Name of the Drug
Non-proprietary Name - Oxpentifylline 400 mg controlled release tablet.
DESCRIPTION
A trisubstituted xanthine derivative designated chemically as 1-(5-oxohexyl)-3, 7-dimethylxanthine, IUPAC name: 3,7-dimethyl-1-(5-oxohexyl)-3.7-dihydro-1H-purine-2,6-dione. Oxpentifylline is soluble in water and ethanol, and sparingly soluble in toluene.
Trental 400 tablets also contain the following excipients: hydroxyethylcellulose, povidone, talc-purified, magnesium stearate, hypromellose, titanium dioxide, erythrosine, and macrogol 8000.
Pharmacology
Site and Mode of Action
It is thought that oxpentifylline and its metabolites improve the flow properties of blood by decreasing its viscosity. In patients with chronic peripheral arterial disease, this increases blood flow to the affected microcirculation and enhances tissue oxygenation. Some of the mechanisms by which this is thought to occur include dose-related haemorrheological effects, such as decreased blood viscosity, increases impaired erythrocyte deformability, decreased plasma fibrinogen and enhanced platelet deaggregation. However the precise mode of action of oxpentifylline and the sequence of events leading to clinical improvement are still to be clearly defined.
Pharmacokinetics
After oral administration in aqueous solution oxpentifylline is almost completely absorbed. It undergoes a first-pass effect and the various metabolites appear in plasma very soon after dosing.
Peak plasma levels of the parent compound and its metabolites are reached within 1 hour. The major metabolites are Metabolite I (1-[5-hydroxy-hexyl]-3,7-dimethylxanthine) and Metabolite V (1-[3-carboxypropyl]-3,7-dimethylxanthine), and plasma levels of these metabolites are 5 and 8 times greater, respectively, than of oxpentifylline. Following oral administration of aqueous solutions containing 100 to 400 mg of oxpentifylline, the pharmacokinetics of the parent compound and Metabolite I are dose-related and not proportional (non-linear), with half-life and area under the blood-level time curve (AUC) increasing with dose. The elimination kinetics of Metabolite V are not dose-dependent. The apparent plasma half-life of oxpentifylline varies from 0.4 to 0.8 hours and the apparent plasma half-lives of its metabolites vary from 1 to 1.6 hours. There is no evidence of accumulation or enzyme induction (cytochrome P450) following multiple oral doses.
Excretion is almost totally urinary: the main biotransformation product is Metabolite V. Essentially no parent drug is found in the urine. Despite large variations in plasma levels of parent compound and its metabolites, the urinary recovery of Metabolite V is consistent and shows dose proportionality. Less than 4% of the administered dose is recovered in faeces. Food intake shortly before dosing delays absorption of an immediate release dosage form but does not affect total absorption. The pharmacokinetics and metabolism of Trental 400 have not been studied in patients with renal and/or hepatic dysfunction, but AUC was increased and elimination rate decreased in an older population (60-68 years) compared to younger individuals (22-30 years). After administration of the 400 mg controlled-release Trental 400 tablet, plasma levels of the parent compound and its metabolites reach their maximum within 2 to 4 hours and remain constant over an extended period of time. The controlled release of oxpentifylline from the tablet eliminates peaks and troughs in plasma levels for improved gastrointestinal tolerance.
Indications
Oxpentifylline is indicated in the treatment of peripheral occlusive vascular disease and circulatory disorders of arteriosclerotic, diabetic, inflammatory or function origin; trophic disorders (e.g., leg ulcers and gangrene).
Circulatory disorders in the eye and ear associated with degenerative vascular processes resulting in a decrease of visual and auditory function.
Contraindications
Patients who have previously exhibited intolerance to this product or methylxanthines, such as caffeine, theophylline and theobromine.
Trental should not be given to patients with severe haemorrhage, eg. massive retinal haemorrhage, cerebral haemorrhage, acute myocardial infarction or patients with peptic ulcer or a recent history thereof.
Severe coronary or cerebral arteriosclerosis with hypertension as well as serious cardiac arrhythmias are relative contraindications to parenteral treatment.
Precautions
Since oxpentifylline is extensively metabolised in the liver and eliminated through the kidneys, the use of this drug is not recommended in patients with marked impairment of kidney or liver function.
Patients with less severe impairment of these organs should be closely monitored during Trental therapy and may require lower doses.
Patients with chronic occlusive arterial disease of the limbs frequently show other manifestations of arteriosclerotic disease. Trental has been used safely for treatment of peripheral arterial disease in patients with concurrent coronary artery and cerebrovascular diseases, but there have been occasional reports of angina, hypotension and arrhythmia. Controlled trials do not show that Trental causes such adverse effects more often than placebo, but, as it is a methylxanthine derivative, it is possible that some individuals will experience such responses. Careful monitoring is required in patients with acute arrhythmias.
