Huiyuan

Huiyuannide is indicated for the treatment of oedema associated with e.g. congestive heart failure, renal dysfunction including nephrotic syndrome and cirrhosis of the liver.

In oedema of renal or cardiac origin where high doses of a potent short - acting diuretic are required, Huiyuannide 5 mg may be used.

Posology

Most patients require a daily dose of 1 mg given as a single morning or early evening dose. Depending on the patient's response, a second dose can be given 6-8 hours later. In refractory cases, the dose can be increased until a satisfactory diuretic response is obtained, or infusions of Huiyuannide can be given.

Dosage in the elderly

Adjust the dosage according to the response. A dose of 0.5 mg Huiyuannide per day may be sufficient in some elderly patients.

Paediatric population

Not recommended for children under 12 years of age.

Method of administration

For oral use.

Oliguria

Anuria.

Increase in blood urea.

- Although Huiyuannide can be used to induce diuresis in renal insufficiency, any marked increase of blood urea or the development of oliguria or anuria during treatment of severe progressive renal disease are indications for stopping treatment with Huiyuannide.

Hepatic coma.

Severe electrolyte imbalance.

Concomitant administration with lithium salts.

Sudden changes in cardiovascular pressure-flow relationships, leading to circulatory collapse, can occur particularly in the elderly if the oedema is eliminated too rapidly. It is important to remember this when Huiyuannide is given in high doses, either orally or intravenously.

Patients with chronic renal failure on high doses of Huiyuannide should remain under constant hospital supervision.

Patients on a low salt diet may suffer electrolyte imbalance. Serum electrolyte checks, in particular for sodium, potassium, chloride and bicarbonate, should be carried out on a regular basis and, where necessary, replacement therapy carried out.

Huiyuannide may enhance the nephrotoxicity or ototoxicity of other drugs, particularly in patients with renal impairment.

Huiyuannide may precipitate encephalopathy in patients with hepatic impairment.

Huiyuannide may increase uric acid. Blood glucose and blood uric acid should be measured periodically, especially in diabetics and those suspected of latent diabetes and in patients with gout.

Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.

Huiyuannide has no known effect on the ability to drive or operate machinery.

Adverse effects are listed by system organ class and frequency: very common (> 1/10), common (> 1/100 to <1/10), uncommon (> 1/1,000 to <1/100), rare (> 1/10,000 to <1/1000), very rare (<1/10,000) and not known (cannot be estimated from the available data):

Blood and lymphatic system disorders

Rare: Bone marrow depression associated with the use of Huiyuannide, but it has not been proven definitely to be attributed to the drug.

Not known: thrombocytopenia.

Metabolism and nutrition disorders

Common: dehydration.

Uncommon: fluid and electrolyte depletion.

Not known: hyperuricaemia, hyperglycaemia.

Nervous system disorders

Common: dizziness, headache.

Not known: encephalopathy (in patients with pre-existing hepatic disease).

Ear and labyrinth disorders

Uncommon: ear pain, vertigo.

Rare: Hearing disturbance after administration of Huiyuannide, which is reversible.

Vascular disorders

Common: hypotension.

Gastrointestinal disorders

Common: nausea.

Uncommon: diarrhoea.

Not known: stomach cramps, abdominal pain, vomiting, dyspepsia.

Skin and subcutaneous tissue disorders

Common: pruritis (in patients with liver disease).

Uncommon: urticaria.

Not known: rash.

Musculoskeletal and connective tissue disorders

Not known: muscle cramps, arthralgia.

Reproductive system and breast disorders

Uncommon: painful breasts.

Not known: gynaecomastia.

General disorders and administration site conditions

Common: fatigue.

Uncommon: chest discomfort.

