Pyrexia is the medical term for fever. The word “pyrexia” comes from the Greek word pyretos, which means “fire.” A pyrogen is any substance that produces fever. Pyrogens may be:
- Exogenous pyrogens – come from outside the body, usually microbes or their toxins (e.g., LPS from gram-negative bacteria, enterotoxins from Staphylococcus aureus)
- Endogenous pyrogens – produced inside the body by immune cells (e.g., IL-1, IL-6, TNF-α)
Fever is defined as a rise in body temperature above the normal range of 36–37°C (98–100°F). It is a protective response indicating infection or inflammation. Body temperature can be measured using oral, axillary, rectal or tympanic routes.
Types of Fever
- Continuous fever: Temperature remains above normal for long periods (e.g., pneumonia, typhoid, UTI)
- Intermittent fever: Temperature rises and falls at intervals (e.g., malaria)
- Relapsing fever: Fever returns after a normal temperature period (e.g., infective endocarditis)
Signs and Symptoms
Common symptoms of pyrexia include:
- Shivering or chills
- Loss of appetite
- Dehydration
- Lethargy
- Poor concentration
- Increased sleepiness
- Cold sensation
Severe fever may also cause irritability, confusion, delirium or even convulsions, especially in children.
Medications That May Increase Body Temperature
Certain drugs can induce fever as a side effect:
- Antimicrobials: Isoniazid
- Anti-arrhythmics: Procainamide, Quinidine
- Antiepileptics: Phenytoin, Carbamazepine
- Antihypertensives: Alpha-methyldopa
- Antifungals: Amphotericin-B
- Ephedrine
- Sulfa drugs
- Interferons
- Narcotics/illicit drugs: Cocaine, Cannabis
Pathophysiology
The body maintains temperature through a balance of heat production and heat loss. The hypothalamus
Mechanism of fever:
- Pyrogens (either microbial products or cytokines) enter the bloodstream
- They reach the hypothalamus and raise the body’s “set point” temperature
- To reach this new set point, the body reduces heat loss through vasoconstriction
- Shivering increases heat production
- Fever persists until the blood temperature matches the new set point
Children often develop faster and higher fevers due to a more reactive immune system.
Non-Pharmacological Management
Mild fever usually does not require medication. Supportive care is often sufficient.
- Drink plenty of fluids (water, ORS)
- Rest in a comfortable environment
- Wear light clothing; avoid excess blankets
- Keep room cool and well-ventilated
- Use lukewarm sponging if fever is high (avoid cold water or ice — they increase shivering)
Prevention
As most fevers are infection-related, general hygiene is essential:
- Wash hands before meals and after washroom use
- Avoid contact with sick individuals
- Use masks during infections
- Maintain clean surroundings
Home Remedies
Traditional supportive remedies may provide comfort:
- Bed rest and hydration
- Cold compress on the forehead
- Tepid sponge bath to reduce heat
- Turmeric milk: 1 tsp turmeric in warm milk for GI or respiratory infections
- Mint herbal mix: Mint leaves + pepper + ginger boiled in water (helps in GI-related fever)
- Lemongrass tea with honey for mild fever
- Sandalwood paste on forehead for cooling effect
Pharmacological Management
The main goal is to reduce fever and increase comfort.
Paracetamol (First-line drug)
- Adults (≥ 12 years): 325–650 mg every 6 hours
- Children 4–11 years: 320–500 mg every 6 hours
- Children < 4 years: 5 mL (16 mg/mL) as per paediatric dosing
Paracetamol works by inhibiting prostaglandin synthesis in the brain and is safe when used in recommended doses.
When to Refer to a Doctor
Referral is necessary when the patient shows:
- Very high fever not responding to medication
- Convulsions
- Stiff neck or severe headache
- Breathing difficulties
- Persistent vomiting
- Rashes along with fever
- Dehydration signs (dry mouth, no urine, sunken eyes)
- Fever lasting more than 3 days
Detailed Notes:
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