Concept: Duration of Pharmaceutical Use
Last Updated: 20051201
Is there a dose/response and/or duration effect of highlyanticholinergic antidepressants vs. less anticholinergic antidepressants on incidence of hip fracture in communitydwelling elderly?It is an example of a pharmacoepidemiologic question where one would need to codify and examine:
Time
in Days 
Date1

Date2

Diff
in Days 
DS

QTY

INTCOMP

Days W/O

Days Over

0

1/6/96

2/22/96

47

30

100

0.64

17

0

47

2/22/96

3/20/96

27

30

120

1.11

0

3

74

3/20/96

4/17/96

28

30

120

1.07

0

2

102

4/17/96

5/23/96

36

30

120

0.83

6

0

138

5/23/96

6/25/96

33

60

120

1.82

0

27

171

6/25/96

7/18/96

23

30

100

1.30

0

7

194

7/18/96





25

100







TOTAL 
194

210

23

39


MEDINT 
219
(194+25) 

MEDTOTAL 
0.96
(210/219) 

MEDOUT 
0.11
(23/219) 
First prescription (Rx) dispensation: 06 Jan 1996
Last prescription (Rx) dispensation: 18 Jul 1996
Last Rx day supply 25 days
Medication interval (MED_INT) : 194 + 25 = 219 days
Sum of days of medication supplied (DAYSUPP): 210
Medication interval (MED_INT): 219
(Assumed) proportion of days on medication (MED_TOTAL): 210/219 = 0.96 ((Sum DAYSUPP)/MED_INT)
Days in Rx interval: 06 Jan 1996 to 22 Feb 1996: 47
Days supplied for this prescription (Rx): 30
Difference: 17
Sum of days without medication (including the 6 days from 06 Jan 1996 to 18 Jul 1996) : 23
This is an interim calculation needed to determine how many days a person was likely without sufficient medication supply (MED_OUT) to have a therapeutic effect. It is done on a dispensation to dispensation basis and the differences between days in the interval and days supply over a person's history of dispensations are summed. It is 'twinned' with the calculation of days over on medication (TOTDOVER).
(In other words, the total number of days with medication is 194 and the net of days without and days over is 16 or 210 days supplied in total. However, if one adds the last days supplied amount to what we know is the number of days of possession (n=194 days) then one is left with an approximation of medication interval (MED_INT) (n=219 days).
See SAS code.
Sum of days of medication without (TOTDWOUT): 23
Medication interval (MED_INT): 219
(Assumed) proportion of days not on medication (MED_OUT) 23/219 = 0.11
(TOTDWOUT / MED_INT)
Days in Rx interval: 23 May 1996 to 25 Jun 1996: 33
Days supplied for this prescription (Rx): 60
Difference: 27
Sum of days over with medication (including 12 days from 06 Jan 1996 to 18 Jul 1996): 39
This is a companion calculation to the total days without calculation (TOTDWOUT). It is done on a dispensation to dispensation basis and the differences in the interval and days supply over a person's history of dispensations are summed. It is 'twinned' with the calculation of days without medication (TOTDWOUT).
In other words, the total number of days with medication is 194 and the net of days without and days over is 16 or 210 days supplied in total. However, if one adds the last days supplied amount to what we know is the number of days of possession (n=194 days) then one is left with an approximation of medication interval (MED_INT) (n=219 days).
See SAS code.
Days in Rx interval: 22 Feb 1996 to 20 Mar 1996: 27See SAS code.
Days Supplied for Rx dispensed 22 Feb 1996: 30
(Assumed) proportion of days on medication during one medication interval (INT_COMP) 30/27 = 1.11 (DAYSUPP/MED_INT)
Calculation: In one year (01 August31 July), one only prescription or two to three prescriptions with a total duration of use of less than 100 days; total days without medication of = 61 days (TOTDWOUT) and MED_OUT (i.e., sum of days without medications / sum of days in all refill intervals) = 0.61 (about 0.0 if taking drug more than episodically)
(2) Intermittent: Use according to the following algorithm approximated those taking NSAIDs intermittently for neurovascular (e.g., menstrual headache) or gynecological problems (menstrual cramping).
Calculation: In one year (01 August31 July), total days without medication of between 31 and 60 days (TOTDWOUT), MED_TOTAL (i.e., sum of days supply dispensed / sum of days in all refill intervals) between 0.4 and 0.79 and MED_OUT (i.e., sum of days without medications / sum of days in all refill intervals) between 0.21 and 0.61.
(3) Chronic: Use according to the following algorithm approximated those taking NSAIDs episodically for osteoarthritis or rheumatoid arthritis.
Calculation : In one year (01 August31 July), total days without medication of = 30 days (TOTDWOUT), MED_TOTAL (i.e., sum of days supply dispensed / sum of days in all refill intervals) = 0.8 and MED_OUT (i.e., sum of days without medications / sum of days in all refill intervals) = 0.2.
The definition of chronic use depends on the type of drug being studied. In general, a person must have been dispensed two (2) or more prescriptions and be on medication for a percentage (x%) of time. The x is dependent on the drug therapy. For example, NSAID users had to have been taking a NSAID 80% of the time to be defined as a 'chronic user'.