Drug Interactions between dexamethasone / ketorolac / moxifloxacin and thalidomide

MONITOR CLOSELY: Coadministration of thalidomide with glucocorticoids and/or antineoplastic agents in the treatment of malignancy may potentiate the risk of thromboembolism. The exact mechanism is unknown but likely multifactorial. Thalidomide alone has been associated with the development of deep-vein thrombosis (DVT), and malignancy itself is also a common cause. In a study of 100 patients receiving induction chemotherapy (combinations of dexamethasone, vincristine, doxorubicin, cyclophosphamide, etoposide, and cisplatin) for multiple myeloma, the addition of thalidomide was associated with an increased incidence of DVT compared to chemotherapy without thalidomide (28% vs. 4%). Administration of thalidomide was safely resumed in 75% of patients after initiation of appropriate anticoagulation therapy. In another study, 9 of 21 (43%) patients with metastatic renal cell carcinoma (RCC) receiving gemcitabine, 5-FU, and thalidomide developed venous thromboembolism, including one case of fatal cardiac arrest. This rate is substantially higher than the 3% rate observed in a group of 125 patients previously treated at the same institution with similar regimens of gemcitabine and 5-FU but without thalidomide. It is also higher than the 9% rate (12 of 140 patients) the investigators found in a review of published data from five RCC trials that used thalidomide therapy without concomitant cytotoxic therapy. Another study found a significant association of DVT with exposure to doxorubicin in patients receiving thalidomide. Specifically, 31 of 192 (16%) multiple myeloma patients treated with DT-PACE (a regimen of dexamethasone, thalidomide, cisplatin, doxorubicin, cyclophosphamide, and etoposide) developed DVT, while only 1 of 40 (2.5%) did so on DCEP-T (similar to DT-PACE but without doxorubicin). The time to DVT was also significantly decreased with doxorubicin exposure. In a pooled analysis of 39 prospectively monitored clinical trials involving 1784 thalidomide-treated patients, the incidence of thromboembolism was 5% when thalidomide was used as a single agent, 13% when combined with corticosteroids (8% to 26% has been reported in individual studies with dexamethasone), and 17% when combined with chemotherapy. Among thalidomide-treated patients with multiple myeloma, thromboembolism rates ranged from a low of 1/30 among those treated with concomitant cyclophosphamide, etoposide, and cisplatin to a high of about 1/3 in those treated with doxorubicin-containing regimens.

MANAGEMENT: Close monitoring for DVT or pulmonary embolism is recommended in patients who require thalidomide therapy in combination with glucocorticoids and/or cytotoxic agents. Patients should be advised to seek medical attention if they develop potential signs and symptoms of thromboembolism such as chest pain, shortness of breath, and pain or swelling in the arms or legs. Prophylaxis with anticoagulants such as low-molecular weight heparins or warfarin may be appropriate, but the decision to take thromboprophylactic measures should be made after careful assessment of underlying risk factors. If a thromboembolic event occurs during therapy with thalidomide, treatment must be discontinued and standard anticoagulation therapy started. Once anticoagulation is stabilized and complications of the thromboembolic event under control, thalidomide may be restarted at the original dose if benefit is deemed to outweigh the risks. Anticoagulation therapy should be continued during the remaining course of thalidomide treatment.

MONITOR CLOSELY: Concomitant administration of corticosteroids may potentiate the risk of tendinitis and tendon rupture associated with fluoroquinolone treatment. The mechanism is unknown. Tendinitis and tendon rupture have most frequently involved the Achilles tendon, although cases involving the rotator cuff (the shoulder), the hand, the biceps, and the thumb have also been reported. Some have required surgical repair or resulted in prolonged disability. Tendon rupture can occur during or up to several months after completion of fluoroquinolone therapy.

MANAGEMENT: Caution is recommended if fluoroquinolones are prescribed in combination with corticosteroids, particularly in patients with other concomitant risk factors (e.g., age over 60 years; recipient of kidney, heart, and/or lung transplant). Patients should be advised to stop taking the fluoroquinolone, avoid exercise and use of the affected area, and promptly contact their physician if they experience pain, swelling, or inflammation of a tendon. In general, fluoroquinolones should only be used to treat conditions that are proven or strongly suspected to be caused by bacteria and only if the benefits outweigh the risks.

