Pharmacokinetics is the study of drug movement throughout the body, which includes absorption, distribution, metabolism, and excretion of the drug determine how much drug will be at its sites of action at any given time, and are the major determinants of the time course over which drug responses take place. Absorption of a drug is influenced by the physical and chemical properties of the drug and by physiologic and anatomic factors at the absorption site. The drug-metabolizing capacity and its excretion in infants and older people are decreased and dosage may be carefully adjusted to prevent toxicity. As an advanced practice nurse, good knowledge on the pharmacodynamics (the study of the biochemical and physiologic effects of drugs on the body and the molecular mechanisms by which those effects are produced) and pharmacokinetics is essential to achieve the therapeutic objective.
A recent incident I remember is a 79-year-old lady, who came to the Emergency room with complaining tremors, fatigue, dizziness, and occasional chest discomfort started 45 minutes ago. The patient provides past medical history of hypertension, vertigo, and hypothyroidism and past surgical history of cervical laminectomy. The patient is allergic to penicillin, Lisinopril, Amlodipine, Ace inhibitors, and Hydrochlorothiazide. Vital signs are Heart rate 88/minute, BP 141/84, Respiratory rate 18 and SPO2 100% on room air. On reviewing old records, this patient was presented to ED a few months ago for dizziness and was discharged with a diagnosis of vertigo. Patient further reports that her primary provider starts a new medication, Spironolactone (potassium-sparing diuretic) 3 weeks ago for her blood pressure. Cardiac workup including EKG was initiated and EKG reading was normal. Laboratory results were significant for low sodium level of 131 (reference range 135 to 145 mEq/L), and blood glucose 160mg/dL. All other lab values were within normal limits. Patient felt better after the infusion of a bolus of 1.5-liter Normal saline and was discharged home.
Modification of plan of care in this scenario include discontinuation or readjustment of the dose of Spironolactone, educate patient and family about the medication, its potential complications and discuss methods to avoid side effects and complications, educate about the importance of regular blood work to evaluate electrolytes and advice to avoid high potassium diets and to encourage adequate hydration while on Spironolactone. In old age, renal function often declines result in a decrease in the excretion of drugs through kidneys. As a prescriber or an advanced practitioner, it is our responsibility to monitor the patient’s response for both positive effects and adverse effects to determine whether too much or too little medication has been administered as individual patient’s response to medication varies.