SUMMARY OF PRODUCT CHARACTERISTICS

1 NAME OF THE MEDICINAL PRODUCT

Azapress Tablets 50 mg Azathioprine Tablets 50 mg

2 QUALITATIVE AND QUANTITATIVE COMPOSITION

Each tablet contains 50 mg Azathioprine BP

3    PHARMACEUTICAL FORM

Pale yellow biconvex tablets scored on one side and engraved with ‘A10’ on the other side.

4    CLINICAL PARTICULARS

4.1    Therapeutic indications

Azathioprine is used in facilitating the survival of organ and tissue transplants, where it is mainly used as an immunosuppressant.

Azathioprine is used in the treatment of patients exhibiting the following conditions, where it has been shown to have a marked therapeutic effect: chronic active hepatitis, severe rheumatoid arthritis, systemic lupus erythematosus (SLE), idiopathic thrombocytopenic purpura, acquired haemolytic anaemia and severe cases of specified dermatological diseases (pemphigus vulgaris, dermatomyositis, polyarteritis nodosa, pyoderma gangrenosa) when these conditions are: (a) refractory to corticosteroids or (b) when corticosteroids are contra-indicated or (c) when controlled by corticosteroids in dosages which are producing severe side-effects. In patients who are experiencing such side-effects, the aim of azathioprine treatment is to reduce the required maintenance dose of steroids.

Azathioprine is used in the treatment of pemphigus and rheumatoid arthritis where it has significant therapeutic activity when used without corticosteroids.

4.2 Posology and method of administration

Adults and children:

Transplantation

Depending on the immunosuppressive regimen employed, a dosage of up to 5 mg/kg body weight/day may be given on the first day of therapy, either orally or intravenously.

Maintenance dosage should range from 1 to 4 mg/kg body weight/day and must be adjusted according to clinical requirements and haematological tolerance.

Evidence indicates that Azathioprine therapy should be maintained indefinitely, even if only low doses are necessary, because of the risk of graft rejection.

Dosage in other conditions - adults and children

In general, starting dosage is from 1 to 3 mg/kg body weight/day, and should be adjusted, within these limits, depending on the clinical response (which may not be evident for weeks or months) and haematological tolerance.

When therapeutic response is evident, consideration should be given to reducing the maintenance dosage to the lowest level compatible with the maintenance of that response. If no improvement occurs in the patient's condition within 3 months, consideration should be given to withdrawing Azathioprine.

The maintenance dosage required may range from less than 1 mg/kg body weight/day to 3 mg/kg body weight/day, depending on the clinical condition being treated and the individual patient response, including haematological tolerance.

In patients with renal and/or hepatic insufficiency, dosages should be given at the lower end of the normal range (see Special Warnings and Precautions for Use for further details).

Use in the elderly (see Renal and/or hepatic insufficiency)

There is limited experience of the administration of Azathioprine to elderly patients. Although the available data do not provide evidence that the incidence of side effects among elderly patients is higher than that among other patients treated with Azathioprine, it is recommended that the dosages used should be at the lower end of the range.

Particular care should be taken to monitor haematological response and to reduce the maintenance dosage to the minimum required for clinical response.

4.3 Contraindications

Hypersensitivity to azathioprine. Hypersensitivity to 6-mercaptopurine (6-MP) should alert the prescriber to probable hypersensitivity to Azathioprine.

Azathioprine therapy should not be initiated in patients who may be pregnant, or who are likely to become pregnant without careful assessment of risk versus benefit (see Special Warnings and Precautions for Use and Pregnancy and Lactation).

4.4 Special warnings and precautions for use

Azathioprine should not be prescribed unless the patient can be adequately monitored for toxic effects throughout the duration of the therapy.

During the first eight weeks of therapy with azathioprine, complete blood counts, including platelet counts, must be performed at least weekly (and more frequently when higher dosages are used or in the presence of disturbed renal or hepatic function), and with decreasing frequency thereafter. The blood count frequency may be reduced later in therapy, but it is suggested that complete blood counts are repeated monthly, or at least at intervals of not longer than 3 months.

