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.

Update on niacin - Results from the HPS2-THRIVE study

In a previous blog post, niacin for dyslipidemia, we discussed the concerns regarding niacin's lack of improvement of clinically meaningful endpoints in addition to some of its adverse effects and how to deal with them.  Recently, final results of the HPS2-THRIVE study have been published.  Here are a few highlights of the results of this study.

More cardiovascular safety data for azithromycin

There has been concern in recent years regarding cardiovascular risk in patients using azithromycin which I discussed in an earlier post found here.

A recent study in JAMA further examined cardiovascular risk and mortality in a retrospective review of more than 60,000 patients in the VA Health System.  This study specifically identified patients with a diagnosis of pneumonia who were treated with antibiotics including azithromycin compared to other guideline-concordant antibiotics.  Their outcomes of measure were 30-day mortality, 90-day mortality, any cardiovascular event, myocardial infarction, heart failure, or cardiac arrhythmias.  The mean patient age was 78 years old and comorbid conditions were fairly common (35% with diabetes, 52% with COPD, 26% with heart failure).

Converting systemic corticosteroids

Let’s start with a patient case.  A patient is being treated with methylprednisolone 20 mg IV q6 hours for some inflammatory process and is clinically improving.  She can now tolerate oral medication and we would like to simplify her dosing regimen to transition to outpatient care. How can we manage her methylprednisolone dosing?

One issue that comes up frequently on the internal medicine service is the potency of different corticosteroids relative to each other and the correct way to convert the doses. Below is the chart that shows the equivalent dose of the various agents we commonly use.

Piperacillin-tazobactam (Zosyn) extended-infusion dosing

Let's start with a patient case.  A 70 year old male patient is admitted to the hospital for a diabetic foot infection.  He has a past medical history of HTN, hyperlipidemia, CKD, gout, and obesity.  He weighs 100 kg and has a Scr of 2.8 mg/dL.  You recall that piperacillin-tazobactam is indicated for diabetic foot infections and are deciding what dosing regimen should be started.  Upon consulting Lexicomp or Micromedex, you will find that piperacillin-tazobactam has a wide dosing range depending on the type of infection being treated in addition to the extent of renal impairment.  Recommended doses range from 2.25 g to 4.5 g intravenously every 6 to 12 hours depending on these factors, leaving much room for uncertainty in many cases.

The following will briefly discuss piperacillin-tazobactam, its pharmacokinetics and pharmacodynamics, and how computer modeling has generated new dosing strategies.  If you just want a simplified way of dosing this medication, feel free to skip down to the 'Take home pearls' at the bottom of the article.

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?