Antibiotic Selection & Dosing Guide

Antibiotics only work against bacteria. Do not use them for viral infections (colds, flu, COVID-19, most sore throats). Signs suggesting bacterial infection rather than viral:

• Fever lasting >3 days
• Productive cough with thick, purulent (pus-like) sputum
• Localized warmth, swelling, redness, or pus at a wound site
• Dysuria (painful urination) with urgency and frequency
• Abdominal pain with diarrhea lasting >2 days
• Severe sore throat with white/yellow patches and difficulty swallowing

In survival scenarios without lab testing, observe for 48–72 hours. If symptoms worsen or signs of systemic infection appear (high fever, chills, spreading redness), proceed with antibiotics. If symptoms improve or remain stable, avoid unnecessary antibiotics.

Unnecessary antibiotic use accelerates resistance and can cause serious side effects including allergic reactions, GI dysfunction, and secondary infections.

First-line: Amoxicillin

• Standard dose: 500 mg orally three times daily (or 875 mg twice daily)
• Duration: 7–10 days minimum
• Best for: community-acquired pneumonia, acute bronchitis, sinusitis in non-severe cases

If Penicillin-Allergic: Doxycycline

• Standard dose: 100 mg orally twice daily
• Duration: 7–10 days

If Moderate-to-Severe (high fever, severe dyspnea, altered mental status):

• Escalate to Amoxicillin-clavulanate 875/125 mg twice daily if available
• Or use Doxycycline 100 mg twice daily (covers atypicals like Mycoplasma)

Signs to watch: Worsening shortness of breath, confusion, chest pain with breathing, or failure to improve after 48–72 hours of treatment indicate need for escalation or specialist care if available.

Standard Cellulitis/Minor Wound Infection: Amoxicillin-clavulanate

• Standard dose: 875/125 mg orally twice daily
• Duration: 7–10 days
• Covers Staphylococcus and Streptococcus; clavulanate prevents beta-lactamase resistance

Alternative: Cephalexin (if amoxicillin unavailable)

• Standard dose: 500 mg orally four times daily
• Duration: 7–10 days
• Cross-reactivity with penicillin allergy is 1–3%; safer than amoxicillin in true penicillin allergy

Suspected or Confirmed MRSA (Methicillin-Resistant Staph aureus):

• Doxycycline 100 mg twice daily, OR
• Trimethoprim-Sulfamethoxazole (TMP-SMX) 160/800 mg twice daily
• Duration: 10–14 days

Also required: Drain pus if localized abscess; wash wound daily with clean water and soap; apply sterile dressing to prevent secondary contamination.

Spreading redness beyond the initial area, rapid progression, or fever >39°C (102°F) suggest systemic involvement or MRSA; escalate to doxycycline or TMP-SMX.

First-line: Ciprofloxacin (fluoroquinolone)

• Standard dose: 500 mg orally twice daily (cystitis: 3 days; pyelonephritis: 7 days)
• Excellent urinary penetration and broad activity

Alternative: Trimethoprim-Sulfamethoxazole (TMP-SMX)

• Standard dose: 160/800 mg (1 double-strength tablet) twice daily
• Duration: 3 days for uncomplicated cystitis; 14 days for pyelonephritis

Uncomplicated Cystitis (bladder only):

• Fever absent; dysuria, urgency, frequency only
• Shorter courses (3 days) are sufficient

Pyelonephritis (kidney infection):

• Fever ≥38.5°C (101°F), flank pain, nausea/vomiting
• Requires 7–14 day course
• If vomiting prevents oral intake or signs of sepsis, seek medical care

Supportive care: Increase fluid intake to dilute urine and flush bacteria; avoid caffeine and alcohol which irritate the bladder.

Pyelonephritis with high fever, rigors, or hypotension can progress to sepsis; this is a medical emergency if available care exists.

For Suspected Parasitic or Anaerobic GI Infection: Metronidazole

• Standard dose: 500 mg orally three times daily
• Duration: 7–10 days
• Covers Giardia, Entamoeba, Clostridium difficile, and anaerobic bacteria

For Bacterial Enteritis (Salmonella, Shigella, Campylobacter): Ciprofloxacin

• Standard dose: 500 mg orally twice daily
• Duration: 3–5 days (do not overtreat; diarrhea often self-limited)
• Only use if fever or bloody stools are present

Combination for Mixed or Severe Infections:

• Metronidazole 500 mg three times daily PLUS Ciprofloxacin 500 mg twice daily
• Duration: 7–10 days

Critical supportive care: Oral rehydration solution (ORS) is more important than antibiotics for diarrheal illness. Replace electrolytes and fluid losses aggressively to prevent shock, especially in children and elderly.

Caution: Avoid antimotility agents (loperamide/Imodium) in bacterial diarrhea; they can trap organisms and worsen infection.

Signs of severe dehydration (extreme thirst, dark urine, confusion, rapid heartbeat) or bloody diarrhea with high fever indicate potential dysentery or invasive infection requiring urgent care.

Untreated dental infections can spread to soft tissues of the neck and airway, causing life-threatening cellulitis or Ludwig's angina.