Azathioprine may be given long-term unless the patient cannot tolerate the preparation. Withdrawal of an effective dose in certain circumstances, e.g. SLE with nephritis, may result in a serious relapse of the condition. In other instances, such as rheumatoid arthritis and certain haematological conditions, treatment may be withdrawn after a suitable interval without any ill-effect. Withdrawal should always be a gradual process performed under close supervision.

Patients receiving azathioprine should be instructed to report immediately any evidence of infection, unexpected bruising or bleeding or other manifestations of bone marrow depression.

There are individuals with an inherited deficiency of the enzyme thiopurine methyltransferase (TPMT) who may be unusually sensitive to the myelosuppressive effect of azathioprine and prone to developing rapid bone marrow depression following the initiation of treatment with azathioprine. This problem could be exacerbated by co-administration with drugs that inhibit TPMT, such as olsalazine, mesalazine or sulfasalazine. Also it has been reported that decreased TPMT activity increases the risk of secondary leukaemias and myelodysplasia in individuals receiving 6-mercaptopurine (the active metabolite of azathioprine) in combination with other cytotoxics (see section 4.8 Undesirable effects).

Renal and/or hepatic insufficiency

It has been suggested that the toxicity of azathioprine may be enhanced in the presence of renal insufficiency, but controlled studies have not supported this suggestion. Nevertheless, it is recommended that the dosages used should be at the lower end of the normal range and that haematological response should be carefully monitored. Dosage should be further reduced if haematological toxicity occurs.

Caution is necessary during the administration of azathioprine to patients with hepatic dysfunction, and regular complete blood counts and liver function tests should be undertaken. In such patients the metabolism of azathioprine may be impaired, and the dosage of azathioprine should therefore be reduced if hepatic or haematological toxicity occurs.

Limited evidence suggests that azathioprine is not beneficial to patients with hypoxanthine-guanine-phosphoribosyltransferase deficiency (Lesch-Nyhan syndrome). Therefore, given the abnormal metabolism in these patients, it is not prudent to recommend that these patients should receive azathioprine.

Mutagenicity

Chromosomal abnormalities have been demonstrated in both male and female patients treated with azathioprine. It is difficult to assess the role of azathioprine in the development of these abnormalities.

Effects on Fertility

Relief of chronic renal insufficiency by renal transplantation involving the administration of azathioprine has been accompanied by increased fertility in both male and female transplant recipients.

Carcinogenicity (see also section 4.8 Undesirable Effects)

Patients receiving immunosuppressive therapy are at an increased risk of developing non-Hodgkin's lymphomas and other malignancies, notably skin cancers (melanoma and non-melanoma), sarcomas (Kaposi's and non-Kaposi's) and uterine cervical cancer in situ. The risk appears to be related to the intensity and duration of immunosuppression rather than to the use of any specific agent. It has been reported that reduction or discontinuation of immunosuppression may be associated with partial or complete regression of non-Hodgkin's lymphomas and Kaposi's sarcomas.

Patients receiving multiple immunosuppressive agents may be at risk of overimmunosuppression, therefore such therapy should be maintained at the lowest effective level.

Exposure to sunlight and UV light should be limited and patients should wear protective clothing and use a sunscreen with a high protection factor to minimize the risk of skin cancer and photosensitivity (see also section 4.8 Undesirable Effects).

Varicella Zoster Virus Infection (see also section 4.8 Undesirable Effects)

Infection with varicella zoster virus (VZV; chickenpox and herpes zoster) may become severe during the administration of immunosuppressants. Caution should be exercised especially with respect to the following:

Before starting the administration of immunosuppressants, the prescriber should check to see if the patient has a history of VZV. Serologic testing may be useful in determining previous exposure. Patients who have no history of exposure should avoid contact with individuals with chickenpox or herpes zoster. If the patient is exposed to VZV, special care must be taken to avoid patients developing chickenpox or herpes zoster, and passive immunisation with varicella “ zoster immunoglobulin (VZIG) may be considered.

If the patient is infected with VZV, appropriate measures should be taken, which may include antiviral therapy and supportive care.

4.5 Interaction with other medicinal products and other forms of interaction

Allopurinol/ oxipurinol/ thiopurinol

Xanthine oxidase activity is inhibited by allopurinol, oxipurinol and thiopurinol which results in reduced conversion of biologically active 6^_ thioinosinic acid to biologically inactive 6-thiouric acid. When allopurinol, oxipurinol and/or thiopurinol are given concomitantly with 6 ^_ mercaptopurine or azathioprine, the dose of 6-mercaptopurine and azathioprine should be reduced to one-quarter of the original dose.

