All EMS presentations
General MedicalClinical presentation

Medication side effect / adverse reaction

A streamlined, differential-led presentation for rapid clinical review.

Clinical snapshot

Twenty-second review

  • Adverse drug effects arise from predictable pharmacology, allergy, interaction, overdose, withdrawal, or impaired clearance and may affect any organ system.
  • Airway swelling, shock, severe rash or mucosal injury, dysrhythmia, seizure, respiratory depression, or severe bleeding is time-sensitive.
  • Keep new unrelated illness in the differential; overlapping or concurrent illness remains possible.
  • For medication side effect / adverse reaction, trends and combinations of findings are more informative than one isolated vital sign.
Differentials

Compare the clinical patterns

The repeated material is grouped inside each possibility. Open only the condition you need.

Serious4 conditions
AnaphylaxisTime-sensitive high-risk possibility

HPI

Clarify medication and indication; start date or dose change; symptoms and temporal relationship.

Signs & symptoms

Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.

Focused exam

Perform a targeted cardiorespiratory, neurologic, abdominal, skin, and hydration assessment guided by the history; Assess function against baseline rather than relying on a single normal-looking measurement.

Brief pathophysiology

Anaphylaxis may cause medication side effect / adverse reaction through a time-sensitive process capable of rapid physiological deterioration.

Vital-sign pattern

What the trend may show

Possible pattern

Anaphylaxis may involve airway, breathing, or circulation alone or in combination. Do not wait for hypotension, hypoxemia, or skin findings before recognizing a severe reaction.

Blood pressure (mmHg)

May fall

Vasodilation and capillary leak can cause rapid hypotension.

Heart rate (bpm)

Often rises

Tachycardia may accompany shock, distress, or epinephrine treatment.

Respiratory rate (breaths/min)

Often rises

Tachypnea may reflect bronchospasm, airway edema, or shock.

Oxygen saturation (SpO₂)

May fall

Desaturation suggests significant respiratory involvement but may be late.

Front-load in the triage report

  • Anaphylaxis: Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.
  • Medication and indication?
  • Start date or dose change?
Toxic overdoseTime-sensitive high-risk possibility

HPI

Clarify start date or dose change; symptoms and temporal relationship; last dose.

Signs & symptoms

Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.

Focused exam

Assess function against baseline rather than relying on a single normal-looking measurement; Identify all medicines, recent starts or dose changes, last doses, renal and hepatic function, supplements, adherence, and symptom timing.

Brief pathophysiology

Toxic overdose may cause medication side effect / adverse reaction through a time-sensitive process capable of rapid physiological deterioration.

Vital-sign pattern

What the trend may show

Possible pattern

General medical differentials have overlapping physiology. These four observations screen for deterioration and common reversible causes without implying a diagnosis.

Respiratory rate (breaths/min)

Trend rate / effort

Respiratory rate can reveal early physiologic stress.

Blood pressure (mmHg)

Compare with baseline

Relative hypotension may be important before an absolute threshold is crossed.

Heart rate (bpm)

Trend rate / rhythm

Interpret with hydration, perfusion, medications, and symptoms.

Blood glucose (mmol/L)

Check when indicated

Glucose disturbance can cause weakness or altered mentation.

Front-load in the triage report

  • Toxic overdose: Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.
  • Start date or dose change?
  • Symptoms and temporal relationship?
Severe cutaneous reactionTime-sensitive high-risk possibility

HPI

Clarify symptoms and temporal relationship; last dose; allergy vs side effect.

Signs & symptoms

Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.

Focused exam

Assess function against baseline rather than relying on a single normal-looking measurement; Identify all medicines, recent starts or dose changes, last doses, renal and hepatic function, supplements, adherence, and symptom timing.

Brief pathophysiology

Severe cutaneous reaction may cause medication side effect / adverse reaction through a time-sensitive process capable of rapid physiological deterioration.

