Table 1.
Methods to Assess Adherence to Oral Medications
| Test | Advantages | Disadvantages |
|---|---|---|
| Direct Methods | ||
| Medication consumed under direct observation | Most accurate | Impractical for routine use. Patients can hide pills in the mouth and discard them. |
| Measurement of the level of medicine or metabolite in blood | Objective | Lower metabolism and “white coat” adherence can give a false impression of adherence; expensive; invasive; requires laboratory; need multiple levels to calculate individual variability; validity of therapeutic ranges varies; each drug has its pharmacokinetic profile, which is poorly investigated; can over- or underestimate depending on behavior immediately prior to test; metabolism is influence by genetic, environmental and personal variables |
| Measurement of a biologic marker in blood | Objective; in clinical trials, can also be used to measure placebo | Requires expensive quantitative assays and collection of bodily fluids; impractical |
| Indirect Methods | ||
| Self-reporting by the patient (interview, diary, questionnaire) | Subjective; simple and easy to use; noninvasive; readily available; inexpensive; sensitive for non-adherence; the most useful in a clinical setting for large studies | No evidence that the drug is actually ingested; not accurate, results are easily distorted by the patient; patient is aware of the measurement |
| Physician perception | Subjective; simple; non-invasive | Validity is extremely poor; physicians overestimate adherence |
| Pill counts | Objective, quantifiable and easy to perform | Time consuming; data easily altered by the patient (eg, pill dumping); provides no information about timing of missed doses or about times of day that medications are taken; requires patients bring pills for counting |
| Rates of prescription refills | Objective: easy to obtain data | A prescription refill is not equivalent to ingestion of medication; requires a closed pharmacy system |
| Assessment of the patient’s clinical response | Simple; generally easy to perform | Factors other than medication adherence can affect clinical response |
| Electronic medication monitors | Precise; results are easily quantified; tracks patterns of taking medication | Expensive; poorly integrates with the elderly; assumes medication is consumed when bottle/compartment is opened; requires return visits and downloading data from medication vials and expertise in interpreting data |
| Measurement of physiologic markers (eg, heart rate in patients taking beta-blockers) | Often easy to perform | Marker may be absent for another reason |