Neuromuscular blocking agents

Azathioprine can potentiate the neuromuscular blockade produced by depolarising agents such as succinylcholine and can reduce the blockade produced by non-depolarising agents such as tubocurarine. There is considerable variation in the potency of this interaction.

Warfarin

Inhibition of the anticoagulant effect of warfarin, when administered with azathioprine, has been reported.

Cytostatic/myelosuppressive agents

Where possible, concomitant administration of cytostatic drugs, or drugs which may have a myelosuppressive effect, such as penicillamine, should be avoided. There are conflicting clinical reports of interactions, resulting in serious haematological abnormalities, between Azathioprine and co-trimoxazole.

There has been a case report suggesting that haematological abnormalities may develop due to the concomitant administration of Azathioprine and captopril.

It has been suggested that cimetidine and indometacin may have myelosuppressive effects, which may be enhanced by concomitant administration of Azathioprine.

Other interactions

As there is in vitro evidence that aminosalicylate derivatives (eg. olsalazine, mesalazine or sulfasalazine) inhibit the TPMT enzyme, they should be administered with caution to patients receiving concurrent Azathioprine therapy (see Special Warnings and Special Precautions for Use).

Furosemide has been shown to impair the metabolism of azathioprine by human hepatic tissue in vitro. The clinical significance is unknown.

Vaccines

The immunosuppressive activity of Azathioprine could result in an atypical and potentially deleterious response to live vaccines and so the administration of live vaccines to patients receiving Azathioprine therapy is contra-indicated on theoretical grounds.

A diminished response to killed vaccines is likely and such a response to hepatitis B vaccine has been observed among patients treated with a combination of azathioprine and corticosteroids.

A small clinical study has indicated that standard therapeutic doses of Azathioprine do not deleteriously affect the response to polyvalent pneumococcal vaccine, as assessed on the basis of mean anti-capsular specific antibody concentration.

4.6 Fertility, Pregnancy and lactation

If you become pregnant, or are planning to become pregnant, you must contact your doctor

Immediately. Azathioprine should not be given to patients who are pregnant or likely to become pregnant. Pregnant women should be treated only if the expected benefit outweighs the possible risks to the pregnant woman and foetus.

The use of azathioprine during breast-feeding should be avoided.

4.7 Effects on ability to drive and use machines

None.

4.8 Undesirable effects

For this product there is no modern clinical documentation that can be used as support for determining the frequency of undesirable effects. Undesirable effects may vary in their incidence depending on the indication. The following convention has been utilised for the classification of frequency: Very common, ^ 1/10; common, ^ 1/100 and < 1/10; uncommon, ^ 1/1000 and < 1/100; rare, ^ 1/10000 and < 1/1000; very rare, < 1/10000.

Infection and infestations

Transplant patients receiving Azathioprine in combination with other immunosuppressants.

Very common:	Viral, fungal, and bacterial infections.
Other indications.
Uncommon:	Viral, fungal and bacterial infections.

Patients receiving Azathioprine alone, or in combination with other immunosupressants, particularly corticosteroids, have shown increased susceptibility to viral, fungal and bacterial infections, including severe or atypical infection with varicella, herpes zoster and other infectious agents (see also section 4.4 Special Warnings and Precautions for Use).

Neoplasms benign and malignant (including cysts and polyps)

Rare:	Neoplasms including non-Hodgkin's lymphomas, skin
	cancers (melanoma and non-melanoma), sarcomas
	(Kaposi's and non-Kaposi's) and uterine cervical cancer

The risk of developing non-Hodgkin's lymphomas and other malignancies, notably skin cancers (melanoma and non-melanoma), sarcomas, (Kaposi's and non-Kaposi's) and uterine cervical cancer in situ, is increased in patients who receive immunosuppressive drugs, particularly in transplant recipients receiving aggressive treatment and such therapy should be maintained at the lowest effective levels. The increased risk of developing non-Hodgkin's lymphomas in immunosuppressed rheumatoid arthritis patients compared with the general population appears to be related at least in part to the disease itself.

