
Adverse effects
- Coombs'-positive regenerative spherocyte anemia
- Aggressiveness
- Proteinuria
- Thrombocytopenia
- Elevations in liver enzymes and bile acids
- Dermatologic effects (small pustules, dry crusty nose, ecchymosis, itching, rashes, mouth ulcers, jaundice)
- Myopathy (staggering, difficulty chewing)
- Lethargy
- Sulfur odor of the urine
- GI distress
- Allergic reactions (adenopathy)
- Arthralgias
- Dyspnea
- Fever
- Edema
- Nephrotic syndrome
Precautions
Hematologic Toxicity: Can cause severe blood dyscrasias. Use with extreme caution in patients with pre-existing hematologic abnormalities.
Immune-Mediated Reactions: Associated with Coombs'-positive regenerative spherocyte anemia in dogs. If this occurs, discontinue immediately and initiate appropriate treatment (corticosteroids, blood component therapy).
Organ Impairment: Use cautiously in patients with impaired renal or hepatic function.
Pregnancy/Nursing: FDA Category C. Teratogenic effects (skeletal defects, cleft palates) and decreased fetus viability have been noted with related drugs (penicillamine) or at high doses. Not recommended for use in nursing animals as it may be excreted in milk.
Drug interactions
Potentially additive toxic effects
Potentially additive toxic effects
Potentially additive toxic effects
Monitoring
- Physical examination (1, 3, 6, & 12 months after start, then twice a year)
- Ultrasonography/radiography of the urinary tract
- Urinalyses (specific gravity, protein, pH, sediment, and cyanide nitroprusside reaction) using AM samples
- CBC (with platelets)
- Liver enzymes (alkaline phosphatase, ALT)
- Quantitative measurements of urinary cystine excretion related to urinary creatinine excretion (AM samples, before start and once a year during treatment)
Pharmacokinetics
Absorption
Rapid onset of action.
Elimination
Primarily via renal routes. In humans, up to 48% of a dose is found in the urine within 4 hours of dosing. Relatively short duration of action (effect in humans disappears in about 10 hours).
Overdose
There is little information available regarding acute toxicity or overdosage of tiopronin in veterinary species. It is suggested to contact an animal poison control center for further information and guidance in the event of an overdose situation. Treatment would likely be supportive and symptomatic.
Available products
Formulations
- Tablets
Human-labeled
- Tiopronin Tablets: 100 mg (Thiola)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets at room temperature in tight containers.
Client information
Important Note: Tiopronin is a specialized medication used to dissolve and prevent cystine bladder stones. It works best when combined with a specific prescription diet and plenty of fresh water.
- Consistency is Key: Give this medication exactly as prescribed. Skipping doses can allow stones to reform quickly.
- Diet and Water: Encourage your dog to drink as much water as possible to help flush the bladder. Stick strictly to the diet recommended by your veterinarian.
- Watch for Side Effects: Contact your vet immediately if you notice extreme tiredness, pale gums, unusual bruising or bleeding, skin rashes, crusting on the nose, changes in behavior (like sudden aggression), or difficulty chewing.
- Urine Odor: You may notice a slight sulfur ("rotten egg") smell to your dog's urine; this is a normal and expected effect of the medication.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.