Drugs used to control pain

Drugs used to control pain range from mild, over-the-counter(OTC) preparations such as acetaminophen to potent general anesthetics.

They include:• nonopioid analgesics, antipyretics, and

nonsteroidal antiinflammatory drugs (NSAIDs)

• opioid agonist and antagonist drugs• anesthetic drugs.

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- Nonopioid analgesics, antipyretics, and NSAIDs are a broad group of pain medications.

- in addition to pain control, they produce antipyretic and anti-inflammatory effects.

- They have a ceiling (upper limit or maximum)effect (maximum dose above which there’s no added benefit) and don’t cause physical dependence.

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The drug classes included in this group are: • salicylates (especially aspirin). Aspirin is the most commonly used

salicylate. • para-aminophenol derivative

acetaminophen. • NSAIDs. • the urinary tract analgesic

phenazopyridine.

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salicylates are absorbed partly in the stomach, but primarily in the upper part of the small intestine.

Food or antacids in the stomach also delay absorption.

Salicylates are distributed widely throughout body tissues and fluids, including breast milk. In addition, they easily cross the placental barrier.

The liver extensively metabolizes salicylates into several metabolites.

The kidneys excrete the metabolites.

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They relieve pain primarily by inhibiting the synthesis of prostaglandin. (Recall that prostaglandin is a chemical mediator that sensitizes nerve cells to pain.)

In addition, they may also reduce inflammation by inhibiting the prostaglandin synthesis and release that occurs during inflammation.

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Salicylates reduce fever by stimulating the hypothalamus,producing dilation of the peripheral blood vessels and increased sweating.

Also, because prostaglandin E increases bodytemperature, inhibiting its production lowers a

fever. aspirin, permanently inhibits platelet

aggregation by interfering with the production of a substance called thromboxane A2, necessary for platelet aggregation.

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Salicylates are used primarily to relieve pain and reduce fever.

they don’t effectively relieve visceral pain or severe pain from trauma.

Salicylates won’t reduce a normal body temperature.

They can reduce an elevated body temperature, and will relieve headache and muscle ache at the same time.

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Salicylates can provide considerable relief in 24 hours when they’re used to reduce inflammation in rheumatic fever, rheumatoid arthritis, and osteoarthritis.

As a result of its anticlotting properties, aspirin can be used to enhance blood flow during myocardial infarction (MI) and to prevent recurrence of MI.

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the main guideline of salicylate therapy is to use the lowest dose that provides relief.

This reduces the likelihood of adverse reactions.

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• Oral anticoagulants, heparin, methotrexate, oral antidiabetic agents, and insulin are among the drugs that have an increased effect or risk of toxicity when taken with salicylates.

• Corticosteroids may decrease plasma salicylate levels and increase the risk of ulcers.

• NSAIDs may have a reduced therapeutic effect and an increased risk of GI effects when taken with salicylates.

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The most common adverse reactions to salicylates include gastric distress, nausea, vomiting,and bleeding tendencies.

Other adverse reactions include: • hearing loss (when taken for prolonged

periods) • diarrhea, thirst, sweating,tinnitus,

confusion,dizziness, impaired vision,and hyperventilation.

• Reye’s syndrome(when given to children with chickenpox or flulike symptoms

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Children and teenagers: Don’t use aspirin or salicylates to treat flulike symptoms or chickenpox because of the risk of triggering Reye’s syndrome.

Pregnant women: Aspirin is classified as pregnancy risk category D,and salicylates are classified as category C. Salicylates appear in breast milk.

Surgical patients: Discontinue aspirin, if possible,one week before surgery .

Asthmatics: These patients have an increased risk of sensitivity to aspirin, leading to bronchospasm, urticaria, angioedema, or shock.

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Although the class of para-aminophenol derivatives includes two drugs—phenacetin and cetaminophen—only acetaminophen is available in the United States.

Acetaminophen is an OTC drug that produces analgesic and antipyretic effects.

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Acetaminophen is absorbed rapidly and completely from the GI tract. It’s also absorbed well from the mucous membranes of the rectum.

Acetaminophen is distributed widely in body fluids and readily crosses the placental barrier.

After acetaminophen is metabolized by the liver, it’s excreted by the kidneys and, in small amounts, in breast milk.

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Acetaminophen reduces pain and fever, but unlike salicylates, it doesn’t affect inflammation or platelet function.

The pain-control effects of acetaminophen aren’t well understood.

It reduces fever by acting directly on the heat-regulating center in the hypothalamus.

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Acetaminophen is used to reduce fever and relieve headache,muscle ache, and general pain.

Acetaminophen is the drug of choice to treat fever and flulike symptoms in children.

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• The effects of oral anticoagulants and thrombolytic drugs may be slightly increased.

• The risk of liver toxicity is increased when long-term alcohol use, phenytoin, barbiturates, carbamazepine, and isoniazid are combined with acetaminophen.

