Antrex

Antrex is indicated

a) to diminish the toxicity and counteract the action of folic acid antagonists such as methotrexate in cytotoxic therapy and overdose in adults and children. In cytotoxic therapy, this procedure is commonly known as “Antrex Rescue”;

b) in combination with 5-fluorouracil in cytotoxic therapy.

For intravenous and intramuscular administration only. In the case of intravenous administration, no more than 160 mg of Antrex should be injected per minute due to the calcium content of the solution.

For intravenous infusion, Antrex may be diluted with 0.9% sodium chloride solution or 5% glucose solution before use.6.

Antrex rescue in methotrexate therapy:

Since the Antrex rescue dosage regimen depends heavily on the posology and method of the intermediate- or high-dose methotrexate administration, the methotrexate protocol will dictate the dosage regimen of Antrex rescue. Therefore, it is best to refer to the applied intermediate or high dose methotrexate protocol for posology and method of administration of Antrex.

The following guidelines may serve as an illustration of regimens used in adults, elderly and children:

Antrex rescue has to be performed by parenteral administration in patients with malabsorption syndromes or other gastrointestinal disorders where enteral absorption is not assured. Dosages above 25-50 mg should be given parenterally due to saturable enteral absorption of Antrex.

Antrex rescue is necessary when methotrexate is given at doses exceeding 500 mg/m² body surface and should be considered with doses of 100 mg - 500 mg/m² body surface.

Dosage and duration of Antrex rescue primarily depend on the type and dosage of methotrexate therapy, the occurrence of toxicity symptoms, and the individual excretion capacity for methotrexate. As a rule, the first dose of Antrex is 15 mg (6-12 mg/m²) to be given 12-24 hours (24 hours at the latest) after the beginning of methotrexate infusion. The same dose is given every 6 hours throughout a period of 72 hours. After several parenteral doses treatment can be switched over to the oral form.

In addition to Antrex administration, measures to ensure the prompt excretion of methotrexate (maintenance of high urine output and alkalinisation of urine) are integral parts of the Antrex rescue treatment. Renal function should be monitored through daily measurements of serum creatinine.

Forty-eight hours after the start of the methotrexate infusion, the residual methotrexate-level should be measured. If the residual methotrexate-level is >0.5 µmol/l, Antrex dosages should be adapted according to the following table:

In combination with 5-fluorouracil in cytotoxic therapy:

Different regimens and different dosages are used, without any dosage having been proven to be the optimal one.

The following regimens have been used in adults and elderly in the treatment of advanced or metastatic colorectal cancer and are given as examples. There are no data on the use of these combinations in children:

Bimonthly regimen: Antrex 200 mg/m² by intravenous infusion over two hours, followed by bolus 400 mg/m² of 5-FU and 22-hour infusion of 5-FU (600 mg/m²) for 2 consecutive days, every 2 weeks on days 1 and 2.

Weekly regimen: Antrex 20 mg/m² by bolus i.v. injection or 200 to 500 mg/m² as i.v. infusion over a period of 2 hours plus 500 mg/m² 5-fluorouracil as i.v. bolus injection in the middle or at the end of the Antrex infusion.

Monthly regimen: Antrex 20 mg/m² by bolus i.v. injection or 200 to 500 mg/m² as i.v. infusion over a period of 2 hours immediately followed by 425 or 370 mg/m² 5-fluorouracil as i.v. bolus injection during five consecutive days.

For the combination therapy with 5-fluorouracil, modification of the 5-fluorouracil dosage and the treatment-free interval may be necessary depending on patient condition, clinical response and dose limiting toxicity as stated in the product information of 5-fluorouracil. A reduction of Antrex dosage is not required.

The number of repeat cycles used is at the discretion of the clinician.

Antidote to the folic acid antagonists trimetrexate, trimethoprim, and pyrimethamine:

Trimetrexate toxicity:

- Prevention: Antrex should be administered every day during treatment with trimetrexate and for 72 hours after the last dose of trimetrexate. Antrex can be administered either by the intravenous route at a dose of 20 mg/m² for 5 to 10 minutes every 6 hours for a total daily dose of 80 mg/m², or by oral route with four doses of 20 mg/m² administered at equal time intervals. Daily doses of Antrex should be adjusted depending on the haematological toxicity of trimetrexate.

- Overdosage (possibly occurring with trimetrexate doses above 90 mg/m² without concomitant administration of Antrex): after stopping trimetrexate, Antrex 40 mg/m² IV every 6 hours for 3 days.

Trimethoprim toxicity:

- After stopping trimethoprim, 3-10 mg/day Antrex until recovery of a normal blood count.

Pyrimethamine toxicity:

- In case of high dose pyrimethamine or prolonged treatment with low doses, Antrex 5 to 50 mg/day should be simultaneously administered, based on the results of the peripheral blood counts.

- Known hypersensitivity to Antrex, or to any of the excipients.

- Pernicious anaemia or other anaemias due to vitamin B12 deficiency.

