Every drug can harm as well as help. Nurses are usually the last check before a drug reaches the client and the first to see a reaction, so recognizing reactions and preventing errors are core nursing skills.

Key terms

Two broad types

• Type A (augmented) — dose-related extension of the known effect; common and predictable (bleeding with anticoagulants, hypotension with antihypertensives)
• Type B (bizarre) — not dose-related; uncommon and unpredictable (anaphylaxis, Stevens–Johnson syndrome, idiosyncratic reactions)

Hypersensitivity reactions

Drugs most often linked to serious reactions

Pharmacogenomic screening — genetic tests before starting some drugs prevent severe reactions:

• HLA-B*15:02 before carbamazepine (and consider for phenytoin) in people of Asian ancestry — risk of SJS/TEN
• HLA-B*57:01 before abacavir — hypersensitivity
• HLA-B*58:01 before allopurinol in high-risk groups (e.g., Han Chinese, Korean, Thai, and African American ancestry) — severe skin reactions
• G6PD deficiency — hemolysis with primaquine, rasburicase, dapsone, sulfonamides, nitrofurantoin

Allergy labels. Most people labeled "penicillin allergic" are not truly allergic when tested. Record the drug, the reaction, and when it happened; distinguish true allergy from intolerance (nausea, diarrhea). Cross-reactivity between penicillins and most cephalosporins is low (about 1–2%) and is related to similar side chains; follow the prescriber's and pharmacist's plan, especially after a severe or recent reaction.

Anaphylaxis — recognize it early. Sudden onset (minutes) of skin or mucosal signs (hives, flushing, swollen lips or tongue) plus respiratory compromise (wheeze, stridor, dyspnea, hypoxemia), low blood pressure or signs of end-organ hypoperfusion (syncope, collapse), or severe GI symptoms. It can also present as hypotension or bronchospasm alone after exposure to a known allergen. Skin signs may be absent.

Severe skin reaction warning signs — flu-like prodrome, then painful, spreading red or purple rash, blisters, skin peeling, mucosal erosions (mouth, eyes, genitals), target lesions, fever.

Medication errors — common causes

• Wrong client (missed identification), wrong drug (look-alike, sound-alike names), wrong dose (decimal and unit errors, mg vs mcg, mL vs mg), wrong route, wrong time, omission, wrong rate on infusion pumps
• Interruptions, fatigue, unclear orders, verbal orders, error-prone abbreviations, workarounds of barcode scanning

• Documented true allergy: the drug and structurally related drugs are avoided unless an allergist or prescriber directs a graded challenge or desensitization
• Prior SJS/TEN or DRESS to a drug: permanent contraindication to that drug; caution with related drugs
• ACE inhibitor angioedema: contraindication to all ACE inhibitors; sacubitril-valsartan is contraindicated with ACE inhibitors (36-hour washout) and in clients with prior ACE inhibitor angioedema
• High-risk populations for ADRs: older adults, polypharmacy, kidney or liver impairment, children, pregnancy, narrow therapeutic index drugs
• Drug–drug interactions: screen every new order, including over-the-counter and herbal products (see Topics 1 and 2)
• Drug–food interactions: grapefruit (CYP3A4 drugs), tyramine (MAOIs), vitamin K intake (warfarin — keep intake consistent), dairy and minerals (tetracyclines, fluoroquinolones)

Listed in priority order.

1. Suspected anaphylaxis — act immediately
   • Stop the suspected drug or infusion; call for help (rapid response)
   • Epinephrine IM into the mid-outer thigh: 0.01 mg/kg of the 1 mg/mL solution, maximum 0.5 mg in adults (0.3 mg in children); repeat every 5–15 minutes as needed. There is no absolute contraindication to epinephrine in anaphylaxis
   • Airway and breathing: high-flow oxygen; prepare for airway support if stridor or swelling
   • Position supine with legs raised if hypotensive (sitting up if breathing is difficult; do not stand or walk the client); large-volume IV isotonic fluids for hypotension
   • Second-line only after epinephrine: H1 antihistamines for skin symptoms, inhaled bronchodilators for wheeze, corticosteroids per order
   • Observe for a biphasic reaction (can recur hours later); discharge with an epinephrine auto-injector and teaching
2. Any new adverse reaction: assess ABCs and vital signs; hold the next dose and notify the prescriber; treat as ordered
3. Serious skin signs: stop the suspected drug and notify immediately; SJS/TEN is managed like a burn (fluids, wound and eye care, pain control, infection prevention)
4. Preventing errors
   • Identify the client with two identifiers; check allergies before every new drug
   • Follow the rights of medication administration and the three checks against the medication record
   • Use barcode scanning and smart pumps as designed; do not bypass alerts without review
   • Independent double checks for high-alert drugs where policy requires (insulin, heparin infusions, chemotherapy, concentrated electrolytes, opioid infusions, pediatric doses)
   • Avoid error-prone abbreviations; use leading zeros (0.5 mg) and no trailing zeros (5 mg)
   • Minimize interruptions during preparation
   • Medication reconciliation on admission, transfer, and discharge
   • Clarify any unclear, incomplete, or unsafe order before acting
5. If an error occurs: assess and monitor the client first, notify the prescriber, give ordered treatment, document the facts and the client's condition in the record, complete an incident report per policy (not referenced in the chart), and disclose honestly per policy
6. Report suspected ADRs and errors through internal systems and national programs — reporting improves the system; a just culture focuses on system causes rather than blame
7. Document allergies with the reaction type and severity

• Know the name and purpose of each drug and the most important adverse effects to report
• Tell every provider, pharmacist, and dentist about any past drug reactions — describe what happened
• Wear or carry allergy identification for serious allergies; carry two epinephrine auto-injectors if prescribed and know how to use them (outer thigh, through clothing if needed; call emergency services)
• Stop the drug and seek care immediately for swelling of the face, lips, or tongue; difficulty breathing; a blistering or peeling rash; mouth sores with fever
• Keep an updated medication list, including over-the-counter and herbal products; use one pharmacy when possible
• Ask questions if a pill looks different from usual

• Side effect = expected, usually mild; ADR = harmful at normal dose; ADE includes errors
• Allergy is immune-mediated; nausea or diarrhea is an intolerance, not an allergy
• Anaphylaxis: epinephrine IM mid-outer thigh first — 0.01 mg/kg, max 0.5 mg adult, 0.3 mg child; antihistamines and steroids are second-line
• Watch for biphasic anaphylaxis; discharge with auto-injectors
• SJS/TEN: blisters, peeling, mucosal sores — stop the drug; never rechallenge
• HLA-B*15:02 before carbamazepine in people of Asian ancestry; HLA-B*57:01 before abacavir
• ACE inhibitor angioedema is an airway emergency and can appear after years
• Vancomycin infusion reaction is rate-related, not an allergy — infuse over at least 60 minutes or no faster than 10 mg/min, whichever is longer
• Error response: client first, then notify, document facts, incident report (not in the chart)
• High-alert drugs need independent double checks where required; use two identifiers and barcode scanning
• Report ADRs and errors — reporting supports a just culture