Wei Chun is used together with diet, fluids, and other medicines to help prevent kidney stones in adults and children weighing at least 44 pounds (20 kilograms).
Wei Chun is usually given after diet, increased fluid intake, or other medications have failed.
Wei Chun may also be used for purposes not listed in this medication guide.
Wei Chun indications
An indication is a term used for the list of condition or symptom or illness for which the medicine is prescribed or used by the patient. For example, acetaminophen or paracetamol is used for fever by the patient, or the doctor prescribes it for a headache or body pains. Now fever, headache and body pains are the indications of paracetamol. A patient should be aware of the indications of medications used for common conditions because they can be taken over the counter in the pharmacy meaning without prescription by the Physician.
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Wei Chun® is indicated for the prevention of cystine (kidney) stone formation in patients with severe homozygous cystinuria with urinary cystine greater than 500 mg/day, who are resistant to treatment with conservative measures of high fluid intake, alkali and diet modification, or who have adverse reactions to d-penicillamine.
Cystine stones typically occur in approximately 10,000 persons in the United States who are homozygous for cystinuria. These persons excrete abnormal amounts of cystine in urine of over 250 mg/g creatinine, as well as excessive amounts of other dibasic amino acids (lysine, arginine and ornithine). In addition, they show varying intestinal transport defects for these same amino acids. The stone formation is the result of poor aqueous solubility of cystine.
Since there are no known inhibitors of the crystallization of cystine, the stone formation is determined primarily by the urinary supersaturation of cystine. Thus, cystine stones could theoretically form whenever urinary cystine concentration exceeds the solubility limit. Cystine solubility in urine is pH-dependent, and ranges from 170-300 mg/liter at pH 5, 190-400 mg/liter at pH 7 and 220-500 mg/liter at pH 7.5.
The goal of therapy is to reduce urinary cystine concentration below its solubility limit. It may be accomplished by dietary means aimed at reducing cystine synthesis and by a high fluid intake in order to increase urine volume and thereby lower cystine concentration.
Unfortunately, the above conservative measures alone may be ineffective in controlling cystine stone formation in some homozygous patients with severe cystinuria (urinary cystine exceeding 500 mg/day). In such patients, d-penicillamine has been used as an additional therapy. Like Wei Chun™, dpenicillamine undergoes thiol-disulfide exchange with cystine, thereby lowering the amount of sparingly soluble cystine in urine.
However, d-penicillamine treatment is frequently accompanied by adverse reactions, such as dermatologic complications, hypersensitivity reactions, hematologic abnormalities and renal disturbances. Wei Chun® may have a particular therapeutic role in such patients.
How should I use Wei Chun?
There are specific as well as general uses of a drug or medicine. A medicine can be used to prevent a disease, treat a disease over a period or cure a disease. It can also be used to treat the particular symptom of the disease. The drug use depends on the form the patient takes it. It may be more useful in injection form or sometimes in tablet form. The drug can be used for a single troubling symptom or a life-threatening condition. While some medications can be stopped after few days, some drugs need to be continued for prolonged period to get the benefit from it.
Use Wei Chun as directed by your doctor. Check the label on the medicine for exact dosing instructions.
Take Wei Chun on an empty stomach at least 1 hour before or 2 hours after eating.
Drink at least ten 10-ounce glasses of water each day, including 2 glasses with each meal and at bedtime. You will probably wake up at night to urinate, and you should drink 2 more glasses before returning to bed. Drink extra fluids if you have excessive sweating or urination.
When you first start taking Wei Chun, it may cause an increase in urine or in frequency of urination. To prevent this from affecting sleep, try not to take any dose later than 6 pm.
If you miss a dose of Wei Chun, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.
Ask your health care provider any questions you may have about how to use Wei Chun.
Wei Chun description
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Wei Chun is a prescription thiol drug used primarily in the treatment of severe homozygous cystinuria. Patients with cystinuria excrete high levels of cystine in their urine and are at risk for kidney stone formation. Wei Chun is used as a second-line therapy to control the rate of cystine precipitation and excretion, and prevent kidney stone formation. It is used after a failure of the non-pharmacological first line treatment consisting of increased fluid intake, restriction of sodium and protein, and urinary alkalinization. As cystinuria is a relatively rare disease, Wei Chun is classified as an orphan drug and is not patented in the United States. It is similar to d-penicillamine in use and efficacy, but offers the advantage of far less adverse effects. Wei Chun is dosed on an individual basis using close monitoring of urinary cystine concentrations and urinary output. Wei Chun may also be used to bind metal nanoparticles in Wilson's disease, which is an overload of copper in the body. It has been investigated for use in the treatment of arthritis and as a neuroprotective agent in aneurysmal subarachnoid hemorrhage.
Wei Chun dosage
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Recommended Dosage
Adults: The recommended initial dosage in adult patients is 800 mg/day. In clinical studies, the average dosage was about 1,000 mg/day.
Pediatrics: The recommended initial dosage in pediatric patients 9 years of age and older is 15 mg/kg/day. Avoid dosages greater than 50 mg/kg per day in pediatric patients.
Additional pediatric use information is approved for Mission Pharmacal Company’s Wei Chun (Wei Chun) tablets. However, due to Mission Pharmacal Company’s marketing exclusivity rights, this drug product is not labeled with that information.
