<p><strong>Food</strong>: 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.<br />
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<strong>Drug interactions</strong>: 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.<br />
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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.<br />
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Administration of penicillins may cause a transient reduction in plasma concentrations of oestrogens and gestagens. The effectiveness of oral contraceptives is therefore uncertain.<br />
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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.<br />
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<strong>Interference with laboratory and diagnostic tests</strong>: Non-enzymatic urine glucose determinations and tests for urobilinogen may give false-positive results.</p>