Mechanism of action and physicochemical properties
Like all beta-lactam antibiotics, carbenicillin disrupts the synthesis of bacterial cell wall peptidoglycan. A structural feature of carboxypenicillins is the presence of a carboxyl group in the side chain, which imparts a negative charge to the molecule and provides some resistance to beta-lactamases.
At the same time, due to the absence of an amino group, carbenicillin has difficulty diffusing through porin channels of gram-negative bacteria ($G-$). The substance belongs to hydrophilic broad-spectrum compounds, but high doses are required to achieve the necessary bactericidal concentration inside the microbial cell.
Pharmacokinetics and administration features
The drug is acid-labile — it is completely destroyed by hydrochloric acid in the stomach and is practically unabsorbed when taken orally. For this reason, carbenicillin is administered exclusively parenterally: intramuscularly or intravenously.
In the body, the drug is approximately 50% bound to plasma proteins, does not cross the blood-brain barrier (BBB), and is excreted primarily by the kidneys. Due to its short half-life, injections are prescribed 4–6 times a day. The solution for intravenous administration is prepared ex tempore (immediately before use): 1.0 g of powder is diluted in 10 ml of 0.9% sodium chloride solution and administered at a rate of about 60 drops per minute.
Spectrum of antimicrobial activity
Carbenicillin is active against many members of the family Enterobacteriaceae, as well as bacteria of the genera Pseudomonas and Enterobacter (due to resistance to their chromosomal beta-lactamases).
Among carboxypenicillins, carbenicillin has the lowest efficacy against Pseudomonas aeruginosa (Pseudomonas aeruginosa), inferior to ticarcillin, mezlocillin, azlocillin, and piperacillin. Natural gaps in the spectrum (resistant microorganisms) include Klebsiella spp., Proteus vulgaris, Citrobacter diversus, and Enterococcus faecalis.
Side effects and therapy risks
During carbenicillin administration, both standard allergic reactions typical of penicillins (urticaria, angioedema, anaphylactic shock) and specific toxic effects develop:
- Hypernatremia: caused by the fact that the drug is manufactured as a disodium salt. It poses a serious risk for patients with chronic heart failure (CHF).
- Hypokalemia: occurs due to the accelerated excretion of potassium ions ($K^+$) along with the non-reabsorbed negatively charged anion of the antibiotic in the distal renal tubules.
- Bleeding disorders: develop as a result of platelet aggregation inhibition.
CarbeNICIllin = SODIUM (natrium) sodium-based (risk of hypernatremia) and LOW activity against Pseudomonas aeruginosa compared to ureidopenicillins.
Class and exam questions
Why can't carbenicillin be taken in tablets?
The drug is an acid-labile compound: it is destroyed by hydrochloric acid in the stomach and is practically not absorbed from the gastrointestinal tract, which is why it is administered only parenterally (IM or IV).
What causes electrolyte imbalances (hypernatremia and hypokalemia) during carbenicillin treatment?
Hypernatremia is caused by the chemical form of the drug (disodium salt), while hypokalemia occurs due to the active renal excretion of potassium cations along with an excess of unabsorbed negative anions of the antibiotic.
What is the rank of carbenicillin among antipseudomonal penicillins in terms of efficacy?
Carbenicillin rounds out this group, exhibiting the lowest activity against Pseudomonas aeruginosa (Pseudomonas aeruginosa) compared to ticarcillin, mezlocillin, azlocillin, and piperacillin.
What else to study on this topic
- Comparative characteristics of carboxy- and ureidopenicillins
- Mechanisms of natural and acquired resistance to beta-lactams
- Pharmacokinetic features of parenteral penicillins
- Antibiotic dose adjustment in impaired renal excretion function
- Prevention and management measures for anaphylactic shock
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