medicines and drugs

antibacterials

antibacterials

• D 6.1 Outline the historical development of penicillins.

• D 6.2 Explain how penicillins work and discuss the effects of modifying the side-chain.

• D 6.3 Discuss and explain the importance of patient compliance and the effect of penicillin overprescription.

antibacterials

• How do bacteria act?

• What infectious diseases are caused by bacteria?

• How are bacteria spread?

• What were the contributions of Fleming, Florey and Chain?

diseases caused by bacteria

• tuberculosis, • syphilis, • cholera, • salmonella, • bronchitis, • anthrax, • meningitis, • gonorrhea, • chlamydia.

antibacterials• Antibacterials are drugs that kill or inhibit the

growth of bacteria that cause infectious diseases.

• Penicillins are a group of compounds produced by microrganisms to be used against other harmful microrganism.

historical development of penicillins• Alexander Fleming, Howard Florey and

Ernst Chain shared the Nobel Prize (1945) for “the discovery of penicillin and its curative effect in various infectious diseases”.

• Discovered by chance that penicillin inhibited growth or killed bacteria; Fleming had left a bacteria culture and later found a clear zone in the culture in which bacteria had been killed. That zone had been contaminated by a fungus called Penicillium notatum.

historical development of penicillins

Howard Florey and Ernst Chain overcame the problems associated with

isolating and concentrating the penicillin as penicillin G

showed that penicillin is harmless and effective on mice

first to use penicillin on a human grew penicillin in large amounts grew strains of penicillin in corn-steep

liquor

What is the molecular formula of a penicillin G molecule? What functional groups?

penicillin G C16H18O4N2S (Mr= 334)

Functional groups: 4-membered ring with N

(beta-lactam ring) benzene ring amide carbonyl carboxylic acid tertiary amine secondary amine sulphur atom

penicillin action• Penicillins work by deactivating the proteins that

a bacteria needs to form a cell wall. This prevents the formation of cross-links within the cell wall.

• As a result the bacterial cell absorbs too much water and bursts as the result of increased osmotic pressure.

administering of antibacterials

There are two types of antibacterials

obroad-spectrum antibacterials are effective against a wide range of bacteria

onarrow-spectrum only kill a limited range of bacteria

administering antibacterials

With some diseases, e.g. tuberculosis (TB) it is important to administer a “cocktail” of different antibacterials (broad spectrum) because bacteria which cause TB are usually extremely resistant to penicillins so a mixture of different antibacterials is used.

bacterial resistance

• Explain

Increased bacterial resistance to penicillin

oresistant bacteria produce penicillinase, an enzyme, which breaks open the

4-membered ring in the penicillin molecule

oresistant bacteria reproduce and pass on their resistance to succeeding generations

bacterial resistance to penicillin

The more bacteria are exposed to antibacterials, the more opportunities there are for the bacteria to mutate into bacteria that have genes to produce penicillinase.

Increased resistance because of misuse

• Antibacterials are used in animal feedstock even when the animals do not have a disease. The antibacterials end up in the food chain

• Overprescription by doctors.• Patient compliance: Patients not completing a

full course of penicillin or antibiotics and not killing all harmful bacteria

modifying side-chain of penicillin G

Modern or semi-synthetic penicillins, such as ampicillin, are penicillin molecules in which the side-chain has been modified to alter its properties. In the case of ampicillin (can be taken orally), the side chain now contains: a benzene or C6H5 ring, an amine (-NH2) group

and a hydrogen

Modifying side-chain of penicillin GThe different side-chain brings advantages:

o reducing the occurence of penicillin resistant bacteria as the modified penicillins are able to withstand the action of the enzyme penicillinase that is produced by resistant bacteria.

o resistance to breakdown by stomach acid (so can be taken orally); penicillin G had to be injected because it was broken down by stomach acid. Ampillicin is a modified penicillin G molecule can be taken orally.