Standard Treatment: Amoxicillin + Metronidazole (Combination)

• Amoxicillin: 500 mg three times daily
• Metronidazole: 500 mg three times daily
• Duration: 7–10 days
• Covers both aerobic (Streptococcus, Staph) and anaerobic (Peptostreptococcus, Prevotella) oral flora

If Penicillin-Allergic:

• Doxycycline 100 mg twice daily PLUS Metronidazole 500 mg three times daily
• Duration: 7–10 days

Alternative (if combination unavailable):

• Amoxicillin-clavulanate 875/125 mg twice daily (covers anaerobes better than plain amoxicillin)

Also required: Drainage of pus if abscess is fluctuant; this is critical and cannot be replaced by antibiotics alone. Salt water rinses (1 teaspoon salt per 8 oz warm water) four times daily. Avoid hard, hot, or cold foods that irritate the tooth.

Swelling of the jaw, difficulty swallowing, muffled voice, or trismus (inability to open mouth) suggest deep space infection spreading to neck tissues—this is a surgical emergency if possible to reach care.

Key Principles:

1. Complete the Full Course: Do not stop antibiotics when symptoms improve. Incomplete courses breed resistance and allow relapse. Finish every tablet/capsule as prescribed, even if you feel better after 3–4 days.

2. Consistent Spacing: Take doses at regular intervals (e.g., every 8 hours for three-times-daily dosing). Set reminders if needed. Irregular spacing drops blood levels and allows bacterial regrowth.

3. Take with Food (Context-Dependent):

   • Amoxicillin: Can take with or without food
   • Doxycycline: Take with full glass of water on empty stomach; food impairs absorption (do not take with dairy, iron, or antacids)
   • Ciprofloxacin: Take with or without food; avoid dairy, iron, antacids, and calcium supplements within 2 hours
   • Metronidazole: Can take with food if GI upset occurs
   • TMP-SMX: Can take with or without food

4. Storage: Keep antibiotics in cool, dry place away from sunlight. Liquid suspensions expire sooner than tablets; use liquid within 14 days of reconstitution if refrigerated.

5. Typical Course Duration:

   • Uncomplicated infections: 7–10 days
   • Pyelonephritis, pneumonia: 7–14 days
   • Serious/deep infections: 14 days or longer

Dose Adjustments (If Kidney Impairment Suspected): If the person has chronic kidney disease or is elderly, reduce fluoroquinolone doses by 25–50%; consult documentation if available.

Reassess at 48–72 hours after starting antibiotics. Infection may be worsening if:

• Fever remains high (>39°C / 102°F) or returns after initial improvement
• Redness, warmth, or swelling is spreading beyond initial boundaries
• Purulent discharge is increasing rather than decreasing
• Systemic signs develop: Chills, malaise, muscle aches, rapid heartbeat, rapid breathing
• For respiratory infections: Worsening shortness of breath, confusion, or chest pain
• For UTIs/pyelonephritis: Pain is worsening, fever is climbing, or nausea/vomiting prevents oral rehydration
• For GI infections: Bloody diarrhea develops, dehydration is severe, or abdominal pain is intense

Possible Reasons for Failure:

1. Wrong antibiotic for the organism (e.g., using amoxicillin for MRSA)
2. Inadequate dose or irregular dosing
3. Resistant bacteria (MRSA, ESBL-producing Gram-negatives)
4. Abscess or loculated infection that requires surgical drainage, not just antibiotics
5. Immunocompromised state (HIV, severe malnutrition, uncontrolled diabetes)

Response:

• If available, switch to a broader-spectrum antibiotic (e.g., Doxycycline or Fluoroquinolone if not already used)
• Ensure the infection site is drained of pus (wound care, abscess drainage)
• Verify compliance and dosing schedule
• Seek professional medical care if possible; escalating infections can lead to sepsis and death

Spreading cellulitis with systemic toxicity, persistent high fever despite antibiotics, or signs of shock (weakness, confusion, rapid weak pulse, cool skin) indicate sepsis—a life-threatening emergency requiring IV antibiotics and fluid resuscitation.

True Penicillin Allergy (IgE-Mediated Anaphylaxis/Severe Rash):

Avoid all penicillins and cephalosporins (small cross-reactivity risk, 1–3%). Instead:

• Doxycycline 100 mg twice daily (respiratory, skin, mixed infections)
• Ciprofloxacin 500 mg twice daily (UTIs, GI infections, respiratory)
• Trimethoprim-Sulfamethoxazole 160/800 mg twice daily (skin, UTIs, some respiratory)
• Metronidazole 500 mg three times daily (GI, anaerobic, dental infections)

Mild Rash to Penicillin (Non-IgE Maculopapular Rash):

Risk of cross-reactivity with cephalosporins is very low. Cephalexin is generally safe; monitor for rash recurrence.

Sulfa Allergy:

Avoid TMP-SMX (Bactrim, Septra). Use Doxycycline or Fluoroquinolones instead.

Tetracycline (Doxycycline) Contraindications:

• Pregnancy (causes fetal bone/teeth discoloration)
• Children <8 years (same reason)
• Severe renal impairment (accumulates in body)
• Photosensitivity risk in sunny survival scenarios (wear protective clothing)

Fluoroquinolone Cautions:

• Avoid in pregnancy if possible
• Can weaken tendons (Achilles tendon rupture risk), especially in elderly or those taking corticosteroids
• May cause QT prolongation (heartbeat irregularity); use with caution if access to cardiac medication or history of arrhythmia

Document your allergies clearly in your survival kit or on your person so that others administering aid know what to avoid.

If true anaphylaxis (throat swelling, wheezing, rapid pulse, loss of consciousness) occurs, stop the antibiotic immediately and seek emergency care. Anaphylaxis requires epinephrine if available.