calcium channel blockers Adverse reactions and Contraindicated

The agents commonly called the  calcium channel blockers comprise an increasing number of agents, including the prototypical verapamil (Calan, Isoptin), nifedipine (Adalat, Procardia), and diltiazem (Cardizem). These agents are a chemically and pharmacologically heterogeneous group of synthetic drugs, but they possess the common property of selectively antagonizing Ca++movements that underlie the process of excitation contraction coupling in the cardiovascular system. The primary use of these agents is in the treatment of angina, selected cardiac arrhythmias, and hypertension.

Although the Ca++ channel blockers are potent vasodilating drugs, they lack the fluidaccumulating properties of other vasodilators and the persistent activation

of the sympathetic and renin–angiotensin–aldosterone axes. Furthermore, the broad potential range of activities, both within and without the cardiovascular system,

suggests that they may be clinically useful in disorders from vertigo to failure of gastrointestinal smooth muscle to relax .

A number of second-generation analogues are known, particularly in the nifedipine (1,4-dihydropyridine) series, including nimodipine (Nimotop), nicardipine (Cardene), felodipine (Plendil), nisoldipine (Sular), and amlodipine (Norvasc). These agents differ from nifedipine principally in their potency, pharmacokinetic characteristics, and selectivity of action.Nimodipine has selectivity for the cerebral vasculature; amlodipine exhibits very slow kinetics of onset and offset of blockade;and felodipine and nisoldipine are vascular-selective 1,4-dihydropyridines.

 Adverse reactions

Adverse reactions to the calcium channel blocking drugs usually are not serious and rarely require discontinuation of the drug therapy. The more common adverse reactions include dizziness, light-headedness, nausea,diarrhea, constipation, peripheral edema, headache,

bradycardia, flushing, dermatitis, skin rash, and nervousness. Antianginal

Drugs for a more specific listing of the adverse reactions

of the calcium channel blockers. 

 Contraindicated 

Calcium channel blockers are contraindicated in patients who are hypersensitive to the drugs and those with sick sinus syndrome, second- or third-degree AV block (except with a functioning pacemaker), hypotension (systolic less than 90 mm Hg), ventricular dysfunction,

or cardiogenic shock. The calcium channel blockers are used cautiously during pregnancy (Pregnancy Category C) and lactation and in patients with congestive heart

failure (CHF), hypotension, or renal or hepatic impairment.

The effects of the calcium channel blockers are increased when administered with cimetidine or ranitidine. A decrease in effectiveness of the calcium channel blockers may occur when the agents are administered with phenobarbital or phenytoin. The calcium channel blockers have an antiplatelet effect (inhibition of platelet function) when administered with aspirin, causing easy bruising, petechiae (pin point purplish red spot caused by intradermal hemorrhage), and bleeding. There is an additive depressive effect on the myocardium when the calcium channel

blockers are administered with the  -adrenergic blocking drugs. When the calcium channel blockers are administered with digoxin, there is an increased

risk for digitalis toxicity.

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Unknown Adverse Reactions, calcium channel blockers, Contraindicated

Narcotic Antagonists Contraindicated Actions and Adverse Reactions

An antagonist is a substance that counteracts the action of something else. A drug that is an antagonist has an affinity for a cell receptor, and by binding to it, prevents the cell from responding. Thus, a narcotic antago-nist reverses the actions of a narcotic. Specific antagonists have been developed to reverse the respiratory depression associated with the opiates. The two narcotic antagonists in use today are naloxone (Narcan) and naltrexone Naloxone is capable of restoring respiratory function within 1 to 2 minutes after administration.
Naltrexone is used primarily for the treatment of narcotic dependence to block the effects of the opiates, especially the euphoric effects experienced in opiate dependence.


NALOXONE


ACTIONS

Administration of naloxone prevents or reverses the effects of the opiates. The exact mechanism of action is
not fully understood, but it is believed that naloxone reverses opioid effects by competing for opiate receptor site If the individual has taken or180 received an opiate, the effects of the opiate are reversed.If the individual has not taken or received an opiate,naloxone has no drug activity.

