Mode of action 
Ora-K (Phenoxymethylpenicillin) kills bacteria by interfering synthesis of bacterial cell wall. Peptidoglycan is a hetaropolymeric structure that provides the cell wall with mechanical stability. Ora-K (Phenoxymethylpenicillin) inhibits the transpeptidase enzyme that performs this step. As a result, cell wall becomes weakened, the cells swells and ruptures.
Pharmacokinetics
Ora-K is rapidly but incompletely absorbed from the intestine. Peak serum concentration occurs within 0.75 h. When taken in a fasting state, blood level of Ora-K is at least twice as high as that seen with an equal quantity of oral penicillin G. The urinary excretion over 10 hours is 37-43% of the dose. Over 24 hours, almost the entire absorbed drug is recovered in the urine.
Indication 
Ora-K (Phenoxymethylpenicillin) affords a very convenient means of treating gram positive infections but is not indicated for gram negative infections involving the respiratory and urinary tracts. It is indicated in the treatment of infections caused by susceptible strains of the designated organism in the condition as follows:
Skin & soft tissue infections: Caused by penicillin susceptible Staphylococci and Streptococci species.
Respiratory tract infections: Caused by Staphylococci species including pneumococcal infections.
It may be indicated for prophylaxis of recurrent rheumatic fever. 
Dosage and administration
The doses of penicillin should be determined according to the susceptibility of the causative organism and the severity of infection and adjusted to the clinical response of the patients.
Penicillin is administered by mouth, preferably at least 30 minutes before meal. 
Adult: 250-500 mg every 6 hours.
Children (over 12 years): 1-2 tablets or 2-4 teaspoonfuls syrup (250-500 mg) every 6 hours.
Children (6-12 years): ½ -1 tablet or 1-2 teaspoonfuls syrup (125-250 mg) every 6 hours. 
Children (1-5 years): 1 teaspoonful syrup (125 mg), every 6 hours.
 Children (up to 1 year): ½ teaspoonful syrup (62.5 mg), every 6 hours.
For prophylaxis of rheumatic fever, 500 mg of Phenoxymethylpenicillin (2 Ora-K tablets) daily for at least 5 years after last attack is recommended. Alternatively, the same dose should be continued until the patients reaches at least 20 years of age.
Contraindication 
Hypersensitivity to Penicillin is a contraindication.
Use in pregnancy and lactation 
Human experience with the penicillin, during pregnancy has not shown any positive evidence of adverse effects on the fetus. However, penicillin should be used during pregnancy only if clearly needed. Phenoxymethylpenicillin is excreted into breast milk and may lead to allergic reactions in the infant. So caution should be exercised when Ora-K is administered to the lactating woman.
Side effects
The most common untoward effects include nausea, vomiting, epigastric distress and diarrhea. The hypersensitivity reactions reported are skin eruption, urticaria and other serum sickness reactions, laryngeal edema and anaphylaxis.
Precaution
Before initiating therapy with any penicillin, careful inquiry should be made concerning previous hypersensitivity reactions.
Overdosage
Ora-K exhibits very low toxicity when taken in overdose. Gastrointestinal symptoms including nausea and vomiting may occasionally occur. Gastric lavage and symptomatic treatment is rarely needed.
Drug interaction 
Aspirin and sulfamethoxypyridazine inhibit the serum of Phenoxymethylpenicillin. Aminoglycosides may be inactivated by penicillin but this is unlikely to be a problem. The excretion of Phenoxymethylpenicillin is retarded by probenecid.  
Pharmaceutical precaution 
Store in a cool, dry place and protect from light. Keep out of reach of children. 
Packing
Ora-K Tablet: Box containing 10 × 10 / 50 × 10 tablets in strip pack.