Vital-sign pattern

What the trend may show

Possible pattern

General medical differentials have overlapping physiology. These four observations screen for deterioration and common reversible causes without implying a diagnosis.

Respiratory rate (breaths/min)

Trend rate / effort

Respiratory rate can reveal early physiologic stress.

Blood pressure (mmHg)

Compare with baseline

Relative hypotension may be important before an absolute threshold is crossed.

Heart rate (bpm)

Trend rate / rhythm

Interpret with hydration, perfusion, medications, and symptoms.

Blood glucose (mmol/L)

Check when indicated

Glucose disturbance can cause weakness or altered mentation.

Front-load in the triage report

  • Severe cutaneous reaction: Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.
  • Symptoms and temporal relationship?
  • Last dose?
Major bleedingTime-sensitive high-risk possibility

HPI

Clarify last dose; allergy vs side effect; other new medications or interactions.

Signs & symptoms

Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.

Focused exam

Assess function against baseline rather than relying on a single normal-looking measurement; Identify all medicines, recent starts or dose changes, last doses, renal and hepatic function, supplements, adherence, and symptom timing.

Brief pathophysiology

Major bleeding may cause medication side effect / adverse reaction through a time-sensitive process capable of rapid physiological deterioration.

Vital-sign pattern

What the trend may show

Possible pattern

Hemorrhage is a trend diagnosis: tachycardia and narrowing pulse pressure may precede hypotension. Age, pregnancy, medications, and pacing can blunt expected responses.

Heart rate (bpm)

Often rises

Tachycardia is a common compensatory response but may be absent.

Pulse pressure (mmHg)

May narrow

Narrowing pulse pressure can reflect reduced stroke volume.

Blood pressure (mmHg)

May fall late

A normal pressure does not exclude significant compensated hemorrhage.

MAP (mmHg)

May fall

A falling trend supports worsening perfusion; interpret with mental status and skin signs.

Front-load in the triage report

  • Major bleeding: Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.
  • Last dose?
  • Allergy vs side effect?
Common2 conditions
Dose-related side effectCommon presentation pattern

HPI

Clarify medication and indication; start date or dose change; symptoms and temporal relationship.

Signs & symptoms

Timing and known pharmacology may fit a milder predictable reaction.

Focused exam

Perform a targeted cardiorespiratory, neurologic, abdominal, skin, and hydration assessment guided by the history; Assess function against baseline rather than relying on a single normal-looking measurement.

Brief pathophysiology

Dose-related side effect may explain the presenting symptoms through a common clinical mechanism, while serial assessment checks for complications or an alternate cause.

Vital-sign pattern

What the trend may show

Possible pattern

General medical differentials have overlapping physiology. These four observations screen for deterioration and common reversible causes without implying a diagnosis.

Respiratory rate (breaths/min)

Trend rate / effort

Respiratory rate can reveal early physiologic stress.

Blood pressure (mmHg)

Compare with baseline

Relative hypotension may be important before an absolute threshold is crossed.

Heart rate (bpm)

Trend rate / rhythm

Interpret with hydration, perfusion, medications, and symptoms.

Blood glucose (mmol/L)

Check when indicated

Glucose disturbance can cause weakness or altered mentation.

Front-load in the triage report

  • Timing and known pharmacology may fit a milder predictable reaction.
  • Medication and indication?
  • Start date or dose change?
InteractionCommon presentation pattern

HPI

Clarify start date or dose change; symptoms and temporal relationship; last dose.

Signs & symptoms

Timing and known pharmacology may fit a milder predictable reaction.

Focused exam

Assess function against baseline rather than relying on a single normal-looking measurement; Identify all medicines, recent starts or dose changes, last doses, renal and hepatic function, supplements, adherence, and symptom timing.

Brief pathophysiology

Interaction may explain the presenting symptoms through a common clinical mechanism, while serial assessment checks for complications or an alternate cause.