USES
This drug is used for complete or partial reversal of narcotic depression, including respiratory depression Narcotic depression may be due to intentional or acci dental overdose (self-administration by an individual)
accidental overdose by medical personnel, and drug idiosyncrasy. Naloxone also may be used for diagnosis of a suspected acute opioid overdosage.

ADVERSE REACTIONS

Although not a true adverse reaction, abrupt reversal of narcotic depression may result in nausea, vomiting, sweat-ing, tachycardia, increased blood pressure, and tremors.

CONTRAINDICATIONS, PRECAUTIONS,
AND INTERACTIONS
Naloxone is contraindicated in those with a hypersensi-tivity to the narcotic antagonists. Naloxone is used cautiously in those with a narcotic addiction. Naloxone is used cautiously in patients with cardiovascular dis-
ease; those who are pregnant (Pregnancy Category B);
and in infants of opioid-dependent mothers. These drugs may produce withdrawal symptoms in those physically dependent on the narcotics. The patient must not have taken any opiate for the last 7 to
10 days. Naloxone may prevent the action of opioid antidiarrheals, antitussives, and analgesics. This drug is used cautiously during lactation.

NALTREXONE

ACTIONS

Naltrexone completely blocks the effects of IV opiates,as well as drugs with agonist-antagonist actions
(butorphanol, nalbuphine, and pentazocine). The mechanism of action appears to be the same as that for
naloxone.

USES

Naltrexone is used to treat persons dependent on opioids. Patients receiving naltrexone have been detoxified and are enrolled in a program for treatment of narcotic addiction. Naltrexone, along with other methods of
treatment (counseling, psychotherapy), is used to maintain an opioid-free state. Patients taking naltrexone on a scheduled basis will not experience any narcotic effects if they use an opioid.

ADVERSE REACTIONS

Administration of naltrexone may result in anxiety, dif-ficulty sleeping, abdominal cramps, nasal congestion,joint and muscle pain, nausea, vomiting, dizziness, irritability, depression, fatigue, and drowsiness.

CONTRAINDICATIONS, PRECAUTIONS,
AND INTERACTIONS

Naltrexone is contraindicated in those with a hyper- sensitivity to the narcotic antagonists. Naltrexone is contraindicated during pregnancy (Category C).
Naltrexone is used cautiously in those with a narcotic addiction; in patients with cardiovascular disease, acute hepatitis, liver failure, or depression; and in patients who are suicidal. Naltrexone is used cau-tiously during lactation.Naltrexone may produce withdrawal symptoms in those physically dependent on narcotics. The patient must not have taken any opiate for the last 7 to 10 days.Concurrent use of naltrexone with thioridazine may cause increased drowsiness and lethargy. Naltrexone may prevent the action of opioid antidiarrheals, antitussives, and analgesics .

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Unknown Actions, Adverse Reactions, Contraindicated, Narcotic Antagonists

Narcotic Analgesics ACTIONS USES ADVERSE REACTIONS and CONTRAINDICATIONS

Pain is a complex occurrence that is uniquely experienced by each individual. It has been defined as the emotional and sensory perceptions associated with real or Acute pain is a warning that something is not right in the body. Chronic pain is pain that persists beyond the expected time for healing. Analgesics are drugs that relieve pain. The narcotic analgesics are con-trolled substances used to treat moderate to severe pain. Nurses must be knowledgeable concerning pain assessment and management if the patient’s pain is to be adequately managed. Despite advances in technology and pharmacologic measures, evidence exists indicating that for many, pain is not managed adequately.Drugs that counteract the effects of the narcotic analgesics are the narcotic antagonists. These drugs compete with the narcotics at the receptor sites and are used to reverse the depressant effects of the narcotic analgesics.

NARCOTIC ANALGESICS

Opioid analgesics are the narcotic analgesics obtained from the opium plant. More than 20 different alkaloids are obtained from the unripe seed of the opium poppy plant. The analgesic properties of opium have been known for hundreds of years. The narcotics obtained from raw opium (also called the opiates, opioids, or opiate narcotics) include morphine, codeine, hydrochlorides of opium alkaloids, and camphorated tincture of opium. Morphine, when extracted from raw opium and treated chemically, yields the semisynthetic narcotics hydromorphone, oxymorphone, oxycodone, and heroin.Heroin is an illegal narcotic in the United States and is not used in medicine. Synthetic narcotics are those man-made analgesics with properties and actions simi-lar to the natural opioids. Examples of synthetic narcotic analgesics are methadone, levorphanol, remifen-tanil, and meperidine. Additional narcotics are listed in the Summary Drug Table: Narcotic Analgesics.

