Penicillins dosages

Penicillin is the dmg of choice for the treatment of group B streptococcal, meningococcal and pneumococcal infections but, as discussed earlier, CSF concentrations of penicillin are significantly influenced by the intensity of the inflammatoiy response. To achieve therapeutic concentrations within the CSF, high dosages are required, and in the case of pneumococcal meningitis should be continued for 10-14 days. 

As mentioned earlier in this chapter, penicillins are very unstable in aqueous solution by virtue of hydrolysis of the p-lactam ring. A successful method of stabilizing penicillins in liquid dosage forms is to prepare their insoluble salts and formulate them in suspensions. The reduced solubility of the drug in a suspension decreases the amount of drug available for hydrolysis. An example of improved stability of a... 

In contrast, parenteral suspensions have relatively low solids contents, usually between 0.5 and 5%, with the exception of insoluble forms of penicillin in which concentrations of the antibiotic may exceed 30%. These sterile preparations are designed for intramuscular, intradermal, intralesional, intraarticular, or subcutaneous injection. Syringeability is an important factor to be taken into consideration with injectable dosage forms. The viscosity of a parenteral suspension should be sufficiently low to facilitate injection. Common suspending vehicles include preserved isotonic saline solution or a parenterally acceptable vegetable oil. Ophthalmic and optic suspensions that are instilled into the eye/ear must also be prepared in a sterile manner. The vehicles are essentially isotonic and aqueous in composition. The reader should refer to Chapter 12 for further discussion on parenteral products. 

Prophylactic penicillin is recommended for children with SCD until they are 5 years old. Beginning at age 2 months or earlier, the dosage is penicillin V potassium, 125 mg orally twice daily until 3 years of age and then 250 mg twice daily until age 5 years, or benzathine penicillin, 600,000 units intramuscularly every 4 weeks from age 6 months to 6 years. 

Penicillin G 24 million units/24 h IV in four to six equally divided doses may be used in place of nafcillin or oxacillin if strain is penicillin susceptible (minimum inhibitory concentration <0.1 mcg/mL) and does not produce/ lactamase. cGentamicin should be administered in close temporal proximity to vancomycin, nafcillin, or oxacillin dosing See Table 37-3 for appropriate dosage of gentamicin. 

For pregnant patients, penicillin is the treatment of choice at the dosage recommended for that particular stage of syphilis. To ensure treatment success and prevent transmission to the fetus, some experts advocate an additional intramuscular dose of benzathine penicillin G, 2.4 million units, 1 week after completion of the recommended regimen. 

Penicillins available with specific efficacy against Pseudomonas spp. include carbenicillin and ticarcillin. Both are very effective but require high dosage (50 mg/kg). They can also be used concurrently with aminoglycosides but should be injected separately. Cost is a limiting factor in the use of these drugs. 

Penicillin or cephalosporin therapy The PSP excretion test may be used to determine the effectiveness of probenecid in retarding penicillin excretion and maintaining therapeutic levels. The renal clearance of PSP is reduced to about the normal rate when dosage of probenecid is adequate. 

Adults-2 g/day in divided doses. Reduce dosage in older patients in whom renal impairment may be present. Not recommended in conjunction with penicillin or a cephalosporin in the presence of known renal impairment. 

Penicillin V Uses and Dosages for Adults and Children >12 Years of... 

Perform periodic urinalysis, BUN, and creatinine determinations during therapy with penicillinase-resistant penicillins, and consider dosage alterations if these values become elevated. 

Probenecid can impair the renal active secretion of a variety of acidic compounds, including sulfinpyrazone, sulfonylureas, indomethacin, penicillin, sulfonamides, and 17-ketosteroids. If these agents are to be given concomitantly with probenecid, their dosage should be modified appropriately. Salicylates interfere with the clinical effects of both sulfinpyrazone and probenecid and should be avoided in patients treated with uricosuric agents. Uricosuric agents also can influence the volume of distribution and hepatic metabolism of a number of drugs. 

I Indications and Dosages Penicillins maybe used to treat a large number of infections, including pneumonia and other respiratory diseases, urinary tract infections, septicemia, meningitis, intra-abdominal infections, gonorrhea, syphilis, and bone and joint infections. 

Dosages Doses vary depending on the drug used. In general, penicillins should be taken on an empty stomach. Patients with impaired renal function may require dose adjustment. 

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