The questionable role of digoxin in atrial fibrillation

Let's start with a patient case.  An elderly patient is admitted to the hospital with complaints of intermittent shortness of breath and a fluttering feeling in his chest.  He has a past medical history of hypertension, atrial fibrillation, and heart failure (EF 6 months ago = 30%).  He is currently taking ramipril 10 mg daily, metoprolol succinate 50 mg daily, and warfarin 6 mg M/W/F and 3 mg the rest of the week.  Other findings include a BP of 106/56 mm Hg, a creatinine clearnace of 40 mL/minute, an INR of 1.28, and atrial fibrillation with a heart rate in the 80s but a rapid ventricular response intermittently into the 120s bpm.  What should be recommended at this time to control this patient's atrial fibrillation and what is the role of digoxin, if any?

Risk of serotonin toxicity with procarbazine

A question recently came up regarding the risk of serotonin toxicity from a drug interaction between procarbazine and a number of different serotonergic agents.  When checking for an interaction between procarbazine and medications like sertraline, duloxetine, nortriptyline, and tramadol on resources such as Lexicomp and Micromedex, the interactions are listed inconsistently, from no interaction to contraindicated, with varying degrees of evidence, from theoretical to established.

Doxycycline food and OTC interactions

Since it's the time of year again when Lyme disease is a concern for patients in many parts of the United States, I thought it would be good to discuss one issue concerning doxycycline.  Doxycycline is a preferred oral agent for Lyme disease and many of its complications.  It is recommended for a variety of situations when Lyme disease is suspected or confirmed such as1:

• Single dose prophylaxis after tick bite
• Erythema migrans
• Cranial nerve palsy
• Carditis
• Lyme arthritis
• Acrodermatitis chronica atrophicans
• Co-infection with human granulocytic anaplasmosis

When ordering or verifying the typical adult dose of 100 mg orally twice daily, an alert may pop up for an interaction with several drugs including iron, calcium, magnesium, aluminum, or bismuth subsalicylate.  The proposed mechanism for this interaction is chelation in the gastrointestinal tract, compounded by the enterohepatic circulation of doxycycline.  Let's look at some of the data regarding these interactions.

Dealing with statin-induced myopathy

Let’s start with a patient case.  An 82 year old female patient presents to clinic with complaints of weakness in her lower extremities. She describes her weakness as symmetrical heaviness and identifies some stiffness and cramping. Other causes of her complaints are ruled out except for her medications. Her hyperlipidemia is currently being managed with simvastatin 40 mg orally daily and niacin ER 1 g orally daily. What are our options for dealing with suspected statin-induced myopathy?

Drug interaction between warfarin and acetaminophen?

The management of anticoagulant therapy is an important component of the treatment of various disease states. Maintaining the narrow therapeutic range required for the safe and effective use of warfarin is essential to avoid suboptimal dosing and adverse events. Numerous drug interactions with warfarin are present due to alterations in absorption, distribution, and metabolism.  The severity of interactions with warfarin varies greatly and dictates very different recommendations for management and monitoring. In the most insignificant interactions, no change in dosage or monitoring is necessary, whereas some interactions require a significant empiric reduction in warfarin dosage and close monitoring of INR.

Interaction between linezolid (Zyvox®) and SSRIs

Linezolid is an oxazolidinone antibiotic (see more about its mechanism here) that is active against many gram-positive organisms including those that are resistant to multiple other agents such as methicillin-resistant staphylococci, penicillin-resistant streptococci, and vancomycin-resistant enterococci.  Linezolid is also a weak, reversible, inhibitor of monoamine oxidase (MAO), predominantly MAO-A, which is responsible for the metabolism of neurotransmitters such as serotonin, in the brain.  This effect has led to an increased risk of serotonin syndrome in patients taking other medications that increase serotonergic tone.  SSRIs fall in this category as they increase synaptic serotonin concentrations by preventing transport into the presynaptic neuron.  They are commonly prescribed for numerous psychiatric conditions. Due to the high prevalence of both depressive disorders and nosocomial infections in patients with chronic medical illnesses, this medication combination may be encountered in the hospital setting.  Though case reports are few, deaths have been reported due to serotonin syndrome and a Food and Drug Administration Safety Alert was issued in 2011 specifically warning about the linezolid-SSRI interaction.