Caution should be exercised when administering Trental to patients with low or labile blood pressure. In such patients any dose increase should be done gradually.
Trental should be used with caution in elderly patients as peak plasma levels of oxpentifylline and its metabolites are moderately higher in this age group. Elderly patients had a slight increase in the incidence of some adverse effects. Careful dose adjustment is therefore recommended.
Hypersensitivity reactions, such as pruritus, rashes and urticaria do occur but progression to anaphylactoid shock and angioedema are rare.
Careful monitoring and adjustment (see 'Dosage and Administration') are necessary in patients with impaired renal function (creatinine clearance below 30 mL/min).
Trental 400 may exacerbate bleeding; careful patient selection and monitoring of at risk patients via haematocrit and/or haemoglobin determinations are recommended.
Use in Pregnancy
Category B1.
In teratogenic studies in rats and rabbits, oral doses of Trental 400 up to 25 and 10 times the maximum recommended human daily dose caused no foetal malformation. Increased resorption was seen in rats at high doses. However, since no well-controlled studies in pregnant women have been carried out, Trental 400 should not be used in pregnancy unless clearly needed.
Use in Lactation
Trental 400 and its metabolites are excreted in human milk. A decision should therefore be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Paediatric Use
Safety and effectiveness in children below the age of 18 years has not been established.
Carcinogenicity
Long-term (18 month) studies to determine any carcinogenic potential of oxpentifylline have been conducted in mice and rats. No carcinogenic potential for oxpentifylline was noted in the mouse study. In the rat study, there was a statistically significant increase in benign mammary fibroadenomas in females in the high dose group. The relevance of this finding to human use is uncertain since this was only a marginal statistically significant increase for a tumour that is common in aged rats.
Interactions with Other Medicines
There have been reports of bleeding (eg. skin, mucosa, gastrointestinal tract) and/or prolonged prothrombin time in patients treated with Trental with and, rarely without anticoagulants or platelet aggregation inhibitors. Patients on warfarin should have more frequent monitoring of prothrombin times, while patients without risk factors complicated by haemorrhage (eg. recent surgery, peptic ulceration) should have periodic examinations for bleeding including haematocrit and/or haemoglobin.
Trental has been used concurrently with digitalis and antiarrhythmics without observed problems. Small decreases in blood pressure have been observed in some patients treated with Trental. Periodic systemic blood pressure monitoring is recommended for patients receiving Trental concomitantly with antihypertensive drugs, beta blockers, diuretics and other drugs with blood pressure lowering potential as their blood pressure lowering effects may be increased. If indicated, dosage of the antihypertensive agents should be reduced.
Combined use with other xanthines or with sympathomimetics may cause excessive CNS stimulation.
An increase in the level of theophylline and therefore an increase in the intensity and frequency of adverse events associated with theophylline may result from concomitant use with Trental.
In patients treated with hypoglycaemic agents, a moderate decrease in the dose of these agents may be required when Trental is prescribed. Patients undergoing such therapy should be monitored closely.
Effect on Laboratory Tests
Urinary assays for pregnanediol may show false positive results in the presence of oxpentifylline and its metabolites.
ADVERSE EFFECTS
Clinical trials with Trental 400 have been conducted in Australia, the United States and in Europe. The slow release formulation, Trental 400, was used in studies in Australia and Europe, while in the United States, studies were conducted using the capsule formulation, containing 200 mg oxpentifylline. In these studies, dosages used were 400 mg (tablets) two to three times daily or 200 mg - 400 mg (capsules) three times daily. Treatment periods for studies with Trental 400 ranged up to 60 weeks. Adverse reactions reported in these studies and considered to be drug related were as follows.
Gastrointestinal
The most frequent (greater than 1% incidence) types of side effects seen with Trental (all formulations) were gastrointestinal upsets, including nausea, dyspepsia, vomiting, belching/flatus/bloating, abdominal pain and diarrhoea. However, the controlled release preparation of Trental 400 resulted in much fewer gastrointestinal side effects, the most common being dyspepsia 2.8% (placebo 4.7%), nausea 2.2% (placebo 0.8%), vomiting 1.2% and belching/flatus/bloating (0.6%). Anorexia, cholecystitis, constipation and a dry mouth/thirst have been reported with a frequency of less than 1%.
Central Nervous System
Side effects related to C.N.S. disturbances with an incidence of greater than 1% included dizziness, headache, insomnia, blurred vision, agitation/nervousness, drowsiness and tremor. Of these, the following were reported for the controlled release preparation Trental 400: dizziness 1.9% (placebo 3.1%), headache 1.2% (placebo 1.6%) and tremor 0.3% (placebo 0.8%). Anxiety and confusion have been reported with a frequency of less than 1%. Isolated cases of aseptic meningitis have been reported.