Antrex should only be given by intramuscular or intravenous injection and must not be administered intrathecally. When folinic acid has been administered intrathecally following intrathecal overdose of methotrexate death has been reported.

General

Antrex should be used with methotrexate or 5-fluorouracil only under the direct supervision of a clinician experienced in the use of cancer chemotherapeutic agents.

Antrex treatment may mask pernicious anaemia and other anaemias resulting from vitamin B12 deficiency.

Many cytotoxic medicinal products - direct or indirect DNA synthesis inhibitors - lead to macrocytosis (hydroxycarbamide, cytarabine, mecaptopurine, thioguanine). Such macrocytosis should not be treated with folinic acid.

In epileptic patients treated with phenobarbital, phenytoin, primidone, and succinimides there is a risk to increase the frequency of seizures due to a decrease of plasma concentrations of anti-epileptic drugs.).

Antrex/5-fluorouracil

Antrex may enhance the toxicity risk of 5-fluorouracil, particularly in elderly or debilitated patients. The most common manifestations are leucopenia, mucositis, stomatitis and/or diarrhoea, which may be dose limiting. When Antrex and 5-fluorouracil are used in combination, the 5- fluorouracil dosage has to be reduced more in cases of toxicity than when 5-fluorouracil is used alone.

Combined 5-fluorouracil/Antrex treatment should neither be initiated nor maintained in patients with symptoms of gastrointestinal toxicity, regardless of the severity, until all of these symptoms have completely disappeared.

Because diarrhoea may be a sign of gastrointestinal toxicity, patients presenting with diarrhoea must be carefully monitored until the symptoms have disappeared completely, since a rapid clinical deterioration leading to death can occur. If diarrhoea and/or stomatitis occur, it is advisable to reduce the dose of 5-FU until symptoms have fully disappeared. Especially the elderly and patients with a low physical performance due to their illness are prone to these toxicities. Therefore, particular care should be taken when treating these patients.

In elderly patients and patients who have undergone preliminary radiotherapy, it is recommended to begin with a reduced dosage of 5-fluorouracil.

Antrex must not be mixed with 5-fluorouracil in the same IV injection or infusion.

Calcium levels should be monitored in patients receiving combined 5-fluorouracil/Antrex treatment and calcium supplementation should be provided if calcium levels are low.

Antrex/methotrexate

For specific details on reduction of methotrexate toxicity refer to the SPC of methotrexate.

Antrex has no effect on non-haematological toxicities of methotrexate such as the nephrotoxicity resulting from methotrexate and/or metabolite precipitation in the kidney. Patients who experience delayed early methotrexate elimination are likely to develop reversible renal failure and all toxicities associated with methotrexate (please refer to the SPC for methotrexate). The presence of pre-existing- or methotrexate-induced renal insufficiency is potentially associated with delayed excretion of methotrexate and may increase the need for higher doses or more prolonged use of Antrex.

Excessive Antrex doses must be avoided since this might impair the antitumour activity of methotrexate, especially in CNS tumours where Antrex accumulates after repeated courses.

Resistance to methotrexate as a result of decreased membrane transport implies also resistance to folinic acid rescue as both medicinal products share the same transport system.

An accidental overdose with a folate antagonist, such as methotrexate, should be treated as a medical emergency. As the time interval between methotrexate administration and Antrex rescue increases, Antrex effectiveness in counteracting toxicity decreases.

The possibility that the patient is taking other medications that interact with methotrexate (e.g., medications which may interfere with methotrexate elimination or binding to serum albumin) should always be considered when laboratory abnormalities or clinical toxicities are observed.

There is no evidence that Antrex has an effect on the ability to drive or use machines.

Frequencies are defined using the following convention:

Very common (>1/10);

common (>1/100 to <1/10);

uncommon (>1/1,000 to <1/100);

rare (>1/10,000 to <1/1,000);

very rare (<1/10,000);

not known (cannot be estimated from the available data).

Immune system disorders

Very rare (<0.01%): allergic reactions, including anaphylactoid/ anaphylactic reactions and urticaria.

Psychiatric disorders

Rare (0.01-0.1%): insomnia, agitation and depression after high doses.

Gastrointestinal disorders

Rare (0.01-0.1%): gastrointestinal disorders after high doses.

Neurological disorders

General disorders and administration site conditions

Uncommon (0.1-1%): fever has been observed after administration of Antrex as solution for injection.

Combination therapy with 5-fluorouracil only:

Generally, the safety profile depends on the applied regimen of 5-fluorouracil due to enhancement of the 5-fluorouracil induced toxicities:

Metabolism and Nutritional Disorder:

Not known: Hyperammonaemia

Blood and lymphatic system disorders:

Very common: bone marrow failure, including fatal cases

General disorders and administration site conditions

Very common (>10%): mucositis, including stomatitis and chelitis. Fatalities have occurred as a result of mucositis

Skin and subcutaneous tissue disorders:

Common: Palmar-Plantar Erythrodysaesthesia

Monthly regimen:

Gastrointestinal disorders

Very common (>10%): vomiting and nausea

No enhancement of other 5-fluorouracil induced toxicities (e.g. neurotoxicity).

