Filtration

Part of Antibiotics

Methods for separating penicillin-containing broth from mold mycelia and particulate matter using improvised filtration equipment.

Why This Matters

Raw penicillin broth contains the mold mat, mycelial fragments, growth medium residues, spores, and the penicillin itself dissolved in solution. Before concentration and administration, this mixture must be clarified — the liquid separated from solid matter.

This step matters for two reasons. First, injecting material containing large particulates or mold fragments causes local tissue reactions and potential granuloma formation. Second, mycelial fragments and spores in an oral dose add unnecessary immune burden and may cause reactions in sensitive patients.

Filtration in modern pharmaceutical production uses sterile membrane filters with 0.22 micron pore sizes that remove even bacteria and spores. This is not achievable with improvised materials. The achievable goal is removal of visible particulates and mold fragments — a clarified preparation safe for oral use and adequate for IM injection with appropriate precautions.

Stages of Filtration

Stage 1: Gross Separation (Decanting)

Before any filtration, separate the majority of mold mass:

1. Allow culture vessel to sit undisturbed for 15–20 minutes after harvest
2. The mold mat typically floats or settles
3. Carefully pour off the liquid (broth) from below the mold mat, leaving the mat behind
4. Tilt vessel slowly to minimize disturbance

This removes 70–80% of mold mass without any filter needed.

Stage 2: Coarse Filtration

Remove remaining mold fragments and large particles:

Method A — Cloth filtration:

1. Layer 4–6 pieces of tightly woven cloth (clean linen or cotton) inside a clean funnel or strainer
2. Pour broth through slowly — do not press or force
3. Allow gravity drainage; forcing pushes particles through filter
4. Rinse filter cloth with small amount of sterile water to wash through retained broth

Method B — Paper filtration:

1. Use quality paper — parchment, thick handmade paper, or folded document paper
2. Wet paper first to improve flow
3. Fold into cone shape and seat in funnel
4. Filter rate will be slow; allow time

Method C — Charcoal/sand filter:

1. Layer clean sand (washed and sterilized by dry heat) over a layer of activated charcoal in a funnel
2. Top with a layer of cloth
3. Pre-wet the entire filter with sterile water before use
4. Note: charcoal may adsorb some penicillin — minimize contact time by running through quickly

Stage 3: Fine Filtration

For preparations intended for injection, additional clarification is needed:

Diatomite filter (if available): Diatomaceous earth — fine silica powder from fossilized algae, found in lake sediments and some geological deposits — forms an excellent filter bed:

1. Mix 10 g diatomite per 100 mL water to form slurry
2. Pour slurry onto cloth filter; allow to compact and dry partially
3. Pre-filter broth through diatomite layer
4. The diatomite bed captures particles down to 1–2 microns

Multiple pass filtration: Pass clarified broth through successive clean cloth layers, each time using freshly laundered and sterilized cloth. Each pass removes progressively smaller particles. Four to six passes produces a noticeably clearer solution.

Stage 4: Sterilization Filtration (Advanced)

True sterile filtration requires membrane filters unavailable in most contexts. If injectable preparations are intended, the alternative is heat treatment:

• Penicillin degrades at temperatures above 37–40°C
• However, very brief heat treatment (60°C for 30 minutes — pasteurization equivalent) kills most bacteria and fungi without completely destroying penicillin
• Activity loss is approximately 30–50% but the preparation is far safer for injection
• This is not sterile filtration, but it significantly reduces bacterial load

Equipment Sterilization

All filtration equipment must be pre-sterilized:

Equipment	Sterilization Method
Glass funnels, bottles	Dry heat 160°C x 60 min
Cloth filters	Boiling water 15 min
Rubber tubing	Boiling water 15 min or alcohol soak
Ceramic/clay filters	Dry heat 200°C x 60 min
Paper filters	Single use, fresh each batch

After sterilization, cool completely before use. Introducing hot filter material into penicillin broth will destroy the penicillin.

Evaluating Clarity

After filtration, assess the preparation:

Acceptable for oral use:

• No visible floating particles or mold fragments
• May have slight haze or color
• Normal odor (earthy, slightly medicinal)

Acceptable for IM injection:

• Visibly clear when held to light
• No visible particles
• No cloudiness (which indicates bacterial contamination or protein aggregates)
• If any cloudiness, perform additional filtration passes or heat treatment

Discard if:

• Unusual color (pink, brown, black — may indicate contamination)
• Foul odor (putrefaction, bacterial overgrowth)
• Visible moving particles (bacteria) under strong light

Practical Filtration Setup

A workable continuous filtration station:

1. Sterile collection flask at bottom (sealed with cloth cover)
2. Funnel above, seated in flask mouth
3. Multiple cloth layers in funnel
4. Broth poured into top of funnel
5. Second funnel with different filter medium below first (series filtration)

For larger volumes, a drip filtration system with controlled flow rate produces cleaner output than rapid batch filtration. Gravity-fed systems are preferable to pressurized systems — pressure forces particles through filter media.

Storage After Filtration

Filtered broth should be:

• Stored in sealed glass containers (not metal)
• Kept cold and dark (cellar, cold room, ice if available)
• Used within 7 days of production without refrigeration
• Used within 30 days if stored at 4°C

Re-filter through fresh cloth immediately before use if storage has been longer than 48 hours at room temperature — bacterial regrowth can occur in nutrient broth even after initial filtration.

Label every container with production date, batch number, and filtration method used. This allows traceability if a patient experiences an adverse reaction.