Antimicrobials are the drugs used to treat a microbial infections. An anti–microbial is a substance that kills (microbicidal) or inhibits the growth of microorganisms(microbiostatic) such as bacteria, fungi, or protozoan.
‘Antimicrobial’ is a general term that refers to a group of drugs that includes antibiotics, antifungals, antiprotozoals, and antivirals.
Antibiotics:
The word antibiotic comes from the Greek word ‘anti’ meaning ‘against’ and ‘bios’ meaning
‘Life’ (a bacterium is a life form). ‘Antibiotics’ are also known as antibacterials,these are the drugs used to treat
infections caused by bacteria. Bacteria are tiny organisms that can sometimes cause illness to humans and animal. Diseases such
as tuberculosis, salmonella, syphilis and some forms of meningitis are caused by bacteria.
Antibiotics target microorganisms such as bacteria, fungi and parasites. However, they are not effective against viruses. If antibiotics are over used or used incorrectly there is a chance that the bacteria will become resistant – the antibiotic becomes less effective against that type of bacterium.
The first antibiotic was penicillin. Such penicillin–related antibiotics as ampicillin, amoxicillin and benzylpenicilllin are widely used today to treat a variety of infections, these antibiotics have been around for a long time. There are several different types of modern antibiotics are also available.
Penicillins work by damaging and penetrating the cell walls of bacteria, thus killing the bacteria cells.
A broad–spectrum antibiotic can be used to treat a wide range of infections, the common examples are tetracyclin, chloromycetin, chloramphenicol. A narrow–spectrum antibiotic is only effective against a few types of bacteria, example penicillin.
Antibiotics are usually taken by orally, however, they can also be administered by injection, or applied directly to the affected part of the body. Most antibiotics start having an effect on an infection within a few hours.
Below is a list of the most common side–effects of antibiotics:
- Diarrhoea
- Feeling and being sick
- Fungal infections of the mouth, digestive tract and vagina.
| Drug | Viruses | Chemical Type |
|---|---|---|
| Vidarabine | Herpesviruses | Nucleoside analogue |
| Acyclovir | Herpes simplex(HSV) | Nucleoside analogue |
| Gancyclovir | Cytomegalovirus (CMV) | Nucleoside analogue |
| Nucleoside–analog reverse transcriptase inhibitors (NRTI): AZT(Zidovudine), ddl(Didanosine), ddC(Zalcitabine), d4T (Stavudine), 3TC (Lamivudine) | Retroviruses (HIV) | Nucleoside analogue |
| Non–nucleoside reverse transcriptase inhibitors (NNRTI) : Nevirapine, Delavirdine | Retroviruses (HIV) | Nucleoside analogue |
| Protease Inhibitors : Saquinavir, Ritonavir, Indinavir, Nelfinavir | HIV | Peptide analogue |
| Ribavirin | Broad spectrum : HCV, HSV, measles, mumps, Lassa fever | Triazole carboxamide |
| Amantadine/ Rimantadine | Influenza A strains | Tricyclic amine |
| Interferons | Hepatitis B and C | Protein |
Antivirals:
Antiviral drugs are a class of medication used specifically for treating viral infections. These drugs do not kill the virus
but they are used to inbit their growth. Specific antiviral drugs are used against specific viruses.
Most of the antiviral drugs now available are designed to help deal with HIV, herpes viruses the hepatitis ‘B’ and ‘C’ viruses, which can cause liver cancer, and influenza ‘A’; and ‘B’ viruses. Researchers are working to extend the range of antivirals to other families of pathogens. Some of antiviral drugs are as follow
Acyclovir is used for the treatment of herpes simplex virus infections, as well as in the treatment of varicella zoster (chickenpox) and herpes zoster (shingles).
Vidarabine is an antiviral drug which is active against herpes simplex and varicella zoster viruses.
Nucleoside–analog reverse transcriptase inhibitors (NRTI): AZT (Zidovudine), ddI (Didanosine), ddC (Zalcitabine), d4T (Stavudine), 3TC (Lamivudine) are used in HIV treatment.
Antifungal Agents
Antifungals:
Fungal diseases are called mycoses and those affecting humans can be divided into four groups based on the level of penetration
of pathogen into the body tissues.These are Superficial mycoses, Cutaneous mycoses,Subcutaneous mycoses and Systemic or deep
mycoses is able to infect internal organs and become widely disseminated throughout the body. This type is often fatal.
Common systemic fungal diseases are: Systemic candidiasis, Cryptococcal meningitis or endocarditis, Pulmonary or cerebral Aspergillosis. Rhinocerebral Mucormycosis, Blastomycosis, Histoplasmosis, Coccidiomycosis and Paracoccidiomycosis.
An antifungal agent is a drug that selectively eliminates fungal pathogens from a host with minimal toxicity
to the host. Some of the antifungal drugs are as follow:
Amphotericin, nystatin, and pimaricin interact with sterols in the cell membrane (ergosterol in fungi, cholesterol in humans)
to form channels through which small molecules leak from the inside of the fungal cell to the outside resulting in the fungal
death.
Azole Antifungal Drugs:
Fluconazole, itraconazole, and ketoconazole inhibit cytochrome P450–dependent enzymes (particularly
C14–demethylase) involved in the biosynthesis of ergosterol, which is required for fungal cell membrane structure and
function of fungi.