Mechanism of action and physicochemical properties
Like all beta-lactam antibiotics, carbenicillin disrupts the synthesis of the peptidoglycan bacterial cell wall. 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 lack of an amino group in carbenicillin, diffusion through porin channels of Gram-negative bacteria ($G-$) is hindered. 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 binds to plasma proteins by approximately 50%, 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.
طيف النشاط المضاد للميكروبات
Carbenicillin is active against many members of the Enterobacteriaceae family, 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 its spectrum (resistant microorganisms) include Klebsiella spp., Proteus vulgaris, Citrobacter diversus, and Enterococcus faecalis.
Side effects and therapy risks
During carbenicillin therapy, standard penicillin-like allergic reactions (urticaria, angioedema, anaphylactic shock) develop, alongside specific toxic effects:
- Hypernatremia: caused by the drug being formulated as a disodium salt. It poses a serious risk to patients with chronic heart failure (CHF).
- Hypokalemia: occurs due to the accelerated excretion of potassium ions ($K^+$) along with the unabsorbed negatively charged antibiotic anion in the distal renal tubules.
- Bleeding tendency: develops due to the inhibition of platelet aggregation.
Carbenicillin contains SODIUM (risk of hypernatremia) and has LOW activity against Pseudomonas aeruginosa compared to ureidopenicillins.
أسئلة من المحاضرات والامتحانات
Why can carbenicillin not 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 imbalance disorders (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 excess unabsorbed negative anions of the antibiotic.
What is the efficacy ranking of carbenicillin among antipseudomonal penicillins?
Carbenicillin closes this series, having the lowest activity against Pseudomonas aeruginosa (Pseudomonas aeruginosa) compared to ticarcillin, mezlocillin, azlocillin, and piperacillin.
مواضيع أخرى للمراجعة في نفس السياق
- 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 excretory function
- Prevention and management measures for anaphylactic shock
مواضيع أخرى من قسم «الأدوية والوصفات الطبية»
دروس فيديو مجانية: علم الأфарماكولوجيادروس قصيرة مع ملخصات — بدون تسجيل.
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