Penicillinase-Resistant Penicillin

Aka: Penicillinase-Resistant Penicillin, Penicillinase-Resistant Semisynthetic Penicillin, Second Generation Penicillin, Cloxacillin, Methicillin

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II. Indications

  1. Staphylococcus Infection
    1. Staphylococcus Aureus
    2. Staphylococcus Epidermidis
  2. Specific Infections
    1. Skin Infection
    2. Soft tissue infection
    3. Lymphatic infection
    4. Bone Infection
    5. Joint infection

III. Mechanism

  1. Antibiotic activity
    1. Same action to Natural Penicillins
    2. Large, bulky side chain
      1. Blocks Penicillinase hydrolysis of Beta Lactam ring
      2. Hydrophobic side chain prevents penetration of Gram Negative Bacteria membrane via hydrophilic pores
        1. Therefore Penicillinase-Resistant Penicillins are inactive against Gram Negative Bacteria
  2. Bacterial Resistance mechanisms
    1. Alteration of Bacterial cell wall

IV. Mechanism: Activity Spectrum

  1. Same as for Natural Penicillins

V. Preparations: Oral

  1. Directions
    1. Take on an empty Stomach
    2. Take more than 1 hour before or two hours after food
  2. Dicloxacillin (Dynapen)
    1. Adult: 125 to 500 mg PO qid
    2. Child: 12.5 to 25 mg/kg/day orally divided four times daily
  3. Cloxacillin (Cloxapen)
    1. Still used internationally, but no longer available in the U.S.
    2. Adults: 250-500 mg orally four times daily

VI. Preparations: Parenteral

  1. Methicillin (Staphcillin)
  2. Nafcillin (Nafcil, Unipen)
    1. Adult: 1 to 2 grams IM or IV every 4 hours
    2. Child: 50 to 200 mg/kg/day divided every 4 to 6 hours
  3. Oxacillin (Bactocill)
    1. Adult: 1 to 2 grams IM or IV every 4 to 6 hours

VII. Adverse effects

  1. Nephritis (Methicillin)
  2. Venous inflammation (Nafcillin)

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