McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 9  Antibiotics

TABLE 9.8

DRUGS IN FOCUS Antimycobacterials

Drug name

Dosage/route

Usual indications

Antituberculosis drugs First-line drugs ethambutol (Myambutol)

Adult: 15 mg/kg/day PO as a single dose Paediatric: not recommended for children <13 years

Treatment of Mycobacterium tuberculosis

Adult: 5 mg/kg/day PO Paediatric: 10–12 mg/kg/day PO

Treatment of M. tuberculosis

isoniazid (INH) (generic)

rifampicin (Rifadin, Rimycin) Second-line drug rifabutin (Mycobutin) Leprostatic drugs clofazimine (Lamprene)

Adult: 600 mg PO or IV as a single daily dose Paediatric: 10–20 mg/kg/day PO or IV

Treatment of M. tuberculosis

Adult: 300 mg PO daily

Second-line treatment of M. tuberculosis

Adult: 50 mg PO daily and 300 mg PO monthly

Treatment of multibacillary forms of leprosy Treatment of leprosy, Pneumocystis carinii pneumonia in people with AIDS, and a variety of infections caused by susceptible bacteria and brown recluse spider bites

dapsone (generic)

Adult: 50–100 mg/day PO Paediatric: adjust dosage according to bodyweight

the treatment of tuberculosis or leprosy (as previously indicated). The antituberculosis drugs are always used in combination to affect the bacteria at various stages and to help decrease the emergence of resistant strains. See Table 9.8. Pharmacokinetics The antimycobacterial agents are generally well absorbed from the GI tract. These drugs, given orally, are metabolised in the liver and excreted in the urine; they cross the placenta and enter breast milk, placing the fetus or child at risk for adverse reactions (see contra­ indications and cautions). Contraindications and cautions Antimycobacterials are contraindicated for people with any known allergy to these agents; in those with severe renal or hepatic failure, which could interfere with the metabolism or excretion of the drug ; in those with severe CNS dysfunction, which could be exacerbated by the actions of the drug ; and in pregnancy because of possible adverse effects on the fetus. If an anti­ tuberculosis regimen is necessary during pregnancy, the combination of isoniazid, ethambutol and rifampicin is considered the safest. Adverse effects CNS effects, such as neuritis, dizziness, headache, malaise, drowsiness and hallucinations, are often reported and are related to direct effects of the drugs on neurons. These drugs also are irritating to the GI tract,

■■ BOX 9.6  New indication for thalidomide

In the 1950s, the drug thalidomide became internationally known because it caused serious abnormalities (e.g. lack of limbs, defective limbs) in the fetuses of many women who received the drug during pregnancy to help them sleep and to decrease stress. This tragedy led to the recall of thalidomide in the US and the establishment of more stringent standards for drug testing and labelling. In 2010, the TGA approved the use of this controversial drug for the treatment of erythema nodosum leprosum, which is a painful inflammatory condition related to an immune reaction to dead bacteria that occurs after treatment for leprosy. It is also approved for use in the treatment of multiple myeloma, brain tumours, Crohn’s disease, human immunodeficiency virus–wasting syndrome and graft–host reaction in bone marrow transplant. To take thalidomide, a woman must have a negative pregnancy test, receive instruction in using birth control and sign a release stating that she understands the risks associated with the drug. These limits on the use of a drug were the first such restrictions ever ordered by the TGA. Thalidomide ( Thalomid ) is given in doses of 100 to 400 mg/day PO at bedtime for at least 2 weeks, followed by tapered dose in 50-mg increments over the next 2 to 4 weeks.

Isoniazid specifically affects the mycolic acid coat around the bacterium. Although many of the anti­ mycobacterial agents are effective against other species of susceptible bacteria, their primary indications are in