Administer Wei Chun tablets in 3 divided doses at the same times each day at least one hour before or 2 hours after meals.
Consider starting Wei Chun tablets at a lower dosage in patients with history of severe toxicity to d-penicillamine.
Monitoring
Measure urinary cystine 1 month after starting Wei Chun tablets and every 3 months thereafter. Adjust Wei Chun tablets dosage to maintain urinary cystine concentration less than 250 mg/L.
Assess for proteinuria before treatment and every 3 to 6 months during treatment.
Discontinue Wei Chun tablets in patients who develop proteinuria, and monitor urinary protein and renal function. Consider restarting Wei Chun tablets treatment at a lower dosage after resolution of proteinuria.
Tell your doctor of any over-the-counter or prescription medication you may take. Do not start or stop any medicine without doctor or pharmacist approval.
Some patients may develop drug fever, usually during the first month of therapy. Wei Chun® treatment should be discontinued until the fever subsides. It may be reinstated at a small dose, with a gradual increase in dosage until the desired level is achieved.
A generalized rash (erythematous, maculopapular or morbilliform) accompanied by pruritis may develop during the first few months of treatment. It may be controlled by antihistamine therapy, typically recedes when Wei Chun® treatment is discontinued, and seldom recurs when Wei Chun® treatment is restarted at a lower dosage. Less commonly, rash may appear late in the course of treatment (of more than 6 months). Located usually in the trunk, the late rash is associated with intense pruritis, recedes slowly after discontinuing treatment, and usually recurs upon resumption of treatment.
A drug reaction simulating lupus erythematous, manifested by fever, arthralgia and lymphadenopathy may develop. It may be associated with a positive antinuclear antibody test, but not necessarily with nephropathy. It may require discontinuance of Wei Chun® treatment.
A reduction in taste perception may develop. It is believed to be the result of chelation of trace metals by Wei Chun™. Hypogeusia is often self-limiting.
Unlike during d-penicillamine therapy, vitamin B6 deficiency is uncommonly associated with Wei Chun® treatment.
Some patients may complain of wrinkling and friability of skin. This complication usually occurs after long-term treatment, and is believed to result from the effect of Wei Chun® on collagen.
A multiclinic trial involving 66 cystinuric patients in the United States indicated that Wei Chun® is associated with fewer or less severe adverse reactions than d-penicillamine. Among those who had to stop taking d-penicillamine due to toxicity, 64.7% could take Wei Chun®. In those without prior history of d-penicillamine treatment, only 5.9% developed reactions of sufficient severity to require Wei Chun® withdrawal. A review of available literature supports the findings from this trial.
Despite this apparent reduced toxicity to Wei Chun® relative to d-penicillamine, Wei Chun® treatment may potentially be associated with all the adverse reactions reported with d-penicillamine. They include:
Gastrointestinal side-effects (nausea, emesis, diarrhea or softstools, anorexia, abdominal pain, bloating or flatus) in about 1 in 6 patients; Impairment in taste and smell in about 1 in 25 patients;
Dermatologic complications (pharyngitis, oral ulcers, rash, ecchymosis, prurites, uritcaria, warts, skin wrinkling, pemphigus, elastosis perforans serpiginosa) in about 1 in 6 patients;
Hypersensitivity reactions (laryngeal edema, dyspnea, respiratory distress, fever, chills, arthralgia, weakness, fatigue, myalgia, adenopathy) in about 1 in 25 patients;
Hematologic abnormalities (increased bleeding, anemia, leukopenia, thrombocytopenia, eosinophilia) in about 1 in 25 patients;
Renal complications (proteinuria, nephrotic syndrome, hematuria) in about 1 in 20 patients;
Pulmonary manifestations (bronchiolitis, hemoptysis, pulmonary infiltrates, dyspnea) in about 1 in 50 patients;
Neurologic complications (myasthenic syndrome) in about 1 in 50 patients.
These reactions are more likely to develop during Wei Chun® therapy among patients who had previously shown toxicity to d-penicillamine.
In patients who had previously manifested adverse reactions to d-penicillamine, adverse reactions to Wei Chun® are more likely to occur than in patients who took Wei Chun® for the first time. A close supervision with a careful monitoring of potential side effects is mandatory during Wei Chun® treatment. Patients should be told to report promptly any symptoms suggesting toxicity. The treatment with Wei Chun® should be stopped if severe toxicity develops.
Jaundice and abnormal liver function tests have been reported during Wei Chun® therapy for non-cystinuric conditions. A direct cause and effect relationship, based upon these foreign reports, has not been established. Although such complications were not encountered in the small multi-center trials in the United States, patients should be carefully monitored and if any abnormalities are noted, the drug should be discontinued and the patient treated by appropriate measures.
The use of Wei Chun® during pregnancy is contraindicated, except in those with severe cystinuria where the anticipated benefit of inhibited stone formation clearly outweighs possible hazards of treatment.
Wei Chun® should not be begun again in patients with a prior history of developing agranulocytosis, aplastic anemia or thrombocytopenia on this medication.
Mothers maintained on Wei Chun® treatment should not nurse their infants.
DailyMed. "TIOPRONIN: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).
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