Secondary prevention
Once a person has been diagnosed with ARF, the objective is to prevent further GAS pharyngitis infections. For this reason, the use of prophylactic penicillin (via intramuscular injection, administered every 28 days) is recommended. Use of prophylactic penicillin is associated with an 87-96 per cent reduction in ARF recurrence, a 71-91 per cent reduction in GAS pharyngitis and may also reduce severity and mortality of RHD. (15)
Box 2. Penicillin--injection therapy for rheumatic disease
PENICILLIN--THE recommended drug to treat acute rheumatic
fever--was the first antibiotic to be used in clinical practice. It
was discovered in the 1920s, although not used to treat patients
until 1940. Penicillin is a narrow-spectrum antibiotic, acting only
on aerobic Gram-positive bacteria. It is classed as a beta-lactam
antibiotic, which refers to a ring in the chemical structure of
penicillin and similar antibiotics, which allows the drug to bind
to and act upon its target in the bacterial cell.
Gram-positive bacteria have no outer membrane, which leaves exposed
the layer of peptidoglycan molecules that make up the rigid cell
wall. When penicillin encounters a Gram-positive bacterium, the
drug binds to a receptor (the penicillin-binding protein) and
inhibits assembly of the peptidoglycan wall. Loss of cell wall
structure causes the bacterial cell to burst (lysis), making
penicillin a bacteriocidal antibiotic.
Penicillin resistance occurs when the bacterial species either
modifies the penicillin-binding protein so the drug cannot bind to
its target, or synthesises an enzyme (beta-lactamase) that destroys
the drug before it can act. GAS has not shown resistance to
penicillin. Sometimes treatment failure occurs where there is poor
infiltration of the drug into cells in which GAS is latent.
Benzylpenicillin (penicillin G) is the original form of penicillin.
It is very poorly absorbed orally because it is affected by stomach
acid (acid labile) so it must be given by intravenous or
intramuscular injection. Benzathine benzylpenicillin G is the
recommended form for long-term therapy in prophylaxis of ARF and
RHD. This form of the drug has an attached molecule that delays
absorption, and provides a steady concentration of the drug in the
plasma for up to
four weeks.
[ILLUSTRATION OMITTED]
Phenoxymethyl penicillin (penicillin V) is a modified version of
benzylpenicillin that is able to be absorbed orally. Absorption is
variable due to acid effects and the presence of food, so the drug
should be given on an empty stomach. Oral penicillin has a very
nasty taste.
Penicillin is a remarkably safe drug, with few adverse effects.
Because it is excreted largely unchanged in the urine, it should be
administered with caution to the very young and people with
impaired renal function. Hypersensitivity reactions (allergies)
occur in about 0.1 per cent (anaphylaxis) to seven per cent (skin
reactions) of the population. Allergies to penicillin occur where
the degradation products of the drug bind to proteins in the body
and become antigenic. This triggers the immune system to produce
antibodies, and on subsequent exposures an immune response occurs.
When administering the drug at any time, including initially,
adequate precautions should be in place to treat for
hypersensitivity and anaphylaxis. A high index of suspicion should
exist for people with a history of allergy, asthma, hay fever or
urticaria (hives).