Penicillins are group of drugs that inhibit cell wall synthesis in the bacteria and indicated for various bacterial infections. This group includes various pencillins with a common structure beta-lactam ring. That’s why these are also called as bet-lactam antibiotics.
Duration of action of any drug depends on how much time it is available in the serum which is controlled by two processses such as distibution and elimiation. Elimination plays key role in influencing duration of many drugs.
Normally, two important organs that involved in the elimination of the drugs from the body include liver and kidney.
See elimination and excretion for more information on eliminitation process.
Penicillins are such drugs which mainly excreted as unchanged in the urine. It can be metabolized in the liver to penicilloic acid and then excreted. It can also be directly excreted as it is without metabolism (unchanged) by renal tubular secretion. Most of the penicillins are excreted unchanged in urine.
So, any factor that influences renal tubular secretion may affect serum concentration of penicillins.
Probenecid is such a drug that inhibits active tubular secretion thereby inhibits secretion of penicillins into renal tubules. As excretion of penicillins somewhat decreased, the duration of action increases.
This drug interaction can be used for a clinical benefit. Hence probenecid can be combined penicillins to increase their duration of action.