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- Most patients tolerate acetaminophen well. - Unlike the salicylates,acetaminophen rarely

causes gastric irritation or bleeding tendencies. - Acetaminophen may cause severe liver

toxicity, and the total daily dose should be monitored.

- (The total daily dose shouldn’t exceed 4,000 mg/day.)

- Other adverse reactions include: • skin rash • hypoglycemia • neutropenia.

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Acetyl systein

The word opioid refers to derivatives of the opium plant or to synthetic drugs that imitate natural narcotics.

Opioid agonists (also called narcotic agonists) include opium derivatives and synthetic drugs with similar properties.

They’re used to relieve or decrease pain without causing the person to lose consciousness.

Some opioid agonists may also have antitussive effects that suppress coughing and antidiarrheal actions that can control diarrhea.

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- Opioid antagonists aren’t pain medications. - Instead, they block the effects of opioid

agonists and are used to reverse adverse drug reactions, such as respiratory and CNS depression, produced by those drugs.

- Unfortunately, by reversing the analgesic effect, they also cause the patient’s pain to recur.

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• codeine • fentanyl • hydrocodone • hydromorphone • levorphanol • meperidine • methadone • morphine sulfate • oxycodone • oxymorphone • propoxyphene • remifentanil • sufentanil.

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A person may receive an opioid agonist by any administration route, although inhalation administration is uncommon.

Oral doses are absorbed readily from the GI tract; however, transmucosal and intrathecal opiates are faster-acting.

Opioid agonists administered I.V. provide the most rapid (almost immediate) and reliable pain relief.

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Distribution- Opioid agonists are distributed widely

throughout body tissues.- They have a relatively low plasma protein-

binding capacity (30% to 35%).MetabolismOpioid agonists are metabolized extensively in

the liver.ExcretionMetabolites are excreted by the kidneys. A small

amount is excreted in stool through the biliary tract.

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- Opioid agonists reduce pain by binding to opiate receptor sites (mu receptors and N-methyl-D-aspartate receptors) in the peripheral nervous system and the CNS.

- When these drugs stimulate the opiate receptors, they mimic the effects of endorphins (naturally occurring opiates that are part of the body’s own pain relief system).

This receptor-site binding produces the therapeutic effects of analgesia and cough suppression.

It also produces adverse reactions such as respiratory depression and constipation.

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- Opioid agonists, especially morphine, affect the smooth muscle of the GI and genitourinary tracts (the organs of the reproductive and urinary systems).

- This causes contraction of the bladder and ureters. It also slows intestinal peristalsis (rhythmic contractions

- that move food along the digestive tract), resulting in constipation,a common adverse effect of opiates.

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These drugs also cause blood vessels to dilate, especially in the face, head, and neck.

In addition, they suppress the cough center in the brain, producing antitussive effects and causing constriction of the bronchial muscles.

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- Opioid agonists are prescribed to relieve severe pain in acute, chronic, and terminal illnesses.

- They also reduce anxiety before a patient receives anesthesia and are sometimes prescribed to control diarrhea and suppress coughing.

- Morphine relieves shortness of breath in patients with pulmonary edema and heart failure .

- It does this by dilating peripheral blood vessels, and decreasing cardiac preload.

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• The use of opioid agonists with other drugs that also decrease respirations, such as alcohol, sedatives, hypnotics, and anesthetics,increases the patient’s risk of severe respiratory depression.

• Taking tricyclic antidepressants, phenothiazines, or anticholinergics with opioid agonists may cause severe constipation and urine retention.

• Drugs that may affect opioid analgesic activity include amitriptyline, diazepam, phenytoin, protease inhibitors, and rifampin.

• Drugs that may be affected by opioid analgesics include carbamazepine,warfarin, beta-adrenergic blockers, and calcium channel blockers

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One of the most common adverse reactions to opioid agonists is decreased rate and depth of breathing that worsens as the dose of opioid is increased.

- Other adverse reactions include:• flushing• orthostatic hypotension• pupil constriction.- Adverse reactions to meperidine include:• tremors• palpitations• tachycardia• delirium• seizures.

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Opioid antagonists have a greater attraction for opiate receptors than opioids do; however, they don’t stimulate those receptors.

As a result, opioid antagonists block the effects of opioid drugs,enkephalins, and endorphins.

Opioid antagonists include:• naloxone• naltrexone

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Pharmacokinetics Naloxone is administered I.M., subQ, or I.V.

Naltrexone is administered orally in tablet or liquid form.

Both drugs are metabolized by the liver and excreted by the kidneys.

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Pharmacotherapeutics Naloxone is the drug of choice for managing an

opioid overdose. It reverses respiratory depression and sedation and

helps stabilize the patient’s vital signs within seconds after administration.

Naloxone also reverses the analgesic effects of opioids. Therefore,after naloxone administration, the patient may complain of pain or even experience withdrawal symptoms.

Naltrexone is used along with psychotherapy or counseling to treat drug abuse;

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