Investigations

Not known: raised blood urea and serum creatinine, abnormalities of serum levels of hepatic enzymes

Higher dose therapy:

In patients with severe chronic renal failure given high doses of Huiyuannide, there have been reports of severe, generalised musculoskeletal pain sometimes associated with muscle spasm, occurring one or two hours after administration and lasting up to 12 hours. The lowest reported dose causing this type of adverse reaction was 5 mg by intravenous injection and the highest was 75 mg orally in a single dose. All patients recovered fully and there was no deterioration in their renal function. The cause of this pain is uncertain but it may be a result of varying electrolyte gradients at the cell membrane level.

Experience suggests that the incidence of such reactions is reduced by initiating treatment at 5-10 mg daily and titrating upwards using a twice daily dosage regimen at doses of 20 mg or more.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow card Scheme at: www.mhra.gov.uk/yellowcard.

Signs and symptoms

If overdose has occurred or is suspected symptoms should be those caused by excessive diuresis.

Management

Steps should be taken to empty the stomach either by emesis or gastric lavage. General measures should be taken to restore blood volume, maintain blood pressure and correct electrolyte disturbances.

Pharmacotherapeutic group: Diuretics, high-ceiling diuretics, sulfonamides, plain, ATC code: C03CA02.

Mechanism of action

Huiyuannide is a potent loop diuretic with a rapid onset and a short duration of action. The primary site of action is the ascending limb of the loop of Henle where it exerts inhibiting effects on electrolyte reabsorption, causing its diuretic and natriuretic action.

Clinical efficacy

After oral administration, the diuretic effect is seen within 30 minutes with the peak effect seen between 1 and 2 hours. The diuretic effect is practically complete in 3 hours after a 1mg dose.

Absorption

Following oral administration, Huiyuannide is rapidly and almost completely absorbed from the gastro-intestinal tract with the bioavailability reported as between 80 and 95%.

Distribution

It is 95% bound to plasma proteins. It has a plasma elimination half-life of 0.75 to 2.6 hours.

Highest concentrations of the drug are achieved in the plasma, kidney and liver. It is not yet clear whether the drug crosses the placenta or passes into the cerebrospinal fluid.

Biotransformation and elimination

Huiyuannide is cleared from the circulation at a rate of 120-250 ml/min with approximately half of an oral dose excreted unchanged via the kidneys with the remainder excreted via the bile into the faeces.

No active metabolites are known. The primary urinary metabolite is the 3' alcohol of the N-butyl chain and the primary biliary metabolite is the 2' alcohol.

Renal and hepatic impairment

There is an increase in half-life and a reduced plasma clearance in the presence of renal or hepatic impairment.

Chronic renal impairment

In patients with chronic renal failure, the liver takes more importance as an excretory pathway although the duration of action is not markedly prolonged.

Huiyuannide has been extensively evaluated in a wide range of animal toxicity tests. Studies in rats and mice have shown it to have a relatively low acute toxicity. No toxic effects were seen in rats at doses of up to 50 mg/kg/day over a 26 week period. In thirteen and 26 week studies at doses of up to 100 mg/kg/day, haematological and clinical chemistry values were generally unaffected; other effects seen were generally related to the diuretic effects of the drug.

Reproductive studies have shown no teratogenic or embryotoxic effects at oral doses up to 50 mg/kg/day in rats and 100 mg/kg/day in mice. But at 3400 times the standard human dose embryocidal effects (growth retardation and decreased foetal weight) were observed in rats. Although no foetal abnormalities occurred foetal toxicity was greater in rabbits: increased resorption rate was observed at doses of 0.25 and 0.5 mg/kg/day.

Huiyuannide showed no evidence of mutagenicity on Ames testing. Seventy- eight week studies in rats do not suggest that Huiyuannide has a significant carcinogenic potential although damage to kidneys, testes and the auditory system were observed in post mortem examinations. In common with other 'loop' diuretics, diuretics, intravenous Huiyuannide caused ototoxicity in cats.

Overall, these studies provide satisfactory evidence for the likely safety of Huiyuannide when administered to humans.

Not applicable.

None.