75
a A teaspoonful is 5 mL.
This is an easy‐to‐follow table for prescribing clarithromycin to pediatric patients; the usual recommended dosage is 15 mg/kg/day divided q12h for 10 days.
Table 3.11 How the clarithromycin (Biaxin) prescription should be written
| Rx: clarithromycin oral suspension 250 mg/5 mL |
| Disp: 1 bottle (100 mL) |
| Sig: Take 1 teaspoonful orally twice a day for 7 days for dental infection |
3.2.4 Azithromycin
3.2.4.1 Oral Suspension (Table 3.12)
Dose required: 10 mg/kg/day q24h × 3 days.
How supplied: oral suspension comes in concentrations of 100 mg/5 mL, 200 mg/5 mL, 1 g powder packet.
1 Q. When should the 100 mg/5 mL suspension be prescribed?
2 A. The 100 mg/5 mL strength is prescribed for younger children weighing less than 44 lb (20 kg). Table 3.12 Calculating the dose of azithromycin oral suspension in mL for a 10‐year‐old child weighing 70 lb and how the prescription should be writtenStep 1 Convert pounds to kg:70 lb × 1 kg/2.2 lb = 31.8 kgStep 2 Calculate the dose in mg:31.8 kg × 10 mg/kg/day = 318 mg/dayStep 3 Divide the dose by the frequency:318 mg/day once a day = 318 mg/doseStep 4 Convert the mg dose to mL:318 mg/dose ÷ 200 mg/5 mL = 7.9 mL q24h Rx: azithromycin oral suspension 200 mg/5 mLDisp: 1 bottle (100 mL)Sig: Take 7.9 mL orally once a day for 3 days for dental infectionTable 3.13 Calculating the dose of azithromycin tablets in mg for a 10‐year‐old child weighing 70 lbStep 1 Convert pounds to kg:70 lb × 1 kg/2.2 lb = 31.8 kgStep 2 Calculate the dose in mg:31.8 kg × 10 mg/kg/day = 318 mg/dayStep 3 Divide the dose by the frequency:318 mg/day once a day = 318 mg/dose once a dayThe strengths of tablets are 250, 500, or 600 mg. Since the dose is 318 mg once a day, it is probably more precise to prescribe the oral suspension.Table 3.14 Calculating the dose of clindamycin oral solution in mL for a 10‐year‐old child weighing 70 lb and how the prescription should be writtenStep 1 Convert pounds to kg:70 lb × 1 kg/2.2 lb = 31.8 kgStep 2 Calculate the dose in mg:31.8 kg × 10 mg/kg/day = 318 mg/dayStep 3 Divide the dose by the frequency:318 mg/day ÷ 3 (tid) = 106 mg/dose q8hStep 4 Convert the mg dose to mL:106 mg/dose ÷ 75 mg/5 mL = 7 mL tidStep 5 Convert mL into teaspoonfulsa7 mL ÷ 5 mL = 1.4 teaspoonful Rx: Clindamycin oral solution 75 mg/5 mLDisp: 1 bottleSig: Take 1.4 teaspoonful orally three times a day for 7 days for dental infectiona Each teaspoonful is 5 mL.
3.2.4.2 Azithromycin Tablets (Table 3.13)
Dose required: 10 mg/kg/day q24h × 3 days.
How supplied: 250 mg, 500 mg, 600 mg tablets.
3.2.5 Clindamycin
3.2.5.1 Clindamycin Oral Solution (Table 3.14)
Dosage required: 10–30 mg/kg/day q6–8 h.
How supplied: oral solution 75 mg/5 mL (100 mL bottle).
3.2.5.2 Clindamycin Capsules (Table 3.15)
Dosage required: 10–30 mg/kg/day q6–8 h.
How supplied: 75, 150, 300 mg capsules.
Table 3.15 Calculating the dose of clindamycin capsules in mg for a 10‐year‐old child weighing 70 lb
| Step 1 Convert pounds to kg: | 70 lb × 1 kg/2.2 lb = 31.8 kg |
| Step 2 Calculate the dose in mg: | 31.8 kg × 10 mg/kg/day = 318 mg/day |
| Step 3 Divide the dose by the frequency: | 318 mg/day ÷ 4 (qid) = 80 mg/dose q6h |
The dose is 80 mg; either 75 mg capsules can be prescribed and increase the number of days of therapy, or it may be best to use the oral suspension.
3.3 Pregnant and Nursing Patients
1 Q. Why may dosage adjustment be required in the pregnant patient?
2 A. Pregnancy and the first weeks of life represent two physiological situations in which there are continuous and significant changes in the levels of plasma proteins, and it may therefore be necessary to adjust the doses of medication during these times (Moore 1998).
3 Q. Why is it important to be aware of the effect of drugs in the nursing mother?
4 A. Nearly all drugs pass into human milk by passive diffusion. Almost all medication appears in very small amounts, usually less than 1% of the maternal dose. The higher the dosage, the more the drug transfers into milk. Different features of drugs including molecular weight, fat solubility, and half‐life will affect how much of the drug is transferred into the milk. The pH of milk is 7, which is slightly lower than plasma (pH 7.4) so that drugs that are weak bases (e.g., erythromycins, tetracyclines) will achieve high concentrations in breast milk and should be avoided.
5 Q. What are the “new” FDA pregnancy categories?
6 A. Approximately 30 years ago, the FDA required that all prescription drugs absorbed systemically or known to be potentially harmful to the fetus be given a pregnancy category of A, B, C, D or X. Table 3.16 lists all categories (Lynch et al. 1991). In 2014, the FDA replaced the letter categories with new labeling that is more explanatory to patients and clinicians and enables more effective patient counseling. This classification was revised in 2015. The new Pregnancy and Lactation Labeling Final Rule (PLLR) started on June 30, 2015 and can be found on the package insert of the medication. The PLLR consists of narrative sections and subsections which include the following (www.drugs.com/pregnancy‐categories.html). Table 3.16 FDA pregnancy categoriesDrug categoryDescriptionAControlled