Vital-sign pattern

What the trend may show

Possible pattern

General medical differentials have overlapping physiology. These four observations screen for deterioration and common reversible causes without implying a diagnosis.

Respiratory rate (breaths/min)

Trend rate / effort

Respiratory rate can reveal early physiologic stress.

Blood pressure (mmHg)

Compare with baseline

Relative hypotension may be important before an absolute threshold is crossed.

Heart rate (bpm)

Trend rate / rhythm

Interpret with hydration, perfusion, medications, and symptoms.

Blood glucose (mmol/L)

Check when indicated

Glucose disturbance can cause weakness or altered mentation.

Front-load in the triage report

  • Timing and known pharmacology may fit a milder predictable reaction.
  • Start date or dose change?
  • Symptoms and temporal relationship?
Mimics1 condition
New unrelated illnessImportant alternative presentation

HPI

Clarify medication and indication; start date or dose change; symptoms and temporal relationship.

Signs & symptoms

Temporal association does not prove medication causation.

Focused exam

Perform a targeted cardiorespiratory, neurologic, abdominal, skin, and hydration assessment guided by the history; Assess function against baseline rather than relying on a single normal-looking measurement.

Brief pathophysiology

New unrelated illness can resemble medication side effect / adverse reaction through overlapping symptoms or referred physiology despite a different primary mechanism.

Vital-sign pattern

What the trend may show

Possible pattern

General medical differentials have overlapping physiology. These four observations screen for deterioration and common reversible causes without implying a diagnosis.

Respiratory rate (breaths/min)

Trend rate / effort

Respiratory rate can reveal early physiologic stress.

Blood pressure (mmHg)

Compare with baseline

Relative hypotension may be important before an absolute threshold is crossed.

Heart rate (bpm)

Trend rate / rhythm

Interpret with hydration, perfusion, medications, and symptoms.

Blood glucose (mmol/L)

Check when indicated

Glucose disturbance can cause weakness or altered mentation.

Front-load in the triage report

  • Temporal association does not prove medication causation.
  • Medication and indication?
  • Start date or dose change?
Red flags

Findings that should escalate concern

  • Airway swelling, shock, severe rash or mucosal injury, dysrhythmia, seizure, respiratory depression, or severe bleeding is time-sensitive.
  • Anaphylaxis, toxic overdose, severe cutaneous reaction, or major bleeding: Airway, shock, ECG, neurologic, mucosal, or hemorrhagic signs.
Related medications

Medication recognition

CetirizineDiphenhydramineEpinephrine auto-injector
Related EMS presentations

Continue the clinical pathway

General MedicalGeneral weakness / malaiseToxicologyOverdose / drug poisoningAllergic/ImmunologicAllergic reaction / anaphylaxisIntegumentaryRash / skin eruptionHematologicBleeding while anticoagulated
References

Clinical and academic sources

Curated clinical guidance and peer-reviewed evidence supporting this presentation. Current BCEHS guidance, medical direction, and local policy remain authoritative for practice.

BCEHS Handbook — specific CPGs

  1. E09: AnaphylaxisBC Emergency Health Services Handbook

    Official BCEHS clinical practice guidance for anaphylaxis.

  2. J01: Approach to Chemical or Toxic ExposuresBC Emergency Health Services Handbook

    Official BCEHS clinical practice guidance for approach to chemical or toxic exposures.

Supporting clinical and academic evidence

  1. CEDIS Presenting Complaint List updateCanadian Association of Emergency Physicians

    Presenting-complaint terminology and categorization context. It does not establish a prehospital “top 100” ranking.

  2. WHO Medical Emergency ChecklistWorld Health Organization

    A structured emergency assessment framework intended to reduce missed life-threatening conditions.

  3. Management of serotonin syndrome (toxicity)British Journal of Clinical Pharmacology · 2025

    Medication reconciliation, toxidrome recognition, autonomic and neuromuscular findings, and supportive toxicity care.