ACTIONS

Narcotic analgesics are classified as agonists, partial agonists, and mixed agonists-antagonists. The agonist binds to a receptor and causes a response. A partial agonist binds to a receptor, but the response is limited (ie, is not as great as with the agonist). Antagonists bind to a recep-tor and cause no response. An antagonist can reverse the effects of the agonist. This reversal is possible because the antagonist competes with the agonist for a receptor site.

Drugs that act as antagonists are discussed at the end of this chapter. An agonist-antagonist has properties of
both the agonist and antagonist. These drugs have some agonist activity at the receptor sites and some antagonist activity at the receptor sites.
Classification of the narcotic analgesics is based on their activity at the opioid receptor sites. Although five
categories of opioid receptors have been identified, only three of these receptors affect the action of the narcotic analgesics:
• mu
• kappa
• delta
The narcotic agonists have activity at the mu and kappa receptors (and possi-bly the delta sites). Remifentanil is a very short-acting agonist with potent analgesic activity. It is a mu opioid agonist with rapid onset, peak effect, and short duration of action. The mixed agonist-antagonist drugs act on the mu receptors by competing with other substances at the mu receptor (antagonist activity) and are agonists at other receptors. Partial agonists have limited agonist activity at the mu receptor. The actions of the narcotic analgesics on the various organs and structures of the body (also called secondary pharmacological effects) are

USES

The major use of the narcotic analgesic is to relieve or manage moderate to severe acute and chronic pain. The ability of a narcotic analgesic to relieve pain depends on several factors, such as the drug, the dose, the route of administration, the type of pain, the patient, and the length of time the drug has been administered. Morphine is the most widely used opioid and an effective drug for moderately severe to severe pain. Morphine is considered the prototype or “model” narcotic. Morphine’s actions, uses, and ability to relieve pain are the standards to which other narcotic analgesics are often compared.Other narcotics, such as meperidine and levorphanol, are effective for the treatment of moderate to severe pain. For mild to moderate pain, the primary health care provider may order a narcotic such as codeine or pentazocine.
In addition to the relief or management of moderate to severe acute and chronic pain, the narcotic analgesics may be used for the following reasons:
• To lessen anxiety and sedate the patient before surgery. Patients who are relaxed and sedated when
anesthesia is given are easier to anesthetize (requiring a smaller dose of an induction anesthetic), as
well as easier to maintain under anesthesia
• Support of anesthesia (ie, as an adjunct during
anesthesia)
• Obstetrical analgesia
• Relief of anxiety in patients with dyspnea associated
with pulmonary edema
• Intrathecally or epidurally for pain relief for
extended periods without apparent loss of motor,
sensory, or sympathetic function
• Relief of pain associated with a myocardial infarc-
tion (morphine)
• Management of opiate dependence (levomethadyl)
• Detoxification of and temporary maintenance of
narcotic addiction (methadone)
• To induce conscious sedation before a diagnostic
or therapeutic procedure in the hospital setting
• Treatment of severe diarrhea and intestinal
cramping (camphorated tincture of opium)
• Relief of severe, persistent cough (codeine, although
the drug’s use has declined)

Use in Management of Opioid Dependence

Two opioids are used in the treatment and management of opiate dependence: levomethadyl and methadone.Levomethadyl is given in an opiate dependency clinic to maintain control over the delivery of the drug. Because of its potential for serious and life-threatening proarrhythmic effects, levomethadyl is reserved for use in the treatment of addicted patients who have no response to other treatments. Levomethadyl is not taken daily; the drug is administered three times a week (Monday/Wednesday/Thursday or uesday/Thursday/
Saturday). Daily use of the usual dose will cause serious overdose.
Methadone, a synthetic narcotic, may be used for the relief of pain, but it also is used in the detoxifi-cation and maintenance treatment of those addicted to narcotics. Detoxification involves withdrawing the patient from the narcotic while preventing withdrawal symptoms.Maintenance therapy is designed to reduce the
patient’s desire to return to the drug that caused addic-tion, as well as to prevent withdrawal symptoms. The dosages used vary with the patient, the length of time the individual has been addicted, and the average amount of drug used each day. Patients enrolled in an outpatient methadone program for detoxification or
maintenance therapy on methadone must continue to receive methadone when hospitalized.

