View Table: Mechanisms of Drug Interactions

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 the over-the-counter (OTC) sale of Narcan (Emergent), a nasal spray that delivers 4 mg of the opioid antagonist naloxone. Narcan nasal spray has been available by prescription since 2015 for emergency treatment of opioid overdose. Generic formulations of Narcan have also been approved; the manufacturers of these products will be required to switch them to OTC status and amend their labeling accordingly. Kloxxado, an 8-mg naloxone nasal spray, remains available only by prescription.

The Medical Letter review of Palladone (hydromorphone HCl) extended-release capsules (March 14, 2005) warned that a lethal dose could be released if the new formulation was taken with alcohol. Because of that risk, the FDA asked the manufacturer (Purdue) to withdraw the drug from the market (FDA News. July 13, 2005; FDC Reports – “The Pink Sheet” July 18, 2005; 67:3).

Percutaneous transluminal coronary angioplasty (PTCA), in which a balloon catheter distends the vessel at the site of obstruction (Medical Letter, 25:97, 1983), is now an established therapeutic option for treatment of patients with coronary artery disease, especially those with single-vessel disease. Major problems related to PTCA include acute occlusion during the procedure (usually caused by dissection), restenosis at the site of angioplasty, and inability to treat complete occlusions and long or ostial lesions. Some cardiologists have tried using lasers during PTCA to deal with these...

The FDA has approved RiVive (Harm Reduction Therapeutics), a 3-mg naloxone nasal spray, as an over-the-counter (OTC) product for emergency treatment of opioid overdose. Two 4-mg naloxone nasal spray formulations, Narcan and one of its generics, were approved for OTC sale in 2023.

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.

A once-daily extended-release (ER) oral formulation of the opioid analgesic hydromorphone hydrochloride (Palladone - Purdue Pharma) has been approved by the FDA for treatment of opioid-tolerant patients with persistent moderate to severe pain. Hydromorphone HCl, a semisynthetic congener of morphine and active metabolite of hydrocodone that has been used since the 1920s, is also available in immediate-release oral, injectable and suppository forms (Dilaudid, and others).

The FDA has approved a higher-dose injectable formulation of the opioid antagonist naloxone (Zimhi – Adamis) for emergency treatment of opioid overdose. A single IM or SC injection of the new formulation delivers 5 mg of naloxone; injectable formulations that deliver 0.4 mg or 2 mg of the drug have been available for years. Naloxone is also available in intranasal formulations for the same indication (see Table 1).

Recent reports of inappropriate use and diversion of OxyContin tablets have prompted Purdue Pharma to include a "Black Box Warning"in the product labeling to call attention to the potential for abuse and to reinforce the FDA-approved indication "...for the management of moderate to severe pain when a continuous, around-the-clock analgesic is needed for an extended period of time..."