Penicillin V Potassium
For general information on the penicillins, including adverse effects, contraindications, overdosage, drug interactions and monitoring parameters, refer to the monograph: Penicillins, General Information.
Chemistry - A natural penicillin, penicillin V is produced from Penicillium chrysogenum and is usually commercially available as the potassium salt. It may also be known as phenoxymethylpenicillin potassium. Penicillin V potassium occurs as an odorless, white, crystalline powder that is very soluble in water and slightly soluble in alcohol. Potency of penicillin V potassium is usually expressed in terms of weight (in mg) of penicillin V, but penicillin V units may also be used. One mg of penicillin V potassium is equivalent to 1380-1610 USP Units of penicillin V. Manufacturers, however, generally state that 125 mg of penicillin V potassium is approximately equivalent to 200,000 USP units of penicillin V.
Storage/Stability/Compatibility - Penicillin V potassium tablets and powder for oral solution should be stored in tight containers at room temperature (15-30°C). After reconstitution, the oral solution should be stored at 2-8°C (refrigerated) and any unused portion discarded after 14 days.
Pharmacology, Uses/Indications - Penicillin V may be slightly less active than penicillin G against organisms susceptible to the natural penicillins, but its superior absorptive characteristics after oral administration make it a better choice against mild to moderately severe infections when oral administration is desired in monogastric animals. For more information on the types of organisms that penicillin V generally covers, refer to the general statement on penicillins and the penicillin G monograph.
Pharmacokinetics (specific) - The pharmacokinetics of penicillin V are very similar to penicillin G with the exception of oral bioavailability and the percent of the drug that is bound to plasma proteins. Penicillin V is significantly more resistant to acid-catalyzed inactivation in the gut and bioavailability after oral administration in humans is approximately 60-73%. In veterinary species, actual bioavailability measurements have been measured in calves (30%), but studies performed in horses and dogs have demonstrated that therapeutic serum levels can be achieved with the drug after oral administration. In dogs, it has been shown that food will decrease the rate and extent of absorption of the drug from the gut.
Distribution of penicillin V follows that of penicillin G but, at least in humans, the drug is bound to a larger extent to plasma proteins (approximately 80% with penicillin VK vs. 50% with penicillin G).
Like penicillin G, penicillin V is excreted rapidly in the urine via the kidney. Elimination half-lives are generally less than 1 hour in animals with normal renal function, but an elimination half-life of 3.65 hours has been reported after oral dosing in horses (Schwark et al. 1983).
For susceptible infections:
a) 66,000 U/kg (41.25 mg/kg) PO gives levels greater than 0.1 micrograms/ml for greater than 325 minutes which should be effective against Streptococci. (Beech 1987a) (Author’s (Plumb) note: Because of the post-antibiotic effect phenomenon; dosing every 6-8 hours should be sufficient)
b) 110,000 U/kg (68.75 mg/kg) PO q8h (may yield supra-optimal levels against uncomplicated infections by sensitive organisms). (Schwark et al. 1983)
c) 110,000 U/kg PO q6-12h (Brumbaugh 1987)
Client Information - Unless otherwise instructed by the veterinarian, this drug should be given on an empty stomach, at least 1 hour before feeding or 2 hours after. Keep oral suspension in the refrigerator and discard any unused suspension after 14 days.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times -
Veterinary-Approved Products: None
Penicillin V Potassium Oral Tablets 125 mg, 250 mg, 500 mg; (Rx)
Penicillin V Potassium Oral Powder for Suspension 125 mg/5 ml in 100 ml, 150 ml and 200 ml, 250 mg/5 ml in 100 ml, 150 ml and 200 ml; (Rx)
There are a multitude of proprietary penicillin VK products, some more widely known include: V-Cillin K® (Lilly), Pen-Vee K® (Wyeth), Veetids® (Squibb), Uticillin VK® (Upjohn), Beepen-VK® (Beecham), Ledercillin® VK (Lederle)
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