Dosage Guidelines

Part of Antibiotics

Reference dosing for penicillin and alternative antimicrobials, including weight-based adjustments and modifications for crude preparations.

Why This Matters

Antibiotic dosing is not intuitive. Too little and the drug fails to achieve adequate tissue concentrations to kill bacteria — the infection persists and resistant organisms are selected. Too much and adverse effects accumulate, wasting precious supply, and in some cases causing toxicity.

With crude, incompletely characterized preparations, dosing is further complicated because you cannot know exact concentration. This article provides frameworks for working with uncertain potency — calibrating from bioassay results, erring toward adequacy rather than conservation, and adjusting for patient characteristics.

The guiding principle: underdosing is more dangerous than overdosing with penicillin. Penicillin has a wide safety margin — it is very difficult to achieve toxic doses by oral or intramuscular routes. The greater risk is always underdosing and treatment failure.

Pharmaceutical Reference Doses

These are the dosing standards for pharmaceutical penicillin, provided as calibration targets:

Penicillin G (Injectable)

Indication	Dose	Frequency	Route
Mild infections	1–2 million units	Every 6 hours	IM
Severe infections	4–24 million units/day	Every 4–6 hours	IV/IM
Strep throat	1.2 million units	Single dose	IM
Pneumonia	4–8 million units/day	Divided doses	IV/IM

Note: 1 million International Units (IU) of penicillin G = approximately 600 mg

Penicillin V (Oral)

Indication	Dose	Frequency
Strep throat	500 mg	Four times daily x 10 days
Mild skin infection	250–500 mg	Four times daily x 7–10 days
Prevention (rheumatic fever)	250 mg	Twice daily ongoing

Amoxicillin (Broader Penicillin Derivative)

Indication	Dose	Frequency
Ear/sinus infection	500 mg	Three times daily x 7–10 days
Pneumonia	1,000 mg	Three times daily x 7 days
Urinary tract infection	500 mg	Three times daily x 7 days

Dosing Crude Preparations

Without exact concentration data, use relative potency from bioassay:

Bioassay-Based Dosing

If your inhibition zone is:

• Less than 10 mm: Preparation is weak. Use 3–4x normal volume per dose. Uncertain efficacy.
• 10–15 mm: Moderate potency. Use 1.5–2x normal volume per dose.
• 15–20 mm: Good potency. Use standard volume equivalent to pharmaceutical reference.
• Greater than 20 mm: High potency. May use slightly less than pharmaceutical reference.

For injections, “normal volume” is the volume you have standardized as your production unit (e.g., 5 mL per dose). Adjust up or down based on bioassay relative to pharmaceutical reference of known potency.

Practical Dosing Protocol for Crude Oral Penicillin

Without concentration data, administer crude broth orally at:

• 30–50 mL concentrated extract (10x concentrate) per dose
• 150–250 mL raw broth per dose (impractical for very dilute preparations)
• Four times daily for serious infections
• Three times daily for mild infections if supply limited

Adjust upward if no clinical response at 48 hours.

Weight-Based Adjustments

Standard adult doses assume approximately 70 kg body weight. Adjust as follows:

Patient Weight	Dose Multiplier
Under 30 kg (child)	0.4–0.5x adult dose
30–50 kg	0.7x adult dose
50–80 kg	1x (standard adult)
Over 100 kg	1.2–1.5x adult dose

Pediatric Dosing

For children:

• Penicillin V oral: 12.5 mg/kg per dose, four times daily
• Amoxicillin oral: 25 mg/kg per dose, three times daily
• Maximum: Do not exceed adult dose regardless of weight

Children metabolize some antibiotics more rapidly than adults, requiring dose adjustment. Err toward adequate dosing — the risk of undertreating a child’s serious infection is greater than the risk of mild overdose.

Renal Impairment

Penicillin is excreted primarily by the kidneys. In patients with signs of kidney failure (markedly reduced urine output, edema, elevated creatinine if testable):

• Extend dosing intervals rather than reducing individual doses
• Twice daily instead of four times daily for mild impairment
• Once daily instead of twice daily for severe impairment
• Monitor for signs of toxicity (twitching, seizures at very high accumulation)

Frequency and Timing

Penicillin is a time-dependent antibiotic. Concentration must stay above the MIC continuously. Missing doses is far more damaging than reducing individual dose size.

Priority: Maintain frequency over maximizing individual dose.

If a patient vomits within 30 minutes of oral penicillin, repeat the dose. If vomiting is persistent, consider intramuscular administration if possible.

Food effects: Penicillin absorption is reduced by food. Administer 30–60 minutes before meals when possible. In severely ill patients who cannot tolerate empty-stomach administration, with-food dosing is acceptable — absorption is reduced by 30–50% but maintaining the dose is still beneficial.

Switching Routes

If a patient cannot take oral medication (vomiting, unconscious, severely ill):

Intramuscular injection at same dose is the alternative:

• Absorption is near 100% vs. 30–70% oral
• Reduce dose to 60–70% of oral dose when switching to IM to account for better absorption
• Use large muscle (gluteus, thigh) for injection

When to switch IM to oral:

• Patient can tolerate liquids without vomiting
• Fever trending down, clinical improvement clear
• Switch to oral at equivalent dose to complete course (“step-down therapy”)

Alternative Antimicrobial Dosing

Substance	Dose	Frequency	Notes
Garlic extract (allicin)	2–4 crushed cloves or 300 mg extract	Three times daily	Gut and mild systemic
Honey (medical grade/Manuka equivalent)	Applied topically to wound	Every 12–24 hours	Wound only
Berberine tea	50 mL strong decoction	Three times daily	Gut infections
Thyme tea	200 mL strong infusion	Four times daily	Throat, mild infections
Vinegar wound wash	5 mL diluted 1:3 in water	Applied every 6–8 hours	External wound only

Safety Margins and Overdose

Penicillin toxicity from oral or IM overdose is rare and requires massive doses:

• Neurological effects (twitching, seizures) can occur at very high IV doses — not achievable with crude oral preparations
• Allergic reactions (not dose-dependent) — the primary safety concern; occurs at any dose in sensitized individuals

Practical conclusion: For crude preparations via oral or IM routes, err toward giving more rather than less. The limiting factor is supply and allergic risk, not toxicity from overdose.

Document every dose given, time, route, and patient response. This record is essential for adjusting subsequent doses and for learning from outcomes.