Penicillins are β-lactam antibiotics. All the β-lactam antibiotics including Amoxil interfere with the synthesis of bacterial cell wall by inhibiting the transpeptidases so that crosslinking does not take place.
They are bactericidal but it kills only when bacteria are growing and synthesizing cell wall. However, penicillin is inactive against organisms devoid of peptidoglycan cell walls, such as mycobacteria, protozoa, fungi, and viruses.
Penicillin is prescribed by the physicians for infections caused by susceptible organisms unless the patient is allergic.
Although the use of penicillin has declined due to the risk of anaphylactic reactions, they are administered to the patients with certain diseases like chlamydia infections in pregnancy, gas gangrene, H. pylori-associated gastritis or peptic ulcer disease, syphilis, leptospirosis, typhoid fever, meningitis etc.
In addition, penicillin also possesses the prophylactic importance to prevent rheumatic fever, bacterial endocarditis, and respiratory tract infections.
Its mechanisms of action is as follows:
- Penicillin inhibits the synthesis of bacterial cell wall peptidoglycan by inhibiting transpeptidation enzyme (transpeptidase).
- Penicillin inactivates the inhibitor of autolytic enzymes in the bacterial cell wall.
- This causes activation of the autolytic enzyme (e.g. murein hydrolases), which degrades the peptidoglycan and thus causes lysis of the bacterium.
All the penicillins are categorized into following groups on the basis of spectrum of activity:
Narrow spectrum penicillins:
-
Natural penicillins:
- Benzylpenicillin (Penicillin G)
- Phenoxymethylpenicillin (penicillin V)
-
Semisynthetic penicillins (β-lactamase resistant):
- Methicillin
- Cloxacillin
- Dicloxacillin
Broad spectrum penicillins (semisynthetic, destroyed by β-lactamase):
- Ampicillin
- Amoxicillin
- Bacampicillin
Extended spectrum penicillins (broad spectrum + antipseudomonal):
- Carbenicillin
- Piperacillin
- Mezlocillin
Penicillins are available in tablet, capsule, dry powder for suspension/solution, syrup, and some other special dosage forms such as extended release tablet and chewable tablet.
You can get this medicine only with your doctor’s prescription
If you are about to start Amoxil, the risk-benefit ratio of this drug should be considered. This is a decision that your doctor will make with your active participation.
There are some important factors such as drug interaction, metabolic impairment, hypersensitivity reaction, pregnancy, lactation etc. which may alter the drug action. That’s why you should know about the drug prior administration.
The penicillins of general practice which are clinically used by the healthcare professionals are discussed below:
Penicillin-G (Benzylpenicillin)
It is a narrow spectrum antibiotic. Activity is limited primarily to gram-positive bacteria, few gram-negative ones, and anaerobes.
It is acid labile, therefore, destroyed by gastric acid. As such, less than 1/3rd of an oral dose is absorbed in the active form. On the contrary, absorption of sodium penicillin-G from the intramuscular site is rapid and complete.
Peak plasma level is attained in 30 minutes. It is distributed mainly extracellularly and reaches most of the body fluids. But its penetration in serous cavities and CSF is poor. However, in the presence of inflammation (e.g. meningitis), adequate amounts may reach these sites.
Repository penicillin G injections
These are insoluble salts of penicillin G which must be given by deep intramuscular injection but never intravenously. They release penicillin-G slowly at the site of injection, which meets the same fate as soluble penicillin-G.
Phenoxymethylpenicillin (Penicillin V)
It is regarded as an acid-resistant alternative to Penicillin G and it differs from penicillin-G only in that it is acid stable. Oral absorption is better and peak blood level is reached in 1 hour.
Its plasma half-life is 30-60 minutes. The antibacterial spectrum of penicillin V is identical to penicillin-G, but it cannot be depended upon for more serious infections and is used only for streptococcal pharyngitis, sinusitis, otitis media, prophylaxis of rheumatic fever, less serious pneumococcal infections and trench mouth.
Penicillinase-resistant penicillins:
Methicillin is highly penicillinase-resistant but not acid resistant, that’s why must be injected.
Cloxacillin and dicloxacillin are more active than methicillin against penicillinase-producing Staphylococci but not against MRSA (methicillin resistant Staph. aureus). Both are incompletely but dependably absorbed from the oral route, especially if taken in empty stomach.
Ampicillin: It is active against all organisms sensitive to penicillin-G. In addition, many gram-negative bacilli, e.g. H. influenza, E. coli, Proteus, Salmonella, Shigella and Helicobacter pylori are inhibited.
