2. Penicillins Flashcards
Penicillins mechanism of action
Prevents peptidoglycan from cross-linking in bacterial cells wall - therefore bactericidal.
Broad spectrum pencillins
- amoxicillin
- ampicillin (high bacterial reisistance and should not be used in hospital without a culture/sensitivity test)
- antipseudomonal pencillins (reserved for serious infections and giving parenterally).
Narrow spectrum penicillins
- Benzylpenicllin (giving parenterally, usually treats meningitis)
- Phenoxymethylpenicillins (treats strep throat and taken orally QDS)
- Flucloxacillin reserved for stapphylococcal infections, so is therefore reserved for skin infections. (Can cause choleostatic jaundice so used with caution).
Penicillins are typically used to treat
streptococcal, gonococcal and meningococcal infections
Benzylpenicllin administration
Benzylpenicllin must be given by injection as it is unstable in gastric acid. Only used in relation to CNS infections in meningitis, as they poorly permeate the blood brain barrier, unelss it is inflammed, this occurs in instances such as meningitis.
Phenoxymethylpenicillin (Penicillin V) administration
Suitable for oral administration as it is stable in gastric acid
Phenoxymethylpenicillin (Penicillin V) typical indications
Prophylaxis against streptococcal infections following rheumatic fever and prophylaxis against pneumococcal infections following splenectomy in sickle cell disease
Alternatives antibiotics that can be used to treat antistapphyloccal infections since benzylpenicllins have now become resistant to them
Anti-stapphylococcal penicillins (Flucloxacillin)
Flucloxacillin administration
Can be given orally and by injection as it is acid-stable
Adverse reactions associated with flucloxacilln treatment
Cholestatic jaundice and hepatitis may occur up to 2 months following treatment
What can alternatively be given in antistapphylococcal infections
Temocillin in gram-negative infections
Ampicillin typically treats
Exacerbations of chronic bronchitis, middle ear infections and urinary tract infections
Ampicillin counselling advice
Ampicillin must be taken on an empty stomach to increase its absorption
Common side effect of ampicillin
Maculopapular rash occur with ampicillin, (not related to a penicillin allergy). More commonly seen in patients with leukaemia or cytomegalovirus infection.
Amoxicillin counselling advice
Can be taken with or without food, absorption remains unaffected
Amoxicillin typically treats
Respiratory tract infections, H.pylor, CAP, otitis media. Good choice for empirical therapy and want to target a wide range of bacteria. SHOULD NOT be used to blindly treat sore throats, as a sore throat may be caused by glandular fever, where maculopapular rashes are a common symptom. This may confuse for a pencillin allergy.
Amoxicillin doses
1-11 months old: 125mg TDS
1-4 years old 250mg TDS
Adult : 500mg-1000mg TDS
Clinical significance of co-amoxicalv
Co-amoxicalv is clavulanic acid and amoxcillin. Clavulanic acid makes amoxicillin active against beta-lactamase producing bacteria. Clavulanic acid has no antibacterial activity on its own and can cause choleosatic jaundice.
Consequences to other types of therapy if patient has immediate hypersensitivity to pencillins
Patients may also react the same way to cephalosporins
Common side effect of co-amoxiclav
Choleostatic jaundice - more common in patients above the age of 65. Jaundice is usually self-limiting and rarely fatal
Examples of anti-pseudomonal penicillins
Piperacillin (+ tazobactam)
Ticarcillin (+ clavulanic acid)
Co-amoxiclav should be used with caution
In patients with hepatic impairment
Anti-pseudomonal pencillins spectrum of activity
Broad spectrum against both gram negative and gram positive bacteria, and anaerobes
Anti-pseudomonal pencillins are typically used to treat
septicaemia, hospital acquired pneumonia, and infections involving the skin, soft tissues or intra abdomen
What are anti-pseudomonal pencillins typically given with and why?
Aminoglycosides to achieve a synergistic effect
Common Side effects of pencillins
Hypersensitivity, diarrhoea (more common in broad spectrum antibiotics), vomiting, skin reactions
Patients that are at higher risk of of anaphylactic reactions to penicillins
Patients with asthma, hay fever and eczema
Patients that should not receive a penicillin
Patients with a history of anaphylaxis, urticaria, or rash immediately after administration of penicillins. Should not recievee any beta -lactam antibiotics.
Patients that can still receive a penicillin
Patients with a history of a minor rash, non-confluent, non-pruritic rash restricted to a small area of the body or a rash that occurs over 72 hours after penicillin administration. Penicllins should only be used for serious infections, in these patients.
Penicllins should NEVR be administered via…
INTRATHECALLY, can damage the brain
Flucloxacillin should be used with caution
In patients with hepatic impairment
Apropriateness of pencillins in pregnancy
Penicillins are suitable for use in pregnancy
Penicillin interactions
Are generally safe antibitiotics but
1. Reduce the renal clearance of methotrexate, raising its levels and therefore risk of toxicity
- Increase the anticoagulant effect of warfarin by killing normal gut flora, that synthesize vitamin K
- Flucloxacillin and Clavulanic acid (in co-amoxiclav) are hepatotoxic drugs. Increased risk of hepatotoxicity when two or more hepatotoxic drugs are taken at the same time.
Examples of hepatotoxic drugs include anti-epileptics (carbamazepine and valproate), anti-fungals (fluconazole), isoniazid, methotrextate, statins, sulfasalazine, tetracycline drugs
