Higher risk of potential drug-drug interactions in HIV patients over 60

Mark Mascolini, for

HIV-positive people over 60 years old had HIV longer, used antiretrovirals longer, took more total drugs, and had a higher rate of potential drug-drug interactions than HIV patients 60 or younger seen at the same clinic.

Older people had a doubled rate of potential interactions between protease inhibitors (PIs) or nonnucleosides (NNRTIs) and cardiovascular drugs.

Because older people tend to have more illnesses requiring pharmacotherapy, they run a higher risk of drug-drug interactions resulting from polypharmacy. To analyse prescription and nonprescription drug use in older and younger people with HIV infection, researchers at the Toronto General Hospital Immunodeficiency Clinic retrospectively compared relevant HIV- and treatment-related data in 528 people under 60 years old and 38 people who were 60 or older. All study participants tested positive for HIV between 1 January 1996 and 31 December 2009.

Compared with younger patients, the 60-plus group were diagnosed with HIV in an earlier year (2001 versus 2003, p<0.01) and started antiretroviral therapy earlier (2002 versus 2004, p=0.04). The older people were more likely to be Caucasian (65% versus 47%, p=0.06), less likely to be black (19% versus 35%), less likely to be immigrants (13% versus 30%, p=0.02), and less likely to come from an HIV-endemic area (19% versus 35%, p=0.05).

A higher proportion of older study participants had a current viral load below 50 copies/mL (89% versus 74%, p=0.03), and a slightly higher proportion of older people were taking antiretrovirals (95% versus 87%). Current CD4 count did not differ substantially between the 60-and-older group and the under-60 contingent (median 496 versus 475 cells/mm3).

Older people had taken a higher median number of total drugs than younger people (7, interquartile range [IQR] 5 to 11, versus 4, IQR 3 to 7), a highly significant difference (p<0.0001). Among people taking antiretrovirals, similar proportions of older and younger people were currently taking nucleosides (97% versus 91%), NNRTIs (39% versus 41%), and PIs (61% versus 53%).

The 60-and-over group took certain types of drugs significantly more often than younger people: drugs for gastrointestinal problems (63% versus 38%, p<0.01), drugs for cardiovascular disease (55% versus 24%, p<0.0001), anticoagulants or antiplatelets (18% versus 7%, p=0.01), systemic hormonal agents (16% versus 5%, p=0.01), musculoskeletal agents (24% versus 9%, p<0.01), and narcotics or analgesics (39% versus 17%, p<0.001). Anticonvulsant therapy was more frequent in the older group (16% versus 7%, p=0.06), but older people took psychotropic agents at virtually the same rate as younger people (34% versus 30%).

Four potential drug interactions were significantly more frequent in older people:

  • PI/NNRTI plus a cardiovascular drug: 42% versus 20%, p=0.003
  • PI/NNRTI plus an anticonvulsant: 16% versus 5%, p=0.02
  • PI plus a cardiovascular drug: 34% versus 13%, p=0.001
  • PI plus warfarin: 8% versus 1%, p=0.01

Relatively high (and statistically similar) proportions of older and younger people were taking atazanavir with an acid-reducing agent (16% versus 10%, p=0.37).

The investigators noted that their study is limited by its cross-sectional nature, by their inability to determine whether prescribing physicians had modified doses, and by the lack of data on actual consequences of potentially harmful drug-drug interactions. Still, the findings offer a look at age-related polypharmacy in people with HIV and underline the greater risk of drug-drug interactions among older patients, who generally take more drugs than their younger HIV-infected counterparts.

Ref: Tseng A, Raboud J, Walmsley S, Sterling S, Salit I. Polypharmacy in older patients: a study of medication use and potential drug interactions in an
aging ambulatory HIV clinic population. 1st International Workshop on HIV and Aging. 4-5 October 2010. Baltimore. Abstract O_08.

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