MONITOR: The combined use of corticosteroids and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the potential for serious gastrointestinal (GI) toxicity, including inflammation, bleeding, ulceration, and perforation. In a large, case-control study of elderly patients, those who used corticosteroids and NSAIDs concurrently had an estimated relative risk (RR) for peptic ulcer disease and GI hemorrhage of 14.6 compared to those who used neither. Corticosteroid use was associated with a doubling of the risk (estimated RR = 2.0), but the risk was confined to those who also used NSAIDs. It is possible that both categories of agents are ulcerogenic and have additive effects on the GI mucosa during coadministration. Some investigators have also suggested that the primary effect of corticosteroids in this interaction is to delay healing of erosions caused by NSAIDs rather than cause de novo ulcerations.

MANAGEMENT: Caution is advised if corticosteroids and NSAIDs are used together, especially in patients with a prior history of peptic ulcer disease or GI bleeding and in elderly and debilitated patients. During concomitant therapy, patients should be advised to take the medications with food and to immediately report signs and symptoms of GI ulceration and bleeding such as severe abdominal pain, dizziness, lightheadedness, and the appearance of black, tarry stools. The selective use of prophylactic anti-ulcer therapy (e.g., antacids, H2-antagonists) may be considered.

MONITOR: Coadministration with nonsteroidal anti-inflammatory drugs (NSAIDs) may potentiate the risk of central nervous system toxicity sometimes associated with fluoroquinolone use. The interaction has been reported most often with enoxacin. It may occur with other fluoroquinolones as well, but is poorly documented. The exact mechanism of interaction is unknown. Some investigators suggest that the piperazine ring of fluoroquinolones may inhibit the binding of gamma-aminobutyric acid (GABA) to brain receptors and that NSAIDs may synergistically add to this effect. Patients with a history of seizures may be at greater risk.

MANAGEMENT: Clinical monitoring for signs of CNS stimulation such as tremors, involuntary muscle movements, hallucinations, or seizures is recommended if fluoroquinolone antibiotics are prescribed in combination with NSAIDs.

MONITOR: Thalidomide can cause peripheral neuropathy, and concurrent use of other agents that are also associated with this adverse effect can potentiate the risk and/or severity of nerve damage. Peripheral neuropathy is a common, potentially severe side effect of thalidomide that may be irreversible. The condition generally occurs following chronic use over a period of months, although there have also been reported cases following relatively short-term use. The median time to first neuropathy event was 42.3 weeks in one phase 3 study. Occasionally, symptoms may occur some time after thalidomide treatment has been discontinued. The incidence of neuropathy requiring thalidomide discontinuation, dosage reduction, or interruption increases with cumulative dose and duration of therapy.

MANAGEMENT: Caution is advised if thalidomide is used in combination with other neurotoxic agents. All patients treated with thalidomide should be examined at monthly intervals for the first three months of therapy and periodically thereafter to detect early signs of neuropathy such as burning, tingling, pain, or numbness in the hands and feet. Electrophysiological testing may be performed at baseline and every six months during therapy to detect asymptomatic neuropathy. Consideration should be given to immediate discontinuation of thalidomide in patients who develop peripheral neuropathy to limit further damage. Symptoms may improve or return to baseline in some patients upon discontinuation of thalidomide, although the complete time course of this toxicity has not been fully characterized. If necessary, therapy should generally be reinstituted only after neuropathy returns to baseline status. A dosage reduction of thalidomide may be required as clinically indicated.

MONITOR: Thalidomide can cause bradycardia and may potentiate the risk of torsade de pointes arrhythmia associated with the use of drugs that prolong the QT interval. Cases of bradycardia have been associated with thalidomide use, some requiring medical interventions. The clinical significance and underlying aetiology of the bradycardia observed with thalidomide treatment have not been established.

MANAGEMENT: Because bradycardia is a risk factor for torsade de pointes arrhythmia, caution is advised when thalidomide is used with drugs that can prolong the QT interval or induce torsade de pointes arrhythmia. Patients should be monitored for bradycardia, atrioventricular block and syncope, and advised to seek medical attention if they experience dizziness, lightheadedness, fainting, shortness of breath, or slow or irregular heartbeat. A dose reduction of thalidomide or discontinuation may be required.