The FDA has approved the use of ambrisentan (Letairis) and tadalafil (Adcirca) together for treatment of pulmonary arterial hypertension (PAH). It is the first 2-drug regimen to be approved for this indication.

The FDA has approved selexipag (Uptravi – Actelion), an oral selective prostacyclin IP receptor agonist, for treatment of pulmonary arterial hypertension (PAH). Treprostinil (Orenitram), an oral prostacyclin analog, was approved earlier for this indication.

The FDA has approved macitentan (ma" si ten' tan; Opsumit – Actelion), for oral treatment of pulmonary arterial hypertension (PAH). Macitentan is the second nonselective endothelin receptor antagonist approved for PAH. It is a derivative of bosentan (Tracleer), which is also manufactured by Actelion, and is scheduled to become available generically in 2015. Riociguat (Adempas), another new drug for this indication, will be reviewed in a future issue. Volibris

The ability of grapefruit juice to increase serum concentrations of drugs was first discovered during a study of the effect of ethanol on felodipine (Plendil) pharmacokinetics. Double-strength grapefruit juice used to disguise the taste of ethanol resulted in higher than expected serum concentrations of felodipine (DG Bailey et al, Clin Invest Med 1989; 12:357).

Sexual complaints related to desire, arousal, orgasm and painful intercourse are common in women. Since the last Medical Letter article on this subject, some new information has become available.

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.

The FDA has approved avanafil (Stendra – Vivus), an oral phosphodiesterase type-5 (PDE5) inhibitor, for treatment of erectile dysfunction. It is the fifth PDE5 inhibitor to be approved for this indication. Advertisements on Stendra’s website imply that it has a faster onset of action than other PDE5 inhibitors.

Amprenavir is the fifth protease inhibitor to become available for treatment of HIV infection. It was approved by the FDA for use with other drugs in the treatment of HIV-infected adults and children at least four years old.

BiDil (NitroMed), a fixed-dose combination of isosorbide dinitrate and hydralazine, was approved by the FDA for adjunctive use in the treatment of heart failure in black patients.Both drugs are oral vasodilators that have been used together off-label for many years to treat heart failure in patients not responding to other drugs.

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.