Penicillin intravenous dosage

The rates of absorption, clearance, and elimination of penicillin G are further influenced by the route of administration. Intramuscular and subcutaneous injections provide drug to the bloodstream more slowly, but maintain concentrations longer than the intravenous administration. Absorption of penicillin G from intramuscular or subcutaneous sites can be further slowed down by the use of the relatively insoluble procaine salt. When equivalent dosages of penicillin G and procaine penicillin G were injected parenterally, peak residues concentration in blood occurred after 2 h and the drug had cleared the blood by 8 following penicillin G administration. With the procaine penicillin G, peak residues concentration appeared 5 h after injection and the drug cleared the plasma 24 h after administration (57). 

Steady-state peak and trough concentrations are chosen for the patient based on the site and severity of the infection, as well as the known or suspected pathogen and avoidance of potential side effects. Cmax.ss values of between 20 and 40 mg/L and C in.ss values of between 5 and 10 mg/L typically are used for patients with moderate to severe methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis, or penicillin-resistant enterococcal infections. After appropriate steady-state concentrations are chosen, the dosage interval required to attain those concentrations is computed, and r is rounded to a clinically acceptable value (12, 18, 24, 36, 48, or 72 hours) r = (In Cmax.ss - In Cmin.ss)/ - Finally, the maintenance dose is computed for the patient using a one-compartment-model intravenous bolus equation at steady state, and the dose is rounded off to the nearest 100 to 250 mg ... 

This discussion is not complete, however, as the methods of administration — oral, intravenous, or intramuscular — and the dosage levels and frequency, as well as other factors, must be estabhshed for successful clinical therapy. Thus, a drug or remedy may be effective if administered intravenously but not orally, because the digestive processes may affect the drug itself. An exception is penicillin and some other antibiotics, which can be successfully used orally. And it can be added that there are such peripheral matters that in vitro, in vivo, and clinical test results do not always agree. There is also biochemical individuality among patients, with the result that what works on one does not necessarily work on another. 

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