Chap 50: Misc antimicrobial agents

METRONIDAZOLE
- antiprotozoal + antibacterial (anerobes) - bacteroides, clostridium
- well absorbed po - use as 1st line
- crosses BBB
- iv/pr/po
- metabolised by liver
- clinical uses

• anerobes - intra-abdominal infection
• vaginosis - can use topically
• clostridium
• brain abscess

- adverse

• GI - N/V/D
• peripheral neuropathy with prolonged use (never discharge someone on long term flagyl) - irreversible

MUPIROCIN
- produced Pseudomonas fluorescens
- inactived after po --> only topical
- MOA and uses

• g+ve cocci - MSSA and MRSA
• inhibit isoleucyl tRNA synthetase
• can induce resistance
• topical treatment for minor skin infection - impetigo
• intranasal elimination of MRSA
• NOT recommended for long term ulcers/surgical wound due to emergence of resistance

NITROFURANTOIN
- g+ve, g-ve bacteria
- well absorbed - rapidly metabolised and excreted --> no systemic antibacterial action, only in urine - renal impairment can cause systemic toxicity
- clinically - prophylaxis of chronic UTI - keep urine pH <5.5 (enhances activity)
- SE - N/V, G6PD def (neuropathy, hemolytic anemia)

DISINFECTANTS, ANTISEPTICS, STERILANTS
Disinfectants - strong chemicals that inhibit/kill microbes
Antiseptics - disinfectants with low toxicity to host cell - used on mucous membrane, skin
Sterilants - kills vegetative cells and spores

Alcohol
- disinfectant + antiseptic - denatures proteins
- NOT sporicidal hence not sterilant
- ethanol and isopropyl alcohol (isopropanol)
- quick - kills vegetative bacteria, mycobacteria, many fungi, lipophilic viruses
- optimal concentration - 60-90% by volume in water
- disadvantages

• lack residual action - evaporate quickly
• skin drying effect - can add emollient
• damages corneal tissue - tonometer has to be wait till completely evaporated/water rinsed
• flammable

Chlorhexidine
- active for vegetative bac, mycobacteria, moderate against fungi and viruses
- strongly binds to bac membranes --> leakage of small molecules + precipitation of cytoplasmic proteins
- slower action than alcohol --> but has residual activity hence similar to alcohol action if used repeatedly
- most effective - g+ve cocci, inhibit spore germination
- less irritating to skini
- no oral toxicity (poorly gut absorbed) - can cause ototoxicity and neurotoxicity (never used in such surgeries)

Halogens
- Iodine

• most active antiseptic for intact skin
• bactericidal in 1 min; kills spores in 15 mins
• problems: hypersensitivity reaction, stains clothing + dressings

- Iodophors

• complexes of I2
• retain activity as above
• less irritating to skin + producing less toxicity

- Chlorine

• universal disinfectant - oxidizing agent - must be kept in air sealed containers
• inactivated by serum/blood/feces/urine/protein containing stuff --> hence surfaced must be cleaned before using