There have been rare reports of acute myeloid leukaemia and myelodysplasia (some in association with chromasomal abnormalities).

Blood and lymphatic system disorders

Very common:	Depression of bone marrow function; leucopenia.
Common:	Thrombocytopenia.
Uncommon:	Anaemia.
Rare:	Agranulocytosis, pancytopenia, aplastic anaemia, megaloblastic anaemia, erythriod hypoplasia.

Azathioprine may be associated with a dose-related, generally reversible, depression of bone marrow function, most frequently expressed as leucopenia, but also sometimes as anaemia and thrombocytopenia, and rarely as agranulocytosis, pancytopenia and aplastic anaemia. These occur particularly in patients predisposed to myelotoxicity, such as those with TPMT deficiency and renal or hepatic insufficiency and in patients failing to reduce the dose of Azathioprine when receiving concurrent allopurinol therapy.

Reversible, dose-related increases in mean corpuscular volume and red cell haemoglobin content have occurred in association with Azathioprine therapy. Megaloblastic bone marrow changes have also been observed but severe megaloblastic anaemia and erythroid hypoplasia are rare.

Respiratory, thorasic and mediastinal disorders

Reversible pneumonitis has been described very rarely. Gastrointestinal disorders

Rare:	Colitis, diverticulitis and bowel perforation reported in
	transplant population, severe diarrhoea in inflammatory
	bowel disease population.

A minority of patients experience nausea when first given Azathioprine. This appears to be relieved by administering the tablets after meals.

Serious complications, including colitis, diverticulitis and bowel perforation, have been described in transplant recipients receiving immunosuppressive therapy. However, the aetiology is not clearly established and high-dose corticosteroids may be implicated. Severe diarrhoea, recurring on re-challenge, has been reported in patients treated with Azathioprine for inflammatory bowel disease. The possibility that exacerbation of symptoms might be drug-related should be borne in mind when treating such patients.

Pancreatitis has been reported in a small percentage of patients on Azathioprine therapy, particularly in renal transplant patients and those diagnosed as having inflammatory bowel disease. There are difficulties in relating the pancreatitis to the administration of one particular drug, although re-challenge has confirmed an association with Azathioprine on occasions.

Hepato-biliary disorders

Uncommon:	Cholestasis and degeneration of liver function tests.
Rare:	Life-threatening hepatic damage.

Cholestasis and deterioration of liver function have occasionally been reported in association with Azathioprine therapy and are usually reversible on withdrawal of therapy. This may be associated with symptoms of a hypersensitivity reaction (see Hypersensitivity reactions).

Rare, but life-threatening hepatic damage associated with chronic administration of azathioprine has been described primarily in transplant patients. Histological findings include sinusoidal dilatation, peliosis hepatis, veno-occlusive disease and nodular regenerative hyperplasia. In some cases withdrawal of azathioprine has resulted in either a temporary or permanent improvement in liver histology and symptoms.

Skin and subcutaneous tissue disorders

Hair loss has been described on a number of occasions in patients receiving azathioprine and other immunosuppressive agents. In many instances the condition resolved spontaneously despite continuing therapy. The relationship between alopecia and azathioprine treatment is uncertain.

Immune system disorders

Uncommon:	Hypersensitivity reactions
Very rare:	Stevens-Johnson syndrome and toxic epidermal necrolysis.

Several different clinical syndromes, which appear to be idiosyncratic manifestations of hypersensitivity, have been described occasionally following administration of Azathioprine. Clinical features include general malaise, dizziness, nausea, vomiting, diarrhoea, fever, rigors, exanthema, rash, vasculitis, myalgia, arthralgia, hypotension, renal dysfunction, hepatic dysfunction and cholestasis (see Hepato-biliary disorders).

In many cases, re-challenge has confirmed an association with Azathioprine.

Immediate withdrawal of azathioprine and institution of circulatory support where appropriate have led to recovery in the majority of cases.

Other marked underlying pathology has contributed to the very rare deaths reported.

Following a hypersensitivity reaction to Azathioprine, the necessity for continued administration of Azathioprine should be carefully considered on an individual basis.

