Mary Ross, R.Ph., M.B.A.
Peer Review Status: Internally Reviewed
Almost all patients receiving peginterferon alfa-2b experience one or more side effects. However, most events resolve after discontinuing peginterferon. The most common adverse events include psychiatric adverse events (57%), "flu-like" symptoms (50%), injection site disorders (47%), and alopecia. One percent of patients experience suicidal behavior. Other adverse effects reported include headache, fatigue, rigors, nausea, anorexia, diarrhea, musculoskeletal pain, and insomnia. Serious adverse effects that occur at a frequency <1% include cardiomyopathy, myocardial infarction, retina ischemia, retinal vein thrombosis, transient ischemic attack, supraventricular arrhythmias, loss of consciousness, neutropenia, infection, autoimmune thrombocytopenia, hyperthyroidism, rheumatoid arthritis, interstitial nephritis, lupus-like syndrome, aggravated psoriasis, and urticaria.
Peginterferon alfa-2b (~ 1 mcg/kg) should be administered subcutaneously once weekly, on the same day each week, for one year. In patients who develop serious adverse reactions, the dose of peginterferon alfa-2b should be reduced to one-half the starting dose or discontinued until the reaction has abated or lessened. In patients with persistent or recurrent adverse reactions peginterferon alfa-2b should be permanently discontinued.
Although peginterferon alfa-2b has been studied in combination with ribavirin, an antiviral drug, the combination therapy is not currently approved by the FDA. Ribavirin is only available in combination with non-pegylated interferon alfa-2b in a kit called REBETRON®. Oral ribavirin capsules cannot legally be separated and dispensed independently. Peginterferon alfa-2b injection is commercially available as single-dose vials in four strengths - 100, 160, 240, and 300 mcg/ml.
Calcium Carbonate and Hypothyroidism
Levothyroxine, a thyroid hormone, has several documented drug interactions that can lead to either an increase or decrease in therapeutic effect. Recently, there have been reports of exacerbation of hypothyroidism in patients taking levothyroxine and calcium carbonate concurrently.
Two cases have been reported in which TSH levels were found to be elevated after the patients began taking calcium carbonate concurrently with levothyroxine. One of these patients also experienced symptoms of hypothyroidism. After the patients’ medication schedules were changed to separate administration of these two medications by at least four hours, TSH levels returned to normal.
It appears that calcium carbonate reduces levothyroxine absorption and increases serum TSH levels when both medications are taken simultaneously. To ensure maximum absorption, levothyroxine should be taken at least an hour before breakfast or two hours after eating any meal. Conversely, calcium is better absorbed with meals. Therefore, administration of levothyroxine and calcium carbonate should be separated by at least four hours. Patients should be counseled to be consistent with their schedule for taking levothyroxine and calcium supplements on a daily basis.