Streptococcal infections, scarlet fever, mild erysipelas, bacterial endocarditis, lobar pneumonia.
Phenoxymethyl penicillin or penicillin V is acid-stable and is absorbed from the upper part of the small intestine. Of different forms of Phenoxymethyl penicillin, the potassium salt of Phenoxymethyl penicillin is best absorbed. This may be given with meals but maximum absorption is achieved when drug is administered orally at least 1 hour before or 2 hours after the meal. Phenoxymethyl penicillin offers a very convenient means of treating Grampositive infections. Phenoxymethyl penicillin has the distinct advantage over penicillin G in resistance to inactivation by gastric acid.
250 to 500 mg every 6 hourly.
Food: Concurrent intake of food leads to a reduction in the rate of absorption. Therefore, Phenoxymethyl penicillin is best taken on an empty stomach, preferably one hour before meals, in order to reach the highest possible rate of absorption.
Drug interactions: Concomitant administration of penicillins may lead to increased levels of methotrexate in serum and potentiate its toxic effects. Monitoring of methotrexate serum levels is therefore necessary.
If diarrhoea occurs as a consequence of treatment with Phenoxymethyl penicillin, the absorption of other orally administered drugs may be disturbed and their effcacy may consequently be impaired. If penicillins are combined with bacteriostatic chemotherapeutics or antibiotics (e.g., tetracyclines, chloramphenicol), the activity of penicillins may be attenuated or abolished. Concurrent administration of probenecid inhibits the renal excretion of penicillins. Concurrent use of indomethacin, phenylbutazone, salicylates or sulfinpyrazone may cause elevated and prolonged serum levels of phenoxymethylpenicillin.
Administration of penicillins may cause a transient reduction in plasma concentrations of oestrogens and gestagens. The effectiveness of oral contraceptives is therefore uncertain.
The absorption of Phenoxymethyl penicillin may be reduced where intestinal sterilization with aminoglycosides (e.g. neomycin) has just been performed or is still in progress. Combined use of penicillins and oral anticoagulants (e.g. warfarin) may prolong prothrombin time/INR.
Interference with laboratory and diagnostic tests: Non-enzymatic urine glucose determinations and tests for urobilinogen may give false-positive results.
Known to be hypersensitive, severe acute infections.
Diarrhoea, abdominal discomfort, nausea, vomiting, spontaneous petechial hemorrhages, serum sickness.
There is no contraindication to the use of penicillin in pregnancy.
The toxicity of phenoxymethylpenicillin is low, and it has a broad therapeutic range. When a multiple therapeutic dose is taken orally once only, phenoxymethylpenicillin has no acute toxicity. There is a risk of encephalopathy in cases of administration of beta-lactam antibiotics, particularly in case of overdose or renal impairment. Special measures in the event of overdosage, other than discontinuation of the medication, are not required. Elimination of phenoxymethylpenicillin can be accomplished through haemodialysis.
Store in a cool and dry place, protect from light.
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