ADVERSE REACTIONS

The adverse reactions differ according to whether the narcotic analgesic acts as an agonist or as an agonistantagonist.
Agonists
One of the major hazards of narcotic administration is respiratory depression, with a decrease in the respira-
tory rate and depth. The most common adverse reactions include light-headedness, dizziness, sedation, constipation, anorexia, nausea, vomiting, and sweating.
When these effects occur, the primary health care provider may lower the dose in an effort to eliminate or
decrease the intensity of the adverse reaction. Other adverse reactions that may be seen with the administration of an agonist narcotic analgesic include:
• Central nervous system—euphoria, weakness,headache, pinpoint pupils, insomnia, agitation,tremor, and impairment of mental and physical tasks
• Gastrointestinal—dry mouth and biliary tractspasms
• Cardiovascular—flushing of the face, peripheral circulatory collapse, tachycardia, bradycardia, and palpitations
• Genitourinary—spasms of the ureters and bladder sphincter, urinary retention or hesitancy
• Allergic—pruritus, rash, and urticaria
• Other—physical dependence, pain at injection site, and local tissue irritation

Agonist-Antagonists
Administration of a narcotic agonist-antagonist may result in symptoms of narcotic withdrawal in those addicted to narcotics. Other adverse reactions associated with the administration of a narcotic agonist antagonist include sedation, nausea, vomiting, sweating, headache,vertigo, dry mouth, euphoria, and dizziness.

CONTRAINDICATIONS

All narcotic analgesics are contraindicated in patients with known hypersensitivity to the drugs. These drugs are contraindicated in patients with acute bronchial asthma, emphysema, or upper airway obstruction and
in patients with head injury or increased intracranial pressure. The drugs are also contraindicated in patients with convulsive disorders, severe renal or hepatic dysfunction, acute ulcerative colitis, and increased intracranial pressure. The narcotic anal-gesics are Pregnancy Category C drugs (oxycodone,Category B) and are not recommended for use during pregnancy or labor (may prolong labor or cause respi-ration depression of the neonate). The use of narcotic analgesics is recommended during pregnancy only if the benefit to the mother outweighs the potential harm to the fetus.

PRECAUTIONS

These drugs are used cautiously in the elderly and in patients with undiagnosed abdominal pain, liver dis-ease, history of addiction to the opioids, hypoxia,supraventricular tachycardia, prostatic hypertrophy, and renal or hepatic impairment. The obese must be monitored closely for respiratory depression while tak-ing the narcotic analgesics. The drug is used cautiously during lactation (wait at least 4 to 6 hours after taking the drug to breastfeed the infant). The narcotics are used cautiously in patients undergoing biliary surgery because the drug may cause spasm of the sphincter of Oddi.

INTERACTIONS

The narcotic analgesics potentiate the central nervous system (CNS) depressant properties of other CNS
depressants, such as alcohol, antihistamines, antide-pressants, sedatives, phenothiazines, and monoamine oxidase inhibitors. Use of the narcotic analgesics within 14 days of the MAO inhibitors may potentiate the effect of either drug. Patients taking the agonist-antagonist narcotic analgesics may experience withdrawal symptoms if the patient has been abusing or using narcotics. The agonist-antagonists drugs can cause opioid with drawal symptoms in those who are physically dependent on the opioids. There is an increased risk of respiratory depression, hypotension, and sedation when narcotic analgesics are administered too soon after barbiturate general anesthesia.

