BENZYL PENICILLIN; Penicillin-g and related drugs:
Spectrum:
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Gram _+ve: Streptococcus spp, Pneumococci, Staphylcoccus spp
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Gram _–ve: Gonorrhea and Treponemae
Cons: Taken by Injections Only, short half life, Beta Lactamase susceptible, Narrow spectrum
Drugs: Procaine; I.M. w/ Comb P.G; I.V. & I.M.., Benzathine; I.M. , Penicillin V; oral + Phenethicillin -The only antibiotic that can be used for prophylaxis (Benzathine)
Classification:
A.Injectable preparations: Short-acting preparation e.g. benzyl penicillin (penicillin-G): (6 hours) Its distribution is all over the body except CSF But it diffuses to CSF if meninges are inflamed (meningitis). Can be destroyed by B lactamase.
B. Long-acting preparations: To overcome the drawback of the short duration of action of benzyl penicillin, which necessitates its frequent parenteral administration, long acting preparations of benzyl penicillin were prepared. These preparations are given only intramuscularly and never intravenously. The long acting penicillins include
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Procaine penicillin-G: 12-24 hours - This is a combination of procaine & benzyl penicillin. It consists of 100.000 units of procaine penicillin + 100.000 units of benzyl penicillin.
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Fortified procaine penicillin: 24 hours - It consists of 300.000 units of procaine penicillin + 100.000 units of benzyl penicillin-Given once daily IM.
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Benzathine penicillin: This preparation produces low blood levels lasting from few days to 4 weeks depending on the dose. It should not be used in acute infections because the blood levels are low. So it is used in chemoprophylaxis of rheumatic fever.
C. Oral preparations: These penicillins are stable in acid medium and hence escape destruction in the gastric juice. They include: Phenoxymethyl penicillin (penicillin V) & - Phenethicillin
Other therapeutic uses in Prophylaxis (Benzathine only)
- To prevent recurrency of Acute Rheumatic Fever
- To prevent gonorrheal opthlamia in neonates
- To prevent subacute bacterial infective endocarditis occurring due to
- Operative procedures (eg. Dental extraction, Tonsillectomy)
- Congenital or acquired vascular diseases
- Immunocompromised