Analgesics: Nursing pharmacology

Analgesics, also commonly known as painkillers, are medications primarily used to relieve pain, such as a headache, muscle and neuropathic pain, as well as pain related to trauma and fractures.

Analgesics can be subdivided into two main groups: non-opioid analgesics, and opioid analgesics. Keep in mind though that there are a number of other medications that primarily serve other purposes, but can be used as analgesics.

These medications include antidepressants like amitriptyline, anticonvulsants like gabapentin, and corticosteroids like dexamethasone, as well as local anesthetics like lidocaine.

Now, let’s start with non-opioid analgesics, which include non-steroidal anti-inflammatory drugs or NSAIDs, and acetaminophen. NSAIDs inhibit the enzyme cyclooxygenase or COX, both in the central nervous system and peripheral tissues.

Now, there are two types of COX enzymes. The first one is called COX-1, which is indirectly involved in platelet aggregation, production of protective mucus in the stomach and vasodilation of the renal vasculature.

On the flip side, COX-2 is only active in inflammatory cells and vascular endothelium during inflammation, and is involved in the production of small pro-inflammatory compounds like prostaglandins.

Now, a very commonly used NSAID is acetylsalicylic acid, often referred to as aspirin, which is taken orally. On the other hand, non-aspirin NSAIDs can be further classified as non-selective COX inhibitors that act on both COX-1 and COX-2, like ibuprofen, naproxen and ketorolac; and selective COX-2 inhibitors, like celecoxib.

Non-aspirin NSAIDs are most often administered orally, but some can also be given intramuscularly, intravenously, topically, or rectally.

Now the most important side effects of NSAIDs include gastrointestinal problems, such as gastritis, gastric ulcers, or even bleeding, and that’s a boxed warning!

Additionally, chronic use of NSAIDs can impair normal blood flow in the kidneys and may increase the risk of hyperkalemia, nephropathy, or renal failure.

It’s important to note that these side effects are less frequent with selective COX-2 inhibitors. Other side effects that can occur in clients taking NSAIDs include headache, drowsiness and dizziness, as well as severe hypersensitivity reactions, such as anaphylaxis and Stevens-Johnson Syndrome.

NSAIDs should not be used during the third trimester of pregnancy, as well as in clients with renal or hepatic impairment. Also, NSAIDs should be avoided in individuals who have experienced allergic reactions to one NSAID because they can experience the same reaction when taking other NSAIDs, due to cross-hypersensitivity.

NSAIDs also have a boxed warning in the setting of coronary artery bypass graft, due to the increased risk of adverse thrombotic events leading to myocardial infarction or stroke.

A specific contraindication for aspirin is children with viral infections, as it is associated with Reye syndrome, which is characterized by liver damage and progressive hepatic encephalopathy.

The only exception is the treatment of children with Kawasaki disease, which is a condition associated with inflammation of blood vessels.

Lastly, ketorolac has a few boxed warnings; it is contraindicated for children, while for adults, it indicated for only short term use, no longer than 5 days, and clients older than 65 require dosage adjustment; ketorolac is also contraindicated in clients with renal disease, cerebrovascular bleeding, and a history of peptic ulcers; and finally, it is contraindicated during labor.

Moving on, acetaminophen is often referred to as paracetamol, and can be administered orally, rectally or intravenously. This medication is not classified as an NSAID because it reversibly inhibits COX enzymes only in the central nervous system.

For that reason, acetaminophen is preferred to treat fever or pain in clients with bleeding disorders, peptic ulcers and individuals allergic to aspirin. Also, it’s the first-line therapy for children with fever or pain, especially when it’s associated with a viral infection.

Now, oral acetaminophen is metabolized in the liver, so it can precipitate acute liver failure in some clients and intravenous acetaminophen poses an increased risk for medication errors and overdose.

An important boxed warning is to limit acetaminophen from all sources, including cold medicines, to no more than 4 grams/day.

Early symptoms of acetaminophen overdose include nausea, vomiting, and abdominal pain; while late symptoms include jaundice, coagulopathy, hepatic encephalopathy, and even renal failure. Acetaminophen is contraindicated in clients with hepatic disease.

Now, switching gears, opioid analgesics are primarily administered orally, intravenously, intramuscularly, or subcutaneously. Other routes of administration include transdermal, epidural, intrathecal, and topical.

These medications primarily work by activating opioid receptors mu, delta, and kappa in the brain. Now, based on the effect on opioid receptors, opioid analgesics are subdivided into three main groups.

The first group covers full agonists and it includes morphine, methadone, meperidine, codeine, oxycodone, and fentanyl; while the second group includes partial agonists, such as tramadol.

Finally, the third group includes mixed agonist-antagonists, such as buprenorphine, which has an agonist effect on kappa opioid receptors, and a weak antagonist effect on mu receptors.

Common side effects include sedation, nausea, vomiting, constipation, as well as urinary retention, which is typically seen in older clients. Also, analgesic opioids can decrease blood pressure or cause orthostatic hypotension.

An important thing to keep in mind is that opioids have a number of boxed warnings, including respiratory depression, severe sedation, coma, and death. In addition, using opioids during pregnancy can result in neonatal opioid withdrawal syndrome.

Finally, a very important boxed warning is that clients can develop dependence and addiction to opioids, leading to abuse and misuse.

Contraindications to opioid analgesics include respiratory depression, head trauma, increased intracranial pressure, and clients in a coma.

It’s important to note that opioid analgesics should not be used in combination with other CNS depressants like alcohol, barbiturates, or benzodiazepines, since their additive effect can lead to respiratory depression, coma, and even death.