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Unknown Adverse Reactions, Contraindications, Narcotic Analgesics, Uses

Antiviral Drugs Action Uses and Adverse Reactions

More than 200 viruses have been identified as capable of producing disease. Acute viruses, such as the common cold, have a rapid onset and quick recovery. Chronic viral infections, such as acquired immunodeficiency syndrome (AIDS), have recurrent episodes of exacerba-tions (increases in severity of symptoms of the disease) and remissions (periods of partial or complete disappearance of the signs and symptoms).Although viral infections are common, for many years only a limited number of drugs were available for their treatment. Over the past several years, the number of antiviral drugs has increased significantly. Several of the antiviral drugs will be discussed in greater detail than oth-ers. These include acyclovir (Zovirax), amantadine(Symmetrel), didanosine (Videx), ribavirin (Virazole),zanamivir (Relenza), and zidovudine (AZT, Retrovir). The Summary Drug Table: Antiviral Drugs presents a more complete listing of the antiviral drugs currently in use.

ACTIONS
Viruses can reproduce only within a living cell. A virus consists of either DNA or RNA surrounded by a protein shell. The virus is capable of reproducing only when it uses the body’s cellular materia most antiviral drugs act by inhibiting viral DNA or RNA replication in the virus, causing viral death.

USES
Although infections caused by a virus are common, antiviral drugs have limited use because they are effective against only a small number of specific viral infections.General uses of the antiviral drugs include the treatment of:
• Initial and recurrent mucosal and cutaneous herpes simplex virus (HSV) 1 and 2 infections in
immunocompromised patients, encephalitis, and herpes zoster.
• Human immunodeficiency virus (HIV) (combined with other drugs)
• Cytomegalovirus (CMV) retinitis (inflammation of the retina of the eye)
• Genital herpes
• Influenza A respiratory tract illness
• Respiratory syncytial virus (RSV), a severe lower respiratory tract infection
• Viral herpes infections

Unlabeled Uses
Because there are a limited number of antiviral drugs and more than 200 viral diseases, the primary health care provider may decide to prescribe an antiviral drug for an unlabeled use even though documentation of its effectiveness is lacking. Approval by the Food and Drug Administration (FDA) is necessary for a drug to be prescribed. On occasion, the use of a drug for a specific disorder or condition may be under investigation or may be approved for use in another country. In this instance, the drug may be prescribed by the primary health care provider for the condition under investiga-tion. The use of the drug for a specific disorder or con-
dition that is not officially approved by the FDA is called an “unlabeled use.” Examples of unlabeled uses of the antiviral drugs include treatment of CMV and HSV infections after transplant and varicella pneumonia; the treatment of CMV retinitis in immunocompro-mised patients; and the use of ribavirin for influenza A and B (aerosol form), acute and chronic hepatitis, herpes genitalis, and measles (oral form).

GENERAL ADVERSE REACTIONS
Antiviral drugs are given systemically or as topical drugs. When used systemically these drugs may be administered orally or intravenously (IV). Rapid IV administration can result in crystalluria (presence of crystals in the urine). The most common adverse reactions when these drugs are administered systemically
are gastrointestinal disturbances, such as nausea, vomit-ing, diarrhea, and anorexia. When administered topi-cally, the antiviral drugs can cause transient burning,stinging, and pruritus at the application site. 

ADVERSE REACTIONS FOR
SPECIFIC DRUGS


Acyclovir
Acyclovir is available for use orally, topically, and par-enterally (for IV use). When given IV, acyclovir can cause phlebitis, lethargy, confusion, tremors, skin rashes, nau-sea, and crystalluria. Side effects when given orally include nausea, vomiting, diarrhea, headache, dizziness,and skin rashes. Topical administration causes transientburning, stinging, and pruritus.

Amantadine
Adverse reactions of amantadine include gastrointestinal upset with nausea and vomiting, anorexia, asthenia
(weakness, loss of strength), constipation, depression, visual disturbances, psychosis, urinary retention, and
orthostatic hypotension.

Didanosine
Adverse reactions reported with didanosine include headache, peripheral neuropathy, rhinitis, cough, diar-rhea, nausea, vomiting, anorexia, hepatotoxicity, and pancreatitis.

Ribavirin
Ribavirin is given by inhalation and can cause worsening of respiratory status, hypotension, and ocular irritation,including erythema (redness of skin), conjunctivitis, and blurred vision.

