Ibrutinib for chronic lymphocytic leukaemia and mantle cell lymphoma

The approval is based on a single-arm phase II trial¹ and a comparative phase III trial with ofatumumab.² Most enrolled patients had chronic lymphocytic leukaemia with only 5% having small lymphocytic lymphoma. Approximately a third of those in each trial had an abnormal chromosome 17 (17p deletion), which is associated with a poorer prognosis.

Patients were given daily ibrutinib until their disease progressed or they developed unacceptable adverse effects. In the phase II trial, patients were given 420 mg or 840 mg. Overall, 71% of patients responded to treatment (Table 1). These were mainly partial responses. At 26 months, the progression-free survival rate was estimated at 75% and overall survival was 83%.

In the phase III trial, ibrutinib 420 mg significantly improved rates of progression-free survival, overall survival and treatment responses compared to ofatumumab (Table 1).² The efficacy of ibrutinib was similar in patients with and without the 17p deletion.^1,2

The approval of daily ibrutinib 560 mg for mantle cell lymphoma is based on an open-label, uncontrolled phase II trial of 111 patients with relapsed or refractory disease.³ Over two-thirds of patients responded to ibrutinib – 23 patients had a complete response and 35 had a partial response (Table 2). The response rate seemed to be independent of age, previous bortezomib exposure and prognosis at baseline. The estimated median duration of response was 17.5 months and the estimated median progression-free survival was just under 14 months.

In a cohort of 357 patients, 6% discontinued treatment because of an adverse event (including infection and subdural haematoma). The most common adverse events were diarrhoea, musculoskeletal pain, upper respiratory tract infection, bruising, rash, nausea, fever, neutropenia and constipation. These were reported in at least 20% of patients. Anaemia, neutropenia, pneumonia and thrombocytopenia were the most common serious adverse effects (grade 3 or 4) and occurred in 5% or more of patients.

In total, 26 patients died during the trials. Apart from progressive disease, causes included pneumonia (5 patients), sepsis (2 patients), secondary malignancy (2 patients), cardiac arrest (1 patient) and hypovolaemic shock (1 patient).

Bleeding-related adverse events were common with ibrutinib and ranged from bruising and nosebleeds to blood in the urine, gastrointestinal bleeding and intracranial haemorrhage. Warfarin, fish oil and vitamin E should not be given concomitantly with ibrutinib.

Atrial fibrillation is a risk with ibrutinib, particularly during acute infections or in people with a history of atrial fibrillation or other cardiac risk factors. Regular cardiac monitoring is recommended. Alternatives to ibrutinib should be considered in patients who need oral anticoagulants.

Blood counts should be monitored every month as severe neutropenia, thrombocytopenia and anaemia can occur. Skin cancers have been reported with ibrutinib so regular skin examination is important.

Ibrutinib caused a transient increase in lymphocyte count at the beginning of treatment in 75% of patients with chronic lymphocytic leukaemia and 35% of patients with mantle cell lymphoma. Lymphocytosis often occurred at the same time as a reduction in lymph node and spleen size and is thought to be a pharmacodynamic effect unrelated to progressive disease. Leukostasis (clumping of white blood cells) was occasionally reported and may be related to an increase in circulating lymphocytes. It can cause local hypoxaemia and bleeding which can present as headache, blurred vision, transient ischaemia, cerebrovascular accident and dyspnoea. Patients should be monitored closely and ibrutinib may need to be interrupted if this occurs.

Ibrutinib is rapidly absorbed after oral administration and metabolised in the liver by cytochrome P450 (CYP) 3A4. The half-life is 4−6 hours and metabolites are eliminated in the faeces (90%) and urine (10%).

Co-administration of moderate or strong CYP3A4 inhibitors such as ketoconazole, clarithromycin, erythromycin or verapamil should be avoided. If they are needed, the ibrutinib dose should be reduced to 140 mg or interrupted for up to a week. Avoid grapefruit and Seville oranges as they can inhibit CYP3A4.

Strong CYP3A4 inducers and drugs that increase the pH of the stomach can decrease ibrutinib concentrations and are not recommended. St John’s wort should also be avoided. As ibrutinib could theoretically inhibit intestinal P-glycoprotein, substrates of this transporter with a narrow therapeutic index (e.g. digoxin) should be taken at least six hours before or after the ibrutinib dose.

Ibrutinib offers another option for people with chronic lymphocytic leukaemia or mantle cell lymphoma, particularly those who have relapsed after previous treatments. Adverse effects are common and sometimes severe so patient monitoring is very important with this drug.

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