Weekly regimen:

Gastrointestinal disorders

Very common (>10%): diarrhoea with higher grades of toxicity, and dehydration, resulting in hospital admission for treatment and even death.

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:

Yellow Card Scheme

Website: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store

There have been no reported sequelae in patients who have received significantly more Antrex than the recommended dosage. However, excessive amounts of Antrex may nullify the chemotherapeutic effect of folic acid antagonists.

Should overdosage of the combination of 5-fluorouracil and Antrex occur, the overdosage instructions for 5-FU should be followed.

Pharmacotherapeutic group: Detoxifying agents for antineoplastic treatment; ATC code: V03AF03

Antrex is the calcium salt of 5-formyl tetrahydrofolic acid. It is an active metabolite of folinic acid and an essential coenzyme for nucleic acid synthesis in cytotoxic therapy.

Antrex is frequently used to diminish the toxicity and counteract the action of folate antagonists, such as methotrexate. Antrex and folate antagonists share the same membrane transport carrier and compete for transport into cells, stimulating folate antagonist efflux. It also protects cells from the effects of folate antagonist by repletion of the reduce folate pool. Antrex serves as a pre-reduced source of H4 folate; it can therefore bypass folate antagonist blockage and provide a source for the various coenzyme forms of folic acid.

Antrex is also frequently used in the biochemical modulation of fluoropyridine (5-FU) to enhance its cytotoxic activity. 5-FU inhibits thymidylate synthase (TS), a key enzyme involved in pyrimidine biosynthesis, and Antrex enhances TS inhibition by increasing the intracellular folate pool, thus stabilising the 5FU-TS complex and increasing activity.

Finally intravenous Antrex can be administered for the prevention and treatment of folate deficiency when it cannot be prevented or corrected by the administration of folic acid by the oral route. This may be the case during total parenteral nutrition and severe malabsorption disorders. It is also indicated for the treatment of megaloblastic anaemia due to folic acid deficiency, when oral administration is not feasible.

Absorption

Following intramuscular administration of the aqueous solution, systemic availability is comparable to an intravenous administration. However, lower peak serum levels (Cmax) are achieved.

Metabolism

Antrex is a racemate where the L-form (L-5-formyl-tetrahydrofolate, L-5-formyl-THF), is the active enantiomer. The major metabolic product of folinic acid is 5-methyl-tetrahydrofolic acid (5-methyl-THF) which is predominantly produced in the liver and intestinal mucosa.

Distribution

The distribution volume of folinic acid is not known.

Peak serum levels of the parent substance (D/L-5-formyl-tetrahydrofolic acid, folinic acid) are reached 10 minutes after i.v. administration.

AUC for L-5-formyl-THF and 5-methyl-THF were 28.4±3.5 mg.min/l and 129±112 mg.min/l after a dose of 25 mg. The inactive D-isomer is present in higher concentration than L-5-formyltetrahydrofolate.

Elimination

The elimination half-life is 32 - 35 minutes for the active L-form and 352 - 485 minutes for the inactive D-form, respectively.

The total terminal half-life of the active metabolites is about 6 hours (after intravenous and intramuscular administration).

Excretion

80-90 % with the urine (5- and 10-formyl-tetrahydrofolates inactive metabolites), 5-8 % with the faeces.

There are no preclinical data considered relevant to clinical safety beyond data included in other sections of the SPC.

Incompatibilities have been reported between injectable forms of Antrex and injectable forms of droperidol, fluorouracil, foscarnet and methotrexate.

Droperidol

1. Droperidol 1.25 mg/0.5 ml with Antrex 5 mg/0.5 ml, immediate precipitation in direct admixture in syringe for 5 minutes at 25° C followed by 8 minutes of centrifugation.

2. Droperidol 2.5 mg/0.5 ml with Antrex 10 mg/0.5 ml, immediate precipitation when the drugs were injected sequentially into a Y-site without flushing the Y-side arm between injections.

Fluorouracil

Antrex must not be mixed in the same infusion as 5-fluorouracil because a precipitate may form. Fluorouracil 50 mg/ml with Antrex 20 mg/ml, with or without dextrose 5% in water, has been shown to be incompatible when mixed in different amounts and stored at 4°C, 23°C, or 32° C in polyvinyl chloride containers.

Foscarnet

Foscarnet 24 mg/ml with Antrex 20 mg/ml formation of a cloudy yellow solution reported.

Prior to administration, Antrex should be inspected visually. The solution for injection or infusion should be a clear and yellowish solution. If cloudy in appearance or particles are observed, the solution should be discarded. Antrex solution for injection or infusion is intended only for single use. Any unused portion of the solution should be disposed of in accordance with the local requirements.