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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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.

On February 27, 2021, the FDA issued an Emergency Use Authorization (EUA) for the Johnson & Johnson adenovirus-based vaccine for prevention of COVID-19 in persons ≥18 years old. It is the third COVID-19 vaccine to become available in the US and the first to require only a single dose. Two-dose mRNA-based vaccines manufactured by Pfizer-BioNTech and Moderna received EUAs in December 2020.

The US Advisory Committee on Immunization Practices (ACIP) recommends routine use of the following vaccines in adults residing in the US: influenza, tetanus/diphtheria alone (Td) and in combination with acellular pertussis (Tdap), measles/mumps/rubella (MMR), varicella (VAR), herpes zoster (RZV; ZVL), human papillomavirus (HPV), and pneumococcal conjugate (PCV13) and polysaccharide (PPSV23) vaccines. For adults with certain medical conditions or occupational, behavioral, or other risk factors, hepatitis A (HepA), hepatitis B (HepB), meningococcal (MenACWY; MenB), and Haemophilus influenzae type b (Hib) vaccines are also recommended. Recommendations for vaccination against seasonal influenza and vaccination of travelers are reviewed separately.

Treatment of atrial fibrillation includes anticoagulation, rate control, and rhythm control. US guidelines were recently updated.

Drugs available for treatment of chronic hypertension and their dosages, adverse effects, and costs are listed in the tables. Treatment of hypertensive urgencies and emergencies is not discussed here.

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.

Nonopioid drugs can be used in the treatment of many nociceptive and neuropathic pain conditions. Use of opioids for pain will be reviewed in a future issue.

The tables in this article list drugs used for treatment of cancer in the USA and Canada and their major adverse effects. The choice of drugs in Table I is based on the opinions of Medical Letter consultants. Some drugs are listed for indications for which they have not been approved by the US Food and Drug Administration. In some cases, such as elderly patients or those with many co-morbid illnesses, the regimen of choice might not be suitable. For many of the cancers listed, surgery and/or radiation therapy may be the treatment of choice or may also be part of the management. Anticancer drugs and their adverse effects are listed in Table II on page 46. A partial list of brand names appears on page 52.

The antiplatelet drug clopidogrel (Plavix, and others) reduces major cardiovascular events, but can cause bleeding. Proton pump inhibitors (PPIs) are often used with clopidogrel to prevent gastrointestinal bleeding, however, some evidence suggests that PPIs may interfere with the activation of clopidogrel and diminish its antiplatelet effect. FDA-approved labeling recommends avoiding concurrent use of the PPIs omeprazole and esomeprazole with clopidogrel.