Bacampicillin: It is an ester prodrug of ampicillin which is nearly completely absorbed from the gastrointestinal tract and is largely hydrolyzed during absorption. Thus, higher plasma levels are attained. The incidence of diarrhea is claimed to be lower, because of lesser alteration in intestinal ecology.
Amoxicillin: It is a close congener of ampicillin but not a pro-drug. Its oral absorption is better and food does not interfere with absorption. As a result, higher and more sustained blood levels are produced.
Many physicians now prefer it over ampicillin for bronchitis, urinary infections, subacute bacterial endocarditis, and gonorrhea. It is a component of most triple drug H. pylori eradication regimens.
Carbenicillin: It is neither penicillinase-resistant nor acid-resistant. It is inactive orally and is excreted rapidly in urine. At the higher doses, enough sodium may be administered to cause fluid retention and CHF in patients with borderline renal or cardiac function. High doses have also caused bleeding by interfering with platelet function.
Piperacillin: This antipseudomonal penicillin is about 8 times more active than carbenicillin. It has good activity against Klebsiella, many Enterobacteriaceae, and some Bacteroides.
Sometimes the presence of other health disorders affects the beneficial effects of this medicine and even may cause serious complications.
Make sure you mention your doctor if you have any other medical problems. The use of penicillin is contraindicated in those patients who have known hypersensitivity reactions (e.g. anaphylaxis) to penicillins or to other β-lactam antibiotics (e.g. cephalosporins).
Certain drugs should not be used concurrently with such medications. It is always recommended to consult with your doctor if you are in need of some other drugs for another health problem in order to avoid unwanted serious effects.
In addition, you should not use estrogen-containing oral contraceptives, methotrexate, probenecid etc. along with penicillins in order to avoid following drug interactions:
- Concurrent use of penicillins with estrogen-containing oral pill may increase the chance of pregnancy by preventing the contraceptive’s effect.
- Use of methotrexate together with penicillin increases the risk of toxicity of methotrexate.
- Probenecid may increase the adverse effects of penicillin when taken simultaneously.
Amoxil should be used following the directions given by your doctor. The frequency of your daily drug administration and the duration of drug therapy depend on the particular medical problem for which you are taking the medicine.
In addition, they may vary because of different types of drug preparations as follows:
- Sodium penicillin-G injection: 0.5-5 MU is given at every 6-12 hours intramuscularly or intravenously. It is available as a dry powder in vials to be dissolved in sterile water at the time of injection.
- Procaine penicillin-G injection: 0.5-1 MU is given through intramuscular route 12-24 hourly as an aqueous suspension. Plasma concentrations attained are lower, but are sustained for 12-24 hours.
- Fortified procaine penicillin-G injection: It contains 3 lac U procaine penicillin and 1 lac U sodium penicillin G to provide rapid as well as sustained blood levels.
- Benzathine penicillin-G injection: 0.6-2.4 MU given intramuscularly every 2-4 weeks as an aqueous suspension. It releases penicillin extremely slowly. Its plasma concentrations are very low but remain effective for prophylactic purposes for up to 4 weeks.
- Penicillin V: This penicillin is orally active. 250-500 mg in an adult, 60 mg in infants, 125-250 mg in children are given 6 hourly. (250 mg= 4 lac U).
- Cloxacillin/Dicloxacillin: 0.25-0.5 g is given orally at every 6 hours. For severe infections, 0.25-1 g may be injected intramuscularly or intravenously.
- Ampicillin: Depending on severity of infection, 0.5-2 g oral/i.m./ i.v. every 6 hours; children 50-100 mg/kg/day.
- Bacampicillin: 400-800 mg twice daily.
- Amoxicillin: 0.25-1 g is given orally or intramuscularly or by slow i.v. injection. Children should be treated with 25-75 mg/kg/day.
- Carbenicillin: It is used as the sodium salt in a dose of 1-2 g i.m. or 1-5 g i.v. every 4-6 hours.
- Piperacillin: 100-150 mg/kg/day in 3 divided doses (max 16 g/day).
You should take this medicine in time until the prescribed course is finished. If you miss any dose of this medicine, you should take it as soon as possible. But if it is time for your next dose, then you should skip the missed dose and go back to your regular treatment schedule.
You should store the medicine in a closed container at room temperature away from heat, moisture, and direct light.
All kinds of medicines should be kept out of the reach of children. Additionally, outdated medicines should be disposed of in an appropriate way.
