The FDA has approved isavuconazonium sulfate (Cresemba – Astellas) for intravenous and oral treatment of invasive aspergillosis and invasive mucormycosis in adults. Isavuconazonium sulfate is a prodrug of isavuconazole, a broad-spectrum triazole antifungal.

The FDA has approved an IV formulation of the antifungal drug posaconazole (Noxafil - Merck) for prophylaxis of Aspergillus and Candida infections in adults at high risk for these infections, such as those with prolonged neutropenia. Posaconazole is also available as delayed-release tablets and an oral suspension.

With activity against Aspergillus and Candida, posaconazole has an antifungal spectrum similar to that of voriconazole (Vfend, and generics), but unlike voriconazole it is also active against many species of Mucorales (formerly called Zygomycetes), such as Mucor and Rhizopus. Posaconazole has variable activity against Fusarium spp. and Scedosporium spp.1

Fever, diarrhea, nausea, vomiting, rash, headache, fatigue, hypokalemia, QT interval prolongation, and abnormal liver function have been reported with posaconazole. Arrhythmias, toxic epidermal necrolysis, angioedema, and anaphylaxis have occurred rarely.

Posaconazole is primarily metabolized via UDP glucuronidation; it is also a substrate of P-glycoprotein (P-gp). Drugs that inhibit or induce these clearance pathways may alter serum concentrations of posaconazole. Posaconazole is a strong inhibitor of CYP3A4 and may increase serum concentrations of drugs that are primarily metabolized by this pathway.2 Taking posaconazole with other drugs that prolong the QT interval (www.crediblemeds.org), especially those metabolized by CYP3A4, may increase the risk of QT interval prolongation.

The new formulation of posaconazole is available in 300 mg/16.7 mL vials. The recommended dosage is 300 mg administered intravenously over 90 minutes twice on day 1 and once daily thereafter. To avoid accumulation of the vehicle, patients with moderate or severe renal impairment should not receive IV posaconazole. One vial of Noxafil costs $530.50.3

1. Antifungal drugs. Treat Guidel Med Lett 2012; 10:61.
2. Inhibitors and inducers of CYP enzymes and P-glycoprotein. Med Lett Drugs Ther 2013; 55:e44.
3. Approximate WAC. WAC = wholesaler acquisition cost or manufacturer’s published price to wholesalers; WAC represents a published catalogue or list price and may not represent an actual transactional price. Source: AnalySource® Monthly. January 5, 2015. Reprinted with permission by First Databank, Inc. All rights reserved. ©2015. www.fdbhealth.com/policies/drug-pricing-policy.

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The treatment of atrial fibrillation includes anticoagulation, rate control, and rhythm control. New US guidelines for the management of atrial fibrillation have recently been published.

The drugs of choice for treatment of fungal infections are listed in the table that begins on page 62. Some of the indications and dosages recommended here have not been approved by the FDA. More detailed guidelines for some of these infections are available online from the Infectious Diseases Society of America (www.idsociety.org).

The FDA has announced changes in the labeling of simvastatin to reduce the risk of myopathy. These changes include limiting the use of the 80-mg maximum dose to patients who have been taking it for 12 months or more without evidence of myopathy and new recommendations for use of simvastatin with other drugs. Simvastatin is available alone (Zocor, and others) and in combination with ezetimibe (Vytorin) and with niacin (Simcor).

The drugs of choice for treatment of some fungal infections are listed. Some of the indications and dosages recommended here have not been approved by the FDA. More detailed guidelines are available online from the Infectious Diseases Society of America (www.idsociety.org).

Many drugs can cause psychiatric symptoms, but a causal connection is often difficult to establish. Psychiatric symptoms that emerge during drug treatment could also be due to the underlying illness, previously unrecognized psychopathology, or psychosocial factors. The withdrawal of some drugs can cause symptoms such as anxiety, psychosis, delirium, agitation or depression.

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A recent letter to the editor of the Annals of Internal Medicine documented a single case of myopathy apparently due to an interaction between simvastatin (Zocor, and others) and green tea. Since it became available generically, simvastatin has surpassed atorvastatin (Lipitor) as the best selling statin. As such, it is probably the most common cause of statin-induced myopathy, which is often a result of drug interactions.