4.9 Overdose

Symptoms and signs

Unexplained infection, ulceration of the throat, bruising and bleeding are the main signs of overdosage with Azathioprine and result from bone marrow depression which may be maximal after 9 to 14 days. These signs are more likely to be manifest following chronic overdosage, rather than after a single acute overdose. There has been a report of a patient who ingested a single overdose of 7.5 g of azathioprine. The immediate toxic effects of this overdose were nausea, vomiting and diarrhoea, followed by mild leucopenia and mild abnormalities in liver function. Recovery was uneventful.

Treatment

There is no specific antidote. Gastric lavage has been used. Subsequent monitoring, including haematological monitoring, is necessary to allow prompt treatment of any adverse effects which may develop. The value of dialysis in patients who have taken an overdose of Azathioprine is not known, though azathioprine is partially dialysable.

5 PHARMACOLOGICAL PROPERTIES

5.1 Pharmacodynamic properties

Azathioprine is an imidazole derivative of 6-mercaptopurine (6-MP). It is rapidly broken down in vivo into 6-MP and a methylnitroimidazole moiety. The 6-MP readily crosses cell membranes and is converted intracellularly into a number of purine thioanalogues, which include the main active nucleotide, thioinosinic acid. The rate of conversion varies from one person to another. Nucleotides do not traverse cell membranes and therefore do not circulate in body fluids. Irrespective of whether it is given directly or is derived in vivo from azathioprine, 6-MP is eliminated mainly as the inactive oxidised metabolite thiouric acid. This oxidation is brought about by xanthine oxidase, an enzyme that is inhibited by allopurinol. The activity of the methylnitroimidazole moiety has not been defined clearly. However, in several systems it appears to modify the activity of azathioprine as compared with that of 6-MP. Determination of plasma concentrations of azathioprine or 6-MP have no prognostic values as regards effectiveness or toxicity of these compounds.

While the precise modes of action remain to be elucidated, some suggested mechanisms include:

1.    the release of 6-MP which acts as a purine antimetabolite.

2.    the possible blockade of -SH groups by alkylation.

3.    the inhibition of many pathways in nucleic acid biosynthesis, hence preventing proliferation of cells involved in determination and amplification of the immune response.

4.    damage to deoxyribonucleic acid (DNA) through incorporation of purine thio-analogues.

Because of these mechanisms, the therapeutic effect of Azathioprine may be evident only after several weeks or months of treatment.

Azathioprine appears to be well absorbed from the upper gastro-intestinal tract.

Studies in mice with [ S]-azathioprine showed no unusually large concentration in any particular tissue, and there was very little [ S]-label found in brain.

Plasma levels of azathioprine and 6-MP do not correlate well with the therapeutic efficacy or toxicity of Azathioprine.

5.2 Pharmacokinetic properties

Azathioprine is well absorbed following oral administration. After oral administration of [ S]-azathioprine, the maximum plasma radioactivity occurs at 1-2 hours and decays with a half-life of 4-6 hours. This is not an estimate of the half-life of azathioprine itself, but reflects the elimination from plasma of azathioprine and the [³⁵S]-containing metabolites of the drug. As a consequence of the rapid and extensive metabolism of azathioprine, only a fraction of the radioactivity measured in plasma is comprised of unmetabolised drug. Studies in which the plasma concentration of azathioprine and 6-MP have been determined following intravenous administration of azathioprine have estimated the mean plasma T¹/2 for azathioprine to be in the range of 6-28 minutes and the mean plasma T¹/₂ for 6-MP to be in the range 38-114 minutes after i.v. administration of the drug.

Azathioprine is principally excreted as 6-thiouric uric acid in the urine. 1-methyl-4-nitro-5-thioimidazole has also been detected in urine as a minor excretory product. This would indicate that, rather than azathioprine being exclusive cleaved by nucleophilic attack at the 5-position of the nitroimidazole ring to generate 6-MP and 1-methyl-4-nitro-5-(S-glutathionyl)imidazole. A small proportion of the drug may be cleaved between the sulphur-atom and the purine ring. Only a small amount of the dose of azathioprine administered is excreted unmetabolised in the urine.

5.3 Preclinical safety data

None provided.

6 PHARMACEUTICAL PARTICULARS

6.1 List of excipients

Starch maize BP Microcrystalline cellulose BP Lactose BP

Magnesium stearate BP

Purified talc BP

Sodium starch glycollate BP

10 DATE OF REVISION OF THE TEXT

05/02/2015