Zanamivir
Common adverse effects include headache, nausea, diarrhea, anorexia, rhinitis, and flu-like symptoms. The
most serious adverse reactions are related to respiratory effects and include severe bronchospasm that may lead to death.

Zidovudine
Adverse reactions associated with zidovudine include headache, weakness, malaise, nausea, abdominal pain,and diarrhea. Hematologic changes include anemia and granulocytopenia (low levels of granulocytes, a type of white blood cell, in the blood).

GENERAL CONTRAINDICATIONS,
PRECAUTIONS, AND INTERACTIONS

All antiviral drugs are contraindicated in patients with previous hypersensitivity to the individual antiviral drug. The antiviral drugs are also contraindicated in patients with congestive heart failure, seizures, renal dis-ease, and during lactation. The antiviral drugs are given with caution in patients with renal impairment and require dosage adjustments. Antivirals are used with caution in children, during pregnancy (except ribavirin,a Pregnancy Category X drug), and during lactation.Other contraindications and precautions are listed below, according to the specific drug. Numerous interactions are possible with the antiviral drugs. Only the most significant interactions are listed for selected drugs. The nurse should consult an appropriate source for a more extensive listing of interactions.

Acyclovir
This drug is used cautiously in patients with pre-exist- ing neurologic, renal, hepatic, respiratory, or fluid and electrolyte abnormalities. The nurse gives the drug with caution to patients with a history of seizures. Acyclovir
is a Pregnancy Category C drug and is used cautiously during pregnancy and lactation. Incidences of extreme drowsiness have occurred when acyclovir is given with zidovudine. There is an increased risk of nephrotoxicity when acyclovir is administered with other nephrotoxic drugs. When administered with amphotericin B, the risk of nephrotoxicity is increased. Administration with probenecid causes a decrease in the renal excretion of acyclovir, prolonging the effects of acyclovir and increasing the risk of drug toxicity.

Amantadine
Amantadine is used cautiously in patients with seizure disorders, psychiatric problems, renal impairment, and cardiac disease. Amantadine is a Pregnancy Category B drug and is used cautiously during pregnancy and lacta-tion. Concurrent use of antihistamines, phenothiazines,tricyclic antidepressants, disopyramide, and quinidine may increase the anticholinergic effects (dry mouth,blurred vision, constipation) of amantadine.

Didanosine
This drug is used cautiously in patients with peripheral vascular disease, neuropathy, chronic pancreatitis, or impaired liver function. Didanosine is a Pregnancy Cate- gory B drug and is used cautiously during pregnancy and lactation. There may be a decrease in the effectiveness of dapsone in preventing Pneumocystis carinii pneumonia when didanosine is administered with dapsone. Use of didanosine with zalcitabine may cause additive neuropa-thy. Absorption of didanosine is decreased when it isadministered with food.

Ribavirin
Ribavirin may be teratogenic and embryotoxic (Pregnancy Category X) and is contraindicated during pregnancy, in patients with chronic obstructive pulmonary disease (COPD), and during lactation. Ribavirin is used cautiously at all times during administration of the drug. Ribavirin may antagonize the antiviral

action of zidovudine and potentiate the hematologic toxic effects of zidovudine. When ribavirin is used con-
currently with digitalis, the risk of digitalis toxicity increases.

Zanamivir
Zanamivir is used cautiously with pregnancy (Category C), lactation, asthma, COPD, or other underlying respi-ratory diseases. No significant drug interactions have been reported with the use of zanamivir.

Zidovudine
This drug is used cautiously in patients with bone mar-row depression or severe hepatic or renal impairment.Zidovudine is a Pregnancy Category C drug and is used cautiously during pregnancy and lactation. There is an increased risk of bone marrow depression when zidovudine is administered with antineoplastic drugs,other drugs causing bone marrow depression, and in patients having or recently taking radiation therapy.An additive neurotoxicity may occur when zidovu-dine is administered with acyclovir. Clarithromycin de-creases blood levels of zidovudine. The blood levels of zidovudine are increased when it is given with lamivudine.

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Unknown Action, Adverse Reactions, Antiviral Drugs, Uses