Cardiovascular
Only angina/chest pain was reported for Trental 400 tablets, with an incidence of 0.3%, while for the capsule formulation flushing and arrhythmia/palpitation/tachycardia were also reported, with an incidence of greater than 1%. Reports of hypotension were rare (<0.1%). Dyspnea and oedema have been reported with a frequency of less than 1%.
Hepatic
Isolated cases of intrahepatic cholestasis and jaundice as well as hepatitis and transaminase elevation have been reported.
Haemic and Lymphatic
Decreased fibrinogen, pancytopenia, purpura, aplastic anaemia and leukopenia. Isolated cases of thrombocytopenia have been noted.
Respiratory
Epistaxis, flu-like symptoms, laryngitis and nasal congestion have been reported rarely.
Hypersensitivity
Pruritus, rashes and urticaria may occur with a frequency of 0.1% to 1% but progression to anaphylactoid shock (angioedema, bronchospasm) occurs only in isolated cases.
Miscellaneous
Rarely, the following were reported: brittle fingernails, blurred vision, conjunctivitis, earache, scotoma, bad taste in the mouth, excessive salivation, malaise, sore throat, swollen neck glands, weight change.
Dosage and Administration
Oral
The usual dosage of Trental in controlled release tablet form is one tablet (400 mg) three times a day with or after meals, to be swallowed whole with some liquid. While the effect of Trental may be seen within 2-4 weeks, it is recommended that treatment be continued for at least 8 weeks. Efficacy has been demonstrated in double blind clinical studies of 6 months duration.
Digestive and central nervous system side effects are dose related. If patients develop these side effects it is recommended that dosage be lowered to one tablet twice a day (800mg/day). If side effects persist at this lower dosage the administration of Trental should be discontinued.
In patients with low or labile blood pressure, or with renal or hepatic dysfunction, an individual dosage adjustment is required. This also applies to patients with renal dysfunction (creatinine clearance of less than 30 mL/min) where, according to individual tolerance, a dosage adjustment of 30 to 50% may be necessary.
Parenteral
Intravenous Injection
An intravenous injection of 1 ampoule of 5 mL should be given slowly (over not less than 5 minutes) with the patient in a prone position. It is advisable to test for individual susceptibility by giving an initial dose of half an ampoule of Trental (2.5 mL = 50 mg) diluted with physiological saline to 10 mL. Provided there are no ill effects, the dose may be gradually increased up to 200 mg (2 ampoules). When this dose is given it is of particular importance to adhere to the recommended injection time of 5 minutes/5 mL.
Intravenous Infusion
Trental should be given by intravenous infusion after dilution in a suitable infusion fluid (normal saline or Ringer's solution). Dosage for intravenous infusion is generally based on the following guidelines and is determined by the doctor in accordance with individual requirements. One infusion of 100-600 mg Trental in 100-500 mL of infusion fluid should be administered once or twice daily. This infusion may be supplemented by oral therapy up to a total daily dose of 1200 mg oxpentifylline. The infusion time must be at least 60 minutes per 100 mg oxpentifylline. In advanced cases, either a continuous infusion of up to 1200 mg over 24 hours or two infusions of up to 600 mg each over periods of at least 6 hours may be indicated. The precise dose should be calculated on the basis of 0.6 mg oxpentifylline/kg body weight per hour. A maximum intravenous dose of 1200 mg oxpentifylline per 24 hours should not be exceeded.
In patients with low or labile blood pressure, or with renal or hepatic dysfunction, an individual dosage adjustment is required. This also applies to patients with renal dysfunction (creatinine clearance of less than 30 mL/min) where, according to individual tolerance, a dosage adjustment of 30 to 50% may be necessary.
Children
Trental is not recommended for children.
Overdosage
Symptoms
Symptoms appear to be dose-related. A report from a poison control centre on 44 patients taking overdoses of enteric-coated oxpentifylline tablets noted that symptoms usually occurred 4-5 hours after ingestion and lasted about 12 hours. The highest amount ingested was 80 mg/kg; flushing, hypotension, convulsions, somnolence, loss of consciousness, fever and agitation occurred. All patients recovered.
Treatment
In addition to symptomatic treatment and gastric lavage, special attention must be given to supporting respiration, maintaining systemic blood pressure and controlling convulsions. Activated charcoal has been used to absorb oxpentifylline in patients who have overdosed.
Contact the Poisons Information Centre for advice on management of overdosage.
Presentation and Storage Conditions
Trental 400mg tablets are oblong, pink, film-coated tablets, available in blister packs of 50 tablets for oral administration. Trental tablets are a controlled release formulation. Store below 25oC. Protect from light.
Trental injection* is a colourless clear solution in clear colourless ampoules of 5 mL (boxes of 5 ampoules). Store below 30oC. Protect from light.
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