A reader expressed disappointment that our recent listing of “Some Warfarin Drug Interactions”1 did not include acetaminophen. Perhaps it should have. Acetaminophen can increase the anticoagulant effect of warfarin, particularly with continued use, but it does so inconsistently. The mechanism of this interaction has not been established, but may be related to an acetaminophen metabolite inhibiting vitamin K-epoxide reductase, the target for warfarin’s anticoagulant effect.2

Patient susceptibility varies, possibly on a genetic basis; occasional use of acetaminophen generally has little or no effect on the international normalized ratio (INR) in patients on chronic warfarin therapy, but in some, even a few grams of the drug may cause a dramatic increase in INR. One study in healthy subjects found no effect of acetaminophen 4 g per day for 2 weeks, while another study in patients with the same acetaminophen dose for the same period of time found a moderate increase in INR.3,4 It might be prudent to monitor INR in patients on chronic warfarin therapy more closely than usual when they take more than 2 g per day of acetaminophen for more than a few days.

1. Pharmacogenetic-based dosing of warfarin. Med Lett Drugs Ther 2008; 50:39.
2. HH Thijssen et al. Paracetamol (acetaminophen) warfarin interaction: NAPQI, the toxic metabolite of paracetamol, is an inhibitor of enzymes in the vitamin K cycle. Thromb Haemost 2004; 92:797.
3. D Kwan et al. The effects of acetaminophen on pharmacokinetics and pharmacodynamics of warfarin. J Clin Pharmacol 1999; 39:68.
4. I Mahe et al. Paracetamol: A haemorrhagic risk factor in patients on warfarin. Br J Clin Pharmacol 2005; 59:371.

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Warfarin sodium (Coumadin, and others) and other coumarin anticoagulants prevent thrombosis, but patient response is highly variable and overanticoagulation can lead to hemorrhage. Genotyping patients for single nucleotide polymorphisms (SNPs) that affect coumarin metabolism and sensitivity may help clinicians estimate the therapeutic warfarin dose. The FDA has added a note to warfarin labeling recommending lowrange doses for patients with such genetic variations. Commercial tests for these variants are now available and cost about $500 per test.

The drugs of choice for treatment of some fungal infections are listed in the tables. Some of the indications and dosages recommended here have not been approved by the FDA. Other guidelines are available from the Infectious Diseases Society of America (www.idsociety.org).

Posaconazole (Noxafil - Schering-Plough), an oral azole antifungal with a chemical structure similar to that of itraconazole (Sporanox), has been approved by the FDA to prevent Candida and Aspergillus infections in severely immunocompromised patients and for treatment of oropharyngeal candidiasis. It is likely also to be used off-label for treatment of other fungal infections, including those caused by Mucor and other Zygomycetes.

The FDA recently cleared the AmpliChip CYP450 Test (Roche), which analyzes blood-derived DNA to detect genetic variations in the activity of cytochrome P450 (CYP) enzymes CYP2D6 and CYP2C19 and determines the metabolizer status of the patient. The test is intended to help guide clinicians in prescribing individualized drug therapy. About 25% of all drugs, including many antidepressants and antipsychotics, are substrates of either CYP2D6 or CYP2C19. The test is being promoted initially to psychiatrists.

Serious adverse interactions between drugs continue to be reported. Many of these are due to inhibition or induction of cytochrome P450 (CYP) enzymes, particularly CYP3A4. CYP3A is thought to be involved in the metabolism of more than 50 percent of currently prescribed drugs.2 CYP3A4, which is more abundantly expressed than CYP3A5, accounts for most CYP3A activity in vivo.

Micafungin sodium (Mycamine - Astellas), the second echinocandin antifungal to become available in the US, has been approved by the FDA for intravenous treatment of esophageal candidiasis and prophylaxis of invasive Candida infections in patients undergoing hematopoietic stem cell transplantation (HSCT).

The drugs of choice for treatment of some fungal infections are listed in the table that begins on page 8. Some of the indications and dosages recommended here have not been approved by the FDA.

Changes caused by one drug in the absorption, distribution, metabolism or excretion of another may lead to a pharmacokinetic adverse drug interaction (DN Juurlink et al, JAMA 2003; 289:1652). Additive drug interactions, such as vasodilation caused by both sildenafil (Viagra) and nitrates, can also have adverse effects.

Voriconazole (Vfend -- Pfizer), an antifungal triazole structurally related to fluconazole (Diflucan) with a spectrum of action similar to that of itraconazole, has been approved by the FDA for primary treatment of invasive aspergillosis and for refractory infection with Scedosporium apiospermum (the asexual form of Pseudallescheria boydii) or Fusarium spp.